Endogenous Rab38 regulates LRRK2's membrane recruitment and substrate Rab phosphorylation in melanocytes

Abstract

Point mutations in LRRK2 cause Parkinsons Disease and augment LRRK2s kinase activity. However, cellular pathways that enhance LRRK2 kinase function have not been identified. While overexpressed Rab29 draws LRRK2 to Golgi membranes to increase LRRK2 kinase activity, there is little evidence that endogenous Rab29 performs this function under physiological conditions. Here we identify Rab38 as a novel physiological regulator of LRRK2. In mouse melanocytes, which express high levels of Rab38, Rab32, and Rab29, knockdown of Rab38 but not Rab32 or Rab29 decreases phosphorylation of multiple LRRK2 substrates, including Rab10 and Rab12, by both exogenous and endogenous LRRK2. In B16-F10 mouse melanoma cells, Rab38 drives LRRK2 membrane association, and overexpressed kinase-active but not kinase-inactive LRRK2 shows striking pericentriolar recruitment, which is dependent on the presence of endogenous Rab38 but not Rab32 or Rab29. Deletion or mutation of LRRK2 at the Rab38 binding site in the N-terminal armadillo domain decreases LRRK2 membrane association, pericentriolar recruitment, and ability to phosphorylate Rab10. Consistently, overexpression of LRRK2350-550, a fragment that encompasses the Rab38 binding site, blocks endogenous LRRK2s phosphorylation of Thr73-Rab10. Finally, disruption of BLOC-3, the guanine nucleotide exchange factor for Rab38 and 32, inhibits Rab38s regulation of LRRK2. In sum, our data identify Rab38 as a physiologic regulator of LRRK2 function and lend support to a model in which LRRK2 plays a central role in Rab GTPase coordination of vesicular trafficking.