A Genome-wide CRISPR Screen Reveals ZDHHC8-Dependent Gαq Palmitoylation as a Key Regulator of GPCR Signaling

G protein-coupled receptors (GPCRs) that couple to the Gq signaling pathway control diverse physiological processes, yet the full complement of cellular regulators for this pathway remains unknown. Here, we report the first genome-wide CRISPR knockout screen targeting a Gq-coupled GPCR signaling cascade. Using a Drosophila model of adipokinetic hormone receptor (AkhR) signaling, we identified CG34449 (Zdhhc8), encoding a palmitoyl acyltransferase and its adapter protein CG5447, as a top hit required for robust Gq-mediated GPCR signaling. We show that Zdhhc8 enhances GPCR signaling through palmitoylation of Gq, which promotes its membrane localization and function. Loss of Zdhhc8 markedly reduces palmitoylation of Gaq resulting in attenuation of AkhR/Gq signaling and a reduction in receptor stability. Mechanistically, Zdhhc8 is necessary for palmitoylation of Gq. These findings uncover Zdhhc8-dependent Gq palmitoylation as a pivotal regulatory mechanism in GPCR signal transduction and highlight palmitoyl transferase as potential modulators of GPCR pathways.