Structural and functional association of androgen receptor with telomeres in prostate cancer cells

Abstract

Telomeres protect the ends of linear chromosomes from being recognized as damaged DNA, and telomere stability is required for genome stability. Here we demonstrate that telomere stability in androgen receptor (AR)-positive LNCaP human prostate cancer cells is dependent on AR and androgen, as AR inactivation by AR antagonist bicalutamide (Casodex), AR-knockdown, or androgen-depletion caused telomere dysfunction, and the effect of androgen-depletion or Casodex was blocked by the addition of androgen. Notably, neither actinomycin D nor cycloheximide blocked the DNA damage response to Casodex, indicating that the role of AR in telomere stability is independent of its role in transcription. We also demonstrate that AR is a component of telomeres, as AR-bound chromatin contains telomeric DNA, and telomeric chromatin contains AR. Importantly, AR inactivation by Casodex caused telomere aberrations, including multiple abnormal telomere signals, remindful of a fragile telomere phenotype that has been described previously to result from defective telomere DNA replication. We suggest that AR plays an important role in telomere stability and replication of telomere DNA in prostate cancer cells, and that AR inactivation-mediated telomere dysfunction may contribute to genomic instability and progression of prostate cancer cells.

ATM Inhibition Potentiates Death of Androgen Receptor-inactivated Prostate Cancer Cells with Telomere Dysfunction

“…Therefore, cells containing immunofluorescent foci of 53BP1 and phosphorylated H2AX (␥H2AX) colocalized with telomeric protein TIN2, which are referred to as telomere-dysfunction induced foci (TIF), were scored as a measure of DNA damage response as described previously (3,4). Individual cells with Ͼ5 53BP1 or ␥H2AX foci were considered as being TIF response-positive.…”

“…Therefore, there is an urgent need for novel therapeutic strategies for the treatment of prostate cancer. Our studies point to a novel role of AR in telomere stability (3,4) that may be harnessed to potentiate the efficacy of currently available AR-targeted therapies for a more effective treatment of prostate cancer.…”

“…DDR at Telomeres-DNA damage is marked by the phosphorylation of histone H2AX (␥-H2AX) at the sites of damaged DNA (28), and colocalization of ␥-H2AX and TIN2 (a shelterin protein unique to telomeres (22)) indicates telomere DNA damage (4,29). Fig.…”

“…We recently reported that AR itself is an accessory protein associated with telomeres in prostate cancer cells; AR chromatin immunoprecipitate prepared using AR antibodies (AR-ChIP) contains telomeric DNA, telomeric chromatin isolated using a protocol called "proteomics of isolated chromatin" (PICh) (6) contains AR, and AR immunoprecipitates and colocalizes with telomeric proteins in LNCaP cells (3,4). A functional role of AR in telomere stability is indicated from the observations that (a) AR inactivation by androgen-depletion, treatment with antiandrogens such as bicalutamide (Casodex) or MDV3100 (Enzalutamide), or treatment with AR-siRNA results in telomere dysfunction, and (b) the synthetic androgen R1881 blocks androgen depletion-mediated telomere dysfunction (3,4).…”

“…In patients with prostate cancer, genomic instability due to telomere shortening is reported to be associated with worse prognosis (13). Interestingly, telomere aberrations of the kind seen in TRF1-or TRF2-deficient cells with telomere dysfunction (14,15) are also seen in AR-inactivated prostate cancer cells (4). However, it is not known whether AR inactivation-induced telomere dysfunction triggers activation of DDR signaling pathways that promote survival of AR inactivated prostate cancer cells.…”