MOLECULAR MECHANISMS OF C-JUN N-TERMINAL KINASE-MEDIATED APOPTOSIS INDUCED BY ANTICARCINOGENIC ISOTHIOCYANATES

Isothiocyanates have strong chemopreventive properties against many ca rcinogen-induced cancers in experimental animal models. Here, we repor t that phenylmethyl isocyacyanate (PMITC) and phenylethyl isothiocyana te (PEITC) induced sustained c-Jun N-terminal kinase (JNK) activation in a dose-dependent manner. The sustained JNK activation caused by iso thiocyanates was associated with apoptosis induction in various cell t ypes, An inhibitor of the caspase/interleukin-1 beta-converting enzyme blocked isothiocyanate-induced apoptosis without inhibiting the JNK a ctivation, which suggests that JNK activation by isothiocyanates is an event that is independent or upstream of the activation of caspase/in terleukin-1 beta-converting enzyme proteases. PEITC-induced apoptosis was suppressed by interfering with the JNK pathway with a dominant-neg ative mutant of JNK1 or MEKK1 (JNK1(APF) and MEKK1(KR), respectively), implying that the JNK pathway is required for apoptotic signaling. Is othiocyanate-induced JNK activation was blocked by the antioxidants 2- mercaptoethanol and N-acetyl-L-cysteine, suggesting that the death sig naling was triggered by oxidative stress. Overexpression of Bcl-2 supp ressed PEITC-induced JNK activation. In addition, Bcl-2 and Bcl-x(L) s uppressed PEITC-induced apoptosis, but failed to protect cells from de ath induced by overexpression of activated JNK1. These results suggest that Bcl-2 and Bcl-x(L) are upstream of JNK. Taken together, our resu lts indicate (i) that JNK mediates PMITC- and PEITC-induced apoptosis and (ii) that PMITC and PEITC may have chemotherapeutic functions besi des their chemopreventive functions.