Regulation of NK Cell Function by Vav-family Proteins

描述（由申请人提供）：Vav蛋白是鸟嘌呤核苷酸交换因子和分子接头，在淋巴细胞抗原受体的信号转导中起关键作用。最近的几项研究也表明Vav1与自然杀伤（NK）细胞介导的肿瘤细胞毒性有关。然而，Vav1是否影响所有NK细胞激活途径尚不清楚，可能有其他Vav家族分子参与NK细胞的触发。NK细胞通过多种具有不同结构、特异性和信号接头的激活受体识别肿瘤或病毒感染的细胞。激活NK细胞受体NKG2D识别主要在病毒感染细胞和肿瘤细胞中高水平表达的内源性主要组织相容性复合体（MHC） i类相关分子，而Ly49H介导对m157的选择性识别，m157是一种小鼠巨细胞病毒（MCMV）编码的i类分子，在感染细胞上表达。NKG2D和Ly49H都传递刺激信号，触发IFN-？释放含有穿孔素和颗粒酶的细胞毒性颗粒。然而，目前还不清楚这种刺激信号是如何在NK细胞内转导的。NKG2D和Ly49D/H缺乏细胞质信号元件，只能通过与跨膜接头蛋白结合来传递刺激信号。Ly49D和Ly49H通过DAP12（也称为KARAP）发出信号，DAP12含有免疫受体酪氨酸激活基元（ITAM），该基元被磷酸化，并作为Syk和ZAP70蛋白酪氨酸激酶的对接位点。相比之下，NKG2D通过DAP10发出信号，DAP10是一种独特的适配器，包含一个YxNM motif，可招募磷脂酰肌醇3-激酶（PI3-K）和Grb-2。

DESCRIPTION (provided by applicant): Vav proteins are guanine nucleotide exchange factors and molecular adaptors that play a key role in signal transduction of lymphocyte antigen receptors. Several recent studies have also implicated Vav1 in natural killer (NK) cell-mediated cytotoxicity of tumor cells. However, whether Vav1 effects all NK cell activating pathways is not known, and it is possible that other Vav family molecules are involved in NK cell triggering. NK cells recognize tumor or virally-infected cells through multiple activating receptors with diverse structures, specificities and signaling adaptors. The activating NK cell receptor NKG2D recognizes endogenous major histocompatibility complex (MHC) class I-related molecules expressed at high levels primarily in virally infected and tumor cells while Ly49H mediates selective recognition of m157, a murine cytomegalovirus (MCMV)-encoded class I-like molecule that is expressed on infected cells. Both NKG2D and Ly49H deliver stimulatory signals which trigger secretion of IFN-? and release of cytotoxic granules that contain perforin and granzymes. However, it is not know exactly how such stimulatory signals are transduced inside the NK cells. NKG2D and Ly49D/H lack cytoplasmic signaling elements and can deliver stimulatory signals only by associating with transmembrane adaptor proteins. Ly49D and Ly49H signal through DAP12 (also called KARAP) which contains immunoreceptor tyrosine-based activation motifs (ITAM) that are phosphorylated and function as docking sites for Syk and ZAP70 protein tyrosine kinases. In contrast, NKG2D signals through DAP10, a unique adapter that contains a YxNM motif which recruits phosphatidyl inositol 3-kinase (PI3-K) and Grb-2. As part of our preliminary studies for this proposal we generated mice lacking the individual, or all, Vavfamily proteins and began to examine the potential contribution of these proteins to NK cell cytotoxicity. Intriguingly, these data indicate that Vav is essential for DAP10- but not for DAP12-mediated natural cytotoxicity. Thus, these data suggest a new paradigm regarding the utilization of Vav in activation of natural cytotoxicity downstream of NK cell surface receptors associated with non-ITAM- vs. ITAM-containing adaptors. Here, we propose to use several in vitro and in vivo approaches to determine Vav mechanism in NK cell function and development of natural cytotoxicity against virally-infected and tumor cells.