Analysis of cellular function of Neurofibromatosis Type 2 tumor suppressor gene product (Merlin)

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The neurofibromatosis type 2 (NF2) is an autosomal dominantly inherited disorder, and strongly associated with development of benign intracranial tumors including bilateral vestibular schwannomas and meningiomas. NF2 gene was recently cloned, and the protein it encodes (termed as merlin/schwannomin) was found to be striking similarity to the moesin-ezrin-radixin (MER) family of cytoskeleton-associated proteins. To elucidate the biological function of NF2 protein (merlin), we analyzed the mutation pattern of merlin, its cellular localization, and the cellular signals via merlin. 1) NF2 gene mutations in NF2 patients were analyzed by protein truncation test. The majority of NF2 mutations are nonsense, frame shift, or exon-missing mutations. More than 70%of the mutations are clustered in the region encoding the N-terminal half of merlin. In addition, post-transrational proteolytic cleavage of N-terminal merlin by the ubiquitous protease calpain was found in some schwannomas and meningioma … More s. These results suggest that the N-terminal region of merlin is the most important for the tumor suppressive function, 2) Cellular expression systems of mutants or wild NF2 were established, and their cellular localization was analyzed by confocal lazer scanning Microscopy (CLSM). The wild merlin showed cytoplasmic and submembranous localization that was found to be directed by its nuclear export signal (NES) dependent transport mechanism. The N-terminal mutation resulted in nuclear accumulation of merlin. 3) Cellular binding proteins of merlin were purified from bovine brain extracts and identified as poly ADP-ribose polymerase, DNA-PK subunits Ku-antigen 85 and 70 by the analysis of their internal amino-acid sequences. The N-terminal(19-339) region of merlin is essential for their interaction. The immuno-precipitation, western blotting, and CLMS study confirmed their cellular co-localization. NF2 mutations impair the merlin-related complex formation and their cellular signal transport. This loss of cellular function of merlin may link to the intracranial tumor generation. Less