Gankyrin is a regulatory subunit of the 26kD proteasome complex. As a novel oncoprotein, gankyrin is expressed aberrantly in cancers from several different sites and has been shown to contribute to oncogenesis in endometrial and cervical carcinomas. Neither gankyrin's contribution to the development of epithelial ovarian cancer nor its interaction with follicle-stimulating hormone (FSH)-driven proliferation in ovarian cancer has been studied. Here we have found that gankyrin is overexpressed in ovarian cancers compared with benign ovarian cystadenomas and that gankyrin regulates FSH upregulation of cyclin D1. Importantly, gankyrin regulates PI3K/AKT signaling by downregulating PTEN. Prolonged AKT activation by FSH stimulation of the FSH receptor (FSHR) promotes gankyrin expression, which, in turn, enhances AKT activation by inhibiting PTEN. Overexpression of gankyrin decreases hypoxia inducible factor-1α (HIF-1α) protein levels, but has little effect on HIF-1α mRNA levels, which could be attributed to gankyrin mediating HIF-1α protein stability via the ubiquitin-proteasome pathway. Reduction in HIF-1α protein stability led to attenuation of the binding with cyclin D1 promoter, resulted in abolishment of the negative regulation of cyclin D1 by HIF-1α, which promotes proliferation of ovarian cancer cells. Our results document that gankyrin regulates HIF-1α protein stability and cyclin D1 expression, ultimately mediating FSH-driven ovarian cancer cell proliferation.

Chemoresistance is the major obstacle to cure endometrial cancer, whereas metformin has demonstrated sensitization to chemotherapy in endometrial cancer. A novel finding states that isocitrate dehydrogenase 1 (IDH1) involves in cancer chemoresistance. Recent studies have revealed that epigenetic modifications facilitate chemoresistance. However, whether IDH1 play a role in metformin-induced endometrial cancer chemosensitivity through epigenetic modification is incompletely understood. Immunohistochemistry and Elisa assays were used to evaluate the expression pattern of IDH1 in endometrial tissue and serum, respectively. Western blot was performed to determine changes in expression of key molecules in the IDH1-ɑ-KG-TET1-Nrf2 signaling pathway after various treatments. Dot blot assays were used to assess global hydroxymethylation levels after metformin administration or plasmid transfection. Antioxidant response element (ARE) activity in the IDH1 promoter region was monitored by luciferase assay. Cancer cell sensitivity to chemotherapy was detected by SRB assay. We found that activation of the IDH1 signaling pathway in endometrial cancer tissue resulting from aberrant expression of IDH1 and its downstream mediators conferred chemoresistance. We found that this effect was abated by metformin treatment. Dot blot and HMeDIP assays revealed that metformin blocked IDH1-ɑ-KG-TET1-mediated enhancement of Nrf2 hydroxymethylation levels, eliminating chemoresistance. Moreover, we observed that chemoresistance was enhanced via a regulatory loop in which Nrf2 activated IDH1-ɑ-KG-TET1-Nrf2 signaling via binding to the ARE sites in the IDH1 promoter region. Our findings highlight a critical role of IDH1-ɑ-KG-TET1-Nrf2 signaling in chemoresistance and suggest that rational combination therapy with metformin and chemotherapeutics has the potential to suppress chemoresistance.

Abstract. OCT4 plays a critical role in the maintenance of stem cell pluripotency and proliferation, and is overexpressed in multiple human tumors, including endometrial cancer. OCT4 expression can be modulated by miR-145 and the OCT4 pseudogene 5 (OCT4-pg5), which share similar binding sites in the OCT4 3'-untranslated region. The goal of the present study was to evaluate the interaction between miR-145 and OCT4-pg5 on OCT4 expression in endometrial cancer. We assessed OCT4-pg5 expression in 14 benign endometrium and 29 endometrial carcinoma samples. Furthermore, miR-145 mimic transfection was performed to explore its effect on OCT4-pg5 and OCT4 expression, and small interfering RNA (siRNA)-mediated knockdown of OCT4 was conducted to determine whether the effect of OCT4-pg5 on cellular growth was OCT4-dependent. We observed that OCT4-pg5 was abnormally activated in the endometrial carcinomas, and that overexpression of OCT4-pg5 contributed to enhanced cell proliferation and OCT4-PI3K/AKT-cyclin D1 signaling. Moreover, the miR-145 mimic depleted OCT4 expression, whereas elevated OCT4-pg5 restored OCT4 expression and OCT4-PI3K/AKT-cyclin D1 signaling. In conclusion, these data indicate that OCT4-pg5 can act as an RNA sponge to protect OCT4 transcripts from being inhibited by miR-145, providing novel insight into the control of OCT4 expression.

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