LncRNA-dependent mechanisms of androgen receptor-regulated gene activation programs [GRO-seq I]
While thousands of long non-coding RNAs (lncRNAs) are expressed in higher eukaryotes, the potential regulatory roles of lncRNAs in regulated gene transcription programs remain rather poorly understood. Here, we report that two lncRNAs highly overexpressed in aggressive prostate cancer, PRNCR1 and PCGEM1, bind successively to the androgen receptor (AR) and strongly enhance both ligand-dependent and ligand-independent AR-mediated gene activation programs and proliferation in prostate cancer cells. Binding of PRNCR1 to the C-terminally acetylated AR on enhancers and its association with DOT1L appear to be required for recruitment of the second lncRNA, PCGEM, to the N-terminally methylated AR. Unexpectedly, recognition of the H3K4me3 promoter  mark by the PHD finger-domain of Pygopus2, recruited by PCGEM1, proves to enhance selective looping of AR-bound enhancers to target gene promoters in these cells, revealing a novel aspect of ligand-induced enhancer-promoter interactions. In “resistant” prostate cancer cells, these overexpressed lncRNAs can interact with, and are required for the robust activation of both truncated and full length AR, causing DHT-independent activation of the AR transcriptional program and cell proliferation. Conditionally-expressed short hairpin RNA (shRNA)-mediated targeting of these lncRNAs in these resistant cancer cell lines strongly suppressed xenograft growth in vivo. Together, these results suggest that these overexpressed lncRNAs can potentially serve as a required component of castration-resistance in prostatic tumors. Overall design: Global Run On (GRO) assay followed by high throughput sequencing (GRO-seq); after knocking down PYGO2 LNCaP cells were grown to 30-50% confluence and siRNA/ASO transfections were carried out using Lipofectamine 2000 (Invitrogen) according to the  manufacturer’s instructions. Control samples were transfected with scramble  ASO and control siRNA, respectively. On the following day of transfection,  the cells were cultured in UltraCULTURE (Phenol red free) + 5% Charcoal  Dextran Stripped (CDS) serum for 48 hours. For androgen induction, we treat  cells with DHT from a 100 uM stock in 70% ethanol to a final concentration of 100 nM for 1 hour Control siRNA, -DHT Control siRNA, +DHT Pygo2 siRNA, -DHT Pygo2 siRNA, +DHT