Identification of Putative Androgen Receptor Interaction Protein Modules

Development of biomarkers for predicting recurrence by determining the metastatic ability of cancer cells

Adjuvant chemotherapy has been carried out for patients with cancer who underwent curative resection, but it is basically not needed for patients without micro-metastatic lesions who undergo a perfectly curative surgical operation. The patients who need adjuvant chemotherapy are defined as those whose micro-metastases cannot be detected by imaging modalities in the other sites of the resective areas, despite curative resection for the primary sites. If biomarkers to efficiently evaluate the metastatic potential of each patient could be developed, we may be able to provide personalized adjuvant chemotherapy in the clinical setting. Actinin-4 (ACTN4, gene name ACTN4) is an actin-bundling protein that we identified in 1998 as a novel molecule involved in cancer invasion and metastasis. Protein overexpression of actinin-4 in cancer cells leads to the invasive phenotype, and patients with gene amplification of ACTN4 have a worse prognosis than patients with a normal copy number in some cancers, including pancreas, lung, and salivary gland cancers. In this review, the biological roles of actinin-4 for cancer invasion and metastasis are summarized, and the potential usefulness of actinin-4 as a biomarker for evaluation of metastatic ability is examined.

The mechanobiome: a goldmine for cancer therapeutics

Cancer progression is dependent on heightened mechanical adaptation, both for the cells' ability to change shape and to interact with varying mechanical environments. This type of adaptation is dependent on mechanoresponsive proteins that sense and respond to mechanical stress, as well as their regulators. Mechanoresponsive proteins are part of the mechanobiome, which is the larger network that constitutes the cell's mechanical systems that are also highly integrated with many other cellular systems, such as gene expression, metabolism, and signaling. Despite the altered expression patterns of key mechanobiome proteins across many different cancer types, pharmaceutical targeting of these proteins has been overlooked. Here, we review the biochemistry of key mechanoresponsive proteins, specifically nonmuscle myosin II, α-actinins, and filamins, as well as the partnering proteins 14-3-3 and CLP36. We also examined a wide range of data sets to assess how gene and protein expression levels of these proteins are altered across many different cancer types. Finally, we determined the potential of targeting these proteins to mitigate invasion or metastasis and suggest that the mechanobiome is a goldmine of opportunity for anticancer drug discovery and development.

Integrin αvβ3 in the Mediating Effects of Dihydrotestosterone and Resveratrol on Breast Cancer Cell Proliferation

Hormones and their receptors play an important role in the development and progression of breast cancer. Hormones regulate the proliferation of breast cancer cells through binding between estrogen or progestins and steroid receptors that may reside in the cytoplasm or be transcriptionally activated as steroid–protein nuclear receptor complexes. However, receptors for nonpeptide hormones also exist in the plasma membrane. Via those receptors, hormones are able to stimulate breast cancer cell proliferation when activated. Integrins are heterodimeric structural proteins of the plasma membrane. Their primary functions are to interact with extracellular matrix proteins and growth factors. Recently, integrin αvβ3 has been identified as a receptor for nonpeptide hormones, such as thyroid hormone and dihydrotestosterone (DHT). DHT promotes the proliferation of human breast cancer cells through binding to integrin αvβ3. A receptor for resveratrol, a polyphenol stilbene, also exists on this integrin in breast cancer cells, mediating the anti-proliferative, pro-apoptotic action of the compound in these cells. Unrelated activities of DHT and resveratrol that originate at integrin depend upon downstream stimulation of mitogen-activated protein kinase (MAPK, ERK1/2) activity, suggesting the existence of distinct, function-specific pools of ERK1/2 within the cell. This review will discuss the features of these receptors in breast cancer cells, in turn suggesting clinical applications that are based on the interactions of resveratrol/DHT with integrin αvβ3 and other androgen receptors.

Proteomics contribution to the elucidation of the steroid hormone receptors functions

Steroid hormones have far-ranging biological impacts and more are continuously being uncovered. Over the last decades, proteomics approaches have become key to better understand biological processes. Due to multiple technical breakthroughs allowing for the concurrent identification and/or quantification of thousands of analytes using mass spectrometers, researchers employing proteomics tools today can now obtain truly holistic views of multiple facets of the human proteome. Here, we review how the field of proteomics has contributed to discoveries about steroid hormones, their receptors and their impact on human pathologies. In particular, the involvement of steroid receptors in cancer initiation, development, metastasis and treatment will be highlighted. Techniques at the forefront of the proteomics field will also be discussed to present how they can contribute to a better understanding of steroid hormone receptors.

Subphenotype meta-analysis of testicular cancer genome-wide association study data suggests a role for RBFOX family genes in cryptorchidism susceptibility

STUDY QUESTION

Can subphenotype analysis of genome-wide association study (GWAS) data from subjects with testicular germ cell tumor (TGCT) provide insight into cryptorchidism (undescended testis, UDT) susceptibility?

SUMMARY ANSWER

Suggestive intragenic GWAS signals common to UDT, TGCT case-case and TGCT case-control analyses occur in genes encoding RBFOX RNA-binding proteins (RBPs) and their neurodevelopmental targets.

WHAT IS KNOWN ALREADY

UDT is a strong risk factor for TGCT, but while genetic risk factors for TGCT are well-known, genetic susceptibility to UDT is poorly understood and appears to be more complex.

STUDY DESIGN, SIZE, DURATION

We performed a secondary subphenotype analysis of existing GWAS data from the Testicular Cancer Consortium (TECAC) and compared these results with our previously published UDT GWAS data, and with data previously acquired from studies of the fetal rat gubernaculum.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Studies from the National Cancer Institute (NCI), United Kingdom (UK) and University of Pennsylvania (Penn) that enrolled white subjects were the source of the TGCT GWAS data. We completed UDT subphenotype case-case (TGCT/UDT vs TGCT/non-UDT) and case-control (TGCT/UDT vs control), collectively referred to as 'TECAC' analyses, followed by a meta-analysis comprising 129 TGCT/UDT cases, 1771 TGCT/non-UDT cases, and 3967 unaffected controls. We reanalyzed our UDT GWAS results comprising 844 cases and 2718 controls by mapping suggestive UDT and TECAC signals (defined as P < 0.001) to genes using Ingenuity Pathway Analysis (IPA®). We compared associated pathways and enriched gene categories common to all analyses after Benjamini-Hochberg multiple testing correction, and analyzed transcript levels and protein expression using qRT-PCR and rat fetal gubernaculum confocal imaging, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

