F A C U L T Y P R O F I L E
STEINBERG, SUSAN F., M.D.
Signal transduction that mediate the cardiac actions of G protein-coupled receptors for catecholamines as well as thrombin.
Office: Presbyterian Hospital | Room 312
The research in my laboratory focuses on the cellular actions of three signaling protein that play key roles in pathological remodeling of the heart, namely protein kinase C-delta (PKC-delta), protein kinase D (PKD, a downstream effector of PKC-delta in cardiomyocytes), and p66Shc (a PKC-delta binding partner). PKC-delta is a serine/threonine kinase that regulates cardiac contraction, ischemic preconditioning, and the pathogenesis of cardiac hypertrophy and failure. Traditional models of PKC-delta activation focus on lipid cofactors that allosterically activate the enzyme at membranes. Our studies have extended this model to show that PKC-delta activity is ‘fine tuned’ as a result of a dynamically-regulated autophosphorylation reaction within the activation loop segment of the kinase domain and a Src-dependent phosphorylation at Tyr311 in the hinge region of the enzyme. We have demonstrated that PKC-delta is phosphorylated at Tyr311 in cardiomyocytes subjected to oxidative stress and that the tyrosine phosphorylated form of PKC-delta exhibits de novo activity toward substrates that are not phosphorylated by the allosterically-activated PKC-delta enzyme; this phosphorylation-dependent switch in PKC-delta activity influences contractile protein phosphorylation and cardiac contraction. Our goal is to identify  the structural determinants that distinguish the catalytic function of the allosterically-activated versus the tyrosine phosphorylated forms of PKC-delta and  the cellular substrates unique to the tyrosine phosphorylated form of PKC-delta. These differences in PKC-delta actions during growth factor stimulation and during oxidative stress that could provide the basis for new therapies that prevent pathological cardiac remodeling.
We have taken a similar approach to studies of proten kinase D, a PKC-activated enzyme that also is regulated through a phosphorylation-dependent mechanism. We have identified novel PKD substrates in cardiomyocytes, agonist-specific modes of PKD activation, and novel PKD autophosphorylation sites that regulate activity in vivo in cardiomyocytes.
Finally, we have examined the cardiac actions of p66Shc, an adapter protein induced by hypertrophic stimuli that is implicated as a major regulator of reactive oxygen species (ROS) production and cardiovascular oxidative stress responses. Our recent studies implicate p66Shc in an alpha1-adrenergic receptor pathway that requires ROS, EGFR, and PKC activities, is localized to caveolae, and leads to AKT-FOXO3a phosphorylation in cardiomyocytes. This alpha1-receptor pathway that selectively phosphorylates/inactivates FOXO transcription factors leads to the downregulation of ROS-scavenging proteins such as manganese superoxide dismutase (MnSOD). We showed that RNA interference-mediated downregulation of endogenous p66Shc derepresses FOXO3a-regulated genes such as MnSOD, p27Kip1, and BIM-1 and induces cardiomyocyte hypertrophy. A role for p66Shc as an inhibitor of cardiomyocytes hypertrophy was unanticipated. Ongoing studies focus on the structural determinants required for p66Shc’s cardiac actions and the role of p66Shc in mechanisms that lead to cardiomyocyte remodeling and the evolution of heart failure phenotypes.
1. Rybin VO, Guo J, Gertsberg Z, Elouardighi H, and Steinberg SF. PKC-epsilon and Src control PKC-delta activation loop phosphorylation in cardiomyocytes. J Biol Chem 282:23631-23638, 2007.
2. Ozgen N, Obreztchikova M, Guo J, Rybin VO, Elouardighi H, Dorn GW, Wilson BA, and Steinberg SF. Protein kinase D links Galphaq receptors to CREB-S133 phosphorylation in the heart. J Biol Chem 283:17009-17019, 2008.
3. Sumandea MP, Rybin VO, Wang C, Hinken A, Kobayashi T, Harleton E. Sievert G, Feinmark SJ, Balke CW, Solaro RJ, Steinberg SF. Tyrosine phosphorylation modifies PKC-delta phosphorylation of cardiac troponin I. J Biol Chem 283:22680-22689, 2008. PMC2504892
4. Steinberg SF. Structural basis of PKC isoform function. Physiological Reviews 88:1341-1378, 2008.
5. Rybin VO, Guo J, Gertsberg Z, Feinmark SJ and Steinberg SF. PMA-dependent PKC-delta-Y311 phosphorylation in cardiomyocyte caveolae. J Biol Chem 283:17777-17788, 2008. PMCID: PMC2440626
6. Rybin VO, Guo J, and Steinberg SF. Protein kinase D autophosphorylation via distinct mechanisms at Ser744/Ser748 and Ser916. J Biol Chem 284:2332-2343, 2009.
7. Guo J, Gertsberg Z, Ozgen N and Steinberg SF. p66Shc links alpha1-adrenergic receptors to a ROS-dependent pathway that regulates AKT and FOXO3a phosphorylation in cardiomyocytes. Circ Res 104:660-669, 2009. PMCID: PMC286158
8. Guo J, Gertsberg Z, Ozgen N, and Steinberg SF. Protein kinase D isoforms are activated in an agonist-specific manner in cardiomyocytes. J Biol Chem (in press), 2011.
9. Steinberg SF and Sumandea M. Redox signaling and cardiac sarcomeres. J bio chem, 286, 9921-9927, 2011.