Gα13 and Rho Mediate Endosomal Trafficking of CXCR4 into Rab11+ Vesicles upon Stromal Cell-Derived Factor-1 Stimulation

Abstract

CXCR4, like other G protein-coupled receptors, signals via heterotrimeric guanine nucleotide-binding proteins (G proteins) to regulate gene transcription, migration, development, growth, and transformation. We describe a formerly uncharacterized function of a G protein: a role in receptor trafficking. We previously showed that CXCR4 and the TCR physically associate and form a heterodimer upon stromal cell-derived factor-1 or CXCL12 (SDF-1) stimulation in human T cells to prolong ERK activation and, thereby, lead to gene upregulation and cytokine secretion. The CXCR4–TCR heterodimers occur on the cell surface and in an intracellular compartment in response to SDF-1. Neither the intracellular compartment to which the CXCR4–TCR heterodimers localize nor the mechanism for localization has been elucidated. In this article, we characterize molecular mechanisms required for postendocytic trafficking of CXCR4. Upon SDF-1 stimulation, CXCR4 localizes to Rab11+ vesicles, a recycling compartment near the microtubule organizing center and Golgi apparatus. This trafficking requires the CXCR4 C-terminal tail domain but not the CXCR4 ubiquitination sites. The TCR also constitutively localizes to this Rab11+ compartment. Trafficking of CXCR4 into the Rab11+, TCR-containing endosomes requires actin polymerization. Furthermore, inhibiting Rho activation or depleting Gα13 prevented trafficking of CXCR4 into the Rab11+ endosomes without hindering the ability of CXCR4 to endocytose. These results indicated that, upon SDF-1 treatment, Gα13 and Rho mediate the actin polymerization necessary for trafficking CXCR4 into the Rab11+, recycling endosomal compartment, which also contains constitutively recycling TCR and, thus, CXCR4–TCR heterodimers. To our knowledge, this is the first report of Gα13 as a mediator of receptor trafficking.