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

Abstract

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.