Identification of SH2-B as a signaling molecule for growth hormone, platelet-derived growth factor and nerve growth factor.

Polypeptide hormones and growth factors regulate a variety of vital activities via binding and activating their cognate cell surface receptors which in turn recruit intracellular signaling molecules and transmit signals inside cells. In this dissertation, SH2-B is identified as an important intracellular signaling protein for growth hormone (GH), platelet-derived growth factor (PDGF) and nerve growth factor(NGF). SH2-B was found to be phosphorylated in response to GH, PDGF and NGF. However, the mechanisms by which SH2-B was phosphorylated are different among these polypeptide hormones and growth factors. GH stimulates activation of JAK2, and promotes association of SH2-B with JAK2 and tyrosyl phosphorylation of SH2-B by JAK2 in 3T3-F442A fibroblasts. PDGF stimulates the binding of SH2-B directly to tyrosyl phosphorylated PDGF receptor, and promotes the phosphorylation of SH2-B on both tyrosines and serines and/or threonines in 3T3-F442A and NIH3T3 cells. NGF stimulates phosphorylation of SH2-B predominantly on serines and/or threonines via a MEK-dependent pathway in PC12 cells. SH2-B was found to play an essential role in PDGF-induced actin rearrangement including membrane ruffling, and is required for NGF-induced neurite outgrowth in which actin cytoskeletal rearrangement is thought to be a driving force. The SH2 domain of SH2-B was found to be vital for SH2-B binding to JAK2 and PDGF receptor as well as for its phosphorylation by JAK2 and NGF stimulation. The SH2 domain is also required for the action of SH2-B in GH- and PDGF-stimulated membrane ruffling and NGF-induced neurite outgrowth. These data indicate that SH2-B is a crucial, previously unknown signaling molecule involved in the regulation of the actin cytoskeleton and cell morphology by polypeptide hormones and growth factors including GH, PDGF and NGF.Ph.D.BiochemistryBiological SciencesCellular biologyMolecular biologyNeurosciencesPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131319/2/9840641.pd