Role of nuclear factor-kappaB in the expression by tumor necrosis factor-alpha of the human polymeric immunoglobulin receptor (plgR) gene.

We analyzed the mechanism of human polymeric immunoglobulin receptor (pIgR) gene upregulation by tumor necrosis factor (TNF)-alpha. Northern blot analysis showed that the expression of pIgR mRNA was enhanced by TNF-alpha stimulation. This activation was completely inhibited by RNA polymerase or protein synthesis inhibitors, suggesting that the regulation of pIgR gene expression depends on de novo RNA and protein synthesis. Furthermore, the stimulation of pIgR mRNA by TNF-alpha was decreased by pyrrolidinedithiocarbamate and L-1-4'-tosylamino-phenylethyl-chloromethyl ketone, which are known nuclear factor (NF)-kappaB inhibitors. For further analysis of gene regulation, we cloned and sequenced the 1.5-kb 5'-flanking region of the pIgR gene. In the upstream region, we found two NF-kappaB-binding motifs (named kappaB1 and kappaB2 from the 5' region). An electrophoretic mobility shift assay indicated that two components of the NF-kappaB/Re1 family, p50 and p65, bound with higher affinity to the KB2 element than to the kappaB1 element. We also analyzed plgR gene expression using reporter plasmids expressing the firefly luciferase gene. Stimulation by TNF-alpha significantly activated the pIgR gene promoter, as a 775-bp upstream region of the pIgR gene increased luciferase gene expression in cells treated with TNF-alpha. The activation of promoter activity by TNF-alpha was abolished when a mutation was inserted into kappaB1 or kappaB2. These data indicated that pIgR gene expression induced by TNF-alpha is transcriptionally regulated via activation of NF-kappaB. In addition, there is a possibility that another factor may act in concert with NF-kappaB.