Phosphorylation-driven effector switching of Rab7 and Rab12 by the Leucine-Rich Repeat kinase 1 (LRRK1) in mast cells

Jana Omar¹Sewar Omari¹Yaara Gorzalczany¹Fatima Amer-Sarsour¹Mitsunori Fukuda²Avraham Ashkenazi¹Ronit Sagi-Eisenberg^1*

• ¹Cellular, Developmental, and Regenerative Biology, Tel Aviv University, Tel Aviv, Israel
• ²Tohoku Daigaku - Aobayama Campus, Sendai, Japan

Mast cells (MCs) mediate immune, allergic, and neuroinflammatory responses upon activation by adaptive signals through their immunoglobulin E (IgE) binding receptor FcεRI or by innate signals acting via Mas-related G protein coupled receptors (Mrgprs). Here we show that activation by either IgE/antigen or the neuropeptide substance P, which binds to MRGPRX2, induces phosphorylation of the Rab GTPases Rab7 and Rab12. Phosphorylation of both Rabs, following either cell trigger, displayed similar sensitivity to inhibitors of protein kinase C (PKC) and resistance to inhibitors of the Leucine-Rich Repeat kinase 2 (LRRK2), which is known to phosphorylate Rab12. Furthermore, knockdown of the Leucine-Rich Repeat kinase 1 (LRRK1) suppressed phosphorylation of both Rab7 and Rab12, implicating LRRK1 in their phosphorylation in activated MCs by a PKC-dependent mechanism. Similarly to phosphorylation by LRRK2, Rab12 phosphorylation by LRRK1 increases Rab12 affinity for RILP-Like 1(RILP-L1) and RILP-Like 2 (RILP-L2), while phosphorylation by either kinase decreases its affinity for Rab-Interacting Lysosomal Protein (RILP), demonstrating effector-specific regulation. In contrast, Rab7 phosphorylation by LRRK1 increases its affinity for RILP. Taken together, these findings identify LRRK1 as a novel signalling module engaged by both adaptive and innate pathways of MC activation and highlight phosphorylation as a key mechanism that differentially regulates RILP distribution between Rab7 and Rab12.