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Regulation of the Ras‐GTPase activating protein neurofibromin by C‐tail phosphorylation: implications for protein kinase C/Ras/extracellular signal‐regulated kinase 1/2 pathway signaling and neuronal differentiation
Authors:George Leondaritis  Loizos Petrikkos  Dimitra Mangoura
Affiliation:Neurosciences, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
Abstract:PKC, Ras, and ERK1/2 signaling is pivotal to differentiation along the neuronal cell lineage. One crucial protein that may play a central role in this signaling pathway is the Ras GTPase‐activating protein, neurofibromin, a PKC substrate that may exert a positive role in neuronal differentiation. In this report, we studied the dynamics of PKC/Ras/ERK pathway signaling, during differentiation of SH‐SY5Y neuroblastoma cells upon treatment with the PKC agonist, phorbol ester 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA). Surprisingly, we observed that, among other PKC‐dependent signaling events, TPA induced a rapid and sustained decrease of neurofibromin immunoreactivity which was not due to proteolysis. Instead, we identified a specific phosphorylation event at the C‐tail of neurofibromin. This phosphorylation was acute and correlated perfectly with the signaling dynamics of the Ras/ERK pathway. Moreover, it persisted throughout prolonged treatment and TPA‐induced differentiation of SH‐SY5Y cells, concurrently with sustained activation of ERK1/2. Most importantly, C‐tail phosphorylation of neurofibromin correlated with a shift of neurofibromin localization from the nucleus to the cytosol. We propose that PKC‐dependent, sustained C‐tail phosphorylation is a requirement for prolonged recruitment of neurofibromin from the nucleus to the cytosol in order for a fine regulation of Ras/ERK pathway activity to be achieved during differentiation.
Keywords:adaptin  differentiation  drebrin  epitope masking  metabolic labeling  neurofibromatosis  PKCα  
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