MicroRNAs as novel molecular targets of green tea polyphenol epigallocatechin-3-gallate (EGCG): relevance and importance to nutrition sciences and cancer prevention

MicroRNAs (miRNAs) are a class of single-stranded and non-coding endogenous RNAs with 18-25 nucleotides in length. By binding to the complementary sequences in the 3’untranslated region (3’UTR) of protein coding genes, miRNAs regulate posttranscriptionally the mRNA expression of target genes and enzymes involved in various biological processes. The application of high-throughput sequencing, bioinformatics analysis, and novel detection methods has high-lighted promising roles of miRNAs as both novel biomarkers for tumor diagnosis and critical regulators involved in almost all stages of carcinogenesis including cancer initiation, promotion and progression. Epigallocatechin-3-gallate (EGCG), the most investigated active catechin in green tea, has been linked to various health-promoting benefits including chemoprevention and treatment of cancers. In this review, we first present a brief description of EGCG and its major metabolic pathway. It is followed by reviewing the roles of EGCG in the modulation of oncogenic and tumor suppressing miRNAs in some common cancers. These findings suggest that the capacity of EGCG to regulate expression of specific miRNAs provides insights of its new mechanisms of action underlying its chemopreventive and potential beneficial  activities against various cancers.