Cellular mechanisms associated with chemotherapy induced ribosomal RNA disruption in ovarian cancer cells

Abstract

The degradation of RNA is a ubiquitous process prevalent in all cells; employed to maintain nucleotide turnover, maturation, and quality control of RNA. A recent breast cancer clinical trial demonstrated that the degradation of ribosomal RNA (rRNA) in tumour biopsies, referred to as RNA disruption, could serve as a potential biomarker for patients receiving chemotherapy treatment. Given that most, if not all, chemotherapy treatments are associated with toxic side effects, the ability to differentiate early in treatment between patients whose tumours respond to chemotherapy versus patients whose tumours do not would be a very useful tool to prevent needless toxicity in nonresponding patients. Further research, in vitro, demonstrated that this phenomenon was reproducible using a number of different chemotherapy agents in a variety of cancer cell lines. While studies have indicated measuring RNA disruption can be a useful tool in clinical diagnosis, the mechanism(s) of RNA disruption in response to chemotherapy treatment are not well understood. The aim of this study was to investigate the role of Nonfunctional RNA Decay (NRD), RNase L, autophagy, and apoptosis in chemotherapyinduced RNA disruption. Treatment of A280 ovarian carcinoma cells with a proteasome inhibitor did not reduce chemotherapy-induced RNA disruption, suggesting that NRD does not play a role. However, treating A2780 cells with the synthetic dsRNA Poly I:C and a small molecule RNase L activator (RLA), induced an rRNA disruption pattern comparable to that of docetaxel (DXL). Furthermore, A2780 cells transfected with the RNase L inhibitor ABCE1 reduced rRNA disruption in response to DXL or RLA treatment, demonstrating a potential link between RNase L and RNA disruption. Immunoblot experiments revealed that DXL and RLA induced elevated levels of protein associated with the activation of autophagy (LC3-II) at 12, 24, and 48 hours after treatment. DXL and RLA also induces increased levels of proteolytic products associated with apoptosis (PARP) at 12 and 24 hours post-treatment. DXL and RLA-induced RNA disruption was strongest at 48 hours, suggesting that that DXL and RLA-induced RNA disruption are not concurrent with autophagy and apoptosis. The results of the study provide greater insight into the mechanisms associated with chemotherapy-dependent RNA disruption, which could be helpful in the future in improving the accuracy of the RNA disruption assay as a chemotherapy response biomarker.