We found suggestive signals within 19 genes common to all three analyses, including RBFOX1 and RBFOX3, neurodevelopmental paralogs that encode RBPs targeting (U)GCATG-containing transcripts. Ten of the 19 genes participate in neurodevelopment and/or contribute to risk of neurodevelopmental disorders. Experimentally predicted RBFOX gene targets were strongly overrepresented among suggestive intragenic signals for the UDT (117 of 628 (19%), P = 3.5 × 10-24), TECAC case-case (129 of 711 (18%), P = 2.5 × 10-27) and TECAC case-control (117 of 679 (17%), P = 2 × 10-21) analyses, and a majority of the genes common to all three analyses (12 of 19 (63%), P = 3 × 10-9) are predicted RBFOX targets. Rbfox1, Rbfox2 and their encoded proteins are expressed in the rat fetal gubernaculum. Predicted RBFOX targets are also enriched among transcripts differentially regulated in the fetal gubernaculum during normal development (P = 3 × 10-31), in response to in vitro hormonal stimulation (P = 5 × 10-45) and in the cryptorchid LE/orl rat (P = 2 × 10-42).

LARGE SCALE DATA

GWAS data included in this study are available in the database of Genotypes and Phenotypes (dbGaP accession numbers phs000986.v1.p1 and phs001349.v1p1).

LIMITATIONS, REASONS FOR CAUTION

These GWAS data did not reach genome-wide significance for any individual analysis. UDT appears to have a complex etiology that also includes environmental factors, and such complexity may require much larger sample sizes than are currently available. The current methodology may also introduce bias that favors false discovery of larger genes.

WIDER IMPLICATIONS OF THE FINDINGS

Common suggestive intragenic GWAS signals suggest that RBFOX paralogs and other neurodevelopmental genes are potential UDT risk candidates, and potential TGCT susceptibility modifiers. Enrichment of predicted RBFOX targets among differentially expressed transcripts in the fetal gubernaculum additionally suggests a role for this RBP family in regulation of testicular descent. As RBFOX proteins regulate alternative splicing of Calca to generate calcitonin gene-related peptide, a protein linked to development and function of the gubernaculum, additional studies that address the role of these proteins in UDT are warranted.

STUDY FUNDING/COMPETING INTEREST(S)

The Eunice Kennedy Shriver National Institute for Child Health and Human Development (R01HD060769); National Center for Research Resources (P20RR20173), National Institute of General Medical Sciences (P20GM103464), Nemours Biomedical Research, the Testicular Cancer Consortium (U01CA164947), the Intramural Research Program of the NCI, a support services contract HHSN26120130003C with IMS, Inc., the Abramson Cancer Center at Penn, National Cancer Institute (CA114478), the Institute of Cancer Research, UK and the Wellcome Trust Case-Control Consortium (WTCCC) 2. None of the authors reports a conflict of interest.

Measurement of copy number of ACTN4 to optimize the therapeutic strategy for locally advanced pancreatic cancer

The standard therapeutic strategy recommended for locally advanced pancreatic cancer (LAPC) is typically chemotherapy or chemoradiotherapy (CRT). Although the clinical benefit of chemotherapy alone versus CRT for LAPC has been compared in a number of clinical trials, the optimal therapy for LAPC remains unclear. Moreover, the clinical benefit derived from treatment in each clinical trial is a matter of controversy, and the superiority of one treatment over another has yet to be definitively demonstrated. The poor outcomes seen among patients with LAPC owe largely to the emergence of metastatic disease; therefore, accurately evaluating occult distant metastasis before choosing a therapeutic strategy could be expected to help stratify patients with LAPC into the most appropriate treatment regimen, namely local control or systemic therapy. In 1998, we identified the actinin-4 gene (ACTN4) as an actin-binding protein and showed its molecular mechanisms had clinical implications for cancer metastasis. We also identified ACTN4 gene amplification in pancreatic, ovarian, and salivary gland cancer, and demonstrated its utility as a strong prognostic biomarker for stage I lung adenocarcinoma in patients who had never received chemotherapy. Moreover, we recently reported that ACTN4 gene amplification could be a useful biomarker for predicting the efficacy of CRT for LAPC. In the present review, we summarize current knowledge regarding therapeutic strategies for LAPC and discuss the potential development of personalized medicine using ACTN4 measurement for patients with LAPC.

A hnRNP K⁻AR-Related Signature Reflects Progression toward Castration-Resistant Prostate Cancer

The major challenge in castration-resistant prostate cancer (CRPC) remains the ability to predict the clinical responses to improve patient selection for appropriate treatments. The finding that androgen deprivation therapy (ADT) induces alterations in the androgen receptor (AR) transcriptional program by AR coregulators activity in a context-dependent manner, offers the opportunity for identifying signatures discriminating different clinical states of prostate cancer (PCa) progression. Gel electrophoretic analyses combined with western blot showed that, in androgen-dependent PCa and CRPC in vitro models, the subcellular distribution of spliced and serine-phosphorylated heterogeneous nuclear ribonucleoprotein K (hnRNP K) isoforms can be associated with different AR activities. Using mass spectrometry and bioinformatic analyses, we showed that the protein sets of androgen-dependent (LNCaP) and ADT-resistant cell lines (PDB and MDB) co-immunoprecipitated with hnRNP K varied depending on the cell type, unravelling a dynamic relationship between hnRNP K and AR during PCa progression to CRPC. By comparing the interactome of LNCaP, PDB, and MDB cell lines, we identified 51 proteins differentially interacting with hnRNP K, among which KLK3, SORD, SPON2, IMPDH2, ACTN4, ATP1B1, HSPB1, and KHDRBS1 were associated with AR and differentially expressed in normal and tumor human prostate tissues. This hnRNP K–AR-related signature, associated with androgen sensitivity and PCa progression, may help clinicians to better manage patients with CRPC.

Functions of nuclear actin-binding proteins in human cancer

Nuclear actin-binding proteins (ABPs) perform distinguishable functions compared with their cytoplasmic counterparts in extensive activities of living cells. In addition to the ability to regulate actin cytoskeleton dynamics, nuclear ABPs are associated with multiple nuclear biological processes, including chromatin remodeling, gene transcriptional regulation, DNA damage response, nucleocytoplasmic trafficking and nuclear structure maintenance. The nuclear translocation of ABPs is affected by numerous intracellular or extracellular stimuli, which may lead to developmental malformation, tumor initiation, tumor progression and metastasis. Abnormal expression of certain ABPs have been reported in different types of cancer. This review focuses on the newly identified roles of nuclear ABPs in the pathological processes associated with cancer.

