The Protean Nature of 14-3‑3 Proteins in G Protein-Coupled Receptor Signaling: Emphasizing Selectivity and Dynamic...

Recent models of GPCR signaling extend beyond the canonical paradigm of ligand-induced activation primarily mediated by G-proteins and β-arrestins. Indeed, the various outcomes of GPCR activation are precisely regulated by several factors, including GPCR-interacting proteins, isoform diversity, and GPCR phosphorylation patterns catalyzed by kinases. One underexplored source contributing to the pleiotropic activities of GPCRs is the dynamic recruitment and dissociation of 14-3-3 proteins, a family of ubiquitously expressed adaptor proteins that modulate key cellular processes. Recent studies have shown that GPCR-14-3-3 protein interactions are isoform-specific and can be modulated in a spatiotemporal manner by ligands; however, an investigation of 14-3-3 dynamics across all seven human isoforms and throughout a large panel of GPCRs has yet to be conducted. Thus, this work provides the first characterization of proximal GPCR-14-3-3 protein interactions at a GPCRome scale, achieved by constructing stable reporter cell lines expressing all human 14-3-3 isoforms and performing cell-based high-throughput screening to probe 82 GPCR interactomes. Among the notable findings from this screen, the NK3 receptor emerged as a promising candidate for an in-depth examination of 14-3-3 protein modulation of GPCR activity, especially given the limited literature regarding NK3 signaling, including its relation to G-proteins or β-arrestins. Our findings suggest that different combinations of hetero- and homodimers of 14-3-3 isoforms result in varying functional outcomes at NK3, such as upregulation of NK3 surface expression by 14-3-3γ. Furthermore, 14-3-3γ was found to modulate canonical signaling pathways by attenuating G-protein dissociation and enhancing β-arrestin recruitment signals.