REEP2

REEP2 is an integral endoplasmic reticulum membrane protein that shapes the peripheral tubular ER through membrane binding and modulates the trafficking and signaling of secretory cargoes (PMID:24388663, PMID:24098485). Its membrane association is the core determinant of function: a dominant-negative variant (p.Val36Glu) blocks normal membrane binding of wild-type protein and a recessive variant (p.Phe72Tyr) lowers mutant affinity for membranes, and loss of this association causes hereditary spastic paraplegia SPG72 (PMID:24388663). Beyond ER morphogenesis, REEP2 physically associates with select GPCRs — the T1R2/T1R3 sweet receptor subunits and α2C adrenergic receptors — where it enhances signaling by recruiting receptors into lipid raft microdomains and by augmenting ER cargo capacity and surface delivery rather than by globally increasing surface expression (PMID:20943918, PMID:24098485). REEP2 functions in an integrated program of ER remodeling that supports regulated secretion: it is restricted to neuronal and neuroendocrine exocytotic tissues (PMID:24355597), promotes ER-to-Golgi transport of secretory cargoes from ER exit sites (PMID:41292834), and is transcriptionally upregulated by p53 upon DNA damage to extend tubular ER, build ER-mitochondria contacts, and drive Ca2+ transfer-dependent apoptosis (PMID:30030520). REEP2 also acts as a negative regulator of adipogenic differentiation in mesenchymal stem cells (PMID:36879811).

1. 2010 High

   Established that REEP2 is not merely structural but actively modulates GPCR signaling, by showing it physically associates with sweet receptor subunits and recruits receptors into lipid rafts.

   Evidence Reciprocal co-IP, lipid raft fractionation, and siRNA knockdown with heterologous receptor functional assays in taste/GLUTag cells

   PMID:20943918

   Open questions at the time

   • Does not define the structural basis of REEP2-receptor binding
   • Mechanism of raft recruitment versus direct receptor stabilization not resolved
2. 2013 Medium

   Localized REEP2 to the ER and showed it interacts with and alters glycosidic processing of specific GPCR cargoes (α2C but not α2A AR), framing it as a selective ER cargo-capacity factor.

   Evidence Immunolocalization, co-IP, glycosylation processing assays, and dominant-negative C-terminal truncation in cell models

   PMID:24098485

   Open questions at the time

   • REEP2-specific conclusions partially inferred from shared REEP1 experiments
   • Basis of cargo selectivity (α2C vs α2A) unknown
3. 2013 Medium

   Defined the tissue scope of REEP2, restricting expression to neuronal and neuroendocrine exocytotic tissues and pointing to a specialized secretory role.

   Evidence Validated antibody immunoblotting, immunofluorescence, RT-PCR, and microarray across tissues

   PMID:24355597

   Open questions at the time

   • Tissue expression does not establish cell-type-specific function
   • Subcellular distribution within secretory cells not detailed
4. 2014 High

   Demonstrated that membrane association is mechanistically required for REEP2 function and that disrupting it causes disease, defining the basis of SPG72.

   Evidence In vitro membrane-binding assays with defined mutant alleles, fibroblast ER morphology analysis, and exome sequencing with functional validation

   PMID:24388663

   Open questions at the time

   • No structural model of the membrane-binding interface
   • Connection between ER-shaping defect and axonal/neuronal pathology not mechanistically traced
5. 2018 Medium

   Placed REEP2 in a stress-responsive pathway, showing p53-driven upregulation extends tubular ER and promotes ER-mitochondria Ca2+ transfer and apoptosis.

   Evidence p53 reporter assays, live-cell ER imaging, ER-mitochondria contact quantification, Ca2+ transfer and apoptosis readouts with knockdown/overexpression

   PMID:30030520

   Open questions at the time

   • REEP2 contribution shared with REEP1 and EI24
   • Whether REEP2 directly forms or only enables contact sites unresolved
6. 2023 Medium

   Identified a developmental role for REEP2 as a negative regulator of adipogenic differentiation, expanding its function beyond neuronal secretion.

   Evidence Gene expression analysis, siRNA/overexpression during induced adipogenesis, and HDAC inhibition with chidamide in BM-MSCs

   PMID:36879811

   Open questions at the time

   • Molecular mechanism linking REEP2 to adipogenic suppression not defined
   • Whether ER-shaping activity underlies the effect unknown
7. 2025 Medium

   Connected REEP2-mediated ER-to-Golgi cargo transport to a tumor-promoting secretory program controlled by a ZEB1/miR-183/miR-193a regulatory axis.

   Evidence In vivo CRISPRi screen, miRNA functional assays, ER-to-Golgi trafficking assays, and orthotopic syngeneic mouse model (preprint)

   PMID:41292834

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Specific secreted cargoes dependent on REEP2 not fully enumerated
   • Direct biochemical role at ER exit sites not resolved

• How REEP2 mechanistically couples its ER-shaping membrane activity to cargo selection, raft recruitment, and contact-site formation remains unresolved.
• No structural model of the membrane-binding or cargo-binding interfaces
• Unclear whether tubulation, trafficking, and GPCR modulation are one mechanism or separable activities
• Causal chain from ER defect to neuronal axonopathy in SPG72 undefined