Investigating Mechanisms of Chemotherapy Resistance in Quiescent Cancer Cells

Abstract

Chemotherapy resistance remains a significant challenge in cancer treatment, with chemotherapy failing in up to 90% of cancer cases. Here, we report on our investigation of chemotherapy resistance, in which we have made three key discoveries. First, we found that the RNA-binding protein FXR1 induces selective translation of survival genes in quiescent (G0) acute monocytic leukemia cells, driving chemotherapy resistance. To understand this phenomenon, we performed ribosome profiling and functional analyses of FXR1-overexpressing cells. Our results indicate that FXR1 activates the integrative stress response and causes the translation of key genes responsible for survival and resistance. Second, we discovered that chemoresistant breast cancer cells secrete increased amounts of extracellular vesicles (EVs) that contain proteins and RNAs that contribute to cancer proliferation and chemoresistance, suggesting a possible mechanism of spreading their oncogenic properties to neighboring cancer cells. We used tangential flow filtration to isolate these EVs and nanoparticle tracking analysis to determine their size distribution, as we performed RT-qPCR and Western blotting to identify their biomolecular components. Finally, we found that EVs secreted by chemoresistant breast cancer cells are enriched in circular RNAs, which are known to be associated with chemotherapy resistance and may be translated to form novel proteins. We used RNA-seq and BLAST analysis to identify these circRNAs and found that they contained m6A motifs and non-AUG start sites, and we used polysome profiling to show that these circRNAs bind to ribosomes. Overall, these results suggest potential therapeutic targets to allow chemotherapy treatments to be more effective, and they shed insight into the mechanisms of resistance in cancer cells.