Affinage

SPAG4

Sperm-associated antigen 4 protein · UniProt Q9NPE6

Length
437 aa
Mass
48.2 kDa
Annotated
2026-04-28
17 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SPAG4 (SUN4) is a spermatid-specific inner nuclear membrane SUN-domain protein that assembles LINC complexes to mechanically couple cytoskeletal structures to the nuclear envelope during sperm differentiation, and is co-opted in cancer cells to promote migration and metabolic reprogramming. In spermatids, SPAG4 binds outer dense fiber protein ODF1 via its leucine zipper domain, interacts with spermiogenesis-specific lamin B3 at the nucleoplasmic face, and forms heteromeric assemblies with SUN3/Nesprin1 at the posterior nuclear envelope; loss of SPAG4 in mice causes manchette disorganization, failed nuclear elongation, HTCA detachment, and globozoospermia with infertility (PMID:10373309, PMID:26417726, PMID:26621829, PMID:29663073, PMID:36825599). In carcinoma cells, SPAG4 expression is induced by HIF-1 under hypoxia and promotes cell migration through interaction with Nesprin3, while also activating PI3K/Akt/mTOR/HIF-1α signaling and a c-MYC/SULT2B1 glycolytic axis to drive proliferation and aerobic glycolysis (PMID:23818324, PMID:29901114, PMID:39410830, PMID:40287810). Alternative splicing of SPAG4 regulated by the tRF-3005a/RALY axis produces an oncogenic long isoform (SPAG4-L) that activates GRB14/PI3K/AKT signaling in gastric cancer (PMID:41872130).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1998 Medium

    Identification of SPAG4 as a sperm-associated gene product that physically interacts with the major outer dense fiber protein ODF27, establishing its connection to sperm tail structural components.

    Evidence Yeast two-hybrid interaction assay and FISH chromosomal mapping in human spermatids

    PMID:9691178

    Open questions at the time
    • Interaction domain not mapped
    • No functional assay for the ODF27-SPAG4 interaction
    • Protein localization not determined
  2. 1999 High

    Demonstration that SPAG4 binds ODF1 specifically through a leucine zipper domain and localizes to the manchette and axoneme of elongating spermatids, establishing it as a structural mediator connecting the nuclear periphery to cytoskeletal sperm tail elements.

    Evidence Yeast two-hybrid, co-immunoprecipitation, leucine zipper mutagenesis, and immunofluorescence in rat spermatids

    PMID:10373309

    Open questions at the time
    • Function of SPAG4-ODF1 interaction in vivo not tested
    • Whether SPAG4 is a nuclear envelope protein or cytoplasmic remained unclear
  3. 2010 High

    Genetic evidence from Drosophila demonstrated that Spag4 is required at the nuclear surface for centriole/basal body attachment to the spermatid nucleus, placing it functionally upstream of dynein-dynactin in this pathway and establishing an evolutionarily conserved role in nuclear-centrosome coupling during spermatogenesis.

    Evidence Spag4 loss-of-function mutant flies with immunofluorescence and epistasis analysis with yuri gagarin and dynein-dynactin mutants

    PMID:20647369

    Open questions at the time
    • Mammalian in vivo confirmation still needed at this point
    • KASH-domain partner in this system not identified
    • Whether SUN domain mediates this function not tested
  4. 2013 Medium

    Discovery that SPAG4 is transcriptionally induced by HIF-1 under hypoxia and functionally promotes cancer cell invasion, revealing an unexpected oncogenic role outside spermatogenesis.

    Evidence siRNA knockdown and overexpression in renal clear cell carcinoma cells with scratch and invasion assays; VHL-dependent HIF-1 regulation demonstrated

    PMID:23818324

    Open questions at the time
    • Downstream signaling pathway in cancer not identified
    • Whether SPAG4's LINC complex function is relevant in cancer cells unknown
    • In vivo cancer model not tested
  5. 2015 High

    Three independent studies collectively established that SPAG4/SUN4 is an inner nuclear membrane SUN-domain protein essential for manchette-nuclear envelope coupling, LINC complex integrity (SUN3/Nesprin1), and sperm head formation, with knockout mice displaying globozoospermia and infertility; additionally, SEPT12 was identified as a SPAG4 partner at the nuclear envelope linking it to septin-lamin complexes.

