Involvement of the extracellular signal-regulated protein kinase (ERK) pathway in the induction of apoptosis by cadmium chloride in CCRF-CEM cells

When CCRF-CEM cells were incubated with 5-40 μM CdCl_2, apoptosis was observed most clearly at 10 μM. Prior to the development of apoptosis, mitogen-activated protein kinases (MAPKs), i.e. extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, were activated with different sensitivity to CdCl₂ exposure. ERK and p38 MAPK were phosphorylated with incubation of 1 μM CdCl_2, but higher than 20 μM CdCl₂ was required for the clear phosphorylation of JNK. In the time-course study, ERK and p38 MAPK were phosphorylated earlier than JNK after CdCl₂ exposure. The in vitro activities of MAPKs also increased in response to CdCl₂ exposure. Pretreatment with an intracellular Ca²⁺ chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA/AM), suppressed almost completely CdCl₂-induced phosphorylation of JNK and p38 MAPK, but not ERK phosphorylation, indicating that the activation of JNK and p38 MAPK depends on the intracellular Ca²⁺ but that of ERK does not. On the other hand, treatment with a MAPK/ERK kinase (MEK) inhibitor, U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butadiene), suppressed CdCl₂-induced ERK activation and the apoptosis as well. The inhibition of p38 MAPK activity with SB203580 (4-[4-fluorophenyl]-2-[4-methylsulfinylphenyl]-5-[4-pyridyl]1H-im idazole) did not protect cells from apoptosis. The present results showed that the activation of ERK, JNK, and p38 MAPK is differently regulated in CCRF-CEM cells exposed to CdCl_2, and that the ERK pathway seems to be responsible for the induction of apoptosis by CdCl₂ exposure in this human T cell line. (C) 2000 Elsevier Science Inc.