Article

Interrogating androgen receptor function in recurrent prostate cancer

Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Ángeles, California, United States
Cancer Research (Impact Factor: 9.33). 09/2003; 63(15):4552-60.
Source: PubMed

ABSTRACT

The early androgen-dependent (AD) phase of prostate cancer is dependent on the androgen receptor (AR). However, it is unclear whether AR is fully functional in recurrent prostate cancer after androgen withdrawal. To address this issue we interrogated AR signaling in AD and recurrent prostate cancer xenografts using molecular imaging, chromatin immunoprecipitation, and immunohistochemistry. In the imaging experiments, an adenovirus bearing a two-step transcriptional activation cassette, which amplifies AR-dependent firefly luciferase reporter gene activity, was injected into tumors implanted into severe combined immunodeficiency mice. A charge-coupled device optical imaging system detected the initial loss and then resumption of AR transcriptional activity in D-luciferin-injected mice as tumors transitioned from AD to recurrent growth. The results of chromatin immunoprecipitation and immunohistochemical localization experiments correlated with the Ad two-step transcriptional activation imaging signal. AR localized to the nucleus and bound to the endogenous prostate-specific antigen enhancer in AD tumors but exited the nucleus and dissociated from the enhancer upon castration. However, AR reentered the nucleus and rebound the prostate-specific antigen enhancer as the cancer transitioned into the recurrent phase. Surprisingly, RNA polymerase II and the general factor TFIIB remained bound to the gene throughout the transition. Our data support the concept that AR is fully functional in recurrent cancer and suggest a model by which a poised but largely inactive transcription complex facilitates reactivation by AR at castrate levels of ligand.

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    • "AR activation under castrated conditions is thought to be the major mechanism leading to prostate cancer progression to castration resistance [6] [7]. Thus, abnormal AR nuclear localization in the absence of androgens may represent a key step leading to castration resistance [13] [14] [15] [16]. AR transactivation of downstream genes in castration-resistant prostate cancer cells requires its nuclear localization under castration conditions. "
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    ABSTRACT: Nucleocytoplasmic trafficking of the androgen receptor (AR) represents an essential step in androgen action. To determine whether the amino-terminal domain (NTD) contains potential nuclear import and/or export signals, deletion mutants of the NTD tagged with green fluorescent protein (GFP) were generated and tested for their intracellular localization in both AR-negative and AR-positive cell lines. Subcellular localization analysis suggested a role of the NTD in regulating AR subcellular localization and revealed that the region of a.a. 50-250 of the NTD of AR (AR(50-250)) could promote cytoplasmic localization. Leptomycin B inhibited the activity of AR(50-250), suggesting that AR(50-250) export is mediated through exportin 1, either directly or indirectly. These observations argue for an important role of the NTD in regulating AR nucleocytoplasmic trafficking and will facilitate further investigation of interactions among different signals in regulating AR nucleocytoplasmic trafficking, which may lead to new approaches to inhibit AR nuclear localization.
    Full-text · Article · Oct 2013 · The Journal of Steroid Biochemistry and Molecular Biology
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    • "Notably, during cancer progression, androgen receptor (AR) undergoes androgen-independent nuclear import through a mechanism involving MAPK pathway activation (Zhang et al. 2003). Estradiol activation of PI3-K/Akt (protein kinase B) pathway regulates estradiol receptor (ER) alpha nuclear export and cell cycle progression in MCF-7 cells (Lombardi et al. 2008). "
    Dataset: JCCS 2010

    Full-text · Dataset · Nov 2012
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    • "A redistribution of AR subcellular localization in disease states may therefore be indicative of an altered status of receptor activation or response. This is most commonly observed in prostate cancer following the failure of androgen deprivation therapy, whereby the AR subcellular distribution shifts to become predominately nuclear (Zhang et al. 2003). Understanding how the AR translocates to the nucleus, and the role of the chaperone complex in this process, is therefore imperative for our overall appreciation of AR action in both normal development and cancer. "
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    ABSTRACT: Ligand-dependent activity of steroid receptors is affected by tetratricopeptide repeat (TPR)-containing co-chaperones, such as small glutamine-rich tetratricopeptide repeat-containing alpha (SGTA). However, the precise mechanisms by which the predominantly cytoplasmic TPR proteins affect downstream transcriptional outcomes of steroid signaling remain unclear. In this study, we assessed how SGTA affects ligand sensitivity and action of the androgen receptor (AR) using a transactivation profiling approach. Deletion mapping coupled with structural prediction, transcriptional assays, and in vivo regulation of AR-responsive promoters were used to assess the role of SGTA domains in AR responses. At subsaturating ligand concentrations of ≤ 0.1 nM 5α-dihydrotestosterone, SGTA overexpression constricted AR activity by an average of 32% (P<0.002) across the majority of androgen-responsive loci tested, as well as on endogenous promoters in vivo. The strength of the SGTA effect was associated with the presence or absence of bioinformatically predicated transcription factor motifs at each site. Homodimerizaion of SGTA, which is thought to be necessary for chaperone complex formation, was found to be dependent on the structural integrity of amino acids 1-80, and a core evolutionary conserved peptide within this region (amino acids 21-40) necessary for an effect of SGTA on the activity of both exogenous and endogenous AR. This study provides new insights into the subdomain structure of SGTA and how SGTA acts as a regulator of AR ligand sensitivity. A change in AR:SGTA ratio will impact the cellular and molecular response of prostate cancer cells to maintain androgenic signals, which may influence tumor progression.
    Preview · Article · Jun 2012 · Journal of Molecular Endocrinology
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