Is cumulative frequency of mitochondrial DNA variants a biomarker for colorectal tumor progression?

Felix O Aikhionbare,Rodney Go,Joel Okoli,Masood Khan,Delicia Carey

doi:10.1186/1476-4598-3-30

Abstract

To examine the relationship between mitochondrial DNA (mtDNA) alterations and colorectal tumorigenesis, we used high-resolution restriction endonucleases and sequencing to assess the mitochondrial genome from three histologic subtypes of colorectal adenomas (tubular = 8; tubulovillous = 9; and villous = 8), colorectal cancer (CRC) tissues = 27, and their matched surrounding normal tissue (MSNT) = 52. The mitochondrial genomes were amplified using 9 pairs of overlapping primers and systematically analyzed by means of high-resolution analysis. DNA fragments showing a shift in banding patterns between the three adenomas, CRC, in comparison to the MSNT were sequenced to identify the mtDNA alterations. A total of thirty-eight germ-line mtDNA variants were observed in this study. Twenty-two of the thirty-eight were identified as mutations and 59% (13 of 22) were silent mutations and one was a 1-bp insertion. Sixteen of thirty-eight were distinct SNPs in flanking regions of the restriction sites and, 6 of the 16 (37%) SNPs were not previously reported. Most of these mutations/SNPs were homoplasmic and distributed in various regions of mitochondrial genes including the 16S and 12S rRNA. Based on our results, mtDNA germline variants increased in prevalence with adenoma CRC progression. To the best of our knowledge, this is the first report to show an increased prevalence of mitochondrial gene variants in CRC tumorigenesis.

Highlights

Colorectal polyps are a frequent occurrence in the general population and adenomatous changes in these polyps are associated with the overwhelming majority of colorectal cancer (CRC)
Given the connection between mitochondria, reactive oxygen species (ROS), and neoplasia, mitochondrial DNA (mtDNA) from CRC adenoma, cancer tissues, and pathologically determined matched surrounding non-cancerous tissue were screened for variants, which may be used as biomarkers for colorectal cancer progression
A total of thirty-eight germ-line mtDNA variants were observed and all mutations/SNPs were considered as germ-line origin since the variants found in the colorectal adenoma polyps or cancerous tissues were found in the matched surrounding normal tissue (MSNT) tissues

Summary

Introduction

Given the connection between mitochondria, ROS, and neoplasia, mtDNA from CRC adenoma, cancer tissues, and pathologically determined matched surrounding non-cancerous tissue were screened for variants, which may be used as biomarkers for colorectal cancer progression. We speculated that there is an association between one or more mtDNA mutations in the adenomatous polyps and CRC progression and the cumulative frequencies of such mtDNA mutations may eventually be demonstrated to be an important marker in adenoma colorectal progression. Results of the high-resolution restriction analyses and sequencing of the entire mitochondrial genome yielded 38 sequence variants (including 16 SNPs from the flanking restriction sites) for the precursor adenomatous polyps and cancer tissues.

Results

Conclusion