Mitochondrial DNA mutations in lung cancer

BACKGROUND AND OBJECTIVE: Mitochondiral DNA (mtDNA) mutations has been identified in various cancers, but their significance was unknown. This study aimed to detect mtDNA mutations in lung cancer, and to investigate their roles in the carcinogenesis of human lung. METHODS: Total DNA (including nuclear DNA and mtDNA) was extracted from the tumor tissues, corresponding distal non-cancerous lung tissues, and peripheral lymphocytes derived from 58 patients with lung cancer. Fifty-eight overlapping fragments and covering complete sequence of mtDNA were amplified by nested PCR, and the PCR products were sequenced directly with the cycle sequencing methods. The mtDNA mutations in the tumor tissue were determined by comparing with corresponding and peripheral lymphocytes. RESULTS: Sixty-six mutations were identified in 36 cases (62.1%) of lung cancer, including 58 point mutations, 4 insertions, and 4 deletions. These mutations were dispersedly distributed in the full length of mtDNA. The frequency of mutation in D-loop is the highest, in which 18 mutations were detected. No mutation hot spot was found in peptide-coding regions. Among 43 point mutations identified in protein-coding region, 20 were silent mutations. In 8 patients, identical mutations were detected both in the tumor tissues and corresponding distal non-cancerous tissues. CONCLUSION: Most of mtDNA mutations in the lung cancers investigated were occurred randomly and might have no impact on carcinogenesis; whereas the homoplasmic mutations may provide a potential diagnostic marker for lung cancer.