ABSTRACT
Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer and other proliferative disorders. We have recently isolated and characterized a novel protease-activated member of the PDGF family, PDGF D. PDGF D has been shown to be proliferative for cells of mesenchymal origin, signaling through PDGF receptors. Comprehensive and systematic PDGF D transcript analysis revealed expression in many cell lines derived from ovarian, renal, and lung cancers, as well as from astrocytomas and medulloblastomas. beta PDGF receptor profiling further suggested autocrine signaling in several brain tumor cell lines. PDGF D transforming ability and tumor formation in SCID mice was further demonstrated. Exploiting a sensitive PDGF D sandwich ELISA using fully human monoclonal antibodies, PDGF D was detected at elevated levels in the sera of ovarian, renal, lung, and brain cancer patients. Immunohistochemical analysis confirmed PDGF D localization to ovarian and lung tumor tissues. Together, these data demonstrate that PDGF D plays a role in certain human cancers.
Subject(s)
Neoplasms/metabolism , Platelet-Derived Growth Factor/physiology , 3T3 Cells , Animals , Cell Transformation, Neoplastic , Humans , Immunohistochemistry , Mice , Mice, SCID , Neoplasms/blood , Neoplasms/pathology , Phosphorylation , Platelet-Derived Growth Factor/biosynthesis , Platelet-Derived Growth Factor/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Receptor, Platelet-Derived Growth Factor beta/metabolism , Receptor, Platelet-Derived Growth Factor beta/physiology , Signal Transduction/physiology , Tumor Cells, CulturedABSTRACT
Endostatin, a type XVIII collagen fragment, is a potent antiangiogenic molecule that inhibits endothelial cell migration, promotes apoptosis, and induces cell cycle arrest in vitro. We have investigated the mechanism by which endostatin causes G(1) arrest in endothelial cells. Endostatin decreased the hyperphosphorylated retinoblastoma gene product and down-regulated cyclin D1 mRNA and protein. Importantly, endostatin was unable to arrest cyclin D1 overexpressing endothelial cells, suggesting that cyclin D1 is a critical target for endostatin action. Next, we analyzed cyclin D1 promoter activity in endothelial cells and found that endostatin down-regulated the cyclin D1 promoter. Using a series of deletion and mutant promoter constructs, we identified the LEF1 site in the cyclin D1 promoter as essential for the inhibitory effect of endostatin. Finally, we showed that endostatin can repress cyclin D1 promoter activity in cells over-expressing beta-catenin but not in cells over-expressing a transcriptional activator that functions through the LEF1 site and is insensitive to beta-catenin. Collectively, our data pointed to a role for cyclin D1, and in particular, transcription through the LEF1 site as critical for endostatin action in vitro and suggest that beta-catenin is a target for endostatin.
