Abstract
The adapter protein SH2B1 (SH2-B, PSM) is recruited to multiple ligand-activated receptor tyrosine kinases, including the receptors for nerve growth factor (NGF), insulin, and IGF-I as well as the cytokine receptor-associated Janus kinase family kinases. In this study, we examine SH2B1's function in NGF signaling. We show that depleting endogenous SH2B1 using short hairpin RNA against SH2B1 inhibits NGF-dependent neurite outgrowth, but not NGF-mediated phosphorylation of Akt or ERKs 1/2. SH2B1 has been hypothesized to localize and function at the plasma membrane. We identify a nuclear localization signal within SH2B1 and show that it is required for nuclear translocation of SH2B1beta. Mutation of the nuclear localization signal has no effect on NGF-induced activation of TrkA and ERKs 1/2 but prevents SH2B1beta from enhancing NGF-induced neurite outgrowth. Disruption of SH2B1beta nuclear import also prevents SH2B1beta from enhancing NGF-induced transcription of genes important for neuronal differentiation, including those encoding urokinase plasminogen activator receptor, and matrix metalloproteinases 3 and 10. Disruption of SH2B1beta nuclear export by mutation of its nuclear export sequence similarly prevents SH2B1beta enhancement of NGF-induced transcription of those genes. Nuclear translocation of the highly homologous family member SH2B2(APS) was not observed. Together, these data suggest that rather than simply acting as an adapter protein linking signaling proteins to the activated TrkA receptor at the plasma membrane, SH2B1beta must shuttle between the plasma membrane and nucleus to function as a critical component of NGF-induced gene expression and neuronal differentiation.