| 1995 |
SURF4 (Surf-4) is a ~30 kDa integral membrane protein with at least two (predicted seven) transmembrane domains, a C-terminal double-lysine ER retrieval motif, and localizes to the ER (not plasma membrane), as shown by salt/detergent microsomal fractionation and immunofluorescence of myc-tagged chimeras. |
In vitro translation, salt/detergent extraction, proteolysis protection assay, immunofluorescence of myc-tagged Surf4 transfectants |
Molecular membrane biology |
Medium |
7540914
|
| 2008 |
SURF4 physically interacts with ERGIC-53 and p24 proteins in the early secretory pathway. Co-silencing SURF4 with ERGIC-53, or silencing the p24 family member p25, causes reduced ERGIC cluster number and Golgi fragmentation, partial redistribution of COPI (but not Golgi matrix proteins) to the cytosol, and partial brefeldin-A resistance of the cis-Golgi—without blocking anterograde transport. Live imaging showed decreased ERGIC cluster stability after p25 knockdown. |
Co-immunoprecipitation, siRNA knockdown, live-cell imaging, immunofluorescence, brefeldin A treatment |
Molecular biology of the cell |
High |
18287528
|
| 2018 |
SURF4 is the primary ER cargo receptor mediating efficient secretion of PCSK9 in HEK293T cells. SURF4 localizes to the early secretory pathway, physically interacts with PCSK9, and its deletion causes ER accumulation and reduced extracellular secretion of PCSK9, rescued by SURF4 cDNA re-expression. |
Proximity-dependent biotinylation (BioID) proteomics, genome-scale CRISPR screen, multiple independent sgRNAs, clonal SURF4-deficient cell lines, functional rescue with SURF4 cDNA, co-immunoprecipitation, subcellular fractionation |
eLife |
High |
30251625
|
| 2018 |
SURF4 functions as a cargo receptor that binds amino-terminal tripeptide motifs (ER-ESCAPE motifs) exposed after signal sequence cleavage on soluble cargo proteins, enabling their preferential ER export. Binding affinity scales with aggregation propensity of the cargo; single amino acid changes in the tripeptide alter ER retention. Human cells lacking SURF4 lose preferential trafficking of strong ER-ESCAPE motif cargoes; re-expression of SURF4 or yeast Erv29p rescues this. |
Mutagenesis of N-terminal tripeptide motifs, SURF4 knockout human cells, functional rescue with SURF4 or Erv29p, systematic survey of 8,000 tripeptide variants, secretion assays |
PLoS biology |
High |
30086131
|
| 2018 |
SFT-4 (C. elegans SURF4 homolog) localizes predominantly to ER exit sites (ERES) and physically interacts with the yolk lipoprotein VIT-2, promoting its ER export. Mammalian SURF4 physically interacts with apolipoprotein B and its loss causes ER accumulation of apoB in human hepatic HepG2 cells. Loss of SFT-4/SURF4 also reduces the number of COPII-positive ERES. |
Co-immunoprecipitation, immunofluorescence colocalization, in vivo interaction assay in C. elegans, siRNA knockdown in HepG2 cells, ERES quantification |
The Journal of cell biology |
High |
29643117
|
| 2012 |
SURF4 associates with STIM1 in the ER. Deletion of Surf4 in DT40 B cells results in markedly increased store-operated Ca²⁺ entry (SOCE) and facilitated STIM1 clustering upon store depletion, indicating SURF4 negatively modulates STIM1-mediated SOCE. |
Affinity purification for STIM1-binding proteins, co-immunoprecipitation, Surf4 knockout DT40 B cells, Ca²⁺ entry measurements |
Biochemical and biophysical research communications |
Medium |
22609200
|
| 2020 |
SURF4 functions as an ER cargo receptor mediating efficient secretion of erythropoietin (EPO). SURF4 disruption causes intracellular EPO accumulation in the ER and reduced extracellular EPO; SURF4 and EPO physically interact. SURF4 overexpression increases EPO secretion. These findings were confirmed in multiple cell lines including endogenous EPO-secreting Hep3B cells under hypoxia. |
