Affinage

HSPA4L

Heat shock 70 kDa protein 4L · UniProt O95757

Round 2 corrected
Length
839 aa
Mass
94.5 kDa
Annotated
2026-04-28
47 papers in source corpus 15 papers cited in narrative 16 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HSPA4L (also known as Osp94/Apg-1) is an HSP110-family cochaperone that functions in protein quality control through holdase, disaggregase, and refolding activities, with its SBDβ domain required for disaggregation and its C-terminal H domain required for refolding of denatured substrates (PMID:35237814). Transcription of HSPA4L is activated by hypertonic stress via a TonE/ORE-like promoter element bound by TonEBP and by mild heat shock (32–39°C) via HSF1 binding to upstream HSEs (PMID:15018608, PMID:9006898). HSPA4L is essential for spermatogenesis: knockout mice exhibit massive germ cell apoptosis, reduced sperm count and motility, and partial male infertility, and the protein is developmentally regulated in spermatocytes and spermatids (PMID:16923965, PMID:9144406). HSPA4L and its paralog HSPA4 act redundantly as cochaperones during embryonic lung maturation, as double-knockout mice display pulmonary hypoplasia, accumulation of ubiquitinated proteins, impaired pneumocyte differentiation, and neonatal lethality (PMID:23980576).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1996 Medium

    Identification of HSPA4L as a new HSP110-subfamily member with predicted ATP-binding and peptide-binding domains established it as a candidate molecular chaperone responsive to osmotic stress.

    Evidence cDNA cloning, in vitro translation, Northern blot in mIMCD3 cells and mouse kidney under hyperosmotic/heat stress

    PMID:8647834

    Open questions at the time
    • No direct chaperone activity demonstrated
    • Mechanism of osmotic induction unknown at the time
  2. 1997 Medium

    Demonstration that HSPA4L is constitutively expressed in germ cells but not heat-inducible there, while somatic induction occurs at mild (32–39°C) rather than classical heat shock temperatures via HSF1-HSE binding, revealed a unique transcriptional regulation mode distinguishing HSPA4L from canonical heat shock proteins.

    Evidence Northern blot, in situ hybridization in purified germ cells and somatic cell lines; nuclear run-on and EMSA for HSF1-HSE binding

    PMID:9006898 PMID:9144406

    Open questions at the time
    • No direct test of HSF1 requirement (e.g., HSF1-knockout)
    • Mechanism of developmental regulation in germ cells unresolved
  3. 2004 Medium

    Identification of a TonE/ORE-like promoter element bound by TonEBP and requirement for MAPK signaling defined the transcriptional mechanism underlying hypertonic stress induction of HSPA4L, resolving the promoter architecture.

    Evidence Luciferase reporter assay, EMSA for TonEBP binding, pharmacological inhibition of MAPKs and proteasome

    PMID:15018608

    Open questions at the time
    • Pharmacological inhibitors lack single-target specificity
    • No chromatin immunoprecipitation for TonEBP occupancy in vivo
  4. 2006 High

    The Hspa4l-knockout mouse proved that HSPA4L is required for normal spermatogenesis in vivo, with loss causing germ cell apoptosis, reduced sperm count and motility, and partial male infertility — the first genetic evidence for a non-redundant physiological function.

    Evidence Gene targeting (knockout mouse), histology, TUNEL assay, sperm motility analysis, osmotic stress challenge

    PMID:16923965

    Open questions at the time
    • Molecular substrates/clients protected by HSPA4L in germ cells not identified
    • Whether HSPA4 partially compensates for HSPA4L in fertile knockouts not tested
  5. 2013 Medium

    Identification of Nogo-A as a selective binding partner of HSPA4L in hippocampal neurons, with co-regulation under hypoxic and oxidative stress, expanded the functional context of HSPA4L to neuronal stress responses.

    Evidence Affinity precipitation, co-immunoprecipitation, proximity ligation assay in primary hippocampal neurons

    PMID:23909438

    Open questions at the time
    • Functional consequence of the Nogo-A/HSPA4L interaction on neuronal survival not demonstrated
    • Whether HSPA4L acts as a chaperone for Nogo-A folding or as a signaling partner is unknown
  6. 2014 High

    Double knockout of Hspa4l and Hspa4 revealed redundant cochaperone roles in embryonic lung maturation, with loss causing ubiquitinated protein accumulation, impaired pneumocyte differentiation, and neonatal lethality — demonstrating that the two paralogs jointly maintain proteostasis during organogenesis.

