Loss of DBC1 (CCAR2) affects TNFα-induced lipolysis and Glut4 gene expression in murine adipocytes.

STAT5A (signal transducer and activator of transcription 5A) is a transcription factor that plays a role in adipocyte development and function. In this study, we report DBC1 (deleted in breast cancer 1; also known as CCAR2) as a novel STAT5A-interacting protein. DBC1 has been primarily studied in tumor cells, but there is evidence that loss of this protein may promote metabolic health in mice. Currently, the functions of DBC1 in mature adipocytes are largely unknown. Using immunoprecipitation and immunoblotting techniques, we confirmed that there is an association between endogenous STAT5A and DBC1 proteins under physiological conditions in the adipocyte nucleus that is not dependent upon STAT5A tyrosine phosphorylation. We used siRNA to knockdown DBC1 in 3T3-L1 adipocytes to determine the impact on STAT5A activity, adipocyte gene expression, and TNFα (tumor necrosis factor α)-regulated lipolysis. The loss of DBC1 did not affect the expression of several STAT5A target genes including Socs3, Cish, Bcl6, Socs2, and Igf1 However, we did observe decreased levels of TNFα-induced glycerol and free fatty acids released from adipocytes with reduced DBC1 expression. In addition, DBC1-knockdown adipocytes had increased Glut4 expression. In summary, DBC1 can associate with STAT5A in adipocyte nucleus, but it does not appear to impact regulation of STAT5A target genes. Loss of adipocyte DBC1 modestly increases Glut4 gene expression and reduces TNFα-induced lipolysis. These observations are consistent with in vivo observations that show loss of DBC1 promotes metabolic health in mice.