["Aberrant activation of MAPK has been implicated to play important roles in pathological processes of endometriosis. However, how MAPK are constitutively activated in endometriotic tissues remains largely unknown. microRNA are small noncoding RNA that regulate the stability or translational efficiency of target mRNA by interacting with the 3' untranslated region. Thus, miRNA are thought to be modulators of the transcriptional response, fine-tuning gene expression.", 'The aim of this study was to evaluate the functional roles of microRNA-20a (miR20a) in MAPK activation and the pathogenesis of endometriosis.', 'miR20a expression was analyzed in nonpaired (endometrium = 17; endometriosis = 37) and paired (n = 12) endometriotic tissues by quantitative RT-PCR. Overexpression of miR20a in eutopic endometrial stromal cells or inhibition of miR20a in ectopic endometriotic stromal cells was used to evaluate its impact on ERK phosphorylation and subsequently angiogenesis- and proliferation-related gene expression.', 'Levels of miR20a were up-regulated in endometriotic stromal cells. Elevation of miR20a was up-regulated by hypoxia inducible factor-1α. The up-regulation of miR20a causes the down-regulation of dual-specificity phosphatase-2, which leads to prolonged ERK phosphorylation and an increase in the expression of several angiogenic genes. Furthermore, the up-regulation of miR20a enhances the prostaglandin E(2)-induced expression of fibroblast growth factor-9, a potent mitogen that stimulates both endothelial and endometrial cell proliferation.'] Does hypoxia-induced microRNA-20a expression increase ERK phosphorylation and angiogenic gene expression in endometriotic stromal cells?