Integrins are heterodimeric surface receptors, which link extracellular matrix to cytoplasmic proteins. In striated muscle, integrin receptors are co-localized with alpha-actinin and vinculin-containing structures at z-bands. In addition, a specific beta1 integrin isoform, beta1D, has been described in adult striated muscle, which is proposed to form mechanical connection between the plasma membrane and the acto-myosin fibrils required in muscle cells as compared to other cells. Mechanical stress applied to integrin receptors induces a rapid increase in tyrosine phosphorylated proteins associated with the cytoskeleton and an increase in activation of the ERK pathway. Hypertrophy is manifested through an increase load, stress, on cardiac cells through either pressure or volume-overload. Therefore, integrin receptors are well positioned to respond to alterations in both extracellular matrix and cytoplasmic proteins by activating signaling pathways. Thus, we hypothesize that integrin mediated adhesion and signaling plays a role in hypertrophic responses in neonatal rat ventricular monocytes (NRVM). To test this hypothesis the specific aims are (1) to determine the effect of expression of dominant negative integrins (IL2-beta1A, IL2- beta1D) on signaling pathways induced by hypertrophic agents and (2) to determine the effect of expression of constitutively active alpha5 and beta1D integrins on signaling pathways induced by hypertrophic agents. To approach these aims, we will use alpha-adrenergic receptor stimulation of NRVM as the model of cardiac hypertrophy. Over-expression of integrins will be performed using adenoviral infection of NRVM. Activation of signaling pathways, specifically p38 and c-jun NH2- terminal kinase, will be determined by analyzing phosphorylation of p38 and INK. In addition, focal adhesion kinase (FAK)-dependent and independent pathways will be assessed by over-expression of focal adhesion related non-kinase an inhibitor of FAK. We expect that over- expression of dominant negative integrins will inhibit activation of signaling pathways by alpha-adrenergic receptor stimulation. The long- term goal is to understand the role of integrin receptors in mediating responses of the cardiac cell to mechanical stresses.
| Valencik, Maria L; Keller, Rebecca S; Loftus, Joseph C et al. (2002) A lethal perinatal cardiac phenotype resulting from altered integrin function in cardiomyocytes. J Card Fail 8:262-72 |
