Bijli Kaiser M, Fazal Fabeha, Minhajuddin Mohd, Rahman Arshad
Department of Pediatrics (Neonatology), Lung Biology and Disease Program, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
J Biol Chem. 2008 May 23;283(21):14674-84. doi: 10.1074/jbc.M802094200. Epub 2008 Mar 24.
Protein kinase C-delta (PKC-delta) plays a pivotal role in mediating thrombin-induced NF-kappaB activation and ICAM-1 expression in endothelial cells. However, the downstream mechanisms mediating its function are unclear. In this study, we show that PKC-delta-mediated activation of protein-tyrosine kinase Syk plays an important role in thrombin signaling of NF-kappaB activation and intercellular adhesion molecule-1 (ICAM-1) expression in endothelial cells. Stimulation of human vascular endothelial cells with thrombin resulted in a time-dependent phosphorylation of Syk on tyrosine 525 and 526, an indication of Syk activation. Inhibition of PKC-delta by pharmacological and genetic approaches prevented Syk activation by thrombin. These results place Syk downstream of PKC-delta in transmitting thrombin-activated signaling in endothelial cells. Consistent with this, thrombin-induced NF-kappaB activity and ICAM-1 expression were prevented by the expression of a kinase-defective mutant or RNA interference knockdown of Syk. Similarly, inhibiting Syk also impaired NF-kappaB activity and ICAM-1 expression induced by a constitutively active mutant of PKC-delta. Analysis of the NF-kappaB pathway showed that Syk contributes to thrombin-induced NF-kappaB activation by controlling its transactivation potential and that this response is associated with tyrosine phosphorylation of RelA/p65. Thus, these data unveil a novel pathway in which Syk signals downstream of PKC-delta to mediate thrombin induced ICAM-1 expression in endothelial cells by increasing transcriptional capacity of NF-kappaB via a mechanism that relies on tyrosine phosphorylation of RelA/p65.
蛋白激酶C-δ（PKC-δ）在内皮细胞中介导凝血酶诱导的核因子κB（NF-κB）激活和细胞间黏附分子-1（ICAM-1）表达过程中起关键作用。然而，介导其功能的下游机制尚不清楚。在本研究中，我们发现PKC-δ介导的蛋白酪氨酸激酶Syk激活在内皮细胞中凝血酶信号传导的NF-κB激活和ICAM-1表达中起重要作用。用凝血酶刺激人血管内皮细胞导致Syk在酪氨酸525和526位点发生时间依赖性磷酸化，这表明Syk被激活。通过药理学和遗传学方法抑制PKC-δ可阻止凝血酶对Syk的激活。这些结果表明在传递内皮细胞中凝血酶激活信号时Syk位于PKC-δ的下游。与此一致的是，激酶缺陷型突变体的表达或Syk的RNA干扰敲低可阻止凝血酶诱导的NF-κB活性和ICAM-1表达。同样，抑制Syk也损害了由PKC-δ组成型活性突变体诱导的NF-κB活性和ICAM-1表达。对NF-κB信号通路的分析表明，Syk通过控制其反式激活潜能促进凝血酶诱导的NF-κB激活，并且这种反应与RelA/p65的酪氨酸磷酸化有关。因此，这些数据揭示了一条新的信号通路，其中Syk在PKC-δ下游发出信号，通过一种依赖于RelA/p65酪氨酸磷酸化的机制增加NF-κB的转录能力，从而介导凝血酶诱导的内皮细胞ICAM-1表达。
