Emerging functions of microRNA-146a/b in development and breast cancer: microRNA-146a/b in development and breast cancer.

MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression through translational repression or mRNA degradation. These molecules play critical roles in regulating normal developmental processes, but when deregulated, are causally linked to the pathogenesis of numerous diseases, including cancer. MicroRNA-146a and -146b are encoded by two different genes, but differ by only two bases and appear to function redundantly in many systems. Initial studies branded miR-146a/b as important mediators of inflammatory signaling, documenting the ability of these miRNAs to influence differentiation, proliferation, apoptosis and effector immune mechanisms within the hematopoietic system. Numerous contemporary studies now implicate miR-146a/b as pleiotropic regulators of tumorigenesis, as a polymorphism in miR-146a and altered expression of both miR-146a/b have been linked with cancer risk, tumor histogenesis and invasive and metastatic capacity in diverse cancers. Despite the numerous reports concerning miR-146a/b in human cancers, the mechanistic contributions of these miRNAs in both normal and neoplastic mammary gland development and biology remains poorly characterized.