Activation of Gz attenuates Rap1-mediated differentiation of PC12 cells

Abstract

We previously identified a specific activation-dependent interaction between the a subunit of the heterotrimeric G protein, Gz, and a regulator of Rap1 signaling, Rap1GAP (Meng, J., Glick, J. L., Polakis, P., and Casey, P. J. (1999) J. Biol. Chem. 274, 36663-36669). We now demonstrate that activated forms of Gαz are able to recruit Rap1GAP from a cytosolic location to the membrane. Using PC12 cells as a model for neuronal differentiation, the influence of Gz activation on Rap1-mediated cell differentiation was examined. Introduction of constitutively-activated Gαz into PC12 cells markedly attenuated the differentiation process of these cells induced by a cAMP analogue. Treatment of PC12 cells expressing wild type Gαz with a specific agonist to the α2A-adrenergic receptor also attenuated cAMP-induced PC12 cell differentiation, demonstrating that receptor-mediated activation of Gz was also effective in this regard. Furthermore, activation of Gz decreased the ability of the cAMP analogue to trigger both Rap1 and extracellular-regulated kinase (ERK) activation. Differentiation of PC12 cells induced by nerve growth factor (NGF) is also thought to be a Rap1-mediated process, and Gz activation was found to attenuate this process as well. Rap1 activation, ERK phosphorylation, and PC12 cell differentation induced by NGF treatment were all significantly attenuated by either transfection of constitutively activated Gαz or receptor-mediated Gz activation. Based on these findings, a model is proposed in which activation of Gz results in recruitment of Rap1GAP to the membrane where it can effectively down-regulate Rap1 signaling. The implications of these findings in regard to a possible role for Gz in neuronal development are discussed.