6,AandB). cultures enhanced macrophage chemotaxis and promotedin vitroangiogenesis, both prevented by pretreating melanoma cells with inhibitors of caspases-1 and -5 or IL-1 receptor blockade. These findings implicate IL-1-mediated autoinflammation Rabbit Polyclonal to Sirp alpha1 as contributing to the development and progression of human melanoma and suggest that inhibiting the inflammasome pathway or reducing IL-1 activity can be a therapeutic option for melanoma patients. Keywords:Cancer, Cytokines, Immunology, Caspase, Inflammation, Autoinflammation, Caspase-1, Inflammasome, Interleukin == Introduction == In humans and mice, tumors secrete pro-inflammatory cytokines, chemokines, and other soluble factors in the tumor microenvironment, thereby promoting tumor development and progression (13). Interleukin-1 (IL-1)3is a pleiotropic pro-inflammatory cytokine involved in cell growth, differentiation, tissue repair, and regulation of immune response (4). IL-1 is often detected in human cancer tissues including breast cancer, pancreatic cancer, glioblastoma, and melanoma (513), where the expression levels of the IL-1 protein or gene are NADP associated with the invasiveness and metastasis of cancers. Experiments using exogenously administered IL-1 or IL-1 knock-out mice suggest that stromal-derived IL-1 plays an important role in the progression of murine tumors (1419), whereas recent reports have shown that tumor-derived IL-1 is associated with tumor growth, immunosuppression, and chemoresistance (7,8,13,15). Considering the large portfolio of genes induced by IL-1 (4), it is thus critical to elucidate the biological mechanisms responsible for the dysregulated secretion of IL-1 in human cancer cells. IL-1 is first synthesized as biologically inactive precursor (pro-IL-1) in response to Toll-like receptor (TLR) agonists in macrophages (4). Pro-IL-1 is then cleaved by caspase-1 to biologically active mature IL-1, resulting in its release into the extracellular space, where it initiates the inflammatory response (4,20). A pioneering study to investigate the molecular mechanisms controlling caspase-1 activity led to the NADP identification and characterization of the inflammasome, an elaborate multi-protein complex whose assembly and activation is responsible for the recruitment and activation of caspases-1 and -5 (21). Each inflammasome includes members of the nucleotide oligomerization domain-like receptor (NLR) family of proteins. Diverse pathogen-associated molecular patterns and nonmicrobial danger-associated molecular patterns are sensed intracellularly by NLRs, resulting in oligomerization of NLRs. Following oligomerization, NLRs interacts with ASC (apoptosis-associatedspeck-like protein containing acaspase recruitment domain (CARD)), a central adaptor protein of inflammasome, through homotypic interactions of pyrin domain. ASC then interacts with pro-caspase-1 through its homotypic interactions of CARD domain, yielding cleavage and activation of caspase-1, which cleaves pro-IL-1 to the active IL-1 (2225). NALP (NACHT,LRR, andpyrin domain-containing protein) 1 inflammasome and NALP2/3 inflammasome are two of the best characterized human inflammasomes (2225). Constitutive activation of NALP3 inflammasome caused by the single amino acid mutations in the NALP3 gene leads to several autoinflammatory diseases characterized by sustained local and systemic inflammation mediated by IL-1 (2629). In the present study, we provide evidence that constitutively activated inflammasome mediates the conversion of the cytoplasmic (inactive) IL-1 precursor to a secreted and active form of IL-1 in human melanoma cells. Furthermore, we demonstrate that human melanoma cells from the late stage of the disease spontaneously secrete biologically active IL-1 in the absence of exogenous stimuli because of constitutive activation of the inflammasome NADP and NADP IL-1 receptor (IL-1R) signaling. This feature falls into the category of autoinflammatory diseases, which may be unique to late stage melanoma. == EXPERIMENTAL PROCEDURES.