    Evidence Two independent SUN4 knockout mouse models with EM, immunofluorescence, fertility assays, and LINC component mislocalization analysis; SEPT12-SPAG4-LAMINB1 complex identified by Y2H and Co-IP with a patient mutation disrupting complex formation

    PMID:25775403 PMID:26417726 PMID:26621829

    Open questions at the time
    • Structural basis for SUN4-SUN3 heteromerization unknown
    • Whether SUN4 deficiency causes human infertility not confirmed
    • Role of SEPT12-SPAG4 complex versus LINC complex in nuclear shaping not dissected
  6. 2018 High

    Refined understanding of SPAG4's role: it tightens HTCA-to-nucleus anchorage rather than initiating HTCA assembly, and in cancer cells it promotes migration through direct interaction with Nesprin3, linking its LINC-complex function to oncogenic cell motility.

    Evidence SPAG4 KO mouse TEM showing lateral HTCA detachment; Co-IP and BiFC confirming SPAG4-Nesprin3 interaction in lung carcinoma with RNAi migration assays

    PMID:29663073 PMID:29901114

    Open questions at the time
    • Force-coupling mechanism between HTCA and nucleus not characterized
    • Whether Nesprin3 interaction mediates nuclear positioning or cytoskeletal force transduction in cancer unknown
  7. 2023 High

    Definitive topology mapping established SPAG4 as a type II inner nuclear membrane protein with its SUN domain in the perinuclear space and N-terminus binding spermiogenesis-specific lamin B3 in the nucleoplasm, and confirmed heteromeric assembly with SUN3 in vivo, completing the molecular architecture of the spermatid LINC complex.

    Evidence Topology mapping, co-immunoprecipitation, and in vivo interaction studies in spermatids

    PMID:36825599

    Open questions at the time
    • High-resolution structure of SUN4-SUN3 heteromer not available
    • How lamin B3 binding contributes to manchette coupling not functionally tested
  8. 2024 Medium

    Identification of PI3K/Akt/mTOR/HIF-1α as the downstream signaling axis through which SPAG4 promotes proliferation, migration, and metabolic reprogramming (aerobic glycolysis and mitochondrial respiration) in colorectal cancer, with pharmacological rescue confirming pathway dependence.

    Evidence SPAG4 knockdown/overexpression in CRC cells with Seahorse metabolic flux analysis and PI3K inhibitor LY294002 rescue

    PMID:39410830

    Open questions at the time
    • Direct molecular target of SPAG4 activating PI3K not identified
    • In vivo tumor model validation lacking
    • How a nuclear envelope protein activates cytoplasmic PI3K signaling unclear
  9. 2025 Medium

    Establishment of a SPAG4→c-MYC→SULT2B1 epistatic axis controlling glycolysis in colorectal cancer, and discovery that tRF-3005a/RALY-dependent alternative splicing of SPAG4 produces an oncogenic long isoform (SPAG4-L) that activates GRB14/PI3K/AKT signaling in gastric cancer.

    Evidence siRNA/overexpression epistasis with metabolic readouts in CRC cells; RNA pulldown and splicing analysis identifying tRF-3005a/RALY control of SPAG4 exon 8 inclusion in gastric cancer

    PMID:40287810 PMID:41872130

    Open questions at the time
    • Functional distinction between SPAG4-L and short isoform not characterized at the protein level
    • How SPAG4 regulates c-MYC expression mechanistically not defined
    • Relevance of alternative splicing to the spermatogenesis function unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include: the structural basis for SUN4-SUN3 heteromerization, the mechanism by which a nuclear envelope protein activates cytoplasmic PI3K signaling in cancer, whether SPAG4 mutations cause human male infertility, and the functional divergence between SPAG4 splice isoforms.
  • No high-resolution structural data for SPAG4 or its complexes
  • No causative human SPAG4 mutations linked to globozoospermia
  • Nuclear envelope-to-PI3K signaling mechanism entirely unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 5
Localization
GO:0005635 nuclear envelope 4 GO:0005634 nucleus 2 GO:0005856 cytoskeleton 1
Pathway
R-HSA-1474165 Reproduction 6 R-HSA-1430728 Metabolism 2 R-HSA-162582 Signal Transduction 2
Partners
GRB14LMNB3NESPRIN1NESPRIN3ODF1RALYSEPT12SUN3
Complex memberships
LINC complex (SUN4-SUN3-Nesprin1)SEPT12-SPAG4-LAMINB1 complex

