Overexpression of cyclooxygenase-2 (COX-2) has been observed in human colorectal cancer. COX-2 expression in human tumors can be induced by growth factors, cytokines, oncogenes, and other factors. The mechanisms regulating COX-2 expression in human colon cancer have not been completely elucidated. We hypothesized that the proinflammatory cytokine interleukin-1 beta (IL-1 beta) mediates COX-2 expression in HT-29 human colon cancer cells. Treatment of HT-29 cells with IL-1 beta induced expression of COX-2 mRNA and protein in a time- and dose-dependent manner. Inhibitors of the extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase, P38 mitogen-activated protein kinase, and nuclear factor-kappa B (NF-kappa B) signaling pathways blocked the ability of IL-1 beta to induce COX-2 mRNA. In contrast, Wortmannin, a phosphoinositide 3-kinase inhibitor upstream of protein kinase B/Akt, led to a slight increase in COX-2 mRNA expression after IL-1 beta treatment. Electrophoretic mobility shift assay on nuclear extracts demonstrated that IL-1 beta induced NF-kappa B DNA binding activity in HT-29 cells, and the activated NF-kappa B complex was eliminated after treatment with an inhibitor of NF-kappa B. Supershift assay indicated that the two NF-kappa B subunits, p65 and p50, were involved in activation of NF-kappa B complex by IL-1 beta stimulation. The stability of COX-2 mRNA was not altered by IL-1 beta treatment. These data demonstrate that IL-1 beta induces COX-2 expression in HT-29 cells through multiple signaling pathways and NF-kappa B.