Ikaros is expressed in human extravillous trophoblasts and involved in their migration and invasion.

The transcriptional factor Ikaros was originally found to function as a key regulator of lymphocyte differentiation. In addition, we have reported that Ikaros regulates the human placental leucine aminopeptidase (P-LAP)/insulin-regulated aminopeptidase (IRAP) gene in choriocarcinoma trophoblastic cells, suggesting that Ikaros might be involved in placental development, while even its presence in human placenta remains undetermined. We therefore sought to clarify the location and roles of Ikaros in human placenta. Immunohistochemical analysis showed modest Ikaris expression in syncytium, and intense expression in extravillous trophoblasts (EVTs) in first trimester placenta. Western blot analysis showed that villous trophoblasts principally expressed Ikaros-2/3, while Ikaros-x (Ikx) was predominantly expressed in cultured EVTs. Furthermore, to investigate the functional role of Ikx in EVTs, the EVT cell line HTR-8/SVneo was infected with a retrovirus vector expressing the hemagglutinin (HA)-tagged dominant negative isoform Ikaros-6 (Ik6), which prevents the DNA-binding activity of Ikx. Antibody against HA showed successful transduction of Ik6 in HTR-8/SVneo cells on immunocytochemistry and Western blotting. Transduction of Ik6 significantly reduced the migratory and invasive abilities of HTR-8/SVneo cells. These results suggest that Ikx is involved in migration and invasion of EVTs in early placentation.