title: Essential role of PACT-mediated PKR activation in tunicamycin-induced apoptosis.
abstract: Cellular stresses such as disruption of calcium homeostasis, inhibition of protein glycosylation, and reduction of disulfide bonds result in accumulation of misfolded proteins in the endoplasmic reticulum (ER) and lead to cell death by apoptosis. Tunicamycin, which is an inhibitor of protein glycosylation, induces ER stress and apoptosis. In this study, we examined the involvement of double-stranded RNA (dsRNA)-activated protein kinase (PKR) and its protein activator PACT in tunicamycin-induced apoptosis. We demonstrate for the first time that PACT is phosphorylated in response to tunicamycin and is responsible for PKR activation by direct interaction. Furthermore, PACT-induced PKR activation is essential for tunicamycin-induced apoptosis, since PACT as well as PKR null cells are markedly resistant to tunicamycin and show defective eIF2alpha phosphorylation and C/EBP homologous protein (CHOP, also known as GADD153) induction especially at low concentrations of tunicamycin. Reconstitution of PKR and PACT expression in the null cells renders them sensitive to tunicamycin, thus demonstrating that PACT-induced PKR activation plays an essential function in induction of apoptosis.
authors.affiliation: Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, USA.
authors.forename: Madhurima
authors.initials: M
authors.lastname: Singh
authors.forename: Vennece
authors.initials: V
authors.lastname: Fowlkes
authors.forename: Indhira
authors.initials: I
authors.lastname: Handy
authors.forename: Chandrashekhar V
authors.initials: CV
authors.lastname: Patel
authors.forename: Rekha C
authors.initials: RC
authors.lastname: Patel
mesh_terms: D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005816:Genetic Complementation Test; D051379:Mice; D010766:Phosphorylation; D011485:Protein Binding; D014415:Tunicamycin / Q000494:pharmacology*; D019892:eIF-2 Kinase / Q000172:deficiency / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; C491290:Rbbp6 protein, mouse; D014415:Tunicamycin; D019892:eIF-2 Kinase