Thiol protease that plays a key role in programmed cell death by acting as a molecular switch for apoptosis, necroptosis and pyroptosis, and is required to prevent tissue damage during embryonic development and adulthood (PubMed:23516580, PubMed:35338844, PubMed:35446120, PubMed:8681376, PubMed:8681377, PubMed:8962078, PubMed:9006941, PubMed:9184224). Initiator protease that induces extrinsic apoptosis by mediating cleavage and activation of effector caspases responsible for FAS/CD95-mediated and TNFRSF1A-induced cell death (PubMed:23516580, PubMed:35338844, PubMed:35446120, PubMed:8681376, PubMed:8681377, PubMed:8962078, PubMed:9006941, PubMed:9184224). Cleaves and activates effector caspases CASP3, CASP4, CASP6, CASP7, CASP9 and CASP10 (PubMed:16916640, PubMed:8962078, PubMed:9006941).

Binding to the adapter molecule FADD recruits it to either receptor FAS/TNFRSF6 or TNFRSF1A (PubMed:8681376, PubMed:8681377). The resulting aggregate called the death-inducing signaling complex (DISC) performs CASP8 proteolytic activation (PubMed:9184224). The active dimeric enzyme is then liberated from the DISC and free to activate downstream apoptotic proteases (PubMed:9184224).

Proteolytic fragments of the N-terminal propeptide (termed CAP3, CAP5 and CAP6) are likely retained in the DISC (PubMed:9184224). Also cleaves and activates BID, thereby promoting cytochrome C release from mitochrondria (By similarity). In addition to extrinsic apoptosis, also acts as a negative regulator of necroptosis: acts by cleaving RIPK1 at 'Asp-324', which is crucial to inhibit RIPK1 kinase activity, limiting TNF-induced apoptosis, necroptosis and inflammatory response (PubMed:31827280, PubMed:31827281).

Also able to initiate pyroptosis by mediating cleavage and activation of gasdermin-C and -D (GSDMC and GSDMD, respectively): gasdermin cleavage promotes release of the N-terminal moiety that binds to membranes and forms pores, triggering pyroptosis (PubMed:32929201, PubMed:34012073). Initiates pyroptosis following inactivation of MAP3K7/TAK1 (By similarity). Also acts as a regulator of innate immunity by mediating cleavage and inactivation of N4BP1 downstream of TLR3 or TLR4, thereby promoting cytokine production (By similarity).

May participate in the Granzyme B (GZMB) cell death pathways (PubMed:8755496). Cleaves PARP1 and PARP2 (PubMed:8681376). Independent of its protease activity, promotes cell migration following phosphorylation at Tyr-380 (PubMed:18216014, PubMed:27109099)

Heterotetramer that consists of two anti-parallel arranged heterodimers, each one formed by a 18 kDa (p18) and a 10 kDa (p10) subunit (PubMed:10508784). Component of the death-induced signaling complex (DISC) composed of cell surface receptor FAS/CD95 or TNFRSF1A, adapter protein FADD and the CASP8 protease; recruitment of CASP8 to the complex is required for processing of CASP8 into the p18 and p10 subunits (PubMed:8681376, PubMed:8681377, PubMed:9184224). Component of the AIM2 PANoptosome complex, a multiprotein complex that drives inflammatory cell death (PANoptosis) (By similarity).

Interacts with CFLAR and PEA15 (PubMed:10442631). Interacts with TNFAIP8L2 (By similarity). Interacts with CASP8AP2 (PubMed:16378960).

Interacts with RFFL and RNF34; negatively regulate CASP8 through proteasomal degradation (PubMed:15069192). Interacts with NOL3; decreases CASP8 activity in a mitochondria localization- and phosphorylation-dependent manner and this interaction is dissociated by calcium (PubMed:15509781). Interacts with UBR2ca (PubMed:28602583).

Interacts with RIPK1 (By similarity). Interacts with stimulated TNFRSF10B; this interaction is followed by CASP8 proteolytic cleavage and activation (PubMed:18846110). Interacts (phosphorylated on Tyr-380) with PIK3R1 (PubMed:27109099)

Interacts at the endoplasmic reticulum with a complex containing BCAP31, BAP29, BCL2 and/or BCL2L1

(Microbial infection) Interacts with human cytomegalovirus/HHV-5 protein vICA/UL36; this interaction inhibits CASP8 activation

(Microbial infection) Interacts with NleF from pathogenic E.coli

(Microbial infection) Interacts with molluscum contagiosum virus protein MC160

(Microbial infection) Interacts (via RIP homotypic interaction motif) with herpes simplex virus 1/HHV-1 protein RIR1/ICP6 (via RIP homotypic interaction motif); this interaction prevents necroptosis activation

(Microbial infection) Interacts (via RIP homotypic interaction motif) with herpes simplex virus 2/HHV-2 protein RIR1/ICP10 (via RIP homotypic interaction motif); this interaction prevents necroptosis activation

Isoform 1, isoform 5 and isoform 7 are expressed in a wide variety of tissues. Highest expression in peripheral blood leukocytes, spleen, thymus and liver. Barely detectable in brain, testis and skeletal muscle

The catalytic domain is sufficient for recruitment to lamellipodia but catalytic activity is not necessary

Contains a N-terminal extension that is required for interaction with the BCAP31 complex

• Caspase-8 deficiency (CASP8D)

  Disorder resembling autoimmune lymphoproliferative syndrome (ALPS). It is characterized by lymphadenopathy, splenomegaly, and defective CD95-induced apoptosis of peripheral blood lymphocytes (PBLs). It leads to defects in activation of T-lymphocytes, B-lymphocytes, and natural killer cells leading to immunodeficiency characterized by recurrent sinopulmonary and herpes simplex virus infections and poor responses to immunization.