Dual Activity of Pyrrolidine Dithiocarbamate on κB-Dependent Gene Expression in U937 Cells: I. Regulation by the Phorbol Ester TPA

Abstract

Pyrrolidine dithiocarbamate (PDTC) has been widely used as an inhibitor of the nuclear factor-κB (NF-κB) signalling pathway. Here, we show that κB-dependent reporter gene expression induced by low concentrations of 12- O-tetradecanoylphorbol-13-acetate (TPA) is potentiated by PDTC in the human promonocytic U937 cell line. The stimulatory effect of PDTC on κB-dependent gene expression was shown with a 4 × κB chloramphenicol acetyltransferase construct and required an intact κB element in the human immunodeficiency virus long terminal repeat (HIV-1 LTR). Unexpectedly, an HIV-1 LTR construct with a mutation of the activator protein 2 (AP-2) binding site located between the two κB elements was unresponsive to the stimulatory effect of PDTC with TPA. The stimulation or inhibition of κB-dependent gene expression was dependent on PDTC pre-treatment and the concentration of TPA. No stimulatory effect on HIV-1 LTR activity was observed with the metal chelator dipyridyl or the anti-oxidant N-acetyl- l-cysteine. These results are consistent with the hypothesis that PDTC treatment potentiated κB-dependent gene expression in a manner dependent on the concentration of TPA.