Adenoviral-Directed Expression of the Type 1A Angiotensin Receptor Promotes Cardiomyocyte Hypertrophy via Transactivation of the Epidermal Growth Factor Receptor

Abstract

Abstract-Angiotensin II (Ang II) may cause cardiac hypertrophy via type 1 Ang II receptors (AT 1 ) on cardiomyocytes and through growth factors released from cardiac fibroblasts. Whereas cardiomyocyte-specific AT 1 receptor expression produces cardiac hypertrophy and remodeling in vivo, delineation of the signals that mediate growth to Ang II is challenging because the prevailing in vitro model (cultured neonatal cardiomyocytes) expresses low levels of AT 1 receptor and responds inconsistently to Ang II. In this study, when AT 1A receptors were expressed using adenovirus in cultured neonatal cardiomyocytes, Ang II stimulated a robust hypertrophy that was not secondary to the release of cardiac fibroblast-derived factors, specifically endothelin-1. Hypertrophy was accompanied by the induction of the immediate-early response genes, c-fos and c-jun, and reexpression of atrial natriuretic peptide (ANP). Ang II-induced activation of an ANP promoter-reporter was inhibited by the dominant/negative mutants, G␣qI and N17Ras, indicating that hypertrophic signaling by the AT 1A receptor is via heterotrimeric G protein coupling and downstream Ras pathways. AT 1A -mediated cardiomyocyte hypertrophy and mitogen-activated protein kinase (MAPK) activation were inhibited by the MAPK kinase inhibitor, PD98059, and the epidermal growth factor (EGF) receptor kinase antagonist, AG1478, but not by PKC inhibitor, bisindolylmaleimide-1. Moreover, Ang II-induced MAPK activation was prevented by treatment with a matrix metalloproteinase inhibitor, consistent with the tyrosine phosphorylation of the EGF receptor in response to AT 1A receptor activation. These data unequivocally demonstrate that Ang II can directly promote cardiac myocyte growth via AT 1A receptors expressed on these cells and reveal for the first time the important contribution of EGF receptor-transactivated MAPK signaling to this process. Key Words: AT 1A receptor Ⅲ angiotensin Ⅲ cardiomyocyte hypertrophy Ⅲ adenovirus Ⅲ EGF receptor transactivation A ngiotensin II (Ang II) regulates blood pressure, cardiovascular homeostasis, and cellular growth via type 1 (AT 1 ) angiotensin receptors, which activate G␣ q/11 -phospholipase C-␤1 to generate inositol trisphosphate and diacylglycerol, and thereby increase intracellular calcium and activate protein kinase C (PKC). 1 Activation of PKC and the calcium-dependent phosphatase, calcineurin, has been linked to Ang II-mediated growth. 2,3 Activation of AT 1 receptors also promotes tyrosine phosphorylation, stimulation of mitogen-activated protein kinases, and growth, particularly in vascular and cardiac cells. 1 How AT 1 receptors, which lack intrinsic tyrosine kinase activity, induce tyrosine phosphorylation, MAP kinase, and growth factor signaling pathways is not clear, but recent evidence from vascular smooth muscle cells, 4 liver epithelial cells, 5 and cardiac fibroblasts 6 suggest that a major mechanism is the "transactivation" 7 of the EGF receptor (EGFR).Cardiac hypertrophy involves cardiomyocyte growth as well as extracell...

Convergence of Protein Kinase C and JAK-STAT Signaling on Transcription Factor GATA-4

“…Surprisingly, the mechanisms by which AII regulates transcription in the heart remain undefined. Within the heart, AII targets both myocytes and nonmyocytes (64,74). Except for the c-fos gene (61), few direct transcription targets of AII in cardiomyocytes have been identified.…”

“…Interestingly, MAPK signaling did not appear to play a role in relaying AII signaling at the level of the ANF promoter. This may reflect a more specific role for the MAPK pathway in the growth (hypertrophic) effects of AII that are dependent on the EGF receptor (74). In contrast, ANF is a cardioprotective hormone that antagonizes cardiac hypertrophy (30).…”

“…At the level of the heart, AT1R activation causes myocyte hypertrophy and apoptosis (55) and is associated with upregulation of c-jun, c-fos, and the cardiac-specific atrial natriuretic factor (ANF) gene, which is induced during hypertrophy (55,74) AII also activates several STAT family members which have themselves been implicated in cardioprotection, apoptosis, and hypertrophy through mechanisms and effectors that remain to be elucidated (reviewed in reference 9). Similarly, the various signaling pathways activated by AII have all been implicated in cardiac hypertrophy, apoptosis, or both (1,24,46).…”

Proliferation of Neointimal Smooth Muscle Cells after Arterial Injury

“…Recombinant Dominant Negative FGFR-2 and FGFR-3 Adenoviruses-The pAd-Easy1 virus and shuttle plasmid pAd-TrackCMV were obtained from Dr. R. Hannan, Peter MacCallum Cancer Institute, Melbourne, Australia (24). Adenoviruses expressing dominant negative (DN) FGFR-2␤IIIcAB (devoid of Ig-like domain I and containing the acidic box), FGFR-3␣IIIbAB, and FGFR-3␣IIIcAB (both containing all three Ig-like domains and the acidic box and differing from each other only in the alternate presence of either the IIIb or IIIc exon in the carboxyl terminus of Ig-like domain III) were prepared by amplifying their cDNAs from rat SMC RNA and truncating these cDNAs at the transmembrane domain with the inclusion of a FLAG epitope tag immediately distal to the last amino acid of the transmembrane domain.…”

Atorvastatin Slows the Progression of Cardiac Remodeling in Mice with Pressure Overload and Inhibits Epidermal Growth Factor Receptor Activation

“…It is known that EGFR transactivation plays an important role in cardiovascular remodeling (8,20,(30)(31)(32). It has been reported that activation of ADAM12 (8) or ADAM17 (22) could induce the release of HB-EGF and subsequent EGFR phosphorylation, which may eventually lead to cardiomyocyte hypertrophy, while inhibition of ADAM12 or administration of an HB-EGF neutralizing antibody blocked GPCR agonist-stimulated myocyte hypertrophy (8).…”