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 protein activation in mediating angiotensin II-dependent tyrosine phosphorylation 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 heterotrimeric G proteins with NaF resulted in a divergent signaling effect; NaF treatment was sufficient to increase tyrosine phosphorylation levels of some proteins independent of angiotensin II treatment. In the same cells, NaF alone had no effect on other cellular proteins, but greatly potentiated the ability of angiotensin II to increase the tyrosine phosphorylation levels of these proteins. Two proteins identified in these studies were paxillin and Jak2. We found that NaF treatment alone, independent of angiotensin II stimulation, was sufficient to increase the tyrosine phosphorylation levels of paxillin. Furthermore, the ability of either NaF and/or angiotensin II to increase tyrosine phosphorylation levels of paxillin is critically dependent on intracellular Ca²⁺. In contrast, angiotensin II-mediated Jak2 tyrosine phosphorylation was independent of intracellular Ca²⁺ mobilization and extracellular Ca²⁺ entry. Thus, our data suggest that angiotensin II-dependent tyrosine phosphorylation signaling cascades are mediated through a diverse set of signaling pathways that are partially dependent on Ca²⁺ mobilization and heterotrimeric G protein activation.