Deckert M, Elly C, Altman A, Liu Y C
Division of Cell Biology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
J Biol Chem. 1998 Apr 10;273(15):8867-74. doi: 10.1074/jbc.273.15.8867.
Cross-linking of the T cell antigen receptor (TCR)-CD3 complex induces rapid tyrosine phosphorylation and activation of Src (Lck and Fyn) and Syk (Syk and Zap-70) family protein tyrosine kinases (PTKs) which, in turn, phosphorylate multiple intracellular substrates. Cbl is a prominent PTK substrate suggesting a pivotal role for it in early signal transduction events. However, the regulation of Cbl function and tyrosine phosphorylation in T cells by upstream PTKs remains poorly understood. In the present study, we used genetic and biochemical approaches to demonstrate that Cbl directly interacts with Syk and Fyn via its N-terminal and C-terminal regions, respectively. Tyr-316 of Syk was required for the interaction with Cbl as well as for the maximal tyrosine phosphorylation of Cbl. However, both wild-type Syk and Y316F-mutated Syk phosphorylated equally well the C-terminal fragment of Cbl in vivo, suggesting the existence of an alternative, N terminus-independent mechanism for the Syk-induced tyrosine phosphorylation of Cbl. This mechanism appears to involve Fyn, since, in addition to its association with the C-terminal region of Cbl, Fyn also associated with Syk and enhanced the Syk-induced tyrosine phosphorylation of Cbl. These findings implicate Fyn as an adaptor protein that facilitates the interaction between Syk and Cbl, and suggest that Src and Syk family PTKs coordinately regulate the tyrosine phosphorylation of Cbl.
T细胞抗原受体（TCR）-CD3复合物的交联可诱导Src（Lck和Fyn）家族和Syk（Syk和Zap-70）家族蛋白酪氨酸激酶（PTK）迅速发生酪氨酸磷酸化并激活，进而使多种细胞内底物发生磷酸化。Cbl是一种重要的PTK底物，提示其在早期信号转导事件中起关键作用。然而，上游PTK对T细胞中Cbl功能和酪氨酸磷酸化的调控仍知之甚少。在本研究中，我们采用遗传学和生物化学方法证明，Cbl分别通过其N端和C端区域与Syk和Fyn直接相互作用。Syk的Tyr-316对于与Cbl的相互作用以及Cbl的最大酪氨酸磷酸化是必需的。然而，野生型Syk和Y316F突变型Syk在体内对Cbl的C端片段的磷酸化效果相同，这表明存在一种不依赖N端的Syk诱导Cbl酪氨酸磷酸化的替代机制。这种机制似乎涉及Fyn，因为除了与Cbl的C端区域结合外，Fyn还与Syk结合并增强了Syk诱导的Cbl酪氨酸磷酸化。这些发现表明Fyn作为一种衔接蛋白促进了Syk与Cbl之间的相互作用，并提示Src家族和Syk家族PTK协同调节Cbl的酪氨酸磷酸化。
