Affinage

CASP5

Caspase-5 · UniProt P51878

Round 2 corrected
Length
434 aa
Mass
49.7 kDa
Annotated
2026-04-28
31 papers in source corpus 11 papers cited in narrative 11 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

Caspase-5 is an inflammatory cysteine protease that functions as a cytoplasmic sensor of lipopolysaccharide (LPS) and a key effector of the non-canonical inflammasome pathway in human myeloid and epithelial cells. Upon cytoplasmic LPS encounter, caspase-5 undergoes CARD-mediated oligomerization—normally restrained by SERPINB1—and activates to cleave gasdermin D, trigger pyroptosis, and directly process pro-IL-18 via a binary exosite/catalytic-pocket recognition mechanism, while also engaging the NLRP3 inflammasome for IL-1β maturation (PMID:26173988, PMID:30692621, PMID:37993714). Beyond canonical inflammasome signaling, activated caspase-5 phosphorylates Lyn kinase downstream of endosomal LPS sensing to drive Snail/Slug-dependent E-cadherin loss and epithelial barrier disruption (PMID:34747049). During Fas-induced apoptosis, caspase-5 cleaves the transcription factor Max at an atypical glutamate residue in a phosphorylation-regulated manner, linking it to apoptotic transcriptional reprogramming (PMID:11535131).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1995 High

    Cloning of CASP5 established it as a new ICE/CED-3 family cysteine protease with auto-processing capability and apoptosis-inducing potential, but its natural substrates remained unknown.

    Evidence Molecular cloning from human monocytes, catalytic cysteine mutagenesis, overexpression apoptosis assay in COS cells

    PMID:7797592 PMID:8617266

    Open questions at the time
    • No endogenous substrate identified
    • Physiological activation stimulus unknown
    • Inability to process pro-IL-1β left functional distinction from caspase-1 unresolved
  2. 2000 Medium

    Demonstration that CASP5 expression is specifically induced by LPS (at both mRNA and protein level) in monocytes, unlike constitutively expressed CASP1, linked caspase-5 to innate immune activation.

    Evidence Quantitative RT-PCR and western blotting in LPS-stimulated THP-1 cells

    PMID:10986288

    Open questions at the time
    • Mechanism of transcriptional induction not defined
    • Single study without genetic loss-of-function
    • Whether LPS-induced caspase-5 has a distinct function from caspase-1 remained unclear
  3. 2001 High

    Identification of the transcription factor Max as the first caspase-5 substrate—cleaved at an atypical glutamate residue during Fas-induced apoptosis—revealed that caspase-5 recognizes structural determinants in substrates and is regulated by CK2-mediated phosphorylation.

    Evidence In vitro cleavage with purified caspase-5, site-directed mutagenesis of Max cleavage site, CK2 phosphorylation assay, Fas-apoptosis model

    PMID:11535131

    Open questions at the time
    • Biological consequence of Max cleavage for transcription not determined
    • In vivo relevance beyond Fas-induced apoptosis not tested
    • No structural basis for atypical glutamate recognition
  4. 2002 High

    Placement of caspase-5 in the inflammasome complex alongside caspase-1, ASC/Pycard, and NALP1 established its role in a multiprotein platform for proinflammatory caspase activation and IL-1β processing.

    Evidence Cell-free caspase activation system, immunodepletion of Pycard, dominant-negative expression in THP-1 cells

    PMID:12191486

    Open questions at the time
    • Whether caspase-5 directly processes pro-IL-1β or acts indirectly through caspase-1 was unresolved
    • Stoichiometry and architecture of the caspase-5-containing inflammasome not defined
    • Activation trigger within the complex not identified
  5. 2015 High

    Genetic deletion studies resolved the non-redundant roles of caspase-4 and caspase-5 as cytoplasmic LPS sensors: caspase-5 is required for pyroptosis and NLRP3-dependent IL-1β maturation upon bacterial infection, establishing the non-canonical inflammasome pathway in human cells.

    Evidence CRISPR KO of CASP4/CASP5 in monocytic lines, NLRP3 inhibitor MCC950, Salmonella infection, LPS transfection, siRNA in primary human monocytes with Syk/Ca²⁺ pathway dissection

    PMID:26173988 PMID:26508369

    Open questions at the time
    • Structural basis for LPS binding by caspase-5 CARD not determined
    • Relative contributions of caspase-4 vs caspase-5 across different infection contexts not systematically compared
    • Downstream mechanism by which caspase-5 engages NLRP3 not defined
  6. 2019 High

    Identification of SERPINB1 as an endogenous inhibitor that suppresses caspase-5 CARD oligomerization—via a domain distinct from its serine protease-inhibiting reactive center loop—provided the first mechanism restraining non-canonical inflammasome assembly.

