Androgen receptor phosphorylation and activity are regulated by an association with protein phosphatase 1

Nuclear lamin A/C phosphorylation by loss of androgen receptor leads to cancer-associated fibroblast activation

Alterations in nuclear structure and function are hallmarks of cancer cells. Little is known about these changes in Cancer-Associated Fibroblasts (CAFs), crucial components of the tumor microenvironment. Loss of the androgen receptor (AR) in human dermal fibroblasts (HDFs), which triggers early steps of CAF activation, leads to nuclear membrane changes and micronuclei formation, independent of cellular senescence. Similar changes occur in established CAFs and are reversed by restoring AR activity. AR associates with nuclear lamin A/C, and its loss causes lamin A/C nucleoplasmic redistribution. AR serves as a bridge between lamin A/C and the protein phosphatase PPP1. Loss of AR decreases lamin-PPP1 association and increases lamin A/C phosphorylation at Ser 301, a characteristic of CAFs. Phosphorylated lamin A/C at Ser 301 binds to the regulatory region of CAF effector genes of the myofibroblast subtype. Expression of a lamin A/C Ser301 phosphomimetic mutant alone can transform normal fibroblasts into tumor-promoting CAFs.

Regulating Androgen Receptor Function in Prostate Cancer: Exploring the Diversity of Post-Translational Modifications

Androgen receptor (AR) transcriptional activity significantly influences prostate cancer (PCa) progression. In addition to ligand stimulation, AR transcriptional activity is also influenced by a variety of post-translational modifications (PTMs). A number of oncogenes and tumor suppressors have been observed leveraging PTMs to influence AR activity. Subjectively targeting these post-translational modifiers based on their impact on PCa cell proliferation is a rapidly developing area of research. This review elucidates the modifiers, contextualizes the effects of these PTMs on AR activity, and connects these cellular interactions to the progression of PCa.

Protein signaling and drug target activation signatures to guide therapy prioritization: Therapeutic resistance and sensitivity in the I-SPY 2 Trial

Molecular subtyping of breast cancer is based mostly on HR/HER2 and gene expression-based immune, DNA repair deficiency, and luminal signatures. We extend this description via functional protein pathway activation mapping using pre-treatment, quantitative expression data from 139 proteins/phosphoproteins from 736 patients across 8 treatment arms of the I-SPY 2 Trial (ClinicalTrials.gov: NCT01042379). We identify predictive fit-for-purpose, mechanism-of-action-based signatures and individual predictive protein biomarker candidates by evaluating associations with pathologic complete response. Elevated levels of cyclin D1, estrogen receptor alpha, and androgen receptor S650 associate with non-response and are biomarkers for global resistance. We uncover protein/phosphoprotein-based signatures that can be utilized both for molecularly rationalized therapeutic selection and for response prediction. We introduce a dichotomous HER2 activation response predictive signature for stratifying triple-negative breast cancer patients to either HER2 or immune checkpoint therapy response as a model for how protein activation signatures provide a different lens to view the molecular landscape of breast cancer and synergize with transcriptomic-defined signatures.

The androgen receptor

The Androgen Receptor (AR) is a ligand (androgen) activated transcription factor and a member of the nuclear receptor (NR) superfamily. It is required for male sex hormone function. AR-FL (full-length) has the domain structure of NRs, an N-terminal domain (NTD) required for transactivation, a DNA-binding domain (DBD), a nuclear localization signal (NLS) and a ligand-binding domain (LBD). Paradoxes exist in that endogenous ligands testosterone (T) and 5α-dihydrotestosterone (DHT) have differential effects on male sexual development while binding to the same receptor and transcriptional specificity is achieved even though the androgen response elements (AREs) are identical to those seen for the progesterone, glucocorticoid and mineralocorticoid receptors. A high resolution 3-dimensional structure of AR-FL by either cryo-EM or X-ray crystallography has remained elusive largely due to the intrinsic disorder of the NTD. AR function is regulated by post-translational modification leading to a large number of proteoforms. The interaction of these proteoforms in multiprotein complexes with co-activators and co-repressors driven by interdomain coupling mediates the AR transcriptional output. The AR is a drug target for selective androgen receptor modulators (SARMS) that either have anabolic or androgenic effects. Protstate cancer is treated with androgen deprivation therapy or by the use of AR antagonists that bind to the LBD. Drug resistance occurs due to adaptive AR upregulation and the appearance of splice variants that lack the LBD and become constitutively active. Bipolar T treatment and NTD-antagonists could surmount these resistance mechanisms, respectively. These recent advances in AR signaling are described.

Reciprocal regulation of CIP2A and AR expression in prostate cancer cells

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is an oncoprotein overexpressed in human malignancies, including prostate cancer (PCa). In this study, we aimed to explore the oncogenic function of CIP2A in PCa cells and its underlying mechanism. We showed that 63.3% (38/60 cases) of PCa tissues exhibited a high CIP2A immunostaining, compared to 25% (3/12 cases) of BPH samples (p = 0.023). Furthermore, the protein level of CIP2A was positively correlated with patients' short survival time and nuclear AR levels in PCa tissues. Compared to PZ-HPV-7, an immortalized prostate cell line, androgen-sensitive LNCaP C-33, androgen-independent LNCaP C-81, or 22Rv1 cells exhibited a high CIP2A level, associated with high protein and phosphorylation levels of AR. While AR expression and activity modulated CIP2A expression, manipulating CIP2A expression in PCa cells regulated their AR protein levels and proliferation. The reduction of CIP2A expression also enhanced the sensitivity of PCa cells toward Enzalutamide treatment. Our data further showed that depletion of polo-kinase 1 (PLK1) expression or activity in C-81 or 22Rv1 cells caused reduced protein levels of c-Myc and AR. Notably, inhibition of PLK1 activity could abolish CIP2A-promoted expressions in c-Myc, AR, and prostate-specific antigen (PSA) in C-33 cells under an androgen-deprived condition, suggesting the role of PLK1 activity in CIP2A-promoted AR expression. In summary, our data showed the existence of a novel regulation between CIP2A and AR protein levels, which is critical for promoting PCa malignancy. Thus, CIP2A could serve as a therapeutic target for PCa.

PP1 catalytic isoforms are differentially expressed and regulated in human prostate cancer

The Ser/Thr-protein phosphatase PP1 (PP1) is a positive regulator of the androgen receptor (AR), which suggests major roles for PP1 in prostate carcinogenesis. However, studies dedicated to the characterization of PP1 in PCa are currently scarce. Here we analyzed the expression and localization of the PP1 catalytic (PP1c) isoforms in formalin-fixed, paraffin-embedded prostate tissue samples, as well as in PCa cell lines. We also analyzed well-characterized PCa cohorts to determine their transcript levels, identify genetic alterations, and assess promoter methylation of PP1c-coding genes. We found that PP-1A was upregulated and relocalized towards the nucleus in PCa and that PPP1CA was frequently amplified in PCa, particularly in advanced stages. PP-1B was downregulated in PCa but upregulated in a subset of tumors with AR amplification. PP-1G transcript levels were found to be associated with Gleason score. PP1c-coding genes were rarely mutated in PCa and were not prone to regulation by promoter methylation. Protein phosphorylation, on the other hand, might be an important regulatory mechanism of PP1c isoforms' activity. Altogether, our results suggest differential expression, localization, and regulation of PP1c isoforms in PCa and support the need for investigating isoform-specific roles in prostate carcinogenesis in future studies.

