Selective down-regulation of c-jun gene expression by pentoxifylline and c-jun antisense interrupts platelet-derived growth factor signaling: pentoxifylline inhibits phosphorylation of c-Jun on serine 73.
Platelet-derived growth factor (PDGF) signals through several pathways, including mitogen-activated protein (MAP) kinase, Jun kinase, and C kinase, and stimulates proliferation of fibroblasts. Pentoxifylline inhibits PDGF-driven proliferation of fibroblasts. We have reported that pentoxifylline did not inhibit binding of PDGF to its specific cell-surface receptors or PDGF receptor phosphorylation. In this study, we investigated the effect of PDGF on the expression of c-fos and c-jun, because c-fos and c-jun form activator protein-1 complexes that stimulate genes involved in proliferation. We determined whether pentoxifylline would alter the expression of c-fos and c-jun. Our results indicate that PDGF induced the expression of both c-fos and c-jun. Pentoxifylline effectively reduced c-jun gene expression, which had been up-regulated by PDGF, but did not alter c-fos gene expression. The lack of effect on c-fos supports other studies from this laboratory, which indicate that pentoxifylline did not inhibit PDGF activation of MAP kinase. Treatment of fibroblasts with a phosphothioate c-jun antisense oligodeoxynucleotide reduced the levels of c-Jun protein and blocked PDGF-stimulated proliferation, suggesting a critical role for c-jun in PDGF-mediated proliferation. Combination of pentoxifylline and c-jun antisense suggested that they were likely inhibiting PDGF-stimulated proliferation at a single site in the PDGF signaling pathway. These results suggest that pentoxifylline inhibits PDGF-stimulated proliferation by selectively decreasing c-jun expression. To further define the mechanism of action of pentoxifylline, we assessed the effect of pentoxifylline on c-Jun and phosphorylated c-Jun immunoreactivity in cells treated with PDGF and cells that were transfected with wild-type c-jun plasmid using immunocytochemistry and Western blot analyses, and our results indicate that pentoxifylline inhibited phosphorylation of c-Jun on serine 73.
Peterson
Theresa C
TC
Department of Medicine, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada. TCPMED@IS.DAL.CA
Peterson
Marc R
MR
Robertson
Harold A
HA
During
Matthew
M
Dragunow
Michael
M
D000818:Animals; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D016758:Genes, jun / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D016716:PC12 Cells; D010431:Pentoxifylline / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D016376:Oligonucleotides, Antisense; D010982:Platelet-Derived Growth Factor; D012694:Serine; D010431:Pentoxifylline