Identification of JAK family tyrosine kinases as receptor-associated signaling molecules for growth hormone (GH) receptors (GHR) and the many other members of the cytokine receptor superfamily was a major step forward in our understanding of the cellular basis for GH actions. Upon GH binding, GHR-associated JAK2 is activated and phosphorylates tyrosines within JAK2 itself and GHR. These phosphotyrosines form binding sites for a variety of signaling molecules whose recruitment to and/or activation by JAK2-GHR complexes initiates the signaling pathways that lead to the diverse physiological responses to GH. While some signaling molecules bind to phosphotyrosines within GHR, little is known about the signaling molecules that bind to phosphotyrosines within JAK2, despite the presence of 49 tyrosines within JAK2. SH2B1 (formerly known as SH2-B) is one of the few known JAK2 binding proteins. In response to GH, SH2B1 has been shown to bind to JAK2, be phosphorylated by JAK2 and under some circumstances, enhance GH-induced activation of JAK2. Independent of its ability to activate JAK2, SH2B1 enhances GH regulation of the actin cytoskeleton and cell motility. Finally, SH2B1 shuttles between the plasma membrane, cytoplasm and nucleus.
The aim of this proposal is to test the hypothesis that SH2B1 functions as a GH-regulated adapter/scaffolding protein that coordinates the movement of SH2B1 """"""""signaling complexes"""""""" to specific locations in the cell (e.g. plasma membrane, lamellopodia, nucleus) to enhance both GH regulation of the actin cytoskeleton and GH responses in the nucleus. Experiments in Aim 1 are designed to elucidate the mechanism by which SH2B1? reversibly binds to the plasma membrane.
Aim 2 will further define the role of SH2B1 in GH-mediated changes in cell morphology and motility. Factors determining SH2B1 localization to cytoskeletal complexes will be determined as will the potential for SH2B1? to mediate nuclear localization of a focal adhesion protein complex. The contributions of SH2B1 to GH-induced motility will be examined in primary macrophages and a GH-mediated model of breast cancer.
Aim 3 will examine the role of SH2B1 in regulating nuclear functions of GH, including potential roles in transcription factor/regulatory protein shuttling and facilitation of transcription. New SH2B1- sensitive, GH-dependent genes will be identified and tested in animal models. These studies will provide insight into the role of SH2B1 in the function of GH and the many other cytokines, hormones and growth factors (e.g. leptin, insulin, nerve growth factor) that also utilize SH2B1 as a signaling protein. Such insight is relevant to understanding the mechanism(s) by which GH elicits its diverse effects in the body, including body growth and metabolism, and other SH2B1 activating ligands contribute to, prevent and/or alleviate symptoms of a variety of diseases including various cancers, diabetes, multiple sclerosis, and diseases of the immune system.
These studies will provide insight into the role of the multifunctional adapter protein SH2B1 in the function of growth hormone and the many other cytokines, hormones and growth factors (e.g. leptin, insulin, nerve growth factor) that use SH2B1? to elicit some of their cellular effects. Such insight is critical to our understanding of how growth hormone brings about its well-known diverse effects in the body, including body growth and metabolism. These studies may therefore ultimately suggest ways to prevent and/or alleviate symptoms of a variety of disease, including various cancers, diabetes, obesity, multiple sclerosis, and immune diseases
