Loss of CHD1 promotes chromatin dysregulation leading to heterogeneous mechanisms of resistance to hormone therapy in prostate cancer [shRNA screen]

To explore the functional consequences of these copy number alterations, we screened an shRNA library targeting all genes deleted in prostate cancer (the prostate cancer deletome: 4380 shRNAs targeting 730 genes) for next generation antiandrogen resistance using a clinically-validated model of enzalutamide-sensitive, AR-driven mCRPC LNCaP/AR. The Chromatin helicase DNA-binding factor (CHD1) scored as a top candidate and was validated in vitro and in vivo using multiple independent shRNAs and CRISPR guides. Mechanistically, CHD1 loss led to global changes in open and closed chromatin (ATAC-seq) as well as downregulation of canonical AR target genes upon the challenge of antiandrogen, despite robust AR expression. Integrative analysis of ATAC- and RNA-seq changes following CHD1 deletion identified 23 candidate transcription factor drivers of enzalutamide resistance. CRISPR-based unbiased functional screening identified 4 of these drivers may drive the AR-independent resistance, including glucocorticoid receptor (GR), BRN2, NR2F1 and TBX2. Genetic studies further establish that CHD1 loss confers antiandrogen resistance by converting mCRPC cells from AR-dependence to GR-dependence in one of the resistant LNCaP/AR clone. Thus, CHD1 functions as a molecular tuner to regulate chromatin plasticity and maintain oncogenic AR signaling, as well as AR dependency.