Mouse trophoblastic cell lines: I--Relationship between invasive potential and TGF-beta 1.

In the present study five mouse trophoblastic cell lines were used, SM9-1, SM9-2 and SM10 from outbred (Swiss) mice, and HLA-B1 and HLA-B3 from inbred transgenic (HLA-B27) mice placentas generated in the laboratory of Dr. Joan S Hunt (K U Medical Center, Kansas City, KS). All of the cell lines demonstrated a basic set of characteristics that are strongly associated with and probably exclusive to trophoblast cells. Successful propagation of normal trophoblast cell lines with distinct phenotypes cultured in vitro provides an excellent model for the study of mechanisms regulating trophoblast invasion very similar to invasion by tumor cells. Application of these cells to in vitro invasion assay has uncovered some of the molecular mechanisms responsible for trophoblast invasiveness and its control. Using the in vitro invasion assay SM9-2 and SM-10 were identified as the most invasive and least invasive cell lines, respectively. By using RT-PCR we have shown that all lines express TNF-alpha mRNA and this level is high in HLA-B derived cell lines. Other experiments has revealed that only Swiss mice derived cell lines (SM9-1, SM9-2 and SM-10) express the TGF-beta 1 mRNA and among these lines SM9-2 has the highest level. In TGF-beta 1 activity assay, secreted conditioned medium of these cell lines further showed that SM9-2 line has the highest inhibitory activity on Mv-1-Lu cell line. Exogenous TGF-beta 1 down-regulates invasion as well as mRNA level in SM9-2 trophoblasts. However, neutralizing TGF-beta 1 antibody in this cell line up-regulates invasion minimally. Late gestational trophoblast cells show a major reduction of invasive ability which is an autocrine type negative regulation of trophoblast invasion, and is possibly mediated by TGF-beta 1 production by the trophoblasts. Thus trophoblast TGF-beta 1 could be implicated in the invasion of these cells and this invasive phenotype is retained with complete fidelity during their further propagation in culture.