The androgen receptor depends on ligand-binding domain dimerization for transcriptional activation.

Whereas dimerization of the DNA-binding domain of the androgen receptor (AR) plays an evident role in recognizing bipartite response elements, the contribution of the dimerization of the ligand-binding domain (LBD) to the correct functioning of the AR remains unclear. Here, we describe a mouse model with disrupted dimerization of the AR LBD (ARLmon/Y ). The disruptive effect of the mutation is demonstrated by the feminized phenotype, absence of male accessory sex glands, and strongly affected spermatogenesis, despite high circulating levels of testosterone. Testosterone replacement studies in orchidectomized mice demonstrate that androgen-regulated transcriptomes in ARLmon/Y mice are completely lost. The mutated AR still translocates to the nucleus and binds chromatin, but does not bind to specific AR binding sites. In vitro studies reveal that the mutation in the LBD dimer interface also affects other AR functions such as DNA binding, ligand binding, and co-regulator binding. In conclusion, LBD dimerization is crucial for the development of AR-dependent tissues through its role in transcriptional regulation in vivo. Our findings identify AR LBD dimerization as a possible target for AR inhibition.

Rational evolution for altering the ligand preference of estrogen receptor alpha.

Estrogen receptor α is commonly used in synthetic biology to control the activity of genome editing tools. The activating ligands, estrogens, however, interfere with various cellular processes, thereby limiting the applicability of this receptor. Altering its ligand preference to chemicals of choice solves this hurdle but requires adaptation of unspecified ligand-interacting residues. Here, we provide a solution by combining rational protein design with multi-site-directed mutagenesis and directed evolution of stably integrated variants in Saccharomyces cerevisiae. This method yielded an estrogen receptor variant, named TERRA, that lost its estrogen responsiveness and became activated by tamoxifen, an anti-estrogenic drug used for breast cancer treatment. This tamoxifen preference of TERRA was maintained in mammalian cells and mice, even when fused to Cre recombinase, expanding the mammalian synthetic biology toolbox. Not only is our platform transferable to engineer ligand preference of any steroid receptor, it can also profile drug-resistance landscapes for steroid receptor-targeted therapies.

Study of novel androgen receptor V770 variant in androgen insensitivity syndrome patients reveals the transitional state of the androgen receptor ligand binding domain homodimer.

We report the discovery of the androgen receptor missense mutation V770D, that was found in two sisters suffering from complete androgen insensitivity. Experimental validation of AR V770 variants demonstrated that AR V770D was transcriptionally inactive due to the inability to dimerize and a reduced ligand binding affinity. The more conservative AR V770A variant showed a dimerization defect at low levels of DHT with a partial recovery of the transcriptional activity and of the receptor's ability to dimerize when increasing the DHT levels. With V770 located outside of the proposed LBD dimerization interface of the AR LBD homodimer crystal structure, the effects of the V770A mutation on AR dimerization were unexpected. We therefore explored whether the AR LBD dimerization interface would be better described by an alternative dimerization mode based on available human homodimeric LBD crystal structures of other nuclear receptors. Superposition of the monomeric AR LBD in the homodimeric crystal structures of GR, PR, ER, CAR, TRß, and HNF-4α showed that the GR-like LBD dimer model was energetically the most stable. Moreover, V770 was a key energy residue in the GR-like LBD dimer while it was not involved in the stabilization of the AR LBD homodimer according to the crystal structure. Additionally, the observation that 4 AIS mutations impacted the stability of the AR LBD dimer while 16 mutations affected the GR-like LBD dimer, suggested that the AR LBD dimer crystal is a snapshot of a breathing AR LBD homodimer that can transition into the GR-like LBD dimer model.

Exploiting Ligand-binding Domain Dimerization for Development of Novel Androgen Receptor Inhibitors.

Currently, all clinically used androgen receptor (AR) antagonists target the AR ligand-binding pocket and inhibit T and dihydrotestosterone (DHT) binding. Resistance to these inhibitors in prostate cancer frequently involves AR-dependent mechanisms resulting in a retained AR dependence of the tumor. More effective or alternative AR inhibitors are therefore required to limit progression in these resistant stages. Here, we applied the structural information of the ligand-binding domain (LBD) dimerization interface to screen in silico for inhibitors. A completely new binding site, the Dimerisation Inhibiting Molecules (DIM) pocket, was identified at the LBD dimerization interface. Selection of compounds that fit the DIM pocket via virtual screening identified the DIM20 family of compounds which inhibit AR transactivation and dimerization of the full-length AR as well as the isolated LBDs. Via biolayer interferometry, reversible dose-dependent binding to the LBD was confirmed. While DIM20 does not compete with 3H-DHT for binding in the LBP, it limits the maximal activity of the AR indicative of a noncompetitive binding to the LBD. DIM20 and DIM20.39 specifically inhibit proliferation of AR-positive prostate cancer cell lines, with only marginal effects on AR-negative cell lines such as HEK 293 and PC3. Moreover, combination treatment of DIM compounds with enzalutamide results in synergistic antiproliferative effects which underline the specific mechanism of action of the DIM compounds.

