Role of conserved hydrophobic amino acids in androgen receptor AF-1 function

The evolution and polymorphism of mono-amino acid repeats in androgen receptor and their regulatory role in health and disease

Androgen receptor (AR) is a key member of nuclear hormone receptors with the longest intrinsically disordered N-terminal domain (NTD) in its protein family. There are four mono-amino acid repeats (polyQ1, polyQ2, polyG, and polyP) located within its NTD, of which two are polymorphic (polyQ1 and polyG). The length of both polymorphic repeats shows clinically important correlations with disease, especially with cancer and neurodegenerative diseases, as shorter and longer alleles exhibit significant differences in expression, activity and solubility. Importantly, AR has also been shown to undergo condensation in the nucleus by liquid-liquid phase separation, a process highly sensitive to protein solubility and concentration. Nonetheless, in prostate cancer cells, AR variants also partition into transcriptional condensates, which have been shown to alter the expression of target gene products. In this review, we summarize current knowledge on the link between AR repeat polymorphisms and cancer types, including mechanistic explanations and models comprising the relationship between condensate formation, polyQ1 length and transcriptional activity. Moreover, we outline the evolutionary paths of these recently evolved amino acid repeats across mammalian species, and discuss new research directions with potential breakthroughs and controversies in the literature.

Non-nuclear AR Signaling in Prostate Cancer

Despite the key role played by androgen receptor (AR) in tumor cell aggressiveness and prostate cancer (PCa) progression, its function in the tumor microenvironment (TME) is still controversial. Increasing studies highlight the crucial role played by TME modulation in treatment outcome and tumor cell spreading. In this context, targeting specific constituents of the TME could be considered an alternative approach to classic treatments directed against cancer cells. Currently, androgen deprivation therapy (ADT) is a routinely adopted strategy in the management of PCa, with initial success, and consecutive fail. A possible justification to this is the fact that ADT aims to target all the transcription/translation-related activities of AR, which are typical of tumor epithelial cells. Less is still known about side effects of ADT on TME. Cancer Associated Fibroblasts (CAFs), for example, express a classic AR, mostly confined in the extra-nuclear portion of the cell. In CAFs ADT exerts a plethora of non-transcriptional effects, depending by the protein partner linked to AR, leading to cell migration, proliferation, and differentiation. In recent years, substantial progress in the structure-function relationships of AR, identification of its binding partners and function of protein complexes including AR have improved our knowledge of its signaling axis. Important AR non-genomic effects and lots of its cytoplasmatic binding partners have been described, pointing out a fine control of AR non-genomic pathways. Accordingly, new AR inhibitors have been designed and are currently under investigation. Prompt development of new approaches to target AR or block recruitment of its signaling effectors, or co-activators, is urgently needed. The present review takes an in-depth look at current literature, furnishing an exhaustive state-of-the-art overview of the non-genomic role of AR in PCa, with particular emphasis on its involvement in TME biology.

An Amyloidogenic Sequence at the N-Terminus of the Androgen Receptor Impacts Polyglutamine Aggregation

The human androgen receptor (AR) is a ligand inducible transcription factor that harbors an amino terminal domain (AR-NTD) with a ligand-independent activation function. AR-NTD is intrinsically disordered and displays aggregation properties conferred by the presence of a poly-glutamine (polyQ) sequence. The length of the polyQ sequence as well as its adjacent sequence motifs modulate this aggregation property. AR-NTD also contains a conserved KELCKAVSVSM sequence motif that displays an intrinsic property to form amyloid fibrils under mild oxidative conditions. As peptide sequences with intrinsic oligomerization properties are reported to have an impact on the aggregation of polyQ tracts, we determined the effect of the KELCKAVSVSM on the polyQ stretch in the context of the AR-NTD using atomic force microscopy (AFM). Here, we present evidence for a crosstalk between the amyloidogenic properties of the KELCKAVSVSM motif and the polyQ stretch at the AR-NTD.

