RAB5IF

RAB5IF is a mitochondrial protein that couples mitochondrial respiration and ribosome biogenesis to a SUMO2-dependent signaling axis governing angiogenesis, neuronal resilience, and tumor cell growth (PMID:41390488, PMID:41915731). Mechanistically, RAB5IF sustains the translational efficiency of SUMO2 mRNA, and loss of RAB5IF lowers SUMO2 protein levels by suppressing SUMO2 translation initiation (PMID:41390488, PMID:41915731). The resulting SUMO2 is required for SUMOylation of Gαi1/3 at Lys277, which licenses assembly of TrkB-SUMO2-Gαi1/3 signaling complexes and downstream Akt-mTOR activation in response to VEGF and BDNF (PMID:41390488, PMID:41915731). Through this axis, endothelial RAB5IF is required for physiological and pathological retinal angiogenesis (PMID:41390488), hippocampal RAB5IF supports dendritic branching, synaptic density, and protection against depressive-like behavior (PMID:41915731), and in NSCLC cells RAB5IF promotes proliferation and migration via the AKT-mTOR pathway (PMID:40318299). Across these settings, RAB5IF function is consistently tied to maintenance of mitochondrial function (PMID:41390488, PMID:41915731, PMID:40318299).

1. 2025 High

   Established that RAB5IF acts upstream of SUMO2 at the translational level by linking mitochondrial respiration and ribosome biogenesis to SUMO2 mRNA translation initiation, defining the entry point of its mechanism.

   Evidence Proteomic sequencing, gene silencing, Western blot, and mitochondrial respiration assays in retinal microvascular endothelial cells

   PMID:41390488

   Open questions at the time

   • The molecular mechanism by which RAB5IF selectively controls SUMO2 mRNA translation initiation is not defined
   • Whether RAB5IF directly binds ribosomal components or SUMO2 mRNA is not shown
2. 2025 High

   Connected the RAB5IF-SUMO2 axis to VEGF signaling by showing SUMO2-dependent SUMOylation of Gαi1/3 at Lys277 and assembly of TrkB-SUMO2-Gαi1/3 complexes are required for pro-angiogenic activity.

   Evidence Endothelial-specific knockout/silencing in mouse retinal angiogenesis models, Gαi1/3 SUMOylation-site mutagenesis, VEGF signaling assays, and co-immunoprecipitation

   PMID:41390488

   Open questions at the time

   • The SUMO E3 ligase mediating Gαi1/3 SUMOylation is not identified
   • How TrkB participates in a VEGF-driven complex is not mechanistically resolved
3. 2026 High

   Generalized the RAB5IF-SUMO2-Gαi1/3 axis to BDNF/TrkB signaling in neurons, showing it drives Akt-mTOR activation and supports neuronal structure and resilience to depressive stimuli.

   Evidence Neuronal knockdown and conditional knockout, overexpression rescue, SUMOylation-site mutagenesis, co-IP, behavioral and dendritic/synaptic morphology assays in mouse hippocampus

   PMID:41915731

   Open questions at the time

   • Whether mitochondrial dysfunction and impaired SUMO2 translation are independent or sequential contributors to the depressive phenotype is not separated
   • Direct molecular interactions of RAB5IF within mitochondria remain uncharacterized
4. 2025 Medium

   Extended RAB5IF function to cancer, showing it promotes NSCLC proliferation and migration through the AKT-mTOR pathway while maintaining mitochondrial function.

   Evidence Lentiviral knockdown/overexpression in NSCLC cell lines with viability/proliferation/migration assays, AKT-mTOR Western blots, and nude mouse xenografts

   PMID:40318299

   Open questions at the time

   • Whether the NSCLC effect proceeds through the same SUMO2-Gαi1/3 axis is not directly tested
   • Single-lab study with limited mechanistic depth beyond pathway-level Western blots

• How RAB5IF physically achieves selective control of SUMO2 mRNA translation and what its direct molecular interactions are within mitochondria remain unresolved.
• No direct binding partners or RNA targets of RAB5IF are identified
• No structural information on RAB5IF is available in the corpus