GSK3β and endoplasmic reticulum stress mediate rotenone-induced death of SK-N-MC neuroblastoma cells

Abstract

Rotenone, an environmental toxin that inhibits mitochondrial complex I, has been used to induce experimental Parkinsonism in animals and cell cultures. We investigated the mechanism underlying rotenone-induced death of SK-N-MC neuroblastoma cells. Rotenone-induced cell death preceded intracellular accumulation of reactive oxygen species, and antioxidants failed to protect cells, indicating that oxidative stress was minimally involved in rotenone-induced death of SK-N-MC cells. Glycogen synthase kinase 3beta (GSK3beta), a multifunctional serine/threonine kinase, has been implicated in the pathogenesis of neurodegeneration. We showed that rotenone activated GSK3beta by enhancing its phosphorylation at tyrosine 216 while inhibiting phosphorylation at serine 9. Inhibitors of GSK3beta and dominant negative (kinase deficient) GSK3beta partially protected SK-N-MC cells against rotenone cytotoxicity. Rotenone also induced endoplasmic reticulum (ER) stress which was evident by an increase in phosphorylation of PERK, PKR, and eIF2alpha as well as the expression of GRP78. Rotenone had a modest effect on the expression of CHOP. An eIF2alpha siRNA significantly reduced rotenone cytotoxicity. ER stress was experimentally induced by tunicamycin and thapsigargin, but tunicamycin/thapsigargin did not activate GSK3beta in SK-N-MC cells. Down-regulation of eIF2alpha also offered partial protection against rotenone cytotoxicity. Combined treatment of GSK3beta inhibitors and eIF2alpha siRNA provided much greater protection than either treatment alone. Taken together, the results suggest that GSK3beta activation and ER stress contribute separately to rotenone cytotoxicity.