NEGATIVE SIGNALLING BY KILLER CELL INHIBITORY RECEPTORS

人类自然杀伤（NK）细胞表现出一种独特的激活机制，主要受包括杀伤细胞抑制受体（KIR）在内的抑制受体的调节。KIR是主要的NK细胞受体，结合经典的主要组织相容性复合体I类分子（MHC-I）并转导抑制NK细胞活化的负信号。KIR负信号的一个组成部分是蛋白质酪氨酸磷酸酶SHP-1在受体细胞质域中磷酸化酪氨酸残基的募集。SHP-1如何抑制NK细胞活化以及是否有其他信号效应分子在这一过程中发挥作用仍有待确定。我们最近发现蛋白质酪氨酸激酶（PTK）， Csk，也可以结合酪氨酸磷酸化的KIR。KIR募集Csk为我们未来的研究提供了一个令人兴奋的基础，因为这种PTK具有磷酸化Src家族受体近端PTK上的调节酪氨酸残基并终止其活性的独特能力。这种新的负信号机制尚未被任何抑制性受体发现，我们假设Csk的募集使KIR具有抑制蛋白酪氨酸磷酸化介导的早期激活事件的能力。其他数据支持我们的假设，即KIR上两个单独的酪氨酸磷酸化位点的磷酸化状态直接调节效应酶结合谱和功能结果。我们提出以三个具体目标来验证我们的假设：(1)生化表征Csk募集到KIR及其对Src家族PTKs的影响，(2)确定Csk募集对KIR抑制NK细胞活化的功能贡献，(3)表征单个KIR酪氨酸在抑制信号反应中的作用。这些研究将极大地促进我们对kir介导的负信号传导机制的理解。更好地了解主要调节NK细胞活化的机制，最终将允许开发治疗方法，以有益地操纵它们在治疗癌症，病毒感染和预防组织移植排斥反应中的功能。

Human natural killer (NK) cells exhibit a unique activation mechanism that is dominantly regulated by inhibitory receptors, including Killer Cell Inhibitory Receptors (KIR). KIR are the major NK cell receptors that bind classical major histocompatibility complex class I molecules (MHC-I) and transduce negative signals that restrain NK cell activation. A component of KIR negative signalling is recruitment of the protein tyrosine phosphatase SHP-1 to phosphorylated tyrosine residues within the receptor cytoplasmic domain. How SHP-1 functions to inhibit NK cell activation and whether additional signalling effector molecules also play roles in this process remain to be established. We have recently discovered that the protein tyrosine kinase (PTK), Csk, can also bind to tyrosine phosphorylated KIR. Csk recruitment by KIR provides an exciting basis for our future studies, since this PTK has the unique capacity to phosphorylate the regulatory tyrosine residues on receptor proximal PTKs of the Src family and terminate their activity. Such a novel negative signalling mechanism has not yet been identified for any inhibitory receptor, and we hypothesize that Csk recruitment provides KIR with capacity to dampen protein tyrosine phosphorylation-mediated activation events at an early stage. Additional data supports our hypothesis that phosphorylation status of the two individual tyrosine phosphorylation sites on KIR directly regulates effector enzyme binding profiles and functional outcomes. We propose to test our hypotheses with three specific aims: (1) to biochemically characterize Csk recruitment to KIR and its impact on PTKs of the Src family, (2) to determine the functional contributions of Csk recruitment on KIR inhibition of NK cell activation, and (3) to characterize the roles of the individual KIR tyrosines on inhibitory signalling responses. These studies will contribute substantially to our understanding of the mechanisms of KIR-mediated negative signalling. A better understanding of the mechanisms that dominantly regulate NK cell activation should ultimately allow for the development of therapeutic methods to beneficially manipulate their functions in therapies for cancer, viral infection, and prevention of tissue transplant rejection.