Exploring the Role of Posttranslational Modifications in Spinal and Bulbar Muscular Atrophy

Spinal and Bulbar Muscular Atrophy (SBMA) is an X-linked adult-onset progressive neuromuscular disease that affects the spinal and bulbar motor neurons and skeletal muscles. SBMA is caused by expansion of polymorphic CAG trinucleotide repeats in the Androgen Receptor (AR) gene, resulting in expanded glutamine tract in the AR protein. Polyglutamine (polyQ) expansion renders the mutant AR protein toxic, resulting in the formation of mutant protein aggregates and cell death. This classifies SBMA as one of the nine known polyQ diseases. Like other polyQ disorders, the expansion of the polyQ tract in the AR protein is the main genetic cause of the disease; however, multiple other mechanisms besides the polyQ tract expansion also contribute to the SBMA disease pathophysiology. Posttranslational modifications (PTMs), including phosphorylation, acetylation, methylation, ubiquitination, and SUMOylation are a category of mechanisms by which the functionality of AR has been found to be significantly modulated and can alter the neurotoxicity of SBMA. This review summarizes the different PTMs and their effects in regulating the AR function and discusses their pathogenic or protective roles in context of SBMA. This review also includes the therapeutic approaches that target the PTMs of AR in an effort to reduce the mutant AR-mediated toxicity in SBMA.

Modulation of serine/threonine-protein phosphatase 1 (PP1) complexes: A promising approach in cancer treatment

Cancer is the second leading cause of death worldwide. Despite the availability of numerous therapeutic options, tumor heterogeneity and chemoresistance have limited the success of these treatments, and the development of effective anticancer therapies remains a major focus in oncology research. The serine/threonine-protein phosphatase 1 (PP1) and its complexes have been recognized as potential drug targets. Research on the modulation of PP1 complexes is currently at an early stage, but has immense potential. Chemically diverse compounds have been developed to disrupt or stabilize different PP1 complexes in various cancer types, with the objective of inhibiting disease progression. Beneficial results obtained in vitro now require further pre-clinical and clinical validation. In conclusion, the modulation of PP1 complexes seems to be a promising, albeit challenging, therapeutic strategy for cancer.

GRB10 sustains AR activity by interacting with PP2A in prostate cancer cells

Prostate cancer (PCa) progression is driven by androgen receptor (AR) signaling. Unfortunately, androgen-deprivation therapy and the use of even more potent AR pathway inhibitors (ARPIs) cannot bring about a cure. ARPI resistance (ie, castration-resistant PCa, CRPC) will inevitably develop. Previously, we demonstrated that GRB10 is an AR transcriptionally repressed gene that functionally contributes to CRPC development and ARPI resistance. GRB10 expression is elevated prior to CRPC development in our patient-derived xenograft models and is significantly upregulated in clinical CRPC samples. Here, we analyzed transcriptomic data from GRB10 knockdown in PCa cells and found that AR signaling is downregulated. While the mRNA expression of AR target genes decreased upon GRB10 knockdown, AR expression was not affected at the mRNA or protein level. We further found that phosphorylation of AR serine 81 (S81), which is critical for AR transcriptional activity, is decreased by GRB10 knockdown and increased by its overexpression. Luciferase assay using GRB10-knockdown cells also indicate reduced AR activity. Immunoprecipitation coupled with mass spectrometry revealed an interaction between GRB10 and the PP2A complex, which is a known phosphatase of AR. Further validations and analyses showed that GRB10 binds to the PP2Ac catalytic subunit with its PH domain. Mechanistically, GRB10 knockdown increased PP2Ac protein stability, which in turn decreased AR S81 phosphorylation and reduced AR activity. Our findings indicate a reciprocal feedback between GRB10 and AR signaling, implying the importance of GRB10 in PCa progression.

Pathogenic mechanisms underlying spinocerebellar ataxia type 1

The family of hereditary cerebellar ataxias is a large group of disorders with heterogenous clinical manifestations and genetic etiologies. Among these, over 30 autosomal dominantly inherited subtypes have been identified, collectively referred to as the spinocerebellar ataxias (SCAs). Generally, the SCAs are characterized by a progressive gait impairment with classical cerebellar features, and in a subset of SCAs, accompanied by extra-cerebellar features. Beyond the common gait impairment and cerebellar atrophy, the wide range of additional clinical features observed across the SCAs is likely explained by the diverse set of mutated genes that encode proteins with seemingly disparate functional roles in nervous system biology. By synthesizing knowledge obtained from studies of the various SCAs over the past several decades, convergence onto a few key cellular changes, namely ion channel dysfunction and transcriptional dysregulation, has become apparent and may represent central mechanisms of cerebellar disease pathogenesis. This review will detail our current understanding of the molecular pathogenesis of the SCAs, focusing primarily on the first described autosomal dominant spinocerebellar ataxia, SCA1, as well as the emerging common core mechanisms across the various SCAs.

Molecular Origin, Expression Regulation, and Biological Function of Androgen Receptor Splicing Variant 7 in Prostate Cancer

The problem of resistance to therapy in prostate cancer (PCa) is multifaceted. Key determinants of drug resistance include tumor burden and growth kinetics, tumor heterogeneity, physical barriers, immune system and microenvironment, undruggable cancer drivers, and consequences of therapeutic pressures. With regard to the fundamental importance of the androgen receptor (AR) in all stages of PCa from tumorigenesis to progression, AR is postulated to have a continued critical role in castration-resistant prostate cancer (CRPC). Suppression of AR signaling mediated by the full-length AR (AR-FL) is the therapeutic goal of all AR-directed therapies. However, AR-targeting agents ultimately lead to AR aberrations that promote PCa progression and drug resistance. Among these AR aberrations, androgen receptor variant 7 (AR-V7) is gaining attention as a potential predictive marker for as well as one of the resistance mechanisms to the most current anti-AR therapies in CRPC. Meanwhile, development of next-generation drugs that directly or indirectly target AR-V7 signaling is urgently needed. In the present review of the current literature, we have summarized the origin, alternative splicing, expression induction, protein conformation, interaction with coregulators, relationship with AR-FL, transcriptional activity, and biological function of AR-V7 in PCa development and therapeutic resistance. We hope this review will help further understand the molecular origin, expression regulation, and role of AR-V7 in the progression of PCa and provide insight into the design of novel selective inhibitors of AR-V7 in PCa treatment.

Protein phosphatase 1 in tumorigenesis: is it worth a closer look?

Cancer cells take advantage of signaling cascades to meet their requirements for sustained growth and survival. Cell signaling is tightly controlled by reversible protein phosphorylation mechanisms, which require the counterbalanced action of protein kinases and protein phosphatases. Imbalances on this system are associated with cancer development and progression. Protein phosphatase 1 (PP1) is one of the most relevant protein phosphatases in eukaryotic cells. Despite the widely recognized involvement of PP1 in key biological processes, both in health and disease, its relevance in cancer has been largely neglected. Here, we provide compelling evidence that support major roles for PP1 in tumorigenesis.