Endogenous androgen receptor proteomic profiling reveals genomic subcomplex involved in prostate tumorigenesis

Androgen receptor (AR) is a key player in prostate cancer development and progression. Here we applied immunoprecipitation mass spectrometry of endogenous AR in LNCaP cells to identify components of the AR transcriptional complex. In total, 66 known and novel AR interactors were identified in the presence of synthetic androgen, most of which were critical for AR-driven prostate cancer cell proliferation. A subset of AR interactors required for LNCaP proliferation were profiled using chromatin immunoprecipitation assays followed by sequencing, identifying distinct genomic subcomplexes of AR interaction partners. Interestingly, three major subgroups of genomic subcomplexes were identified, where selective gain of function for AR genomic action in tumorigenesis was found, dictated by FOXA1 and HOXB13. In summary, by combining proteomic and genomic approaches we reveal subclasses of AR transcriptional complexes, differentiating normal AR behavior from the oncogenic state. In this process, the expression of AR interactors has key roles by reprogramming the AR cistrome and interactome in a genomic location-specific manner.

Surfactant Protein A Enhances Constitutive Immune Functions of Clathrin Heavy Chain and Clathrin Adaptor Protein 2

NF-κB transcription factors are key regulators of pulmonary inflammatory disorders and repair. Constitutive lung cell type- and microenvironment-specific NF-κB/inhibitor κBα (IκB-α) regulation, however, is poorly understood. Surfactant protein (SP)-A provides both a critical homeostatic and lung defense control, in part by immune instruction of alveolar macrophages (AMs) via clathrin-mediated endocytosis. The central endocytic proteins, clathrin heavy chain (CHC) and the clathrin adaptor protein (AP) complex AP2, have pivotal alternative roles in cellular homeostasis that are endocytosis independent. Here, we dissect endocytic from alternative functions of CHC, the α-subunit of AP2, and dynamin in basal and SP-A-modified LPS signaling of macrophages. As revealed by pharmacological inhibition and RNA interference in primary AMs and RAW264.7 macrophages, respectively, CHC and α-adaptin, but not dynamin, prevent IκB-α degradation and TNF-α release, independent of their canonical role in membrane trafficking. Kinetics studies employing confocal microscopy, Western analysis, and immunomagnetic sorting revealed that SP-A transiently enhances the basal protein expression of CHC and α-adaptin, depending on early activation of protein kinase CK2 (former casein kinase II) and Akt1 in primary AMs from rats, SP-A(+/+), and SP-A(-/-) mice, as well as in vivo when intratracheally administered to SP-A(+/+) mice. Constitutive immunomodulation by SP-A, but not SP-A-mediated inhibition of LPS-induced NF-κB activity and TNF-α release, requires CHC, α-adaptin, and dynamin. Our data demonstrate that endocytic proteins constitutively restrict NF-κB activity in macrophages and provide evidence that SP-A enhances the immune regulatory capacity of these proteins, revealing a previously unknown pathway of microenvironment-specific NF-κB regulation in the lung.

Pathway analysis supports association of nonsyndromic cryptorchidism with genetic loci linked to cytoskeleton-dependent functions

STUDY QUESTION

What are the genetic loci that increase susceptibility to nonsyndromic cryptorchidism, or undescended testis?

SUMMARY ANSWER

A genome-wide association study (GWAS) suggests that susceptibility to cryptorchidism is heterogeneous, with a subset of suggestive signals linked to cytoskeleton-dependent functions and syndromic forms of the disease.

WHAT IS KNOWN ALREADY

Population studies suggest moderate genetic risk of cryptorchidism and possible maternal and environmental contributions to risk. Previous candidate gene analyses have failed to identify a major associated locus, although variants in insulin-like 3 (INSL3), relaxin/insulin-like family peptide receptor 2 (RXFP2) and other hormonal pathway genes may increase risk in a small percentage of patients.

STUDY DESIGN, SIZE, DURATION

This is a case-control GWAS of 844 boys with nonsyndromic cryptorchidism and 2718 control subjects without syndromes or genital anomalies, all of European ancestry.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All boys with cryptorchidism were diagnosed and treated by a pediatric specialist. In the discovery phase, DNA was extracted from tissue or blood samples and genotyping performed using the Illumina HumanHap550 and Human610-Quad (Group 1) or OmniExpress (Group 2) platform. We imputed genotypes genome-wide, and combined single marker association results in meta-analyses for all cases and for secondary subphenotype analyses based on testis position, laterality and age, and defined genome-wide significance as P = 7 × 10(-9) to correct for multiple testing. Selected markers were genotyped in an independent replication group of European cases (n = 298) and controls (n = 324). We used several bioinformatics tools to analyze top (P < 10(-5)) and suggestive (P < 10(-3)) signals for significant enrichment of signaling pathways, cellular functions and custom gene lists after multiple testing correction.

MAIN RESULTS AND THE ROLE OF CHANCE

In the full analysis, we identified 20 top loci, none reaching genome-wide significance, but one passing this threshold in a subphenotype analysis of proximal testis position (rs55867206, near SH3PXD2B, odds ratio = 2.2 (95% confidence interval 1.7, 2.9), P = 2 × 10(-9)). An additional 127 top loci emerged in at least one secondary analysis, particularly of more severe phenotypes. Cytoskeleton-dependent molecular and cellular functions were prevalent in pathway analysis of suggestive signals, and may implicate loci encoding cytoskeletal proteins that participate in androgen receptor signaling. Genes linked to human syndromic cryptorchidism, including hypogonadotropic hypogonadism, and to hormone-responsive and/or differentially expressed genes in normal and cryptorchid rat gubernaculum, were also significantly overrepresented. No tested marker showed significant replication in an independent population. The results suggest heterogeneous, multilocus and potentially multifactorial susceptibility to nonsyndromic cryptorchidism.

LIMITATIONS, REASONS FOR CAUTION

The present study failed to identify genome-wide significant markers associated with cryptorchidism that could be replicated in an independent population, so further studies are required to define true positive signals among suggestive loci.

