Effect of a mutant form of IkappaB-alpha on 5-fluorouracil-induced apoptosis in transformed human salivary gland cells.

Increasing evidence indicates that transcription factor NF-kappaB may play a role in cell survival, and that some chemotherapeutic agents activate NF-kappaB, while inhibition of NF-kappaB renders cells sensitive to these drugs. 5-Fluorouracil (5-FU) exerts its cytotoxic effect through the induction of apoptosis. However, it still remains uncertain whether 5-FU treatment in combination with the inhibition of NF-kappaB largely exerts an anti-proliferative effect on the growth of neoplastic human salivary gland cells. Thus, we investigated whether NF-kappaB suppression in transformed human salivary gland (NS-SV-AC) cells leads to a marked reduction in cell growth in response to 5-FU treatment. Our results demonstrated that under unstimulated conditions, the ability of cell growth in the super-repressor form of IkappaB-alpha (srIkappaB-alpha) cDNA-transfected cell clones (ACMT-6 and -7) was significantly lower than that in the empty vector-transfected cell clone (ACpRc-1). In addition, the growth inhibition caused by 5-FU was greatly enhanced in ACMT-6 and -7 as compared to ACpRc-1. Based on fractional inhibition analysis, this growth inhibition was due to an additive effect of both inhibitors. Electrophoretic mobility shift assay revealed that NF-kappaB activity in these cell clones was not affected by treatment with 5-FU. Accordingly, our data provide evidence that the combination of 5-FU and NF-kappaB suppression cooperatively functions in the growth inhibition of NS-SV-AC cells.