Abstract
Deregulated expression of circular RNAs (circRNAs) is associated with various human diseases, including many types of cancer. Despite their growing links to cancer, there has been limited characterization of circRNAs in metastatic castration-resistant prostate cancer, the major cause of prostate cancer mortality. Here, through the analysis of an exome-capture RNA-seq dataset from 47 metastatic castration-resistant prostate cancer samples and ribodepletion and RNase R RNA-sequencing of patient-derived xenografts (PDXs) and cell models, we identified 13 circRNAs generated from the key prostate cancer driver gene-androgen receptor (AR). We validated and characterized the top four most abundant, clinically relevant AR circRNAs. Expression of these AR circRNAs was upregulated during castration-resistant progression of PDXs. The upregulation was not due to global increase of circRNA formation in these tumors. Instead, the levels of AR circRNAs correlated strongly with that of the linear AR transcripts (both AR and AR variants) in clinical samples and PDXs, indicating a transcriptional mechanism of regulation. In cultured cells, androgen suppressed the expression of these AR circRNAs and the linear AR transcripts, and the suppression was attenuated by an antiandrogen. Using nuclear/cytoplasmic fractionation and RNA in-situ hybridization assays, we demonstrated predominant cytoplasmic localization of these AR circRNAs, indicating likely cytoplasmic functions. Overall, this is the first comprehensive characterization of circRNAs arising from the AR gene. With greater resistance to exoribonuclease compared to the linear AR transcripts and detectability of AR circRNAs in patient plasma, these AR circRNAs may serve as surrogate circulating markers for AR/AR-variant expression and castration-resistant prostate cancer progression.
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Acknowledgements
We are grateful to Dr. Alan Meeker at Johns Hopkins University for providing LNCaP95 cells. We appreciate the support from the Tulane Cancer Next Generation Sequence Analysis core for utilization of resources and expertize for this work.
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This work was supported by the following grants: the National Institutes of Health grants R01CA188609, R01AI101046, R01AI106676, P01CA214091, PNW Prostate Cancer SPORE P50CA097186, P01CA163227, RCMI 2U54MD007595, and 5P20GM103424-17; Department of Defense grants W81XWH-15-1-0439, W81XWH-16-1-0317, and W81XWH-16-1-0318; The Prostate Cancer Foundation. The Richard M. Lucas Foundation supported the development of the LuCaP models. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies.
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Cao, S., Ma, T., Ungerleider, N. et al. Circular RNAs add diversity to androgen receptor isoform repertoire in castration-resistant prostate cancer. Oncogene 38, 7060–7072 (2019). https://doi.org/10.1038/s41388-019-0947-7
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DOI: https://doi.org/10.1038/s41388-019-0947-7
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