10.1074/jbc.275.15.11418 áginas, 9 figuras -- PAGS nros. 1418-11424, Pulse treatment of U-937 promonocytic cells with cadmium chloride (2 h at 200 μm) provoked apoptosis and induced a rapid phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) as well as a late phosphorylation of extracellular signal-regulated protein kinases (ERK1/2). However, although the p38MAPK-specific inhibitor SB203580 attenuated apoptosis, the process was not affected by the ERK-specific inhibitor PD98059. The attenuation of the cadmium-provoked apoptosis by SB203580 was a highly specific effect. In fact, the kinase inhibitor did not prevent the generation of apoptosis by heat shock and camptothecin, nor the generation of necrosis by cadmium treatment of glutathione-depleted cells, nor the cadmium-provoked activation of the stress response. The generation of apoptosis was preceded by intracellular H2O2 accumulation and was accompanied by the disruption of mitochondrial transmembrane potential, both of which were inhibited by SB203580. On the other hand, the antioxidant agent butylated hydroxyanisole-inhibited apoptosis but did not prevent p38MAPK phosphorylation. In a similar manner, p38MAPK phosphorylation was not affected by the caspase inhibitors Z-VAD and DEVD-CHO, which nevertheless prevented apoptosis. These results indicate that p38MAPK activation is an early and specific regulatory event for the cadmium-provoked apoptosis in promonocytic cells. Cadmium and other heavy metals are frequent environmental contaminants with well known mutagenic, carcinogenic, and teratogenic effects (1). Another property of heavy metals (and of other physical and chemical agents, such as heat and inhibitors of energy metabolism) is the capacity to induce the stress response, characterized by the synthesis and accumulation of heat-shock proteins (HSPs)1 (2). The stimulation of HSP gene expression by stress inducers in higher eukaryotes seems to be specifically regulated by heat-shock factor 1 (HSF1). Thus, under stressful conditions, HSF1 undergoes trimerization, translocation to the nucleus, binding to the heat-shock consensus elements, and finally hyperphosphorylation to fully acquire the transactivation capacity (3). In addition, stress inducers may provoke cell death, either apoptotic or necrotic, depending on the intensity of the treatments (4, 5). The morphological characteristics of apoptosis and necrosis are well known (6-8). Thus, during apoptosis the cells undergo nuclear and cytoplasmic shrinkage, the chromatin is partitioned into multiple fragments, and the cells are broken into multiple membrane-surrounded bodies (“apoptotic bodies”), but the cell membrane retains its integrity during the process. By contrast, necrosis is characterized by cell swelling and a rapid loss of membrane integrity. However, the regulation of apoptosis and necrosis and the factors that decide the selection of one or the other mode of death are still poorly known., One of the most relevant aspects in the regulation of both the stress response and apoptosis is the involvement of mitogen-activated protein kinases (MAPKs), a family of serine/threonine kinases that mediate intracellular signal transduction in response to different stimuli (9). The MAPK family members are themselves activated by reversible dual phosphorylation on a Thr-Xaa-Tyr conserved motif, by specific mitogen-activated protein kinases kinases. To date, three major MAPKs have been identified, namely the extracellular signal-regulated kinases (ERK1/2, p44/p42), the stress-activated protein kinases (c-Jun NH2-terminal kinases, stress-activated protein kinase 1), and the p38 mitogen-activated protein kinases (p38MAPK, stress-activated protein kinase 2). ERK1/2 are mainly (although not exclusively) activated by growth factors (10, 11) and are critically involved in the regulation of mitogenesis. On the other hand, c-Jun NH2-terminal kinases and p38MAPK are mainly activated by cytotoxic insults and are often associated with apoptosis (12-18). It was recently reported that cadmium chloride induced the stress response and caused a dose-dependent activation of ERK1/2 and p38MAPK (but not of c-Jun NH2-terminal kinases) in association with mitogenesis and apoptosis, respectively, in rat brain tumor cells (19). Whereas it was demonstrated that both kinases were involved in the regulation of the stress response, it is not clear whether they were also required to induce cell death. In the present work we investigated the capacity of cadmium chloride to induce p38MAPK and ERK1/2 activation and to cause cell death in U-937 human promonocytic cells. It was concluded that p38MAPK activation is an early and specific requirement for the cadmium-provoked apoptosis, which precedes and probably modulates the expression of other regulatory events, This work was supported by Grant PB97-0144 from the Dirección General de Enseñanza Superior e Investigación Cientı́fica, Grant 08.1/0027/1997 from the Comunidad Autónoma de Madrid, Spain (to P. A.), Grant RPG-97-092-01-CNE from the American Cancer Society, and Grant ROI-CA 74197-01 from the National Institutes of Health (to M. G. K.).The costs of publication of this article were defrayed in part by the payment of page charges. 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