Expression of metalloproteinases and their inhibitors in human trophoblast continuous cell lines

Trophoblasts cells which are derived from the outer layer of the blastocyst have developed mechanisms by which they can invade the uterus and tap into the maternal circulation. In contrast to tumor cell invasion trophoblast invasion is precisely regulated, being confined spatially to the uterus and temporally to early pregnancy. The invasive properties manifested by trophoblasts are made possible by the secretion of proteolytic enzymes which can degrade components of the extracellular matrix (ECM). A number of investigators have shown that the matrix metalloproteinases (MMPs) are important mediators of trophoblast invasion. The two type IV collagenases, MMP-2 and MMP-9, which specifically degrade type IV collagen and gelatins have been of particular interest in this respect. In this paper we examine the expression and regulation of MMPs and their inhibitors in a series of trophoblast continuous cell lines. These cell lines, ED27, ED31, ED77, and a choriocarcinoma cell line, BeWo, were initially characterized with respect to various properties, including cytokeratin, hCG, and hPL expression. We have looked at the expression of MMPs and their inhibitors in these cell lines and their in vitro invasive behavior. Using zymography and RT-PCR we show that the trophoblast cell lines produce both MMP-2 and MMP-9, while the BeWo produce only MMP-2. Using an in vitro invasion assay the trophoblast cell lines were shown to be capable of invading while the BeWo were unable to invade. These results suggest that expression of MMP-9 in these cells is crucial for invasion. We have also examined the regulation of MMP expression by cytokines and found that MMP-9 expression could be modulated by IL-1 beta in these cell lines. The data presented in this paper suggest that these trophoblast cell lines present an ideal model system to investigate the regulation of metalloproteinases in trophoblast invasion.