Expression of serum amyloid A4 in human trophoblast-like choriocarcinoma cell lines and human first trimester/term trophoblast cells.

Trophoblast invasion into uterine tissues represents a hallmark of first trimester placental development. As expression of serum amyloid A4 (SAA4) occurs in tumorigenic and invasive tissues we here investigated whether SAA4 is present in trophoblast-like human AC1-M59/Jeg-3 cells and trophoblast preparations of human first trimester and term placenta. SAA4 mRNA was expressed in non-stimulated and cytokine-treated AC1-M59/Jeg-3 cells. In purified trophoblast cells SAA4 mRNA expression was upregulated at weeks 10 and 12 of pregnancy. Western-blot and immunohistochemical staining of first trimester placental tissue revealed pronounced SAA4 expression in invasive trophoblast cells indicating a potential role of SAA4 during invasion.

Trophoblast invasion: tuning through LIF, signalling via Stat3.

Aberrant activity of the signal transducer and activator of transcription 3 (Stat3) is believed to be essential for neoplastic cell behaviour and thus for the malignancy of tumor cells [Bowman T, Garcia R, Turkson J, Jove R. STATs in oncogenesis. Oncogene 2000;19:2474-88]. Extravillous trophoblast cells resemble malignancies in their invasive and destructive features, excluding the fact of sequential restriction to the first trimester of pregnancy. Trophoblast cells from term placentas have reduced invasive capacity [Hohn HP, Denker HW. Experimental modulation of cell-cell adhesion, invasiveness and differentiation in trophoblast cells. Cells Tissues Organs 2002;172:218-36]. Constitutively activated Stat3 DNA-binding activity in choriocarcinoma cells, carcinomatous derivates of trophoblast cells, have been reported to correlate with its invasiveness [Corvinus FM, Fitzgerald JS, Friedrich K, Markert UR. Evidence for a correlation between trophoblast invasiveness and STAT3 activity. Am J Reprod Immunol 2003;50:316-21]. Here we demonstrate using RNAi that Stat3 activation is necessary in the invasive phenotype of trophoblast cells and can be controlled via Leukemia Inhibitory Factor (LIF). LIF provides a soluble extracellular signal that stimulates invasion in trophoblast and Jeg-3 choriocarcinoma cells. Loss of LIF-mediated invasion in these cells subsequent to STAT3 knock-down strongly suggests that STAT3 plays a crucial role in mediating this invasion.