The small GTPase Rab43 is a novel regulator of G protein‐coupled receptor trafficking

Ras‐like small Rab GTPases are master regulators of vesicle‐mediated membrane traffic. Recent studies have identified several Rab GTPases involved in the anterograde cell surface transport of newly synthesized G protein‐coupled receptors (GPCRs). Here, we have screened the Rab GTPase family using stable cells expressing α 2B ‐adrenergic receptor (α 2B ‐AR), a prototypic GPCR, and demonstrated that Rab43 is a novel regulator of GPCR trafficking. Attenuation of Rab43 function, via expression of its dominant‐negative mutants, siRNA‐mediated depletion, and expression of its GTPase‐activating protein RN‐tre, significantly attenuated the cell surface expression of α 2B ‐AR and induced an extensive accumulation of the receptor in the endoplasmic reticulum (ER). The studies using inducible α 2B ‐AR‐expressing cell lines and a previously characterized Golgi‐localized α 2B ‐AR mutant, in combination with bredeldin A treatment/washout assay, further showed that Rab43 controlled the ER export rate and content of nascent receptors. More interestingly, in addition to α 2B ‐AR, the cell surface transport of a number of other GPCRs, but not VSVG and EGF receptor, was regulated by Rab43. Furthermore, Rab43 was shown to directly interact with α 2B ‐AR, specifically its third intracellular loop, in an activation‐dependent fashion, but it was unable to associate with the tethering factor protein p115, a downstream effector of Rab1 GTPase which is well‐known to control the ER‐Golgi traffic. Altogether, these data demonstrate a novel Rab43‐mediated, as yet undefined pathway for members of the GPCR family to move forward from the ER to the Golgi. Support or Funding Information R01GM118915