Rhee Sang Hoon, Jones Bryan W, Toshchakov Vladimir, Vogel Stefanie N, Fenton Matthew J
The Pulmonary Center, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
J Biol Chem. 2003 Jun 20;278(25):22506-12. doi: 10.1074/jbc.M208633200. Epub 2003 Apr 9.
Engagement of Toll-like receptor (TLR) proteins activates multiple signal transduction pathways. These studies show that engagement of TLR2 and TLR4 leads to rapid phosphorylation of the transcription factor STAT1 at serine 727 (Ser-727 STAT1) in murine macrophages. Only TLR4 engagement induced STAT1 phosphorylation at tyrosine 701, although this response was delayed compared with Ser-727 STAT1 phosphorylation. Inhibition of phosphatidylinositol 3'-kinase using LY294002 blocked TLR4-induced STAT1 tyrosine phosphorylation, but this inhibitor had no effect on STAT1 serine phosphorylation. TLR-induced phosphorylation of Ser-727 STAT1 could be blocked by the selective p38 mitogen-activated protein kinase inhibitor SB203580. However, activation of p38 was not sufficient to induce Ser-727 STAT1 phosphorylation in macrophages. TLR2-induced activation of Ser-727 STAT1 phosphorylation required the adapter protein MyD88, whereas TLR4-induced activation of Ser-727 STAT1 phosphorylation was not solely dependent on MyD88. Lastly, TLR4-induced activation of Ser-727 STAT1 phosphorylation could be blocked by rottlerin, a specific inhibitor of protein kinase C-delta. In contrast, rottlerin had no effect on STAT1 phosphorylation induced via TLR2. Together, these data demonstrate that activation STAT1 tyrosine and serine phosphorylation are distinct consequences of TLR engagement in murine macrophages. Furthermore, p38 mitogen-activated protein kinase, protein kinase C-delta, and a novel TLR2-specific signaling pathway appear to be necessary to induce Ser-727 STAT1 phosphorylation.
Toll样受体（TLR）蛋白的激活可启动多种信号转导途径。这些研究表明，在小鼠巨噬细胞中，TLR2和TLR4的激活会导致转录因子STAT1在丝氨酸727（Ser-727 STAT1）处迅速磷酸化。只有TLR4的激活会诱导STAT1在酪氨酸701处磷酸化，不过与Ser-727 STAT1磷酸化相比，这种反应出现延迟。使用LY294002抑制磷脂酰肌醇3'-激酶可阻断TLR4诱导的STAT1酪氨酸磷酸化，但该抑制剂对STAT1丝氨酸磷酸化没有影响。TLR诱导的Ser-727 STAT1磷酸化可被选择性p38丝裂原活化蛋白激酶抑制剂SB203580阻断。然而，p38的激活并不足以在巨噬细胞中诱导Ser-727 STAT1磷酸化。TLR2诱导的Ser-727 STAT1磷酸化激活需要衔接蛋白MyD88，而TLR4诱导的Ser-727 STAT1磷酸化激活并不完全依赖于MyD88。最后，TLR4诱导的Ser-727 STAT1磷酸化激活可被rottlerin（一种蛋白激酶C-δ的特异性抑制剂）阻断。相比之下，rottlerin对通过TLR2诱导的STAT1磷酸化没有影响。总之，这些数据表明，激活STAT1酪氨酸和丝氨酸磷酸化是小鼠巨噬细胞中TLR激活的不同结果。此外，p38丝裂原活化蛋白激酶、蛋白激酶C-δ以及一条新的TLR2特异性信号通路似乎是诱导Ser-727 STAT1磷酸化所必需的。
