p63RhoGEF Couples Gαq/11-Mediated Signaling to Ca2+ Sensitization of Vascular Smooth Muscle Contractility
Rationale: In normal and diseased vascular smooth muscle (SM), the RhoA pathway, which is activated by multiple agonists through G protein-coupled receptors (GPCRs), plays a central role in regulating basal tone and peripheral resistance. This occurs through inhibition of myosin light chain phosphatase, leading to increased phosphorylation of the myosin regulatory light chain. Although it is thought that specific agonists and GPCRs may couple to distinct RhoA guanine nucleotide exchange factors (GEFs), thus raising the possibility of selective targeting of specific GEFs for therapeutic use, this notion is largely unexplored for SM contraction.
Objective: We examine whether p63RhoGEF, known to couple specifically to Gαq/11 in vitro, is functional in blood vessels as a mediator of RhoA activation and if it is selectively activated by Gαq/11 coupled agonists.
Methods and Results: We find that p63RhoGEF is present across SM tissues and demonstrate that silencing of the endogenous p63RhoGEF in mouse portal vein inhibits contractile force induced by endothelin-1 to a greater extent than the predominantly Gα12/13-mediated thromboxane analog U46619. This is because endothelin-1 acts on Gαq/11 as well as Gα12/13. Introduction of the exogenous isolated pleckstrin-homology (PH) domain of p63RhoGEF (residues 331–580) into permeabilized rabbit portal vein inhibited Ca2+ sensitized force and activation of RhoA, when phenylephrine was used as an agonist. This reinforces the results based on endothelin-1, because phenylephrine is thought to act exclusively through Gαq/11.
Conclusion: We demonstrate that p63RhoGEF selectively couples Gαq/11 but not Gα12/13, to RhoA activation in blood vessels and cultured cells and thus mediates the physiologically important Ca2+ sensitization of force induced with Gαq/11-coupled agonists. Our results suggest that signaling through p63RhoGEF provides a novel mechanism for selective regulation of blood pressure.
- Received May 19, 2011.
- Revision received August 20, 2011.
- Accepted August 25, 2011.
- © 2011 American Heart Association, Inc.