Differential Requirement for the Stress-Activated Protein Kinase/c-Jun NH_2-Terminal Kinase in RNA Damage-Induced Apoptosis in Primary and in Immortalized Fibroblasts

摘要

Onconase, an anticancer ribonuclease, damages cel. lular tRNA and causes caspase-dependent apoptosis in targeted cells (M. S. Iordanov, 0. P. Ryabinina, J, Wong, T. H. Dinh, D. L. Newton, S. M. Rybak, and B. E, Magun. Cancer Res. 60, 1983-1994, 2000). The proapop. totic action of onconase depends on its RNase activity, but the molecular mechanisms leading to RNA damage-induced caspase activation are completel~ unknown. In this study, we have investigated whether onconase activates two signal-transduction pathways commonly stimulated by conventional chemo- and ra. diotherapy, namely the stress-activated protein ki. nase (SAPK) cascade and the pathway leading to the activation of nuclear factor-kappa B (NF-KB). We found that, in all cell types tested, onconase is a potent activator of SAPK1 (JNK1 and JNK2) and SAPK2 (p38 MAP kinase), but that it is incapable of activating NF-KB. Inhibition of p38 MAP kinase activity with a pharmacological inhibitor, SB203580, demonstrated that p38 MAP kinase is not required for onconase cy. totoxicity. Using explanted fibroblasts from mice that contain targeted disruption of bothjnkl andjnk2 al. leles, we found that JNKs are important mediators of onconase-induced cytotoxicity. Surprisingly, following the immortalization of these same cells with human papilloma virus (HPV16) gene products E6 and E7, additional proapoptotic pathways (exclusive of JNK) were provoked by onconase. Our results demon- strate that onconase may activate proapoptotic path- ways in tumor cells that are not able to be accessed in normal cells. These results present the possibility that the cytotoxic activity of onconase in normal cells may be reduced by blocking the activity of JNKs.