Targeting alternative sites on the androgen receptor to treat castration-resistant prostate cancer

Recurrent, metastatic prostate cancer continues to be a leading cause of cancer-death in men. The androgen receptor (AR) is a modular, ligand-inducible transcription factor that regulates the expression of genes that can drive the progression of this disease, and as a consequence, this receptor is a key therapeutic target for controlling prostate cancer. The current drugs designed to directly inhibit the AR are called anti-androgens, and all act by competing with androgens for binding to the androgen/ligand binding site. Unfortunately, with the inevitable progression of the cancer to castration resistance, many of these drugs become ineffective. However, there are numerous other regulatory sites on this protein that have not been exploited therapeutically. The regulation of AR activity involves a cascade of complex interactions with numerous chaperones, co-factors and co-regulatory proteins, leading ultimately to direct binding of AR dimers to specific DNA androgen response elements within the promoter and enhancers of androgen-regulated genes. As part of the family of nuclear receptors, the AR is organized into modular structural and functional domains with specialized roles in facilitating their inter-molecular interactions. These regions of the AR present attractive, yet largely unexploited, drug target sites for reducing or eliminating androgen signaling in prostate cancers. The design of small molecule inhibitors targeting these specific AR domains is only now being realized and is the culmination of decades of work, including crystallographic and biochemistry approaches to map the shape and accessibility of the AR surfaces and cavities. Here, we review the structure of the AR protein and describe recent advancements in inhibiting its activity with small molecules specifically designed to target areas distinct from the receptor’s androgen binding site. It is anticipated that these new classes of anti-AR drugs will provide an additional arsenal to treat castration-resistant prostate cancer.

Prot-Prop: J-tool to predict the subcellular location of proteins based on physiochemical characterization

PROT-PROP is a computational tool to characterize 27 physicochemical properties of a protein along with its subcellular location (intra or extra) in a single-window application. Other significant features of this software include calculation of numerical values for hydrophobicity, hydrophilicity; composition of small and large amino acids; net hydrophobic content in terms of low/high; and Navie's algorithm to calculate theoretical pI. PROT-PROP is an easy-to-install platform independent implementation of JAVA under a user-friendly interface. It is a standalone version as a virtual appliance and source code for platforms supporting Java 1.5.0 and higher versions, and downloadable from the web http://www.mzu.edu.in/schools/biotechnology.html . PROT-PROP can run under Windows and Macintosh Operating Systems. PROT-PROP is distributed with its source code so that it may be adapted or customized, if desired.

Ligand-independent androgen receptor antagonism caused by the newly developed pesticide pyrifluquinazon (PFQ)

Androgen receptor (AR) is an essential component to activate AR dependent gene transcriptions. Despite wide acceptance of pharmacological controls on transcriptional pathway depending on competitive inhibitions of ligand binding, only a few examples, AR antagonism via ligand-independent mechanisms, have been recognized. Pyrifluquinazon(PFQ), a newly developed pesticide, induced representative AR antagonism against rats in in vivo and in vitro. Intriguingly, this AR antagonism was not based on inhibition of ligand binding. Instead, the evidence suggested that the AR antagonism was induced as a consequence of decline of cellular AR protein level. This study demonstrated that AR N-terminal region could be an essential element for a ligand-independent mechanism underling the AR antagonism by PFQ. Our findings should provide a novel insight into the regulation of AR-mediated transcription.

A small RNA derived from RNA coactivator SRA blocks steroid receptor signaling via inhibition of Pus1p-mediated pseudouridylation of SRA: evidence of a novel RNA binding domain in the N-terminus of steroid receptors

