Study On The Mitochondrial DNA Mutations In Tumor Tissues And Peripheral Lymphocytes Of Laryngeal Squamous Cell Carcinoma

Background Laryngeal squamous cell carcinoma is the most common malignant tumor in the head and neck. So far,its pathogenesis is a difficult problem which has spanned sever centuries.People are faced with two problems in the field of basic research and clinical practise.First,a research on the pathogenesis of laryngeal squamous cell carcinoma has not achieve a considerable medical breakthrough. Second,its incidence and mortality increase year by year. The research on the tumorigenesis is focused on nuclear DNA mutations.But in recent years, attention has been paid to what the role the mitochondnal DNA(mtDNA) plays in the tumorigenesis.With the research on mitochondnal and mtDNA increasingly deep,we have found that the struture and function alteration of mitochondrial and mtDNA are not only closely related to some degenerative diseases,but also plays an important role in the tumorigenesis.The researchers proposed many hypotheses that mitochondrial will lead to tumor.Objective To investigate the clinical significance of mtDNA mutations in tumor tissues of laryngeal squamous cell carcinoma and their role in the pathogenesis and development of tumor.Methods mtDNA was extracted from the tumor tissues,corresponding distal normal tissues and peripheral lymphocytes derived from 54 patients withlaryngeal squamous cell carcinoma.Fifty-four complete sequences of mtDNA were amplified by PCR and the PCR products 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-eight mutations were identified in 32 cases(60%)of laryngeal squamous cell carcinoma,including 58 point mutations,4 insertions and 4 deletions.The insertions and deletions were located in the D-loop repeat sequence.All the point mutations belong to T-*C or G-*A mutations. Among these mutations , homoplasmic mutations and heteroplasmic mutations were 83.8%(57/68) and 16.2%(ll/68) respectively. These mutations were dispersedly distributed in the full length of mtDNA.The frequency of mutation in D-loop is the highest,in which 43 mutations were detected.21 mutations are located in th peptide-coding regions.Other 7 mutations are located in the 165rRNA> tRNA coding region and non-coding region between COH and tRNALysine coding region. Conclusions In summary,our results suggest that:?Sixty-eight mutations were identified in 36 cases(60%)of laryngeal squamous cell carcinoma, including 58 point mutations,4 insertions and 4 deletions ,suggest that as well as other tumors,there are high frequent mtDNA mutations in the pathogenesis and development of laryngeal squamous cell carcinoma.(2)The mutation of the normal tissues beside the tumor tissues is negative .which suggests that the mutation generally do not occur in the normal tissues.? Among these mutations , homoplasmic mutations and heteroplasmic mutations were 83.8%(57/68) and 16.2%(ll/68) respectively. The mutation of the normal and degenerative tissues is heteroplasmic, while the tumortissues, homoplasmic. There is abnormal change in almost all the mtDNA of tumor tissues.This is of the same view with our results. ? These mutations were dispersedly distributed in the full length of mtDNA.The frequency of mutation in D-loop is the highest,in which 43 mutations were detected.21 mutations are located in the peptide-coding regions. Other 7 mutations are located in the 165rRNAN tRNA coding region and non-coding region between COH and tRNALysine coding region.This suggests that D-loop region is the mutation hot spot.No mutation hot spot was found in peptide-coding regions. ?By analysing the relationship between mtDNA mutation and the clinopathological indexes of laryngeal squamous cell carcinoma,we found that mtDNA mutation was closely related to the clinical stage of laryngeal squamous cell carcinoma(P = 0.02), but was irrelative to patients' age and the number and type of the tumor.This demonstrates that mtDNA mutation is the late phenomenon of the orgin of laryngeal squamous cell carcinoma and will continue exsist in the whole course of the tumor development.?In this study , high frequence of mtDNA mutations to the extene of 60% was foune in the tissues of laryngeal squamous cell carcinoma,most of which is homoplasmic mutation.So, mtDNA mutation may become a potential diagnostic marker for laryngeal squamous cell carcinoma.By detecting mtDNA mutation will increase the sensitivity the diagnosis of tumor and mitochondrial DNA may become the target of some anticancer drugs.