p38 Activation is required upstream of potassium current enhancement and caspase cleavage in thiol oxidant-induced neuronal apoptosis

Oxidant-induced neuronal apoptosis has been shown to involve potassium and zinc dysregulation, energetic dysfunction, activation of stress-related kin ases, and caspase cleavage. The temporal ordering and interdependence of th ese events was investigated in primary neuronal cultures exposed to the sul fhydryl oxidizing agent 2,2'-dithiodipyridine (DTDP), a compound that induc es the intracellular release of zinc. We previously observed that tetraethy lammonium (TEA), high extracellular potassium, or cysteine protease inhibit ors block apoptosis induced by DTDP. We now report that both p38 and extrac ellular signal-regulated kinase phosphorylation are evident in neuronal cul tures within 2 hr of a brief exposure to 100 muM DTDP. However, only p38 in hibition is capable of blocking oxidant-induced toxicity. Cyclohexamide or actinomycin D does not attenuate DTDP-induced cell death, suggesting that p osttranslational modification of existing targets, rather than transcriptio nal activation, responsible for the deleterious effects of p38. Indeed, an early robust increase in TEA-sensitive potassium channel currents induced b y DTDP is attenuated by p38 inhibition but not by caspase inhibition. Moreo ver, we found that activation of p38 is required for caspase 3 and 9 cleava ge, suggesting that potassium currents enhancement is required for caspase activation. Finally, we observed that DTDP toxicity could be blocked with n iacinamide or benzamide, inhibitors of poly (ADP-ribose) synthetase. Based on these findings, we conclude that oxidation of sulfhydryl groups on intra cellular targets results in intracellular zinc release, p38 phosphorylation , enhancement of potassium currents, caspase cleavage, energetic dysfunctio n, and translationally independent apoptotic cell death.