Abstract 1989: SRRM4 and the loss of REST may promote the emergence of the neuroendocrine /neuronal phenotype in castration resistant prostate cancer
Authors: Zhang Xiaotun , Coleman Ilsa , Coleman Roger , Brown Lisha , Kollath Lori , Chéry Lisly , Lucas Jared , Corey Eva , Roudier Martine , Lange Paul , Higano Celestia , True Lawrence , Nelson Peter , Vessella Robert , Morrissey Colm 
Published: May 2015

Abstract
Introduction: Recent findings suggest that neuroendocrine/neuronal (NE) differentiation may be associated with the development of metastatic castration-resistant prostate cancer (CRPC). Our objective was to characterize the NE phenotype in CRPC.
Methods: Using specimens obtained at rapid autopsy at the University of Washington, 2 tissue microarrays were made from (1) 155 metastatic sites from 50 autopsy patients who died from CRPC and (2) 24 LuCaP prostate cancer xenografts. NE markers, including Chromogranin A (CHGA), Synaptophysin (SYN), androgen receptor (AR), and prostate specific antigen (PSA) were analyzed by immunohistochemistry (IHC). To characterize the molecular features of the NE phenotype in CRPC, transcript levels in 78 corresponding metastatic sites and 24 LuCaP xenografts were determined by hybridization to whole genome microarrays.
Results: Co-expression of CHGA and SYN (by at least &gt;10% of cells) was observed in 22 of 155 sites (11 sites were AR-). PSA, a surrogate of AR activity, was absent in all NE CRPC tumors that did not express AR. Four of the 24 LuCaP xenografts displayed an NE phenotype (all were AR-). Gene expression data were generated from 78 laser captured metastases, and 24 LuCaP xenografts. Five metastatic sites were CHGA+, SYN+ and AR-, and 5 were CHGA+, SYN+ and AR+, 4 LuCaP xenografts were CHGA+, SYN+ and AR- by IHC. Only CHGA+, SYN+ sites had a NE transcript signature, with the CHGA+, SYN+ and AR- specimens expressing a greater number of genes associated with the NE phenotype. In addition, a decrease in the expression of REST was observed in the 10 CHGA+, SYN+ metastatic sites and LuCaP xenografts. SRRM4 transcript expression was associated with the NE signature in 5 of the 6 CHGA+, SYN+ patients and the LuCaP xenografts. Furthermore RT-PCR comparing the epithelial to the NE LuCaP xenografts correlated the expression of SRRM4 with a splice variant of REST that lacks the repressor domain and the NE phenotype.
Conclusions: Our data suggest that a) the CRPC NE phenotype can be defined by CHGA+, SYN+ dual positivity and is more common in CRPC than historically in hormone sensitive primary disease, b) NE status from different sites in the same patient can be heterogeneous c) the NE phenotype is not necessarily associated with the loss of AR activity, and d) the loss of REST expression or the splicing of REST through the activity of SRRM4 could promote the NE phenotype in CRPC. These molecular studies suggest that evolution from hormone sensitive, to castration resistant on to NE disease involves the loss of REST or the loss of REST repressor activity due to alternate splicing by SRRM4.
Citation Format: Xiaotun Zhang, Ilsa Coleman, Roger Coleman, Lisha Brown, Lori Kollath, Lisly Chéry, Jared Lucas, Eva Corey, Martine Roudier, Paul Lange, Celestia Higano, Lawrence True, Peter Nelson, Robert Vessella, Colm Morrissey. SRRM4 and the loss of REST may promote the emergence of the neuroendocrine /neuronal phenotype in castration resistant prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1989. doi:10.1158/1538-7445.AM2014-1989