RILPL2

RILPL2 is a phospho-Rab effector and Myosin Va co-regulator that couples LRRK2 kinase signaling to ciliogenesis control and cytoskeletal dynamics. Its RH2 domain forms an α-helical dimer that bridges two LRRK2-phosphorylated Rab8a (pT72) molecules in a heterotetrameric complex, with an X-cap motif orienting key arginine residues toward the phosphothreonine (PMID:32017888). RILPL2 binds the globular tail domain of Myosin Va and, together with Rab36 and melanophilin, sequentially activates Myosin Va ATPase activity and processive motility; in neurons, this RILPL2–MyoVa axis activates Rac1–PAK signaling to promote dendritic spine morphogenesis (PMID:31175157, PMID:19812310). Under pathogenic LRRK2 conditions, phosphoRab10-dependent recruitment of RILPL2 sequesters Myosin Va to the pericentriolar region, blocking ciliogenesis (PMID:33727250, PMID:23264467).

1. 2009 Medium

   Establishing that RILPL2 is a direct Myosin Va partner that activates Rac1–PAK signaling answered how a Rab-linked adaptor could influence dendritic spine morphogenesis in neurons.

   Evidence Co-immunoprecipitation, shRNA knockdown and rescue, PAK-PBD Rac1 activation assay in hippocampal neurons

   PMID:19812310

   Open questions at the time

   • Structural basis of the RILPL2–MyoVa interaction was not determined
   • Upstream signal linking RILPL2 to Rac1 activation not identified
   • In vivo relevance in animal models not tested
2. 2012 Medium

   Demonstrating RILPL2 localization to the primary cilium and centrosome, and that its depletion causes ciliary membrane protein accumulation, established a ciliary trafficking function for RILPL2.

   Evidence Live-cell microscopy and RNAi depletion in epithelial cells with 3D culture phenotypic readout

   PMID:23264467

   Open questions at the time

   • Combined depletion with RILPL1 makes individual contribution of RILPL2 uncertain
   • Molecular cargo and vesicular carriers mediating ciliary protein removal not identified
   • Connection to Rab phosphorylation not yet made
3. 2019 High

   Reconstituting Myosin Va activation in vitro showed that RILPL2 and melanophilin act as sequential co-regulators — with Rab36 promoting RILPL2–GTD binding that then exposes the melanophilin site — resolving how autoinhibited MyoVa becomes processive.

   Evidence ATPase assays, single-molecule motility assays, GST pulldowns, and analytical ultracentrifugation with purified proteins

   PMID:31175157

   Open questions at the time

   • Structural details of the RILPL2–GTD interface at atomic resolution not resolved
   • Whether this sequential activation operates in all MyoVa-dependent cell types is unknown
   • Role of Rab36 GTP/GDP cycling in regulating RILPL2 binding not tested
4. 2020 High

   The crystal structure of phospho-Rab8a bound to the RILPL2 RH2 domain revealed a 2:2 heterotetramer with an X-cap motif that reads the phosphothreonine, explaining the molecular basis of LRRK2-phosphorylated Rab selectivity.

   Evidence X-ray crystallography of pRab8a–RILPL2 RH2 complex with X-cap mutagenesis

   PMID:32017888

   Open questions at the time

   • Structure of full-length RILPL2 (including regions beyond RH2) not determined
   • Whether the same binding mode applies to phospho-Rab10 not crystallographically confirmed
   • How phospho-Rab binding integrates with the MyoVa-activating function of RILPL2 is unclear
5. 2021 High

   Showing that pathogenic LRRK2 drives phosphoRab10-dependent sequestration of RILPL2 and Myosin Va to the mother centriole, thereby blocking ciliogenesis, connected the phospho-Rab effector function to Parkinson's disease-relevant biology.

   Evidence Co-immunoprecipitation, FLIP microscopy, overexpression and RNAi in RPE cells

   PMID:33727250

   Open questions at the time

   • Whether ciliogenesis defect occurs in LRRK2-mutant neurons or patient-derived cells not shown
   • Downstream ciliary signaling pathways disrupted by RILPL2-mediated MyoVa retention not characterized
   • Relative contributions of phosphoRab8a versus phosphoRab10 to pericentriolar RILPL2 recruitment not resolved

• How RILPL2 integrates its phospho-Rab binding, Myosin Va activation, and ciliary trafficking functions into a unified regulatory mechanism — and whether its dysfunction contributes to neurodegeneration in vivo — remains unresolved.
• No full-length RILPL2 structure exists to explain how RH2, GTD-binding, and ciliary targeting regions are coordinated
• In vivo knockout phenotype in mammalian models not reported
• Mechanism by which RILPL2 removes ciliary membrane proteins is unknown