Abstract 3068: Tumor suppressor functions of Kinesin superfamily 7 (Kif7) in choriocarcinoma

Abstract

Abstract Background: Gestational choriocarcinoma is a member of the gestational trophoblastic disease with high malignant potential derived from placental trophoblasts. We have earlier demonstrated aberrant expression of stem cell transcription factors Nanog, Oct4, Sox2 and Stat3 in choriocarcinomas. The Hedgehog signal pathway is known to be important in embryological development and dysregulated Hedgehog pathway has been reported in human malignancies including our studies on cancers of the ovary and endometrium. Kinesin superfamily 7 (Kif7) is a microtubule motor protein which had recently been shown to be the mammalian homolog of Drosophila Cos2 in the Hedgehog signaling pathway. This study aimed at investigating the expression, regulation and function of Kif7 in choriocarcinomas. Methods: Fresh frozen samples of 10 first-trimester placentas, 5 term placentas and three choriocarcinomas were retrieved. Two choriocarcinoma cell lines (JAR and JEG-3) purchased from ATCC and one normal trophoblast cell line (TEV-1) prepared previously were also studied. RNA expression profiles were compared by quantitative real time PCR. The methylation status of possible CpG islands in Kif7 gene was evaluated by bisulfite sequencing and in vitro treatment by demethylating and acetylating agents. Choriocarcinoma cell lines JAR and JEG stably transfected with Kif7 and control BSTXI vectors were produced for evaluation of functional effects of Kif7 in choriocarcinoma. Results By quantitative real time PCR, the RNA expression level of Kif7 was found to be decreased in choriocarcinoma compared to normal placental tissues. Two choriocarcinoma cell lines, JEG-3 and JAR, also exhibited lower level of Kif7 mRNA when compared to immortalized normal trophoblast lines. Bisulfite sequencing revealed that the methylation status of possible CpG islands in Kif7 gene did not vary significantly among clones of normal trophoblasts and choriocarcinoma cell lines. However, expression level of Kif7 in choriocarcinoma cell lines increased after trichostatin A treatment, suggesting that histone acetylation may epigenetically regulate Kif7 expression. Effects of Kif7 on trophoblast cell functions was investigated. By TUNEL (terminal deoxynucleotidyl transferase (TdT) to transfer biotin-dUTP) and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, the Kif7-stably transfected cells was observed to show increased apoptosis and reduced cell proliferation respectively compared with the controls. Transwell migration/invasion assay performed on plating transfected JAR and JEG-3 cells in uncoated, gelatin-coated and matrix gel-coated transwells also showed reduced cell migration and invasion compared with the controls. Conclusion: Our study demonstrated that Kif7 may act as a tumor suppressor gene in choriocarcinoma via its effect on apoptosis, cell proliferation, invasion and migration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3068.