MicroRNA and colorectal cancer.

MicroRNAs are small 19 to 22 nucleotide sequences of RNA that participate in the regulation of cell differentiation, cell cycle progression, and apoptosis. MicroRNAs act much like small interfering RNA, annealing with RISC, to cleave messenger RNA, and microRNAs exert translational inhibition that is incompletely understood. They are important factors in tumorigenesis and have been the subject of research in many types of cancers, including colon cancer. MicroRNAs may be abnormally down-regulated or up-regulated in colon-cancer tissue. Artificial dysregulation of certain microRNAs will trigger tumorigenesis or apoptosis depending on which microRNA is manipulated. Although the natural mechanisms for the dysregulation of microRNAs is still largely unknown, one theory tested in colon cancers proposes that DNA hypermethylation leads to down-regulation of certain microRNAs. Specific microRNA expression patterns help characterize specific cancers and may be used as a prognostication factor and in following patient response to 5-fluorouracil chemotherapy. This article reviews the existing literature pertaining to the study of microRNA in colorectal cancer.