MYC drives aggressive prostate cancer by disrupting transcriptional pause release at androgen receptor targets

c-MYC (MYC) is a major driver of prostate cancer tumorigenesis and progression. Although MYC is overexpressed in both early and metastatic disease and associated with poor survival, its impact on prostate transcriptional reprogramming remains elusive. We demonstrate that MYC overexpression significantly diminishes the androgen receptor (AR) transcriptional program (the set of genes directly targeted by the AR protein) in luminal prostate cells without altering AR expression. Analyses of clinical specimens reveal that concurrent low AR and high MYC transcriptional programs accelerate prostate cancer progression toward a metastatic, castration-resistant disease. Data integration of single-cell transcriptomics together with ChIP-seq uncover an increase in RNA polymerase II (Pol II) promoter-proximal pausing at AR-dependent genes following MYC overexpression without an accompanying deactivation of AR-bound enhancers. Altogether, our findings suggest that MYC overexpression antagonizes the canonical AR transcriptional program and contributes to prostate tumor initiation and progression by disrupting transcriptional pause release at AR-regulated genes.


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VP, DPL and AP biospecimens for scRNA-seq were harvested from a single WT or Hi-MYC mouse. The impact of MYC overexpression on the Androgen_response was replicated using data from Barfeld et al., Labrecque et al. and the LuCaP PDXs series. Protein expression in VP was assessed from three biological independent biospecimens. The murine ChIP-seq analyses reported comparing genotype conditions uses two pools of biological replicates comprised of at least 8 samples each harvested from distinct mice and key results were replicated using data from Barfeld et al. and the LuCaP PDXs series. Number of independent samples is clearly stated in the manuscript. The combination of the Hallmark Androgen_response / Hallmark MYC_targets_V1 and AR-A / Hallmark MYC_targets_V1 signatures and their association with prostate cancer progression was examined (and replicated) in the META855 cohort using the thresholds obtained from quantiles defined in the TCGA dataset (discovery cohort). This finding was also replicated in a mCRPC cohort (Abida et al.).
Randomization was not relevant to this study because comparisons were across distinct conditions. Histopathological slides were analysed by expert murine uropathologist, who were blind to the experimental conditions. Investigators were blind to the results obtained from the discovery cohort (TCGA) for the validation analysis (META855 cohort). All other experiments were performed in a non-blind fashion in order to perform comparisons across distinct conditions or because of the laboratory structure making blinding impractical. Note that full information on the approval of the study protocol must also be provided in the manuscript.

Human research participants
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FVB Hi-MYC (strain number 01XK8), expressing the human c-MYC transgene in prostatic epithelium (heterozygous for MYC transgene), were obtained from the National Cancer Institute Mouse Repository at Frederick National Laboratory for Cancer Research. Hi-MYC mice were bred with wild-type FVB mice to obtain male wild-type and Hi-MYC mice to be used for this research. At 12 weeks of age, male mice were euthanized and tissues were collected.
No wild animals were used in this study.
No field collected samples were used in the study.
The animal protocol (#13-049) was reviewed and approved by the Dana-Farber Cancer Institute Institutional Animal Care and Use Committee (IACUC), and was in accordance with the Animal Welfare Act. The animal protocol (#2017-7961) also followed the ethical guidelines of the Canadian Council on Animal Care, and was approved by the Research Institute of the McGill University Health Centre Glen Facility Animal Care Committee (FACC).
Informed consent was obtained to collect human mCRPC tissues and generate the patient-derived xenograft tumors as described previously (Labrecque et al., J Clin Oncol, 2017;Nguyen et al., Prostate, 2017). The study was approved by the University of Washington Human Subjects Division Institutional Review Board (no. 2341). All patients were males with advanced prostate cancer that received androgen ablation therapy. Age at diagnosis was captured as well as the source of the tissue.
Patients were approached and enrolled in the prostate cancer donor program by their oncologist at the University of Washington. After confirming consent with the patient and/or the immediate family of a patient with advanced disease, tumor specimens were collected after death. While efforts to recruit minority patients are ongoing, the patient population at the University of Washington and the Seattle catchment area for the program are predominantly white. This leads to a selection bias towards white patients within the patient cohort.