The Role of MicroRNA in Tumorigenesis: Key Players or Innocent Bystanders

摘要

MicroRNAs (MIRs) are a group of small, non-coding RNAs with an average size of 18-24 nucleotides in length. MIRs are believed to play a role in the regulation of posttranscriptional gene expression. By sequence-specific binding to multiple sites on the 3' UTR regions of messenger RNA (mRNA), translation of the mRNA is stopped and degradation occurs.Since the discovery of the first MIR, Lin-4, in C. elegans , hundreds of MIRs have been discovered in prokaryotes and eukaryotic cells. In mammals, MIR production is a process involving several steps. First, a pri-MIR is generated by the enzyme polymerase II. Then, a pre-MIR hairpin-like precursor RNA with an average length of 60-110 nucleotides is generated in the nucleus by the enzyme Drosha. The pre-MIR is transported to the cytoplasm by Exportin 5. In the cytoplasm the pre-MIR is cleaved by the enzyme Dicer to create an 18-24 nucleotide mature double stranded MIR