Dominant negative FTase (DNFTα) inhibits ERK5, MEF2C and CREB activation in adipogenesis

We recently demonstrated that dominant negative FTase/GGTase 1 alpha-subunit-inhibited (DNFT alpha-inhibited) insulin-stimulated adipocytes differentiation. DNFT alpha interferes with Ras prenylation whereby ERK 1/2, CREB and the differentiation cascade are downregulated. To further investigate prettylation in adipogenesis, we examined DNFT alpha's ability to inhibit activation of ERK5, MEF2C and CREB. DNFT alpha-inhibited insulin-stimulated expression, activation and nuclear translocation of ERK5. Inhibition was associated with decreased activation of MEF2C and CREB by 80 and 78%, respectively. PD98059 did not block activation of ERK5 and MEF2C, but inhibited CREB phosphorylation by 90%. ERK5 siRNA-inhibited MEF2C activation, whereas it reduced CREB phosphorylation only 50%. Pre-adipocytes expressing DNFT alpha or treated with PD98059 were unable to differentiate to mature adipocytes, whereas pre-adipocytes transfected with ERK5 siRNA showed moderate inhibition of insulin-induced adipogenesis. Taken together, these data suggest that prenylation plays a critical role in insulin-stimulated adipogenesis, and that the ERK5 plays an important, but less crucial role in adipogenesis as compared to ERK 1/2. (c) 2005 Elsevier Ireland Ltd. All rights reserved.