A perspective on where we are on carcinogenesis, cancer variability and predictors of time to recurrence and future behavior
Author: Larry H Bernstein, MD, FCAP
Word Cloud by Daniel Menzin
I. Background
In “Tumor Imaging and Targeting: Predicting Tumor Response to Treatment: Where we stand? “ ( Dec 13, 2012) Dr. Ritu Saxena attempts to integrate three posts and to embed all comments made to all three papers, allowing the reader a critically thought compilation of evidence-based medicine and scientific discourse.
Dr. Dror Nir authored a post on October 16th titled “Knowing the tumor’s size and location, could we target treatment to THE ROI by applying imaging-guided intervention?” The article attracted over 20 comments from readers including researchers and oncologists debating the following issues:
imaging technologies in cancer
- tumor size, and
- tumor response to treatment.
The debate lead to several new posts authored by:
Dr. Bernstein’s (What can we expect of tumor therapeutic response),
Dr. Saxena, the Author of this post’s, (Judging ‘tumor response’-there is more food for thought) and
Dr. Lev-Ari’s post on Personalized Medicine: Cancer Cell Biology and Minimally Invasive Surgery (MIS) http://pharmaceuticalintelligence.com/2012/12/01/personalized-medicine-cancer-cell-biology-and-minimally-invasive-surgery-mis/#comment-5269
The post was a compilation of the views of authors representing different specialties including research and medicine. In medicine: Pathology, Oncology Surgery and Medical Imaging, are represented.
Dror Nir added a fresh discussion in “New clinical results supports Imaging-guidance for targeted prostate biopsy” based on a study of “Artemis”, a system that is adjunct to ultrasound and performs 3D Imaging and Navigation for Prostate Biopsy by Eigen (a complementary post to “Imaging-guided biopsies: Is there a preferred strategy to choose?”).
Image fusion is the process of combining multiple images from various sources into a single representative image. Ultrasound is the imaging modality used to guide Artemis in performing the biopsies. In this study MRI is used to overcome the “blindness” regarding tumor location. This supports the detection reliability issue made in his “ Imaging-guided biopsies: Is there a preferred strategy to choose?” and “Fundamental challenge in Prostate cancer screening.”
This makes the case that In the future, MRI-ultrasound fusion for lesion targeting is likely to result in fewer and more accurate prostate biopsies than the present use of systematic biopsies with ultrasound guidance alone. Nevertheless, we haven’t completed the case for prediction of recurrence, even if we may eliminate the unnecessary consequences of radical prostatectomy.
Let’s look a little further. A discussion opens up more questions for discussion. I just read an interesting related article. The door has opened wider.
II. Novel technology to detect cancer in early stages
A. nanoparticles
Researchers have developed novel technology to detect the tumors in the body in early stages with the help of nanoparticles .( Nature Biotechnology).
Cancer cells produce many of the proteins that could be used as biomarkers to detect the cancer in the body but the amount of these proteins is not up to the mark or they may get diluted in the body of the patients making it nearly impossible to detect them in early stages.
This new technology has been developed by the researchers from MIT . Nanoparticles (brown) coated with peptides (blue) cleaved by enzymes (green) at the disease site. Peptides than come into the urine to be detected by mass spectrometry. (Credit: Justin H. Lo/MIT)
In this technology, nanoparticles will interact with the tumor proteins helping to make thousands of biomarkers secreted by the cancer cells. We had this ‘aha’ moment: What if you could deliver something that could amplify the signal?”
- Scientists administered ‘synthetic biomarkers’ having peptides bonded to the nanoparticles and
- the particles interact with the protease enzymes often found in large quantities in cancer cells
as they help them to cut the proteins normally holding the cells in place and to spread in other parts of the body.
Researchers found that the proteases break down hundreds of peptides from the nanoparticles and release them in the bloodstream. These peptides are then excreted in the urine, where the process of mass spectrometry could help to detect such peptides.
These “Synthetic biomarkers” perform three functions in vivo:
- they target sites of disease,
- sample dysregulated protease activities and
- emit mass-encoded reporters into host urine (for multiplexed detection by MS).
