Abstract 5875: Cofilin: A Novel Regulator of β-arrestin Signaling
Beta adrenergic receptors (βARs) are important regulators of cardiac function and are desensitized in conditions of heart failure. Recent evidence suggests that actin remodeling may play a role in receptor internalization and signaling. Actin remodeling is a process regulated by many proteins including cofilin. Cofilin is a phospho-protein that is activated by dephosphor-ylation to bring about actin depolymerization. To test whether cofilin regulates βAR signaling, we generated cofilin mutants that mimic constitutively active (S3A) and inactive (S3D) proteins. Isoproterenol (ISO) stimulation of β2AR stable HEK 293 cells coexpressing wild type (Wt), S3A, S3D cofilin showed differential ERK activation as measured by phospho-ERK (pERK). Significant ERK activation was observed with S3D mutant that was markedly reduced in cells expressing S3A cofilin. Interestingly expression of Wt resulted in reduced ERK activation consistent with our observation that Wt cofilin undergoes marked dephosphorylation following ISO stimulation. To further test whether cofilin modulates βAR signaling via β-arrestin that mediates G-protein independent signaling, Wt and mutant cofilins were transfected into HEK cells stably expressing HA-β2AR and β-arrestin GFP. β-arrestin GFP translocation to plasma membrane was visualized by confocal microscopy upon agonist stimulation. Significant inhibition of β-arrestin translocation to the plasma membranes was observed with S3A cofilin mutant that was completely rescued in the presence of S3D mutant. Therefore, suggesting that loss in β-arrestin recruitment to the βAR complex in presence of active cofilin (S3A) could potentially account for the marked reduction in ERK activation. Studies in end-stage human heart failure samples showed significant ERK activation (pERK) in heart failure samples associated markedly higher levels phospho-cofilin (inactive cofilin) compared to non-failing controls. Our findings that actin remodeling play a critical role in β-arrestin mediated signaling is significant in lieu of, a) β-arrestin mediated signaling is cardioprotective and b) actin remodeling is markedly altered in heart failure. Underlying mechanism by which actin remodeling regulates βAR signaling will be presented.