RAB7B

RAB7B is a late endosome/lysosome-associated small GTPase that controls retrograde membrane transport from endosomes to the trans-Golgi network and promotes lysosomal degradation of specific cargo, thereby regulating innate immune signaling, cell migration, and autophagy. It mediates retrograde trafficking of sorting receptors CI-MPR and sortilin, with TBC1D5 serving as its GAP whose activity is enhanced by retromer, and its depletion impairs cathepsin-D maturation and cholera toxin B retrograde transport (PMID:20375062, PMID:22708738, PMID:30111580). RAB7B promotes lysosomal degradation of TLR4 and TLR9 to dampen macrophage inflammatory responses (PMID:17395780, PMID:19587007), directly interacts with myosin II and the lysosomal Ca²⁺ channel TRPML1 to couple lysosomes to the actomyosin cytoskeleton for dendritic cell migration (PMID:25217632, PMID:34494097), and negatively regulates autophagic flux through interaction with the protease Atg4B (PMID:28835545). RAB7B additionally functions in melanosome protein degradation in keratinocytes and negatively regulates oligodendroglial morphological differentiation (PMID:32037382, PMID:37248316).

1. 2004 Medium

   The initial identification of RAB7B as a lysosome-associated Rab GTPase with restricted expression in monocytic lineage cells established it as a candidate regulator of endolysosomal function in immune cells.

   Evidence Immunofluorescence, Northern blot, and RT-PCR in monocytes and monocyte-derived dendritic cells

   PMID:15144907

   Open questions at the time

   • No functional role established
   • Expression in non-monocytic tissues not assessed
   • No interacting partners identified
2. 2007 High

   The discovery that RAB7B promotes lysosomal degradation of TLR4 and dampens LPS-induced cytokine production defined its first functional role as a negative regulator of innate immune signaling.

   Evidence Overexpression and knockdown in macrophages with TLR4 protein level measurement and cytokine quantification

   PMID:17395780

   Open questions at the time

   • Mechanism by which RAB7B targets TLR4 for degradation unclear
   • Whether other TLRs are similarly regulated unknown
3. 2009 High

   Extension of the TLR degradation role to TLR9 demonstrated that RAB7B is a general negative regulator of endosomal TLR signaling, with a feedback loop whereby TLR9 ligation suppresses RAB7B expression via ERK/p38.

   Evidence Overexpression, siRNA knockdown, cytokine ELISA, and kinase inhibitor assays in macrophages

   PMID:19587007

   Open questions at the time

   • Whether RAB7B regulates other endosomal TLRs (TLR3, TLR7, TLR8) not tested
   • Structural basis for TLR recognition unknown
4. 2010 High

   Demonstration that RAB7B controls retrograde transport from late endosomes to the TGN — affecting CI-MPR trafficking, cathepsin-D maturation, and cholera toxin B retrieval — revealed a fundamental membrane trafficking function beyond immune-specific cargo degradation.

   Evidence siRNA knockdown, dominant-negative/constitutively-active mutants, multiple retrograde transport assays, enzyme activity assays

   PMID:20375062

   Open questions at the time

   • Effector proteins mediating retrograde transport not identified
   • Relationship between lysosomal and TGN-retrograde functions unresolved
5. 2012 High

   The finding that RAB7B also regulates sortilin retrograde trafficking and directly interacts with sortilin broadened its role to both MPR-dependent and MPR-independent sorting receptor pathways and identified its first direct cargo interaction.

   Evidence Co-immunoprecipitation, endosome-to-Golgi retrieval assays, live-cell imaging of TGN tubulation

   PMID:22708738

   Open questions at the time

   • Nature of the Rab7b–sortilin binding interface unknown
   • Whether other sorting receptors are directly bound not tested
6. 2014 High

   Identification of myosin II as a direct RAB7B interactor that transports RAB7B-positive endosomes and mediates RAB7B-dependent RhoA activation, stress fiber formation, and cell migration linked RAB7B to actomyosin cytoskeletal control.

   Evidence Co-immunoprecipitation, pulldown, live-cell imaging, myosin II depletion/inhibition, RhoA and MLC phosphorylation assays, migration assays

   PMID:25217632

   Open questions at the time

   • How RAB7B activates RhoA mechanistically not established
   • Whether the myosin II interaction is GTP-dependent not fully resolved
7. 2017 High

   Discovery of the RAB7B–Atg4B interaction and the demonstration that RAB7B depletion increases autophagic flux established RAB7B as a negative regulator of autophagy acting through modulation of LC3 processing.

   Evidence Co-immunoprecipitation, co-localization, autophagic flux assays including LC3 processing and sequestration assays, siRNA knockdown

   PMID:28835545

   Open questions at the time

   • Whether RAB7B directly inhibits Atg4B enzymatic activity or sequesters it from substrates not distinguished
   • In vivo relevance of autophagy regulation not tested
8. 2018 High

   Identification of TBC1D5 as the GAP for RAB7B, with retromer-enhanced activity, and phenocopy of constitutively active RAB7B by TBC1D5 depletion established the regulatory circuit controlling RAB7B GTPase cycling in endosome-to-TGN transport.

   Evidence In vitro GAP assay, siRNA screen of TBC-domain proteins, co-immunoprecipitation, CI-MPR/sortilin vesicle quantification

   PMID:30111580

   Open questions at the time

   • GEF for RAB7B not identified
   • Structural basis of TBC1D5–retromer–RAB7B ternary interaction unknown
9. 2020 High

   Demonstration that RAB7B is recruited to melanosome-containing compartments in keratinocytes and is required for protein degradation on melanosomes expanded its functional repertoire to pigmentation biology.

   Evidence Systematic Rab localization screen, CRISPR/Cas9 knockout and siRNA knockdown with M-INK melanosome degradation probe

   PMID:32037382

   Open questions at the time

   • Effectors mediating melanosome protein degradation not identified
   • Relationship to lysosomal fusion machinery unresolved
10. 2021 High

    The finding that RAB7B directly interacts with the lysosomal Ca²⁺ channel TRPML1 to locally activate myosin II at the cell rear, enabling fast dendritic cell migration, unified the lysosomal and actomyosin functions into a single mechanistic pathway coupling lysosomal signaling to cell motility.

    Evidence Co-immunoprecipitation of RAB7B–TRPML1, Rab7b knockout dendritic cells, 1D and 3D migration assays, MLC phosphorylation and TFEB activity measurements

    PMID:34494097

    Open questions at the time

    • Whether TRPML1-dependent Ca²⁺ release directly activates myosin II or acts through intermediate kinases not fully resolved
    • Relevance to in vivo immune cell trafficking not shown
11. 2023 Medium

    RAB7B was shown to negatively regulate oligodendroglial morphological differentiation, with its depletion rescuing ER-stress-impaired differentiation, revealing a role in CNS glial biology.

    Evidence siRNA knockdown in FBD-102b oligodendroglial cells, differentiation markers, tunicamycin-induced ER stress

    PMID:37248316

    Open questions at the time

    • Mechanism connecting RAB7B to oligodendrocyte differentiation signaling unknown
    • Single cell line used
    • In vivo relevance in myelination not tested

• The GEF activating RAB7B, the structural basis of its interactions with multiple effectors (TRPML1, myosin II, Atg4B, sortilin), and its in vivo roles in immune regulation and myelination remain to be established.
• No GEF for RAB7B has been identified
• No crystal or cryo-EM structure of RAB7B or its effector complexes exists
• In vivo knockout phenotype not reported