Epac not PKA catalytic subunit is required for 3T3-L1 preadipocyte differentiation

Cyclic AMP plays a critical role in adipocyte differentiation and maturation. However, it is not clear which of the two intracellular cAMP receptors, exchange protein directly activated by cAMP/cAMP-regulated guanine nucleotide exchange factor or protein kinase A/cAMP-dependent protein kinase, is essential for cAMP-mediated adipocyte differentiation. In this study, we utilized a well-defined adipose differentiation model system, the murine preadipocyte line 3T3-L1, to address this issue. We showed that knocking down Epac expression in 3T3-L1 cells using lentiviral based small hairpin RNAs down-regulated peroxisome proliferator-activated receptor gamma expression and dramatically inhibited adipogenic conversion of 3T3-L1 cells while inhibiting PKA catalytic subunit activity by two mechanistically distinct inhibitors, heat stable protein kinase inhibitor and H89, had no effect on 3T3-L1 adipocyte differentiation. Moreover, cAMP analog selectively activating Epac was not able to stimulate adipogenic conversion. Our study demonstrated that while PKA catalytic activity is dispensable, activation of Epac is necessary but not sufficient for adipogenic conversion of 3T3-L1 cells.