Estrogen receptors (ERs) and androgen receptors (ARs) are important targets for cancer therapy; however, the efficacy of receptor antagonists is limited, and alternative strategies are needed. Steroid receptor RNA Activator (SRA) is a long, noncoding RNA coactivator (although some protein-encoding 5' splice variants have also been reported) that requires pseudouridylation by Pus1p to stimulate steroid receptor signaling. A uridine at position 206 (U206), which is located in small hairpin structure STR5 in the conserved SRA core sequence, is a critical target for pseudouridylation. We assessed if synthetic STR5 could serve as a novel competitive inhibitor of ERα and AR signaling by disrupting the Pus1p-SRA-steroid receptor axis. STR5 specifically inhibited Pus1p-dependent pseudouridylation of SRA with higher efficiency than STR5 mutant U206A. We show that SRA binds to the N-terminal domain (NTD) of ERα and AR with high affinity despite the absence of a recognizable RNA binding motif (RBM). Finally, we show that STR5 specifically inhibits ERα- and AR-dependent transactivation of target genes in steroid-sensitive cancer cells, consistent with disruption of the targeted Pus1p-SRA pathway. Together, our results show that the NTD of ERα and AR contains a novel RBM that directly binds SRA, and that STR5 can serve as a novel class of RNA inhibitor of ERα and AR signaling by interfering with Pus1p-mediated SRA pseudouridylation. Targeting this unexplored receptor signaling pathway may pave the way for the development of new types of cancer therapeutics.

Allosteric modulators of steroid hormone receptors: structural dynamics and gene regulation

Steroid hormones are synthesized from cholesterol primarily in the adrenal gland and the gonads and play vital roles in normal physiology, the control of development, differentiation, metabolic homeostasis, and reproduction. The actions of these small lipophilic molecules are mediated by intracellular receptor proteins. It is just over 25 yr since the first cDNA for steroid receptors were cloned, a development that led to the birth of a superfamily of ligand-activated transcription factors: the nuclear receptors. The receptor proteins share structurally and functionally related ligand binding and DNA-binding domains but possess distinct N-terminal domains and hinge regions that are intrinsically disordered. Since the original cloning experiments, considerable progress has been made in our understanding of the structure, mechanisms of action, and biology of this important class of ligand-activated transcription factors. In recent years, there has been interest in the structural plasticity and function of the N-terminal domain of steroid hormone receptors and in the allosteric regulation of protein folding and function in response to hormone, DNA response element architecture, and coregulatory protein binding partners. The N-terminal domain can exist as an ensemble of conformers, having more or less structure, which prime this region of the receptor to rapidly respond to changes in the intracellular environment through hormone binding and posttranslation modifications. In this review, we address the question of receptor structure and function dynamics with particular emphasis on the structurally flexible N-terminal domain, intra- and interdomain communications, and the allosteric regulation of receptor action.

The impact of point mutations in the human androgen receptor: classification of mutations on the basis of transcriptional activity

Androgen receptor mediated signaling drives prostate cancer cell growth and survival. Mutations within the receptor occur infrequently in prostate cancer prior to hormonal therapy but become prevalent in incurable androgen independent and metastatic tumors. Despite the determining role played by the androgen receptor in all stages of prostate cancer progression, there is a conspicuous dearth of comparable data on the consequences of mutations. In order to remedy this omission, we have combined an expansive study of forty five mutations which are predominantly associated with high Gleason scores and metastatic tumors, and span the entire length of the receptor, with a literature review of the mutations under investigation. We report the discovery of a novel prevalent class of androgen receptor mutation that possesses loss of function at low levels of androgen yet transforms to a gain of function at physiological levels. Importantly, mutations introducing constitutive gain of function are uncommon, with the majority of mutations leading to either loss of function or no significant change from wild-type activity. Therefore, the widely accepted supposition that androgen receptor mutations in prostate cancer result in gain of function is appealing, but mistaken. In addition, the transcriptional outcome of some mutations is dependent upon the androgen receptor responsive element. We discuss the consequences of these findings and the role of androgen receptor mutations for prostate cancer progression and current treatment options.

