Abstract P5-05-07: Expression of the cocaine- and amphetamine-regulated transcript (CART) recruits SWI/SNF chromatin remodelling complexes to the estrogen receptor

Abstract

Abstract Introduction Cocaine- and amphetamine-regulated transcript (CART) peptides are neuropeptides involved in regulating physiological processes, such as feeding and drug reward. Recent studies have associated high CART expression with worse overall survival in patients with small-bowel carcinoid tumours and estrogen receptor-positive (ER+), lymph node-negative breast cancer. CART was also shown to be associated with poor patient response to tamoxifen, suggesting CART may play a role in conferring tamoxifen resistance. Materials and methods We have previously demonstrated that CART can impact the transcriptional activity of ERα through the use of western blotting and qPCR for specific ERα gene targets. RNA sequencing was carried out using a stable CART-inducible cell line model to identify genes which are upregulated/downregulated in cells expressing CART. Further, using our stable CART-inducible cell line model, we preformed ERα-Immunoprecipitation followed by in-solution mass spectrometry to identify differentially recruited protein complexes +/- CART expression. Results and discussion RNA sequencing revealed 156 significantly downregulated, and 100 significantly upregulated, genes in cells expressing CART (p<0.05). Through mining of publicly available ERα ChIP-seq data sets, both upregulated and downregulated gene sets were found to contain genes which have previously been shown to contain ERα binding events within their promotor regions. Mass spectrometry analysis revealed that the majority of proteins recruited to ERα in the presence of CART were members of the SWI/SNF (BAF) chromatin remodelling complex. The identification of SMARCD1 within this complex was of particular interest to this study, as this protein has previously been reported to be a critical mediator of nuclear receptor function. Further in silico analysis demonstrated high expression of SMARCD1 correlates with poor overall survival (OS) (p<0.00001) and distant metastasis free survival (DMFS) (p=0.00708) in a cohort of ER+ breast cancer patients. Intriguingly, SMARCD1 expression did not correlate with poor OS or DMFS in a cohort of ER- breast cancer patients, suggesting that this negative impact on survival is dependent on ER status. Conclusion In conclusion, we suggest that CART expression results in the recruitment of chromatin remodelling complexes to ERα in order to facilitate the regulation of receptor function and this impacts on patient outcome. Citation Format: O'Connor DP, Mooney B, Das S, Klinger R, Moran B, Ni Chonghaile T, Cagney G, Bracken A, Gallagher WM. Expression of the cocaine- and amphetamine-regulated transcript (CART) recruits SWI/SNF chromatin remodelling complexes to the estrogen receptor [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-05-07.