The disruption of protein-protein interactions as a therapeutic strategy for prostate cancer

Prostate cancer (PCa) is one of the most common male-specific cancers worldwide, with high morbidity and mortality rates associated with advanced disease stages. The current treatment options of PCa are prostatectomy, hormonal therapy, chemotherapy or radiotherapy, the selection of which is usually dependent upon the stage of the disease. The development of PCa to a castration-resistant phenotype (CRPC) is associated with a more severe prognosis requiring the development of a new and effective therapy. Protein-protein interactions (PPIs) have been recognised as an emerging drug modality and targeting PPIs is a promising therapeutic approach for several diseases, including cancer. The efficacy of several compounds in which target PPIs and consequently impair disease progression were validated in phase I/II clinical trials for different types of cancer. In PCa, various small molecules and peptides proved successful in inhibiting important PPIs, mainly associated with the androgen receptor (AR), Bcl-2 family proteins, and kinases/phosphatases, thus impairing the growth of PCa cells in vitro. Moreover, a majority of these compounds require further validation in vivo and, preferably, in clinical trials. In addition, several other PPIs associated with PCa progression have been identified and now require experimental validation as potential therapeutic loci. In conclusion, we consider the disruption of PPIs to be a promising though challenging therapeutic strategy for PCa. Agents which modulate PPIs might be employed as a monotherapy or as an adjunct to classical chemotherapeutics to overcome drug resistance and improve efficacy. The discovery of new PPIs with important roles in disease progression, and of novel optimized strategies to target them are major challenges for the scientific and pharmacological communities.

Posttranslational regulation of androgen dependent and independent androgen receptor activities in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer among men in western countries. Androgen receptor (AR) signaling plays key roles in the development of PCa. Androgen deprivation therapy (ADT) remains the standard therapy for advanced PCa. In addition to its ligand androgen, accumulating evidence indicates that posttranscriptional modification is another important mechanism to regulate AR activities during the progression of PCa, especially in castration resistant prostate cancer (CRPC). To date, a number of posttranscriptional modifications of AR have been identified, including phosphorylation (e.g. by CDK1), acetylation (e.g. by p300 and recognized by BRD4), methylation (e.g. by EZH2), ubiquitination (e.g. by SPOP), and SUMOylation (e.g. by PIAS1). These modifications are essential for the maintenance of protein stability, nuclear localization and transcriptional activity of AR. This review summarizes posttranslational modifications that influence androgen-dependent and -independent activities of AR, PCa progression and therapy resistance. We further emphasize that in addition to androgen, posttranslational modification is another important way to regulate AR activity, suggesting that targeting AR posttranslational modifications, such as proteolysis targeting chimeras (PROTACs) of AR, represents a potential and promising alternate for effective treatment of CRPC. Potential areas to be investigated in the future in the field of AR posttranslational modifications are also discussed.

Molecular Mechanisms and Therapeutics for SBMA/Kennedy's Disease

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by a polyglutamine (polyQ) expansion in the androgen receptor (AR). Despite the fact that the monogenic cause of SBMA has been known for nearly 3 decades, there is no effective treatment for this disease, underscoring the complexity of the pathogenic mechanisms that lead to a loss of motor neurons and muscle in SBMA patients. In the current review, we provide an overview of the system-wide clinical features of SBMA, summarize the structure and function of the AR, discuss both gain-of-function and loss-of-function mechanisms of toxicity caused by polyQ-expanded AR, and describe the cell and animal models utilized in the study of SBMA. Additionally, we summarize previously conducted clinical trials which, despite being based on positive results from preclinical studies, proved to be largely ineffective in the treatment of SBMA; nonetheless, these studies provide important insights as researchers develop the next generation of therapies.

Impaired Nuclear Export of Polyglutamine-Expanded Androgen Receptor in Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Prior studies have highlighted the importance of AR nuclear localization in SBMA pathogenesis; therefore, in this study, we sought to determine the role of AR nuclear export in the pathological manifestations of SBMA. We demonstrate here that the nuclear export of polyQ-expanded AR is impaired, even prior to the formation of intranuclear inclusions of aggregated AR. Additionally, we find that promoting AR export with an exogenous nuclear export signal substantially reduces its aggregation and blocks hormone-induced toxicity. Moreover, we show that these protective effects are conferred by destabilization of the mutant protein due to an increase in proteasomal degradation of the cytoplasmic AR. Despite a growing body of evidence that global disruption of nucleo/cytoplasmic transport occurs in ALS and HD, our data suggest that no such global disruption occurs in models of SBMA; rather, AR-specific mechanisms, including reduced phosphorylation at Serine 650, are likely responsible for the impaired nuclear export of polyQ-expanded AR.

Repositioning Dopamine D2 Receptor Agonist Bromocriptine to Enhance Docetaxel Chemotherapy and Treat Bone Metastatic Prostate Cancer

Docetaxel resistance remains a major obstacle in the treatment of prostate cancer bone metastasis. In this study, we demonstrate that the dopamine D2 receptor (DRD2) agonist bromocriptine effectively enhances docetaxel efficacy and suppresses skeletal growth of prostate cancer in preclinical models. DRD2 is ubiquitously expressed in prostate cancer cell lines and significantly reduced in prostate cancer tissues with high Gleason score. Bromocriptine has weak to moderate cytotoxicity in prostate cancer cells, but effectively induces cell-cycle arrest. At the molecular level, bromocriptine inhibits the expression of c-Myc, E2F-1, and survivin and increases the expression of p53, p21, and p27. Intriguingly, bromocriptine markedly reduces androgen receptor levels, partially through Hsp90-mediated protein degradation. The combination of bromocriptine and docetaxel demonstrates enhanced in vitro cytotoxicity in prostate cancer cells and significantly retards the skeletal growth of C4-2-Luc tumors in mice. Collectively, these results provide the first experimental evidence for repurposing bromocriptine as an effective adjunct therapy to enhance docetaxel efficacy in prostate cancer. Mol Cancer Ther; 17(9); 1859-70. ©2018 AACR.

Dual targeting of androgen receptor and mTORC1 by salinomycin in prostate cancer

Androgen receptor (AR) and PI3K/AKT/mTORC1 are major survival signals that drive prostate cancer to a lethal disease. Reciprocal activation of these oncogenic pathways from negative cross talks contributes to low/limited success of pathway-selective inhibitors in curbing prostate cancer progression. We report that the antibiotic salinomycin, a cancer stem cell blocker, is a dual-acting AR and mTORC1 inhibitor, inhibiting PTEN-deficient castration-sensitive and castration-resistant prostate cancer in culture and xenograft tumors. AR expression, its transcriptional activity, and androgen biosynthesis regulating enzymes CYP17A1, HSD3β1 were reduced by sub-micro molar salinomycin. Estrogen receptor-α expression was unchanged. Loss of phosphorylated AR at serine-81, which is an index for nuclear AR activity, preceded total AR reduction. Rapamycin enhanced the AR protein level without altering phosphoAR-Ser81 and CYP17A1. Inactivation of mTORC1, evident from reduced phosphorylation of mTOR and downstream effectors, as well as AMPK activation led to robust autophagy induction. Apoptosis increased modestly, albeit significantly, by sub-micro molar salinomycin. Enhanced stimulatory TSC2 phosphorylation at Ser-1387 by AMPK, and reduced inhibitory TSC2 phosphorylation at Ser-939/Thr-1462 catalyzed by AKT augmented TSC2/TSC1 activity, which led to mTORC1 inhibition. AMPK-mediated raptor phosphorylation further reduced mTOR's kinase function and mTORC1 activity. Our novel finding on dual inhibition of AR and mTORC1 suggests that salinomycin is potentially active as monotherapy against advanced prostate cancer.

