GROWTH HORMONE REGULATION OF SH2B

在理解膜受体的信号转导方面，最近最令人兴奋的进展之一是酪氨酸激酶JAK家族作为生长激素（GH）受体和细胞因子/造血素受体超家族的许多其他成员的受体相关信号分子的鉴定。GH结合后，GH受体相关的JAK2被激活并磷酸化JAK2自身和GH受体内的酪氨酸。这些磷酸酪氨酸形成各种信号分子的结合位点，这些信号分子被JAK2-GH受体复合物募集和/或激活，启动信号通路，最终导致对GH的各种生理反应。一些信号分子与生长激素受体内的磷酸酪氨酸结合。然而，尽管JAK2中存在多个（49）酪氨酸，但对JAK2中与磷酸酪氨酸结合的信号分子知之甚少。利用酵母2-杂交系统鉴定了SH2- b的一个新的剪接变体（SH2- Bbeta）作为JAK2结合蛋白。在对GH的反应中，sh2 - β与JAK2结合并被酪氨酸磷酸化。初步研究还表明sh2 - β刺激JAK2自磷酸化并介导GH诱导的肌动蛋白聚合的变化。本研究的目的是验证SH2-Bbeta作为JAK2的激活因子和JAK2- gh受体复合物信号分子的适配分子的功能，这些分子调节细胞骨架。具体来说，JAK2结合并酪氨酸磷酸化SH2- β的机制将被阐明。JAK2-SH2-Bbeta复合体形成所需的JAK2和SH2-Bbeta区域以及SH2-Bbeta中被JAK2磷酸化以响应GH的酪氨酸将被确定。SH2-Bbeta增强gh刺激的JAK2活性的能力将被检验。将确定与富含脯氨酸的SH2-Bbeta的n端一半和SH2-Bbeta的磷酸化酪氨酸结合的信号分子。最后，我们将确定SH2-Bbeta下游的细胞反应，最初的重点是确定可能介导GH诱导的细胞骨架变化的途径。这些研究将深入了解SH2-Bbeta在GH和其他细胞因子、激素和生长因子（如干扰素- γ、胰岛素、血小板衍生生长因子）的功能中的作用，这些细胞因子、激素和生长因子也利用SH2-Bbeta作为信号分子。这种见解与理解GH调节身体生长和代谢的机制有关，其他SH2-Bbeta激活配体有助于预防和/或减轻各种疾病的症状，包括各种癌症、糖尿病、多发性硬化症、各种发育异常、免疫和造血系统疾病。

One of the most exciting recent advances in understanding signal transduction by membrane receptors is the identification of the JAK family of tyrosine kinases as receptor-associated signaling molecules for growth hormone (GH) receptors and the many other members of the cytokine/hematopoietin receptor superfamily. Upon GH binding, GH-receptor-associated JAK2 is activated and phosphorylates tyrosines within JAK2 itself and GH receptor. These phosphotyrosines form binding sites for a variety of signaling molecules whose recruitment to and/or activation by JAK2-GH receptor complexes initiates the signaling pathways that ultimately lead to the diverse physiological response to GH. Some signaling molecules bind to phosphotyrosines within GH receptor. However, little is known about the signaling molecules that bind to phosphotyrosines within JAK2, despite the presence of multiple (49) tyrosines within JAK2. The yeast 2-hybrid system was used to identify a new splicing variant of SH2-B (SH2- Bbeta) as a JAK2 binding protein. In response to GH, SH2-Bbeta binds to JAK2 and is tyrosyl phosphorylated. Prelim studies also suggest that SH2-Bbeta stimulates JAK2 autophosphorylation and mediates GH induced changes in actin polymerization. The aim of this proposal is to test the hypothesis that SH2-Bbeta functions both as an activator of JAK2 and as an adapter molecule that recruits to activated JAK2-GH receptor complexes signaling molecules that regulate the cytoskeleton. Specifically, the mechanism by which JAK2 binds to and tyrosyl phosphorylates SH2- Bbeta will be elucidated. Regions of JAK2 and SH2-Bbeta required for JAK2-SH2-Bbeta complex formation and tyrosines within SH2- Bbeta that are phosphorylated by JAK2 in response to GH will be determined. The ability of SH2-Bbeta to enhance GH-stimulated JAK2 activity will be examined. Signaling molecules that bind to both the proline-rich, N-terminal half of SH2-Bbeta and to the phosphorylated tyrosines in SH2-Bbeta will be identified. Finally, cellular responses that lie downstream of SH2-Bbeta will be identified, with an initial emphasis on identifying pathways that may mediate GH- induced changes in the cytoskeleton. These studies will provide insight into the role of SH2-Bbeta in the function of GH and other cytokines, hormones and growth factors (e.g. interferon-gamma, insulin, platelet-derived growth factor) that also utilize SH2-Bbeta as a signaling molecule. Such insight is relevant to understanding the mechanisms by which GH regulates body growth and metabolism, and other SH2-Bbeta activating ligands contribute to, prevent and/or alleviate symptoms of a variety of diseases, including various cancers, diabetes, multiple sclerosis, various developmental abnormalities, and diseases of the immune and hematopoietic systems.