According to Bhatia, this biomarker amplification technology could also be used to manage the advancement of the disease and to check the response of the tumors to the drugs.
Reference:
Kwong, G., von Maltzahn, G., Murugappan, G., Abudayyeh, O., Mo, S., Papayannopoulos, I., Sverdlov, D., Liu, S., Warren, A., Popov, Y., Schuppan, D., & Bhatia, S. (2012). Mass-encoded synthetic biomarkers for multiplexed urinary monitoring of disease Nature Biotechnology http://dx.doi.org:/10.1038/nbt.2464
IIB Synthetic Nucleosides
J Gong and SJ Sturla published “A Synthetic Nucleoside Probe that Discerns a DNA Adduct from Unmodified DNA” in JACS Communications on web 4/03/2007). They state that biologically reactive chemicals alkylate DNA and induce structural modifications in the form of covalent adducts that can persist, escape repair, and serve as templates for polymerase-mediated DNA synthesis. Therefore, correlating chemical structures and quantitative levels of adducts with toxicity is essential for targeting specific agents to carcinogenesis.
- DNA adducts are formed at exceedingly low levels.
- Minor lesions may have greater biological impact than more abundant products.
- New molecular approaches for addressing specific low-abundance adducts are needed
They describe the first example of a synthetic nucleoside that may serve as the chemical basis for a probe of a bulky carcinogen-DNA adduct
IIC. MicroRNAs caused by DNA methylation
Another molecular approach “ A microRNA DNA methylation signature for human cancer metastasis” was published in PNAS [2008;105(36):13556-13561)] by A Lujambio , Calin GA, Villanueva A et al.
Different sets of miRNAs are usually deregulated in different cancers, and some miRNAs are aberrantly methylated and silenced, causing tumorigenesis. The authors
- identified aberrantly methylated and silenced miRNAs that are cancer-specific
- using miRNA microarray techniques.
Functional analyses for the selected genes proved that these miRNAs act on C-MYC, E2F3, CDK6 and TGIF2, resulting in metastasis through aberrant methylation of the miRNAs. The authors suggest that these may be applicable to advance research in the clinical setting.
III. New methods require advanced mathematical prediction methods
A. First Case …ProsVue PSA
One of the most elegant papers I have seen in several years has been published in Clinical Biochemistry (CLB–12-00159), by Mark J. Sarnoa1 and Charles S. Davis2. [1Vision Biotechnology Consulting, 19833 Fortuna Del Este Road, Escondido, CA 92029, USA (mjsarno@att.net), 2CSD Biostatistics, Inc., San Diego, CA, 4860 Barlows Landing Cove, San Diego, CA 92130, USA (chuck@csdbiostat.com)]
Robustness of ProsVue™ linear slope for prediction of prostate cancer recurrence: Simulation studies on effects of analytical imprecision and sampling time variation.
Keywords: ProsVue, slope, prostate cancer, random variates.
Financial support for the investigation was provided by Iris Molecular Diagnostics
Abstract: Objective: The ProsVue assay measures
- serum total prostate-specific antigen (PSA) over three time points post-radical prostatectomy and
- calculates rate of change expressed as linear slope. Slopes ≤2.0 pg/ml/month are associated with reduced risk for prostate cancer recurrence.
However, an indicator based on measurement at multiple time points, calculation of slope, and relation of slope to a binary cutpoint may be subject to effects of analytical imprecision and sampling time variation.
They performed simulation studies to determine the presence and magnitude of such effects.
Design and Methods: Using data from a two-site precision study and a multicenter retrospective clinical trial of 304 men, they carried out simulation studies to assess whether analytical imprecision and sampling time variation can drive misclassification of patients with stable disease or classification switching for patients with clinical recurrence.
Results:
- Analytical imprecision related to expected PSA values in a stable disease population results in ≤1.2% misclassifications.
