Functional receptor for platelet‐derived growth factor in rat embryonic heart‐derived myocytes: Role of sequestered Ca²⁺ stores in receptor signaling and antagonism by arginine vasopressin

Abstract

Platelet-derived growth factor (PDGF) is established to function importantly in the growth, development, and function of most cardiovascular tissues. However, evidence that the factor participates directly in the growth and development of the mammalian myocardium is lacking. H9c2 rat embryonic ventricular myocytes were found to respond to PDGF-BB with a rapid mobilization of cell-associated Ca2+ and increased rates of protein synthesis, followed by markedly increased rates of DNA synthesis. PDGF acted as a full mitogen for these myocytes. Evidence is provided that documents the expression of classical PDGF-beta, but not PDGF-alpha, receptors in H9c2 cells. Scatchard analysis revealed the presence of 44,000 beta-receptors per myocyte. Cell shortening and clustering of plasmalemmal beta-receptors occurred within 30 min of exposure to PDGF-BB. Treatment was also associated with a transient increase in the rate of synthesis of GRP78/BiP, consistent with a transitory release of Ca2+ from the sarcoplasmic/endoplasmic reticulum [S(E)R]. Increased rates of protein synthesis at early times of PDGF treatment were additive with those occurring in response to arginine vasopressin, indicating different mechanisms of translational upregulation by these agents. The mitogenic effects of PDGF were delayed by vasopressin, which causes H9c2 myocytes to undergo hypertrophy while promoting the persistent depletion of S(E)R Ca2+ stores. In the presence of PDGF, vasopressin did not induce hypertrophy. As compared to untreated myocytes, DNA synthesis in PDGF-treated myocytes was optimized at lower extracellular Ca2+ concentrations and was significantly less sensitive to inhibition by ionomycin. H9c2 cells appear to provide a useful embryonic cardiomyocyte model in which to examine both PDGF-activated proliferative and vasopressin-activated hypertrophic events and the importance of transient vs. sustained Ca2+ release in these events.

A novel signaling pathway for β-adrenergic receptor-mediated activation of phosphoinositide 3-kinase in H9c2 cardiomyocytes

“…This effect was mediated by the ␤ 2 -subtype of ␤-AR because cotreatment with ICI-118,551 abrogated the effect of Iso, whereas cotreatment with CGP-20712 did not affect the outcome. In H9c2 cells, PDGF is a proven mitogen, an effect that requires PI3K (2). We therefore used PDGF as a positive control in our study.…”

“…We used both in vitro and in vivo approaches to delineate the ␤-AR subtype and PI3K isoform critical for the transactivation. For in vitro study, we used the H9c2 cardiomyocytes, an embryonic ventricular myocyte cell line that has proved to be a useful model for in vitro study of cardiomyocytes (2,12). The results suggest a novel transactivation mechanism between the ␤-AR and PI3K signaling pathway.…”

Glutaredoxin Modulates Platelet-derived Growth Factor-dependent Cell Signaling by Regulating the Redox Status of Low Molecular Weight Protein-tyrosine Phosphatase

“…Recently it has been reported that an antioxidant inhibited cell growth by blocking the phosphorylation of tyrosines in PDGFR␤ elicited by PDGF-BB (36). In H9c2 cells PDGF-BB induces cell proliferation through PDGFR␤ (30). We also examined the PDGF-BB-dependent proliferation of H9c2 cells in culture medium containing 0.5% FCS with different concentrations of PDGF-BB (0 -0.5 nM) and found that the cells proliferated with PDGF-BB in a dose-dependent manner (Fig.…”

“…PDGF-BB or PDGFR␤ knock-out mice die during late gestation from cardiovascular complications (27,28), suggesting the importance of PDGF-BB/PDGFR␤ signaling in the myocardiac development of mice. Although the physiological functions of PDGF-BB/PDGFR␤ signaling in myocardiac cells are not fully understood, PDGFR␤ is expressed in adult rat heart (29) and rat cardiomyocyte-derived H9c2 cells (30), and PDGF-BB/PDGFR␤ signaling also controls the proliferation of neonatal rat cardiomyocytes (31). These reports suggest that the PDGF-BB/PDGFR␤ signaling pathway plays an important role in the cellular physiology of myocardiac cells, although the precise regulatory mechanism for the signaling pathway and its relation to cellular redox-dependent regulation are not yet clarified.…”

Epidermal Growth Factor Receptor-Dependent and -Independent Pathways in Hydrogen Peroxide-Induced Mitogen-Activated Protein Kinase Activation in Cardiomyocytes and Heart Fibroblasts

“…CMCs and HFs also express the FGFR (Liu et al, 1995), PDGFR (Brostrom et al, 2002), and insulin-like growth factor receptor (Velloso et al, 1998). The pharmacologic inhibitors of the FGFR tyrosine kinase or PDGFR tyrosine kinase allowed us to test whether these receptors serve as upstream regulators of ROS-induced MAPK activation.…”