    Evidence In vitro CARD oligomerization assays, SERPINB1 KO with spontaneous caspase-5 activation and IL-1β release readouts

    PMID:30692621

    Open questions at the time
    • Structural details of SERPINB1–CARD interaction not resolved
    • Whether SERPINB1 regulation is modulated during infection in vivo not tested
    • Whether other endogenous regulators cooperate with SERPINB1 unknown
  7. 2021 High

    Discovery that activated caspase-5 phosphorylates Lyn kinase to drive Snail/Slug nuclear translocation and E-cadherin downregulation revealed a non-pyroptotic effector arm of the non-canonical inflammasome that disrupts intestinal epithelial barrier integrity.

    Evidence Co-IP, proximity ligation, SNX10 KO and pharmacological inhibition, murine colitis model, Lyn phosphorylation and E-cadherin immunoblotting

    PMID:34747049

    Open questions at the time
    • Whether caspase-5 directly phosphorylates Lyn or acts through an intermediate kinase not fully established
    • Kinase activity for a caspase is unprecedented and the catalytic mechanism is unknown
    • Relevance to human IBD or other barrier diseases not clinically validated
  8. 2023 High

    Structural and biochemical demonstration that caspase-5 directly processes pro-IL-18 using a binary recognition mechanism (catalytic pocket plus exosite) resolved a long-standing question about whether non-canonical inflammasome caspases can generate mature cytokines independently of caspase-1.

    Evidence In vitro cleavage assay, crystal structure of homologous caspase-4–pro-IL-18 complex informing caspase-5 mechanism, site-directed mutagenesis, bacterial infection model

    PMID:37993714

    Open questions at the time
    • Caspase-5–specific crystal structure with pro-IL-18 not yet available (inferred from caspase-4 complex)
    • Relative physiological contribution of caspase-5 vs caspase-1 to IL-18 maturation in vivo not quantified
    • Whether the exosite is shared with GSDMD recognition or represents distinct binding modes unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis of direct LPS–CARD binding, the mechanism by which a cysteine protease reportedly phosphorylates Lyn, the full spectrum of endogenous caspase-5 substrates, and whether caspase-5 has non-redundant roles in specific human infections or inflammatory diseases.
  • No atomic-resolution structure of caspase-5 CARD bound to LPS
  • Reported Lyn kinase phosphorylation by caspase-5 lacks a defined catalytic mechanism
  • Systematic substrate profiling (e.g. degradomics) not reported

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 6 GO:0016787 hydrolase activity 4 GO:0140299 molecular sensor activity 3
Localization
GO:0005829 cytosol 3 GO:0005768 endosome 1
Pathway
R-HSA-168256 Immune System 6 R-HSA-5357801 Programmed Cell Death 4 R-HSA-162582 Signal Transduction 2
Partners
CASP1GSDMDIL18LYNNLRP1PYCARDSERPINB1SNX10
Complex memberships
NALP1 inflammasomeNon-canonical inflammasome