Intrinsic disorder in the androgen receptor: identification, characterisation and drugability

The androgen receptor (AR) regulates networks of genes in response to the steroid hormones testosterone and dihydrotestosterone. The receptor protein is made up of both stably folded globular domains, involved in hormone and DNA binding, and regions of intrinsic disorder, including the N-terminal domain (NTD). The AR-NTD has a modular activation function (termed AF1) and is important for gene regulation, participating in multiple protein-protein interactions. Biophysical studies have revealed that AR-NTD/AF1 has limited stable secondary structure and conforms to a 'collapsed disordered' conformation. The AR-NTD/AF1 has the propensity to adopt an α-helical conformation in response to a natural osmolyte or a co-regulatory binding partner. The AR is a key drug target in the management of advanced prostate cancer and recently a small molecule inhibitor was identified that interacts with the NTD/AF1 and impairs protein-protein interactions and recruitment of the receptor to target genes. In this review the role of intrinsic disorder in AR function is discussed along with the potential to develop new drugs that will target the structurally plastic NTD.

Molecular characterization of hypoxia inducible factor-1 (HIF-1) from the white shrimp Litopenaeus vannamei and tissue-specific expression under hypoxia

Hypoxia inducible factor 1 (HIF-1) is a key transcription factor that regulates a variety of molecular responses to hypoxia. Some marine crustaceans experience changes of oxygen tension in their aquatic environment, but knowledge about the function and expression of HIF-1 is very limited. HIF-1 is a heterodimer composed by alpha and beta subunits. We report the complete cDNA sequences of HIF-1alpha and HIF-1beta from the white shrimp Litopenaeus vannamei. HIF-1alpha (LvHIF-1alpha) is 3672bp and codes for 1050 amino acids, while HIF-1beta is 2135bp (LvHIF-1beta) and 608 amino acids. Both, the alpha and beta subunits have the helix-loop-helix (bHLH) and PAS domains. HIF-1alpha also has the oxygen dependent degradation (ODD) and the C-terminal transactivation domain (C-TAD), important for regulation in normoxia. Phylogenetic analyses of the proteins indicate separation of invertebrates from vertebrates. Large differences of HIF-1alpha and HIF-1beta transcripts abundance were detected in gills, hepatopancreas and muscle under normoxia (6mg/L dissolved oxygen, DO) and hypoxia (2.5 and 1.5mg/L DO). HIF-1alpha was more abundant in gills and HIF-1beta in hepatopancreas. Large changes in response to hypoxia were detected for HIF-1alpha in gills, while HIF-1beta remained fairly constant. Glucose and lactate in hemolymph increased rapidly in hypoxia in all cases and up to 4.7 and 5.0-fold, respectively, in response to 1.5mg/L DO for 1h.

Amino-terminus domain of the androgen receptor as a molecular target to prevent the hormonal progression of prostate cancer

Prostate cancer has a propensity to metastasize to the bone. Currently the only effective systemic treatment for these patients is androgen ablation therapy. However, the tumor will invariably progress to an androgen-independent stage and the patient will succumb to his disease within approximately 2 years. The earliest indication of hormonal progression is the rising titer of serum prostate specific antigen. Current evidence implicates the androgen receptor (AR) as a key factor in maintaining the growth of prostate cancer cells in an androgen-depleted state. Under normal conditions, binding of ligand activates the receptor, allowing it to effectively bind to its respective DNA element. However, AR is also transformed in the absence of androgen (ligand-independent activation) in prostate cells via multiple protein kinase pathways and the interleukin-6 (IL-6) pathway that converge upon the N-terminal domain of the AR. This domain is the main region for phosphorylation and is also critical for normal coregulator recruitment. Here we discuss evidence supporting the role of the AR, IL-6 and other protein kinase pathways in the hormonal progression of prostate cancer to androgen independence and the mechanisms involved in activation of the AR by these pathways. Receptor-targeted therapy, especially potential drugs targeting the N-terminal domain, may effectively prevent or delay the hormonal progression of AR-dependent prostate cancer.

