Expression of serine proteinase inhibitor PP5/TFPI-2/MSPI decreases the invasive potential of human choriocarcinoma cells in vitro and in vivo

OBJECTIVE: PP5/TFPI-2/MSPI is a Kunitz-type serine proteinase inhibitor with broad inhibitory spectra, abundantly produced by placenta and detected in the blood of pregnant women. Expression of PP5/TFPI-2/MSPI is exclusively detected in syncytiotrophoblasts of placenta, but is barely detectable in choriocarcinoma cells, a trophoblast-derived malignant tumor. Chromosome 7, in which the PP5/TFPI-2/MSPI gene is localized, is frequently lost in various types of tumors. We attempted to elucidate the relation between PP5/TFPI-2/MSPI expression and the malignant properties of choriocarcinoma cells. METHODS: Human choriocarcinoma cells, JAR, were transfected with either a human PP5/TFPI-2/MSPI expression vector or an empty vector, and stable clones were obtained. Messenger RNA expression, protein secretion/localization, growth rate, and plating efficiency were evaluated. In vitro migration and invasive activity were determined by transwell chamber experiments. In vivo tumor growth was evaluated by the subcutaneous injection of cells to nude mice and followed by histological examination. RESULTS: Expression of mRNA and protein of PP5/TFPI-2/MSPI were confirmed, and a high producing clone and a low producing clone were chosen for further analysis. The majority of secreted PP5/TFPI-2/MSPI protein was revealed to associate with the extracellular matrix. Expression of PP5/TFPI-2/MSPI did not affect the growth and migration of the tumor cells, but enhanced their plating efficiency. Its expression significantly inhibited invasion through the Matrigel. Invasive growth into the subcutaneous muscle layer was not evident in the nude mouse tumors of the PP5/TFPI-2/MSPI-expressing cells. CONCLUSION: PP5/TFPI-2/MSPI-expressing choriocarcinoma cells showed suppressed potential of invasion in vitro and in vivo. It is suggested that loss or suppression of PP5/TFPI-2/MSPI expression may result in the acquisition of invasiveness in choriocarcinoma cells.