MicroRNA Role in Thyroid Cancer Development

Abstract

MicroRNAs (miRNAs) are endogenous noncoding RNAs that negatively regulate gene expression by binding the 3' noncoding region of the messenger RNA targets inducing their cleavage or blocking the protein translation. They play important roles in multiple biological and metabolic processes, including developmental timing, signal transduction, and cell maintenance and differentiation. Their deregulation can predispose to diseases and cancer. miRNA expression has been demonstrated to be deregulated in many types of human tumors, including thyroid cancers, and could be responsible for tumor initiation and progression. In this paper we reviewed the available data on miRNA deregulation in different thyroid tumors and describe the putative role of miRNA in thyroid cancer development.

Figure 1

Model for miRNA biogenesis and functional mechanisms. miRNA genes are transcribed by RNA polymerase II (pol II) into primary transcripts (pri-miRNAs) that are cleaved by the Drosha-DGCR8 complex to 60–70 nt pre-miRNAs. Pre-miRNAs are then transported to the cytoplasm by exportin-5 and there processed by the endonuclease Dicer to generate a double-stranded mature miRNA of about 21–23 nt. After a strand selection/separation process, the mature miRNA is incorporated into the RISC complex while the other strand is degraded. RISC complex will recognize and mediate cleavage or repression of specific mRNAs.