Differential regulation of the androgen receptor by protein phosphatase regulatory subunits

The Androgen Receptor (AR) is a key molecule in the development, maintenance and progression of prostate cancer (PC). However, the relationship between the AR and co-regulatory proteins that facilitate AR activity in castrate resistant settings remain understudied. Here we show that protein phosphatase 1 regulatory subunits, identified from a phosphatase RNAi screen, direct PP1 catalytic subunits to a varied yet significant response in AR function. As such, we have characterised the PP1β holoenzyme, myosin phosphatase (MLCP), as a novel ligand independent regulator of the AR. Sustained MLCP activity through down-regulation of the MLCP inhibitory subunit, PPP1R14C, results in impaired AR nuclear translocation, protein stability and transcriptional activity in distinct models of PC progression, culminating in restoration of a non-malignant prostate genotype. Phenotypically, a marked reduction in cell proliferation and migration, characterised by G1 cell cycle arrest is observed, confirming PP1 holoenzyme disruption as a novel treatment approach in PC.

Positive feedback loop mediated by protein phosphatase 1α mobilization of P-TEFb and basal CDK1 drives androgen receptor in prostate cancer

P-TEFb (CDK9/cyclin T) plays a central role in androgen receptor (AR)-mediated transactivation by phosphorylating both RNA polymerase 2 complex proteins and AR at S81. CDK9 dephosphorylation mobilizes P-TEFb from an inhibitory 7SK ribonucleoprotein complex, but mechanisms targeting phosphatases to P-TEFb are unclear. We show that AR recruits protein phosphatase 1α (PP1α), resulting in P-TEFb mobilization and CDK9-mediated AR S81 phosphorylation. This increased pS81 enhances p300 recruitment, histone acetylation, BRD4 binding and subsequent further recruitment of P-TEFb, generating a positive feedback loop that sustains transcription. AR S81 is also phosphorylated by CDK1, and blocking basal CDK1-mediated S81 phosphorylation markedly suppresses AR activity and initiation of this positive feedback loop. Finally, androgen-independent AR activity in castration-resistant prostate cancer (CRPC) cells is driven by increased CDK1-mediated S81 phosphorylation. Collectively these findings reveal a mechanism involving PP1α, CDK9 and CDK1 that is used by AR to initiate and sustain P-TEFb activity, which may be exploited to drive AR in CRPC.

Synergy between Androgen Receptor Antagonism and Inhibition of mTOR and HER2 in Breast Cancer

The androgen receptor (AR) is widely expressed in breast cancer, and evidence suggests dependence on AR signaling for growth and survival. AR antagonists such as enzalutamide and seviteronel have shown success in preclinical models and clinical trials of prostate cancer and are currently being evaluated in breast cancer. Reciprocal regulation between AR and the HER2/PI3K/mTOR pathway may contribute to resistance to HER2- and mTOR-targeted therapies; thus, dual inhibition of these pathways may synergistically inhibit breast cancer growth. HER2+ and triple-negative breast cancer cell lines were treated with AR antagonist plus anti-HER2 mAb trastuzumab or mTOR inhibitor everolimus. Apoptosis, cell proliferation, and drug synergy were measured in vitro Pathway component genes and proteins were measured by qRT-PCR, Western blot, and reverse phase protein array. In vivo, HER2+ breast cancer xenografts were treated with enzalutamide, everolimus, trastuzumab, and combinations of these drugs. AR antagonists inhibited proliferation of both HER2+ and TNBC cell lines. Combining AR antagonist and either everolimus or trastuzumab resulted in synergistic inhibition of proliferation. Dihydrotestosterone caused increased phosphorylation of HER2 and/or HER3 that was attenuated by AR inhibition. Everolimus caused an increase in total AR, phosphorylation of HER2 and/or HER3, and these effects were abrogated by enzalutamide. Growth of trastuzumab-resistant HER2+ xenograft tumors was inhibited by enzalutamide, and combining enzalutamide with everolimus decreased tumor viability more than either single agent. AR antagonists synergize with FDA-approved breast cancer therapies such as everolimus and trastuzumab through distinct mechanisms. Treatment combinations are effective in trastuzumab-resistant HER2+ breast cancer cells in vivoMol Cancer Ther; 16(7); 1389-400. ©2017 AACR.

Lemur Tyrosine Kinase 2, a novel target in prostate cancer therapy

Progression from early forms of prostate cancer to castration-resistant disease is associated with an increase in signal transduction activity. The majority of castration-resistance cancers persist in the expression of the androgen receptor (AR), as well as androgen-dependent genes. The AR is regulated not only by it associated steroid hormone, but also by manifold regulatory and signaling molecules, including several kinases. We undertook evaluation of the role of Lemur Tyrosine Kinase 2 (LMTK2) in modulating AR activity, as several Genome Wide Association Studies (GWAS) have shown a marked association of LMTK2 activity with the development of prostate cancer. We confirm that not only is LMTK2 mRNA reduced in prostate cancer tissue, but also LMTK2 protein levels are markedly diminished. Knockdown of LMTK2 protein in prostate cell lines greatly increased the transcription of androgen-responsive genes. In addition, LMTK2 knockdown led to an increase in prostate cancer stem cell populations in LNCaP cells, indicative of increased tumorogenicity. Using multiple approaches, we also demonstrate that LMTK2 interacts with the AR, thus putting LMTK2 as a component of a signaling complex modulating AR activity. Our finding that LMTK2 is a negative regulator of AR activity defines a novel cellular pathway for activation of AR-responsive genes in castrate resistant-prostate cancer. Moreover, pharmacologic manipulation of LMTK2 activity will provide a novel therapeutic target for more effective treatments for patients with castrate-resistant prostate cancer.

Androgen ablation elicits PP1-dependence for AR stabilization and transactivation in prostate cancer

BACKGROUND

Previous reports have documented protein phosphatase 1 (PP1) as an essential androgen receptor (AR) activator. However, more systemic studies are needed to further define PP1 effects on AR, particularly in the settings of prostate cancer cells and under conditions mimicking androgen ablation.

METHODS

PP1 effects on AR protein expression, degradation, ubiquitination, and stabilization were examined in non-prostate cancer cells, followed by validation on exogenous settings in androgen-sensitive (LNCaP and VCaP) and castration-resistant (C4-2) prostate cancer cells. Effects of PP1 on AR protein expression, on AR-mediated transcription of exogenous reporter and endogenous gene, and on LNCaP and C4-2 cell proliferation were monitored under androgen-containing versus androgen-depleted conditions to assess the effects of PP1 on AR responsiveness to androgen.

RESULTS

In this report, we determined that PP1 functions to stabilize AR proteins that exclusively undergo the proteasome-dependent degradation, and the stimulatory effects of PP1 were predominantly mediated by the AR ligand-binding domain (LBD). Consistently, PP1 enhances AR protein stability by disrupting the LBD-mediated and K48-linked ubiquitination cascade. We further validated the above findings in the prostate cancer cells by showing that PP1 inhibition can increase ubiquitin- and proteasome-dependent degradation of endogenous AR under androgen deprivation. Significantly, we found that PP1 could markedly activate AR transcriptional activities under conditions mimicking androgen ablation and that androgen sensitivity was substantially evoked by PP1 inhibition in the prostate cancer cell lines.

