Squamous cell carcinoma (SCC) of the uterine cervix and oral cavity are most common cancers in India. Telomerase reverse transcriptase (TERT) overexpression is one of the hallmarks for cancer, and activation through promoter mutation C228T and C250T has been reported in variety of tumors and often shown to be associated with aggressive tumors. In the present study, we analyzed these two hot spot mutations in 181 primary tumors of the uterine cervix and oral cavity by direct DNA sequencing and correlated with patient's clinicopathological characteristics. We found relatively high frequency of TERT hot spot mutations in both cervical [21.4 % (30/140)] and oral [31.7 % (13/41)] squamous cell carcinomas. In cervical cancer, TERT promoter mutations were more prevalent (25 %) in human papilloma virus (HPV)-negative cases compared to HPV-positive cases (20.6 %), and both TERT promoter mutation and HPV infection were more commonly observed in advanced stage tumors (77 %). Similarly, the poor and moderately differentiated tumors of the uterine cervix had both the TERT hot spot mutations and HPV (16 and 18) at higher frequency (95.7 %). Interestingly, we observed eight homozygous mutations (six 228TT and two 250TT) only in cervical tumors, and all of them were found to be positive for high-risk HPV. To the best of our knowledge, this is the first study from India reporting high prevalence of TERT promoter mutations in primary tumors of the uterine cervix and oral cavity. Our results suggest that TERT reactivation through promoter mutation either alone or in association with the HPV oncogenes (E6 and E7) could play an important role in the carcinogenesis of cervical and oral cancers.
Breast cancer and cervical cancer are the leading causes of death in women worldwide as well as in India, whilst oral cancer is the top most common cancer among Asian especially in Indian men in terms of both incidence and mortality rate. Genetic factors determining the predisposition to cancer are being explored to identify the signature genetic variations associated with these cancers. Recently, a germline deletion polymorphism in APOBEC3 gene cluster which completely deletes APOBEC3B coding region has been studied for its association with cancer risk. We screened the germline deletion polymorphism in 409 cancer patients (224 breast cancer, 88 cervical cancer and 97 oral cancer samples), 478 controls and 239 cervical cancer tissue DNAs of South Indian origin. The results suggest that the APOBEC3A/3B deletion polymorphism is not significantly associated with cancer risk in our study population (OR 0.739, 95 % CI, p value 0.91457). Considering the viral restriction property of APOBEC3s, we also screened cervical cancer tissue DNAs for the human papilloma virus infection. We observed a gradual increase in the frequency of HPV16 infection from AA/BB cases (66.86 %) to AA/-- cases (71.43) which signifies the impact of this deletion polymorphism in HPV infection. In addition, we performed in silico analysis to understand the effect of this polymorphism on miRNA regulation of the APOBEC3A/3B fusion transcript. Only 8 APOBEC3B targeting miRNAs were observed to regulate the fusion transcript of which miR-34b-3p and miR-138-5p were found to be frequently downregulated in cancers suggesting miRNA-mediated deregulation of APOBEC3A expression in cancer patients harbouring this particular deletion polymorphism.
This is the first study that reports the status of the PIK3CA, CASP8, and NOTCH1 mutations in South Indian oral cancer samples. Our study suggests that either mutations in these genes are uncommon in South Indian oral cancer samples or likely other genes in this pathway might be mutated.
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