title: Regulation of interferon-induced protein kinase PKR: modulation of P58IPK inhibitory function by a novel protein, P52rIPK.
abstract: The cellular response to environmental signals is largely dependent upon the induction of responsive protein kinase signaling pathways. Within these pathways, distinct protein-protein interactions play a role in determining the specificity of the response through regulation of kinase function. The interferon-induced serine/threonine protein kinase, PKR, is activated in response to various environmental stimuli. Like many protein kinases, PKR is regulated through direct interactions with activator and inhibitory molecules, including P58IPK, a cellular PKR inhibitor. P58IPK functions to represses PKR-mediated phosphorylation of the eukaryotic initiation factor 2alpha subunit (eIF-2alpha) through a direct interaction, thereby relieving the PKR-imposed block on mRNA translation and cell growth. To further define the molecular mechanism underlying regulation of PKR, we have utilized an interaction cloning strategy to identify a novel cDNA encoding a P58IPK-interacting protein. This protein, designated P52rIPK, possesses limited homology to the charged domain of Hsp90 and is expressed in a wide range of cell lines. P52rIPK and P58IPK interacted in a yeast two-hybrid assay and were recovered as a complex from mammalian cell extracts. When coexpressed with PKR in yeast, P58IPK repressed PKR-mediated eIF-2alpha phosphorylation, inhibiting the normally toxic and growth-suppressive effects associated with PKR function. Conversely, introduction of P52rIPK into these strains resulted in restoration of both PKR activity and eIF-2alpha phosphorylation, concomitant with growth suppression due to inhibition of P58IPK function. Furthermore, P52rIPK inhibited P58IPK function in a reconstituted in vitro PKR-regulatory assay. Our results demonstrate that P58IPK is inhibited through a direct interaction with P52rIPK which, in turn, results in upregulation of PKR activity. Taken together, our data describe a novel protein kinase-regulatory system which encompasses an intersection of interferon-, stress-, and growth-regulatory pathways.
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle 98195-7242, USA.
authors.forename: M
authors.initials: M
authors.lastname: Gale
authors.forename: C M
authors.initials: CM
authors.lastname: Blakely
authors.forename: D A
authors.initials: DA
authors.lastname: Hopkins
authors.forename: M W
authors.initials: MW
authors.lastname: Melville
authors.forename: M
authors.initials: M
authors.lastname: Wambach
authors.forename: P R
authors.initials: PR
authors.lastname: Romano
authors.forename: M G
authors.initials: MG
authors.lastname: Katze
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D015003:Yeasts; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018076:DNA, Complementary; C494651:DNAJC3 protein, human; D004791:Enzyme Inhibitors; D050956:HSP40 Heat-Shock Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C110409:THAP12 protein, human; D019892:eIF-2 Kinase