CONCLUSIONS

As summarized in a simplified model, our studies defined an essential PP1-mediated pathway for AR protein stabilization that can compensate the loss of androgen and established a mechanistic link between PP1 and androgen responsiveness. The amplified PP1-dependence for AR activation under the androgen ablated conditions provides a rationale to therapeutically target the PP1-AR module in the castration-resistant prostate cancer (CRPC). Our findings also suggested an alternative AR-targeting compounds screening strategy that aims to circumvent PP1-AR interaction.

Protein phosphatase 1 suppresses androgen receptor ubiquitylation and degradation

The phosphoprotein phosphatases are emerging as important androgen receptor (AR) regulators in prostate cancer (PCa). We reported previously that the protein phosphatase 1 catalytic subunit (PP1α) can enhance AR activity by dephosphorylating a site in the AR hinge region (Ser650) and thereby decrease AR nuclear export. In this study we show that PP1α increases the expression of wildtype as well as an S650A mutant AR, indicating that it is acting through one or more additional mechanisms. We next show that PP1α binds primarily to the AR ligand binding domain and decreases its ubiquitylation and degradation. Moreover, we find that the PP1α inhibitor tautomycin increases phosphorylation of AR ubiquitin ligases including SKP2 and MDM2 at sites that enhance their activity, providing a mechanism by which PP1α may suppress AR degradation. Significantly, the tautomycin mediated decrease in AR expression was most pronounced at low androgen levels or in the presence of the AR antagonist enzalutamide. Consistent with this finding, the sensitivity of LNCaP and C4-2 PCa cells to tautomycin, as assessed by PSA synthesis and proliferation, was enhanced at low androgen levels or by treatment with enzalutamide. Together these results indicate that PP1α may contribute to stabilizing AR protein after androgen deprivation therapies, and that targeting PP1α or the AR-PP1α interaction may be effective in castration-resistant prostate cancer (CRPC).

Kinase modulation of androgen receptor signaling: implications for prostate cancer

Androgens and androgen receptors play essential roles in the development and progression of prostate cancer, a disease that claims roughly 28,000 lives annually. In addition to androgen biding, androgen receptor activity can be regulated via several post-translational modifications such as ubiquitination, acetylation, phosphorylation, methylation & SUMO-ylation. Off these modifications, phosphorylation has been the most extensively studied. Modification by phosphorylation can alter androgen receptor localization, protein stability and transcriptional activity, ultimately leading to changes in the biology of cancer cells and cancer progression. Understanding, role of phosphorylated androgen receptor species holds the key to identifying a potential therapeutic drug target for patients with prostate cancer and castrate resistant prostate cancer. Here, we present a brief review of recently discovered protein kinases phosphorylating AR, focusing on the functional role of phosphorylated androgen receptor species in prostate cancer and castrate resistant prostate cancer.

AR-v7 protein expression is regulated by protein kinase and phosphatase

Failure of androgen-targeted therapy and progression of castration-resistant prostate cancer (CRPC) are often attributed to sustained expression of the androgen receptor (AR) and its major splice variant, AR-v7. Although the new generation of anti-androgens such as enzalutamide effectively inhibits AR activity, accumulating pre-clinical and clinical evidence indicates that AR-v7 remains constitutively active in driving CRPC progression. However, molecular mechanisms which control AR-v7 protein expression remain unclear. We apply multiple prostate cancer cell models to demonstrate that enzalutamide induces differential activation of protein phosphatase-1 (PP-1) and Akt kinase depending on the gene context of cancer cells. The balance between PP-1 and Akt activation governs AR phosphorylation status and activation of the Mdm2 ubiquitin ligase. Mdm2 recognizes phosphorylated serine 213 of AR-v7, and induces AR-v7 ubiquitination and protein degradation. These findings highlight the decisive roles of PP-1 and Akt for AR-v7 protein expression and activities when AR is functionally blocked.

Proteomics analysis of malignant and benign prostate tissue by 2D DIGE/MS reveals new insights into proteins involved in prostate cancer

BACKGROUND

The key to a more effective diagnosis, prognosis, and therapeutic management of prostate cancer (PCa) could lie in the direct analysis of cancer tissue. In this study, by comparative proteomics analysis of PCa and benign prostate hyperplasia (BPH) tissues we attempted to elucidate the proteins and regulatory pathways involved in this disease.

METHODS

The samples used in this study were fresh surgical tissues with clinically and histologically confirmed PCa (n = 19) and BPH (n = 33). We used two dimensional difference in gel electrophoresis (2D DIGE) coupled with mass spectrometry (MS) and bioinformatics analysis.

RESULTS

Thirty-nine spots with statistically significant 1.8-fold variation or more in abundance, corresponding to 28 proteins were identified. The IPA analysis pointed out to 3 possible networks regulated within MAPK, ERK, TGFB1, and ubiquitin pathways. Thirteen of the identified proteins, namely, constituents of the intermediate filaments (KRT8, KRT18, DES), potential tumor suppressors (ARHGAP1, AZGP1, GSTM2, and MFAP4), transport and membrane organization proteins (FABP5, GC, and EHD2), chaperons (FKBP4 and HSPD1) and known cancer marker (NME1) have been associated with prostate and other cancers by numerous proteomics, genomics or functional studies. We evidenced for the first time the dysregulation of 9 proteins (CSNK1A1, ARID5B, LYPLA1, PSMB6, RABEP1, TALDO1, UBE2N, PPP1CB, and SERPINB1) that may have role in PCa. The UBE2N, PSMB6, and PPP1CB, involved in cell cycle regulation and progression were evaluated by Western blot analysis which confirmed significantly higher abundances of UBE2N and PSMB6 and significantly lower abundance of PPP1CB in PCa.

CONCLUSION

In addition to the identification of substantial number of proteins with known association with PCa, the proteomic approach in this study revealed proteins not previously clearly related to PCa, providing a starting point for further elucidation of their function in disease initiation and progression.

Mechanisms Regulating Protein Localization

Cellular functions are dictated by protein content and activity. There are numerous strategies to regulate proteins varying from modulating gene expression to post-translational modifications. One commonly used mode of regulation in eukaryotes is targeted localization. By specifically redirecting the localization of a pool of existing protein, cells can achieve rapid changes in local protein function. Eukaryotic cells have evolved elegant targeting pathways to direct proteins to the appropriate cellular location or locations. Here, we provide a general overview of these localization pathways, with a focus on nuclear and mitochondrial transport, and present a survey of the evolutionarily conserved regulatory strategies identified thus far. We end with a description of several specific examples of proteins that exploit localization as an important mode of regulation.

YAP1 and AR interactions contribute to the switch from androgen-dependent to castration-resistant growth in prostate cancer

The transcriptional co-activator Yes-associated protein 1 (YAP1), a key nuclear effector of the Hippo pathway, is a potent oncogene, and yet, the interaction between YAP1 and androgen receptor (AR) remains unexplored. Here we identify YAP1 as a physiological binding partner and positive regulator of AR in prostate cancer. YAP1 and AR co-localize and interact with each other predominantly within cell nuclei by an androgen-dependent mechanism in a hormone naive and an androgen-independent mechanism in castration-resistant prostate cancer cells. The growth suppressor MST1 kinase modulates androgen-dependent and -independent nuclear YAP1-AR interactions through directly regulating YAP1 nuclear accumulation. Disruption of YAP1 signalling by genetic (RNAi) and pharmacological (Verteporfin) approaches suppresses AR-dependent gene expression and prostate cancer cell growth. These findings indicate that the YAP1-AR axis may have a critical role in prostate cancer progression and serves as a viable drug target.