WIDER IMPLICATIONS OF THE FINDINGS

As the only GWAS to date of nonsyndromic cryptorchidism, these data will provide a basis for future efforts to understand genetic susceptibility to this common reproductive anomaly and the potential for additive risk from environmental exposures.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by R01HD060769 (the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD)), P20RR20173 (the National Center for Research Resources (NCRR), currently P20GM103464 from the National Institute of General Medical Sciences (NIGMS)), an Institute Development Fund to the Center for Applied Genomics at The Children's Hospital of Philadelphia, and Nemours Biomedical Research. The authors have no competing interests to declare.

The biological role of actinin-4 (ACTN4) in malignant phenotypes of cancer

Invasion and metastasis are malignant phenotypes in cancer that lead to patient death. Cell motility is involved in these processes. In 1998, we identified overexpression of the actin-bundling protein actinin-4 in several types of cancer. Protein expression of actinin-4 is closely associated with the invasive phenotypes of cancers. Actinin-4 is predominantly expressed in the cellular protrusions that stimulate the invasive phenotype in cancer cells and is essential for formation of cellular protrusions such as filopodia and lamellipodia. ACTN4 (gene name encoding actinin-4 protein) is located on human chromosome 19q. ACTN4 amplification is frequently observed in patients with carcinomas of the pancreas, ovary, lung, and salivary gland, and patients with ACTN4 amplifications have worse outcomes than patients without amplification. In addition, nuclear distribution of actinin-4 is frequently observed in small cell lung, breast, and ovarian cancer. Actinin-4, when expressed in cancer cell nuclei, functions as a transcriptional co-activator. In this review, we summarize recent developments regarding the biological roles of actinin-4 in cancer invasion.

The role of alpha-actinin-4 in human kidney disease

Mutations in the Alpha-actinin-4 gene (ACTN4) cause a rare form of familial focal segmental glomerulosclerosis in humans. Individuals with kidney disease-associated ACTN4 mutations tend to have mild to moderate proteinuria, with many developing decreased kidney function progressing to end stage kidney disease. All of the disease-causing ACTN4 mutations identified to date are located within the actin-binding domain of the encoded protein, increasing its binding affinity to F-actin and leading to abnormal actin rich cellular aggregates. The identification of ACTN4 mutations as a cause of human kidney disease demonstrates a key cellular pathway by which alterations in cytoskeletal behavior can mediate kidney disease. Here we review the studies relevant to ACTN4 and its role in mediating kidney disease.

Research Resource: Androgen Receptor Activity Is Regulated Through the Mobilization of Cell Surface Receptor Networks

The aberrant expression of androgen receptor (AR)-dependent transcriptional programs is a defining pathology of the development and progression of prostate cancers. Transcriptional cofactors that bind AR are critical determinants of prostate tumorigenesis. To gain a deeper understanding of the proteins linked to AR-dependent gene transcription, we performed a DNA-affinity chromatography-based proteomic screen designed to identify proteins involved in AR-mediated gene transcription in prostate tumor cells. Functional experiments validated the coregulator roles of known AR-binding proteins in AR-mediated transcription in prostate tumor cells. More importantly, novel coregulatory functions were detected in components of well-established cell surface receptor-dependent signal transduction pathways. Further experimentation demonstrated that components of the TNF, TGF-β, IL receptor, and epidermal growth factor signaling pathways modulated AR-dependent gene transcription and androgen-dependent proliferation in prostate tumor cells. Collectively, our proteomic dataset demonstrates that the cell surface receptor- and AR-dependent pathways are highly integrated, and provides a molecular framework for understanding how disparate signal-transduction pathways can influence AR-dependent transcriptional programs linked to the development and progression of human prostate cancers.

Androgen receptor and chemokine receptors 4 and 7 form a signaling axis to regulate CXCL12-dependent cellular motility

Background

Identifying cellular signaling pathways that become corrupted in the presence of androgens that increase the metastatic potential of organ-confined tumor cells is critical to devising strategies capable of attenuating the metastatic progression of hormone-naïve, organ-confined tumors. In localized prostate cancers, gene fusions that place ETS-family transcription factors under the control of androgens drive gene expression programs that increase the invasiveness of organ-confined tumor cells. C-X-C chemokine receptor type 4 (CXCR4) is a downstream target of ERG, whose upregulation in prostate-tumor cells contributes to their migration from the prostate gland. Recent evidence suggests that CXCR4-mediated proliferation and metastasis of tumor cells is regulated by CXCR7 through its scavenging of chemokine CXCL12. However, the role of androgens in regulating CXCR4-mediated motility with respect to CXCR7 function in prostate-cancer cells remains unclear.

Methods

Immunocytochemistry, western blot, and affinity-purification analyses were used to study how androgens influenced the expression, subcellular localization, and function of CXCR7, CXCR4, and androgen receptor (AR) in LNCaP prostate-tumor cells. Moreover, luciferase assays and quantitative polymerase chain reaction (qPCR) were used to study how chemokines CXCL11 and CXCL12 regulate androgen-regulated genes (ARGs) in LNCaP prostate-tumor cells. Lastly, cell motility assays were carried out to determine how androgens influenced CXCR4-dependent motility through CXCL12.

Results

Here we show that, in the LNCaP prostate-tumor cell line, androgens coordinate the expression of CXCR4 and CXCR7, thereby promoting CXCL12/CXCR4-mediated cell motility. RNA interference experiments revealed functional interactions between AR and CXCR7 in these cells. Co-localization and affinity-purification experiments support a physical interaction between AR and CXCR7 in LNCaP cells. Unexpectedly, CXCR7 resided in the nuclear compartment and modulated AR-mediated transcription. Moreover, androgen-mediated cell motility correlated positively with the co-localization of CXCR4 and CXCR7 receptors, suggesting that cell migration may be linked to functional CXCR4/CXCR7 heterodimers. Lastly, CXCL12-mediated cell motility was CXCR7-dependent, with CXCR7 expression required for optimal expression of CXCR4 protein.

Conclusions

Overall, our results suggest that inhibition of CXCR7 function might decrease the metastatic potential of organ-confined prostate cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1201-5) contains supplementary material, which is available to authorized users.

