Castration resistance in human prostate cancer is conferred by a frequently occurring androgen receptor splice variant (original) (raw)
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Proceedings of the National Academy of Sciences, 2010
Androgen receptor (AR) splice variants lacking the ligand binding domain (ARVs), originally isolated from prostate cancer cell lines derived from a single patient, are detected in normal and malignant human prostate tissue, with the highest levels observed in late stage, castration-resistant prostate cancer. The most studied variant (called AR-V7 or AR3) activates AR reporter genes in the absence of ligand and therefore, could play a role in castration resistance. To explore the range of potential ARVs, we screened additional human and murine prostate cancer models using conventional and next generation sequencing technologies and detected several structurally diverse AR isoforms. Some, like AR-V7/AR3, display gain of function, whereas others have dominant interfering activity. We also find that ARV expression increases acutely in response to androgen withdrawal, is suppressed by testosterone, and in some models, is coupled to full-length AR (AR-FL) mRNA production. As expected, constitutively active, ligand-independent ARVs such as AR-V7/AR3 are sufficient to confer anchorage-independent (in vitro) and castrationresistant (in vivo) growth. Surprisingly, this growth is blocked by ligand binding domain-targeted antiandrogens, such as MDV3100, or by selective siRNA silencing of AR-FL, indicating that the growthpromoting effects of ARVs are mediated through AR-FL. These data indicate that the increase in ARV expression in castrate-resistant prostate cancer is an acute response to castration rather than clonal expansion of castration or antiandrogen-resistant cells expressing gain of function ARVs, and furthermore, they provide a strategy to overcome ARV function in the clinic.
Androgen receptor splice variant-7 expression emerges with castration resistance in prostate cancer
The Journal of clinical investigation, 2018
Liquid biopsies have demonstrated that the constitutively active androgen receptor splice variant-7 (AR-V7) associates with reduced response and overall survival (OS) from endocrine therapies in castration resistant prostate cancer (CRPC). However, these studies provide little information pertaining to AR-V7 expression in prostate cancer (PC) tissue. Following generation and validation of a novel AR-V7 antibody for immunohistochemistry, AR-V7 protein expression was determined for 358 primary prostate samples and 293 metastatic biopsies. Associations with disease progression, full length AR (AR-FL) expression, response to therapy, and gene expression was determined. We demonstrated that AR-V7 protein is rarely expressed (<1%) in primary PC but is frequently detected (75% of cases) following androgen deprivation therapy, with further significant (P = 0.020) increase in expression following abiraterone acetate or enzalutamide therapy. In CRPC, AR-V7 expression is predominantly (94% ...
Cancer Research, 2009
The androgen receptor (AR) plays a key role in progression to incurable androgen-ablation resistant prostate cancer (PCA). We have identified three novel AR splice variants lacking the ligand binding domain (designated as AR3, AR4 and AR5) in hormone insensitive PCA cells. AR3, one of the major splice variants expressed in human prostate tissues, is constitutively active and its transcriptional activity is not regulated by androgens or antiandrogens. Immunohistochemistry analysis on tissue microarrays containing 429 human prostate tissue samples shows that AR3 is significantly upregulated during PCA progression and AR3 expression level is correlated with the risk of tumor recurrence after radical prostatectomy. Overexpression of AR3 confers ablation-independent growth of PCA cells while specific knock-down of AR3 expression (without altering AR level) in hormone resistant PCA cells attenuates their growth under androgen-depleted conditions in both cell culture and xenograft models, suggesting an indispensable role of AR3 in ablation-independent growth of PCA cells. Furthermore, AR3 may play a distinct yet essential role in ablation-independent growth through regulating a unique set of genes including AKT1, which are not regulated by the prototype AR. Our data suggest that aberrant expression of AR splice variants may be a novel mechanism underlying ablation-independence during PCA progression and AR3 may serve as a prognostic marker to predict patient outcome in response to hormonal therapy. Given that these novel AR splice variants are not inhibited by currently available anti-androgen drugs, development of new drugs targeting these AR isoforms may potentially be effective for treatment of ablation-resistant PCA.
Data in Brief, 2021
These data include secondary analysis of publicly available RNA-seq data from castration-resistant prostate cancer (CRPC) patients as well as RT-qPCR and Western blotting analyses of patient-derived xenograft models and a CRPC cell line. We applied Spearman correlation analysis to assess the relationship between canonical androgen receptor (AR) splicing and alternative AR splicing. We also assessed the ratio of AR splice variants (AR-Vs) to the full-length AR (AR-FL) at the RNA and protein levels by absolute RT-qPCR and Western blotting, respectively. These data are critical for studying the mechanisms underlying upregulated expression of AR-Vs after AR-directed therapies and the importance of AR-Vs to castration-resistant progression of prostate cancer. Data presented here are related to the research article by Ma et al., "Increased transcription and high translation efficiency lead
2022
BackgroundTherapies targeting the androgen receptor (AR) have improved the outcome for patients with castration-sensitive prostate cancer (CSPC). Expression of the constitutively active AR splice variant-7 (AR-V7) has shown clinical utility as a predictive biomarker of AR-targeted therapy resistance in castration-resistant prostate cancer (CRPC), but its importance as predictive biomarker in CSPC remains understudied.MethodsWe explored multiple approaches to quantify AR-V7 mRNA and protein in prostate cancer cell lines and patient-derived xenograft (PDX) models, in both publicly available and independent institutional clinical cohorts, to identify reliable approaches for detecting AR-V7 mRNA and protein, and its association with clinical outcome.ResultsIn publicly available benign prostate, CSPC and CRPC cohorts, AR-V7 mRNA was much less abundant when detected using reads across splice boundaries than when considering isoform-specific exonic reads. The RM7 AR-V7 antibody had increas...
