Regulation of the interferon-inducible protein kinase PKR and (2'-5')oligo(adenylate) synthetase by a catalytically inactive PKR mutant through competition for double-stranded RNA binding.
The interferon-inducible double-stranded RNA-dependent protein kinase PKR has been suggested to function as a tumour suppressor gene product. Catalytically inactive mutants of PKR give rise to a tumorigenic phenotype when overexpressed in NIH-3T3 fibroblasts and this has been attributed to a dominant negative effect on the activity of the wild-type enzyme. Here we show that the mutant with Lys296 replaced by Arg, [K296R]PKR, not only inhibits the protein kinase activity of wild-type PKR but is also inhibitory towards another double-stranded RNA-dependent enzyme, the 40-kDa form of (2'-5')oligo(adenylate) synthetase. Inhibition of both wild-type PKR and (2'-5')oligo(adenylate) synthetase is reversed by adding higher concentrations of double-stranded RNA. These results suggest competition between [K296R]PKR and wild-type PKR or (2'-5')oligo(adenylate) synthetase for limiting amounts of double-stranded RNA. Moreover, the data imply that the tumorigenic effect of this PKR mutant could be due to inhibition of additional pathways requiring low levels of double-stranded RNA for activation and cannot be unambiguously attributed to inhibition of endogenous PKR itself.
Sharp
T V
TV
Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London, England.
Xiao
Q
Q
Justesen
J
J
Gewert
D R
DR
Clemens
M J
MJ
D015088:2',5'-Oligoadenylate Synthetase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001667:Binding, Competitive; D007372:Interferons / Q000494:pharmacology*; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000378:metabolism*; D019892:eIF-2 Kinase
D012330:RNA, Double-Stranded; D007372:Interferons; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D015088:2',5'-Oligoadenylate Synthetase