    Evidence Double-knockout mouse, histology, Ki67/TUNEL assays, Western blot for surfactant proteins, ubiquitin conjugate accumulation

    PMID:23980576

    Open questions at the time
    • Specific client proteins whose misfolding drives lung pathology not identified
    • Relative contribution of each paralog not dissected by single-KO lung phenotyping
  7. 2019 Medium

    HSPA4L upregulation via HSF1 nuclear translocation in bortezomib-treated myeloma cells, and sensitization to bortezomib upon HSPA4L knockdown via caspase-3/PARP activation, established HSPA4L as a pro-survival factor in proteasome-inhibitor stress in cancer.

    Evidence siRNA knockdown, Western blot for cleaved caspase-3/PARP/HSF1, cell viability assays, bone marrow stromal cell co-culture

    PMID:31899217

    Open questions at the time
    • No in vivo tumor model validation
    • Whether HSPA4L directly buffers proteasome-inhibitor-induced misfolded proteins or acts indirectly through HSF1 is unresolved
  8. 2022 High

    In vitro reconstitution with domain deletions defined HSPA4L as a holdase that suppresses aggregation, with SBDβ required for disaggregation and the H domain required for refolding, resolving the domain-level mechanism of its chaperone activity.

    Evidence Luciferase aggregation/refolding assay, targeted deletion mutagenesis, rabbit reticulocyte lysate reconstitution, biotin cross-linking, chimeric protein construction

    PMID:35237814

    Open questions at the time
    • Holdase and disaggregase activities demonstrated only on model substrate (luciferase); endogenous client specificity unknown
    • No structural data for the HSPA4L-substrate complex

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key open questions include the identity of endogenous client proteins in spermatocytes and lung, the structural basis for HSPA4L's substrate selectivity versus HSPA4, and whether the Nogo-A interaction has functional consequences for neuronal proteostasis or signaling.
  • No endogenous substrates identified in any tissue
  • No crystal or cryo-EM structure of HSPA4L or its complexes
  • Functional redundancy boundary with HSPA4 not mapped at the molecular level

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140657 ATP-dependent activity 2 GO:0044183 protein folding chaperone 1
Localization
GO:0005829 cytosol 2 GO:0005634 nucleus 1
Pathway
R-HSA-8953897 Cellular responses to stimuli 4 R-HSA-1266738 Developmental Biology 2 R-HSA-1474165 Reproduction 2 R-HSA-392499 Metabolism of proteins 2 GO:0140657 ATP-dependent activity 1
Partners
HSF1HSPA4NOGO-ATONEBP

