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

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.