Sharp T V, Xiao Q, Justesen J, Gewert D R, Clemens M J
Department of Cellular and Molecular Sciences, St George's Hospital Medical School, London, England.
Eur J Biochem. 1995 May 15;230(1):97-103. doi: 10.1111/j.1432-1033.1995.0097i.x.
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.
干扰素诱导的双链RNA依赖性蛋白激酶PKR被认为具有肿瘤抑制基因产物的功能。当PKR的催化无活性突变体在NIH-3T3成纤维细胞中过表达时会产生致瘤表型，这被归因于对野生型酶活性的显性负效应。在此我们表明，赖氨酸296被精氨酸取代的突变体[K296R]PKR不仅抑制野生型PKR的蛋白激酶活性，而且对另一种双链RNA依赖性酶，即40 kDa形式的（2'-5'）寡腺苷酸合成酶也有抑制作用。通过添加更高浓度的双链RNA可逆转对野生型PKR和（2'-5'）寡腺苷酸合成酶的抑制作用。这些结果表明，[K296R]PKR与野生型PKR或（2'-5'）寡腺苷酸合成酶之间存在对有限量双链RNA的竞争。此外，数据表明该PKR突变体的致瘤作用可能是由于抑制了需要低水平双链RNA激活的其他途径，而不能明确归因于对内源性PKR本身的抑制。
