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Phosphorylation of the androgen receptor at Ser81 is co-sustained by CDK1 and CDK9 and leads to AR-mediated transactivation in prostate cancer.

ABSTRACT: Androgen receptor (AR) is the principal molecule in prostate cancer (PCa) etiology and therapy. AR re-activation still remains a major challenge during treatment of castration-resistant prostate cancer (CRPC) tumors that relapse after castration therapies. Recent reports have indicated the enrichment of Ser81-phosphorylated AR (pS81) in the nucleus of CRPC cells, and CDK1 and CDK9 as the kinases phosphorylating AR at S81. In the current study we showed that pS81 is preferentially localized in the nucleus in both rapid biopsy metastatic CRPC samples and PCa xenografts, and nuclear pS81 localization is correlated with AR transactivation in tumor xenografts. Chromatin immunoprecipitation (ChIP) analysis demonstrated an alignment of S81 phosphorylation and AR-mediated transactivation with the chromatin locus openness. Moreover, pS81-specific ChIP-Seq showed a disproportional occupancy of pS81 on AR-activated promoters, while 3C-ChIP assays further indicated an enrichment of pS81 at the PSA enhancer-promoter loop, a known AR activating hub. In the latter, CDK9 was shown to modulate the transactivation of the AR and RNA Pol II. Indeed, ChIP and re-ChIP assays also confirmed that AR-dependent activation of the PSA enhancer and promoter mediated by pS81 was coupled with activation of Pol II and the pTEFb complex. Mechanistically, we determined that CDK1 and CDK9 sustained the pS81 AR modification in the soluble and chromatin-bound fractions of PCa cells, respectively. Finally, we demonstrated that CDK1 activity was maintained throughout the cell cycle, and that CDK1 inhibitors restored androgen sensitivity in CRPC tumor cells. Based on these findings, CDK1 and CDK9 could be targeted as pS81 kinases in patients with CRPC, either alone or in conjunction with direct AR antagonists.

SUBMITTER: Gao X

PROVIDER: S-EPMC8253089 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The bipolar androgen therapy (BAT) includes the treatment of prostate cancer (PCa) patients with supraphysiological androgen level (SAL). Interestingly, SAL induces cell senescence in PCa cell lines as well as ex vivo in tumor samples of patients. The SAL-mediated cell senescence was shown to be androgen receptor (AR)-dependent and mediated in part by non-genomic AKT signaling. RNA-seq analyses compared with and without SAL treatment as well as by AKT inhibition (AKTi) revealed a specific transcriptome landscape. Comparing the top 100 genes similarly regulated by SAL in two human PCa cell lines that undergo cell senescence and being counteracted by AKTi revealed 33 commonly regulated genes. One gene, ERBB receptor feedback inhibitor 1 (ERRFI1), encodes the mitogen-inducible gene 6 (MIG6) that is potently upregulated by SAL, whereas the combinatory treatment of SAL with AKTi reverses the SAL-mediated upregulation. Functionally, knockdown of ERRFI1 enhances the pro-survival AKT pathway by enhancing phosphorylation of AKT and the downstream AKT target S6, whereas the phospho-retinoblastoma (pRb) protein levels were decreased. Further, the expression of the cell cycle inhibitor p15INK4b is enhanced by SAL and ERRFI1 knockdown. In line with this, cell senescence is induced by ERRFI1 knockdown and is enhanced slightly further by SAL. Treatment of SAL in the ERRFI1 knockdown background enhances phosphorylation of both AKT and S6 whereas pRb becomes hypophosphorylated. Interestingly, the ERRFI1 knockdown does not reduce AR protein levels or AR target gene expression, suggesting that MIG6 does not interfere with genomic signaling of AR but represses androgen-induced cell senescence and might therefore counteract SAL-induced signaling. The findings indicate that SAL treatment, used in BAT, upregulates MIG6, which inactivates both pRb and the pro-survival AKT signaling. This indicates a novel negative feedback loop integrating genomic and non-genomic AR signaling.

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Phosphorylation of the androgen receptor at Ser81 is co-sustained by CDK1 and CDK9 and leads to AR-mediated transactivation in prostate cancer.

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