TNF and CD95 promote IL-8 gene transactivation via independent elements incolon carcinoma cells

The pro-inflammatory cytokine interleukin-8 (IL-8) is produced by HT29 colo n epithelial cells following engagement of either CD95 or tumour necrosis f actor (TNF) receptors. While the IL-8 promotor elements activated by TNF ar e well characterised, those responsible for induction of IL-8 by CD95 are u nknown. We examined the pathway for CD95 induced IL-8 secretion using two l uciferase reporter constructs; the first comprising approximately 500 bp of the IL-8 promotor that includes the nuclear factor kappa B (NF kappaB), C/ EBP and AP-1 sites known to be involved in TNF mediated IL-8 induction; the second that encompasses these elements but extends approximately 1.1 kb fu rther upstream. Although IL-8 mRNA and protein were produced in response to either TNF or CD95 ligation, only TNF induced an increase in the reporter activity of the promoter constructs. Nevertheless, IL-8 induction by CD95 r esulted primarily from increased transcription and not from an increase in IL-8 mRNA stability. These results suggest that promoter elements/enhancers involved in CD95 mediated IL-8 induction are distinct from those used by T NF and not contained within the 1.6 kb region immediately upstream of the i nitiation codon. (C) 2001 Academic Press.