Endogenous Rab29 does not impact basal or nigericin and monensin stimulated LRRK2 pathway activity

Mutations that enhance LRRK2 protein kinase activity cause inherited Parkinsons disease. LRRK2 phosphorylates a group of Rab GTPase proteins, including Rab10 and Rab12, within the effector-binding switch-II motif. Previous work has indicated that the PARK16 locus, which harbors the gene encoding for Rab29, is involved in Parkinsons, and that Rab29 operates in a common pathway with LRRK2. Co-expression of Rab29 and LRRK2 stimulates LRRK2 activity by recruiting LRRK2 to the surface of the trans Golgi network. Here we report that knock-out of Rab29 does not influence endogenous LRRK2 activity, based on assessment of Rab10 and Rab12 phosphorylation, in wildtype LRRK2, LRRK2[R1441C] or VPS35[D620N] knock-in mouse tissues and primary cell lines, including brain extracts and embryonic fibroblasts. We find that in brain extracts, Rab12 phosphorylation is more robustly impacted by LRRK2 inhibitors and pathogenic mutations than Rab10 phosphorylation. Transgenic overexpression of Rab29 in a mouse model was also insufficient to stimulate basal LRRK2 activity. We observed that monovalent cation ionophore antibiotics nigericin and monensin enhance LRRK2-mediated Rab10 and Rab12 phosphorylation 4 to 9-fold, in a manner that is independent from Rab29. Moderate stimulation of Rab10 and Rab12 induced by lysosome stressors chloroquine and LLOMe was also not regulated by Rab29. Our findings indicate that basal, pathogenic, as well as nigericin and monensin stimulated LRRK2 pathway activity is not controlled by Rab29. Further work is required to establish how LRRK2 activity is regulated, and whether other Rab proteins can control LRRK2 by targeting it to diverse membranes.