The NLR-related protein NWD1 is associated with prostate cancer and modulates androgen receptor signaling

Prostate cancer (PCa) is among the leading causes of cancer-related death in men. Androgen receptor (AR) signaling plays a seminal role in prostate development and homeostasis, and dysregulation of this pathway is intimately linked to prostate cancer pathogenesis and progression. Here, we identify the cytosolic NLR-related protein NWD1 as a novel modulator of AR signaling. We determined that expression of NWD1 becomes elevated during prostate cancer progression, based on analysis of primary tumor specimens. Experiments with cultured cells showed that NWD1 expression is up-regulated by the sex-determining region Y (SRY) family proteins. Gene silencing procedures, in conjunction with transcriptional profiling, showed that NWD1 is required for expression of PDEF (prostate-derived Ets factor), which is known to bind and co-regulate AR. Of note, NWD1 modulates AR protein levels. Depleting NWD1 in PCa cell lines reduces AR levels and suppresses activity of androgen-driven reporter genes. NWD1 knockdown potently suppressed growth of androgen-dependent LNCaP prostate cancer cells, thus showing its functional importance in an AR-dependent tumor cell model. Proteomic analysis suggested that NWD1 associates with various molecular chaperones commonly related to AR complexes. Altogether, these data suggest a role for tumor-associated over-expression of NWD1 in dysregulation of AR signaling in PCa.

Self-assembled nanoaggregates based on polyaspartamide graft copolymers for pH-controlled release of doxorubicin

The hydrazone group was effectively cleaved to release doxorubicin (DOX) conjugated on PASPAM in an acidic environment.

Increased gene copy number of VAMP7 disrupts human male urogenital development through altered estrogen action

Vesicle transport is intimately connected with key nuclear functions and transcriptional regulation. Here, children born with congenital genitourinary tract masculinization disorders were analyzed by array-Comparative Genomic Hybridization, which revealed the presence of de novo copy number gains on Xq28 encompassing the VAMP7 gene encoding a vesicle-trafficking protein. Humanized VAMP7 BAC transgenic mice displayed cryptorchidism, urethral defects, and hypospadias. Mutant mice exhibited reduced penile length, focal spermatogenic anomalies, diminished sperm motility, and subfertility. VAMP7 colocalized with estrogen receptor alpha (ESR1) in the presence of ligand. Elevated levels of VAMP7 markedly intensified ESR1 transcriptional activity by increasing ESR1 protein cellular content upon ligand stimulation and up-regulated the expression of estrogen-responsive genes including ATF3, CYR61, and CTGF, all of which are implicated in human hypospadias. Hence, increased gene dosage of the SNARE protein, VAMP7, enhances estrogen receptor action in male genitourinary tissues, affects the virilization of the reproductive tract, and results in genitourinary birth defects in humans.

The non-muscle functions of actinins: an update

α-Actinins are a major class of actin filament cross-linking proteins expressed in virtually all cells. In muscle, actinins cross-link thin filaments from adjacent sarcomeres. In non-muscle cells, different actinin isoforms play analogous roles in cross-linking actin filaments and anchoring them to structures such as cell-cell and cell-matrix junctions. Although actinins have long been known to play roles in cytokinesis, cell adhesion and cell migration, recent studies have provided further mechanistic insights into these functions. Roles for actinins in synaptic plasticity and membrane trafficking events have emerged more recently, as has a 'non-canonical' function for actinins in transcriptional regulation in the nucleus. In the present paper we review recent advances in our understanding of these diverse cell biological functions of actinins in non-muscle cells, as well as their roles in cancer and in genetic disorders affecting platelet and kidney physiology. We also make two proposals with regard to the actinin nomenclature. First, we argue that naming actinin isoforms according to their expression patterns is problematic and we suggest a more precise nomenclature system. Secondly, we suggest that the α in α-actinin is superfluous and can be omitted.

Increased expression of α-actinin-4 is associated with unfavorable pathological features and invasiveness of bladder cancer

In the present study, the association between clinicopathological parameters and α-actinin-4 (ACTN4) expression in bladder cancer specimens was evaluated, and the functional role of ACTN4 in bladder cancer cells was investigated. Immunohistochemistry using anti-ACTN4 antibody was performed in bladder cancer specimens (53 superficial and 42 muscle-invasive cases) from 95 patients who underwent radical cystectomy (n=46) or transurethral resection (TUR) only (n=49). We divided the levels of ACTN4 expression into 2 groups (low or high) by comparing the staining intensity in each specimen with that of the vascular endothelial cells in the same specimen, and we evaluated the correlations between these levels and pathological parameters, recurrence and prognosis. We also investigated the effects of ACTN4 suppression by siRNA on the invasive ability and proliferation of T24 and KU19-19 cells. High ACTN4 expression was significantly associated with higher tumor grade and higher pT stage. In patients with superficial bladder cancer treated only by TUR, the rate of intravesical recurrence did not differ significantly between patients with high ACTN4 expression and patients with low ACTN4 expression. In patients who had muscle‑invasive tumors and underwent radical cystectomy, high ACTN4 expression was associated with neither recurrence nor poor prognosis. Nonetheless, high ACTN4 expression was shown by a large percentage (81%) of patients with muscle-invasive bladder cancer and by a small percentage (17%) of patients with superficial bladder cancer. Furthermore, the leading edges of the invasive bladder cancer showed increased ACTN4 expression. ACTN4 suppression significantly reduced the number of invading bladder cancer cells but unexpectedly increased the proliferation of bladder cancer cells. ACTN4 suppression increased the phosphorylation of ERKs but not AKT or STAT3, suggesting that the increased proliferation due to ACTN4 suppression was mediated in part by the ERK pathway. ACTN4 expression may suppress the proliferation of bladder cancer cells and may produce conditions which facilitate cancer cell invasion.

An image-based multi-label human protein subcellular localization predictor (iLocator) reveals protein mislocalizations in cancer tissues

MOTIVATION

Human cells are organized into compartments of different biochemical cellular processes. Having proteins appear at the right time to the correct locations in the cellular compartments is required to conduct their functions in normal cells, whereas mislocalization of proteins can result in pathological diseases, including cancer.

RESULTS

To reveal the cancer-related protein mislocalizations, we developed an image-based multi-label subcellular location predictor, iLocator, which covers seven cellular localizations. The iLocator incorporates both global and local image descriptors and generates predictions by using an ensemble multi-label classifier. The algorithm has the ability to treat both single- and multiple-location proteins. We first trained and tested iLocator on 3240 normal human tissue images that have known subcellular location information from the human protein atlas. The iLocator was then used to generate protein localization predictions for 3696 protein images from seven cancer tissues that have no location annotations in the human protein atlas. By comparing the output data from normal and cancer tissues, we detected eight potential cancer biomarker proteins that have significant localization differences with P-value < 0.01.