Mutation of androgen receptor N-terminal phosphorylation site Tyr-267 leads to inhibition of nuclear translocation and DNA binding

Reactivation of androgen receptor (AR) may drive recurrent prostate cancer in castrate patients. Ack1 tyrosine kinase is overexpressed in prostate cancer and promotes castrate resistant xenograft tumor growth and enhances androgen target gene expression and AR recruitment to enhancers. Ack1 phosphorylates AR at Tyr-267 and possibly Tyr-363, both in the N-terminal transactivation domain. In this study, the role of these phosphorylation sites was investigated by characterizing the phosphorylation site mutants in the context of full length and truncated AR lacking the ligand-binding domain. Y267F and Y363F mutants showed decreased transactivation of reporters. Expression of wild type full length and truncated AR in LNCaP cells increased cell proliferation in androgen-depleted conditions and increased colony formation. However, the Y267F mutant of full length and truncated AR was defective in stimulating cell proliferation. The Y363F mutant was less severely affected than the Y267F mutant. The full length AR Y267F mutant was defective in nuclear translocation induced by androgen or Ack1 kinase. The truncated AR was constitutively localized to the nucleus. Chromatin immunoprecipitation analysis showed that it was recruited to the target enhancers without androgen. The truncated Y267F AR mutant did not exhibit constitutive nuclear localization and androgen enhancer binding activity. These results support the concept that phosphorylation of Tyr-267, and to a lesser extent Tyr-363, is required for AR nuclear translocation and recruitment and DNA binding and provide a rationale for development of novel approaches to inhibit AR activity.

Phosphoprotein phosphatase 1-interacting proteins as therapeutic targets in prostate cancer

Prostate cancer is a major public health concern worldwide, being one of the most prevalent cancers in men. Great improvements have been made both in terms of early diagnosis and therapeutics. However, there is still an urgent need for reliable biomarkers that could overcome the lack of cancer-specificity of prostate-specific antigen, as well as alternative therapeutic targets for advanced metastatic cases. Reversible phosphorylation of proteins is a post-translational modification critical to the regulation of numerous cellular processes. Phosphoprotein phosphatase 1 (PPP1) is a major serine/threonine phosphatase, whose specificity is determined by its interacting proteins. These interactors can be PPP1 substrates, regulators, or even both. Deregulation of this protein-protein interaction network alters cell dynamics and underlies the development of several cancer hallmarks. Therefore, the identification of PPP1 interactome in specific cellular context is of crucial importance. The knowledge on PPP1 complexes in prostate cancer remains scarce, with only 4 holoenzymes characterized in human prostate cancer models. However, an increasing number of PPP1 interactors have been identified as expressed in human prostate tissue, including the tumor suppressors TP53 and RB1. Efforts should be made in order to identify the role of such proteins in prostate carcinogenesis, since only 26 have yet well-recognized roles. Here, we revise literature and human protein databases to provide an in-depth knowledge on the biological significance of PPP1 complexes in human prostate carcinogenesis and their potential use as therapeutic targets for the development of new therapies for prostate cancer.

Protein phosphatase 1 catalytic isoforms: specificity toward interacting proteins

The coordinated and reciprocal action of serine-threonine protein kinases and protein phosphatases produces transitory phosphorylation, a fundamental regulatory mechanism for many biological processes. Phosphoprotein phosphatase 1 (PPP1), a major serine-threonine phosphatase, in particular, is ubiquitously distributed and regulates a broad range of cellular functions, including glycogen metabolism, cell cycle progression, and muscle relaxation. PPP1 has evolved effective catalytic machinery but in vitro lacks substrate specificity. In vivo, its specificity is achieved not only by the existence of different PPP1 catalytic isoforms, but also by binding of the catalytic moiety to a large number of regulatory or targeting subunits. Here, we will address exhaustively the existence of diverse PPP1 catalytic isoforms and the relevance of their specific partners and consequent functions.

Integrative genomic analysis for the discovery of biomarkers in prostate cancer

Genome-wide association studies (GWAS) have achieved great success in identifying single nucleotide polymorphisms (SNPs, herein called genetic variants) and genes associated with risk of developing prostate cancer. However, GWAS do not typically link the genetic variants to the disease state or inform the broader context in which the genetic variants operate. Here, we present a novel integrative genomics approach that combines GWAS information with gene expression data to infer the causal association between gene expression and the disease and to identify the network states and biological pathways enriched for genetic variants. We identified gene regulatory networks and biological pathways enriched for genetic variants, including the prostate cancer, IGF-1, JAK2, androgen, and prolactin signaling pathways. The integration of GWAS information with gene expression data provides insights about the broader context in which genetic variants associated with an increased risk of developing prostate cancer operate.

Androgen receptor as a driver of therapeutic resistance in advanced prostate cancer

The role of the androgen receptor (AR) signaling axis in the progression of prostate cancer is a cornerstone to our understanding of the molecular mechanisms causing castration-resistant prostate cancer (CRPC). Resistance of advanced prostate cancer to available treatment options makes it a clinical challenge that results in approximately 30,000 deaths of American men every year. Since the historic discovery by Dr. Huggins more than 70 years ago, androgen deprivation therapy (ADT) has been the principal treatment for advanced prostate cancer. Initially, ADT induces apoptosis of androgen-dependent prostate cancer epithelial cells and regression of androgen-dependent tumors. However, the majority of patients with advanced prostate cancer progress and become refractory to ADT due to emergence of androgen-independent prostate cancer cells driven by aberrant AR activation. Microtubule-targeting agents such as taxanes, docetaxel and paclitaxel, have enjoyed success in the treatment of metastatic prostate cancer; although new, recently designed mitosis-specific agents, such as the polo-kinase and kinesin-inhibitors, have yielded clinically disappointing results. Docetaxel, as a first-line chemotherapy, improves prostate cancer patient survival by months, but tumor resistance to these therapeutic agents inevitably develops. On a molecular level, progression to CRPC is characterized by aberrant AR expression, de novo intraprostatic androgen production, and cross talk with other oncogenic pathways. Emerging evidence suggests that reactivation of epithelial-mesenchymal-transition (EMT) processes may facilitate the development of not only prostate cancer but also prostate cancer metastases. EMT is characterized by gain of mesenchymal characteristics and invasiveness accompanied by loss of cell polarity, with an increasing number of studies focusing on the direct involvement of androgen-AR signaling axis in EMT, tumor progression, and therapeutic resistance. In this article, we discuss the current knowledge of mechanisms via which the AR signaling drives therapeutic resistance in prostate cancer metastatic progression and the novel therapeutic interventions targeting AR in CRPC.