Pleiotropic functional properties of androgen receptor mutants in prostate cancer

The androgen receptor (AR) signaling pathway plays an important role during the development of the normal prostate gland, but also during the progression of prostate cancer on androgen ablation therapy. Mutations in the AR gene emerge to keep active the AR signaling pathway and to support prostate cancer cells growth and survival despite the low levels of circulating androgens. Indeed, mutations affecting the ligand binding domain (LBD) of the AR have been shown to generate so-called "promiscuous" receptors that present widened ligand specificity and allow the stimulation of these receptors by a larger spectrum of endogenous hormones. Another class of mutations, arising in the amino-terminal domain (NTD) of the receptor, modulate AR interactions with coregulators involved in cell proliferation regulation. Besides characteristics of these well-known types of mutations, the properties of other classes of AR mutants recently described in prostate cancer are currently under investigation. Most interestingly, in addition to their potential role in the mechanisms which allow prostate cancer cells to escape androgen ablation therapy, data suggest that certain AR mutations are present early in the natural history of the disease and may play a role in many aspects of prostate cancer progression. Surprisingly, singular truncated AR devoid of their carboxy-terminal end (CTE) region seem to exert specific paracrine effects and to induce a clonal cooperation with neighboring prostate cancer cells, which may facilitate both the invasion and metastasis processes. In this article, we review the functional properties of different classes of AR mutants and their potential impact on the natural history of prostate cancer. Hum Mutat 0, 1-14, 2008. (c) 2008 Wiley-Liss, Inc.

Diverse roles of androgen receptor (AR) domains in AR-mediated signaling

Androgens control male sexual development and maintenance of the adult male phenotype. They have very divergent effects on their target organs like the reproductive organs, muscle, bone, brain and skin. This is explained in part by the fact that different cell types respond differently to androgen stimulus, even when all these responses are mediated by the same intracellular androgen receptor. To understand these tissue- and cell-specific readouts of androgens, we have to learn the many different steps in the transcription activation mechanisms of the androgen receptor (NR3C4). Like all nuclear receptors, the steroid receptors have a central DNA-binding domain connected to a ligand-binding domain by a hinge region. In addition, all steroid receptors have a relatively large amino-terminal domain. Despite the overall structural homology with other nuclear receptors, the androgen receptor has several specific characteristics which will be discussed here. This receptor can bind two types of androgen response elements (AREs): one type being similar to the classical GRE/PRE-type elements, the other type being the more divergent and more selective AREs. The hormone-binding domain has low intrinsic transactivation properties, a feature that correlates with the low affinity of this domain for the canonical LxxLL-bearing coactivators. For the androgen receptor, transcriptional activation involves the alternative recruitment of coactivators to different regions in the amino-terminal domain, as well as the hinge region. Finally, a very strong ligand-induced interaction between the amino-terminal domain and the ligand-binding domain of the androgen receptor seems to be involved in many aspects of its function as a transcription factor. This review describes the current knowledge on the structure-function relationships within the domains of the androgen receptor and tries to integrate the involvement of different domains, subdomains and motifs in the functioning of this receptor as a transcription factor with tissue- and cell-specific readouts.

Natural disordered sequences in the amino terminal domain of nuclear receptors: lessons from the androgen and glucocorticoid receptors

Steroid hormones are a diverse class of structurally related molecules, derived from cholesterol, that include androgens, estrogens, progesterone and corticosteroids. They represent an important group of physiologically active signalling molecules that bind intracellular receptor proteins and regulate genes involved in developmental, reproductive and metabolic processes. The receptor proteins share structurally and functionally related ligand binding and DNA-binding domains, but possess distinct N-terminal domains (NTD) of unique length and amino acids sequence. The NTD contains sequences important for gene regulation, exhibit structure plasticity and are likely to contribute to the specificity of the steroid hormone/receptor response.

Structural dynamics of the human androgen receptor: implications for prostate cancer and neurodegenerative disease

The AR (androgen receptor) is a ligand-activated transcription factor that mediates the action of the steroids testosterone and dihydrotestosterone. Alterations in the AR gene result in a number of clinical disorders, including: androgen-insensitivity, which leads to disruption of male development; prostate cancer; and a neuromuscular degenerative condition termed spinal bulbar muscular atrophy or Kennedy's disease. The AR gene is X-linked and the protein is coded for by eight exons, giving rise to a C-terminal LBD (ligand-binding domain; exons 4-8), linked by a hinge region (exon 4) to a Zn-finger DBD (DNA-binding domain; exons 2 and 3) and a large structurally distinct NTD (N-terminal domain; exon 1). Identification and characterization of mutations found in prostate cancer and Kennedy's disease patients have revealed the importance of structural dynamics in the mechanisms of action of receptors. Recent results from our laboratory studying genetic changes in the LBD and the structurally flexible NTD will be discussed.

