Neurofibromatosis 2 (NF2) is a debilitating and devastating genetic disorder in which affected individuals develop multiple tumors on nerves and in the brain and spinal cord. The two most commonly occurring tumors are schwannomas and meningiomas. Approximately 50% of NF2 patients have meningiomas in the brain and a large proportion of these are multiple meningiomas. NF2 patients with these meningiomas die sooner than those without meningiomas. Thus, meningiomas are a significant problem for NF2 patients. NF2 is caused by mutations in the NF2 gene. Meningiomas that occur spontaneously also contain NF2 mutations, suggesting that the NF2 gene and the protein that it forms, merlin, is very important for the development of these tumors. An understanding of the mechanisms by which loss of merlin contributes to the development of meningiomas and other tumors is essential for the development of novel and more directed therapies.

A survey of the literature reveals certain key findings. First, even though a considerable amount has been learned about the function of merlin over the past decade, most of these studies have been done on schwannoma cells or on cell types unrelated to NF2. The relevance of these findings to meningioma tumor growth is unclear. Since genetic defects that cause some cells to form cancer are harmless in other cells, it is important that we study the function of merlin in meningioma cells and the cell type that they arise from, the arachnoidal cell. Second, there are strong indications that merlin has specific functions in meningiomas. Missense mutations that change the identity of a specific amino acid usually result in schwannomas and not meningiomas, while meningiomas usually have mutations that result in a shorter protein or no protein. Also, during the development of meningiomas, merlin does not cooperate with p53, another gene important in cancer, to form a more aggressive cancer, while merlin does cooperate with p53 during the development of schwannomas. These observations suggest that merlin function is unique in meningiomas. One of the major problems with studying the function of merlin in meningiomas is the lack of appropriate model systems, and one reason for this is that meningioma cells are very difficult to grow in culture. We have preliminary data showing that we can make meningioma cells grow continuously in culture by inserting certain genetic changes. Also, we have successfully grown human arachnoidal cells from pieces of tissue removed during surgery. These cells form an invaluable tool to investigate the role of merlin in meningiomas.

The goal of this study is to develop more sophisticated model systems of merlin in meningiomas and to use these model systems to understand how loss of merlin causes a meningioma to form. We will, first, identify meningioma cells that do not have merlin and insert merlin into these cells. We will investigate the consequences of merlin expression on the growth and survival of these cells. Second, we will abolish the expression of merlin in arachnoidal cells and will see if merlin loss causes an arachnoidal cell to become a cancerous meningioma cell. Finally, we will use gene expression technology to identify new genes that are regulated by merlin in meningiomas and arachnoidal cells. This part of the proposal will help us understand, at a molecular level, the reasons for merlin's effects on tumor growth.

NF2 patients are in dire need of new treatments. These studies will significantly increase our knowledge about the molecular basis of merlin function and potentially identify new targets for the design of novel therapeutic approaches. It will also provide model systems that could serve as preclinical models for testing the efficacy of new treatment strategies.