Molecular Mechanism of Lymphocyte Immuneactivation and S

总结：抗原或抗受体抗体对抗原（Ag）受体的干扰通过蛋白酪氨酸激酶活化、磷脂酶C γ-l（PLCgl）的磷酸化和活化以及Ras和相关分子的活化诱导信号传导（“信号1”）。PLCg 1的激活，特别是介导磷酸肌醇（PI）水解，这反过来又控制钙动员和蛋白激酶C激活，在T-或B-淋巴细胞的激活中的强制性事件。此外，某些共刺激分子（例如，CD 2，CD 28）负责“信号2”影响PLCg 1激活。 信号1和2的适当生理组合诱导免疫激活，而不平衡的信号将无法激活细胞。 该实验室致力于建立免疫受体调节PLCg 1的机制。突变分析表明，PLCg 1氨基末端SH 2（SH 2N）结构域是必需的，足以为Ag受体诱导的PLCg 1的酪氨酸磷酸化和PLCg 1与支架适配器的协会。此外，PLCg 1膜转运需要SH 2N结构域，并通过SH 3结构域的突变而减少。 抗原受体诱导的PI水解被废除的突变的SH 2N或羧基末端SH 2（SH 2C）结构域和减少突变的SH 3结构域。脂筏，专门的膜微区，作为一个关键的隔室调节PLCg 1的激活的作用也被证明。除了将Ag受体偶联至PLCg 1介导的PI水解之外，PLCg 1 SH 2C结构域还发挥另外的功能，包括将共刺激信号传导途径偶联至下游效应物。 因此，SH 2C域可能位于信号1和2的交叉路口。 我们的实验室已经表明，SH 2C结构域作为PLCg 1酶活性的自抑制结构域，其与免疫受体偶联的功能受一种可能涉及分子内相互作用的未知机制的调节。 细胞原癌基因c-Cbl是一种衔接子，与许多信号蛋白（包括PLCg 1）相关，参与不同受体的信号转导。C-Cbl是TCR接合后酪氨酸磷酸化的主要靶标。C-Cbl结合PLC g1的SH 3结构域，并且c-Cbl过表达降低TCR诱导的PI水解。 c-Cbl的过表达降低了Ag受体诱导的Ras依赖性和Ca 2+依赖性转录活性，表明c-Cbl在Ag受体诱导的免疫激活中可能起负反馈机制的作用。相反，过度表达的致癌c-Cbl突变体，70 Z/3 Cbl，增强PI水解。 这些数据支持免疫受体诱导的PLCg 1激活的模型，其中施加的SH 2N结构域的支架结合作用和负反馈调节的SH 3结构域与c-Cbl相互作用的正调节。 SH 2C结构域可以作为从信号1到信号2的交叉，以复杂的方式调节，其机制是正在进行的研究的主题。

Summary: Perturbation of the antigen (Ag) receptor by antigen or by anti-receptor antibodies induces signaling ("Signal 1") via protein tyrosine kinase activation, the phosphorylation and activation of phospholipase C gamma-1 (PLCg1), and the activation of Ras and related molecules. The activation of PLCg1, in particular, mediates phosphoinositide (PI) hydrolysis which in turn controls calcium mobilization and protein kinase C activation, obligatory events in the activation of T- or B-lymphocytes. Furthermore, certain co-stimulatory molecules (e.g., CD2, CD28) responsible for "Signal 2" affect PLCg1 activation. The proper physiologic combination of signal 1 and 2 induces immune activation, while an unbalanced signal will fail to activate cells. The laboratory is concerned with establishing the mechanisms by which immune receptors regulate PLCg1. Mutational analysis demonstrated that PLCg1 amino terminal SH2 (SH2N) domain was required and sufficient for Ag receptor-induced tyrosine phosphorylation of PLCg1 and for the association of PLCg1 with scaffold adapters. Furthermore, PLCg1 membrane translocation required the SH2N domain and was decreased by mutation of the SH3 domain. Antigen receptor induced PI hydrolysis was abrogated by mutation of either the SH2N or the carboxyl-terminal SH2 (SH2C) domain and was decreased by mutation of the SH3 domain. A role for lipid rafts, specialized membrane microdomains, as a critical compartment regulating the activation of PLCg1 was also demonstrated. In addition to coupling the Ag receptor to PLCg1-mediated PI hydrolysis, PLCg1 SH2C domain exerts additional functions, including coupling the co-stimulatory signaling pathway to downstream effectors. Hence, the SH2C domain may be at the cross road of signal 1 and 2. Our laboratory has shown that the SH2C domain acts as an auto-inhibitory domain on PLCg1 enzyme activity and that its functionality in coupling to immune receptors is regulated by a yet unknown mechanism that is likely to involve an intramolecular interaction. The cellular proto-oncogene, c-Cbl, is an adapter that associates with numerous signaling proteins, including PLCg1, involved in signal transduction by distinct receptors. C-Cbl is a major target of tyrosine phosphorylation after TCR engagement. C-Cbl binds the SH3 domain of PLCg1 and c-Cbl over-expression decreased TCR-induced PI-hydrolysis. Over-expression of c-Cbl reduced both Ag receptor-induced Ras-dependent and Ca2+-dependent transcriptional activities, suggesting that c-Cbl could act as a negative feed-back mechanism in Ag receptor-induced immune activation. In contrast, over-expression of an oncogenic c-Cbl mutant, 70Z/3 Cbl, enhanced PI-hydrolysis. These data support a model of immune receptor-induced PLCg1 activation whereby positive regulation is exerted by the scaffold-binding role of the SH2N domain and negative feed-back regulation by the SH3 domain interaction with c-Cbl. The SH2C domain, which may acts as a cross-over from signal 1 to signal 2, is regulated in a complex manner whose mechanism is the subject of ongoing studies.