# P-Rex1 limits the agonist-induced internalization of GPCRs independently of its Rac-GEF activity

## TL;DR

P-Rex1 limits the movement of certain receptors inside cells, independent of its usual signaling role, which could impact processes like immunity and cancer.

## Contribution

P-Rex1 controls GPCR trafficking via an adapter function, independent of its Rac-GEF activity.

## Key findings

- P-Rex1 inhibits agonist-induced internalization of S1PR1, CXCR4, PAR4, and GLP1R.
- P-Rex1 binds Grk2 and blocks phosphorylation required for GPCR internalization.
- P-Rex1 does not affect steady-state GPCR levels or PDGFR/EGFR trafficking.

## Abstract

The guanine-nucleotide exchange factor (GEF) P-Rex1 mediates G protein-coupled receptor (GPCR) signaling by activating the small GTPase Rac. We show here that P-Rex1 also controls GPCR trafficking. P-Rex1 inhibits the agonist-stimulated internalization of the GPCR S1PR1 independently of its Rac-GEF activity, through its PDZ, DEP, and inositol polyphosphate 4-phosphatase domains. P-Rex1 also limits the agonist-induced trafficking of CXCR4, PAR4, and GLP1R but does not control steady-state GPCR levels, nor the agonist-induced internalization of the receptor tyrosine kinases PDGFR and EGFR. P-Rex1 blocks the phosphorylation required for GPCR internalization. P-Rex1 binds G protein-coupled receptor kinase 2 (Grk2), both in vitro and in cells, but does not appear to regulate Grk2 activity. We propose that P-Rex1 limits the agonist-induced internalization of GPCRs through its interaction with Grk2 to maintain high levels of active GPCRs at the plasma membrane. Therefore, P-Rex1 plays a dual role in promoting GPCR responses by controlling GPCR trafficking through an adapter function as well as by mediating GPCR signaling through its Rac-GEF activity.

•P-Rex1 controls GPCR trafficking, independently of its Rac-GEF activity•P-Rex1 limits the agonist-induced internalization of S1PR1, CXCR4, PAR4, and GLP1R•P-Rex1 does not control steady-state GPCR levels, nor PDGFR or EGFR trafficking•P-Rex1 binds Grk2 and inhibits the phosphorylation required for GPCR internalization

P-Rex1 controls GPCR trafficking, independently of its Rac-GEF activity

P-Rex1 limits the agonist-induced internalization of S1PR1, CXCR4, PAR4, and GLP1R

P-Rex1 does not control steady-state GPCR levels, nor PDGFR or EGFR trafficking

P-Rex1 binds Grk2 and inhibits the phosphorylation required for GPCR internalization

P-Rex1 activates Rac downstream of GPCRs to regulate processes ranging from innate immunity to neuronal plasticity, its deregulation contributing to cancer. Here, Baker et al. show that P-Rex1 also controls GPCR trafficking, limiting agonist-induced GPCR internalization through an adapter function. Thus, P-Rex1 promotes GPCR responses in a dual manner.