Abstract B11: Loss of the androgen receptor (AR) ligand-binding domain transforms the AR transcriptome in prostate cancer

Abstract

Abstract Classically the AR is a ligand driven transcription factor with both genomic and non-genomic activities. However, it was subsequently shown that the AR behaves differently in the conversion from castration sensitive to castration resistant cancer. This conversion has been suggested to be identified by the expression of the ubiquinating enzyme, UBE2C. In this study we found that generation of ligand-independent xenografts in SCID mice by complete androgen deprivation with the combination of surgical ablation and abiraterone compared to castration alone resulted in the regrowth of tumors with low intracrine dihydrotestosterone (DHT), 3.49 ± 0.42 vs 0.98± 0.37 ng/gm tissue. The regrowth of the abiraterone + castration tumors was associated with a marked increase in the expression of full-length AR (ARfl) as well as the AR splice variants ARV7 and ARv567es. Associated with the increase of the AR variants and tumor recurrence was in increase in UBE2C. The increase in UBE2C did not correlate with ARfl, r=0.2 (ns) but did correlate with ARV7, r=0.77, p<0.002 and ARv567es, r= 0.70 p< 0.01. Additionally, genes associated with progression through the androgen deprivation-induced G1/S inhibition and increased M-phase cell cycle genes CDK-1, C-myc, CDC20, and CCLN were correlated with AR-variant and abiraterone resistance. In addition to genes associated with a change in cell cycle there is a marked increase in the androgen glucuronidating enzyme, UGT2B17. UGT2B17 is markedly increased in castrate resistant prostate cancer tissues from metastases that also express ARV7 or ARv567es in comparison to primary prostate cancer tissues that are castration sensitive. In order to examine more directly the role of constitutively active AR splice variant in the regulation, ARv567es or ARV7 were transfected into LnCaP cells that were grown in charcoal stripped media and had AR deleted by doxycycline inducible shRNAi to exons 6 and 7 of the AR. Cells containing the variants demonstrated a marked increase in UBE2 C and M-phase cell cycle genes as was noted in the xenografts and human metastases expressing the AR variants. In addition, PSA, FKBP5, and ERG were suppressed. These genes were suppressed in parental LnCaP cells expressing the AR and treated with dihydrotestosterone. Similar changes were noted in VCAP cells when ARV7 and ARv567es were induced by treatment with MDV3100. These data indicate that the expression of constitutively active AR splice variants stimulate a unique set of cell proliferation genes not associated with full-length AR and this altered transcriptome may account for the increased aggressiveness reported in prostate cancer metastases expressing AR splice variants as opposed to those expressing only full-length AR. Citation Format: Shihua Sun, Elahe Mosteghal, Cynthia Sprenger, Pete Nelson, Eric Bluemn, Jun Luo, Stephen Plymate. Loss of the androgen receptor (AR) ligand-binding domain transforms the AR transcriptome in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B11.