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Specific NF‐κB blockade selectively inhibits tumour necrosis factor‐α‐induced COX‐2 but not constitutive COX‐1 gene expression in HT‐29 cells

Cyclo‐oxygenase (COX) is the key regulatory enzyme of the prostaglandin/eicosanoid pathway. While COX‐1 is mostly constitutively expressed, the COX‐2 isoform is inducible by proinflammatory cytokines. We used an adenoviral vector containing an NF‐κB super‐repressor (Ad5IκB) to investigate the role of NF‐κB in tumour necrosis factor‐α (TNF‐α)‐mediated COX‐2 gene expression in a colonic epithelial cell line. COX‐1 mRNA and protein were constitutively expressed in uninfected, control Ad5LacZ‐ or Ad5IκB‐infected HT‐29 cells with no apparent change following TNF‐α exposure. COX‐2 mRNA and protein expression was undetectable in unstimulated cells but was strongly up‐regulated after TNF‐α stimulation in uninfected and Ad5LacZ‐infected HT‐29 cells. This induction was prevented in Ad5IκB cells. TNF‐α increased prostaglandin E2 production by 20‐fold in Ad5LacZ‐infected HT‐29 cells compared with uninfected cells and was significantly inhibited in Ad5IκB‐infected cells in agreement with the COX‐2 mRNA findings. We conclude that NF‐κB activation is critical in mediating COX‐2, but not COX‐1 gene expression in HT‐29 cells. Selective inhibition of COX‐2 expression with the NF‐κB super‐repressor may be useful in distinguishing the role of inducible versus constitutive prostaglandins in intestinal function and provides greater specificity than pharmacological inhibitors.