Affinage

PRAF2

PRA1 family protein 2 · UniProt O60831

Length
178 aa
Mass
19.3 kDa
Annotated
2026-04-28
17 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PRAF2 is an ER-resident four-transmembrane domain protein that functions as a gatekeeper controlling the ER-to-Golgi trafficking of polytopic membrane proteins and as a modulator of apoptosis. It retains client proteins—including CCR5, CFTR (both wild-type and F508del), and the GABAB receptor GB1 subunit—in the ER by preventing their recruitment into COPII vesicles, acting through transmembrane domain interactions in a concentration-dependent manner that is opposed by escort proteins such as CD4 (PMID:36167862, PMID:38139265, PMID:26645984). PRAF2 also interacts with the anti-apoptotic proteins Bcl-xL and Bcl-2 via their transmembrane domains; overexpression promotes Bax translocation to mitochondria and apoptosis, while knockdown confers resistance to etoposide-induced cell death (PMID:21203533). Additionally, PRAF2 supports cancer cell migration and invasion, partly through regulation of JAG2-containing exosome release (PMID:31198409, PMID:20412121).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2005 Medium

    The initial discovery that PRAF2 is a four-transmembrane ER/Golgi-localized protein that physically interacts with CCR5 and heterodimerizes with related prenylated Rab acceptor family members established it as a candidate regulator of receptor trafficking.

    Evidence Co-immunoprecipitation, co-localization with ER (calnexin) and Golgi markers, and yeast two-hybrid in transfected cells

    PMID:15757671

    Open questions at the time
    • Functional consequence of the PRAF2–CCR5 interaction on CCR5 trafficking was not tested
    • Whether the Rab-acceptor motif is required for function was not addressed
    • No in vivo validation
  2. 2007 Medium

    Observation that PRAF2 protein levels increase during cerulenin-induced apoptosis in neuroblastoma cells linked PRAF2 for the first time to programmed cell death, beyond its putative trafficking role.

    Evidence Immunofluorescence microscopy with Annexin V staining and PARP cleavage assay in neuroblastoma cells

    PMID:17975142

    Open questions at the time
    • Correlative evidence only; no loss-of-function to establish causality
    • Mechanism by which PRAF2 levels increase during apoptosis unknown
  3. 2010 High

    Two parallel studies established that PRAF2 has dual functions: it interacts with Bcl-xL/Bcl-2 via their transmembrane domains to promote Bax mitochondrial translocation and apoptosis, and its knockdown reduces glioma cell viability, migration, and invasion, revealing PRAF2 as both a pro-apoptotic modulator and a contributor to cancer cell aggressiveness.

    Evidence TAP, Co-IP, domain-deletion mutagenesis, overexpression/knockdown with apoptosis and clonogenicity readouts; RNAi with migration/invasion assays in glioma cells

    PMID:20412121 PMID:21203533

    Open questions at the time
    • Mechanism reconciling pro-apoptotic activity with pro-tumorigenic phenotype in glioma not resolved
    • No structural information on the PRAF2–Bcl-xL transmembrane interaction
    • Cancer phenotypes demonstrated in single cell lines only
  4. 2015 Medium

    Demonstration that PRAF2 acts as an ER gatekeeper preventing GABAB receptor GB1 subunit surface delivery in the absence of its GB2 partner extended the trafficking function to a neuronal receptor and revealed ultrastructural localization in mitochondria and primary cilia beyond the ER.

    Evidence Immunofluorescence and immuno-electron microscopy in mouse CNS tissue

    PMID:26645984

    Open questions at the time
    • Direct biochemical evidence of GB1 retention by PRAF2 (e.g., COPII assay) was not provided
    • Functional significance of mitochondrial and ciliary localization unexplored
  5. 2019 Medium

    Discovery that PRAF2 is required for release of JAG2-rich exosomes from colorectal cancer cells, which promote metastasis in a paracrine fashion, placed PRAF2 in the exosome biogenesis/secretion pathway and extended its oncogenic role to a non-EMT invasion mechanism.

    Evidence siRNA knockdown, transcriptome microarray, exosome isolation and analysis, migration/invasion assays in colorectal cancer cells

    PMID:31198409

    Open questions at the time
    • Mechanism by which PRAF2 controls exosome cargo loading or release not defined
    • Whether JAG2 exosome regulation is direct or indirect not resolved
    • Single cancer type studied
  6. 2022 High

    Stoichiometric interaction between PRAF2 and CFTR (wild-type and F508del) that blocks ER exit site access provided the first biochemically defined mechanism of PRAF2-mediated ER retention and showed that cystic fibrosis pharmacological chaperones partly work by overcoming this retention.

