Objective To evaluate the potential utility of temporal temperature gradient gel electrophoresis (TTGE) in detecting homoplasmic and heteroplasmic mtDNA mutations in patients with cancers. Methods The entire mtDNA of tumor and corresponding normal tissues from total 117 patients were amplified by PCR, and the somatic mutations were screened by TTGE. DNA fragments showing different band patterns in normal and tumor tissues in TTGE were sequened to identify the exact mutations. Results 160 fragments harbouring mtDNA mutations were found by TTGE in total 3 654 fragments. Compared with the direct squencing results, the sensitivity and specificity of TTGE in mutation detection were 96.27% and 94.05% respectively. Conclusion TTGE is an effective method for screening acquired homoplasmic mitochondrial gene mutation and its different percentage.

BACKGROUNDTo detect the somatic mutations in complete mitochondrial genome and to investigate the role of mtDNA mutation in the tumorigenesis of lung cancer.

METHODSDNA were extracted from sixteen lung cancer and corresponding normal tissues. The entire mitochondrial genome was amplified with 32 pairs of overlapping primers. mtDNA mutations were screened by temporal temperature gradient gel electrophoresis. mtDNA fragments showing different banding patterns between tumor and paracancerous tissues were sequenced to identify the exact mutations. The common 4 977 bp deletion was also analyzed in all sixteen tumor tissues as well as the matched paracancerous samples by PCR.

RESULTSTen out of sixteen (62.5%) tumor tissues showed a total of 29 mutations. Half (5/10) of tumors with somatic mutation presented one mutation and the rests had multiple ones. Out of 29 mutations, 17 (58.62%) were in D-loop region, 2 (6.90%) in rRNA and 10 (34.48%) in mRNA. Among 10 mRNA mutations, 7 were silence and 3 were missense mutations. Five out of twenty-nine alterations were heteroplasmic to heteroplasmic change, one was homoplasmic to heteroplasmic and the remains (23/29, 79.3%) were homoplasmic to homoplasmic change. There were five common deletions found, two in tumor tissues and three in paracancerous tissues. There was no mitochondrial microsatellite instability, except for the short deletion or insertion in np303-309.

CONCLUSIONSThe high incidence of mtDNA mutations found in patients with lung cancer suggests that mtDNA alterations might play an important role in tumorigenesis of lung cancer. Further studies should be needed to determine the pathological effects of somatic mtDNA mutations in lung cancer.