Induction of apoptosis by thiuramdisulfides, the reactive metabolites of dithiocarbamates, through coordinative modulation of NFkappaB, c-fos/c-jun, and p53 proteins.

Abstract

Prolinedithiocarbamate (PDTC) and diethyldithiocarbamate (DDTC) are cancer chemopreventive agents and can be biotransformed to prolinethiuramdisulfide (PTDS) and tetraethylthiuramdisulfide (disulfiram; DTDS), respectively. We found that the reactive metabolites PTDS and DTDS induced apoptosis after G1/S arrest. Phosphorylation of cyclin E, inhibition of cyclin-dependent kinase 2 activity, and degradation of cyclin E were found in human hepatoma Hep G2 cells during apoptosis. Moreover, PTDS and DTDS decreased the level of bcl-2 but increased the level of p53. In contrast, PDTC, DDTC, and ammonium dithiocarbamate (ADTC) did not induce apoptosis; rather they led to the induction of p53 and p21 followed by G1/S arrest. PDTC, DDTC, and ADTC also arrested cells in G1 phase. We then examined the effects of PTDS and DTDS on the signal transduction mechanisms leading to apoptosis. Although the transcription factors NFkappaB and AP-1 cooperatively decreased their DNA-binding activities to kappaB and 12-O-tetradecanoylphorbol-13-acetate-responsive elements, respectively, and p53 increased DNA-binding activity in the early stage but decreased it in the latter stage after treatment with PTDS, when the human Hep G2 cells were undergoing apoptosis. In summary, our results indicated that (i) PTDS and DTDS induced apoptosis and G1/S arrest mediated by p53, whereas PDTC, DDTC, and ADTC induced p53-dependent p21 expression leading to G1/S arrest; (ii) PDTC, DDTC, and ADTC induced p21/KIP1/CIP1 expression in a p53-dependent pathway leading to G1/S arrest; and (iii) NFkappaB, AP-1, and bcl-2 were downregulated during PTDS- and DTDS-induced apoptosis. These results suggested that PTDS and DTDS induced p53-dependent apoptosis, whereas PDTC, DDTC, and ADTC induced G1/S arrest. Apoptosis is regulated by the modulation of intracellular effectors such as NFkappaB, AP-1, and bcl-2 and activation of p53 in early stages.