The role of Ca2+ mobilization and heterotrimeric G protein activation in mediating tyrosine phosphorylation signaling patterns in vascular smooth muscle cells

This work investigated the role of Ca2+ mobilization and heterotrimeric G p rotein activation in mediating angiotensin II-dependent tyrosine phosphoryl ation signaling patterns. We demonstrate that the predominant, angiotensin II-dependent, tyrosine phosphorylation signaling patterns seen in vascular smooth muscle cells are blocked by the intracellular Ca2+ chelator BAPTA-AM , but not by the Ca2+ channel blocker verapamil. Activation of heterotrimer ic G proteins with NaF resulted in a divergent signaling effect; NaF treatm ent was sufficient to increase tyrosine phosphorylation levels of some prot eins independent of angiotensin II treatment. In the same cells, NaF alone had no effect on other cellular proteins, but greatly potentiated the abili ty of angiotensin II to increase the tyrosine phosphorylation levels of the se proteins. Two proteins identified in these studies were paxillin and Jak 2. We found that NaF treatment alone, independent of angiotensin II stimula tion, was sufficient to increase the tyrosine phosphorylation levels of pax illin. Furthermore, the ability of either NaF and/or angiotensin II to incr ease tyrosine phosphorylation levels of paxillin is critically dependent on intracellular Ca2+. In contrast, angiotensin II-mediated Jak2 tyrosine pho sphorylation was independent of intracellular Ca2+ mobilization and extrace llular Ca2+ entry. Thus, our data suggest that angiotensin II-dependent tyr osine phosphorylation signaling cascades are mediated through a diverse set of signaling pathways that are partially dependent on Ca2+ mobilization an d heterotrimeric G protein activation.