LncRNA-dependent mechanisms of androgen receptor-regulated gene activation programs [GRO-seq II]

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.