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 SPAG4 (49-kDa) binds specifically to outer dense fiber protein ODF1 (but not ODF2) via a leucine zipper domain, and also self-associates; it localizes to the microtubule-containing manchette and axoneme in elongating spermatids and epididymal sperm, suggesting a role in protein localization to sperm tail structures. Yeast two-hybrid, co-immunoprecipitation, leucine zipper mutagenesis, immunofluorescence localization in spermatids Developmental biology High 10373309
1998 Human SPAG4 gene product interacts specifically with the major 27-kDa outer dense fiber protein ODF27 in elongating spermatids; the gene maps to human chromosome 20q11.2. Yeast two-hybrid interaction assay; fluorescence in situ hybridization (FISH) for chromosomal mapping Cytogenetics and cell genetics Medium 9691178
2010 Drosophila Spag4 (ortholog of mammalian SUN4/SPAG4) is required at the nuclear surface to maintain centriole/basal body attachment to the spermatid nucleus during spermatogenesis; epistasis studies place Yuri Gagarin and dynein-dynactin activity downstream of Spag4 in the centriole attachment pathway, independently of KASH proteins Klarsicht and MSP-300. Genetic loss-of-function (spag4 mutant flies), immunofluorescence localization, epistasis analysis with yuri and dynein-dynactin mutants Journal of cell science High 20647369
2015 SUN4/SPAG4 is an inner nuclear membrane protein in spermatids that couples the manchette microtubule structure to the nuclear periphery; loss of SUN4 in mice causes disorganized manchette microtubules, failure of nuclear elongation, and globozoospermia with infertility. SUN4 knockout mouse model, immunofluorescence, electron microscopy, functional fertility assays Developmental biology High 26417726
2015 SUN4/SPAG4 localizes to the posterior nuclear envelope in spermatids and interacts with SUN3/Nesprin1 LINC components; SUN4 deficiency causes mislocalization of other LINC components, disrupts manchette formation, and produces a globozoospermia-like phenotype, demonstrating its critical role in mammalian sperm head formation via LINC complex function. Sun4 knockout mouse, immunofluorescence, co-localization, analysis of LINC component mislocalization Biology open High 26621829
2015 SEPT12 physically interacts with SPAG4/SUN4 in male germ cells, and together with LAMIN B1 forms a complex at the nuclear periphery of round spermatids; a SEPT12 mutation from an infertile man disrupts integration of this SEPT12/SPAG4/LAMINB1 nuclear envelope complex. Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescence co-localization, analysis of patient mutation PloS one Medium 25775403
2018 SPAG4/SUN4 is required for tight anchorage of the sperm head-to-tail coupling apparatus (HTCA) to the nucleus; SPAG4-deficient sperm show lateral detachment of the HTCA from the nucleus at the implantation fossa, despite the HTCA forming, indicating SPAG4 tightens head-to-tail linkage rather than initiating HTCA assembly. SPAG4 knockout mouse, transmission electron microscopy, immunofluorescence Histochemistry and cell biology High 29663073
2018 In lung carcinoma cells, SPAG4 interacts with Nesprin3 (confirmed by co-IP and bimolecular fluorescence complementation); SPAG4 knockdown reduces A549 cell migration, and SPAG4 levels affect Nesprin3 localization and expression, identifying SPAG4 as a positive regulator of Nesprin3 in cancer cell migration. Co-immunoprecipitation, bimolecular fluorescence complementation (BiFC), RNAi knockdown, scratch/migration assay, immunofluorescence Oncology reports Medium 29901114
2013 SPAG4 expression is regulated by HIF-1 in a VHL-dependent manner under hypoxia; SPAG4 knockdown reduces invasion of renal clear cell carcinoma cells in vitro, while overexpression enhances tumor cell migration. siRNA knockdown, transient overexpression, scratch assay, invasion assay, RNase protection assay, immunofluorescence Molecular carcinogenesis Medium 23818324
2023 SUN4/SPAG4 is an inner nuclear membrane protein with its C-terminal SUN domain in the perinuclear space and N-terminus in the nucleoplasm interacting with spermiogenesis-specific lamin B3; SUN4 forms heteromeric assemblies with SUN3 in vivo and regulates SUN3 expression. Topology mapping, co-immunoprecipitation, in vivo interaction studies, immunofluorescence Journal of cell science High 36825599
2024 SPAG4 promotes colorectal cancer cell proliferation, migration, invasion, mitochondrial respiration, and aerobic glycolysis by activating the PI3K/Akt/mTOR signaling pathway and upregulating HIF-1α; PI3K inhibitor LY294002 abolishes these SPAG4-mediated effects. siRNA knockdown and overexpression in CRC cells, XF24 extracellular flux analysis, PI3K inhibitor rescue, western blot, CCK-8, Transwell assay Journal of biochemical and molecular toxicology Medium 39410830
2025 SPAG4 knockdown suppresses HT29 colorectal cancer cell proliferation and glycolytic metabolism by downregulating c-MYC, which in turn reduces SULT2B1 expression; elevated SULT2B1 rescues glycolytic reduction caused by SPAG4 or c-MYC silencing, placing SPAG4 upstream of a c-MYC/SULT2B1/glycolysis axis. siRNA knockdown, overexpression, CCK-8, colony formation, glucose uptake/lactate/ATP assays, immunofluorescence, 2-DG treatment Discovery medicine Medium 40287810
2026 tRF-3005a binds RALY, enhancing RALY's interaction with SPAG4 mRNA and suppressing exon 8 skipping, thereby increasing production of the oncogenic SPAG4-L isoform, which activates GRB14/PI3K/AKT signaling to promote gastric cancer progression. RNA sequencing, RNA pulldown, co-immunoprecipitation, alternative splicing analysis, functional migration/invasion assays Cell death discovery Medium 41872130