- For recurrent populations, an analysis taking into account correlation between sampling time points demonstrated that classification switching across the 2.0 pg/ml/month cutpoint occurs at a rate ≤11%.
- Lastly, sampling time variation across a wide range of scenarios results in 99.7% retention of proper classification for stable disease patients with linear slopes up to the 75th percentile of the distribution.
Conclusions:
- These results demonstrate the robustness of the ProsVue assay and the linear slope indicator.
- Further, these simulation studies provide a potential framework for evaluation of future assays that may rely on the rate of change principle
The ProsVue Assay has been cleared for commercial use by the US Food and Drug Administration (FDA) as “a prognostic marker in conjunction with clinical evaluation as an aid in
- identifying those patients at reduced risk for recurrence of prostate cancer for the eight year period following prostatectomy.”
The assay measures
- serum total prostate specific antigen (PSA) in post-RP samples and
- calculates rate of change of PSA over the sampling period,
expressing the outcome as linear slope. The assay is novel in at least a few respects.
- the assay is optimized to identify patients at reduced risk for recurrence.
In order to demonstrate efficacy for this indication, the assay employs the immuno-polymerase chain reaction (immuno-PCR) to achieve sensitivity
- an order of magnitude lower than existing “ultrasensitive” PSA assays.
The improved sensitivity allows quantification of PSA at levels exhibited in stable disease (<5 pg/ml), which have been historically below the
measurement range of ultrasensitive assays.
Secondly, the assay is the first to receive clearance based on
- linear slope of tumor marker concentration versus time post-surgery.
- Specifically, PSA is measured in three samples taken between 1.5 and 20 months post-RP and
- the slope calculated using simple least squares regression.
- The calculated slope is compared to a threshold of 2.0 pg/ml/month with values at or below the threshold associated with reduced risk for PCa recurrence.
Does analytical imprecision present a potential risk for misclassification by driving errors in the calculated slope that result in classification switching? Since excursions of precision can occur as point sources in single sampling points or in cumulative effect from the three sampling points, the question is worthy of consideration. They carried out studies
- to address these questions specific to ProsVue and also
- provide a potential framework for evaluation of future assays.
- Similarly, does variation in the time at which samples are taken drive errors resulting in classification switching?
Both questions require evaluating the robustness of the ProsVue Assay and are properly presented for clinical chemists and physicians evaluating use of the assay in clinical practice. Furthermore, since future diagnostic assays may employ the rate of change principle, it is important to develop statistical methods to evaluate effects of variation.
The point is that more sophisticated methods are needed to measure scarce analytes associated with risk for eventual clinical events.
- Accurate measurement at post-RP levels to identify patients with reduced risk of recurrence represents a new development.
- Furthermore, measurement of PSA at multiple time points and calculation of rate of change using linear regression extends application of the analyte markedly beyond traditional use.
Such use presents certain questions of variation effects.
Their results indicate that analytical imprecision in the range of concentrations exhibited in patients at reduced risk for recurrence (the focus of the assay) presents no significant risk of misclassification.
- Classification switching in this population occurs at a frequency of ≤1.2%.
- Slopes for recurrent patients and clinical classification are substantively insensitive to analytical variation even in a subpopulation of recurrent patients with slowly rising PSA values.
- Sampling time variation negligibly affects clinical classification for stable disease patients with slopes at and below the 75th percentile.
Table 1. Side-effects and effects on recovery of treatments for newly diagnosed prostate cancer. The Prostate Brachytherapy Advisory Group: http://www.prostatebrachytherapyinfo.net (Photo credit: Wikipedia)
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IIIB. Other interesting developments are going to need further development and validation.
For instance, research has been published online in the journal Cancer Cell, reports a cellular component that is involved in mobility of cancer to other body parts and inhibition of which could increase the tumor formation. These investigators worked on various animal models including chicken, zebrafish and mouse, and patient samples and have found a cellular component; Prrx1 that stops the cancer cells from staying in organs. Epithelial-mesenchymal transition (EMT) is the process that is required by the cancer cells to spread to other organs. This process helps the cells to become mobile and move with the bloodstream. These cells must lose their mobility before attaching to other body parts.
