Tumor necrosis factor-α-induced caspase-1 gene expression

Abstract

Tumour necrosis factor-α (TNF-α) is a cytokine that is involved in many functions, including the inflammatory response, immunity and apoptosis. Some of the responses of TNF-α are mediated by caspase-1, which is involved in the production of the pro-inflammatory cytokines interleukin-1β , interleukin-18 and interleukin-33. The molecular mechanisms involved in TNF-α-induced caspase-1 gene expression remain poorly defined, despite the fact that signaling by TNF-α has been well studied. The present study was undertaken to investigate the mechanisms involved in the induction of caspase-1 gene expression by TNF-α. Treatment of A549 cells with TNF-α resulted in an increase in caspase-1 mRNA and protein expression, which was preceded by an increase in interferon regulatory factor-1 and p⁷³ protein levels. Caspase-1 promoter reporter was activated by the treatment of cells with TNF-α. Mutation of the interferon regulatory factor-1 binding site resulted in the almost complete loss of basal as well as of TNF-α-induced caspase-1 promoter activity. Mutation of the p⁵³/p⁷³ responsive site resulted in reduced TNF-α-induced promoter activity. Blocking of p⁷³ function by a dominant negative mutant or by a p⁷³-directed small hairpin RNA reduced basal as well as TNF-α-induced caspase-1 promoter activity. TNF-α-induced caspase-1 mRNA and protein levels were reduced when p⁷³ mRNA was down-regulated by small hairpin RNA. Caspase-5 gene expression was induced by TNF-α, which was inhibited by the small hairpin RNA-mediated down-regulation of p⁷³. Our results show that TNF-α induces p⁷³ gene expression, which, together with interferon regulatory factor-1, plays an important role in mediating caspase-1 promoter activation by TNF-α.