Abstract 18630: Targeting Inhibitor of Protein Phosphatase 2A (I2PP2A) Mediates Plasma Membrane Beta-Adrenergic Receptor Resensitization
βAR downregulation and desensitization are hallmarks of heart failure. Agonist occupied βARs undergo desensitization through phosphorylation by G-protein coupled receptor kinases leading to βAR internalization. Phosphorylated βAR becomes resensitized following dephosphorylation by PP2A in the endosome, a paradigm in receptor resensitization. Our recent studies have suggested that resensitization of βARs can occur on the plasma membrane through the inhibition of PP2A activity by I2PP2A. To test whether I2PP2A regulates βAR and cardiac function we generated transgenic mice with cardiac specific over expression of I2PP2A. Assessment of age dependent cardiac function of these mice showed that transgenic mice have cardiac hypertrophic response followed by dilated cardiomyopathy. These observations are further supported by immunohistochemistry. Since we have observed cardiac dysfunction and βAR desensitization in transgenic mice, we tested whether targeting I2PP2A in cells would allow for plasma membrane resensitization. We generated a stable HEK (Human Embryonic Kidney) cell line expressing short hairpin RNA targeting I2PP2A (shRNA-I2PP2A). Confocal microscopy studies show that cells expressing shRNA-I2PP2A resulted in significant loss of receptor phosphorylation despite the presence of the agonist. Furthermore, radioligand binding and confocal imaging showed marked inhibition of receptor internalization upon depletion of I2PP2A with significant PP2A activation. Consistently, we also observed preservation of βAR function despite the presence of agonist as measured by cAMP generation and adenylyl cyclase activity. Together these studies suggest that targeting I2PP2A may lead to plasma membrane receptor resensitization demonstrating that modulating PP2A function can potentially change desensitization and resensitization dynamics of the receptors on the plasma membrane.
- © 2013 by American Heart Association, Inc.