Identification of an Essential Signaling Cascade for Mitogen-activated Protein Kinase Activation by Angiotensin II in Cultured Rat Vascular Smooth Muscle Cells

Abstract

In cultured rat vascular smooth muscle cells, angiotensin II (Ang II) induced a rapid increase in mitogen-activated protein kinase (MAPK) activity through the Ang II type 1 receptor, which was insensitive to pertussis toxin but was abolished by the phospholipase C inhibitor, U73122. The Ang II-induced MAPK activation was not affected by the protein kinase C inhibitor, GF109203X, and was only partially impaired by pretreatment with a phorbol ester, whereas both treatments completely prevented MAPK activation by the phorbol ester. Intracellular Ca2+ chelation by TMB-8, but not extracellular Ca2+ chelation or inhibition of Ca2+ influx, abolished Ang II-induced MAPK activation. The calmodulin inhibitor, calmidazolium, and the tyrosine kinase inhibitor, genistein, completely blocked MAPK activation by Ang II as well as by the Ca2+ ionophore A23187. Ang II caused a rapid increase in the binding of GTP to p21(ras), and this was inhibited by genistein, TMB-8, and calmidazolium but not by pertussis toxin or GF109203X. These data suggest that Ang II-induced MAPK activation through the Ang II type 1 receptor could be mediated by p21(ras)activation through a currently unidentified tyrosine kinase that lies downstream of Gq-coupled Ca2+/calmodulin signals.

Antagonists of Calcium Fluxes and Calmodulin Block Activation of the p21-Activated Protein Kinases in Neutrophils

“…Although the answer to this question is not yet known, a modest amount of speculation may be appropriate here. Certain receptors coupled to pertussis-toxin-sensitive G proteins can trigger activation of Srcrelated tyrosine kinases, Ras and ERK through a stimulatory pathway that contains PI-PLC and CaM (27,28). Fig.…”

“…Previous studies have shown that CaM antagonists can either block (27,28) or prolong (46) the activation of ERKs in various cell types. Because ERKs are effector proteins for the small GTPase Ras, we examined the effects of CaM antagonists on the activation of Ras, MEK, and ERK in neutrophils (Figs.…”

“…Recent studies have shown that heterotrimeric G proteins can activate Ras, Src family tyrosine kinases, and the extracellular signal regulated kinases (ERKs-1/2) through a variety of signal transduction pathways (27,28). One such pathway contains phosphatidylinositolspecific phospholipase C (PI-PLC) and the Ca 2ϩ /calmodulin (CaM) complex as major components in the activation of Src and Ras (28).…”

Arachidonic acid mediates angiotensin II effects on p21ras in renal proximal tubular cells via the tyrosine kinase-Shc-Grb2-Sos pathway

“…Recently, p21ras has been documented to be involved in Gq and phospholipase (PL) C mediated Ang II signaling in cardiac myocytes (7) and vascular smooth muscle cells (8). However, the sequential upstream events linking this GPCR to p21ras were not delineated but seemed to involve the Shc-Grb2-Sos adapter proteins in cardiac myocytes (7).…”

Molecular and cellular mechanisms of action of angiotensin II (AT1) receptors in vascular smooth muscle

“…It has been suggested that this Ca 2+ -dependent tyrosine kinase could be related to another Ca 2+ -dependent tyrosine kinase, PYK2, previously described in neuronal cells. 98 Another class of tyrosine kinases linked to AT 1 receptor activation is the Janus kinase (JAK) family. The JAK/STAT pathway is a signalling pathway comprising a number of tyrosine kinases and transcription factors.…”