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 Spag4, a novel sperm protein, binds outer dense-fiber protein Odf1 and localizes to microtubules of manchette and axoneme. Developmental biology 133 10373309
2015 SUN4 is essential for nuclear remodeling during mammalian spermiogenesis. Developmental biology 62 26417726
2015 The LINC complex component Sun4 plays a crucial role in sperm head formation and fertility. Biology open 59 26621829
2010 The Drosophila SUN protein Spag4 cooperates with the coiled-coil protein Yuri Gagarin to maintain association of the basal body and spermatid nucleus. Journal of cell science 55 20647369
2000 The 'SUN' family: yeast SUN4/SCW3 is involved in cell septation. Yeast (Chichester, England) 50 10870102
2015 SEPT12/SPAG4/LAMINB1 complexes are required for maintaining the integrity of the nuclear envelope in postmeiotic male germ cells. PloS one 46 25775403
2018 Ultra-structure of the sperm head-to-tail linkage complex in the absence of the spermatid-specific LINC component SPAG4. Histochemistry and cell biology 29 29663073
2003 Human sperm associated antigen 4 (SPAG4) is a potential cancer marker. Cell and tissue research 29 14614621
2018 Sperm‑associated antigen 4 (SPAG4) as a new cancer marker interacts with Nesprin3 to regulate cell migration in lung carcinoma. Oncology reports 28 29901114
2013 Hypoxia regulates the sperm associated antigen 4 (SPAG4) via HIF, which is expressed in renal clear cell carcinoma and promotes migration and invasion in vitro. Molecular carcinogenesis 26 23818324
1998 A novel testis-specific gene, SPAG4, whose product interacts specifically with outer dense fiber protein ODF27, maps to human chromosome 20q11.2. Cytogenetics and cell genetics 22 9691178
2023 SUN4 is a spermatid type II inner nuclear membrane protein that forms heteromeric assemblies with SUN3 and interacts with lamin B3. Journal of cell science 8 36825599
2024 SPAG4 enhances mitochondrial respiration and aerobic glycolysis in colorectal cancer cells by activating the PI3K/Akt signaling pathway. Journal of biochemical and molecular toxicology 4 39410830
2022 The impact of glutamine deprivation on the expression of MEIS3, SPAG4, LHX1, LHX2, and LHX6 genes in ERN1 knockdown U87 glioma cells. Endocrine regulations 4 35180817
2024 Integrated multi-level omics profiling of disulfidptosis identifis SPAG4 as an innovative immunotherapeutic target in glioblastoma. Frontiers in immunology 1 39539547
2026 tRF-3005a regulates exon skipping of SPAG4 by interacting with RALY to drive gastric cancer progression. Cell death discovery 0 41872130
2025 SPAG4 Regulates Glycolytic Metabolism in HT29 Cells as a Target via the c-MYC/SULT2B1 Pathway. Discovery medicine 0 40287810