The human androgen receptor AF1 transactivation domain: interactions with transcription factor IIF and molten-globule-like structural characteristics

The AR (androgen receptor) is a ligand-activated transcription factor and member of the steroid receptor superfamily. The AR responds to the ligands testosterone and dihydrotestosterone and activates multiple downstream genes required in development and reproduction. During the events of transactivation, the AR makes specific protein–protein interactions with several basal transcription factors such as TBP (TATA-box-binding protein) and TFIIF (transcription factor IIF). These interactions occur predominantly within a defined region termed AF1 (activation function-1) located within the highly disordered N-terminal domain of the receptor. Our focus is on the structural aspects of AF1 and how this flexible and disordered domain generates functional interactions with regulators of transcription. Our working hypothesis is that AR-AF1 domain exhibits induced folding when contacted by transcription regulators (such as TFIIF) into a more compact and ‘active’ conformation, enabling further co-regulator recruitment and ultimately transcription. Structural flexibility and intrinsic disorder of AR-AF1 were studied using predictive algorithms and fluorescence spectroscopy under different experimental conditions and the results revealed this domain retains characteristics indicative of molten-globule or pre-molten-globule-like structures. We hypothesize that this partially folded intermediate state is important for, and enables the AF1 domain to make, multiple protein–protein interactions. The structural aspects of AR-AF1 and interactions with TFIIF are discussed.

The role of the general transcription factor IIF in androgen receptor-dependent transcription

The androgen receptor (AR) is a member of the steroid receptor subfamily of nuclear receptors and is important for normal male sexual differentiation and fertility. The major transactivation function of the AR, termed activation function 1 (AF1), is modular in structure and has been mapped to the N terminus of the protein. To understand better the mechanisms whereby the AR activates transcription, we have established a novel cell-free transcription assay. This is based on the use of a dual reporter gene template, containing promoter proximal and distal G-less cassettes, which result in different size transcripts that can be easily detected and quantified. The promoter proximal transcript gives an indication of transcription initiation and promoter escape, whereas the relative levels of the distal transcript indicate elongation efficiency. The AR-AF1-Lex protein enhanced production of both transcripts whereas, in the absence of DNA binding, the AF1 domain squelched both initiation and elongation. Mutations in the transactivation domain that impaired transactivation and/or binding of the general transcription factor IIF (TFIIF) were found to reduce the ability of AR-AF1 to squelch transcription. Addition of recombinant TFIIF reversed squelching of the promoter-proximal but not the -distal G-less transcript, whereas addition of TATA-binding protein failed to reverse squelching of either transcript. Taken together, these results demonstrate that the AR N-terminal transactivation function, AF1, has the potential to regulate transcription at both the level of initiation and elongation, and that interactions with TFIIF are important during preinitiation complex assembly/open complex formation and/or promoter escape.

Structure and function of steroid receptor AF1 transactivation domains: induction of active conformations

Steroid hormones are important endocrine signalling molecules controlling reproduction, development, metabolism, salt balance and specialized cellular responses, such as inflammation and immunity. They are lipophilic in character and act by binding to intracellular receptor proteins. These receptors function as ligand-activated transcription factors, switching on or off networks of genes in response to a specific hormone signal. The receptor proteins have a conserved domain organization, comprising a C-terminal LBD (ligand-binding domain), a hinge region, a central DBD (DNA-binding domain) and a highly variable NTD (N-terminal domain). The NTD is structurally flexible and contains surfaces for both activation and repression of gene transcription, and the strength of the transactivation response has been correlated with protein length. Recent evidence supports a structural and functional model for the NTD that involves induced folding, possibly involving alpha-helix structure, in response to protein-protein interactions and structure-stabilizing solutes.

