in about 50% of sporadic meningiomas, including those tumors that do not harbor mutations in the NF-2 gene. Interestingly, alterations in NF-2 gene and protein expression were rarely found in the meningothelial meningioma variant, suggesting the existence of other meningioma susceptibility gene(s).

In spite of intense study of NF-2 gene functions, the molecular mechanisms that enable the NF-2 protein to function as a tumor suppressor are largely unknown. As a member of the band-4.1 superfamily of proteins, the NF-2 protein is considered important in the regulation of actin cytoskeleton and in interactions between cyto-plasmic proteins and membranes. A possible physiological role of the NF-2 protein was suggested by its antiproliferative effect on some cell types, including meningioma cells. The NF-2 protein has also been shown to modulate cellular adhesion [38]. Further clues about NF-2 protein functions come from identification of cellular proteins that physically interact with the NF-2 protein. The list of NF-2 protein-interacting molecules includes:

II-spectrin, an actin-binding protein, extracellular matrix receptor (31-integrin, and regulatory cofactor for an Na+/H+ exchanger. It is, therefore, possible that mutated/inactivated NF-2 protein contributes to meningioma tumorigenesis by impairing signal transduction from the extracellular matrix and/or ion channels to the cytoskeleton, and thus deleteriously alters molecular pathways that control cell differentiation, growth and survival. In addition, naturally occurring mutant forms of NF-2 protein, but not the full-length NF-2 protein that exhibits growth-suppressive activity, physically interact with a novel coiled-coil protein of unknown function, termed "SCHIP-1" [39]. Clearly, the NF-2 protein is a tumor suppressor that is regulated in a complex manner to control diverse biological functions.

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