Downregulation of RIF1 Enhances Sensitivity to Platinum-Based Chemotherapy in Epithelial Ovarian Cancer (EOC) by Regulating Nucleotide Excision Repair (NER) Pathway.

ABSTRACT

BACKGROUND/AIMS: Rap1 interacting factor 1 (RIF1) was deemed to be involved in replication timing regulation and DNA damage response. However, little is known about the role of RIF1 in malignancies. Thus, this study aimed to investigate whether the expression of RIF1 is relevant to the response of epithelial ovarian cancer (EOC) patients to cisplatin chemotherapy and its underlying mechanism. METHODS: Immunohistochemistry was used for detecting the expression of RIF1 in 72 human ovarian cancer tissues followed by association analysis of RIF1 expression with patients' responses to platinum-based chemotherapy. The survival analysis of ovarian patients based on platinum chemotherapy was analyzed using online databases. RNA interference of RIF1 was carried out in OVCAR3 and A2780 cell lines, to determine the effect of lacking RIF1 expression on cellular responses to cisplatin by using MTS assay. The nucleotide excision repair (NER) capacity of these cells was assessed by using host-cell reactivation and UV sensitivity assay. Western Blot analysis was carried out to determine the effect of RIF1 on the proteins of NER and apoptosis signaling pathway by using RIF1 knockdown cells. BALB/c nude mice model was used for detection of response to cisplatin in vivo. RESULTS: RIF1 expression was significantly associated with the response of ovarian patients to platinum-based chemotherapy (P< 0.01). In cohorts from online databases, high expression of RIF1 was associated with higher mortality of EOC patients based on platinum chemotherapy (P < 0.01). RIF1 knockdown increased sensitivity to cisplatin in EOC in vitro and in vivo. Deletion of RIF1 impaired the NER activity by inhibiting the NER proteins in ovarian cancer cells. Besides, knockdown of RIF1 enhanced cisplatin-induced apoptosis. CONCLUSIONS: RIF1 plays an important role in regulating the expression of NER proteins, which in turn contributes to cellular response to cisplatin and EOC patients' response to platinum-based chemotherapy. RIF1 knockdown also promotes cisplatin-induced apoptosis. RIF1 may serve as a novel biomarker for predicting platinum-based chemosensitivity and the prognosis of EOC patients.