In the final analysis the cells have to lose the component Prrx1 to lose mobility and to become stationary. Researchers wrote, “Prrx1 loss reverts EMT & induces stemness, both required for metastatic colonization.” Consequently, Prrx1 has to be turned off for these cells to group together to form other tumours.” It has been found that the tumors with elevated levels of Prrx1 cannot form new tumors.
IIIC. PXR and AhR Nuclear Receptor Activation
- The primary mechanism of cytochrome P450 induction is via increased gene transcription which typically occurs through nuclear receptor activation.
- The most common nuclear receptors involved in the induction of drug metabolizing enzymes include the pregnane X receptor (PXR), the aryl hydrocarbon receptor (AhR), and the constitutive androstane receptor (CAR) which are known to regulate CYP3A4, CYP1A2 and CYP2B6, respectively.
- An industry survey of current practices and recommendations (Chu et al., (2009) Drug Metab Dispos 37: 1339-1354) indicates 64% of survey respondents routinely use nuclear receptor transactivation assays to assess the potential of test compounds to cause enzyme induction
- ‘Because reporter assays are relatively high throughput and cost effective, they can be a valuable tool in drug discovery.’(Chu V, Einolf HJ, Evers R, Kumar G, et. (2009) Drug Metab Dispos 37; 1339-1354)
- Luciferase reporter gene assay
No cytotoxicity was observed for any of six compounds at the concentration range tested with the exception of troglitazone for which cytotoxicity was observed at the highest concentration of 50μM. This data point was excluded in this instance and not used for calculating the Emax or EC50.
In brief, CAR and PXR regulate distinct but overlapping sets of target genes, which include certain phase 1 P450 enzymes (e.g., CYP2B, CYP3A, and CYP2C), phase II conjugation enzymes such as UDP glucuronosyltransferase UGT1A1 and sulfotransferase SULT2A, and phase III transporters such as P-glycoprotein (MDR-1). The AhR receptor has been shown to regulate the expression of CYP1A.
Will this be combined with the other methods for drug selection and prediction of drug free survival?
I have mentioned an improved molecular assay of PSA at the pcg/ml level that is approved for use with an acceptable linear prediction of survival for 8 years post radical prostatectomy. Then there is a report of a method of measuring nanoparticles in urine, to amplify the signal detected by mass spectrometry. This new technology has been developed by the researchers from MIT and led by Sangeeta Bhatia at MIT. (Novel technology to detect cancer in early stages, Nature Biotechnology, Dec 16, 2012). There is still another recent report about using gene expression profiles to predict breast cancer, and a number of articles have shown variability in breast cancer types. I view with reservations until I can see long term predictions of prognosis.
IIID. Prediction of Breast Cancer Metastasis by Gene Expression Profiles
The report in Cancer Informatics (http://www.la-press.com; open access) by M Burton, M Thomassen, Q Tan, and TA Kruse is “Prediction of Breast Cancer Metastasis by Gene Expression Profiles: A Comparison of Metagenes and Single Genes.” The authors state “The diversity of microarray platforms has made the full validation of gene expression profiles across studies difficult and, the classification accuracies are rarely validated in multiple independent datasets. The individual genes between such lists may not match, but genes with comparable function are included across gene lists. However, genes can be grouped together as metagenes (MGs) based on common characteristics such as pathways, regulation, or genomic location. Such MGs might be used as features in building a predictive model applicable for classifying independent data.”
Microarray gene expression analysis has in several previous studies been applied to elucidate the relation between clinical outcome and gene expression patterns in breast cancer and has demonstrated improvement of recurrence prediction. In some studies, genes in such profiles might be fully or partially missing in the test data used for validation due to the choice of microarray platform or the presence of missing values associated with a given probe.
