Abnormal cell proliferation is fundamental to the pathogenesis of many neurologic diseases. Platelet-derived growth factor (PDGF), the principal polypeptide mitogen in serum, may promote the abnormal cell proliferation that occurs in neural tumors, cerebrovascular atherosclerotic plaques, and vasospastic arteries after subarachnoid hemorrhage. PDGF stimulates cell proliferation by binding to a cell surface receptor. In tumors, this stimulation may be autocrine; cells which over-express PDGF may also have PDGF receptors. In atherosclerotic or vasospastic arterial walls, it is mainly paracrine: PDGF from endothelial cells or platelets may induce proliferation of nearby smooth muscle cells and fibroblasts. Little is known about the regulation of PDGF expression. The proposed research will study the control of PDGF expression and test methods of altering it. Preliminary work has identified tumor cell lines that constitutively over-express PDGF and has shown that endothelial cell expression of PDGF can be specifically enhanced by thrombin, TGF-beta, and phorbol esters and decreased by forskolin. The experimental strategy proposed is to compare the regulation of PDGF expression in tumor and endothelial cells, both in vitro and in vivo.
The specific aims are: 1) to identify the mechanisms of regulation of expression of PDGF in endothelial and tumor cells in vitro; 2) to determine the means by which some tumor cells escape normal regulatory mechanisms and constitutively express very high levels of PDGF; 3) to study PDGF autocrine and/or paracrine stimulation in tumors, atherosclerotic plaques, and vasopastic arteries in vivo; and 4) to determine whether expression of PDGF in vivo can be regulated by externally applied agents. Methods to be used include: Southern blotting, nuclear transcription run-on, and RNA solution hybridization-RNase protection assays to analyze nucleic acids from tumor and endothelial cell lines; PDGF binding, receptor activation, mitogenic and cell proliferation assays to measure growth factor production; and in situ mRNA hybridization and immunofluorescent antibody techniques to study PDGF expression and PDGF receptor activation in tissue sections of tumors, atheromas, and vasospastic arteries. Greater understanding of the regulation of PDGF expression should lead to novel therapies for CNS neoplasia, atherosclerosis, and vasospasm.
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