MicroRNAs as Important Players and Biomarkers in Oral Carcinogenesis
Schematic illustration demonstrating biogenesis and function of miRNA. miRNA genes are transcribed into primary miRNA (pri-miRNA) by RNA polymerase III. These miRNAs are further converted into second precursors (pre-miRNA) by Drosha and are exported into cytoplasm by Exportin 5. Additional processing by Dicer produces miRNA:miRN duplex. Only one strand of miRNA:miRN duplex is preferentially assembled into the RNA-induced silencing complex (RISC). RISC acts on target mRNA(s) and leads to either translational repression or mRNA cleavage. Suppression of tumor suppressive genes and/or activation of oncogenes by miRNA lead to excessive cell proliferation and survival, increased antiapoptosis, and enhanced invasive and metastatic potential of oral keratinocytes, resulting into invasive cancerous growth.