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Posts Tagged ‘genetic instability’

Author and Curator: Ritu Saxena, Ph.D.

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Role of mitochondria in cancer has long been speculated. Infact, Warburg in his 1956 publication talked about  how cancer cells exhibit a different mechanism of mitochondrial respiration than normal cells and how this basic difference in glucose metabolism could be utilized to develop targeted therapies against cancer cells. Several decades later, mitochondrial defects, both genetic and functional have been detected and associated with cancer. Here is a brief overview of the mechanisms by which mitochondrial defects could be associated with cancer:

1. Alteration in energy metabolism- well documented function of mitochondria is ATP production through oxidative phosphorylation that involved both mitochondrial and nuclear proteins. Various complexes are involved in the process of electron transport through the respiratory chain. Some electrons might leak, leading to formation of ROS. Further, certain mutations in the ETC could tamper with the mechanism of electron transfer resulting in increased leakage of electrons finally leading to an increase in ROS production. ROS has been associated with cancer, however, the exact mechanism is not known.

2. Alteration of apoptotic machinery- Mitochondrial houses several pro-apoptotic proteins including cytochrome c, apoptosis induced factor (AIF), endonuclease G, and smac/DIABLO. However, when these are released into from mitochondrial, apoptotic signaling is triggered and the cell goes through programmed death. For example, release of cytochrome c into the cytosol triggers a set of proteins referred to as caspases leading to apoptosis of the cell. The exact role of mtDNA mutations in the cellular response to anticancer agents that target apoptotic machinery has not been defined and a lot of research is being done in this area.

3. Somatic mutations- While germline mutations of the mtDNA have implicated in several diseases such as Pearson Marrow syndrome Kearns-Sayre-CPEO, Leber’s hereditary optic neuropathy, Leigh’s syndrome and several others, somatic mutations have also been a associated with several diseases, especially cancer. High rate of mutations in the mtDNA, much more than that of the nuclear genome is the result of several factors – the absence of histone proteins, close proximity to the electron transport chain, reduced repair machinery, lack of introns. The mtDNA mutations could be induced by endogenous or exogenous agents such as ROS, chemical agents, and/or radiation. The mutations could either be detrimental to its survival in which case it would vanish eventually. In case it confers growth advantage to the cell, the mutation would eventually develop into a homoplasmic state where all the alleles of the different copies of the mtDNA harbor it. It may cause a functional change of the protein derived from the mutated gene resulting in the alterations of mitochondrial function. It might be speculated that the mutated mtDNA results in increase in endogenous ROS production further leading to DNA damage, genetic instability and cancer development.

Sources:

Warburg publication: http://www.ncbi.nlm.nih.gov/sites/entrez/13298683?dopt=Abstract&holding=f1000,f1000m,isrctn

Mitochondrial ROS bifurcation: http://informahealthcare.com/doi/abs/10.1080/10715760290021225

Mitochondria and apoptosis: http://www.ncbi.nlm.nih.gov/sites/entrez/11711427?dopt=Abstract&holding=f1000,f1000m,isrctn

Mitochondria and Cancer: http://www.molecular-cancer.com/content/1/1/9/#B7

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http://pharmaceuticalintelligence.com/2012/08/14/detecting-potential-toxicity-in-mitochondria/

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http://pharmaceuticalintelligence.com/2012/07/05/stem-cells-for-the-rescue-of-mitochondrial-dysfunction-in-parkinsons-disease-7/

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