MicroRNAs and cytokines

MicroRNAs (miRNAs) regulate posttranscriptional gene expression by inhibiting protein translation or by destabilizing target mRNA. While most miRNAs are widely expressed in various types of organs or tissues, a few are expressed only in limited developmental stages or in specific tissues or cells. Alteration of miRNA expression in human organs or tissues may contribute to the development of many diseases including cancer and chronic inflammation. Cytokines are also involved in the development of cancer and many other chronic inflammatory diseases such as chronic obstructive pulmonary disease (COPD). MiRNAs can regulate cytokine expression either by directly binding to its target sequence or by indirectly regulating a cluster of adenine and uridine-rich element binding proteins (ARE-BPs). Vice versa, cytokines, especially pro-inflammatory cytokines (IL-1β and TNF-α), can also regulate expression of miRNAs such as miR-146a and miR-155. Expression of miR-146a is dramatically increased in response to the stimulation of inflammatory cytokines in many human cells including human bronchial epithelial cells (HBECs). Transient transfection of miR-146a mimic into HBECs not only protects the cells from death, but also promotes cell proliferation, suggesting miR-146a may provide a link between chronic inflammation and lung cancer or peri-bronchial fibrosis via extending cell survival and stimulating cell proliferation.