Integrin Activation and Focal Complex Formation in Cardiac Hypertrophy

Abstract

Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressureoverloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130Cas , Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagenembedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130Cas association. Therefore, cSrc activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.Cardiovascular diseases such as hypertension, valvular defects, and myocardial infarction are often associated with the development of cardiac hypertrophy. This hypertrophy occurs in response to an increased mechanical (hemodynamic) load on the heart in the form of pressure or volume overload, which is characteristic of hypertension and valvular defects, or to a decrease in functional heart tissue as seen in myocardial infarction. The initial hypertrophic response of the heart is compensatory but frequently deteriorates into heart failure and increased morbidity/mortality (1, 2). This transition from compensation to failure occurs when further hypertrophy of the heart cannot normalize wall stress and maintain contractile function in the face of its hemodynamic load. Although mechanical load appears to directly regulate mass and associated phenotypic changes at the level of the cardiocyte (for a review see Ref.3), the mechanisms that couple load to the hypertrophic growth initiation and to the transition into heart failure have yet to be delineated. Whereas several key players including G-proteins (4), calcineurin (5, 6), mitogen-activated protein kinase (MAPK) 1 family members, namely, extracellular-regulated kinases (ERK1/2) (7) and p38 MAPK (8), as well as protein kinase C (9) and p70/85 S6 kinase (10, 11) have been implicated in the pathways that connect load to hypertrophic growth, the complexity of interaction between signaling pathways make deciphering them a difficult task in hypertrophic research.In an...

α5β1 Integrin Engagement Increases Large Conductance, Ca2+-activated K+ Channel Current and Ca2+ Sensitivity through c-src-mediated Channel Phosphorylation

“…Integrins are a widely expressed class of adhesion receptor whose interactions with extracellular matrix (ECM) proteins lead to activation of signaling cascades, including protein tyrosine phosphorylation (9). In blood vessels, VSM integrins play important roles in the acute regulation of vascular tone (10) and in long term vascular remodeling (11,12).…”

Gene expression changes associated with fibronectin-induced cardiac myocyte hypertrophy

“…FN also induces increased formation of focal adhesions and costameres, which are sites of contact of extracellular matrix with integrins and associated cytoskeletal proteins associated with the Z-disks of the sarcomere (39). As in other models of hypertrophy, the hypertrophic response is accompanied by changes in gene expression, with increased expression of the natriuretic peptides atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and fetal isoforms of sarcomeric proteins such as ␤-myosin heavy chain (␤MHC) and ␣-skeletal actin (␣SkA).The pathophysiological relevance of the FN-induced, integrin-mediated pathway is highlighted by the observation of increased deposition of FN in the extracellular matrix in animal models of cardiac hypertrophy and in patients with cardiac failure (5,20,22,29,42,45). The increased synthesis of FN is in part mediated by stimulation of cardiac fibroblasts by angiotensin II, produced in response to mechanical overload (11,20,26,52).…”

“…The pathophysiological relevance of the FN-induced, integrin-mediated pathway is highlighted by the observation of increased deposition of FN in the extracellular matrix in animal models of cardiac hypertrophy and in patients with cardiac failure (5,20,22,29,42,45). The increased synthesis of FN is in part mediated by stimulation of cardiac fibroblasts by angiotensin II, produced in response to mechanical overload (11,20,26,52).…”

Role of the integrin-linked kinase/PINCH1/alpha-parvin complex in cardiac myocyte hypertrophy

“…23 Cardiac hypertrophy reproduces some of the molecular features of the neoplastic phenotype in other organs and has been associated with remodeling of the extracellular matrix and increased expression and cytoskeletal association of fibronectin (FN), vitronectin and paxillin. 24 Interestingly, ILK and IPAP1 complex assembly are required for cytoskeletal association of paxillin in epithelial cells 14 and a significant increase in ILK mRNA has been observed in a pressure-overload mouse model of cardiac hypertrophy. 25 Studies from our laboratory 26 and others 27,28 have demonstrated that FN induces cardiac myocyte hypertrophy in neonatal rat ventricular myocytes (NRVM).…”