Androgen receptor functions in castration-resistant prostate cancer and mechanisms of resistance to new agents targeting the androgen axis

The metabolic functions of androgen receptor (AR) in normal prostate are circumvented in prostate cancer (PCa) to drive tumor growth, and the AR also can acquire new growth-promoting functions during PCa development and progression through genetic and epigenetic mechanisms. Androgen deprivation therapy (ADT, surgical or medical castration) is the standard treatment for metastatic PCa, but patients invariably relapse despite castrate androgen levels (castration-resistant PCa, CRPC). Early studies from many groups had shown that AR was highly expressed and transcriptionally active in CRPC, and indicated that steroids from the adrenal glands were contributing to this AR activity. More recent studies showed that CRPC cells had increased expression of enzymes mediating androgen synthesis from adrenal steroids, and could synthesize androgens de novo from cholesterol. Phase III clinical trials showing a survival advantage in CRPC for treatment with abiraterone (inhibitor of the enzyme CYP17A1 required for androgen synthesis that markedly reduces androgens and precursor steroids) and for enzalutamide (new AR antagonist) have now confirmed that AR activity driven by residual androgens makes a major contribution to CRPC, and led to the recent Food and Drug Administration approval of both agents. Unfortunately, patients treated with these agents for advanced CRPC generally relapse within a year and AR appears to be active in the relapsed tumors, but the molecular mechanisms mediating intrinsic or acquired resistance to these AR-targeted therapies remain to be defined. This review outlines AR functions that contribute to PCa development and progression, the roles of intratumoral androgen synthesis and AR structural alterations in driving AR activity in CRPC, mechanisms of action for abiraterone and enzalutamide, and possible mechanisms of resistance to these agents.

TGF-β cascade regulation by PPP1 and its interactors -impact on prostate cancer development and therapy

Protein phosphorylation is a key mechanism by which normal and cancer cells regulate their main transduction pathways. Protein kinases and phosphatases are precisely orchestrated to achieve the (de)phosphorylation of candidate proteins. Indeed, cellular health is dependent on the fine-tune of phosphorylation systems, which when deregulated lead to cancer. Transforming growth factor beta (TGF-β) pathway involvement in the genesis of prostate cancer has long been established. Many of its members were shown to be hypo- or hyperphosphorylated during the process of malignancy. A major phosphatase that is responsible for the vast majority of the serine/threonine dephosphorylation is the phosphoprotein phosphatase 1 (PPP1). PPP1 has been associated with the dephosphorylation of several proteins involved in the TGF-β cascade. This review will discuss the role of PPP1 in the regulation of several TGF-β signalling members and how the subversion of this pathway is related to prostate cancer development. Furthermore, current challenges on the protein phosphatases field as new targets to cancer therapy will be addressed.

The regulatory roles of phosphatases in cancer

The relevance of potentially reversible post-translational modifications required for controlling cellular processes in cancer is one of the most thriving arenas of cellular and molecular biology. Any alteration in the balanced equilibrium between kinases and phosphatases may result in development and progression of various diseases, including different types of cancer, though phosphatases are relatively under-studied. Loss of phosphatases such as PTEN (phosphatase and tensin homologue deleted on chromosome 10), a known tumour suppressor, across tumour types lends credence to the development of phosphatidylinositol 3-kinase inhibitors alongside the use of phosphatase expression as a biomarker, though phase 3 trial data are lacking. In this review, we give an updated report on phosphatase dysregulation linked to organ-specific malignancies.

Prostate cancer: the need for biomarkers and new therapeutic targets

Prostate cancer (PCa) incidence and mortality have decreased in recent years. Nonetheless, it remains one of the most prevalent cancers in men, being a disquieting cause of men's death worldwide. Changes in many cell signaling pathways have a predominant role in the onset, development, and progression of the disease. These include prominent pathways involved in the growth, apoptosis, and angiogenesis of the normal prostate gland, such as androgen and estrogen signaling, and other growth factor signaling pathways. Understanding the foundations of PCa is leading to the discovery of key molecules that could be used to improve patient management. The ideal scenario would be to have a panel of molecules, preferably detectable in body fluids, that are specific and sensitive biomarkers for PCa. In the early stages, androgen deprivation is the gold standard therapy. However, as the cancer progresses, it eventually becomes independent of androgens, and hormonal therapy fails. For this reason, androgen-independent PCa is still a major therapeutic challenge. By disrupting specific protein interactions or manipulating the expression of some key molecules, it might be possible to regulate tumor growth and metastasis formation, avoiding the systemic side effects of current therapies. Clinical trials are already underway to assess the efficacy of molecules specially designed to target key proteins or protein interactions. In this review, we address that recent progress made towards understanding PCa development and the molecular pathways underlying this pathology. We also discuss relevant molecular markers for the management of PCa and new therapeutic challenges.

Deubiquitinating enzyme Usp12 is a novel co-activator of the androgen receptor

The androgen receptor (AR), a member of the nuclear receptor family, is a transcription factor involved in prostate cell growth, homeostasis, and transformation. AR is a key protein in growth and development of both normal and malignant prostate, making it a common therapeutic target in prostate cancer. AR is regulated by an interplay of multiple post-translational modifications including ubiquitination. We and others have shown that the AR is ubiquitinated by a number of E3 ubiquitin ligases, including MDM2, CHIP, and NEDD4, which can result in its proteosomal degradation or enhanced transcriptional activity. As ubiquitination of AR causes a change in AR activity or stability and impacts both survival and growth of prostate cancer cells, deubiquitination of these sites has an equally important role. Hence, deubiquitinating enzymes could offer novel therapeutic targets. We performed an siRNA screen to identify deubiquitinating enzymes that regulate AR; in that screen ubiquitin-specific protease 12 (Usp12) was identified as a novel positive regulator of AR. Usp12 is a poorly characterized protein with few known functions and requires the interaction with two cofactors, Uaf-1 and WDR20, for its enzymatic activity. In this report we demonstrate that Usp12, in complex with Uaf-1 and WDR20, deubiquitinates the AR to enhance receptor stability and transcriptional activity. Our data show that Usp12 acts in a pro-proliferative manner by stabilizing AR and enhancing its cellular function.

Castration-resistant prostate cancer: adaptive responses in the androgen axis

The androgen signaling axis in prostate cancer is associated with multiple adaptive mechanisms in response to castration. Herein we review these adaptations with an emphasis on recent molecular insights into the growth and development of castration resistant prostate cancer (CRPC). Alterations include both conventional and novel intracrine androgen synthesis pathways and androgen transport as well as androgen receptor (AR) overexpression, mutation, and splice variation. Each of these underlying mechanisms are potentially linked to post-castration growth, especially after treatment with newer hormonal agents such as abiraterone and enzalutamide. Post-translational AR modifications are well documented and these can affect receptor activity, stability, localization, and interaction with other proteins. Changes in recruitment of androgen receptor associated co-activators/repressors and a distinct AR-induced transcriptional program can dramatically alter proliferation, invasion, and metastasis in a ligand and context-dependent manner. Numerous previously uncharacterized non-coding RNAs, some of which are androgen regulated, may also have important biological function in this disease. Taken together, the view of CRPC has changed dramatically in the last several years. This has occurred not only within the setting of multiple treatment paradigm changes, but also as a multiplicity of potential molecular mechanisms underlying this disease state have been explored and discovered.

Posttranslational modification of the androgen receptor in prostate cancer

The androgen receptor (AR) is important in the development of the prostate by regulating transcription, cellular proliferation, and apoptosis. AR undergoes posttranslational modifications that alter its transcription activity, translocation to the nucleus and stability. The posttranslational modifications that regulate these events are of utmost importance to understand the functional role of AR and its activity. The majority of these modifications occur in the activation function-1 (AF1) region of the AR, which contains the transcriptional activation unit 1 (TAU1) and 5 (TAU5). Identification of the modifications that occur to these regions may increase our understanding of AR activation in prostate cancer and the role of AR in the progression from androgen-dependent to castration-resistant prostate cancer (CRPC). Most of the posttranslational modifications identified to date have been determined using the full-length AR in androgen dependent cells. Further investigations into the role of posttranslational modifications in androgen-independent activation of full-length AR and constitutively active splicing variants are warranted, findings from which may provide new therapeutic options for CRPC.