AVAILABILITY

http://www.csbio.sjtu.edu.cn/bioinf/iLocator/

Alpha-actinin 4 and tumorigenesis of breast cancer

Alpha-actinins (ACTNs) were originally identified as cytoskeletal proteins which cross-link filamentous actin to establish cytoskeletal architect that protects cells from mechanical stress and controls cell movement. Notably, unlike other ACTNs, alpha-actinin 4 (ACTN4) displays unique characteristics in signaling transduction, nuclear translocation, and gene expression regulation. Initial reports indicated that ACTN4 is part of the breast cancer cell motile apparatus and is highly expressed in the nucleus. These results imply that ACTN4 plays a role in breast cancer tumorigenesis. While several observations in breast cancer and other cancers support this hypothesis, little direct evidence links the tumorigenic phenotype with ACTN4-mediated pathological mechanisms. Recently, several studies have demonstrated that in addition to its role in coordinating cytoskeleton, ACTN4 interacts with signaling mediators, chromatin remodeling factors, and transcription factors including nuclear receptors. Thus, ACTN4 functions as a versatile promoter for breast cancer tumorigenesis and appears to be an ideal drug target for future therapeutic development.

Endocytosis and signaling: cell logistics shape the eukaryotic cell plan

Our understanding of endocytosis has evolved remarkably in little more than a decade. This is the result not only of advances in our knowledge of its molecular and biological workings, but also of a true paradigm shift in our understanding of what really constitutes endocytosis and of its role in homeostasis. Although endocytosis was initially discovered and studied as a relatively simple process to transport molecules across the plasma membrane, it was subsequently found to be inextricably linked with almost all aspects of cellular signaling. This led to the notion that endocytosis is actually the master organizer of cellular signaling, providing the cell with understandable messages that have been resolved in space and time. In essence, endocytosis provides the communications and supply routes (the logistics) of the cell. Although this may seem revolutionary, it is still likely to be only a small part of the entire story. A wealth of new evidence is uncovering the surprisingly pervasive nature of endocytosis in essentially all aspects of cellular regulation. In addition, many newly discovered functions of endocytic proteins are not immediately interpretable within the classical view of endocytosis. A possible framework, to rationalize all this new knowledge, requires us to "upgrade" our vision of endocytosis. By combining the analysis of biochemical, biological, and evolutionary evidence, we propose herein that endocytosis constitutes one of the major enabling conditions that in the history of life permitted the development of a higher level of organization, leading to the actuation of the eukaryotic cell plan.

A cell model for conditional profiling of androgen-receptor-interacting proteins

Partial androgen insensitivity syndrome (PAIS) is associated with impaired male genital development and can be transmitted through mutations in the androgen receptor (AR). The aim of this study is to develop a cell model suitable for studying the impact AR mutations might have on AR interacting proteins. For this purpose, male genital development relevant mouse cell lines were genetically modified to express a tagged version of wild-type AR, allowing copurification of multiprotein complexes under native conditions followed by mass spectrometry. We report 57 known wild-type AR-interacting proteins identified in cells grown under proliferating and 65 under nonproliferating conditions. Of those, 47 were common to both samples suggesting different AR protein complex components in proliferating and proliferation-inhibited cells from the mouse proximal caput epididymus. These preliminary results now allow future studies to focus on replacing wild-type AR with mutant AR to uncover differences in protein interactions caused by AR mutations involved in PAIS.

Proteomic analysis of the androgen receptor via MS-compatible purification of biotinylated protein on streptavidin resin

The strength of the streptavidin/biotin interaction poses challenges for the recovery of biotinylated molecules from streptavidin resins. As an alternative to high-temperature elution in urea-containing buffers, we show that mono-biotinylated proteins can be released with relatively gentle heating in the presence of biotin and 2% SDS/Rapigest, avoiding protein carbamylation and minimizing streptavidin dissociation. We demonstrate the utility of this mild elution strategy in two studies of the human androgen receptor (AR). In the first, in which formaldehyde cross-linked complexes are analyzed in yeast, a mass spectrometry-based comparison of the AR complex using SILAC reveals an association between the androgen-activated AR and the Hsp90 chaperonin, while Hsp70 chaperonins associate specifically with the unliganded complex. In the second study, the endogenous AR is quantified in the LNCaP cell line by absolute SILAC and MRM-MS showing approximately 127,000 AR copies per cell, substantially more than previously measured using radioligand binding.

Eight-plex iTRAQ analysis of variant metastatic human prostate cancer cells identifies candidate biomarkers of progression: An exploratory study

BACKGROUND

Due to the heterogeneity in the biological behavior of prostate cancer, biomarkers that can reliably distinguish indolent from aggressive disease are urgently needed to inform treatment choices.

METHODS

We employed 8-plex isobaric Tags for Relative and Absolute Quantitation (iTRAQ), to profile the proteomes of two distinct panels of isogenic prostate cancer cells with varying growth and metastatic potentials, in order to identify novel biomarkers associated with progression. The LNCaP, LNCaP-Pro5, and LNCaP-LN3 panel of cells represent a model of androgen-responsive prostate cancer, while the PC-3, PC-3M, and PC-3M-LN4 panel represent a model of androgen-insensitive disease.

RESULTS

Of the 245 unique proteins identified and quantified (>or=95% confidence; >or=2 peptides/protein), 17 showed significant differential expression (>or=+/-1.5), in at least one of the variant LNCaP cells relative to parental cells. Similarly, comparisons within the PC-3 panel identified 45 proteins to show significant differential expression in at least one of the variant PC-3 cells compared with parental cells. Differential expression of selected candidates was verified by Western blotting or immunocytochemistry, and corresponding mRNA expression was determined by quantitative real-time PCR (qRT-PCR). Immunostaining of prostate tissue microarrays for ERp5, one of the candidates identified, showed a significant higher immunoexpression in pre-malignant lesions compared with non-malignant epithelium (P < 0.0001, Mann-Whitney U-test), and in high Gleason grade (4-5) versus low grade (2-3) cancers (P < 0.05).

CONCLUSIONS

Our study provides proof of principle for the application of an 8-plex iTRAQ approach to uncover clinically relevant candidate biomarkers for prostate cancer progression.

