Characterization of chloride intracellular channel 4 in the regulation of human trophoblast function.

INTRODUCTION: Proper placentation requires well controlled extravillous trophoblast cell (EVT) migration and invasion. Transforming growth factor β (TGFβ) signaling has been well characterized as negatively regulating EVT migration and invasion. CLIC4 is an enhancer of TGFβ signaling, however CLIC4's function in placentation and its association to placental TGFβ signaling is unknown. Here we aimed to investigate the role of CLIC4 on trophoblast cell function and its relationship to TGFβ signaling.

METHODS: CLIC4 was immunolocalized in human placenta throughout gestation and the first trimester decidua. siRNA was used to knockdown CLIC4 in a human trophoblast cell line (HTR8/SVneo) to reveal functional consequences of CLIC4 loss on cell adhesion, proliferation, migration and invasion via xCELLigence. qPCR was used to identify downstream targets of CLIC4 in HTR8/SVNeo cells.

RESULTS: CLIC4 was widely expressed in the syncytiotrophoblast, cytotrophoblast and decidual cells across all trimesters of pregnancy with no significant difference in staining intensity in the different cellular compartments both across gestation and between compartments. Using immunofluorescent co-localization of CLIC4 and EVT marker HLA-G, we confirmed that CLIC4 localized to the cytoplasm of cell column EVTs in the first trimester decidua and nuclei of some EVTs that invaded in the decidua. Knockdown of CLIC4 in HTR8/SVneo cells significantly elevated cell adhesion, migration and invasion. Analysis of TGFβ signaling downstream targets identified that CDH2 and BAMBI expression were significantly increased after CLIC4 knockdown in HTR8/SVneo cells.

DISCUSSION: Our data support an inhibitory role for CLIC4 in regulating trophoblast migration and invasion, likely acting in part via BAMBI and CDH2.