To overcome the obstacles, these authors propose that individual genes could be considered part of a larger network such that their expression being controlled by the expression level of other genes or that a group of genes belong to a specific pathway performing a well-defined task. These genes may be controlled by the same transcription factor or located in the same chromosomal region. In fact these groupings have been collected in public databases (the Kyoto Encyclopedia of Genes and Genomes (KEGG), the Molecular Signature Database (MsigDB), the Gene Ontology database (GO)). This could be upregulation or deregulation of pathways associated with metastasis. Metastasis progressionas well as tumor grading (in breast cancer) are associated with accumulated mutations in several genes, leading to amplification or inactivation of genes.
Several studies have defined metagene/gene modules derived from microarray data using various methods such as penalized matrix decomposition which clusters similar genes but without similar expression profiles – hierarchical clustering, correlation, or combining a priori protein-protein interactions with microarray gene expression data defining interaction networks as features. Few studies have attempted to use such predefined gene sets for prediction models.
Their study compared the performance of either metagene- or single gene-based feature sets and classifiers using random forest and two support vector machines for classifier building. The performance within the same dataset, feature set validation performance, and validation performance of entire classifiers in strictly independent datasets were assessed by 10 times repeated 10-fold cross validation, leave-one-out cross validation, and one-fold validation, respectively. To test the significance of the performance difference between MG- and SG-features/classifiers, we used a repeated down-sampled binomial test approach.
They found MG- and SG-feature sets are transferable and perform well for training and testing prediction of metastasis outcome in strictly independent data sets, both between different and within similar microarray platforms. Further, The study showed that MG- and SG-feature sets perform equally well in classifying independent data. Furthermore, SG-classifiers significantly outperformed MG-classifier when validation is conducted between datasets using similar platforms, while no significant performance difference was found when validation was performed between different platforms.
- The MG- and SG-classifiers had similar performance when conducting classifier validation in independent data based on a different microarray platform.
- The latter was also true when only validating sets of MG- and SG-features in independent datasets, both between and within similar and different platforms.
This study appears to be unique in the same way that the PCa prediction study is unique in that genome-based expression patterns are used to classify and predict metastatic potential.
These studies have the potential to materialize into practice changing behavior.
IIIE. Colon Cancer and Treatment Recurrence
Cancer scientists led by Dr. John Dick at the Princess Margaret Cancer Centre have found a way to follow single tumour cells and observe their growth over time. By using special immune-deficient mice to propagate human colorectal cancer, they found that genetic mutations, regarded by many as the chief suspect driving cancer growth, are only one piece of the puzzle. The team discovered that biological factors and cell behaviour — not only genes — drive tumour growth, contributing to therapy failure and relapse. The findings are published December 13 online ahead of print in Science, are “a major conceptual advance in understanding tumour growth and treatment response” according to Dr. Dick.
[1] only some cancer cells are responsible for keeping the cancer growing.
[2] these kept the cancer growing for long time periods (up to 500 days of repeated tumour transplantation)
[3] a class of propagating cancer cells that could lie dormant before being activated.
[4] the mutated cancer genes were identical for all of these different cell behaviours.
[5] given chemotherapy the long-term propagating cells were generally sensitive to treatment, but dormant cells were not killed by drug treatment.
[6] these became activated andpropagated new tumour.
IV. Related References
Diagnostic efficiency of carcinoembryonic antigen and CA125 in the cytological evaluation of effusions.
M M Pinto, L H Bernstein, R A Rudolph, D A Brogan, M Rosman
Arch Pathol Lab Med 1992; 116(6):626-631 ; ICID: 825503
Medically significant concentrations of prostate-specific antigen in serum assessed.
L H Bernstein, R A Rudolph, M M Pinto, N Viner, H Zuckerman
Clin Chem 1990; 36(3):515-518 ; ICID: 825497
Entropy and Information Content of Laboratory Test Results
R T Vollmer
Am J Clin Pathol. 2007;127(1):60-65.
