Molecular Investigations of the Common Mitochondrial Deletion (MTDNA 49777) Tumoral Tissues as Compared with Adjacent Non-Tumoral Tissues from Gastric Cancer Patients at Baghiyatallah Hospital in Tehran

The human mitochondrial genome has been completely sequenced and each gene has been identified and characterized. The human mtDNA is a supercoiled, double-stranded circular molecule of 16,569 base pairs in size which codes for 13 of the 87 proteins required for oxidative phosphorylation as well as the 12s and 16s rRNAs and 22 tRNAs required for protein synthesis in the mitochondria. One of the common regions and hot spot of the mitochondrial genome so-called the common mitochondrial deletion (AmtDNA4977) was investigated which is at nucleotide number 8470 to 13447. This deletion affects important genes, involved in - OXPHOS (Oxidative Phosphorylation) such as ATPase 6, ATPase 8, Cytochrome Oxidase 111, and NADH subunits ND3, ND4, ND4L, and ND5 which may have a strong metabolic disadvantage. The prevalence of the AmtDNA4977 deletion has been investigated in different cancers. However in this study, we screened the common mitochondrial deletion to determine the prevalence of the common mitochondrial deletion in tumoral tissues as compared with adjacent non-tumoral tissues in gastric cancer by multiplex PCR amplification, polyacrylamide gel electrophoresis and Southern blot. In order to investigate whether a high incidence of mutation exists in mitochondrial DNA of gastric cancer tissues, DNA isolated from these cells was used to amplify hypervariable regions ATPase816, COXIII, ND3, ND4 and ND5 of AmtDNA4977. In 107 cancer patients, AmtDNA4977 was detected in 6 cases (5.60%) of the tumoral tissues and 18 cases (16.82%) of the non-tumoral tissues that were adjacent to the tumors. Levels of AmtDNA4977 deletions were found to be more in non-tumoral tissues than in adjacent tumoral tissues. There was no correlation between the clinical parameters like age, sex, tumor location and tumor size of patients. However there was an obvious relationship with intestinal-type of gastric cancer. The percentage of deleted genome in gastric tumoral tissues ranged from 25% to 74%. The level of the heteroplasmy was quantified by densitometry analysis with a Gel Doc 2000 BIO-RAD instrument (Hercules, CA, USA). The level of heteroplasmy was determined as -25% to 74%. Unknown genetic aspects, ambiguous environmental factors and Reactive Oxygen Species (ROS) can cause the AmtDNA4977 mutation rate to be increased in gastric cancer. The results suggest that percentage level of AmtDNA4977 is less common and intolerable in tumoral tissue, probably because of high metaboIism and ROS generation. We postulate that the cells initially had AmtDNA4977, transformed to tumoral cell and the existence of this deletion confers metabolic disadvantage, thus cells that contain such mtDNA deletion would be overgrown by other cancer cells without this mtDNA deletion. As a result, the presence of AmtDNA4977 will be low in tumoral cell.

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