Regulation of anterograde transport of adrenergic and angiotensin II receptors by Rab2 and Rab6 GTPases

Three Rab GTPases, Rab1, Rab2 and Rab6, are involved in protein transport between the endoplasmic reticulum (ER) and the Golgi. Whereas Rab1 regulates the anterograde ER-to-Golgi transport, Rab2 and Rab6 coordinate the retrograde Golgi-to-ER transport. We have previously demonstrated that Rab1 differentially modulates the export trafficking of distinct G protein-coupled receptors (GPCRs). In this report, we determined the role of Rab2 and Rab6 in the cell-surface expression and signaling of α_2B-adrenergic (α_2B-AR), β₂-AR and angiotensin II type 1 receptors (AT1R). Expression of the GTP-bound mutant Rab2Q65L significantly attenuated the cell-surface expression of both α_2B-AR and β₂-AR, whereas the GTP-bound mutant Rab6Q72L selectively inhibited the transport of β₂-AR, but not α_2B-AR. Similar results were obtained by siRNA-mediated selective knockdown of endogenous Rab2 and Rab6. Consistently, Rab2Q65L and Rab2 siRNA inhibited α_2B-AR and β₂-AR signaling measured as ERK1/2 activation and cAMP production, respectively, whereas Rab6Q72L and Rab6 siRNA reduced signaling of β₂-AR, but not α_2B-AR. Similar to the β₂-AR, AT1R expression at the cell surface and AT1R-promoted inositol phosphate accumulation were inhibited by Rab6Q72L. Furthermore, the nucleotide-free mutant Rab6N126I selectively attenuated the cell-surface expression of β₂-AR and AT1R, but not α_2B-AR. These data demonstrate that Rab2 and Rab6 differentially influence anterograde transport and signaling of GPCRs. These data also provide the first evidence indicating that Rab6-coordinated retrograde transport selectively modulates intracellular trafficking and signaling of GPCRs.