Regulation of the hematopoietic-cell transmembrane phosphatases CD45 and CD148

描述（由申请人提供）：CD45和CD148是调节抗原受体信号传导的跨膜酪氨酸磷酸酶，因此强烈影响哺乳动物免疫应答的敏感性。它们通过使Src家族激酶的C末端尾部去磷酸化来增强信号转导，从而释放自身抑制相互作用并允许激酶活化。然而，高水平的这些磷酸酶会减弱信号传导。调节CD45和CD148的分子机制尚不清楚。有证据表明，CD45是抑制二聚体，但一些研究表明，一个无活性的假磷酸酶域，存在于CD45，但不存在于CD148，可能会干扰二聚体的形成。使用纯化的胞质结构域的CD45和CD148定位到人工膜，我将检查是否二聚抑制磷酸酶活性。我将研究如何假磷酸酶域有助于CD45功能，通过测试它是否阻止二聚化，拴系底物，或作为一个变构调节磷酸化。最后，我将通过确定它们是否在细胞表面异源二聚化来检查细胞中CD 45和CD 148之间存在直接相互作用的可能性。了解控制造血细胞活化和增殖的磷酸酶的调节机制对于理解免疫应答的敏感性和控制机制将是重要的。公共卫生相关性：酪氨酸磷酸酶蛋白CD45和CD148在免疫系统的细胞中以高水平存在，并且对于控制免疫应答的敏感性是重要的。已经提出CD45中的突变与人类和小鼠中的几种自身免疫性疾病相关，包括狼疮、格雷夫斯病、自身免疫性淋巴细胞增生和多发性硬化症。CD148在几种细胞类型中抑制细胞生长和癌症，但其在免疫系统细胞中的功能尚不清楚。了解这些信号蛋白的调节将有助于我们更好地理解维持免疫细胞适当生长模式和敏感性所必需的信号平衡

DESCRIPTION (provided by applicant): CD45 and CD148 are transmembrane tyrosine phosphatases that regulate antigen-receptor signaling and thus strongly influence the sensitivity of the mammalian immune response. They potentiate signal transduction by dephosphorylating the C-terminal tail of the Src-family kinases, which releases autoinhibitory interactions and allows kinase activation. High levels of these phosphatases, however, attenuate signaling. The molecular mechanisms by which CD45 and CD148 are regulated are unclear. There is evidence that CD45 is inhibited by dimerization, but some studies suggest that an inactive pseudophosphatase domain, present in CD45 but not in CD148, may interfere with dimer formation. Using the purified cytoplasmic domains of CD45 and CD148 localized to artificial membranes, I will examine whether dimerization inhibits phosphatase activity. I will investigate how the pseudophosphatase domain contributes to CD45 function by testing whether it blocks dimerization, tethers substrates, or serves as an allosteric modulator upon phosphorylation. Finally, I will examine the possibility that there are direct interactions between CD45 and CD148 in cells by determining whether they heterodimerize on the cell surface. Understanding the regulatory mechanisms of the phosphatases that control the activation and proliferation of hematopoietic cells will be important for understanding the sensitivity and control mechanisms of the immune response. Public Health Relevance: The tyrosine phosphatase proteins CD45 and CD148 are found at high levels in the cells of the immune system and are important for controlling the sensitivity of the immune response. Mutations in CD45 have been proposed to be associated with several autoimmune diseases in humans and mice, including lupus, Graves disease, autoimmune lymphoproliferation, and multiple sclerosis. CD148 suppresses cell growth and cancer in several cell types, but its function in the cells of the immune system is not yet clear. Understanding the regulation of these signaling proteins will help us better understand the balance of signals necessary for maintaining appropriate growth patterns and sensitivity in immune cells