Potent stimulation of the androgen receptor instigates a viral mimicry response in prostate cancer [ChIP-seq]

Inhibiting the androgen receptor (AR), a ligand-activated transcription factor, with androgen deprivation therapy is a standard-of-care treatment for metastatic prostate cancer (PCa). Paradoxically, activation of AR can also inhibit the growth of PCa in some patients and experimental systems, but the mechanisms underlying this phenomenon are poorly understood. This study exploited a potent synthetic androgen, methyltestosterone (MeT), to investigate AR agonist-induced growth inhibition. MeT strongly inhibited growth of PCa cells expressing AR, but not AR-negative models. Genes and pathways regulated by MeT were highly analogous to those regulated by DHT, although MeT induced a quantitatively greater androgenic response in PCa cells. MeT potently down-regulated DNA methyltransferases, leading to global DNA hypomethylation. These epigenomic changes were associated with dysregulation of transposable element expression, with long-term MeT treatment resulting in upregulation of endogenous retrovirus (ERV) transcripts. Increased ERV expression led to accumulation of double-stranded RNA and a “viral mimicry” response characterised by activation of interferon signalling, upregulation of MHC Class I molecules and enhanced recognition of murine PCa cells by CD8+ T cells. Positive associations between AR activity and ERVs/anti-viral pathways were evident in patient transcriptomic data, supporting the clinical relevance of our findings. Collectively, our study reveals that the potent androgen MeT can increase the immunogenicity of PCa cells via a viral mimicry response, a finding that has potential implications for the development of strategies to sensitize this cancer type to immunotherapies. Overall design: Androgen receptor ChIP-seq following androgen treatment in LNCaP prostate cancer cells