Muthusamy N, Leiden J M
Departments of Medicine and Pathology, University of Chicago, Chicago, Illinois 60637, USA.
J Biol Chem. 1998 Aug 28;273(35):22841-7. doi: 10.1074/jbc.273.35.22841.
The cAMP-responsive element-binding protein (CREB) transcription factor is required for normal T cell activation following stimulation through the T cell antigen receptor (TCR). CREB is present in resting T cells in an unphosphorylated and inactive state. TCR engagement results in the rapid phosphorylation of CREB on Ser133 and its concomitant activation. In the studies described in this report, we have investigated the signaling pathway(s) that are responsible for CREB activation in normal T cells. Using pharmacological agonists, we show that protein kinase C (PKC)-, calcium/calmodulin-, and protein kinase A-dependent pathways are each capable of independently eliciting CREB phosphorylation in T cells and thymocytes. Pharmacological inhibitor studies demonstrated that the PKC-mediated signaling pathway is required for TCR-mediated activation of CREB. In contrast, inhibitors of protein kinase A and calmodulin kinases had no effect on CREB phosphorylation following TCR cross-linking. T cells lacking the p56(lck) tyrosine kinase failed to phosphorylate CREB in response to TCR engagement. Overexpression of dominant-negative mutant Ras and Raf-1 proteins in Jurkat T cells abolished TCR-mediated CREB phosphorylation, whereas overexpression of the RSK2 serine/threonine kinase significantly potentiated TCR-mediated CREB phosphorylation. Taken together, these experiments are consistent with a model in which TCR engagement leads to the rapid phosphorylation and activation of CREB via a signaling pathway involving the activation of p56(lck), PKC, Ras, Raf-1, MEK, and RSK2. Given the importance of CREB phosphorylation in normal T cell activation, this pathway may be an attractive target for the development of novel immunosuppressive agents.
环磷酸腺苷反应元件结合蛋白（CREB）转录因子是T细胞通过T细胞抗原受体（TCR）刺激后正常激活所必需的。CREB以未磷酸化的无活性状态存在于静止的T细胞中。TCR的结合导致CREB在Ser133位点快速磷酸化并随之激活。在本报告所述的研究中，我们研究了正常T细胞中负责CREB激活的信号通路。使用药理学激动剂，我们发现蛋白激酶C（PKC）、钙/钙调蛋白和蛋白激酶A依赖性通路均能够独立地引发T细胞和胸腺细胞中CREB的磷酸化。药理学抑制剂研究表明，PKC介导的信号通路是TCR介导的CREB激活所必需的。相比之下，蛋白激酶A和钙调蛋白激酶的抑制剂对TCR交联后CREB的磷酸化没有影响。缺乏p56(lck)酪氨酸激酶的T细胞在TCR结合后无法使CREB磷酸化。在Jurkat T细胞中过表达显性负性突变体Ras和Raf-1蛋白消除了TCR介导的CREB磷酸化，而过表达RSK2丝氨酸/苏氨酸激酶则显著增强了TCR介导的CREB磷酸化。综上所述，这些实验与一个模型一致，即TCR结合通过涉及p56(lck)、PKC、Ras、Raf-1、MEK和RSK2激活的信号通路导致CREB快速磷酸化和激活。鉴于CREB磷酸化在正常T细胞激活中的重要性，该通路可能是开发新型免疫抑制剂的一个有吸引力的靶点。
