Molecular Mechanisms by Which Adapter Protein SH2B1(beta) Facilitates NGF-Dependent Neuronal Differentiation.

[摘要] Nerve Growth Factor (NGF) has long been recognized as a critical factor in the survival and maintenance of sympathetic neurons.Recent findings have shown that NGF is also required for the sympathetic neuron’s axonal growth and appropriate target organ innervation during development.However, the molecular mechanisms by which NGF elicits these effects are largely unknown.The ubiquitously expressed adapter protein SH2B1 binds to active NGF receptor TrkA and has been implicated in NGF-mediated differentiation and survival of sympathetic neurons.This work provides evidence that SH2B1β facilitates the NGF-dependent nuclear export of FoxO1, a pro-apoptotic transcription factor.While SH2B1 was originally thought to localize and function only at the cell membrane, more recent studies indicated that SH2B1β undergoes nucleocytoplasmic shuttling.The work described in this thesis identifies a functional nuclear localization sequence and provides evidence that nuclear cycling of SH2B1β is critical to promote NGF-mediated differentiation of the preneuronal PC12 cell line.SH2B1β was found to specifically enhance the NGF-induced transcription of a primary response gene required for neuronal differentiation, urokinase plasminogen activator receptor (uPAR).Preventing translocation either into or out of the nucleus abolished the ability of SH2B1β to enhance the transcription of uPAR in response to NGF.Similarly, NGF-dependent neurite outgrowth was inhibited in PC12 cells stably expressing a nuclear import defective SH2B1β.Knocking down endogenous levels of SH2B1 inhibited the NGF-induced transcription of uPAR as well as NGF-dependent neurite outgrowth, suggesting that endogenous SH2B1 is required for both NGF-dependent gene expression and neurite outgrowth.TAP tagged-SH2B1β was used to identify nuclear binding partners of SH2B1, including a putative transcription factor that inhibits NGF-dependent neurite outgrowth.Taken together, these results suggest a nuclear role for SH2B1β during NGF-dependent differentiation and survival.The ability of SH2B1β to influence the subcellular localization of FoxO1 and bind to and counteract the function of a novel transcription factor raises the possibility SH2B1β cycling between the nucleus and cytoplasm is required to shuttle transcription factors into or out of the nucleus.

[发布机构] University of Michigan

[效力级别] SH2-B

[关键词] SH2B1;SH2-B;Nerve Growth Factor;Neuronal Differentiation;Molecular;Cellular and Developmental Biology;Science;Cellular & Molecular Biology