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

ABSTRACT: 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.

ORGANISM(S): Homo sapiens

PROVIDER: GSE187413 | GEO | 2022/02/01

REPOSITORIES: GEO

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Project description:The androgen receptor (AR) plays a key role in progression to incurable androgen-ablation resistant prostate cancer (PCA). We have identified three novel AR splice variants lacking the ligand binding domain (designated as AR3, AR4 and AR5) in hormone insensitive PCA cells. AR3, one of the major splice variants expressed in human prostate tissues, is constitutively active and its transcriptional activity is not regulated by androgens or antiandrogens. Immunohistochemistry analysis on tissue microarrays containing 429 human prostate tissue samples shows that AR3 is significantly upregulated during PCA progression and AR3 expression level is correlated with the risk of tumor recurrence after radical prostatectomy. Overexpression of AR3 confers ablation-independent growth of PCA cells while specific knock-down of AR3 expression (without altering AR level) in hormone resistant PCA cells attenuates their growth under androgen-depleted conditions in both cell culture and xenograft models, suggesting an indispensable role of AR3 in ablation-independent growth of PCA cells. Furthermore, AR3 may play a distinct yet essential role in ablation-independent growth through regulating a unique set of genes including AKT1, which are not regulated by the prototype AR. Our data suggest that aberrant expression of AR splice variants may be a novel mechanism underlying ablation-independence during PCA progression and AR3 may serve as a prognostic marker to predict patient outcome in response to hormonal therapy. Given that these novel AR splice variants are not inhibited by currently available anti-androgen drugs, development of new drugs targeting these AR isoforms may potentially be effective for treatment of ablation-resistant PCA. Total RNA was extracted from CWR-R1 and 22Rv1 cells treated with shAR3-1, shARa and the scrambled shRNA control, respectively. Each of CWR-R1 and 22Rv1 cells treated with shAR3-1 was compared with the scrambled shRNA control. The same experiments were performed for the cells treated with shARa.

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

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