FOLR1 increases sensitivity to cisplatin treatment in ovarian cancer cells

Huang et al. Journal of Ovarian Research (2018) 11:15 https://doi.org/10.1186/s13048-018-0387-y RESEARCH Open Access FOLR1 increases sensitivity to cisplatin treatment in ovarian cancer cells Ming-ju Huang1,2†, Wei Zhang1†, Qi Wang1, Zhi-jun Yang1, Sheng-bin Liao1 and Li Li1* Abstract Background: Whether there is a mechanistic link between FOLR1 and response to cisplatin has not been extensively examined. In this study, we determine the expression of FOLR1 in ovarian cancer and examine if FOLR1 levels influence response to cisplatin. Results: (1) FOLR1 protein expression was lowest in normal ovarian tissue, higher in benign ovarian tumors, and highest in malignant tumors (P < 0.01). (2) FOLR1 expression was decreased in platinum drug-resistant ovarian tumors compared to sensitive tumors (P < 0.01). Consistent with this, FOLR1 expression in tumors progressing following cisplatin treatment was lower than levels in tumors in remission (P < 0.01). (3) FOLR1 was successfully overexpressed at both the mRNA and protein levels following transfection in SKOV3 cells. (4) SKOV3 cells with FOLR1 overexpression were the most sensitive to cisplatin treatment (IC50 = 3.60 μg/ml) and exhibited the highest inhibition rates in the presence of the drug (P < 0.05). (5) The rate of apoptosis of SKOV3 cells increased with cisplatin treatment in a dose- and time-dependent manner (P < 0.05). Cisplatin also induced S phase arrest in a concentration-dependent manner (P < 0.05). Apoptosis and S phase proportion were significantly altered by FOLR1 overexpression (P < 0.05). Conclusion: FOLR1 may be a useful biomarker for ovarian cancer, and it may be useful as a therapeutic application to improve sensitivity to cisplatin treatment. Keywords: Folate binding protein, Ovarian cancer, SKOV3 cells, Cisplatin, Apoptosis, Cell cycle, Multidrug resistance Background Ovarian cancer is a serious malignancy, with high mortality and a five-year survival rate of approximately 20% - 30% for the prevailing advanced presentations [1]. Survival in patients with ovarian cancer can be improved with early detection, thorough surgery, and improved sensitivity to cisplatin-based chemotherapy. Folate binding protein (FOLR1) is a member of the human folate binding protein family. The gene is located on chromosome 11q13.3-14.1. FOLR1 is a glycosyl phosphatidylinositol connected membrane glycoprotein, consisting of 257 amino acids. The protein is completely exposed to extracellular molecules and anchored at the cell membrane by GPI [2]. FOLR1 is involved in DNA replication and damage repair. Its expression levels are closely related with tumor progression and cell proliferation [3, 4]. FOLR1, also known as folate * Correspondence: † Equal contributors 1 Department of Gynecology Oncology, Tumor Hospital of Guangxi Medical University, Nanning 530021, China Full list of author information is available at the end of the article receptor proteins, mediates cellular responses to folate, including cell division, proliferation, and tissue growth [5]. Few publications have reported on FOLR1 expression in ovarian tissue. Shen et al. found that FOLR1 expression was decreased in cisplatin-resistant tumors [6],but whether there is a mechanistic link between FOLR1 and response to cisplatin has not been extensively examined. In this study, we determine the expression of FOLR1 in ovarian cancer and examine if FOLR1 levels influence response to cisplatin. The data we provide here suggest that FOLR1 may be a useful predictive biomarker for cisplatin sensitivity in ovarian cancer. Results Expression of FOLR1 in normal ovary, benign ovarian tumors, and ovarian cancer Expression of FOLR1 in normal, benign, and cancerous ovarian tissues was determined by Western blot. GAPDH was used as a loading control. Expression of FOLR1 was lowest in normal ovarian tissue. FOLR1 was © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Huang et al. Journal of Ovarian Research (2018) 11:15 more highly expressed in benign tumors and even higher in malignant disease (P < 0.01)(Fig. 1). Expression of FOLR1 in cancerous ovarian tissue is correlated with clinicopathologic factors FIOG (International Federation of Gynaecology and Obstetrics) system 2000 is used to determine the stages of malignant ovarian patients. The expression of FOLR1 in stage I-II is lower than that in stage III-IV and also lower in the well-differentiated than that in the lowdifferentiated (P<0.05). While there is no difference for expression of FOLR1 in the four different pathologic tissue, the significant difference does exist between the mucinous and the serous (P<0.05). The specific results are shown in Fig. 2. Correlation of expression of FOLR1 with tumor metastasis and ascites Expression of FOLR1 in cancerous ovarian tissue with metastasizing to distant lymph node and/or organ is higher than that without metastasis (P<0.05).However,there’s no significance about correlation of expression of FORL1 with whether metastasizing to the greater omentum or having asites (P > 0.05). The specific results are shown in Fig. 3. FOLR1 expression in ovarian cancer tissue is correlated with patient treatment efficacy and drug resistance FOLR1 protein expression was highest in patients with complete remission (complete response, CR). FOLR1 expression decreased with decreased drug sensitivity (partial response, PR > stable disease, SD > progressive disease, PD). The difference in expression in CR, PR, and SD patients compared to PD patients was statistically significant (P < 0.01). The difference in expression in CR and PR patients compared to PD and SD patients was also significant (P < 0.05). However, there was no statistically Page 2 of 8 significant difference in expression in CR and PR patients compared to SD patients (P > 0.05). Expression of FOLR1 in platinum drug-resistant ovarian cancer was lower than in platinum drug-sensitive tumors (P < 0.01),and after further chemotherapy expression of FOLR1 in PD was still lower than that in remission (p < 0.01) (Fig. 4). Correlation of expression of FOLR1 in ovarian cancer tissue with prognosis of patients ROC curve that determines the relationship of FOLR-1 expression and nature of ovarian cancer demonstrates that maximum Youden index is 3.115. The specific result is shown in Fig. 5a. Univariate analysis of Kaplan-Meier survival curve demonstrates that median overall survival time is 29.4 m (...truncated)