Small-molecule profiling for steroid receptor activity using a universal steroid receptor reporter assay.

A critical step in the development of novel drug candidates for the treatment of steroid related diseases is ensuring the absence of crosstalk with steroid receptors (SRs). Establishing this SR cross-reactivity profile requires multiple reporter assays as each SR associates with its unique enhancer region, a labor intensive and time-consuming approach. To overcome this need for multi-reporter assays, we established a steroid receptor inducible luciferase reporter assay (SRi-Luc) that allows side-by-side examination of agonistic and antagonistic properties of small-molecules on all steroid receptors. This state-of-the-art SRi-Luc consists of a unique alteration of four distinct keto-steroid- and estrogen response elements. As proof of principle, the SRi-Luc assay was used to profile a set of novel designed steroidal 1,2,3-triazoles. These triazolized steroidal compounds were developed via our in-house triazolization methodology, in which an enolizable ketone is converted into a triazolo-fused or -linked analog by treatment with a primary amine or ammonium salt in the presence of 4-nitrophenyl azide. From these designed steroidal 1,2,3-triazoles, six successfully reduced androgen receptor activity by 40 %. Although opted as antiandrogens, their cross-reactivity with other SRs was apparent in our SRi-Luc assay and rendered them unsuited for further antagonist development and clinical use. Overall, the SRi-Luc overcomes the need of multi-reporter assays for the profiling of small-molecules on all SRs. This not only reduces the risk of introducing biases, it as well accelerates early-stage drug discovery when designing particular SR selective (ant)agonists or characterizing off-target effects of lead molecules acting on any drug target.

N/C Interactions Are Dispensable for Normal In Vivo Functioning of the Androgen Receptor in Male Mice.

The androgen receptor (AR) plays a central role in the development and maintenance of the male phenotype. The binding of androgens to the receptor induces interactions between the carboxyterminal ligand-binding domain and the highly conserved 23FQNLF27 motif in the aminoterminal domain. The role of these so-called N/C interactions in AR functioning is debated. In vitro assays show that mutating the AR in the 23FQNLF27 motif (called ARNoC) attenuates the AR transactivation of reporter genes, has no effect on ligand binding, but does affect protein-protein interactions with several AR coregulators. To test the in vivo relevance of the N/C interaction, we analyzed the consequences of the genomic introduction of the ARNoC mutation in mice. Surprisingly, the ARNoC/Y mice show a normal male development, with unaffected male anogenital distance and normal accessory sex glands, male circulating androgen levels, body composition, and fertility. The responsiveness of androgen target genes in kidney, prostate, and testes was also unaffected. We thus conclude that the N/C interactions in the AR are not essential for the development of a male phenotype under normal physiological conditions.

A disease-associated missense mutation in CYP4F3 affects the metabolism of leukotriene B4 via disruption of electron transfer.

