Ubiquitin carboxyl-terminal hydrolase l3 promotes insulin signaling and adipogenesis.

Insulin is a potent adipogenic hormone that triggers the induction of a series of transcription factors and specific proteins governing the differentiation of preadipocytes into mature adipocytes. Here we report that ubiquitin carboxyl-terminal hydrolase (UCH)-L3, a deubiquitinating enzyme, promotes insulin signaling and adipogenesis. Uchl3(-/-) mice had less visceral white adipose tissue compared with wild-type mice. In vitro adipogenesis experiments revealed that mouse embryonic fibroblasts (MEFs) and preadipocytes from Uchl3(-/-) mice had impaired ability to differentiate into mature adipocytes than those from wild-type mice. This difference was diminished by removing insulin from the medium. RT-PCR analysis showed that insulin-regulated expression of srebp1c, fas, glut4, and adiponectin is impaired in Uchl3(-/-) cells. The phosphorylation of insulin/IGF-I receptor, Akt, glycogen synthase kinase-3beta, and FoxO1 was decreased in Uchl3(-/-) MEFs treated with insulin. Moreover, ectopic expression of wild-type UCH-L3 restored the phosphorylation of insulin/IGF-I receptor and adipocyte differentiation in Uchl3(-/-) MEFs. In contrast, hydrolase activity-deficient UCH-L3 did not enhance insulin signaling and the expression of glut4, fabp4, and adiponectin, resulting in impaired formation of large lipid droplets. These results suggest that UCH-L3 promotes adipogenesis by enhancing insulin signaling in a hydrolase activity-dependent manner.