Androgen Receptor Splice Variants In Mouse Prostate Cancer Cell Lines: Altered Distribution In Lines Derived From Castration-Resistant Tumors Relative To Those Primary Tumors

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Prostate cancer is sensitive to androgen deprivation at the primary androgen-dependent growth stage (ADCa). However, it invariably acquires resistance to androgen withdrawal leading to the recurrence of the castration-resistant prostate cancer (CRPC). Androgen receptor (AR) activity that is necessary for the normal prostate development remains active through both phases of the disease. Even at castrate levels of androgen AR remains functional, possibly through several non-mutually exclusive mechanisms including expression of constitutively active AR variants (ARVs). The full-length of AR (ARFL) is a 110 KDa nuclear hormone receptor composed of an N-terminal domain (NTD, exon1), DNA-binding domain (DBD, exon 2 and 3), a hinge region (exon 4), and the C-terminal ligand binding domain (LBD, exon 4-8). To date up to 15 different ARVs lacking LBD have been identified in human prostate cancer cell lines or specimens. It is thought that the altered biological properties of these ARVs may be, in part, correlated to the development of castration resistance. ARVs remain understudied in mouse prostate cancer cell lines; detection of only two ARVs was reported in a mouse cell line. A better definition of ARVs in distinct phases of this cancer in an appropriate mouse model should be valuable for insights into the role of ARVs in therapy and disease progression. To this end, by using cell lines established from the conditional Pten deletion mouse model of prostate adenocarcinoma, we detected low molecular weight AR protein species (∼50 kDa - 80 kDa) besides the presence of the 110 kDa full-length. We performed 3’RACE and subsequent Sanger sequencing on cell lines derived from both ADCa (E-series) and CRPC stages (cE-series) and identified three different ARVs which we named as mARV-abc. Structurally, mARVa is analogous to the previously reported mAR-V4 and the human ARV567es which only lacks LBD domain retaining exon 1-4 followed by the inclusion of a cryptic exon 4 from intron 4 at the 3’-terminal sequence. More interestingly, we identified two novel ARV isoforms (mARV-b and -c) which merely contains the NTD encoded by exon 1 before the addition of specific sequences from different positions of intron 1. Although these mARVs occur in all the murine cell lines tested, their proportion appears to vary with respect to the stage of the disease from which the cell lines originated. In cE-series established from a CRPC tumor, novel ARVb and ARVc are more abundant than that in E-series from an ADCa tumor; in parallel, ARVa displays an opposite expression profile. These new findings together with the results of ongoing experiments, including the single cell expression analysis and on their biological activities of the splice variants will be discussed. Citation Format: Mengmeng Liang, Helty A. Adisetiyo, Xiuqing Li, Ren Liu, Parkash S. Gill, Pradip Roy-Burman. Androgen receptor splice variants in mouse prostate cancer cell lines: altered distribution in lines derived from castration-resistant tumors relative to those primary tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4087. doi:10.1158/1538-7445.AM2013-4087