Profiling of protein interaction networks of protein complexes using affinity purification and quantitative mass spectrometry

Protein-protein interactions are important for nearly all biological processes, and it is known that aberrant protein-protein interactions can lead to human disease and cancer. Recent evidence has suggested that protein interaction interfaces describe a new class of attractive targets for drug development. Full characterization of protein interaction networks of protein complexes and their dynamics in response to various cellular cues will provide essential information for us to understand how protein complexes work together in cells to maintain cell viability and normal homeostasis. Affinity purification coupled with quantitative mass spectrometry has become the primary method for studying in vivo protein interactions of protein complexes and whole organism proteomes. Recent developments in sample preparation and affinity purification strategies allow the capture, identification, and quantification of protein interactions of protein complexes that are stable, dynamic, transient, and/or weak. Current efforts have mainly focused on generating reliable, reproducible, and high confidence protein interaction data sets for functional characterization. The availability of increasing amounts of information on protein interactions in eukaryotic systems and new bioinformatics tools allow functional analysis of quantitative protein interaction data to unravel the biological significance of the identified protein interactions. Existing studies in this area have laid a solid foundation toward generating a complete map of in vivo protein interaction networks of protein complexes in cells or tissues.

Integrin involvement in freeze resistance of androgen-insensitive prostate cancer

Cryoablation has emerged as a primary therapy to treat prostate cancer. While effective, the assumption that freezing serves as a ubiquitous lethal stress is challenged by clinical experience and experimental evidence demonstrating time-temperature related cell death dependence. The age-related transformation from an androgen-sensitive (AS) to an androgen-insensitive (AI) phenotype is a major challenge in the management of prostate cancer. AI cells exhibit morphological changes and treatment resistance to many therapies. Since this resistance has been linked with α6β4 integrin overexpression as a result of androgen receptor (AR) loss, we investigated whether α6β4 integrin expression, as a result AR loss, contributes to the reported increased freeze tolerance of AI prostate cancer. A series of studies using AS (LNCaP LP and PC-3 AR) and AI (LNCaP HP and PC-3) cell lines were designed to investigate the cellular mechanisms contributing to variations in freezing response. Investigation into α6β4 integrin expression revealed that AI cell lines overexpressed this protein, thereby altering morphological characteristics and increasing adhesion characteristics. Molecular investigations revealed a significant decrease in caspase 8, 9, and 3 levels AI cells following freezing. Inhibition of α6β4 integrin resulted in increased caspase activity following freezing (similar to AS cells) and enhanced cell death. These data demonstrate that AI cells show an increase in post-freeze susceptibility following inhibition of α6β4 integrin function. Further understanding the role of androgen-receptor related α6β4 integrin expression in prostate cancer cells responses to freezing might lead to novel options for neo-adjunctive treatments targeting the AR signaling pathway.

Sex-specific responses to stroke

Stroke is a sexually dimorphic disease, with differences between males and females observed both clinically and in the laboratory. While males have a higher incidence of stroke throughout much of the lifespan, aged females have a higher burden of stroke. Sex differences in stroke result from a combination of factors, including elements intrinsic to the sex chromosomes as well as the effects of sex hormone exposure throughout the lifespan. Research investigating the sexual dimorphism of stroke is only in the beginning stages, but early findings suggest that different cell death pathways are activated in males and females after ischemic stroke. A greater understanding of the mechanisms underlying sex differences in stroke will lead to more appropriate treatment strategies for patients of both sexes.

Keratin 18 attenuates estrogen receptor alpha-mediated signaling by sequestering LRP16 in cytoplasm

Background

Oncogenesis in breast cancer is often associated with excess estrogen receptor α(ERα) activation and overexpression of its coactivators. LRP16 is both an ERα target gene and an ERα coactivator, and plays a crucial role in ERα activation and proliferation of MCF-7 breast cancer cells. However, the regulation of the functional availability of this coactivator protein is not yet clear.

Results

Yeast two-hybrid screening, GST pulldown and coimmunoprecipitation (CoIP) identified the cytoplasmic intermediate filament protein keratin 18 (K18) as a novel LRP16-interacting protein. Fluorescence analysis revealed that GFP-tagged LRP16 was primarily localized in the nuclei of mock-transfected MCF-7 cells but was predominantly present in the cytoplasm of K18-transfected cells. Immunoblotting analysis demonstrated that the amount of cytoplasmic LRP16 was markedly increased in cells overexpressing K18 whereas nuclear levels were depressed. Conversely, knockdown of endogenous K18 expression in MCF-7 cells significantly decreased the cytoplasmic levels of LRP16 and increased levels in the nucleus. CoIP failed to detect any interaction between K18 and ERα, but ectopic expression of K18 in MCF-7 cells significantly blunted the association of LRP16 with ERα, attenuated ERα-activated reporter gene activity, and decreased estrogen-stimulated target gene expression by inhibiting ERα recruitment to DNA. Furthermore, BrdU incorporation assays revealed that K18 overexpression blunted the estrogen-stimulated increase of S-phase entry of MCF-7 cells. By contrast, knockdown of K18 in MCF-7 cells significantly increased ERα-mediated signaling and promoted cell cycle progression.

Conclusions

K18 can effectively associate with and sequester LRP16 in the cytoplasm, thus attenuating the final output of ERα-mediated signaling and estrogen-stimulated cell cycle progression of MCF-7 breast cancer cells. Loss of K18 increases the functional availability of LRP16 to ERα and promotes the proliferation of ERα-positive breast tumor cells. K18 plays an important functional role in regulating the ERα signaling pathway.

Identification of a function-specific mutation of clathrin heavy chain (CHC) required for p53 transactivation

The p53 pathway is activated in response to various cellular stresses to protect cells from malignant transformation. We have previously shown that clathrin heavy chain (CHC), which is a cytosolic protein regulating endocytosis, is present in nuclei and binds to p53 to promote p53-mediated transcription. However, details of the binding interface between p53 and CHC remain unclear. Here, we report on the binding mode between p53 and CHC using mutation analyses and a structural model of the interaction generated by molecular dynamics. Structural modeling analyses predict that an Asn1288 residue in CHC is crucial for binding to p53. In fact, substitution of this Asn to Ala of CHC diminished its ability to interact with p53, leading to reduced activity to transactivate p53. Surprisingly, this mutation had little effect on receptor-mediated endocytosis. Thus, the function-specific mutation of CHC will clarify physiological roles of CHC in the regulation of the p53 pathway.

