Abstract LB-31: A snapshot of the expression signature of androgen receptor splicing variants and their distinctive transcriptional activities

Abstract

Abstract Objectives: Multiple androgen receptor (AR) splicing variants implicated in ligand-independent AR signaling have been characterized. These variants are expressed in hormone naïve prostate cancers, and elevated in castration-resistant prostate cancers (CRPC), supporting their potential as biomarkers and therapeutic targets for advanced prostate cancer. The diversity and complexity of AR splicing variants however are not fully understood, raising the need to generate a comprehensive expression signature of AR variants, and to address the relative importance of the individual variants that may confer the castration resistant phenotype. Methodology: A modified RNA amplification method, termed selective linear amplification of sense RNA (SLASR), was developed to amplify all AR transcripts containing AR exon 3. Amplified AR transcripts from CRPC specimens were profiled using expression microarrays with probes tiled across the human AR gene locus. Primers corresponding to novel expression peaks in the AR locus were designed to amplify and decode the splicing junctions. Coding sequences for a subset of selected AR variants were cloned into expression vectors and assessed for their transcriptional activities. Quantitative RT-PCR was used to determine their in vivo expression patterns in an expanded set of clinical specimens. Preliminary data: Tiling microarray results revealed a molecular portrait of both canonical and cryptic AR exons across the human AR locus. In addition to expression peaks in AR intron 3, a novel AR exon, termed exon 9, was discovered. Exon 9 was spliced into multiple novel AR variants. Different AR splicing variants were functionally distinctive, with some demonstrating constitutive activity while others were conditionally active. Conditionally active AR-Vs may activate AR signaling depending on the cellular context. AR variant functions however did not appear to depend on the full-length AR. AR variants demonstrated patterns of expression change in clinical prostate tumor specimens consistent with their role in castration-resistant progression. This study provided the first unbiased snapshot of the AR variant signature consisting of multiple AR variants with distinctive functional properties. Our results suggest that some AR variants previously considered to be inactive may confer the castration resistance phenotype depending on the cellular context. If further confirmed, the aggregate function of multiple AR variants may compensate for the low abundance of individual variants in clinical specimens relative to the full-length AR. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-31. doi:10.1158/1538-7445.AM2011-LB-31