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1995 CASP5 (ICErel-III) was cloned from human monocytic cells as a novel member of the ICE/CED-3 cysteine protease family. It contains the conserved catalytic pentapeptide Gln-Ala-Cys-Arg-Asp, is synthesized as a proenzyme processed to a heterodimeric active form, and can induce apoptosis when overexpressed in COS cells (pro-domain-less truncated form), but cannot process pro-IL-1β. Molecular cloning, transfection, in vitro protease activity assay The Journal of biological chemistry High 7797592
1996 CASP5 (TY/transcript Y) was independently identified as an ICE-family cysteine protease (75% identity to TX/CASP4, 51% to ICE/CASP1). Auto-processing activity requires the catalytic cysteine at position 245. Despite active-site conservation, TY cannot process pro-IL-1β. Overexpression induces apoptosis in COS cells. Molecular cloning, transfection, in vitro protease activity assay, active-site mutagenesis (Cys245) European journal of biochemistry High 8617266
2001 CASP5 cleaves the transcription factor Max at an unusual glutamic acid residue (site IEVE10↓S) during Fas-induced apoptosis, making Max the first identified caspase-5 substrate. Cleavage requires full-length, DNA-binding competent Max but not corresponding peptides, indicating structural determinants are important. Phosphorylation of Max at Ser-11 by protein kinase CK2 inhibits caspase-5-mediated cleavage. Fas-mediated dephosphorylation of Max is a prerequisite for caspase-5 cleavage. In vitro cleavage assay with purified caspase-5, mutational analysis of cleavage sites, in vivo Fas-apoptosis assay, CK2 kinase phosphorylation assay The Biochemical journal High 11535131
2002 CASP5 is a component of the inflammasome, a multiprotein complex comprising caspase-1, caspase-5, Pycard/ASC, and NALP1, which activates proinflammatory caspases and processes pro-IL-1β. Immunodepletion of Pycard in a cell-free system abolished proinflammatory caspase activation and proIL-1β processing. Cell-free caspase activation system, immunodepletion, dominant-negative expression in THP-1 cells Molecular cell High 12191486
2000 CASP5 mRNA and protein are specifically induced by lipopolysaccharide (LPS) in THP-1 monocytic cells (unlike CASP1, which is constitutive), and CASP5 mRNA (but not protein) is induced by IFN-γ in HT-29 colon carcinoma cells. In vitro, caspase-1 subfamily members including caspase-5 display different activities toward pro-caspases 1 and 3 and pro-IL-1β. Quantitative RT-PCR, western blotting, in vitro substrate cleavage assay The Journal of biological chemistry Medium 10986288
2003 The C-terminal helical domain of periphilin (a keratinocyte nuclear protein and cornified envelope constituent) is specifically cleaved by caspase-5 in vitro, identifying periphilin as a caspase-5 substrate in the context of keratinocyte differentiation. In vitro caspase cleavage assay The Journal of biological chemistry Medium 12853457
2015 Both caspase-4 and caspase-5 detect cytoplasmic LPS. Genetic deletion of caspase-4 suppressed cell death and IL-1β production after cytoplasmic LPS transfection or Salmonella infection; caspase-5 deletion reduced cell death and IL-1β after Salmonella infection but not transfected LPS. Double deletion had a synergistic protective effect. IL-1β maturation downstream of caspase-4/5 activation is mediated specifically by NLRP3 inflammasome (blocked by NLRP3 inhibitor MCC950). CRISPR/genetic deletion of caspase-4 and caspase-5 in human monocytic cell lines, NLRP3 inhibitor (MCC950), Salmonella infection, LPS transfection, IL-1β ELISA, cell death assays European journal of immunology High 26173988
2015 In human monocytes, caspase-5 undergoes rapid processing (cleavage) upon LPS stimulation and mediates IL-1α and IL-1β release via a one-step non-canonical inflammasome pathway that requires Syk activity and Ca²⁺ flux downstream of CD14/TLR4-mediated LPS internalization. An additional caspase-5 cleavage product correlates with IL-1 secretion. siRNA knockdown, western blotting of caspase-5 processing, cytokine ELISA, pharmacological inhibition of Syk and Ca²⁺ signaling Nature communications High 26508369
2019 SERPINB1 inhibits caspase-5 (along with caspase-1, -4, and -11) by suppressing CARD oligomerization and enzymatic activation. The C-terminal CARD-binding motif of SERPINB1, distinct from its reactive center loop, restrains pro-caspase-5 activation. SERPINB1 knockdown/deletion leads to spontaneous caspase-5 activation and IL-1β release. In vitro caspase activity assays, CARD oligomerization assays, SERPINB1 knockdown/KO with caspase activation and cytokine readouts Nature immunology High 30692621
2021 CASP5 mediates intestinal barrier dysfunction downstream of cytoplasmic LPS sensing. OMV internalization recruits caspase-5 and PIKfyve to early endosomal membranes via SNX10, enabling LPS release into the cytosol. Cytosolic LPS-activated caspase-5 phosphorylates Lyn kinase, which promotes nuclear translocation of Snail/Slug, downregulation of E-cadherin, and intestinal barrier disruption. SNX10 deletion or inhibition blocked caspase-5 activation and rescued barrier function. Co-immunoprecipitation, proximity ligation, genetic deletion (SNX10), pharmacological inhibition (DC-SX029), murine colitis model, Lyn phosphorylation assay, E-cadherin immunoblotting The EMBO journal High 34747049
2023 Activated human caspase-5 (like caspase-4) directly and efficiently processes pro-IL-18 in vitro and during bacterial infection. Caspase-5 uses a binary (two-site) substrate recognition mechanism: the catalytic pocket engages the tetrapeptide cleavage site, and a unique exosite (similar to that used for GSDMD recognition) binds a structural element formed jointly by the IL-18 propeptide and post-cleavage-site sequences. Cleavage by caspase-5 induces conformational changes in IL-18 that generate two critical IL-18Rα receptor-binding sites. In vitro cleavage assay, crystal structure of caspase-4–pro-IL-18 complex (with exosite structure informing caspase-5 mechanism), bacterial infection model, site-directed mutagenesis Nature High 37993714

