EFR3s are palmitoylated plasma membrane proteins that control responsiveness to G protein-coupled receptors

The yeast Efr3p protein is a major regulator of the Stt4p phosphatidylinositol 4-kinase at ER-PM contact sites. Its mutant fly homologue, Rbo displays diminishing light responses attributed to progressively impaired PLC signaling. Here we find that Efr3s play a role in maintaining responsiveness to angiotensin II (AngII) receptors. RNAi-mediated depletion of EFR3A and EFR3B impaired the sustained phase of cytosolic Ca2+ response to high concentration of AngII in HEK293 cells expressing the wild type but not a truncated AT1a receptor, missing the phosphorylation sites. Efr3 depletion had minimal effect on the recovery of plasma membrane phosphoinositides during stimulation, and AT1 receptors still underwent ligand-induced internalization. A higher level of basal receptor phosphorylation and a larger response was observed after stimulation. Moreover, Gq activation more rapidly desensitized after AngII stimulation in Efr3 downregulated cells. Similar but smaller effect of EFR3 depletion was observed on the desensitization of the cAMP response after isoproterenol stimulation. These data suggest that mammalian Efr3s contribute to the control of the phosphorylation state and hence desensitization of AT1a receptors and could affect GPCR responsiveness in higher eukaryotes.