Upregulation of cyclooxygenase-2 is accompanied by increased expression of nuclear factor-κB and IκB kinase-α in human colorectal cancer epithelial cells

Cyclooxygenase-2 (COX-2) is selectively overexpressed in colorectal tumours. The mechanism of COX-2 induction is not fully understood, but requires de novo messenger RNA and protein synthesis, indicating regulation at the transcriptional level. Sequence analysis of the 5'-flanking region of the COX-2 gene shows two nuclear factor-kappaB (NF-kappaB) sites. Inhibition of this protein in model cell culture systems attenuates COX-2 expression and implies that NF-kappaB plays an important role in COX-2 induction. We measured COX-2, NF-kappaB and IkappaB kinase alpha (IKKalpha) protein expression in matched colonic biopsy samples comprising both nontumour and adjacent tumour tissue from 32 colorectal cancer patients using immunohistochemistry. There was none or very little expression of COX-2, NF-kappaB and IKKalpha in non-neoplastic colon epithelial cells, while the expression of all three of these proteins was significantly increased (P<0.05, Wilcoxon's signed rank test) in adjacent cancerous cells. Moreover, all three proteins were found to be coexpressed in the neoplastic epithelium, with the expression of COX-2 and NF-kappa B highly correlated (Pearson's correlation, P<0.005). There was no apparent correlation between enhanced COX-2, NF-kappaB or IKKalpha expression and tumour Dukes' stages. Our results are compatible with the hypothesis that IKKalpha and NF-kappaB are involved in COX-2 induction in these tumours and the lack of association between COX-2 expression and severity of disease as measured by Dukes' stage is consistent with the proposal that COX-2 expression is an early postinitiation event.