The interaction of G protein‐coupled receptor kinase 4γ with Gα_s is required for inhibition of the β₂‐AR

Abstract

Polymorphisms in G protein receptor kinase 4γ (GRK4γ) have been implicated in hypertension via desensitizing Gs‐coupled receptors, such as the β2‐adrenergic receptor (β2‐AR). However, the molecular mechanism initiating phosphorylation and desensitization is unknown. Previous data demonstrate that GRK4γ interacts with inactive Gαs; thus, we hypothesized that the interaction of GRK4γ with Gαs is required for proper desensitization of the β2‐AR. To test this, we identified Gαs constructs that do not fully interact with GRK4γ and used these constructs in functional studies utilizing GnasE2‐/E2‐ mouse embryonic fibroblasts (MEFs), which are functionally Gαs knockouts. The data suggest that GRK4γ binds to Gαs; however, the precise area and amino acids involved in binding has yet to be identified. Moreover, the data confirm that expression of Gαs in GnasE2‐/E2‐ MEFs restores isoproterenol‐mediated generation of cAMP, which is inhibited by GRK4γ; however, when GRK4γ does not bind to Gαs it cannot inhibit β2‐ARs. In conclusion, the data suggests that GRK4γ binds to inactive Gαs positioning it near the receptor, and upon activation of the receptor Gαs dissociates from the receptor, Gβγ, and GRK4γ, resulting in signaling; then GRK4γ, which has previously been reported to be constitutively active, has access to the receptor and phosphorylates and desensitizes the receptor. This work was supported by the AHAF and is supported by a VISN 15 grant.