Down-regulation of microRNA-34a* in rheumatoid arthritis synovial fibroblasts promotes apoptosis resistance

MicroRNAs and autoimmunity

The role of microRNAs (miRNAs) in the regulation of many physiological and pathological processes has been intensely studied in recent years. Some miRNAs, such as miR-146a and miR-182, play a dominant role in the regulation of the innate and adaptive immune responses, respectively. Many miRNAs are reportedly deregulated in autoimmune diseases, but miR-146a in particular seems to be consistently altered. The overexpression or underexpression of miRNAs can influence specific targets and pathways, leading to autoimmune disease phenotypes, and this is supported also by some in vivo studies. Targeting miRNAs could represent a valid future therapeutic option for autoimmune diseases.

MicroRNA-24 regulates XIAP to reduce the apoptosis threshold in cancer cells

MicroRNAs have been implicated as important mediators of cancer cell homeostasis, and accumulating data suggest compelling roles for them in the apoptosis pathway. X-linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor and an important barrier to apoptotic cell death, but the mechanisms which determine the diverse range of XIAP expression seen in cancer remains unclear. In this study, we present evidence that miR-24 directly targets the 3′UTR of the XIAP mRNA to exert translational repression. Using a heuristic algorithm of bioinformatics analysis and in vitro screening, we identified miR-24 as a candidate regulator of XIAP expression. Array CGH and SKY analysis reveal that genomic copy number loss at the miR-24 locus is concordant with loss of endogenous miR-24 in cancer cells. Using a luciferase construct of the XIAP 3′UTR, we showed that miR-24 specifically coordinates to the XIAP mRNA. And interference with miR-24’s binding of the critical seed region, resulting from site-directed mutagenesis of the 3′UTR, significantly abrogated miR-24’s effects on XIAP expression. Moreover, miR-24 over-expression can overcome apoptosis-resistance in cancer cells via down-regulation of XIAP expression, and the resulting cancer cell death induced by TRAIL is executed by the canonical caspase-mediated apoptosis pathway. In summary, our data suggest a novel mechanism by which miR-24 directly modulates XIAP expression level and consequently the apoptosis threshold in cancer cells.

[Role of microRNA in rheumatoid arthritis]

MicroRNAs (miRNAs) are endogenous non-coding small RNAs of approximately 22 nucleotides in length. miRNAs repress expression of target genes at the posttranscription level. Biological relevance of miRNAs have been investigated in physiological and pathological conditions, revealing their involvement in fine tuning of the biological events, such as cell proliferation, differentiation and cell death. In 2008, miR-146a and miR-155 were reported to be involved in the pathology of rheumatoid arthritis. Subsequently, expression and function of other miRNAs in rheumatoid arthritis have been reported. These reports suggest that miRNAs could be novel candidates for the therapeutic target or biomarker of rheumatoid arthritis. Further investigations are required to identify, characterize and modulate the key miRNA in the pathology of rheumatoid arthritis.