Project description:CRPC remains AR dependent. There are multiple mechanisms for reactivation of AR including expression of constitutively active AR splices variant AR-V7 (AR3). Earlier studies suggest that though the variants regulate many of the same genes as AR, they also have unique targets. Another argument is that the variant is a “weak” AR. We have used an LNCaP cell line that expresses AR-V7 in response to doxycycline to compare DNA interactions of the two isoforms and to identify differential regulation of target genes. ChIP-exo method was used to map AR and AR-V7 interaction with DNA in LNCaP engineered cell line (LNCaP AR-V7) at single base resolution.
Project description:CRPC remains AR dependent. There are multiple mechanisms for reactivation of AR including expression of constitutively active AR splices variant AR-V7 (AR3). Earlier studies suggest that though the variants regulate many of the same genes as AR, they also have unique targets. Another argument is that the variant is a “weak” AR. We have used an LNCaP cell line that expresses AR-V7 in response to doxycycline (LNCaP AR-V7) to compare the activities of the two isoforms and to identify differential regulation of target genes. We also used VCaP cell line that expresses AR-V7 in response to doxycycline (VCaP AR-V7) to validate the activities of the two isoforms in an alternative prostate cancer cell line. The transcriptomes for AR and AR-V7 in these cell lines were identified using RNA-Seq.
Project description:The constitutively active androgen receptor (AR) splice variant 7 (AR-V7) plays an important role in the progression of castration-resistant prostate cancer (CRPC). Although biomarker studies established the role of AR-V7 in resistance to AR-targeting therapies, how AR-V7 mediates genomic functions in CRPC remains largely unknown. Using a ChIP-exo approach, we show AR-V7 binds to distinct genomic regions and recognizes a full-length androgen-responsive element in CRPC cells and patient tissues. Remarkably, we find dramatic differences in AR-V7 cistromes across diverse CRPC cells and patient tissues, regulating different target gene sets involved in CRPC progression. Surprisingly, we discover that HoxB13 is universally required for and colocalizes with AR-V7 binding to open chromatin across CRPC genomes. HoxB13 pioneers AR-V7 binding through direct physical interaction, and collaborates with AR-V7 to up-regulate target oncogenes. Transcriptional coregulation by HoxB13 and AR-V7 was further supported by their coexpression in tumors and circulating tumor cells from CRPC patients. Importantly, HoxB13 silencing significantly decreases CRPC growth through inhibition of AR-V7 oncogenic function. These results identify HoxB13 as a pivotal upstream regulator of AR-V7-driven transcriptomes that are often cell context-dependent in CRPC, suggesting that HoxB13 may serve as a therapeutic target for AR-V7-driven prostate tumors.
Project description: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 biology and expression in prostate cancer (PC) tissue. Following generation and validation of a novel AR-V7 antibody for immunohistochemistry (IHC); nuclear AR-V7 protein expression was determined for 358 primary prostate samples (358 patients) and 293 metastatic biopsies (194 patients). Associations with disease progression, nuclear AR full length (AR-FL) expression, response to abiraterone and/or enzalutamide, and gene signatures (from three independent cohorts) was determined.
Project description:Although AR-V7 has been intensively studied, it remains unclear whether AR-V7 can specifically activate a distinctive transcriptional program from the full-length AR (AR-FL), and whether AR-V7 may play a role in accelerating the metastatic progression of castration-resistant PCa (CRPC). In this study, we hypothesize that AR-V7 can drive a distinct transcription program from AR-FL in CRPC condition. To test this, we used LNCaP model with inducible overexpression of AR-V7 or AR-FL to examine the effects of AR-V7 overexpression or AR-FL overexpression stimulated with DHT for 4 hours on AR-V7 or AR-FL cistromes. We also studied the effects of AR-V7 on cistromes of pioneer factor FOXA1 and active histone marker H3K27ac, and the function of phosphorylation at Ser81 on AR-V7 function in CRPC.
Project description:Since its discovery, there has been one central issue of significant clinical relevance related to expression of the truncated androgen receptor splice variant-7 (AR-v7), which lacks the C-terminal ligand binding domain and thus acquires ligand-independent transcriptional activity in castration-resistant prostate cancer (CRPC). That question is whether AR-v7 is simply a marker of enhanced AR transcriptional activity characteristic of resistance to 2nd generation androgen receptor signaling inhibitors (ARSi) like Abiraterone and Enzalutamide, or whether it drives lethal resistance to ARSi. To address this question, the present study utilized 4 independently derived CRPC patient-derived xenografts in which the genetic and phenotypic changes could be followed before and after the development of ARSi resistance. This allowed evaluation of the correlation between acquired resistance to ARSi and changes in the expression levels of full length AR (AR-FL) vs. AR-v7 during this process. The combined results document that elevated expression of AR-FL alone is sufficient for Abiraterone- but not Enzalutamide-resistance. This is true even if AR-FL has a gain-of-function mutation. Furthermore, Enzalutamide-resistance is consistently correlated with the acquisition of AR-v7 expression. To directly test the requirement for AR-v7 expression in ARSi-refractory CRPC, CRISPR-Cas9 knockout of AR-FL and/or AR-v7 in LNCaP-95 cells was performed to evaluate in vitro and in vivo growth responses. These results document that AR-v7 drives Enzalutamide-resistance and focuses the critical need to develop therapeutic options to prevent and/or inhibit AR-v7 driven lethal progression of CRPC.
Project description:To elucidate the AR-V7 role, we performed ChIP-seq on H3K4me1, H3K4me3, H3K27ac, and AR antibody recognizing the N-terminus of AR and AR splice variants (AR-Vs) using LNCaP and LNCaP95 cells. We showed 399 AR-V7 targeted regions in LNCaP95, most of the AR-V7 target regions could be commonly activated by hormone stimulated AR. However, 22 regions were identified as AR-V7 specific regions. In addition, we show here that AR-V7 can transcript in the ligand independent manner in LNCaP95, unlike LNCaP. We identified the AR-V7 target gene contributing to the CRPC progression.
Project description:Although AR-V7 has been intensively studied, it remains unclear whether AR-V7 and other AR splicing variants can specifically activate a distinctive transcriptional program from the full-length AR (AR-FL), and whether AR-V7 may play a role in accelerating the metastatic progression of castration-resistant PCa (CRPC). In this study, we hypothesize that AR-V7 can drive a distinct transcription program from AR-FL in CRPC condition. To test this, we performed ATAC-seq using LNCaP model with inducible overexpression of AR-V7 to examine the function of AR-V7. We demonstrated that AR-V7 has “pioneer factor-like” activities to access the androgen-responsive elements (AREs) located at compact chromatin regions. More importantly, we found that SOX9, a critical metastasis driver gene, was a direct target and downstream effector of AR-V7, and its protein expression was dramatically upregulated at AR-V7-induced bone lesions.