It is the goal of this project to determine how the interaction of mesothelial cells with the fiber carcinogen, asbestos, leads to the development of mesothelioma. We have previously shown that mesotheliomas over express PDGF-A. We have further shown that T antigen-immortalized human mesothelial cells become tumorigenic after transfection with an expression vector for PDGF-A. A mechanistic understanding of this tumorigenic conversion became problematic when it was reported that the PDGF-alpha receptor (PDGFR-alpha) was not expressed in mesothelioma cell lines. We have investigated the expression of the two receptors for PDGF. Results show that the PDGFR- alpha is expressed in mesotheliomas but at a level much below that of normal mesothelial cells. The levels of PDGFR-beta expression are not significantly different in tumor cells compared with normal mesothelial cells. In experiments with normal mesothelial cells which express the PDGF-alpha receptor at high levels, we showed that treatment with PDGF- A, as expected, decreased receptor expression. Treatment of mesothelioma (tumor) cells with suramin or antibody to PDGF-A increases PDGFR-alpha expression as does transient expression with antisense- PDGF-A. The finding that residual receptor is expressed suggests that this amount of receptor, when fully activated by autocrine ligand, may contribute significantly to oncogenic pathways of signal transduction. The possibility that high level expression of PDGF-A and PDGFR-alpha may be anti-proliferative has been explored. We have created mesothelioma clones stably expressing PDGF-A sense and anti-sense constructs as well as vector controls. In vitro experiments show that PDGFR-alpha levels are increased in the PDGF-A antisense clone relative to vector control or PDGF-A sense. In addition, we are creating an inducible system using the ecdysone inducible constructs from Stratagene. Receptor clones have been established in the mesothelioma cell line and PDGFR-alpha and control vector clones are currently being selected. Selected clones will be used in experiments to analyze dose dependent effects of receptor expression on proliferative potential and apoptotic death.Since these results do not explain how PDGF-A secretion enhances tumorigenicity, we tested the possibility that autocrine effects in vivo may account for the ability of PDGF-A to enhance tumorigenicity. The PDGF-A sense, antisense, and vector-control clones were inoculated into nude mice. In vivo results show that PDGF-A sense clones, compared to vector-control or PDGF-A antisense clones, cause tumors with shorter latencies and more rapid growth rates. These tumors are being analyzed for vascularity and necrosis to examine the hypothesis that the secretion of PDGF-A enhances tumorigenicity by stimulating angiogenesis. - Apoptosis, Asbestos, DNA damage, Mesothelioma, p, , p, , SV, , Growth factors, Regulation of Receptors, autocrine, - Human Tissues, Fluids, Cells, etc.
