The synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid-imidazolide alters transforming growth factor β-dependent signaling and cell migration by affecting the cytoskeleton and the polarity complex

The anti-tumor synthetic triterpenoid 2-cyano-3,12-dioxooleana1,9-dien-28-oic acid (CDDO)-imidazolide (CDDO-Im) ectopically activates the transforming growth factor beta (TGF beta)-Smad pathway and extends the duration of signaling by an undefined mechanism. Here we show that CDDO-Im-dependent persistence of Smad2 phosphorylation is independent of Smad2 phosphatase activity and correlates with delayed TGF beta receptor degradation and trafficking. Altered TGF beta trafficking parallels the dispersal of EEA1-positive endosomes from the perinuclear region of CDDO-Im-treated cells. The effect of CDDO-Im on the EEA1 compartment led to an analysis of the cytoskeleton, and we observed that CDDO-Im alters microtubule dynamics by disrupting the microtubule-capping protein, Clip-170. Interestingly, biotinylated triterpenoid was found to localize to the polarity complex at the leading edge of migrating cells. Furthermore, CDDO-Im disrupted the localization of IQGAP1, PKC zeta, Par6, and TGF beta receptors from the leading edge of migrating cells and inhibited TGF beta-dependent cell migration. Thus, the synthetic triterpenoid CDDO-Im interferes with TGF beta receptor trafficking and turnover and disrupts cell migration by severing the link between members of the polarity complex and the microtubule network.