Mutation Of Noncoding D-loop Region Of Mitochondrial DNA In Lung Squamous Carcinoma

ObjectiveMitochondrial DNA (mtDNA) is the target of various carcinogens because of lacking the protection of histone and the imperfect repair system. Although a high frequency of mtDNA mutations have been identified in many kinds of cancers, it remains unknown the relationship of mtDNA mutation between carcinogenesis and development of cancer. As for lung cancer, lung squamous carcinoma(LSC) is a major kind and smoking is a high-risking factor. So, it is necessary to investigate the relation between the mtDNA mutation and LSC.MethodsPeripheral white blood cells (control sample), pericarcinomatous tissues (PT) and cancer tissues were obtained from 15 cases of lung squamous carcinoma patients and mtDNA were extracted by improved one step method. The mtDNA displacement loop (D-loop) fragments and partial coding regions were amplified by PCR. Direct sequencing was followed and mutations were examined.ResultsFifteen LSCs pairs of PT/cancer tissues samples were screened for mutation at coding and noncoding regions, 9.84%(18/183) mutations were detected in the coding region of mtDNA in 11 patients, of which 10 were smokers. The frequency of mutations in the coding region of smokers was higher than that of nonsmokers; 90.16%(165/183) mtDNA mutations occurred in the D-loop, among which 53.33%(88/165) were in HVRII. Mitochondrial DNA microsatellite instability (mtMSI ) occurred in D-loop in15 cases, in which 15 cases occurred in (C)n region and 9 cases in (CA)n region. Of all mutations in the D-loop region, the special mutations in PT and cancer tissues were 47.88% and 19.76%, respectively. And the same mutations shared by PT and cancer tissues were 30.30%. The frequency of special mutations of mtDNA in PT was the highest.ConclusionsThe sequence of mtDNA coding region is comparatively conservative and mutationsin the coding region were correlative with lung squamous carcinoma. The D-loop region is a mutational hotspot. The high frequency of mutations in the HVRII correlates with LSC. Otherwise, the frequency of special mutations of PT is the highest and the phenomenon of reserve mutation may involve keeping the original biological character of carcinoma cells.