The tumor suppressor gastrokine-1 is expressed in placenta and contributes to the regulation of trophoblast migration.

INTRODUCTION: Gastrokine-1 (GKN1) is a secreted auto-/paracrine protein, described to be expressed in the gastric mucosa. In gastric cancers GKN1 expression is commonly down-regulated. While current research focusses on the exploration of tumor-suppressive properties of GKN1 with regard to its potential clinical use in the treatment of gastroenterologic tumor disease, nothing is known about GKN1 expression and function in other organ systems. We investigated GKN1 expression in placental tissue and cells.
MATERIALS AND METHODS: GKN1 was localized using immunohistochemistry in first and third trimester placental tissue, hydatidiform moles and various gestational trophoblastic neoplasias. We determined the expression of GKN1 in immunomagnetic bead-separated term placental cells and in choriocarcinoma cell lines. The role of GKN1 for JEG-3 migration was studied using live cell imaging. E-cadherin, MMP-2 and -9, TIMP-1 and -2, as well as urokinase (uPA) expression levels were determined.
RESULTS: GKN1 is expressed in healthy third trimester placentas. Its expression is specifically limited to the extravillous trophoblast (EVT). GKN1 expression is significantly reduced in choriocarcinoma cell lines and gestational trophoblastic neoplasias. GKN1 attenuates the migration of JEG-3 choriocarcinoma cells in vitro, possibly via AKT-mediated induction of E-cadherin. GKN1 treatment reduced MMP-9 expression in JEG-3. DISCUSSION: Besides its role in gastric physiology our results clearly indicate regulatory functions of GKN1 in the EVT at the feto-maternal interface during pregnancy. Based on our findings in the JEG-3 choriocarcinoma cell line, an auto-/paracrine role of GKN1 for EVT motility and villous anchorage at the basal plate is conceivable. Thus, the tumor suppressor GKN1 is expressed in placental EVT and might contribute to the regulation of EVT migration/invasion.