Abstract 5298: ShcA Phosphotyrosine-Derived Signaling is Required for Maintenance of Cardiac Function
ShcA, a scaffolding protein, generates signal specificity by docking to tyrosine kinases (TK) through distinct phosphotyrosine (pTyr) recognition motifs, while mediating signal complexity through formation of downstream pTyr complexes. ShcA encodes 3 polypeptides of 46, 52, and 66 kD, each having the common pTyr recognition architecture of an N-terminal PTB domain and a C-terminal SH2 domain, separated by a CH1 region containing tyrosine phosphorylation sites important in Ras-MAPK activation. Although ShcA has been shown to be critical for cardiovascular development, its role and molecular mechanisms of action remain unknown in the adult myocardium. To this end, we used loxP/cre-recombinase technology to generate mice with myocardial specific knockout of ShcA (ShcA CKO) as well as mice with myocardial restricted ShcA mutant knockins (KI) of either the PTB (R175Q) or SH2 (R397K) domains or the CH1 (Y239/240/313F) region. Cardiac-specificity was achieved using Cre-recombinase expressed from the mlc2v locus. ShcA CKO mice survive postnatal development, but develop a dilated cardiomyopathy phenotype by 3 months of life. Echocardiography, hemodynamic and histological data from ShcA CKO mice demonstrate depressed cardiac contractility (% FS: ShcA CKO 40.91±1.57% vs Con 45.57±0.96%, n=7), enlarged chamber dimensions (LVEDD: ShcA CKO 0.452±0.01 vs Con 0.385±0.01, n=7) without changes in wall thickness or sudden death at 1 year of age. Despite reduced global contractility, isolated ShcA CKO cardiomyocytes have preserved contractility (ShcA CKO 8.82±0.37% vs Con 6.50±0.69%), suggesting uncoupling of global heart function from intrinsic myocyte contractilility. Indeed, ShcA CKO papillary muscles show rightward shifts in the passive length-tension relationship suggesting deregulation of extracellular matrix interactions. Subsequent analysis of the various ShcA myocardial restricted domain mutant KI mice suggests that ShcA requires PTB docking to upstream TKs and subsequent phosphorylation of the CH1 tyrosines to maintain cardiac function. Together, these data indicate ShcA is required for proper maintenance of cardiac function, possibly though regulation of extracellular matrix interactions.