Nair Jayasree S, DaFonseca Christopher J, Tjernberg Agneta, Sun Wei, Darnell James E, Chait Brian T, Zhang J Jillian
Department of Pathology, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA.
Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):5971-6. doi: 10.1073/pnas.052159099. Epub 2002 Apr 23.
In response to IFN-gamma, the latent cytoplasmic protein signal transducers and activators of transcription 1 (Stat1) becomes phosphorylated on Y701, dimerizes, and accumulates in the nucleus to activate transcription of IFN-gamma-responsive genes. For maximal gene activation, S727 in the transcription activation domain of Stat1 also is inducibly phosphorylated by IFN-gamma. We previously purified a group of nuclear proteins that interact specifically with the Stat1 transcription activation domain. In this report, we identified one of them as the multifunctional Ca(2+)/calmodulin-dependent kinase (CaMK) II. We demonstrate that IFN-gamma mobilizes a Ca(2+) flux in cells and activates CaMKII. CaMKII can interact directly with Stat1 and phosphorylate Stat1 on S727 in vitro. Inhibition of Ca(2+) flux or CaMKII results in a lack of S727 phosphorylation and Stat1-dependent gene activation, suggesting in vivo phosphorylation of Stat1 S727 by CaMKII. Thus two different cellular signaling events, IFN-gamma receptor occupation and Ca(2+) flux, are required for Stat1 to achieve maximal transcriptional activation through regulation of phosphorylation.
作为对γ干扰素的应答，潜在的细胞质蛋白信号转导及转录激活因子1（Stat1）在Y701位点发生磷酸化，形成二聚体，并在细胞核中积累，从而激活γ干扰素应答基因的转录。为实现最大程度的基因激活，Stat1转录激活结构域中的S727也会被γ干扰素诱导磷酸化。我们之前纯化了一组能与Stat1转录激活结构域特异性相互作用的核蛋白。在本报告中，我们鉴定出其中之一为多功能钙/钙调蛋白依赖性激酶（CaMK）II。我们证明γ干扰素可在细胞中引发钙流并激活CaMKII。CaMKII能直接与Stat1相互作用，并在体外使Stat1的S727位点磷酸化。抑制钙流或CaMKII会导致S727磷酸化缺失以及Stat1依赖性基因激活受阻，这表明在体内CaMKII可使Stat1的S727位点磷酸化。因此，Stat1要通过磷酸化调控实现最大程度的转录激活，需要两种不同的细胞信号事件，即γ干扰素受体被占据和钙流。