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1996 HSPA4L (Osp94) was identified as a new member of the HSP110/SSE gene subfamily, encoding an 838-amino acid protein with a putative N-terminal ATP-binding domain and a putative C-terminal peptide-binding domain, consistent with molecular chaperone function. In vitro translation confirmed the protein migrates at 105–110 kDa on SDS-PAGE. cDNA cloning, in vitro translation, SDS-PAGE, Northern blot The Journal of Biological Chemistry Medium 8647834
1996 HSPA4L (Osp94) mRNA is strongly up-regulated in mouse renal inner medullary collecting duct cells (mIMCD3) in response to hyperosmotic NaCl stress and heat stress, and its renal expression parallels the corticomedullary osmolality gradient (highest in inner medulla), increasing further during water restriction. Northern blot, in situ hybridization, osmotic stress induction assay The Journal of Biological Chemistry Medium 8647834
1997 HSPA4L (Apg-1) transcripts are constitutively and developmentally regulated in testicular germ cells (spermatocytes and spermatids) but are not heat-inducible in germ cells, contrasting with their heat-inducibility in somatic cells. Heat induction was observed only in W/Wv mutant testes lacking germ cells. Northern blot, in situ hybridization histochemistry, purified germ cell fractionation Biochemical and Biophysical Research Communications Medium 9144406
1997 In somatic cells (Sertoli cell line TAMA26, NIH/3T3 fibroblasts), HSPA4L (Apg-1) transcripts are induced by a temperature shift from 32°C to 39°C but NOT by the classical 37°C to 42°C heat shock. Nuclear run-on assay confirmed transcriptional activation, and gel mobility shift assay demonstrated binding of heat shock factor 1 (HSF1) to heat shock elements (HSEs) in the Apg-1 5′-flanking region. Northern blot, nuclear run-on assay, native gel mobility shift assay (EMSA) The Journal of Biological Chemistry Medium 9006898
1998 HSPA4L (Apg-1) mRNA is induced in rat brain neurons following transient forebrain ischemia/reperfusion, peaking at 12 h in cortex and remaining elevated to 24 h in hippocampus, indicating a role in the ischemic stress response in the CNS. Northern blot, in situ hybridization histochemistry Biochemical and Biophysical Research Communications Low 9647773
1999 Human HSPA4L (Apg-1) and its paralog Apg-2 were cloned from a human testis cDNA library. Human HSPA4L shares 91.8% amino acid identity with mouse Apg-1. The human HSPA4L gene was mapped to chromosomal locus 4q28 by fluorescence in situ hybridization (FISH). cDNA library screening, sequence analysis, FISH chromosomal mapping Gene Medium 10524232
2001 HSPA4L (Apg-1) protein is developmentally expressed in human testicular germ cells (spermatocytes and spermatids) but absent from testes with Sertoli-cell-only syndrome or germ cell arrest at spermatogonia, and is detectable in sperm from normal and infertile (non-azoospermic) men, implicating it in human spermatogenesis. Western blot, immunohistochemistry International Journal of Urology Low 11389747
2004 The 5′-flanking region of the HSPA4L (Osp94) gene contains a TonE/ORE-like element (Osp94-TonE: 5′-TGGAAAGGACCAG-3′) distinct from the HSE, which drives hypertonic-stress-induced transcription. EMSA showed TonEBP binding to this element. MAPK inhibitors (SB203580, PD98059, U0126, SP600125) and a proteasome inhibitor (MG132) suppressed NaCl-induced Osp94 upregulation, implicating MAPK signaling and the proteasome in its hypertonic regulation. Reporter gene (luciferase) assay, EMSA, pharmacological inhibition, Northern blot The Biochemical Journal Medium 15018608
2006 Hspa4l-knockout mice display ~42% male infertility due to massively increased germ cell apoptosis, reduced epididymal sperm count, and reduced sperm motility, demonstrating that HSPA4L is required for normal spermatogenesis in vivo. HSPA4L protein was localized to spermatogenic cells (late pachytene spermatocytes through postmeiotic spermatids) and to cortical segments of distal tubules in the kidney. Null mutants showed increased susceptibility to osmotic stress despite normal plasma/urine electrolytes. Gene targeting (knockout mouse), histology, TUNEL apoptosis assay, sperm motility analysis, immunohistochemistry, osmotic stress challenge Molecular and Cellular Biology High 16923965