Nuclear actin and actin-binding proteins in the regulation of transcription and gene expression

Nuclear actin is involved in the transcription of all three RNA polymerases, in chromatin remodeling and in the formation of heterogeneous nuclear ribonucleoprotein complexes, as well as in recruitment of the histone modifier to the active gene. In addition, actin-binding proteins (ABPs) control actin nucleation, bundling, filament capping, fragmentation and monomer availability in the cytoplasm. In recent years, more and more attention has focused on the role of actin and ABPs in the modulation of the subcellular localization of transcriptional regulators. This review focuses on recent developments in the study of transcription and transcriptional regulation by nuclear actin, and the regulation of muscle-specific gene expression, nuclear receptor and transcription complexes by ABPs. Among the ABPs, striated muscle activator of Rho signaling and actin-binding LIM protein regulate actin dynamics and serum response factor-dependent muscle-specific gene expression. Functionally and structurally unrelated cytoplasmic ABPs interact cooperatively with nuclear receptor and regulate its transactivation. Furthermore, ABPs also participate in the formation of transcription complexes.

DNA dependent recruitment of DDX17 and other interacting proteins by the human androgen receptor

An oligonucleotide-based assay (OBA) was used to identify novel co-factors that can be recruited by the deoxyribonucleic acid (DNA)-bound androgen receptor (AR). Nuclear extracts obtained from LNCaP cells, after incubation with R1881, were incubated with biotinylated oligonucleotides bound to streptavidin coated beads. The oligonucleotides contain 3 copies in tandem of the androgen responsive element ARE1 from the prostate specific antigen (PSA) gene promoter. As control incubation, a scrambled version of the tandem ARE1 was used. Immunoblots of the eluents revealed that the AR was bound to the ARE1 oligonucleotide and to a much lesser extent to the scrambled oligonucleotide. Proteins eluted from the oligonucleotides, were separated on a 5-15% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gradient gel, followed by identification using mass spectrometry. Identified proteins were scored for having one or more of the following known properties: nuclear localization, involved in transcription regulation, involvement in steroid hormone receptor (SHR) function, or specifical involvement in AR function. A total number of 85 nuclear proteins were found in two separate OBAs. Based on peptide counting, we found enrichment of 7 proteins eluted from the ARE1 oligonucleotide, compared to the scrambled oligonucleotide. Taken together with the obtained scores, these proteins are considered putative AR co-factors. One of these proteins, DDX17, is known to be a co-factor for estrogen receptor alpha (ERalpha), but has never been associated with AR function. The results indicate that the ARE oligonucleotide-based assay may allow enrichment of new candidate DNA-bound AR interacting proteins.

RNA editing of androgen receptor gene transcripts in prostate cancer cells

Reactivation of the androgen receptor (AR) signaling pathway represents a critical step in the growth and survival of androgen-independent (AI) prostate cancer (CaP). In this study we show the DU145 and PC3 AI human CaP cell lines respond to androgens and require AR expression for optimal proliferation in vitro. Interestingly, AR gene transcripts in DU145 and PC3 cells harbored a large number of single base pair nucleotide transitions that resulted in missense mutations in selected AR codons. The most notable lesion detected in AR gene transcripts included the oncogenic codon 877T-->A gain-of-function mutation. Surprisingly, AR gene transcript nucleotide transitions were not genome-encoded substitutions, but instead the mutations co-localized to putative A-to-I, U-to-C, C-to-U, and G-to-A RNA editing sites, suggesting the lesions were mediated through RNA editing mechanisms. Higher levels of mRNA encoding the A-to-I RNA editing enzymes ADAR1 and ADARB1 were observed in DU145 and PC3 cells relative to the androgen-responsive LNCaP and 22Rv1 human CaP cell lines, which correlated with higher levels of AR gene transcript A-to-I editing detected in DU145 and PC3 cells. Our results suggest that AR gene transcripts are targeted by different RNA editing enzymes in DU145 and PC3 cells. Thus RNA editing of AR gene transcripts may contribute to the etiology of hormone-refractory phenotypes in advanced stage AI CaP.

p68 (Ddx5) interacts with Runx2 and regulates osteoblast differentiation

Runx2 is an essential transcription factor for osteoblast development from mesenchymal progenitors. Runx2 regulates gene expression by interacting with numerous transcription factors and co-activators to integrate signaling events within the nucleus. In this study we used affinity purification and proteomic techniques to identify novel Runx2 interacting proteins. One of these proteins is the DEAD box RNA helicase, p68 (Ddx5). p68 regulates many aspects of RNA expression, including transcription and splicing. p68 co-localized with Runx2 in punctate foci within the nucleus. In transcription assays, p68 functioned as a co-activator of Runx2, but its helicase activity was not essential for co-activation. In accordance, Runx2 transcriptional activity was muted in p68-suppressed cells. Surprisingly, osteoblast differentiation of the multipotent progenitor C2C12 cell line was accelerated by p68 suppression and Runx2 suppressed p68 expression in calvarial progenitor cells. Together these data demonstrate that p68 is a novel co-activator for Runx2, but it inhibits osteogenic differentiation of progenitor cells. Moreover Runx2 has an active role in regulating p68 levels in osteoblast precursors. Thus, crosstalk between Runx2 and p68 controls osteoblast specification and maturation at multiple levels.

Androgen receptor (AR) coregulators: a diversity of functions converging on and regulating the AR transcriptional complex

Androgens, acting through the androgen receptor (AR), are responsible for the development of the male phenotype during embryogenesis, the achievement of sexual maturation at puberty, and the maintenance of male reproductive function and behavior in adulthood. In addition, androgens affect a wide variety of nonreproductive tissues. Moreover, aberrant androgen action plays a critical role in multiple pathologies, including prostate cancer and androgen insensitivity syndromes. The formation of a productive AR transcriptional complex requires the functional and structural interaction of the AR with its coregulators. In the last decade, an overwhelming and ever increasing number of proteins have been proposed to possess AR coactivating or corepressing characteristics. Intriguingly, a vast diversity of functions has been ascribed to these proteins, indicating that a multitude of cellular functions and signals converge on the AR to regulate its function. The current review aims to provide an overview of the AR coregulator proteins identified to date and to propose a classification of these AR coregulator proteins according to the function(s) ascribed to them. Taken together, this approach will increase our understanding of the cellular pathways that converge on the AR to ensure an appropriate transcriptional response to androgens.