IMPAIRMENT OF CELL-ADHESION BY EXPRESSION OF THE MUTANT NEUROFIBROMATOSIS TYPE-2 (NF2) GENES WHICH LACK EXONS IN THE ERM-HOMOLOGY DOMAIN

Neurofibromatosis 2 (NF2) is an inherited disorder characterized by a predisposition to multiple intracranial tumors. The protein encoded by the NF2 gene has striking similarities to ezrin, radixin and moesin ( ERM) proteins which link membrane proteins to the cytoskeleton, Theref ore, it can be speculated that the disruption of cytoskeletal organiza tion by alterations in the Nn gene is involved in the development of t umors. It has been reported that the majority of NF2 mutations were no nsense or frameshift mutations that result in premature termination of translation. To facilitate the detection of these mutations, we perfo rmed protein truncation test and found that 11 of 14 NF2 patients had truncational mutations (79%). Seven of the 11 patients (64%) had a spl icing abnormality which lead to absence of exons in the ERM homology d omain. To examine the biological significance of the exon-missing muta tions in the ERM homology domain, we expressed the wild-type (wt-NF2) and the various mutant NF2s (mu-NF2s) in a fibroblast cell line by usi ng both liposome-mediated transfection and nuclear microinjection of t he expression plasmids, The wt-NF2 showed intense punctate staining in the perinuclear cytoplasm in addition to overall staining of the subm embranous area, whereas the mu-NF2s lacking exons in the ERM homology domain showed granular staining at the perinuclear region without any accumulation at the submembrane region. Microinjection of wt-NF2 cDNA into the nucleus of VA13 cells revealed that wt-NF2 protein induced a progressive elongation of cell processes. Furthermore, cells that expr essed mu-NF2 had decreased adhesion, which resulted in detachment from the substratum. These findings suggested that the exon-missing mutati ons in the ERM-homology domain may affect cell membrane-cytoskeleton s ignaling and consequently disrupt cell-to-cell or cell-to-matrix inter action.