Novel Mechanisms of C-Kit Regulation in Mast Cells

描述（由申请人提供）：肥大细胞激活在哮喘和过敏中起重要的病理生理作用。肥大细胞活化在多发性硬化症、类风湿性关节炎和冠状动脉疾病中也有作用。然而，最近的研究挑战了肥大细胞活化的病理作用的教条，表明其在对致病菌的先天免疫的早期阶段起着突出作用。这些观察结果使我们对肥大细胞生物学的理解比以往任何时候都更加重要。虽然多种细胞因子影响肥大细胞的生长、存活和成熟，但干细胞因子（SCF）及其通过酪氨酸激酶受体的相互作用，c-Kit对正常肥大细胞的发育和功能至关重要。缺乏c-Kit表达的小鼠缺乏肥大细胞，对诱导的细菌感染表现出更高的死亡率。因此，尽管c-Kit和IgE受体启动信号在调节肥大细胞正常发育和功能方面的重要作用已被证明，但这些受体下游调节这些过程的信号通路尚不清楚。识别通过这些受体参与调节肥大细胞发育和功能的关键细胞内信号分子和途径，将有助于设计治疗肥大细胞疾病的特异性分子疗法，包括与c-Kit功能获得性突变相关的人类肥大细胞增多症、慢性炎症、过敏以及促进对细菌感染的免疫。我们的长期目标是了解从细胞因子受体和免疫受体下游控制肥大细胞功能的信号机制。本应用程序的目的是确定SHIP磷酸酶、Lyn Src家族激酶和IA类PI-3Kinase的p85调节亚基（a和b）如何相互作用以调节肥大细胞分化、生长/存活以及细胞因子的产生和脱颗粒。该应用的中心假设是基于我们的初步数据制定的，即Lyn激酶对肥大细胞中SHIP磷酸酶的激活至关重要。在SHIP磷酸化缺失的情况下（由于缺乏Lyn表达），肥大细胞表现出对scf诱导的存活、生长和分化的超敏反应，以及IgE受体诱导的脱颗粒和细胞因子产生的增强。这些表型是由于PI-3Kinase/Akt通路的过度激活。此外，IA类PI-3Kinase的p85ct和p85b|3调节亚基在调节肥大细胞功能中发挥了不同的定量作用。这些差异是由于在p85a和（p85bbbb3）中存在独特的氨基末端序列。我们提出的研究将为IA类PI-3Kinase的SHIP， Lyn和p85调节亚基在调节肥大细胞生物学各方面的体内相互作用的生理学意义提供独特的见解。

DESCRIPTION (provided by applicant): Mast cell activation plays a critical pathophysiologic role in asthma and allergy. A role for mast cell activation has also been described in multiple sclerosis, rheumatoid arthritis and coronary artery disease. However, recent studies challenge the dogma of a pathological role for mast cell activation, demonstrating its prominent role in the early phases of innate immunity to pathogenic bacteria. These observations make our understanding of mast cell biology more crucial than ever. While several cytokines influence the growth, survival, and maturation of mast cells, stem cell factor (SCF) and its interaction via the tyrosine kinase receptor, c-Kit is essential for normal mast cell development and function. Mice deficient in the expression of c-Kit lack mast cells and exhibit enhanced mortality to induced bacterial infections. Thus, although an important role for c-Kit and IgE receptor initiated signals in regulating normal development and function of mast cells has been demonstrated, the signaling pathways downstream from these receptors that regulate these processes are poorly understood. Identification of key intracellular signaling molecules and pathways involved in regulating the development and function of mast cells via these receptors will facilitate the design of specific molecular therapies for the treatment of mast cell disorders, including human mastocytosis associated with gain-of-function mutations of c-Kit, chronic inflammation, allergy as well as for promoting immunity to bacterial infections. Our long-range goal is to understand the signaling mechanism(s) that control mast cell functions downstream from cytokine receptors as well as immunoreceptors. The objective of this application is to determine how SHIP phosphatase, Lyn Src family kinase and p85 regulatory subunits (a and b) of class IA PI-3Kinase interact to regulate mast cell differentiation, growth/survival as well as cytokine production and degranulation. The central hypothesis of this application, which has been formulated on the basis of our preliminary data, is that Lyn kinase is critical for the activation of SHIP phosphatase in mast cells. In the absence of SHIP phosphorylation (due to lack of Lyn expression) mast cells demonstrate hypersensitivity to SCF-induced survival, growth and differentiation as well as enhanced IgE receptor induced degranulation and cytokine production. These phenotypes are due to hyperactivation of the PI-3Kinase/Akt pathway. Furthermore, p85ct and p85|3 regulatory subunits of class IA PI-3Kinase play quantitatively distinct roles in regulating mast cell functions. These differences are due to the presence of unique amino terminal sequences in p85a vs (p85|3). Our proposed studies will provide unique insights into the physiologic significance of the in vivo interactions between SHIP, Lyn and p85 regulatory subunits of class IA PI-3Kinase in regulating all aspects of mast cell biology.