title: Activation of double-stranded RNA dependent protein kinase, a new pathway by which human polynucleotide phosphorylase (hPNPase(old-35)) induces apoptosis.
abstract: Human polynucleotide phosphorylase (hPNPase(old-35)) is a type I IFN-inducible 3',5' exoribonuclease that mediates mRNA degradation. In melanoma cells, slow and sustained overexpression of hPNPase(old-35) induces G(1) cell cycle arrest ultimately culminating in apoptosis, whereas rapid overexpression of hPNPase(old-35) directly promotes apoptosis without cell cycle changes. These observations imply that inhibition of cell cycle progression and induction of apoptosis by hPNPase(old-35) involve multiple intracellular targets and signaling pathways. We now provide evidence that the apoptosis-inducing activity of hPNPase(old-35) is mediated by activation of double-stranded RNA-dependent protein kinase (PKR). Activation of PKR by hPNPase(old-35) precedes phosphorylation of eukaryotic initiation factor-2alpha and induction of growth arrest and DNA damage-inducible gene 153 (GADD153) that culminates in the shutdown of protein synthesis and apoptosis. Activation of PKR by hPNPase(old-35) also instigates down-regulation of the antiapoptotic protein Bcl-x(L). A dominant-negative inhibitor of PKR, as well as GADD153 antisense or bcl-x(L) overexpression, effectively inhibits apoptosis induction by hPNPase(old-35). These studies elucidate a novel pathway by which an evolutionary conserved RNA-metabolizing enzyme, hPNPase(old-35), regulates cell growth and viability.
authors.affiliation: Department of Urology, Herbert Irving Comprehensive Caner Center, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA. ds2039@columbia.edu
authors.forename: Devanand
authors.initials: D
authors.lastname: Sarkar
authors.forename: Eun Sook
authors.initials: ES
authors.lastname: Park
authors.forename: Glen N
authors.initials: GN
authors.lastname: Barber
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fisher
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics; D005095:Exoribonucleases / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D015398:Signal Transduction; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism*; D024101:Mitochondrial Proteins