RGS16 attenuates galphaq-dependent p38 mitogen-activated protein kinase activation by platelet-activating factor

The large gene family encoding the regulators of G protein signaling (RGS) proteins has been implicated in the fine tuning of a variety of cellular events in response to G protein-coupled receptor activation. Several studies have shown that the RGS proteins can attenuate G protein-activated extracellular signal-regulated kinase (ERK) group of mitogen-activated protein kinases. We demonstrate herein that the production of inositol trisphosphate and the activation of the p38 group of mitogen-activated protein kinases by the G protein-coupled platelet-activating factor (PAF) receptor was attenuated by RGS16 in both CHO cells transiently and stably expressing RGS16. The inhibition was not observed with RGS2, RGS5, and a functionally defective form of RGS16, RGS16(R169S/F170C). The PAF-induced p38 and ERK pathways appeared to be preferentially regulated by RGS16 and RGS1, respectively. Overexpression of a constitutively active form of Galpha11 (Galpha11Q209L) prevented the RGS16-mediated attenuation of p38 activity, suggesting that Galphaq/11 is involved in PAF activation of p38. The Galphaq/11 involvement is further supported by the observation that p38 activation by PAF was pertussis toxin-insensitive. These results demonstrate for the first time that apart from ERK, p38 activation by a G protein-coupled receptor can be attenuated by an RGS protein and provide further evidence for the specificity of RGS function in G protein signaling pathways.