Wu J, Katzav S, Weiss A
Department of Microbiology and Immunology, University of California, San Francisco 94143, USA.
Mol Cell Biol. 1995 Aug;15(8):4337-46. doi: 10.1128/MCB.15.8.4337.
Stimulation of the T-cell antigen receptor (TCR) induces activation of multiple tyrosine kinases, resulting in phosphorylation of numerous intracellular substrates. One substrate is p95vav, which is expressed exclusively in hematopoietic and trophoblast cells. It contains a number of structural motifs, including Src homology 2, Src homology 3, and pleckstrin homology domains and a putative guanine nucleotide exchange domain. The role of p95vav in TCR-mediated signaling processes is unclear. Here, we show that overexpression of p95vav alone in Jurkat T cells leads to activation of the nuclear factors, including NFAT, involved in interleukin-2 expression. Furthermore, p95vav synergizes with TCR stimulation in inducing NFAT- and interleukin-2-dependent transcription. In contrast, NFAT activation by a G-protein-coupled receptor is not modulated by p95vav overexpression, suggesting that the effect is specific to the TCR signaling pathways. Although removal of the first 67 amino acids of p95vav activates its transforming potential in NIH 3T3 cells, this region appears to be required for its function in T cells. We further demonstrate that the p95vav-induced NFAT activation is not mimicked by Ras activation, though its function is dependent upon Ras and Raf. Furthermore, the activating function of p95vav is blocked by FK506, suggesting that its activity also depends on calcineurin. To further dissect p95vav involvement in TCR signaling, we analyzed various Jurkat mutants deficient in TCR signaling function or TCR expression and showed that an intact TCR signaling pathway is required for p95vav to function. However, overexpression of p95vav does not appear to influence TCR-induced protein tyrosine phosphorylation or increases in cytoplasmic free calcium. Taken together, our data suggest that p95vav plays an important role at an yet unidentified proximal position in the TCR signaling cascade.
T 细胞抗原受体（TCR）的刺激会诱导多种酪氨酸激酶的激活，从而导致众多细胞内底物发生磷酸化。其中一种底物是 p95vav，它仅在造血细胞和滋养层细胞中表达。它包含许多结构基序，包括Src同源2、Src同源3和普列克底物蛋白同源结构域以及一个假定的鸟嘌呤核苷酸交换结构域。p95vav 在 TCR 介导的信号传导过程中的作用尚不清楚。在此，我们表明，仅在 Jurkat T 细胞中过表达 p95vav 会导致参与白细胞介素-2 表达的核因子（包括 NFAT）的激活。此外，p95vav 与 TCR 刺激协同作用，诱导依赖 NFAT 和白细胞介素-2 的转录。相比之下，G 蛋白偶联受体介导的 NFAT 激活不受 p95vav 过表达的调节，这表明该效应是 TCR 信号通路特有的。尽管去除 p95vav 的前 67 个氨基酸会激活其在 NIH 3T3 细胞中的转化潜能，但该区域似乎是其在 T 细胞中发挥功能所必需的。我们进一步证明，p95vav 诱导的 NFAT 激活不能被 Ras 激活所模拟，尽管其功能依赖于 Ras 和 Raf。此外，p95vav 的激活功能被 FK506 阻断，这表明其活性也依赖于钙调神经磷酸酶。为了进一步剖析 p95vav 在 TCR 信号传导中的作用，我们分析了各种缺乏 TCR 信号功能或 TCR 表达的 Jurkat 突变体，结果表明完整的 TCR 信号通路是 p95vav 发挥功能所必需的。然而，p95vav 的过表达似乎不会影响 TCR 诱导的蛋白酪氨酸磷酸化或细胞质游离钙的增加。综上所述，我们的数据表明 p95vav 在 TCR 信号级联反应中一个尚未明确的近端位置发挥重要作用。
