Study on cellular signal transduction of Neurofibromatosis Type 1 and Type 2 tumor suppressor gene products

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The neurofibromatosis type 1 (NF1) and type 2 (NF2) are autosomal dominantly inherited disorders, and strongly associated with development of intracranial tumors including bilateral vestibular schwannomas, meningiomas and gliomas. NF1 and NF2 genes were recently identified on the different locus, and the proteins they encode (termed as neurofibromin for NF1 and merlin for NF2) were found to be no homologies despite of their pathological similarity. To elucidate the biological function of NF1 and NF2 proteins, we analyzed their signal transductions by cellular proteomic and biological strategies. 1)NF1 : Neurofibromin has a domain acting as a GAP and thought to be an important Ras regulator. We identified 35 novel cellular neurofibromin-associating proteins. 14-3-3 was identified as one of the most interesting core candidates of NF1 regulators. The interaction of 14-3-3 is mainly directed to the C-terminal domain (CTD) of neurofibromin, and the cAMP-dependent protein kinase (PKA)-depend … More ent phosphorylation clustered on CTD-Ser (2576, 2578, 2580, 2813) and Thr (2556) is required for the interaction. Interestingly, the increased phosphorylation and association of 14-3-3 negatively regulate the GAP activity of neurofibromin. These findings indicate that PKA phosphorylation followed by 14-3-3 protein and other protein cluster interactions may modulate the biochemical and biological functions of cellular neurofibromin. 2)NF2 ; Cellular binding proteins of merlin were identified as poly ADP-ribose polymerase, DNA-PK subunits Ku-antigen 85 and 70 by MAS spec analysis. The N-terminal (19-339) region of merlin is essential for their interaction. Subcellular co-localizations of merlin and PARP were observed mainly in their nuclear region with a nuclear export signal (NES) dependent manner of merlin. This nuclear accumulation increased with cellular DNA damages, whereas PARP gene deficient MEF could not accumulate merlin in their nuclear region, even after the treatments of LMB or bleomycin, These results suggest that merlin is a cytoplasmic-nuclear shuttling protein directed by its NES-dependent transport pathway being associated with PARP. The tumor suppressive function of merlin may be linked to cellular DNA-repair and related signals via the interaction of cellular merlin binding proteins such as PARP and DNA-PKs. Less