Source papers

Stage 0 corpus · 31 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 The inflammasome: a molecular platform triggering activation of inflammatory caspases and processing of proIL-beta. Molecular cell 4956 12191486
1999 Mammalian caspases: structure, activation, substrates, and functions during apoptosis. Annual review of biochemistry 2196 10872455
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
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
1997 Caspase cleavage of keratin 18 and reorganization of intermediate filaments during epithelial cell apoptosis. The Journal of cell biology 518 9298992
2015 NLRP3 inflammasome activation downstream of cytoplasmic LPS recognition by both caspase-4 and caspase-5. European journal of immunology 322 26173988
2015 Human caspase-4 and caspase-5 regulate the one-step non-canonical inflammasome activation in monocytes. Nature communications 291 26508369
1995 Molecular cloning and pro-apoptotic activity of ICErelII and ICErelIII, members of the ICE/CED-3 family of cysteine proteases. The Journal of biological chemistry 274 7797592
2007 Bcl-2 and Bcl-XL regulate proinflammatory caspase-1 activation by interaction with NALP1. Cell 262 17418785
2000 Expression analysis of the human caspase-1 subfamily reveals specific regulation of the CASP5 gene by lipopolysaccharide and interferon-gamma. The Journal of biological chemistry 177 10986288
1998 Calpain activation is upstream of caspases in radiation-induced apoptosis. Cell death and differentiation 154 9894612
2023 Recognition and maturation of IL-18 by caspase-4 noncanonical inflammasome. Nature 137 37993714
2018 Caspase-11-mediated tubular epithelial pyroptosis underlies contrast-induced acute kidney injury. Cell death & disease 119 30250284
2019 SERPINB1-mediated checkpoint of inflammatory caspase activation. Nature immunology 118 30692621
2003 The structure and binding mode of interleukin-18. Nature structural biology 111 14528293
2010 Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score. Molecular medicine (Cambridge, Mass.) 108 20379614
2001 Targeting of the transcription factor Max during apoptosis: phosphorylation-regulated cleavage by caspase-5 at an unusual glutamic acid residue in position P1. The Biochemical journal 92 11535131
1997 Involvement of caspase-4(-like) protease in Fas-mediated apoptotic pathway. Oncogene 91 9233763
2001 Effect of mutation and phosphorylation of type I keratins on their caspase-mediated degradation. The Journal of biological chemistry 72 11356849
2010 New genetic associations detected in a host response study to hepatitis B vaccine. Genes and immunity 69 20237496
2008 Genetic variants in apoptosis and immunoregulation-related genes are associated with risk of chronic lymphocytic leukemia. Cancer research 64 19074885
1996 Identification of a cysteine protease closely related to interleukin-1 beta-converting enzyme. European journal of biochemistry 63 8617266
2021 SNX10-mediated LPS sensing causes intestinal barrier dysfunction via a caspase-5-dependent signaling cascade. The EMBO journal 61 34747049
2010 Caspase-5 expression is upregulated in lesional psoriatic skin. The Journal of investigative dermatology 60 21191419
2018 Estrogen-regulated feedback loop limits the efficacy of estrogen receptor-targeted breast cancer therapy. Proceedings of the National Academy of Sciences of the United States of America 59 29987050
2011 Common alleles in candidate susceptibility genes associated with risk and development of epithelial ovarian cancer. International journal of cancer 51 20635389
2015 Altered expression of caspases-4 and -5 during inflammatory bowel disease and colorectal cancer: Diagnostic and therapeutic potential. Clinical and experimental immunology 41 25943872
2008 Mutational analysis of caspase 1, 4, and 5 genes in common human cancers. Human pathology 41 18430458
2003 Characterization of periphilin, a widespread, highly insoluble nuclear protein and potential constituent of the keratinocyte cornified envelope. The Journal of biological chemistry 38 12853457