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 endometrial invasion arrest. Stromal cells and cytotrophoblasts were isolated from endometrial biopsies and first-trimester placental villi, respectively. In our culture conditions, a 57-kDa protein that was secreted by cultured fibroblasts but was absent in the 4-day coculture medium was found to be identical to prometalloproteinase-3 (proMMP-3) through determination of amino acid sequences of NH2-terminal and internal peptides. Northern blotting analysis of endometrial fibroblast total 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 weak when cytotrophoblasts were cultured for 4 days in a polycarbonate membrane 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 fibroblasts became syncytia, and most of the fibroblasts were decidualized. The closeness of the two cell types allowed paracrine relationships 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 migration.