Oncogene, 2012
Reactivation of the androgen receptor (AR) during androgen depletion therapy (ADT) underlies castration-resistant prostate cancer (CRPCa). Alternative splicing of the AR gene and synthesis of constitutively active COOH-terminally truncated AR variants lacking the AR ligand-binding domain has emerged as an important mechanism of ADT resistance in CRPCa. In a previous study, we demonstrated that altered AR splicing in CRPCa 22Rv1 cells was linked to a 35-kb intragenic tandem duplication of AR exon 3 and flanking sequences. In this study, we demonstrate that complex patterns of AR gene copy number imbalances occur in PCa cell lines, xenografts and clinical specimens. To investigate whether these copy number imbalances reflect AR gene rearrangements that could be linked to splicing disruptions, we carried out a detailed analysis of AR gene structure in the LuCaP 86.2 and CWR-R1 models of CRPCa. By deletion-spanning PCR, we discovered a 8579-bp deletion of AR exons 5, 6 and 7 in the LuCaP 86.2 xenograft, which provides a rational explanation for synthesis of the truncated AR v567es AR variant in this model. Similarly, targeted resequencing of the AR gene in CWR-R1 cells led to the discovery of a 48-kb deletion in AR intron 1. This intragenic deletion marked a specific CWR-R1 cell population with enhanced expression of the truncated AR-V7/AR3 variant, a high level of androgen-independent AR transcriptional activity and rapid androgen independent growth. Together, these data demonstrate that structural alterations in the AR gene are linked to stable gain-of-function splicing alterations in CRPCa.
Journal of Biological Chemistry, 2012
Background: Truncated AR splice variants support castration-resistant prostate cancer. Results: The AR NTD/DBD core is sufficient for AR variants to access the nucleus, activate AR target genes, and support androgen-independent prostate cancer cell growth. Conclusion: Diverse truncated AR variants are constitutively active transcription factors. Significance: These novel biochemical properties could lead to the development of new prostate cancer therapies. Synthesis of truncated androgen receptor (AR) splice variants has emerged as an important mechanism of prostate cancer (PCa) resistance to AR-targeted therapy and progression to a lethal castration-resistant phenotype. However, the precise role of these factors at this stage of the disease is not clear due to loss of multiple COOH-terminal AR protein domains, including the canonical nuclear localization signal (NLS) in the AR hinge region. Despite loss of this NLS, we show that diverse truncated AR variant species have a basal level of nuclear localization sufficient for ligand-independent transcriptional activity. Whereas full-length AR requires Hsp90 and importin- for active nuclear translocation, basal nuclear localization of truncated AR variants is independent of these classical signals. For a subset of truncated AR variants, this basal level of nuclear import can be augmented by unique COOH-terminal sequences that reconstitute classical AR NLS activity. However, this property is separable from ligand-independent transcriptional activity. Therefore, the AR splice variant core consisting of the AR NH 2terminal domain and DNA binding domain is sufficient for nuclear localization and androgen-independent transcriptional activation of endogenous AR target genes. Indeed, we show that truncated AR variants with nuclear as well as nuclear/cytoplasmic localization patterns can drive androgen-independent growth of PCa cells. Together, our data demonstrate that diverse truncated AR species with varying efficiencies of nuclear localization can contribute to castration-resistant PCa pathology by driving persistent ligand-independent AR transcriptional activity.
Biomarker Research
Background Androgen receptor (AR) splice variants (AR-Vs) have been discussed as a biomarker in prostate cancer (PC). However, some reports question the predictive property of AR-Vs. From a mechanistic perspective, the connection between AR full length (AR-FL) and AR-Vs is not fully understood. Here, we aimed to investigate the dependence of AR-FL and AR-V expression levels on AR gene activity. Additionally, we intended to comprehensively analyze presence of AR-FL and three clinically relevant AR-Vs (AR-V3, AR-V7 and AR-V9) in different stages of disease, especially with respect to clinical utility in PC patients undergoing AR targeted agent (ARTA) treatment. Methods AR-FL and AR-V levels were analyzed in PC and non-PC cell lines upon artificial increase of AR pre-mRNA using either drug treatment or AR gene activation. Furthermore, expression of AR-FL and AR-Vs was determined in PC specimen at distinct stages of disease (primary (n = 10) and metastatic tissues (n = 20), liquid biops...
Biomedicines
Multiple studies have demonstrated the importance of androgen receptor (AR) splice variants (SVs) in the progression of prostate cancer to the castration-resistant phenotype and their utility as a diagnostic. However, studies on AR expression in non-prostatic malignancies uncovered that AR-SVs are expressed in glioblastoma, breast, salivary, bladder, kidney, and liver cancers, where they have diverse roles in tumorigenesis. AR-SVs also have roles in non-cancer pathologies. In granulosa cells from women with polycystic ovarian syndrome, unique AR-SVs lead to an increase in androgen production. In patients with nonobstructive azoospermia, testicular Sertoli cells exhibit differential expression of AR-SVs, which is associated with impaired spermatogenesis. Moreover, AR-SVs have been identified in normal cells, including blood mononuclear cells, neuronal lipid rafts, and the placenta. The detection and characterization of AR-SVs in mammalian and non-mammalian species argue that AR-SV ex...