    Evidence Co-immunoprecipitation, COPII vesicle recruitment assay, pharmacological chaperone rescue in cell-based system

    PMID:36167862

    Open questions at the time
    • Whether PRAF2 depletion alone is sufficient to rescue F508del-CFTR surface expression in patient-derived cells not tested
    • Structural basis of stoichiometric retention not determined
  7. 2023 High

    Detailed mechanistic dissection showed that PRAF2 retains CCR5 in the ER through transmembrane domain contacts in a dose-dependent manner, directly opposing the COPII-promoting escort protein CD4, thereby completing the molecular model of PRAF2 as a general ER retention factor for polytopic membrane proteins.

    Evidence BRET-based subcellular localization and proximity assays, Co-IP, site-directed mutagenesis of CCR5

    PMID:38139265

    Open questions at the time
    • Whether PRAF2 directly contacts COPII coat components to block vesicle loading is unknown
    • Generalizability to additional client proteins beyond CCR5, CFTR, and GB1 not yet demonstrated
    • No structural model of the PRAF2–client transmembrane interface exists

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis for how PRAF2 recognizes diverse transmembrane clients and how its ER retention and pro-apoptotic functions are coordinately regulated in vivo remain unresolved.
  • No crystal or cryo-EM structure of PRAF2 alone or in complex with any client
  • Physiological phenotype of PRAF2 knockout in animal models not reported
  • Mechanism linking ER retention activity to Bcl-xL/Bax-dependent apoptosis regulation not integrated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0060090 molecular adaptor activity 2
Localization
GO:0005783 endoplasmic reticulum 4 GO:0031410 cytoplasmic vesicle 2 GO:0005739 mitochondrion 1 GO:0005794 Golgi apparatus 1
Pathway
R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-9609507 Protein localization 3 R-HSA-5357801 Programmed Cell Death 1
Partners
BAXBCL2BCL2L1CCR5CD4CFTRGABBR1JAG2

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 PRAF2 (JM4) is a four-transmembrane protein that physically interacts with the CCR5 chemokine receptor, co-localizes with calnexin in the endoplasmic reticulum and with the mannose 6-phosphate receptor in the Golgi, and heterodimerizes with the related proteins JWA and GTRAP3-18; it harbors a Rab-acceptor motif suggesting a role in vesicle formation at the Golgi complex and receptor trafficking. Co-immunoprecipitation, co-localization by immunofluorescence microscopy, yeast two-hybrid (protein interaction screen) FEBS letters Medium 15757671
2007 PRAF2 protein localizes to bright cytoplasmic punctae (vesicle-like structures) in neuroblastoma cells, and its protein levels increase during cerulenin-induced apoptosis. Immunofluorescence microscopy, Annexin V staining, PARP cleavage assay Clinical cancer research Medium 17975142
2010 PRAF2 interacts with Bcl-xL and Bcl-2 via the transmembrane domain of Bcl-xL; overexpression of PRAF2 induces translocation of Bax to mitochondria and apoptotic cell death, which is prevented by co-transfection of Bcl-xL but not by a transmembrane domain-deleted Bcl-xL mutant; knockdown of PRAF2 reduces cell death and increases clonogenicity after etoposide treatment. Tandem affinity purification, Co-immunoprecipitation, domain-deletion mutagenesis, overexpression/knockdown with apoptosis readouts (Annexin V, PARP cleavage), clonogenic assay PloS one High 21203533
2010 PRAF2 localizes to small vesicle-like structures throughout the cytoplasm and in/around cell nuclei of glioma cells; monomeric and dimeric forms associate with different cell compartments; RNAi-mediated knockdown of PRAF2 significantly reduces cell viability, migration, and invasiveness of U-87 glioma cells. Immunofluorescence microscopy, cell fractionation, RNA interference, cell viability/migration/invasion assays Cancer science Medium 20412121
2015 PRAF2 acts as a gatekeeper in the endoplasmic reticulum, preventing progression of the GABAB receptor GB1 subunit through the biosynthetic pathway in the absence of heterodimerization with GB2; electron microscopy additionally reveals PRAF2 localization in mitochondria, primary cilia, and sub-synaptic regions beyond the ER. Immunofluorescence microscopy, electron microscopy, immunocytochemistry in mouse CNS Brain structure & function Medium 26645984
2019 JAG2-rich exosomes are released from colorectal cancer cells in a PRAF2-dependent manner, and these exosomes regulate cancer cell metastasis in a paracrine fashion; JAG2 and PRAF2 are mutually co-expressed and co-regulate migration and invasion independently of EMT. siRNA knockdown, transcriptome microarray, exosome analysis, migration/invasion assays Cancer cell international Medium 31198409
2022 PRAF2 interacts stoichiometrically with both wild-type and F508del mutant CFTR and prevents newly synthesized CFTR from accessing ER exit sites (COPII vesicles); pharmacological chaperones that rescue CFTR-F508del function in CF patients work partly by targeting PRAF2-mediated retention of CFTR in the ER. Co-immunoprecipitation, COPII vesicle recruitment assay, pharmacological chaperone treatment with functional rescue readout Cellular and molecular life sciences High 36167862
2023 PRAF2 inhibits cell-surface targeting of CCR5 in a concentration-dependent manner by interacting with CCR5 transmembrane domains (not the C-terminal RXR motif); this interaction retains CCR5 in the ER and opposes the action of the escort protein CD4, which promotes CCR5 export into COPII vesicles. BRET-based subcellular localization assay, BRET-based proximity assay, Co-immunoprecipitation, site-directed mutagenesis International journal of molecular sciences High 38139265