BACKGROUND: Cytochrome P450 4F3 (CYP4F3) is an ω-hydroxylase that oxidizes leukotriene B4 (LTB4), prostaglandins, and fatty acid epoxides. LTB4 is synthesized by leukocytes and acts as a chemoattractant for neutrophils, making it an essential component of the innate immune system. Recently, involvement of the LTB4 pathway was reported in various immunological disorders such as asthma, arthritis, and inflammatory bowel disease. We report a 26-year-old female with a complex immune phenotype, mainly marked by exhaustion, muscle weakness, and inflammation-related conditions. The molecular cause is unknown, and symptoms have been aggravating over the years. METHODS: Whole exome sequencing was performed and validated; flow cytometry and enzyme-linked immunosorbent assay were used to describe patient's phenotype. Function and impact of the mutation were investigated using molecular analysis: co-immunoprecipitation, western blot, and enzyme-linked immunosorbent assay. Capillary electrophoresis with ultraviolet detection was used to detect LTB4 and its metabolite and in silico modelling provided structural information. RESULTS: We present the first report of a patient with a heterozygous de novo missense mutation c.C1123 > G;p.L375V in CYP4F3 that severely impairs its activity by 50% (P < 0.0001), leading to reduced metabolization of the pro-inflammatory LTB4. Systemic LTB4 levels (1034.0 ± 75.9 pg/mL) are significantly increased compared with healthy subjects (305.6 ± 57.0 pg/mL, P < 0.001), and immune phenotyping shows increased total CD19+ CD27- naive B cells (25%) and decreased total CD19+ CD27+ IgD- switched memory B cells (19%). The mutant CYP4F3 protein is stable and binding with its electron donors POR and Cytb5 is unaffected (P > 0.9 for both co-immunoprecipitation with POR and Cytb5). In silico modelling of CYP4F3 in complex with POR and Cytb5 suggests that the loss of catalytic activity of the mutant CYP4F3 is explained by a disruption of an α-helix that is crucial for the electron shuffling between the electron carriers and CYP4F3. Interestingly, zileuton still inhibits ex vivo LTB4 production in patient's whole blood to 2% of control (P < 0.0001), while montelukast and fluticasone do not (99% and 114% of control, respectively). CONCLUSIONS: A point mutation in the catalytic domain of CYP4F3 is associated with high leukotriene B4 plasma levels and features of a more naive adaptive immune response. Our data provide evidence for the pathogenicity of the CYP4F3 variant as a cause for the observed clinical features in the patient. Inhibitors of the LTB4 pathway such as zileuton show promising effects in blocking LTB4 production and might be used as a future treatment strategy.

Antizyme Inhibitor 1 Regulates Matrikine Expression and Enhances the Metastatic Potential of Aggressive Primary Prostate Cancer.

Molecular drivers of metastasis in patients with high-risk localized prostate cancer are poorly understood. Therefore, we aim to study molecular drivers of metastatic progression in patients with high-risk prostate cancer. A retrospective matched case-control study of two clinico-pathologically identical groups of patients with high-risk prostate cancer was undertaken. One group developed metastatic recurrence (n = 19) while the other did not (n = 25). The primary index tumor was identified by a uro-pathologist, followed by DNA and RNA extraction for somatic copy-number aberration (SCNA) analysis and whole-transcriptome gene expression analysis. In vitro and in vivo studies included cell line manipulation and xenograft models.The integrative CNA and gene expression analyses identified an increase in Antizyme Inhibitor 1 (AZIN1) gene expression within a focal amplification of 8q22.3, which was associated with metastatic recurrence of patients with high-risk prostate cancer in four independent cohorts. The effects of AZIN1 knockdown were evaluated, due to its therapeutic potential. AZIN1 knockdown effected proliferation and metastatic potential of prostate cancer cells and xenograft models. RNA sequencing after AZIN1 knockdown in prostate cancer cells revealed upregulation of genes coding for collagen subunits. The observed effect on cell migration after AZIN1 knockdown was mimicked when exposing prostate cancer cells to bio-active molecules deriving from COL4A1 and COL4A2. Our integrated CNA and gene expression analysis of primary high-risk prostate cancer identified the AZIN1 gene as a novel driver of metastatic progression, by altering collagen subunit expression. Future research should further investigate its therapeutic potential in preventing metastatic recurrence. IMPLICATIONS: AZIN1 was identified as driver of metastatic progression in high-risk prostate cancer through matrikine regulation.

Drivers of AR indifferent anti-androgen resistance in prostate cancer cells.

Inhibition of the androgen receptor (AR) by second-generation anti-androgens is a standard treatment for metastatic castration resistant prostate cancer (mCRPC), but it inevitably leads to the development of resistance. Since the introduction of highly efficient AR signalling inhibitors, approximately 20% of mCRPC patients develop disease with AR independent resistance mechanisms. In this study, we generated two anti-androgen and castration resistant prostate cancer cell models that do not rely on AR activity for growth despite robust AR expression (AR indifferent). They are thus resistant against all modern AR signalling inhibitors. Both cell lines display cross-resistance against the chemotherapeutic drug docetaxel due to MCL1 upregulation but remain sensitive to the PARP inhibitor olaparib and the pan-BCL inhibitor obatoclax. RNA-seq analysis of the anti-androgen resistant cell lines identified hyper-activation of the E2F cell-cycle master regulator as driver of AR indifferent growth, which was caused by deregulation of cyclin D/E, E2F1, RB1, and increased Myc activity. Importantly, mCRPC tissue samples with low AR activity displayed the same alterations and increased E2F activity. In conclusion, we describe two cellular models that faithfully mimic the acquisition of a treatment induced AR independent phenotype that is cross-resistant against chemotherapy and driven by E2F hyper-activation.