Abstract 16202: Cofilin Inhibits β -Arrestin Mediated Erk Activation
The role of β-arrestin in mediating G-protein independent signaling is well understood but nothing is known about how β-arrestin initiated signals are terminated. We report here that cofilin, an actin remodeling protein in addition to its documented role in actin dynamics, plays a pivotal role in regulating β-arrestin-mediated ERK activation upon β-adrenergic receptor (βAR) stimulation. Cofilin a phospho-protein is dynamically regulated by phosphatases like slingshot and kinases like LIM kinase. Agonist activation of βAR leads to cofilin dephosphorylation resulting in increased interaction of cofilin with β-arrestin in cells and in the hearts. To understand the role of cofilin phosphorylation/dephosphorylation in its association with β-arrestin to regulate β-arrestin signaling, we generated cofilin S3A (constitutively active) and S3D (constitutively inactive) mutant expressing cells. Dephosphorylated cofilin mutant (S3A) binds with β-arrestin more efficiently inhibiting β-arrestin mediated ERK activation compared to phospho-mimetic S3D cofilin. Conversely, S3D cofilin results in marked ERK activation which is significantly abrogated following siRNA depletion of β-arrestin1/2 showing that cofilin is a critical determinant in β-arrestin mediated ERK activation. S3A cofilin expressing cells show significantly elevated cAMP consistent with the inhibition of β-arrestin signaling by S3A cofilin mutant. Importantly, siRNA depletion of cofilin results in sustained ERK activation following β-AR stimulation compared to control siRNA indicating that cofilin could act as a brake on β-arrestin mediated ERK activation. Significant inhibition of ERK activation was observed following LIM kinase knockdown with β-AR stimulation showing that dephosphorylated cofilin plays a critical role in terminating β-arrestin mediated ERK activation. Furthermore, end stage human heart failure shows higher phospho-ERK and phospho-cofilin levels which is characterized by reduced interaction of cofilin with β-arrestin emphasizing an important role of this mechanism in physiology. Our study unravels an endogenous mechanism by which cofilin regulates termination of β-arrestin mediated signals in addition to its role in actin remodeling.
- © 2011 by American Heart Association, Inc.