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 Long non-coding RNA HOTAIR functions as a competitive endogenous RNA to regulate PRAF2 expression by sponging miR-326 in cutaneous squamous cell carcinoma. Cancer cell international 45 31649487
2005 JM4 is a four-transmembrane protein binding to the CCR5 receptor. FEBS letters 44 15757671
2010 Praf2 is a novel Bcl-xL/Bcl-2 interacting protein with the ability to modulate survival of cancer cells. PloS one 36 21203533
2007 Expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in neuroblastoma: correlation with clinical features, cellular localization, and cerulenin-mediated apoptosis regulation. Clinical cancer research : an official journal of the American Association for Cancer Research 23 17975142
2010 Subcellular distribution and expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in malignant glioma: Influence on cell survival and migration. Cancer science 22 20412121
2019 Mutual regulation of JAG2 and PRAF2 promotes migration and invasion of colorectal cancer cells uncoupled from epithelial-mesenchymal transition. Cancer cell international 14 31198409
2016 The Glycosylphosphatidylinositol-Anchored Variable Region of Llama Heavy Chain-Only Antibody JM4 Efficiently Blocks both Cell-Free and T Cell-T Cell Transmission of Human Immunodeficiency Virus Type 1. Journal of virology 14 27654286
2020 JHDM1D-AS1 aggravates the development of gastric cancer through miR-450a-2-3p-PRAF2 axis. Life sciences 13 33245963
2006 Genetics of subpeptin JM4-A and subpeptin JM4-B production by Bacillus subtilis JM4. Biochemical and biophysical research communications 12 16647040
2020 Prolonged Beneficial Effect of Brief Erythropoietin Peptide JM4 Therapy on Chronic Relapsing EAE. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 10 32959273
2021 Grape Seed Proanthocyanidins (GSPs) Inhibit the Development of Cutaneous Squamous Cell Carcinoma by Regulating the hsa_circ_0070934/miR-136-5p/PRAF2 Axis. Cancer management and research 8 34103991
2022 PRAF2 is an oncogene acting to promote the proliferation and invasion of breast cancer cells. Experimental and therapeutic medicine 7 36478884
2018 PRAF2 expression indicates unfavorable clinical outcome in hepatocellular carcinoma. Cancer management and research 7 30100755
2022 Pharmacological chaperone-rescued cystic fibrosis CFTR-F508del mutant overcomes PRAF2-gated access to endoplasmic reticulum exit sites. Cellular and molecular life sciences : CMLS 4 36167862
2015 Anatomical and ultrastructural study of PRAF2 expression in the mouse central nervous system. Brain structure & function 4 26645984
2023 Control of CCR5 Cell-Surface Targeting by the PRAF2 Gatekeeper. International journal of molecular sciences 1 38139265
2025 PRAF2 as a novel biomarker for breast cancer with machine learning and experimentation validation. BMC cancer 0 39773456