Genetic susceptibility loci, pesticide exposure and prostate cancer risk

Uncovering SNP (single nucleotide polymorphisms)-environment interactions can generate new hypotheses about the function of poorly characterized genetic variants and environmental factors, like pesticides. We evaluated SNP-environment interactions between 30 confirmed prostate cancer susceptibility loci and 45 pesticides and prostate cancer risk in 776 cases and 1,444 controls in the Agricultural Health Study. We used unconditional logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Multiplicative SNP-pesticide interactions were calculated using a likelihood ratio test. After correction for multiple tests using the False Discovery Rate method, two interactions remained noteworthy. Among men carrying two T alleles at rs2710647 in EH domain binding protein 1 (EHBP1) SNP, the risk of prostate cancer in those with high malathion use was 3.43 times those with no use (95% CI: 1.44–8.15) (P-interaction  = 0.003). Among men carrying two A alleles at rs7679673 in TET2, the risk of prostate cancer associated with high aldrin use was 3.67 times those with no use (95% CI: 1.43, 9.41) (P-interaction  = 0.006). In contrast, associations were null for other genotypes. Although additional studies are needed and the exact mechanisms are unknown, this study suggests known genetic susceptibility loci may modify the risk between pesticide use and prostate cancer.

ARF represses androgen receptor transactivation in prostate cancer

Androgen receptor (AR) signaling is essential for prostate cancer (PCa) development in humans. The initiation of prostate malignancy and progression to a castration-resistant stage are largely contributed by the modulation of AR activity through its coregulatory proteins. We and others previously reported that p14 alternative reading frame (ARF) expression is positively correlated with the disease progression and severity of PCa. Here, we provide evidence that p14ARF physically interacts with AR and functions as an AR corespressor in both an androgen-dependent and androgen-independent manner. Endogenous ARF (p14ARF in human and p19ARF in mouse) and AR colocalize in both human PCa cells in vitro and PCa tissues of mouse and human in vivo. Overexpression of p14ARF in PCa cells significantly attenuates the activities of androgen response region (ARR2)-probasin and prostate-specific antigen (PSA) promoters. The forced expression of p14ARF in cells resulted in a suppression of PSA and NK transcription factor locus 1 (NKX3.1) expression. Conversely, knockdown of endogenous p14ARF in human PCa cells with short hairpin RNA enhanced AR transactivation activities in a dose-dependent and p53-independent manner. Furthermore, we demonstrated that p14ARF binds to both the N-terminal domain and the ligand-binding domain of AR, and the human double minute 2 (HDM2)-binding motif of p14ARF is required for the interaction of p14ARF and AR proteins. p14ARF perturbs the androgen-induced interaction between the N terminus and C terminus of AR. Most importantly, we observed that the expression of PSA is reversely correlated with p14ARF in human prostate tissues. Taken together, our results reveal a novel function of ARF in modulation of AR transactivation in PCa.

Proline-Directed Androgen Receptor Phosphorylation

The androgen receptor (AR) has been identified for decades and mediates essential steroid functions. Like most of biological molecules, AR functional activities are modulated by post-translational modifications. This review is focused on the reported activities and significance of AR phosphorylation, with particular emphasis on proline-directed serine/threonine phosphorylation that occurs predominantly on the receptor. The marked enrichment of AR phosphorylation in the most diverse N-terminal domain suggests that targeting AR phosphorylation can be synergistic to antagonizing the C-terminal domain by clinical antiandrogens.

With a little help from my friends: androgens tap BDNF signaling pathways to alter neural circuits

Gonadal androgens are critical for the development and maintenance of sexually dimorphic regions of the male nervous system, which is critical for male-specific behavior and physiological functioning. In rodents, the motoneurons of the spinal nucleus of the bulbocavernosus (SNB) provide a useful example of a neural system dependent on androgen. Unless rescued by perinatal androgens, the SNB motoneurons will undergo apoptotic cell death. In adulthood, SNB motoneurons remain dependent on androgen, as castration leads to somal atrophy and dendritic retraction. In a second vertebrate model, the zebra finch, androgens are critical for the development of several brain nuclei involved in song production in males. Androgen deprivation during a critical period during postnatal development disrupts song acquisition and dimorphic size-associated nuclei. Mechanisms by which androgens exert masculinizing effects in each model system remain elusive. Recent studies suggest that brain-derived neurotrophic factor (BDNF) may play a role in androgen-dependent masculinization and maintenance of both SNB motoneurons and song nuclei of birds. This review aims to summarize studies demonstrating that BDNF signaling via its tyrosine receptor kinase (TrkB) receptor may work cooperatively with androgens to maintain somal and dendritic morphology of SNB motoneurons. We further describe studies that suggest the cellular origin of BDNF is of particular importance in androgen-dependent regulation of SNB motoneurons. We review evidence that androgens and BDNF may synergistically influence song development and plasticity in bird species. Finally, we provide hypothetical models of mechanisms that may underlie androgen- and BDNF-dependent signaling pathways.

Regulation of the androgen receptor by post-translational modifications

The androgen receptor (AR) is a key molecule in prostate cancer and Kennedy's disease. Understanding the regulatory mechanisms of this steroid receptor is important in the development of potential therapies for these diseases. One layer of AR regulation is provided by post-translational modifications including phosphorylation, acetylation, sumoylation, ubiquitination and methylation. While these modifications have mostly been studied as individual events, it is becoming clear that these modifications can functionally interact with each other in a signalling pathway. In this review, the effects of all modifications are described with a focus on interplay between them and the functional consequences for the AR.

Casein kinase 2 inhibition attenuates androgen receptor function and cell proliferation in prostate cancer cells

BACKGROUND

Casein kinase 2 (CK2) is constitutively active with dual specificity and exists as a hetero-tetrameric complex of α, α', and β subunits. Its aberrant expression and elevated activity have been linked to many human cancers, including prostate cancer. As an effort to develop new chemotherapy for prostate cancers, in this study, we tested the effects of tetra-bromo-cinnamic acid (TBCA), a newly synthetic CK2-selective CK2 inhibitor, on androgen receptor (AR) transactivation, cell proliferation, and viability in multiple prostate cancer cell lines.

METHODS

We utilized a comprehensive approach of a newly synthetic CK2-selective inhibitor TBCA, plus gene-specific siRNAs in multiple cell-based assays to further understand the role of CK2 in AR signaling. Alamar-blue-based cell growth assay, flow cytometry for cell cycle distribution, Luciferase report gene assay for AR transactivation, and immuno-fluorescent approach for AR nuclear localization as well as quantitative PCR assay for AR-mediated gene expression were utilized. The significance of the differences between treatment and control was analyzed using the SPSS software (SPSS, Chicago, IL).

RESULTS

Our data revealed that TBCA reduced cell proliferation and caused G2/M cell cycle arrest in a dose-dependent manner. Further analysis demonstrated that TBCA blocked AR nuclear translocation and gene expression. To confirm the target specificity, we used gene-specific siRNAs for both CK2α and CK2α' subunits, and the results suggested that both CK2 catalytic subunits are involved in androgen-stimulated AR nuclear translocation and AR-mediated gene expression in prostate cancer cells.

CONCLUSIONS

CK2 subunits α and α' are likely involved in AR signaling, and TBCA might be useful in the management of prostate cancers as a chemo-preventive agent in the future.