Abstract
This article introduces the use of information theoretic concepts such as entropy, S, for the evaluation of laboratory test results, and it offers a new measure of information, 1 – S,
which tells us just how far toward certainty a laboratory test result can predict a binary outcome. The derived method is applied to the serum markers troponin I and
prostate-specific antigen and to histologic grading of HER-2/neu staining, to cytologic diagnosis of cervical specimens, and to the measurement of tumor thickness in malignant
melanoma. Not only do the graphic results provide insight for these tests, they also validate prior conclusions. Thus, this information theoretic approach shows promise for
evaluating and understanding laboratory test results.
A map of protein-protein interactions involving calmodulin. Protein-protein interactions are both numerous and incredibly complex, and they can be mapped using the Database of
Interacting Proteins (DIP). This image depicts a DIP map for the protein calmodulin. The interactions with the most confidence are drawn with wider connecting lines. This diagram
highlights one level of complexity involved in understanding the downstream effects of gene regulation and expression.
Related article
- Nanoparticles Enable Earlier Cancer Diagnosis (genesisnanotech.wordpress.com)
- Nanoparticles amplify cancer tumor signals, making them much easier to detect (nextbigfuture.com)
- New nano technology may enable earlier cancer diagnosis (smarteconomy.typepad.com)
- MIT-Harvard Center of Cancer Nanotechnology Excellence: (genesisnanotech.wordpress.com)
- Breakthrough study finds cancer cells hide from treatment (thestar.com)
- Imaging and targeting the tumor & predicting tumor response: Where we stand? (pharmaceuticalintelligence.com)
- Residual Tumor Cells That Drive Disease Relapse after Chemotherapy Do Not Have Enhanced Tumor Initiating Capacity
(plosone.org) - Recurrent somatic mutations in chromatin-remodeling and ubiquitin ligase complex genes in serous endometrial tumors
(pharmaceuticalintelligence.com) - What can we expect of tumor therapeutic response? (pharmaceuticalintelligence.com)
- Exome sequencing of serous endometrial tumors shows recurrent somatic mutations in chromatin-remodeling and ubiquitin ligase
complex genes (pharmaceuticalintelligence.com) - Nanotechnology: Detecting and Treating metastatic cancer in the lymph node
- Phillips, T. (2008) The role of methylation in gene expression. Nature Education 1(1)
- Morgan, H., et al. Activation-induced cytidine deaminase deaminates 5-methylcytosine in DNA and is expressed in pluripotent tissues.
Journal of Biological Chemistry 2004;279: 52353–52360. http://dx.doi.org:/10.1074/jbc.M407695200 - Suzuki, M., & Bird, A. DNA methylation landscapes: Provocative insights from epigenomics. Nature Reviews Genetics 2008; 9: 465–476
http://dx.doi.org:/10.1038/nrg2341 - Tamaru, H., & Selker, E. A histone H3 methyltransferase controls DNA methylation in Neurospora crassa. Nature 2001; 414: 277–283.
doi:10.1038/35104508 - Hoopes, L. (2008) Genetic diagnosis: DNA microarrays and cancer. Nature Education 1(1)
- Tibshirani, R., et al. Distinct types of diffuse large B-cell lymphoma identified by gene expression profiling. Nature 2000; 430: 503–511.
http://dx.doi.org:/10.1038/35000501 - Campbell, A. M., et al. Make microarray data with known ratios. CBE Life Sciences Education 2007; 6: 196–197.
- Adams, J. (2008) The complexity of gene expression, protein interaction, and cell differentiation. Nature Education 1(1)
- Stumpf, M. P. H., et al. Estimating the size of the human interactome. Proceedings of the National Academy of Sciences 2008; 105:
6959–6964. http://dx.doi.org:/10.1073/pnas.0708078105 - Torres-Padilla, M. E., et al. Histone arginine methylation regulates pluripotency in the early mouse embryo. Nature 2007; 445:
214–218. http://dx.doi.org:/10.1038/nature05458 - Nunes Amaral, L. A. A truer measure of our ignorance. Proceedings of the National Academy of Sciences 2008; 105: 6795–6796.
