Inhibition of double-stranded RNA- and tumor necrosis factor alpha-mediated apoptosis by tetratricopeptide repeat protein and cochaperone P58(IPK).
P58(IPK) is a tetratricopeptide repeat-containing cochaperone that is involved in stress-activated cellular pathways and that inhibits the activity of protein kinase PKR, a primary mediator of the antiviral and antiproliferative properties of interferon. To gain better insight into the molecular actions of P58(IPK), we generated NIH 3T3 cell lines expressing either wild-type P58(IPK) or a P58(IPK) deletion mutant, DeltaTPR6, that does not bind to or inhibit PKR. When treated with double-stranded RNA (dsRNA), DeltaTPR6-expressing cells exhibited a significant increase in eukaryotic initiation factor 2alpha phosphorylation and NF-kappaB activation, indicating a functional PKR. In contrast, both of these PKR-dependent events were blocked by the overexpression of wild-type P58(IPK). In addition, the P58(IPK) cell line, but not the DeltaTPR6 cell line, was resistant to dsRNA-induced apoptosis. Together, these findings demonstrate that P58(IPK) regulates dsRNA signaling pathways by inhibiting multiple PKR-dependent functions. In contrast, both the P58(IPK) and DeltaTPR6 cell lines were resistant to tumor necrosis factor alpha-induced apoptosis, suggesting that P58(IPK) may function as a more general suppressor of programmed cell death independently of its PKR-inhibitory properties. In accordance with this hypothesis, although PKR remained active in DeltaTPR6-expressing cells, the DeltaTPR6 cell line displayed a transformed phenotype and was tumorigenic in nude mice. Thus, the antiapoptotic function of P58(IPK) may be an important factor in its ability to malignantly transform cells.
Tang
N M
NM
Department of Microbiology, University of Washington, Seattle, Washington 98195, USA.
Korth
M J
MJ
Gale
M
M
Wambach
M
M
Der
S D
SD
Bandyopadhyay
S K
SK
Williams
B R
BR
Katze
M G
MG
D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D016328:NF-kappa B / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D011070:Poly I-C / Q000378:metabolism / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D012330:RNA, Double-Stranded / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011817:Rabbits; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D019892:eIF-2 Kinase / Q000378:metabolism*
C500846:Dnajc3 protein, mouse; D015852:Eukaryotic Initiation Factor-2; D050956:HSP40 Heat-Shock Proteins; D018832:Molecular Chaperones; D016328:NF-kappa B; D047428:Protein Kinase Inhibitors; D012330:RNA, Double-Stranded; D012097:Repressor Proteins; D014409:Tumor Necrosis Factor-alpha; D019892:eIF-2 Kinase; D011070:Poly I-C