Caspase-4 interacts with TNF receptor-associated factor 6 and mediates lipopolysaccharide-induced NF-kappaB-dependent production of IL-8 and CC chemokine ligand 4 (macrophage-inflammatory protein-1 ).
Human caspase-4 does not have a corresponding mouse ortholog. Caspase-4 falls within the class of "inflammatory caspases," being homologous with human caspases 1 and 5 and mouse caspases 1, 11, and 12. To address the function of caspase-4, we generated caspase-4-deficient human THP1 monocytic cell lines which exhibited substantially reduced LPS-induced secretion of several chemokines and cytokines, including IL-8 (CXCL8), CCL4 (macrophage-inflammatory protein-1beta), CCL20 (macrophage-inflammatory protein-3alpha), and IL-1beta. The LPS-induced expression of the mRNAs encoding these cytokines was correspondingly reduced in the caspase-4-deficient clones. Because a specific NF-kappaB inhibitor blocked LPS-induced IL-8 and CCL4 mRNA expression as well as IL-8 and CCL4 secretion in THP1 cells, we investigated the role of caspase-4 in NF-kappaB signaling. LPS-induced NF-kappaB nuclear translocation and activation were inhibited in all caspase-4-deficient clones. LPS stimulation led to the interaction of endogenous caspase-4 and TNFR-associated factor 6 (TRAF6) via a TRAF6-binding motif (PPESGE), which we identified in caspase-4. Mutation of this site in caspase-4 resulted in the loss of the TRAF6-caspase-4 interaction. Similar TRAF6-binding motifs are known to be functionally important for TRAF6 interactions with other molecules including caspase-8, and for mediating NF-kappaB activation in various immune and nonimmune cell types. Our data suggest that the TRAF6-caspase-4 interaction, triggered by LPS, leads to NF-kappaB-dependent transcriptional up-regulation and secretion of important cytokines and chemokines in innate immune signaling in human monocytic cells.
Lakshmanan
Umayal
U
Cell Death and Human Diseases, Genomics and Genetics Division, Institute of Molecular and Cell Biology, Proteos, Singapore, Republic of Singapore.
Porter
Alan G
AG
D053471:Caspases, Initiator / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D054407:Chemokine CCL4 / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000276:immunology; D008024:Ligands; D008070:Lipopolysaccharides / Q000276:immunology* / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism*
D054407:Chemokine CCL4; D016207:Cytokines; D053583:Interleukin-1beta; D016209:Interleukin-8; D008024:Ligands; D008070:Lipopolysaccharides; D016328:NF-kappa B; D048029:TNF Receptor-Associated Factor 6; C093516:CASP4 protein, human; D053471:Caspases, Initiator