The mechanism of geranylgeraniol-induced apoptosis involves activation, bya caspase-3-like protease, of a c-Jun N-terminal kinase signaling cascade and differs from mechanisms of apoptosis induced by conventional chemotherapeutic drugs

In the present study, we investigated the effects of geranylgeraniol (GGO), a potent inducer of apoptosis in various lines of human tumor cells, on si gnal transduction cascades involved in apoptosis in human leukemia cells. G GO strongly induced the activation of c-Jun N-terminal kinase (JNK/SAPK) wi thin 2 h in U937 and K562 cells, while neither ERK nor p38 was activated to any considerable extent during GGO-induced apoptosis. Transient expression of a constitutively active mutant form of mitogen-activated protein kinase kinase 1 (MEKK1), Delta MEKK1, or of Delta MEKK1-green fluorescent protein (GFP) in K562 cells activated JNK, but not a caspase-3-like protease, and was insufficient to induce cell death but rendered cells susceptible to GGO -induced cell death. Stable expressions of Delta MEKK1-GFP in U937 cells ga ve similar results. In contrast to VP-16-induced apoptosis, GGO-induced act ivation of JNK was almost completely inhibited by benzyloxycarbonyl-Asp-Glu -Val-Asp-fluoromethylketone (Z-DEVD) and by benzyloxycarbonyl-Asp-CH2OC[O]- 2,6,-dichlorobenzene (Z-Asp), indicating that the JNK-activation step is lo cated downstream of the caspase signaling pathway in GGO-induced apoptosis. Moreover, apoptosis induced by GGO was significantly inhibited in two line s of cells with a dominant-negative deletion mutation in c-Jun, indicating a requirement for JNK signaling. In addition, unlike the effects on other i nducers of apoptosis, the activation of JNK and of the caspase-3-like prote ase by GGO was significantly delayed by 12-O-tetradecanoylphorbol-13-acetat e (TPA), suggesting that the site of inhibition by TPA might be located ups tream of the protease and JNK in the GGO-induced apoptotic signaling pathwa y. (C) 2000 Elsevier Science Ltd. All rights reserved.