Phosphorylation of neurofibromatosis type 1 gene product (neurofibromin) by cAMP‐dependent protein kinase

Abstract
The critical function of the neurofibromatosis type 1 NF1) gene product (neurofabromin) is not well defined except that neurofibromin has homology with a family of the GTPase‐activating proteins (GAPs). In this study, we confirmed that neuofibromin is constitutively phosphorylated and detected kinase activities which specifically phosphorylated the cysteine/serine‐rich domain and the C‐terminal domain of the neurofibromin in cell lysate. In vitro and in‐gel kinase assays strongly indicated that cAMP‐dependent protein kinase (PKA) is a candidate for the neurofibromin kinase. The biological significance for the phosphorylation of neuofibromin is unclear at present, but we speculate that neurofibromin plays a crucial role in cellular function since it links the two major cellular pathways which are the GAP‐rins and PKA‐associated signals.

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