Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome that occurs in about 1 out of 6000 live births. Patients with TSC suffer pain, disability, and death from tumors in multiple organs. Skin tumors are frequent, numerous, permanent, and disfiguring. Our long-term goal is to determine the molecular and genetic bases for these tumors. Tumor susceptibility is inherited as a mutation in the TSC2 tumor suppressor gene (or less commonly, the TSC1 gene). Tumors may form as a result of a second mutation eliminating the normal TSC2 allele. Using interphase fluorescence in situ hybridization (I-FISH), we have demonstrated that TSC skin tumors contain a genetically altered neoplastic cell population, marked by allelic deletion of TSC2. These "two-hit" neoplastic cells make up a minority of the cells. This suggests that a major mechanism of TSC tumorigenesis is not rapid proliferation of neoplastic cells, but instead that neoplastic cells induce proliferation of surrounding cells. We hypothesize that TSC neoplastic cells induce proliferation of endothelial cells and fibroblasts by release of soluble factors, and that the surrounding fibroblasts, heterozygous for TSC2, likewise support the growth of the neoplastic cells. The specific aims are: 1) to identify the location and morphology of neoplastic cells in TSC skin tumors by loss of heterozygosity studies on laser microdissected material, 2) to identify soluble factors over-expressed in TSC skin tumors using gene chip arrays combined with protein quantitation, and 3) to determine the effects of soluble factors on TSC tumorigenesis using in vitro assays. These studies focus on the cell-cell interactions that are clearly pertinent for the growth of TSC tumors and that result in the increased blood vessels and collagen formation. The elucidation of growth factors involved in these processes will provide molecular targets for the design of new therapies. [unreadable] [unreadable]