Genome-scale CRISPR screen, multiple independent sgRNAs, SURF4 cDNA rescue, co-immunoprecipitation, subcellular fractionation/immunofluorescence, endogenous EPO secretion assay |
Molecular and cellular biology |
High |
32989016
|
| 2020 |
Homozygous Surf4 knockout mice are embryonic lethal (between E3.5 and E9.5), demonstrating SURF4 is essential for early embryonic development in vivo, and implying additional essential cargoes or functions beyond known ones. |
CRISPR/Cas9 germline knockout mice, embryonic staging |
PloS one |
Medium |
31978056
|
| 2021 |
Progranulin interacts with prosaposin in the ER lumen; prosaposin physically interacts with SURF4, and SURF4 is critical for efficient ER exit of both progranulin and prosaposin. Thus SURF4 mediates lysosomal delivery of progranulin via a prosaposin relay. |
Co-immunoprecipitation, SURF4 knockdown/knockout, subcellular fractionation, secretion assays |
The Journal of cell biology |
Medium |
34919127
|
| 2021 |
Hepatic liver-specific Surf4 knockout mice show no effect on PCSK9 secretion (negative finding for this model), but a significant reduction in plasma cholesterol, triglycerides, and apoB due to impaired VLDL secretion. Surf4 co-immunoprecipitates and colocalizes with apolipoprotein B100 in human hepatocytes. Knockdown of hepatic Surf4 in Ldlr-/- mice reduces atherosclerosis without causing liver lipid accumulation. |
Liver-specific Surf4 knockout mice, co-immunoprecipitation, immunofluorescence colocalization, siRNA knockdown, lipid measurements, atherosclerosis quantification |
Journal of lipid research |
High |
34118252
|
| 2022 |
SURF4 induces a distinct tubular ERGIC (t-ERGIC) that is ERGIC-53-negative but Rab1A/B-positive, with high surface-to-volume ratio and fast ER-to-Golgi travel speed. SURF4 recognizes N-terminal signals of soluble cargoes, co-clusters with them to expand the ER exit site, and t-ERGIC biogenesis and cargo selectivity both depend on SURF4. The fast SURF4-dependent transport is antagonized by KDEL-mediated ER retrieval. |
Live-cell superresolution imaging, SURF4 KO/knockdown, SURF4 rescue, N-terminal signal mutagenesis, trafficking kinetics assays |
Developmental cell |
High |
35051356
|
| 2022 |
SURF4 facilitates ER export of Sonic Hedgehog (Shh) via an ER export signal, and proteoglycans promote dissociation of SURF4 from Shh at the Golgi, constituting a SURF4-to-proteoglycan relay mechanism for Shh secretion. |
Co-immunoprecipitation, ER export signal mutagenesis, proteoglycan competition assays, subcellular fractionation |
Proceedings of the National Academy of Sciences of the United States of America |
Medium |
35271396
|
| 2022 |
Surf4 promotes ER export of proinsulin in pancreatic β-cells by recruiting proinsulin to ERES. Surf4 expression is upregulated under high-glucose conditions. Surf4 forms oligomers and physically interacts with both proinsulin and Sec12 (essential for COPII vesicle formation), suggesting it delivers proinsulin into COPII vesicles cooperatively with Sec12. Surf4 knockdown causes proinsulin ER retention and decreased mature insulin and insulin secretion. |
Surf4 knockdown, co-immunoprecipitation with proinsulin and Sec12, immunofluorescence colocalization at ERES, insulin secretion assays, oligomerization assays |
Communications biology |
High |
35562580
|
| 2022 |
Hepatic Surf4-conditional knockout mice show ~60% reduction in plasma PCSK9, ~50% increase in hepatic LDLR, and a severe defect in hepatic lipoprotein secretion (APOB-containing lipoproteins), causing marked reduction in plasma cholesterol and triglycerides. Acute depletion by liver-targeted CRISPR/Cas9 or siRNA confirms these findings in vivo. |
