Differential effects of p38 and JNK activation by GSK3 on cadmium-induced autophagy and apoptosis

Abstract

Cadmium (Cd) toxicity is associated with endoplasmic reticulum (ER) stress-mediated apoptosis and autophagy. However, the regulatory mechanisms responsible for the signaling pathways initiated by Cd are incompletely understood. Here, we investigated the involvement of glycogen synthase kinase (GSK) 3αβ and mitogen-activated protein kinases (MAPKs) in Cd toxicity. Cd-exposed H460 cells exhibited activation of JNK, p38, PERK, and CHOP and induction of autophagy and apoptosis; in contrast, levels of these proteins were minimal in Cd-resistant H1299 cells. In H460 cells, genetic or pharmacological inhibition of JNK markedly enhanced CHOP, autophagy and apoptosis induced by Cd, which were reversed by overexpression of JNK1. Inhibition of p38 suppressed Cd-induced CHOP, and markedly inhibited autophagy via Atg5 downregulation. Cd-exposed H460 cells showed GSK3αβ phosphorylation at serine (Ser) and tyrosine (Tyr) residues, which was downregulated by a GSK3 inhibitor (SB216763) and by genetic silencing of GSK3β, subsequently suppressing JNK and p38 activation. However, H460 cells pretreated with lithium or overexpressing GSK3β exhibited enhanced JNK and p38 activation. Pretreatment of H460 cells with okadaic acid (a Ser/Thr phosphatase inhibitor) upregulated Cd-induced p-Ser GSK3αβ and enhanced CHOP, p-p38 and autophagy, whereas treatment with vanadate (a tyrosine phosphatase inhibitor) downregulated Cd-induced p-Ser GSK3αβ, enhanced p-JNK and downregulated CHOP and autophagy. Furthermore, H460 cells overexpressing a constitutively active GSK3β mutant (S9A) exhibited enhanced p-JNK and inhibited CHOP, whereas overexpression of constitutively inactive GSK3β (K85A) enhanced p-p38 and autophagy in response to Cd. Pretreatment with N-acetyl cysteine suppressed Cd-induced p-Ser/p-Tyr GSK3αβ and downstream pathways. These findings show that Cd toxicity is regulated by autophagy, which can be countered by prosurvival JNK and prodeath p38 MAPK activation through site-specific phosphorylation of GSK3αβ.