The involvement of nuclear factor-kappa B in cyclooxygenase-2 overexpression in murine colon cancer cells transduced with herpes simplex virus thymidine kinase gene

We have previously reported that transduction of murine colon cancer cells (MC38) with herpes simplex virus thymidine kinase (HSV-tk) gene results in a significant enhancement of tumor growth rate in vivo and overexpression of cyclooxygenase-2 (COX-2). Our current study aimed to investigate the involvement of nuclear factor-kappa B (NF-κB), a pivotal transcriptional regulator of COX-2, in the upregulation of COX-2 expression by HSV-tk. It was found that HSV-tk gene transduction of MC38 cells results in significantly enhanced NF-κB activity, increased phosphorylation and degradation of inhibitor-kappa Bα (IκBα) and enhanced translocation of NF-κB to the nucleus. Treatment of HSV-tk-transduced MC38 cells with sulfasalazine, a potent NF-κB inhibitor, led to dose-dependent inhibition of NF-κB activity, IκB phosphorylation and nuclear translocation of NF-κB, accompanied by significantly decreased COX-2 expression and reduced release of prostaglandin E₂. Transient transfection experiments with COX-2 promoter constructs fused to luciferase reporter gene revealed that mutation in NF-κB-responsive element of COX-2 promoter significantly reduced promoter activity in HSV-tk-transduced MC38 and COS-7 cells, whereas it had no effect on promoter activity in the respective wild-type cells. At last, it was found that HSV-tk gene transduction causes significant enhancement of NF-κB activity and COX-2 expression in two additional tumor cell lines, 9L and T24. These findings suggest that HSV-tk gene transduction results in NF-κB pathway activation, which is essential for COX-2 overexpression by HSV-tk.