2013 HSPA4L (Apg-1) was identified as a novel binding partner of the NiG domain of Nogo-A (RTN4-A) in hippocampal neurons. The interaction is selective: Apg-1 binds Nogo-A but not RTN1-A (closest Nogo-A paralog), and Nogo-A binds Apg-1 but not Apg-2 or Hsp105. Under hypoxic stress, both Nogo-A and Apg-1 are co-upregulated; under oxidative stress (H2O2), both are co-downregulated, indicating tight co-regulation during neuronal stress responses. Affinity precipitation, co-immunoprecipitation, proximity ligation assay (PLA), primary hippocampal neurons from Nogo-deficient mice The Biochemical Journal Medium 23909438
2014 HSPA4L and HSPA4 act as functional cochaperones with complementary roles in embryonic lung maturation. Hspa4l−/−Hspa4−/− double-knockout mice exhibit pulmonary hypoplasia, neonatal lethality, mesenchymal hypercellularity (increased proliferation, decreased apoptosis), upregulation of Bcl-2, impaired type I/II pneumocyte maturation (decreased surfactant proteins B, pro-C, and aquaporin-5), and significant accumulation of ubiquitinated proteins in the lung, directly indicating impaired chaperone activity. Double-knockout mouse generation, histology, Ki67 proliferation assay, TUNEL apoptosis assay, Western blot for Bcl-2/surfactant proteins/aquaporin-5, ubiquitinated protein accumulation assay American Journal of Respiratory Cell and Molecular Biology High 23980576
2015 HSPA4L is a direct target of miR-497 in nasopharyngeal carcinoma cells. miR-497 mimic negatively regulated HSPA4L protein and mRNA levels. Silencing HSPA4L by siRNA suppressed NPC cell proliferation and migration and induced apoptosis, establishing a functional role for HSPA4L in NPC cell survival and motility. miRNA mimic transfection, siRNA knockdown, Western blot, cell proliferation/migration/apoptosis assays, xenograft tumor model Oncotarget Medium 26486082
2016 miR-429 directly targets the 3′UTR of HSPA4L mRNA, suppressing HSPA4L mRNA and protein expression in sperm. Luciferase reporter assay and transfection studies confirmed direct targeting. In asthenospermia patients, miR-429 is upregulated while HSPA4L is downregulated, and their levels are inversely correlated, suggesting miR-429 modulates sperm motility via HSPA4L repression. Luciferase reporter assay, transfection, qRT-PCR, Western blot, clinical sample analysis Journal of Sichuan University (Medical Science Edition) Medium 28598115
2019 HSPA4L (Apg-1) protein levels are upregulated in multiple myeloma cells in response to bortezomib (BTZ) in a concentration-dependent manner, regulated via HSF1 nuclear translocation. Knockdown of HSPA4L by siRNA sensitized myeloma cells to BTZ, associated with increased cleaved caspase-3 and PARP cleavage. Combined HSF1 silencing (shRNA or triptolide) with BTZ further enhanced cell death, particularly in cells adherent to bone marrow stromal cells. siRNA knockdown, Western blot (HSPA4L, cleaved caspase-3, PARP, HSF1), nuclear translocation assay, cell viability assays, co-culture with stromal cell lines Experimental Hematology Medium 31899217
2022 The C-terminal region of HSPA4L (Osp94) is critical for its chaperone function. Osp94 acts as a holdase, suppressing heat-induced luciferase aggregation. The SBDβ domain is required for disaggregation, and the H domain (C-terminal extension) is required for RRL-mediated refolding of heat-inactivated luciferase. The LH domain can reactivate heat-inactivated luciferase independently of PA28α (PSME1), and biotin cross-linking showed the LH domain and PA28α both interact with Hsp90-bound denatured luciferase during refolding. A chimeric protein replacing the H domain with PA28α retained disaggregation and refolding activity. In vitro luciferase aggregation/refolding assay, targeted deletion mutagenesis, rabbit reticulocyte lysate reconstitution, biotin-tag cross-linking, chimeric protein construction Journal of Cell Science High 35237814
2024 The Drosophila HSPA4/HSPA4L ortholog Hsc70Cb is required for two phases of spermatogenesis: spermatogonia survival and sperm individualisation. Strong germline knockdown caused male sterility with absence of germ cells and soma over-proliferation; weaker knockdown caused sperm individualisation defects. Partial rescue was achieved by introducing human HSPA4 or HSPA4L cDNA into infertile Hsc70Cb mutant flies, confirming functional conservation and supporting the hypothesis that HSPA4L is required for male fertility across species. RNA interference (RNAi) in Drosophila germline, Nanos-Gal4 driver, human cDNA rescue experiment, histology bioRxiv (preprint)preprint Medium bio_10.1101_2024.12.09.627449

