miR-148a is a downstream effector of X-box-binding protein 1 that silences Wnt10b during adipogenesis of 3T3-L1 cells

Wnt10b, an endogenous inhibitor of adipogenesis, maintains preadipocytes in an undifferentiated state by suppressing adipogenic transcription factors. We have previously demonstrated that Wnt10b transcription during adipogenesis is negatively regulated by X-box-binding protein 1 (XBP1), an important transcription factor of the unfolded protein response. In this report, we demonstrate that XBP1s can directly induce the transcription of microRNA-148a, which in turn mediates the silencing of Wnt10b mRNA during adipogenic differentiation of 3T3-L1 cells. Stability of Wnt10b mRNA was found to be significantly increased by knockdown of XBP1s. Using computational algorithms, a set of microRNAs was predicted to bind Wnt10b mRNA, of which microRNA-148a was selected as a potential target for XBP1s. Our results revealed that microRNA-148a could bind to the 3′UTR of Wnt10b mRNA. Its ectopic expression significantly suppressed both Wnt10b expression and β-catenin activity. When we altered the expression of XBP1 in 3T3-L1 cells, microRNA-148a levels changed accordingly. A potential XBP1 response element was found in the promoter region of microRNA-148a, and XBP1s directly bound to this response element as shown by point mutation analysis and chromatin immunoprecipitation assay. In addition, a microRNA-148a mimic significantly restored adipogenic potential in XBP1-deficient 3T3-L1 cells. These findings provide the first evidence that XBP1s can regulate Wnt10b by a post-transcriptional mechanism through directly inducing microRNA-148a. Fat cell development is driven in part via the production of a small RNA molecule that eliminates obstacles to cellular maturation. Several studies have shown that a protein known as X-box binding protein 1 (XBP1) is essential for fat cell differentiation by regulating levels of many proteins Researchers led by Oh-Joo Kwon at the Catholic University of Korea have shown that XBP1 achieves this by eliminating the RNA messages encoding Wnt10b, a protein that maintains precursor cells in an immature state. In a series of experiments, Kwon and colleagues showed that XBP1 stimulates the production of microRNA-148a, a small RNA molecule that binds to and destabilizes Wnt10b mRNA. The degradation of this mRNA sharply reduces production of Wnt10b, freeing precursor cells to produce a host of other proteins that contribute to the fat cell developmental process.