Expression of the RNA-binding protein RBM3 is associated with a favourable prognosis and cisplatin sensitivity in epithelial ovarian cancer

Åsa Ehlén,Jonas Manjer,Ian B Jeffrey,Donal J Brennan,Karin Jirström,Jakob Eberhard,Fredrik Pontén,Jenny Brändstedt,Mathias Uhlén,Björn Nodin,Maria Alvarado-Kristensson,Darran P O'Connor

doi:10.1186/1479-5876-8-78

Abstract

BackgroundWe recently demonstrated that increased expression of the RNA-binding protein RBM3 is associated with a favourable prognosis in breast cancer. The aim of this study was to examine the prognostic value of RBM3 mRNA and protein expression in epithelial ovarian cancer (EOC) and the cisplatin response upon RBM3 depletion in a cisplatin-sensitive ovarian cancer cell line.MethodsRBM3 mRNA expression was analysed in tumors from a cohort of 267 EOC cases (Cohort I) and RBM3 protein expression was analysed using immunohistochemistry (IHC) in an independent cohort of 154 prospectively collected EOC cases (Cohort II). Kaplan Meier analysis and Cox proportional hazards modelling were applied to assess the relationship between RBM3 and recurrence free survival (RFS) and overall survival (OS). Immunoblotting and IHC were used to examine the expression of RBM3 in a cisplatin-resistant ovarian cancer cell line A2780-Cp70 and its cisplatin-responsive parental cell line A2780. The impact of RBM3 on cisplatin response in EOC was assessed using siRNA-mediated silencing of RBM3 in A2780 cells followed by cell viability assay and cell cycle analysis.ResultsIncreased RBM3 mRNA expression was associated with a prolonged RFS (HR = 0.64, 95% CI = 0.47-0.86, p = 0.003) and OS (HR = 0.64, 95% CI = 0.44-0.95, p = 0.024) in Cohort I. Multivariate analysis confirmed that RBM3 mRNA expression was an independent predictor of a prolonged RFS, (HR = 0.61, 95% CI = 0.44-0.84, p = 0.003) and OS (HR = 0.62, 95% CI = 0.41-0.95; p = 0.028) in Cohort I. In Cohort II, RBM3 protein expression was associated with a prolonged OS (HR = 0.53, 95% CI = 0.35-0.79, p = 0.002) confirmed by multivariate analysis (HR = 0.61, 95% CI = 0.40-0.92, p = 0.017). RBM3 mRNA and protein expression levels were significantly higher in the cisplatin sensitive A2780 cell line compared to the cisplatin resistant A2780-Cp70 derivative. siRNA-mediated silencing of RBM3 expression in the A2780 cells resulted in a decreased sensitivity to cisplatin as demonstrated by increased cell viability and reduced proportion of cells arrested in the G2/M-phase.ConclusionsThese data demonstrate that RBM3 expression is associated with cisplatin sensitivity in vitro and with a good prognosis in EOC. Taken together these findings suggest that RBM3 may be a useful prognostic and treatment predictive marker in EOC.

Highlights

We recently demonstrated that increased expression of the RNA-binding protein RBM3 is associated with a favourable prognosis in breast cancer
IHC performed on formalin fixed, paraffin embedded small interfering RNA (siRNA) transfected A2780 cells revealed a marked decrease in immunoreactivity in the RBM3 knockdown cells compared to controls as visualized by IHC on cell pellets (Fig. 1A) and Western blotting (Fig. 1B)
We initially confirmed lower RBM3 protein levels in the cisplatin-resistant ovarian cancer cell line A2780-Cp70 compared to their parental cisplatin-sensitive A2780 cells and using RNAi techniques, we demonstrated that silencing of RBM3 led to a decreased cisplatin response in ovarian cancer cells

Summary

Introduction

We recently demonstrated that increased expression of the RNA-binding protein RBM3 is associated with a favourable prognosis in breast cancer. The aim of this study was to examine the prognostic value of RBM3 mRNA and protein expression in epithelial ovarian cancer (EOC) and the cisplatin response upon RBM3 depletion in a cisplatin-sensitive ovarian cancer cell line. Since its inception over 40 years ago, the platinumbased agent cisplatin has had a major impact on cancer therapy, in the treatment of testicular and ovarian cancer [2]. Despite an initial response to cisplatin treatment, many patients with EOC develop resistance to the drug and relapse within a few years [4]. Several mechanisms have been implicated in cisplatin resistance, i.e. decreased drug uptake, insufficient DNA-binding of the drug, increased DNA-repair of cisplatin adducts and failure of induction of apoptosis, reviewed in [2,5,7]

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