ATF-1 Mediates Protease-activated Receptor-1 but Not Receptor Tyrosine Kinase-induced DNA Synthesis in Vascular Smooth Muscle Cells

Abstract

Previously we have demonstrated that activation of p38 mitogen-activated protein kinase (MAPK) and induction of DNA synthesis in response to receptor tyrosine kinase (RTK) and G protein-coupled receptor (GPCR) agonists require NADH/NADPH-like oxidase activity in vascular smooth muscle cells (VSMC). Here we tested the role of p38 MAPK in RTK and GPCR agonistinduced DNA synthesis in VSMC. Platelet-derived growth factor (PDGF)-BB and thrombin (RTK and GPCR agonists, respectively) activated p38 MAPK in a time-dependent manner in VSMC. Inhibition of p38 MAPK led to a 50% decrease in the DNA synthesis induced by thrombin but not PDGF-BB. ATF-1 was found to be the predominant member of the cyclic AMP response element (CRE)-DNA complex formed in VSMC in response to PDGF-BB and thrombin, and both agonists induced its phosphorylation. Regardless of this, inhibition of p38 MAPK reduced only thrombin-but not PDGF-BB-induced ATF-1 phosphorylation. Similarly, inhibition of p38 MAPK caused a 50% decrease in thrombinbut not PDGF-BB-induced CRE promoter-dependent transcription. Ectopic expression of an inhibitory anti-ATF-1 single-chain antibody fragment, ScFv, significantly interfered with DNA synthesis induced by thrombin but not PDGF-BB. Together, these results suggest the following conclusions. 1) Both RTK and GPCR agonists activate p38 MAPK and induce CRE promoter-dependent transcription; 2) both RTK and GPCR agonists induce ATF-1 phosphorylation, and ATF-1 is a predominant member in the CRE-DNA complexes formed in response to these agents; and 3) p38 MAPK-dependent ATF-1 phosphorylation and CRE promoter-mediated transcription are associated with GPCR agonist-induced VSMC growth.

A Requirement for Calcium-independent Phospholipase A2 in Thrombin-induced Arachidonic Acid Release and Growth in Vascular Smooth Muscle Cells

“…A role for iPLA 2 in lymphocyte growth has also been reported (31). Previously, we showed that p38 MAPK plays a role in thrombin-induced VSMC growth via activation of ATF-1 (36). Recently it was demonstrated that iPLA 2 plays a role in double stranded-RNA-induced nitric oxide synthase gene expression via activation of CREB (42).…”

“…Recently, we have reported that p38 MAPK via phosphorylation and activation of ATF-1 is involved in thrombin-induced growth in VSMC (36). Therefore, to understand the possible mechanism(s) by which thrombin stimulates iPLA 2 activity in VSMC, the role of p38 MAPK was FIG.…”

G Protein regulation of MAPK networks

“…GPCRs, primarily through their cognate G proteins, regulate these three-tier MAPK phospho-relay systems to modulate the expression of specific primary as well as secondary response genes involved in cell proliferation, differentiation and apoptosis (Gutkind, 2000;Kranenburg and Moolenaar, 2001;Werry et al, 2005). G proteins have been shown to regulate diverse transcription factors such as AP-1 (Araki et al, 1997), NF-kB, CRE, SRE (Takeuchi and Fukunaga, 2003), ATF1 (Ghosh et al, 2002), STAT3 (Sellers et al, 1999), ELK1 (Todisco et al, 1997), Egr-1 (Gerasimovskaya et al, 2002), HIF-1a (Sodhi et al, 2000), MEF2 (Fukuhara et al, 2000a, b) via ERK-, JNK-, p38MAPKs-or ERK5 modules. However, only recently the dynamic and multilayered mechanisms by which G proteins regulate these MAPK networks have begun to be unraveled.…”

Thrombin induces expression of FGF-2 via activation of PI3K-Akt-Fra-1 signaling axis leading to DNA synthesis and motility in vascular smooth muscle cells

“…Because thrombin is produced at the sites of vascular injury and influences both migration and proliferation of VSMC (20,36), it is implicated in the pathogenesis of vessel wall diseases (14). In addition, the mechanism(s) by which thrombin influences its nonthrombotic actions, particularly the mitogenic effects in VSMC, is fairly well studied (4,30,33,26,31,29,16). Like many other G protein-coupled receptor (GPCR) agonists, thrombin, in addition to activation of its cognate protease-activated receptors, stimulates a number of signaling events in mediating its nonthrombotic effects.…”