Ng J, Cantrell D
Lymphocyte Activation Laboratory, Imperial Cancer Research Fund Laboratories, 44, Lincoln's Inn Fields, London WC2A 3PX, United Kingdom.
J Biol Chem. 1997 Sep 26;272(39):24542-9. doi: 10.1074/jbc.272.39.24542.
Interleukin 2 (IL-2) induces tyrosine phosphorylation of STATs 3 and 5 (signal transducer and activator of transcription). We now show that IL-2 regulation of STAT3 proteins in T cells is a complex response involving activation of two forms of STAT3: 90-kDa STAT3alpha and an 83-kDa carboxyl-terminal truncated STAT3beta. The phosphorylation of STAT proteins on serine residues is also required for competent STAT transcription. A critical serine phosphorylation site in STAT3alpha is at position 727. In this study we have produced an antisera specific for STAT3alpha proteins phosphorylated on serine 727 and used this to monitor the phosphorylation of this residue during T lymphocyte activation. Our results show that phosphorylation of STAT3alpha on serine 727 is not constitutive in quiescent T cells but can be induced by the cytokine IL-2. Interestingly, triggering of the T cell antigen receptor complex or activation of protein kinase C with phorbol esters also induces phosphorylation of serine 727 but without simultaneously inducing STAT3 tyrosine phosphorylation or DNA binding. Hence, the present results show that STAT3 serine phosphorylation can be regulated independently of the tyrosine phosphorylation of this molecule. IL-2 and T cell antigen receptor complex induction of STAT3alpha serine 727 phosphorylation is dependent on the activity of the MEK/ERK pathway. Previous studies have identified H-7-sensitive kinase pathways that regulate STAT3 DNA binding. We show that H-7-sensitive pathways regulate STAT3 DNA binding in T cells. Nevertheless, we show that H-7-sensitive kinases do not regulate STAT3 tyrosine phosphorylation or phosphorylation of serine 727. These results thus show that STAT3 proteins are targets for multiple kinase pathways in T cells and can integrate signals from both cytokine receptors and antigen receptors.
白细胞介素2（IL-2）可诱导信号转导子和转录激活子（STATs）3和5的酪氨酸磷酸化。我们现在发现，IL-2对T细胞中STAT3蛋白的调控是一种复杂的反应，涉及两种形式的STAT3激活：90 kDa的STAT3α和83 kDa的羧基末端截短型STAT3β。STAT蛋白丝氨酸残基的磷酸化对于有效的STAT转录也是必需的。STAT3α中的一个关键丝氨酸磷酸化位点位于727位。在本研究中，我们制备了一种针对在丝氨酸727处磷酸化的STAT3α蛋白的抗血清，并利用它来监测T淋巴细胞激活过程中该残基的磷酸化情况。我们的结果表明，在静止T细胞中，STAT3α丝氨酸727的磷酸化不是组成性的，但可被细胞因子IL-2诱导。有趣的是，T细胞抗原受体复合物的触发或用佛波酯激活蛋白激酶C也可诱导丝氨酸727的磷酸化，但不会同时诱导STAT3酪氨酸磷酸化或DNA结合。因此，目前的结果表明，STAT3丝氨酸磷酸化可以独立于该分子的酪氨酸磷酸化而受到调控。IL-2和T细胞抗原受体复合物诱导的STAT3α丝氨酸727磷酸化依赖于MEK/ERK途径的活性。先前的研究已经确定了调节STAT3 DNA结合的H-7敏感激酶途径。我们表明，H-7敏感途径调节T细胞中STAT3的DNA结合。然而，我们表明，H-7敏感激酶不调节STAT3酪氨酸磷酸化或丝氨酸727的磷酸化。这些结果因此表明，STAT3蛋白是T细胞中多种激酶途径的靶点，并且可以整合来自细胞因子受体和抗原受体的信号。
