IDENTIFICATION OF PROMETALLOPROTEINASE-3 AS A MAJOR PROTEIN SECRETED BY HUMAN ENDOMETRIAL FIBROBLASTS AND INHIBITED BY COCULTURE WITH TROPHOBLAST CELLS

To assess endometrial fibroblast-cytotrophoblast interactions, we used a coculture system allowing analysis of the potential cell morphology modifications and protein secretion variations possibly involved in e ndometrial invasion arrest. Stromal cells and cytotrophoblasts were is olated from endometrial biopsies and first-trimester placental villi, respectively. In our culture conditions, a 57-kDa protein that was sec reted by cultured fibroblasts but was absent in the 4-day coculture me dium was found to be identical to prometalloproteinase-3 (proMMP-3) th rough determination of amino acid sequences of NH2-terminal and intern al peptides. Northern blotting analysis of endometrial fibroblast tota l RNA showed a 38.6% metalloproteinase-3 (MMP-3) mRNA inhibition by 4- day 10(-6) M R5020 treatment. Inhibition of proMMP-3 secretion was wea k when cytotrophoblasts were cultured for 4 days in a polycarbonate me mbrane insert over cultured fibroblasts without possible cell contact in spite of high levels of progesterone produced by cytotrophoblasts. Furthermore, cytotrophoblasts cultured on a monolayer of endometrial f ibroblasts became syncytia, and most of the fibroblasts were deciduali zed. The closeness of the two cell types allowed paracrine relationshi ps that might facilitate the progesterone action. Since MMP-3 is known to activate collagenases, inhibition of its secretion by cell contact might be a mechanism of invasion arrest for trophoblast cell migratio n.