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Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer.

ABSTRACT: The androgen receptor (AR) plays a leading role in the control of prostate cancer (PCa) growth. Interestingly, structurally different AR antagonists with distinct mechanisms of antagonism induce cell senescence, a mechanism that inhibits cell cycle progression, and thus seems to be a key cellular response for the treatment of PCa. Surprisingly, while physiological levels of androgens promote growth, supraphysiological androgen levels (SAL) inhibit PCa growth in an AR-dependent manner by inducing cell senescence in cancer cells. Thus, oppositional acting ligands, AR antagonists, and agonists are able to induce cellular senescence in PCa cells, as shown in cell culture model as well as ex vivo in patient tumor samples. This suggests a dual AR-signaling dependent on androgen levels that leads to the paradox of the rational to keep the AR constantly inactivated in order to treat PCa. These observations however opened the option to treat PCa patients with AR antagonists and/or with androgens at supraphysiological levels. The latter is currently used in clinical trials in so-called bipolar androgen therapy (BAT). Notably, cellular senescence is induced by AR antagonists or agonist in both androgen-dependent and castration-resistant PCa (CRPC). Pathway analysis suggests a crosstalk between AR and the non-receptor tyrosine kinase Src-Akt/PKB and the PI3K-mTOR-autophagy signaling in mediating AR-induced cellular senescence in PCa. In this review, we summarize the current knowledge of therapeutic induction and intracellular pathways of AR-mediated cellular senescence.

SUBMITTER: Kokal M

PROVIDER: S-EPMC7408918 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer.

Kokal Miriam M Mirzakhani Kimia K Pungsrinont Thanakorn T Baniahmad Aria A

Cancers 20200708 7

The androgen receptor (AR) plays a leading role in the control of prostate cancer (PCa) growth. Interestingly, structurally different AR antagonists with distinct mechanisms of antagonism induce cell senescence, a mechanism that inhibits cell cycle progression, and thus seems to be a key cellular response for the treatment of PCa. Surprisingly, while physiological levels of androgens promote growth, supraphysiological androgen levels (SAL) inhibit PCa growth in an AR-dependent manner by inducing ...[more]

PMID: 32650419

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Project description:BackgroundThe benefit of inducing cellular senescence as a tumor suppressive strategy remains questionable due to the senescence-associated secretory phenotype. Hence, studies and development of senolytic compounds that induce cell death in senescent cells have recently emerged. Senescent cells are hypothesized to exhibit different upregulated pro-survival/anti-apoptotic networks depending on the senescent inducers. This might limit the effect of a particular senolytic compound that targets rather only a specific pathway. Interestingly, cellular senescence in prostate cancer (PCa) cells can be induced by either androgen receptor (AR) agonists at supraphysiological androgen level (SAL) used in bipolar androgen therapy or by AR antagonists. This challenges to define ligand-specific senolytic compounds.ResultsHere, we first induced cellular senescence by treating androgen-sensitive PCa LNCaP cells with either SAL or the AR antagonist Enzalutamide (ENZ). Subsequently, cells were incubated with the HSP90 inhibitor Ganetespib (GT), the Bcl-2 family inhibitor ABT263, or the Akt inhibitor MK2206 to analyze senolysis. GT and ABT263 are known senolytic compounds. We observed that GT exhibits senolytic activity specifically in SAL-pretreated PCa cells. Mechanistically, GT treatment results in reduction of AR, Akt, and phospho-S6 (p-S6) protein levels. Surprisingly, ABT263 lacks senolytic effect in both AR agonist- and antagonist-pretreated cells. ABT263 treatment does not affect AR, Akt, or S6 protein levels. Treatment with MK2206 does not reduce AR protein level and, as expected, potently inhibits Akt phosphorylation. However, ENZ-induced cellular senescent cells undergo apoptosis by MK2206, whereas SAL-treated cells are resistant. In line with this, we reveal that the pro-survival p-S6 level is higher in SAL-induced cellular senescent PCa cells compared to ENZ-treated cells. These data indicate a difference in the agonist- or antagonist-induced cellular senescence and suggest a novel role of MK2206 as a senolytic agent preferentially for AR antagonist-treated cells.ConclusionTaken together, our data suggest that both AR agonist and antagonist induce cellular senescence but differentially upregulate a pro-survival signaling which preferentially sensitize androgen-sensitive PCa LNCaP cells to a specific senolytic compound.

Project description:The bipolar androgen therapy (BAT) to treat prostate cancer includes cycles of supraphysiological androgen levels (SAL) under continuous androgen deprivation therapy (ADT). We showed previously that SAL induces cellular senescence in androgen-sensitive PCa cells and ex vivo in PCa tumor samples from patients that underwent radical prostatectomy. Here, we show that SAL induces cellular senescence in both, castration sensitive (CSPC) LNCaP and castration resistant PCa (CRPC) C4-2 cells through the cell cycle inhibitor p15. Treatment with the Akt inhibitor (Akti) potently inhibited SAL-induced expression of p15 and cellular senescence in both cell lines. Proximity ligation assays (PLA) combined with high-resolution laser-scanning microscopy indicate that SAL promotes interaction of endogenous androgen receptor (AR) with endogenous Akt in cytoplasm as well as in nucleus after 72 hours hormone treatment. This suggests that the AR interacts with Akt also in a long-term manner. Transcriptome sequencing (RNA-seq) comparing the SAL-induced transcriptomes of LNCaP with C4-2 cells as well as of Akti treated cells revealed landscapes for cell senescence. Interestingly, one of the identified genes is the lncRNASAT1. SAL treatment of native patient tumor samples ex vivo results in upregulation of lncRNASAT1. The lncRNASAT1 is down-regulated in PCa tumor tissues compared to non-tumor tissues of same patients indicating a tumor suppressive function. Knockdown indicates that the lncRNASAT1 is crucial for SAL-induced cancer cell senescence and regulates LNCaP cell proliferation being an upstream factor for pAkt and for p15. Further, knockdown of lncRNASAT1 inhibits LNCaP cell proliferation by low androgen levels but enhances proliferation by SAL. This suggests that lncRNASAT1 serves as a tumor suppressor with SAL. Interestingly, immunoprecipitation of AR detected lncRNASAT1 as an AR interacting partner that regulates AR target gene expression. Thus, we identified a novel pathway of androgen signaling as the AR- lncRNASAT1- Akt- p15INK4b- axis to mediate SAL-induced cellular senescence.

Dataset Information

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer.

Publications

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer.

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