Conditional KO mice (Surf4 Alb-Cre), acute CRISPR/Cas9 and siRNA depletion in adult mice, plasma PCSK9/LDLR/lipid measurements, lipoprotein metabolism characterization |
eLife |
High |
36193893
|
| 2023 |
SURF4 traffics a broad range of secretory cargoes in HuH7 hepatocytes, as identified by mass spectrometry of conditioned media and cell lysates from SURF4 CRISPR knockout cells. Cargo recognition is governed by complex mechanisms rather than a universal binding motif. |
CRISPR gene inactivation, mass spectrometry of conditioned media and cell lysates |
Journal of proteome research |
Medium |
37844105
|
| 2023 |
Intestinal Surf4 is essential for apolipoprotein (ApoA1, ApoB48, PRAP1) transport and chylomicron/HDL secretion. Intestine-specific Surf4 KO mice display ectopic lipid deposition in the small intestine and hypolipidemia. Surf4 co-localizes with apoB and co-immunoprecipitates with apoB48 in differentiated Caco-2 cells. |
Intestine-specific KO mice, co-immunoprecipitation, immunofluorescence colocalization, proteomics, lipid measurements |
Molecular metabolism |
High |
38042368
|
| 2023 |
Surf4 collaborates with derlin-2 and derlin-1 in ERAD: Surf4 acts downstream of derlin-2 and derlin-1 to mediate COX-2 translocation from the ER lumen to the cytosol. Surf4 knockdown impedes COX-2 ubiquitylation and its interaction with caveolin-1 and p97 in the cytosol. Surf4 and p97 preferentially interact with non-glycosylated COX-2. |
CRISPR library screen, siRNA knockdown, co-immunoprecipitation, ubiquitylation assays, N-glycosylation mutant analysis |
Journal of cell science |
Medium |
37676109
|
| 2024 |
SURF4 recruits different SEC24 paralogs of the COPII coat for export of different cargoes: PCSK9 requires both SURF4 and co-receptor TMED10 for export via SEC24A, whereas Cab45 and NUCB1 require SEC24C/D. ER export signals of Cab45 and NUCB1 bind co-translationally to a lumenal pocket of SURF4, contrasting models requiring cargo folding before receptor engagement. |
Epistasis using SEC24 paralog-specific mutants, co-immunoprecipitation with TMED10, mutagenesis of lumenal SURF4 pocket, co-translational binding assays, secretion assays |
The Journal of cell biology |
High |
39531033
|
| 2024 |
Hepatic SURF4 facilitates SAA1 (serum amyloid A1) secretion. SURF4 co-immunoprecipitates and colocalizes with SAA1. Surf4 liver-specific KO reduces SAA1 secretion from hepatocytes, decreasing hepatic stellate cell (HSC) activation (via SAA1-TLR2 signaling) and attenuating liver fibrosis. |
Conditional Surf4 KO mice, co-immunoprecipitation, colocalization, conditioned medium assays, SAA1 knockdown epistasis, TLR2 knockdown in LX-2 cells, CCl4-fibrosis model |
Research (Washington, D.C.) |
High |
39105051
|
| 2021 |
Surf4 facilitates somatic cell reprogramming to iPSCs by activating the ER stress response (UPR) at an early stage of reprogramming. Surf4 co-expressed with OSKM activates Hspa5 and spliced Xbp1; blocking UPR compromises Surf4's reprogramming effect. |
Secondary reprogramming system, RNA-seq, qPCR, Western blot, alkaline phosphatase staining, UPR inhibition experiments |
Cell proliferation |
Medium |
34585448
|
| 2025 |
YIPF5 directly interacts with SURF4 and negatively regulates SURF4-mediated ER export. YIPF5 depletion alters SURF4 localization, causing elongated ERGIC53- and Rab1-positive tubules from COPII-labeled ER exit sites, and kinetic analysis shows enhanced SURF4-mediated ER export in YIPF5 KO cells. |
Co-immunoprecipitation (direct interaction), YIPF5 KO cells, live-cell imaging of ERGIC tubules, kinetic secretion assays |
bioRxivpreprint |
Medium |
bio_10.1101_2025.06.11.659036
|