RILPL1

RILPL1 is a phospho-Rab effector that couples LRRK2 kinase signaling to centriolar and lysosomal membrane dynamics (PMID:35776681, PMID:38091401). It localizes to the subdistal appendage of the mother centriole, where it captures LRRK2-phosphorylated RAB8 and RAB10 (PMID:35776681); the resulting phospho-Rab/RILPL1 accumulation blocks CP110 release from the mother centriole by preventing TTBK2 recruitment, thereby inhibiting early ciliogenesis, and RILPL1 overexpression alone is sufficient to block CP110 uncapping (PMID:33653948). The same axis displaces CDK5RAP2 from the centrosome to produce centrosome cohesion deficits and impaired cell polarization, in a manner requiring both the GTP and phosphorylation status of the Rab substrate (PMID:35776681, PMID:35721463). At lysosomes, RILPL1 acts as an effector of phosphorylated RAB12, RAB8, and RAB10 to drive perinuclear lysosomal clustering and to compromise lysosomal transport (PMID:37086089, PMID:38091401). Once recruited, RILPL1 engages the lysosomal integral membrane protein TMEM55B through a C-terminal TMEM55B-binding motif (TBM) that inserts into a shallow groove spanning two tandem RING-like Zn2+-stabilized β-sandwich domains, anchored largely by backbone hydrogen bonding from two RILPL1 glutamate residues (PMID:41314214). RILPL1 also binds the dynactin subunit p150Glued to power minus-end-directed transport and retraction of lysosomal (LYTL) tubules, opposing JIP4-mediated plus-end tubule extension to create antagonistic motor forces that govern dynamic lysosomal tubulation (PMID:40990465). Its recruitment to all of these sites depends on the Parkinson's-disease-associated LRRK2 kinase pathway, and the PD-linked VPS35[D620N] mutation feeds into the same phospho-Rab/RILPL1 axis (PMID:35776681, PMID:38091401).

1. 2012 Medium

   Established that RILPL1 is a centriolar/ciliary protein whose loss causes abnormal accumulation of ciliary membrane proteins, framing it as a regulator of ciliary protein content.

   Evidence Live-cell microscopy, RNAi depletion, and 3D culture assays localizing RILPL1 to the mother centriole and primary cilium

   PMID:23264467

   Open questions at the time

   • No molecular partner or recruitment mechanism identified
   • Link to phospho-Rab/LRRK2 signaling not yet known
2. 2019 High

   Placed RILPL1 downstream of LRRK2 by showing LRRK2-phosphorylated RAB8 and RAB10 are recruited to centrosomal RILPL1, and that RILPL1 is required for LRRK2-driven cohesion and ciliogenesis defects.

   Evidence RNAi epistasis with RAB8/RAB10/RILPL1, LRRK2 kinase inhibition in patient-derived cells and mutant LRRK2 mouse astrocytes

   PMID:31428781

   Open questions at the time

   • Molecular mechanism of cohesion disruption not defined
   • Direct binding of phospho-Rab to RILPL1 not structurally resolved
3. 2021 High

   Defined the ciliogenesis-blocking mechanism: phospho-RAB10/RILPL1 prevents CP110 uncapping by failing to recruit TTBK2, the kinase that triggers CP110 release.

   Evidence Live-cell imaging, Rab10/RILPL1 knockout MEFs, RILPL1 overexpression phenocopy, serum-starvation ciliation assays

   PMID:33653948

   Open questions at the time

   • How RILPL1 physically blocks TTBK2 recruitment is unresolved
   • Stoichiometry of phospho-Rab/RILPL1 at the centriole unknown
4. 2022 High

   Refined RILPL1's centriolar position to the subdistal appendage and established Rab-substrate specificity, identifying CDK5RAP2 displacement as the cohesion-disrupting event.

   Evidence Immunofluorescence localization, systematic Rab knockout/RNAi epistasis, scratch-wound polarization assays, iPS cell validation

   PMID:35721463 PMID:35776681

   Open questions at the time

   • Direct interaction between RILPL1 and CDK5RAP2 not demonstrated
   • Mechanism linking RILPL1 to CDK5RAP2 eviction unclear
5. 2023 High

   Extended RILPL1 function to lysosomes, showing it acts as a phospho-RAB12 effector driving perinuclear lysosomal clustering and binds the lysosomal protein TMEM55B upon LRRK2/VPS35[D620N] activation.

   Evidence Organelle imaging, RAB12/RILPL1 knockout and re-expression, phospho-mutant Rab12, lysosomal proteomics, Co-IP, interaction-blocking mutagenesis, mouse tissue analysis

   PMID:37086089 PMID:38091401

   Open questions at the time

   • Functional role of TMEM55B binding in transport not fully defined
   • Mechanism of VPS35[D620N]-driven RILPL1 destabilization unresolved
6. 2025 High

   Identified the motor mechanism: RILPL1 binds p150Glued dynactin to drive minus-end lysosomal tubule retraction, antagonizing JIP4 to create dynamic, metastable lysosomal tubulation.

   Evidence Lysosomal proteome mapping after LRRK2 inhibition, live-cell LYTL tubule imaging, p150Glued binding assays, functional comparison with JIP4

   PMID:38903076 PMID:40990465

   Open questions at the time

   • Quantitative balance of JIP4 vs RILPL1 forces not modeled
   • Whether centriolar and lysosomal pools of RILPL1 are functionally interchangeable is unknown
7. 2025 High

   Provided atomic detail of the RILPL1–TMEM55B interface, defining a C-terminal TBM that docks into a groove across tandem RING-like Zn2+ β-sandwich domains and revealing TMEM55B as a hub for multiple TBM-containing proteins.

   Evidence X-ray crystallography of TMEM55B alone and bound to the RILPL1 TBM peptide, interface mutagenesis, Co-IP/MS

   PMID:41314214

   Open questions at the time

   • Functional consequence of competition among TBM-containing TMEM55B partners not established
   • Affinity/regulation of TBM engagement relative to phospho-Rab binding not quantified

• How RILPL1 mechanistically partitions between its centriolar (ciliogenesis/cohesion) and lysosomal (transport/tubulation) roles, and how these contribute to LRRK2-driven Parkinson's pathology, remains open.
• No unified model coordinating centriolar and lysosomal RILPL1 pools
• In vivo consequence of RILPL1 loss for disease phenotypes not established