PREFERENTIAL INHIBITION OF PLATELET-DERIVED GROWTH FACTOR-STIMULATED DNA-SYNTHESIS AND PROTEIN-TYROSINE PHOSPHORYLATION BY NORDIHYDROGUAIARETIC ACID

Nordihydroguaiaretic acid (NDGA), a reportedly specific lipoxygenase i nhibitor, was found to selectively inhibit platelet-derived growth fac tor (PDGF)-stimulated DNA synthesis in Swiss 3T3 cells. Maximal inhibi tion of PDGF-induced [H-3]thymidine incorporation (96%) was observed u sing 4 mu M NDGA (IC50 = 1.5 mu M). No effect of NDGA was observed upo n DNA synthesis stimulated with either fetal bovine serum, bombesin, o r epidermal growth factor (EGF) in the presence of insulin, or with th e potent mitogen Pasteurella multocida toxin. The selective inhibition of PDGF-stimulated DNA synthesis by NDGA was also observed in diploid murine cells, rat, and human fibroblasts. Furthermore, 4 mu M NDGA al so inhibited PDGF-stimulated anchorage-independent colony growth of ra t-1 cells by 76%. Using Swiss 3T3 cells, we found that PDGF-stimulated arachidonic acid mobilization and prostaglandin E(2) production was a bolished by NDGA in a dose-dependent manner. Inhibition of PDGF-stimul ated arachidonic acid mobilization by NDGA could not, however, explain its potent inhibitory effect upon PDGF-stimulated DNA synthesis. Our results showed that NDGA also selectively inhibited PDGF receptor tyro sine phosphorylation in a dose-dependent manner in intact cells. Prote in tyrosine phosphorylation stimulated by EGF or bombesin was not alte red by NDGA treatment. Crucially, NDGA inhibited in vitro the tyrosine kinase activity of anti-phosphotyrosine and anti-PDGF receptor immuno precipitates prepared from cultures stimulated with PDGF. This inhibit ion of receptor tyrosine phosphorylation in a cell-free system confirm ed that NDGA acts directly at the level of the PDGF receptor tyrosine kinase domain. These results suggest that the potent and selective inh ibitory effect of NDGA on PDGF-stimulated DNA synthesis results from i ts inhibitory action on tyrosine phosphorylation.