Laboratory Medicine and Pathology, Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455.
Androgen depletion for advanced prostate cancer (PCa) targets activity of the androgen receptor (AR), a steroid receptor transcription factor required for PCa growth. The emergence of lethal castration-resistant PCa (CRPCa) is marked by aberrant re-activation of the AR despite ongoing androgen depletion. Recently, alternative splicing has been described as a mechanism giving rise to COOH-terminally truncated, constitutively active AR isoforms that can support the CRPCa phenotype. However, the pathologic origin of these truncated AR isoforms is unknown. The goal of this study was to investigate alterations in AR expression arising in a cell-based model of PCa progression driven by truncated AR isoform activity. We show that stable, high-level expression of truncated AR isoforms in 22Rv1 CRPCa cells is associated with intragenic rearrangement of a ~35kb AR genomic segment harboring a cluster of previously-described alternative AR exons. Analysis of genomic data from clinical specimens indicated that related AR intragenic copy number alterations occured in CRPCa, in the context of AR amplification. Cloning of the break fusion junction in 22Rv1 cells revealed long interspersed nuclear elements (LINE-1) flanking the rearranged segment, and a DNA repair signature consistent with microhomology-mediated break-induced replication. This rearrangement served as a marker for the emergence of a rare sub-population of CRPCa cells expressing high levels of truncated AR isoforms during PCa progression in vitro. Together, these data provide the first report of AR intragenic rearrangements in CRPCa, and an association with pathologic expression of truncated AR isoforms in a cell-based model of PCa progression.
Li Y, Alsagabi M, Fan D, Bova GS, Tewfik AH, Dehm SM. Are you the author?
Reference: Cancer Res. 2011 Jan 19. Epub ahead of print.