PKA Regulates Shp2 Activity: A Role in Cardiac Hypertrophy

Pathological cardiac hypertrophy (an increase in cardiac mass resulting from stress-induced cardiac myocyte growth) is a major factor underlying heart failure. Src homology 2-domain containing phosphatase 2 (Shp2) is critical for cardiac function and mutations resulting in loss of Shp2 catalytic activity are associated with congenital cardiac defects and hypertrophy. I have identified a novel mechanism of Shp2 inhibition that may promote cardiac hypertrophy. I demonstrate that Shp2 is a component of the A-kinase anchoring protein (AKAP)-Lbc complex. AKAP-Lbc facilitates protein kinase A (PKA) phosphorylation of Shp2, which inhibits Shp2 phosphatase activity. I have identified two key amino acids in Shp2 that are phosphorylated by PKA. Utilizing double mutant PKA phospho-deficient (T73A/S189A) and phospho-mimetic (T73D/S189D) constructs, in vitro binding assays and phosphatase activity assays indicate that phosphorylation of these residues disrupts Shp2 interaction with tyrosine-phosphorylated substrates and inhibits its protein tyrosine phosphatase activity. Overall, my data indicate that AKAP-Lbc integrates PKA and Shp2 signaling in the heart and that AKAP-Lbc-associated Shp2 activity is reduced in hypertrophic hearts in response to chronic β-adrenergic stimulation and PKA activation. Thus, while induction of cardiac hypertrophy is a multifaceted process, inhibition of Shp2 activity through AKAP-Lbc-anchored PKA is a previously unrecognized mechanism that may promote cardiac hypertrophy.