Leung S, Qureshi S A, Kerr I M, Darnell J E, Stark G R
Department of Molecular Biology, Cleveland Clinic Foundation, Ohio 44195.
Mol Cell Biol. 1995 Mar;15(3):1312-7. doi: 10.1128/MCB.15.3.1312.
We have isolated U6A, a mutant cell line which lacks the STAT2 subunit of the transcription factor interferon (IFN)-stimulated gene factor 3 (ISGF3). The response of U6A cells to IFN-alpha is almost completely defective, but the response to IFN-gamma is normal. Complementation of U6A cells with a cDNA encoding STAT2 restores the IFN-alpha response, proving that STAT2 is required in this pathway. Binding of IFNs to their receptors triggers tyrosine phosphorylation and activation of the receptors, JAK family kinases, STAT1, and STAT2. In IFN-alpha-treated U6A cells, phosphorylation of the essential tyrosine kinases TYK2 and JAK1 is normal, but the phosphorylation of STAT1 is weak. A mutant STAT2 protein in which the phosphorylated tyrosine at position 690 is changed to phenylalanine does not restore normal phosphorylation of STAT1 in response to IFN-alpha. The dependence of STAT1 phosphorylation on the presence of STAT2 but not vice versa (T. Improta, C. Schindler, C. M. Horvath, I. M. Kerr, G. R. Stark, and J. E. Darnell, Jr., Proc. Natl. Acad. Sci. USA 91:4776-4780, 1994) indicates that in the formation of ISGF3, these two proteins may be phosphorylated sequentially in response to IFN-alpha and that phosphorylated STAT2 may be required to allow unphosphorylated STAT1 to bind to the activated IFN-alpha receptor.
我们分离出了U6A，这是一种缺乏转录因子干扰素（IFN）刺激基因因子3（ISGF3）的STAT2亚基的突变细胞系。U6A细胞对IFN-α的反应几乎完全缺陷，但对IFN-γ的反应正常。用编码STAT2的cDNA对U6A细胞进行互补可恢复IFN-α反应，证明STAT2是该途径所必需的。IFN与其受体结合会触发受体、JAK家族激酶、STAT1和STAT2的酪氨酸磷酸化和激活。在IFN-α处理的U6A细胞中，必需的酪氨酸激酶TYK2和JAK1的磷酸化正常，但STAT1的磷酸化较弱。一种将第690位磷酸化酪氨酸突变为苯丙氨酸的突变STAT2蛋白不能恢复IFN-α刺激下STAT1的正常磷酸化。STAT1磷酸化对STAT2存在的依赖性而非反之（T. Improta、C. Schindler、C. M. Horvath、I. M. Kerr、G. R. Stark和J. E. Darnell，Jr.，《美国国家科学院院刊》91:4776 - 4780，1994）表明，在ISGF3的形成过程中，这两种蛋白可能会响应IFN-α依次磷酸化，并且磷酸化的STAT2可能是未磷酸化的STAT1结合到活化的IFN-α受体所必需的。
