Pyrrolidine dithiocarbamate‐induced neuronal cell death is mediated by Akt, casein kinase 2, c‐Jun N‐terminal kinase, and IκB kinase in embryonic hippocampal progenitor cells

Abstract

Pyrrolidine dithiocarbamate (PDTC) is known to induce cell death by the stimulation of intracellular zinc transport and subsequent modulation of nuclear factor‐κB (NF‐κB) activity. Zinc is a signaling messenger that is released by neuronal activity at many central excitatory synapses. Excessive synaptic release of zinc followed by entry into vulnerable neurons contributes to severe neuronal cell death. In the present study, we explored how PDTC modulates intracellular signal transduction pathways, leading to neuronal cell death. The exposure of immortalized embryonic hippocampal cells (H19‐7) to PDTC within the range of 1–100 μM caused cell death in a dose‐dependent manner. During the cell death, NF‐κB activity increased in response to PDTC, and this activity corresponded well with the increase of intracellular free zinc levels, implying that the activation of NF‐κB transmits the cell death signals of PDTC. Furthermore, PDTC caused the activation of IκB kinase (IKK), casein kinase 2 (CK2), phosphatidylinositol 3‐kinase (PI‐3K), and Akt, as well as mitogen‐activated protein kinases (MAPKs), such as extracellular signal‐regulated kinase (ERK) and c‐Jun N‐terminal kinase (JNK), but not p38 kinase. The blockade of PI‐3K, JNK, and CK2 pathways resulted in a remarkable suppression of PDTC‐induced cell death and also the activation of IKK, which subsequently led to a decrease of IκB phosphorylation. Although the overexpression of dominant‐negative SEK in a transient manner did not inhibit the activation of Akt by PDTC, the transfection of kinase‐inactive Akt mutants did cause a remarkable blockade of JNK activation, implying that Akt is present upstream of JNK in the PDTC‐signaling pathways. Moreover, whereas selective CK2 inhibitors suppressed PDTC‐induced JNK activation, the inhibition of JNK did not affect CK2 activity, suggesting that CK2 is directly related to the regulation of cell viability by PDTC and that the CK2‐JNK pathway could be a downstream target of PDTC. Taken together, our results suggest that PDTC‐mediated accumulation of intracellular zinc ions may affect cell viability by modulating several intracellular signaling pathways in neuronal hippocampal progenitor cells.