Role of miRNA in cancer diagnosis, prognosis, therapy and regulation of its expression by Epstein-Barr virus and human papillomaviruses: With special reference to oral cancer.

MicroRNAs (miRNAs) belong to class of small non-coding RNAs that regulate numerous biological processes by targeting broad set of messenger RNAs. Research on miRNA-based biomarkers has witnessed phenomenal growth, owing to non-invasive nature of miRNA based screening assays and their sensitivity and specificity in detecting cancers. Their discovery in humans in 2000 has led to an explosion in research in terms of their role as biomarker, therapeutic target and trying to elucidate their function. This review aims to summarize the function of microRNAs as well as to examine how dysregulation at any step in their biogenesis or functional pathway can play a role in development of cancer, together with its possible involvement in oral cancer. Overexpression of oncogenic miRNA may reduce protein products of tumor-suppressor genes but loss of tumor-suppressor miRNA expression may cause elevated levels of oncogenic protein. One or both of these alterations could represent new targets for cancer diagnosis and treatment in future. Many researchers have focused on genetic and epigenetic alterations in OSCC cells. The genetic susceptibility, endemic environment factors, and Epstein-Barr virus (EBV) infection are believed to be the major etiologic factors of OSCC. Once metastasis occurs, prognosis is very poor. It is urgently needed to develop biomarkers for early clinical diagnosis/prognosis, and novel effective therapies for oral carcinoma. High-risk HPV infection leads to aberrant expression of cellular oncogenic and tumor suppressive miRNAs. The emergence of miRNA knowledge, and its potential interactive action with such alterations, therefore creates new understanding of cell transformation.