Source papers

Stage 0 corpus · 47 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2007 Large-scale mapping of human protein-protein interactions by mass spectrometry. Molecular systems biology 733 17353931
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2015 A Dynamic Protein Interaction Landscape of the Human Centrosome-Cilium Interface. Cell 433 26638075
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2005 Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome research 409 16344560
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
1996 Normalization and subtraction: two approaches to facilitate gene discovery. Genome research 401 8889548
2015 Aerobic glycolysis tunes YAP/TAZ transcriptional activity. The EMBO journal 362 25796446
2014 A quantitative chaperone interaction network reveals the architecture of cellular protein homeostasis pathways. Cell 325 25036637
2020 Virus-Host Interactome and Proteomic Survey Reveal Potential Virulence Factors Influencing SARS-CoV-2 Pathogenesis. Med (New York, N.Y.) 291 32838362
2012 A high-throughput approach for measuring temporal changes in the interactome. Nature methods 273 22863883
2018 K63 ubiquitylation triggers proteasomal degradation by seeding branched ubiquitin chains. Proceedings of the National Academy of Sciences of the United States of America 227 29378950
2015 ∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis. Nature 209 26618866
2018 An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein interactions and subcellular localizations. Nature communications 201 29568061
2020 Systems analysis of RhoGEF and RhoGAP regulatory proteins reveals spatially organized RAC1 signalling from integrin adhesions. Nature cell biology 194 32203420
2020 UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination. Nature cell biology 168 32807901
2019 A protein-interaction network of interferon-stimulated genes extends the innate immune system landscape. Nature immunology 159 30833792
2020 A High-Density Human Mitochondrial Proximity Interaction Network. Cell metabolism 148 32877691
2011 The diverse members of the mammalian HSP70 machine show distinct chaperone-like activities. The Biochemical journal 144 21231916
2017 RNA-binding activity of TRIM25 is mediated by its PRY/SPRY domain and is required for ubiquitination. BMC biology 135 29117863
2011 Expression of a mutant HSP110 sensitizes colorectal cancer cells to chemotherapy and improves disease prognosis. Nature medicine 133 21946539
2013 A newly uncovered group of distantly related lysine methyltransferases preferentially interact with molecular chaperones to regulate their activity. PLoS genetics 131 23349634
2022 Human transcription factor protein interaction networks. Nature communications 123 35140242
1996 Osmotic stress protein 94 (Osp94). A new member of the Hsp110/SSE gene subfamily. The Journal of biological chemistry 85 8647834
2006 Hspa4l-deficient mice display increased incidence of male infertility and hydronephrosis development. Molecular and cellular biology 68 16923965
1997 A novel hsp110-related gene, apg-1, that is abundantly expressed in the testis responds to a low temperature heat shock rather than the traditional elevated temperatures. The Journal of biological chemistry 62 9006898
2015 The potent tumor suppressor miR-497 inhibits cancer phenotypes in nasopharyngeal carcinoma by targeting ANLN and HSPA4L. Oncotarget 54 26486082
2004 Regulation of expression of the stress response gene, Osp94: identification of the tonicity response element and intracellular signalling pathways. The Biochemical journal 34 15018608
1998 Induction of Apg-1, a member of the heat shock protein 110 family, following transient forebrain ischemia in the rat brain. Biochemical and biophysical research communications 30 9647773
2001 Expression of Apg-1, a member of the Hsp110 family, in the human testis and sperm. International journal of urology : official journal of the Japanese Urological Association 23 11389747
1999 Cloning of human cDNAs for Apg-1 and Apg-2, members of the Hsp110 family, and chromosomal assignment of their genes. Gene 21 10524232
2007 Identification of an overexpressed gene, HSPA4L, the product of which can provoke prevalent humoral immune responses in leukemia patients. Experimental hematology 19 17588478
2014 Respiratory distress and early neonatal lethality in Hspa4l/Hspa4 double-mutant mice. American journal of respiratory cell and molecular biology 18 23980576
1997 Developmentally regulated expression of APG-1, a member of heat shock protein 110 family in murine male germ cells. Biochemical and biophysical research communications 15 9144406
2022 Expression of TXNRD1, HSPA4L and ATP1B1 Genes Associated with the Freezability of Boar Sperm. International journal of molecular sciences 13 36012584
2013 Nogo-A couples with Apg-1 through interaction and co-ordinate expression under hypoxic and oxidative stress. The Biochemical journal 13 23909438
2019 Role of Apg-1 in HSF1 activation and bortezomib sensitivity in myeloma cells. Experimental hematology 3 31899217
2016 [Expression of miR-429 and Its Target Gene HSPA4L in Sperms from Asthenospermia Patients]. Sichuan da xue xue bao. Yi xue ban = Journal of Sichuan University. Medical science edition 3 28598115
2022 Novel function of the C-terminal region of the Hsp110 family member Osp94 in unfolded protein refolding. Journal of cell science 2 35237814
2009 Molecular cloning of OSP94: A significant biomarker protein of hypertensive human heart and a member of HSP110 family. Molecular biotechnology 1 19169850