Differential Activation of p38 Mitogen-activated Protein Kinase and Extracellular Signal-regulated Protein Kinases Confers Cadmium-induced HSP70 Expression in 9L Rat Brain Tumor Cells

Abstract

We have reported that treatment with CdCl 2 at 40 -100 M induces the heat shock proteins (HSPs) in 9L rat brain tumor cells, during which the activation of heat shock factor (HSF) is essentially involved. By exploiting protein kinase inhibitors, we further analyzed the possible participation of specific protein kinases in the above processes. It was found that induction of HSP70 in cells treated with a high concentration of cadmium (i.e. 100 M) is preceded by the phosphorylation and activation of p38 mitogen-activated protein kinase (p38 MAPK ), while that in cells treated with a low concentration (60 M) is accompanied by the phosphorylation and activation of extracellular-regulated protein kinases 1 and 2 (ERK1/2). In 100 M cadmium-treated cells, both HSP70 induction and HSF1 activation are eliminated in the presence of SB203580, a specific inhibitor of p38 MAPK . By contrast, in 60 M cadmium-treated cells, the processes are not affected by SB203580 but are significantly suppressed by PD98059, which indirectly inhibits ERK1/2 by acting on MAPK-ERK kinase. Taken together, we demonstrate that p38 MAPK and ERK1/2 can be simultaneously or independently activated under different concentrations of cadmium and that the signaling pathways participate in the induction of HSP70 by acting on the inducible phosphorylation of HSF1. We thus provide the first evidence that both p38 MAPK and ERK signaling pathways can differentially participate in the activation of HSF1, which leads to the induction of HSP70 by cadmium.Heat shock proteins (HSPs) 1 are induced in cells responding to suboptimal growing conditions (1, 2). Transactivation of the heat shock genes has been centered on the interaction of the HSFs with the HSEs, which are found in all heat shock genes (3-5). Although several members of HSF have been characterized, HSF1 has been demonstrated to be the most crucial transcription factor activated in mammalian cells responding to classical inducers of the heat shock response (5-7). Under normal growing conditions, HSF1 may exist as a latent monomeric form, with neither DNA binding nor transcription activity. Activation of HSF1 is through a multistep pathway, a nuclear localization and trimerization step by which HSF1 acquires the properties of a stable trimer, which correlates with the DNA binding activity, and a phosphorylation step by which HSF1 becomes transcriptionally active (5,8,9). On the other hand, HSF1 may also be constitutively phosphorylated, which represses its transcription activity (10, 11). Thus, HSF1 may be constitutively or inducibly phosphorylated, and only inducible phosphorylation of this factor can confer the transcription activity. Several phosphorylation sites in HSF1 have been identified to contain the consensus sequence for proline-directed kinases including ERK1/2, p38 MAPK , and SAPKs, which can efficiently phosphorylate HSF1 in vitro (11,12). However, it is still unclear whether the MAPKs phosphorylate HSF1 in vivo.MAPKs are proline-directed serine/threonine kinases and are themselves activa...

Stimulation of p38 Mitogen-activated Protein Kinase Is an Early Regulatory Event for the Cadmium-induced Apoptosis in Human Promonocytic Cells

“…This conclusion is based on the following: (a) SB203580 did not prevent the generation of apoptosis by other agents, such heatshock and camptothecin, although the later one also caused p38 MAPK activation; (b) SB203580 did not prevent the generation of necrosis induced by the cadmium treatment of BSOpreincubated cells, although this treatment also increased p38 MAPK phosphorylation; and (c) SB203580 did not prevent the cadmium-provoked activation of the stress response. This later result was somewhat surprising, because SB203580 was reported to prevent HSF1 activation and HSP70 induction in rat brain tumor cells treated with high apoptosis-inducing cadmium concentrations (19). Such a discrepancy suggests the existence of marked differences in the regulation of the stress response in different cell types.…”

“…Activation of Mitogen-activated Protein Kinases-Earlier observations indicated that cadmium caused a dose-dependent activation of ERK1/2 and p38 MAPK , as measured by their increased phosphorylation, in rat brain tumor cells (19). Hence, we decided to measure the phosphorylation/activation of those kinases in cadmium-treated U-937 cells.…”

“…It was reported that heavy metals also induce p38 MAPK activation in different cell types (19,44,45), but the actual relevance of such activation for apoptosis was not known. Our present results indicate that treatment of U-937 promonocytic cells with apoptosis-inducing concentrations of cadmium chloride rapidly causes p38 MAPK activation, as judged by its increased phosphorylation, and proves that this activation is required for apoptosis, as revealed by the capacity of SB203580 to reduce both p38 MAPK phosphorylation and apoptosis.…”

“…It was recently reported that cadmium chloride induced the stress response and caused a dose-dependent activation of ERK1/2 and p38 MAPK (but not of c-Jun NH 2 -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.…”

Rapid activation of ERK1/2 and AKT in human breast cancer cells by cadmium

“…During the last decade, a growing body of evidence has accumulated suggests that in certain cell types micromolar concentration of Cd is able to initiate a series of rapid signaling events including: generation of second massagers (IP3, cAMP) within 15-30 sec (Smith et al,1989;Yamagami et al, 1998); increase in intracellular calcium within 3 min (Smith et al,1989;Yamagami et al, 1998); activation of certain kinases (Hung et al, 1998;Galan et al, 2000;Misra et al, 2002;; and induction of early response genes c-fos and c-myc within 30 min (Beyersmann and Hechtenberg, 1997;Misra et al, 2002;. Since these signals were generated soon after Cd exposure, it argued against a physiological interaction between Cd and intracellular proteins.…”