Reconstitution of Smad3 restores TGF-β response of tissue inhibitor of metalloprotease-1 upregulation in human choriocarcinoma cells

Abstract

Extravillous trophoblast (EVT) cells of the human placenta proliferate, migrate, and invade the pregnant uterus and its vasculature in order to nourish the fetus. However, the normal EVT cell proliferation, migration, and invasiveness are exquisitely controlled in situ by decidua-produced transforming growth factor-β (TGF-β), whereas EVT cancer (choriocarcinoma) cells are TGF-β-resistant. We found that these cells lack in expression of Smad3, a key transcription factor involved in TGF-β signaling pathway. To test whether Smad3 restitution restores TGF-β response in choriocarcinoma cells, we produced a Smad3-expressing cell line (JAR-smad3/c). Since anti-invasive effect of TGF-β in the normal EVT cells was partly mediated by an upregulation of tissue inhibitor of metalloprotease (TIMP)-1, we examined whether Smad3-restituted JAR cells have restored TGF-β response of TIMP-1 upregulation. The expression of TIMP-1 mRNA was found to be low in JAR and JAR-smad3/c cells. Moreover, the basal level of secreted TIMP-1 protein was very low in these cells as compared to the normal EVT cells. TGF-β1 upregulated TIMP-1 mRNA and secreted protein in Smad3-restituted JAR cells as well as in the normal EVT cells, whereas no effect was detected in Smad3-deficient (wild-type) JAR cells. We had earlier shown that Smad3-restituted JAR cells had also restored TGF-β response of plasminogen activator inhibitor-1 upregulation. However, in vitro functional analysis revealed that, in contrast to the normal EVT cells, anti-invasive action of TGF-β was not restored in Smad3-restituted JAR cells. Thus, additional factors (possibly low expression of Smad4 and/or other unknown factors) may contribute to refractoriness to anti-invasive action of TGF-β in JAR cells.