Mutation of the androgen receptor causes oncogenic transformation of the prostate

Recent evidence demonstrates that the androgen receptor (AR) continues to influence prostate cancer growth despite medical therapies that reduce circulating androgen ligands to castrate levels and/or block ligand binding. Whereas the mutation, amplification, overexpression of AR, or cross-talk between AR and other growth factor pathways may explain the failure of androgen ablation therapies in some cases, there is little evidence supporting a causal role between AR and prostate cancer. In this study, we functionally and directly address the role whereby AR contributes to spontaneous cancer progression by generating transgenic mice expressing (i) AR-WT to recapitulate increased AR levels and ligand sensitivity, (ii) AR-T857A to represent a promiscuous AR ligand response, and (iii) AR-E231G to model altered AR function. Whereas transgenes encoding either AR-WT or AR-T857A did not cause prostate cancer when expressed at equivalent levels, expression of AR-E231G, which carries a mutation in the most highly conserved signature motif of the NH2-terminal domain that also influences interactions with cellular coregulators, caused rapid development of prostatic intraepithelial neoplasia that progressed to invasive and metastatic disease in 100% of mice examined. Taken together, our data now demonstrate the oncogenic potential of steroid receptors and implicate altered AR function and receptor coregulator interaction as critical determinants of prostate cancer initiation, invasion, and metastasis.

In vitro regulation of reporter gene transcription by the androgen receptor AF1 domain

The androgen receptor (AR) is a ligand-activated transcription factor that regulates gene expression in response to the steroids testosterone and dihydrotestosterone. AR-dependent gene expression is likely to play an important role in a number of receptor-associated disorders, such as prostate cancer, spinal bulbar muscular atrophy, male type baldness and hirsutism. The AR contains two transactivation domains, termed AF1 (activation function 1) located in the N-terminus and AF2 (activation function 2) in the C-terminal ligand-binding domain. AF2 exhibits weak transcriptional activity, whereas AF1 is a strong regulator of transcription. Transcriptional regulation by AF1 is thought to be modulated by a number of proteins that interact with this region, and by post-translational modifications. Our focus is on the N-terminal-interacting proteins and their regulation of transcription via interaction with the receptor. To better understand the mechanism of AR-AF1 action, we have reconstituted AR activity in HeLa nuclear extracts using a unique dual reporter gene assay. Multiple LexA-binding sites in the promoter allow transcription to be driven by a recombinant AR-AF1–Lex fusion protein. The findings from initial experiments suggest an increase in transcription initiation and elongation rates by AR-AF1–Lex. The role of protein–protein interactions involving co-activators and basal transcription factors and AR-AF1 activity are discussed.

An Androgen Receptor NH2-terminal Conserved Motif Interacts with the COOH Terminus of the Hsp70-interacting Protein (CHIP)

The NH2-terminal sequence of steroid receptors is highly variable between different receptors and in the same receptor from different species. In this study, a primary sequence homology comparison identified a 14-amino acid NH2-terminal motif of the human androgen receptor (AR) that is common to AR from all species reported, including the lower vertebrates. The evolutionarily conserved motif is unique to AR, with the exception of a partial sequence in the glucocorticoid receptor of higher species. The presence of the conserved motif in AR and the glucocorticoid receptor and its absence in other steroid receptors suggests convergent evolution. The function of the AR NH2-terminal conserved motif was suggested from a yeast two-hybrid screen that identified the COOH terminus of the Hsp70-interacting protein (CHIP) as a binding partner. We found that CHIP functions as a negative regulator of AR transcriptional activity by promoting AR degradation. In support of this, two mutations in the AR NH2-terminal conserved motif previously identified in the transgenic adenocarcinoma of mouse prostate model reduced the interaction between CHIP and AR. Our results suggest that the AR NH2-terminal domain contains an evolutionarily conserved motif that functions to limit AR transcriptional activity. Moreover, we demonstrate that the combination of comparative sequence alignment and yeast two-hybrid screening using short conserved peptides as bait provides an effective strategy to probe the structure-function relationships of steroid receptor NH2-terminal domains and other intrinsically unstructured transcriptional regulatory proteins.