Tumor invasion is potentiated by adhesive interactions between tumor cells and extracellular matrix proteins. We have recently demonstrated that the adhesive protein vitronectin (VN) is a marker of highly malignant astrocytomas, also known as glioblastoma (GBM) tumors and potentiates cellular adhesion events in these tumors. The overall goals of this research are to determine if VN or its receptors can be used in the diagnosis of GBM tumors, and to characterize the molecular basis of VN-mediated adhesion and its significance in the proliferation of, and local invasion by, GBM tumors. Recent data has demonstrated VN mRNA both in human GBm tumors and in tumors. In addition, we have identified expression of the avB3 and the avB5 VN receptor intergrins in GBM tumors. In contrast, normal adult brain glial cells failed to express protein or mRNA for intergrins avB3 and avB5, suggesting that these VN receptor intergrins are induced in transformed glial cells and that this regulation occurs at the level of transcription. Our mapping of mRNA and protein expression for the avB3 and avB5 receptor intergrins in GBM tumors has demonstrated distinct cellular localizations, implying they serve discrete functions in situ. This proposal will focus on three specific objectives. First, to determine the source of VN in GBM tumors employing in situ hybridization and immunohistochemical analysis of glioma biopsies, including GBM tumor biopsies VN receptor intergrins expressed on various grade glial tumor biopsies and an intracerebral athymia nude mouse model of human GBM tumors. Second, to characterize the repertoire of VN receptor intergrins expressed on various grade glial tumor biopsies and on cultured cell lines by immunochemical and in situ hybridization analyses. The results on the differential expression of VN and its receptors will be used to determine if they can be used as markers of the malignant glial cell. In addition, the function of the identified VN receptor integrins in GBM tumor cell adhesion and motility will be determined. Third, the role of the VN receptor integrins in the biologic properties of GB tumors will be investigated. The cDNA encoding the beta3 subunit of the VN receptor will be transfected into a GBN cell line that proliferates minimally in vivo and is deficient in this gene product, and in addition a GBM cell line deficient in the av subunit VN receptor gene product will be selected. These will be characterized in vitro, analyzed for in vivo proliferation, reculture and characterized in vitro. GBM tumors are diagnosed in approximately 9,000 individuals per year and they have an increased incidence in the fifth and sixth decades, as well as an extremely poor prognosis (100% mortality). This project is designed to determine the molecular basis for GBM tumor cell adhesion, proliferation, motility and tumor invasiveness. As such, basis for the design of a therapeutic strategy for this disease. As adhesive interactions between proliferating cells and extracellular matrix proteins are of relevance to embryonic cell proliferation, the findings from this research will be of significance to understanding integrin function in situ in brain development.
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