β2-Adrenergic Receptor-induced p38 MAPK Activation Is Mediated by Protein Kinase A Rather than by Gi or Gβγ in Adult Mouse Cardiomyocytes

Abstract

Increasing evidence shows that stimulation of ␤-adrenergic receptor (AR) activates mitogen-activated protein kinases (MAPKs), in addition to the classical G sadenylyl cyclase-cAMP-dependent protein kinase (PKA) signaling cascade. In the present study, we demonstrate a novel ␤ 2 -AR-mediated cross-talk between PKA and p38 MAPK in adult mouse cardiac myocytes expressing ␤ 2 -AR, with a null background of ␤ 1 ␤ 2 -AR double knockout. ␤ 2 -AR stimulation by isoproterenol increased p38 MAPK activity in a time-and dose-dependent manner. Inhibiting G i with pertussis toxin or scavenging G␤␥ with ␤ARK-ct overexpression could not prevent ␤ 2 -AR-induced p38 MAPK activation. In contrast, a specific peptide inhibitor of PKA, PKI (5 M), completely abolished the stimulatory effect of ␤ 2 -AR, suggesting that ␤ 2 -ARinduced p38 MAPK activation is mediated via a PKA-dependent mechanism, rather than by G i or G␤␥. This conclusion was further supported by the ability of forskolin (10 M), an adenylyl cyclase activator, to elevate p38 MAPK activity in a PKI-sensitive manner. Furthermore, inhibition of p38 MAPK with SB203580 (10 M) markedly enhanced the ␤ 2 -AR-mediated contractile response, without altering base-line contractility. These results provide the first evidence that cardiac ␤ 2 -AR activates p38 MAPK via a PKA-dependent signaling pathway, rather than by G i or G␤␥, and reveal a novel role of p38 MAPK in regulating cardiac contractility. Mitogen-activated protein kinases (MAPKs)1 have been implicated in the regulation of multitude vital cellular processes, including cell differentiation, proliferation, cell growth, and cell death (1-4). There are three major subgroups identified, including the extracellular signal-regulated kinase (ERK1/2), c-jun-NH 2 -terminal kinase (JNK), and p38 MAPK. Various extracellular stimuli, such as growth factors, cytokines, mechanical stress, UV light, osmotic stress, and heat shock, can activate MAPK signaling cascades (5). Increasing evidence has shown that G protein-coupled receptors (GPCRs), e.g. ␤-adrenergic receptor (AR), also regulate MAPKs, particularly ERK1/2 MAPK. One major pathway of GPCR-mediated activation of MAPKs is dependent on "transactivation" of a panel of receptor tyrosine kinases (such as epidermal growth factor and insulin-like growth factor) (6 -8). Specifically, stimulation of GPCRs leads to the release of free G␤␥ dimers, which, in turn, activate these receptor tyrosine kinases by unidentified mechanisms, resulting in activation of ERK1/2 MAPKs (9, 10).A large body of evidence has demonstrated that activation of p38 MAPK, also called a stress-activated protein kinase, is associated with the onset of cardiac hypertrophy and cell death in response to in vivo pressure overload or ischemic/reperfusion injury (11-13). In G␣ q transgenic mice, the transition of hypertrophy to apoptosis is coincident with activation of p38 MAPK (14). This paradigm has been further manifested by p38 MAPK-induced apoptosis in cultured neonatal rat cardiac myocytes overexpressing p38 MAPK (15)...

A Novel Protein Kinase A-independent, β-Arrestin-1-dependent Signaling Pathway for p38 Mitogen-activated Protein Kinase Activation by β2-Adrenergic Receptors

“…We show that ␤ 2 -ARs stimulation induces a biphasic activation (early and delayed) of p38 MAPK, which is distinct from a previously described monophasic model in mast cells (1), fat cells, embryonic chick ventricular cells (4), and adult rat cardiac myocytes (8). Interestingly, early phase activation of p38 MAPK can be prevented by reducing the expression of ␤-arrestin-1 by siRNA and inhibiting NADPH oxidase activity.…”

Cutting Edge: Proliferating Fibroblasts Respond to Collagenous C1q with Phosphorylation of p38 Mitogen-Activated Protein Kinase and Apoptotic Features

“…Cytosols of HF stimulated with C1q display high levels of type I protein kinase A (PKA-I) (3). Given that in several systems p38 MAPK is a downstream target of the cAMP/PKA-I pathway, in cultures of HF, C1q-induced PKA-I activity may be a prerequisite for p38 signaling (25,26).…”

Small Heat-Shock Protein Hsp20 Attenuates β-Agonist–Mediated Cardiac Remodeling Through Apoptosis Signal–Regulating Kinase 1

“…neal injections of different doses of ISO (10,15,30, 50 mg/kg body weight) for 30 minutes, and heart tissues were rapidly harvested for analysis of MAPK signaling. We found that the phosphorylated levels of p38, SAPK/JNK, and ERK1/2 were significantly increased in both WT and Hsp20 TG hearts treated with various ISO doses; however, the degree of p38 and SAPK/JNK activation was significantly greater in WT hearts, whereas ERK was similarly activated in the 2 groups (Figure 4).…”