http://dx.doi.org:/10.1073/pnas.0802459105
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PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
PUT IT IN CONTEXT OF CANCER CELL MOVEMENT
The contraction of skeletal muscle is triggered by nerve impulses, which stimulate the release of Ca2+ from the sarcoplasmic reticuluma specialized network of internal membranes, similar to the endoplasmic reticulum, that stores high concentrations of Ca2+ ions. The release of Ca2+ from the sarcoplasmic reticulum increases the concentration of Ca2+ in the cytosol from approximately 10-7 to 10-5 M. The increased Ca2+ concentration signals muscle contraction via the action of two accessory proteins bound to the actin filaments: tropomyosin and troponin (Figure 11.25). Tropomyosin is a fibrous protein that binds lengthwise along the groove of actin filaments. In striated muscle, each tropomyosin molecule is bound to troponin, which is a complex of three polypeptides: troponin C (Ca2+-binding), troponin I (inhibitory), and troponin T (tropomyosin-binding). When the concentration of Ca2+ is low, the complex of the troponins with tropomyosin blocks the interaction of actin and myosin, so the muscle does not contract. At high concentrations, Ca2+ binding to troponin C shifts the position of the complex, relieving this inhibition and allowing contraction to proceed.
Figure 11.25
Association of tropomyosin and troponins with actin filaments. (A) Tropomyosin binds lengthwise along actin filaments and, in striated muscle, is associated with a complex of three troponins: troponin I (TnI), troponin C (TnC), and troponin T (TnT). In (more ) Contractile Assemblies of Actin and Myosin in Nonmuscle Cells
Contractile assemblies of actin and myosin, resembling small-scale versions of muscle fibers, are present also in nonmuscle cells. As in muscle, the actin filaments in these contractile assemblies are interdigitated with bipolar filaments of myosin II, consisting of 15 to 20 myosin II molecules, which produce contraction by sliding the actin filaments relative to one another (Figure 11.26). The actin filaments in contractile bundles in nonmuscle cells are also associated with tropomyosin, which facilitates their interaction with myosin II, probably by competing with filamin for binding sites on actin.
Figure 11.26
Contractile assemblies in nonmuscle cells. Bipolar filaments of myosin II produce contraction by sliding actin filaments in opposite directions. Two examples of contractile assemblies in nonmuscle cells, stress fibers and adhesion belts, were discussed earlier with respect to attachment of the actin cytoskeleton to regions of cell-substrate and cell-cell contacts (see Figures 11.13 and 11.14). The contraction of stress fibers produces tension across the cell, allowing the cell to pull on a substrate (e.g., the extracellular matrix) to which it is anchored. The contraction of adhesion belts alters the shape of epithelial cell sheets: a process that is particularly important during embryonic development, when sheets of epithelial cells fold into structures such as tubes.
The most dramatic example of actin-myosin contraction in nonmuscle cells, however, is provided by cytokinesisthe division of a cell into two following mitosis (Figure 11.27). Toward the end of mitosis in animal cells, a contractile ring consisting of actin filaments and myosin II assembles just underneath the plasma membrane. Its contraction pulls the plasma membrane progressively inward, constricting the center of the cell and pinching it in two. Interestingly, the thickness of the contractile ring remains constant as it contracts, implying that actin filaments disassemble as contraction proceeds. The ring then disperses completely following cell division.
Figure 11.27
Cytokinesis. Following completion of mitosis (nuclear division), a contractile ring consisting of actin filaments and myosin II divides the cell in two.
http://www.ncbi.nlm.nih.gov/books/NBK9961/
This is good. I don’t recall seeing it in the original comment. I am very aware of the actin myosin troponin connection in heart and in skeletal muscle, and I did know about the nonmuscle work. I won’t deal with it now, and I have been working with Aviral now online for 2 hours.
I have had a considerable background from way back in atomic orbital theory, physical chemistry, organic chemistry, and the equilibrium necessary for cations and anions. Despite the calcium role in contraction, I would not discount hypomagnesemia in having a disease role because of the intracellular-extracellular connection. The description you pasted reminds me also of a lecture given a few years ago by the Nobel Laureate that year on the mechanism of cell division.
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