Mitochondrial DNA 4977 Basepair Deletion Occurs More Frequently in Normal Colonic Mucosa Than in Tubular Adenoma: Its Potential Role as Tumor Suppressor in Progression of Colon Cancer
MR Lindberg, CM Quick, H Zhang, DC Phan, S Shree, LW Lamps, BR Smoller, C-Y Fan. University of Arkansas for Medical Sciences, Little Rock, AR; John L. McClellan Memorial Veterans Hospital, Little Rock, AR
Background: Tubular adenoma of the colon has long been established as a precursor of colonic adenocarcinoma. The molecular progression of colorectal carcinoma has been established and shows some common genetic alterations shared by both tubular adenomas and colorectal carcinoma. In this study, we aim to characterize the presence and frequency of a common human mitochondrial DNA deletion, delta mtDNA 4977, in tubular adenoma and normal colonic mucosa. Mitochondria are the primary source of free radicals due to their active roles in oxidative phosphorylation, which in turn causes mitochondrial DNA damage (mutation or deletion) and dysfunction. Mitochondrial DNA deletions occur frequently in the process of aging and malignant transformation. The most frequently occurred and commonly analyzed human mitochondrial DNA deletion is delta mtDNA 4977. This is a 4977 basepair mtDNA deletion between two 13-basepair direct repeats.
Design: A total of 12 cases of normal colonic mucosa and 10 cases of tubular adenoma were included in the study. Tissue sections were used for microdissection and DNA samples from these tissues were extracted and subjected to PCR amplification using a primer set that flanks the breakpoint of delta mtDNA 4977. The primer sequences are as follow: MtDNA 8342 forward: 5'-gaa cca aca cct ctt tac ag-3' and MtDNA 13524 reverse: 5'-gat gat gtg gtc ttt gga g-3'.
Results: Delta mtDNA 4977 was detected in 8 of 12 (66.6%) cases of normal colonic mucosa and 1 of 10 (10%) cases of tubular adenoma of the colon.
Conclusions: Delta mtDNA 4977 occurs much more frequently in normal colonic mucosa (66.6%) than in tubular adenoma (10%). It has been hypothesized that delta mtDNA4977 is intolerable and thus, is less commonly seen in transformed cells, probably due to higher metabolism rate and increased free radical generation. When cells that initially had delta mtDNA4977 progress to more proliferative adenomatous epithelia in tubular adenoma, the deletion may confer a metabolic disadvantage to these cells. Cells with such a mtDNA deletion may be overgrown by other neoplastic cells without this mtDNA deletion. Our results support a tumor-suppressive role of Delta mtDNA 4977 in colorectal carcinogenesis.
Wednesday, March 11, 2009 9:30 AM
Poster Session V # 81, Wednesday Morning