Endocrine Abstracts

The corepressor NCOR2/SMRT regulates multiple nuclear receptors (NRs) and other transcription factors. Disruption to these functions are implicated in prostate cancer (PCa) progression but the details remain enigmatic. Therefore we sought to define the global functions of NCOR2/SMRT using isogenic PCa cell models, PCa mouse models and human PCa cohorts.

We mapped the NCOR2 dependent transcriptome (RNA-seq), miRnome (miRNA-seq), methylome (EPIC methylation array) and cistrome (ChIP-seq) in androgen sensitive (LNCaP) and therapy resistant (LNCaP-C42) PCa cells, both treated with androgen, and stable NCOR2/SMRT knockdown. NCOR2/SMRT knockdown in LNCaP-C42 cells resulted in a striking increase in global hypermethylation (87,078 CpGs > 10% gain, adj.Pval < 0.01), but a divergent transcriptome (1,491 upregulated, 1,195 downregulated). Similar patterns were observed in LNCaP cells, and included regulation of PPARg expression and sensitivity to PPARg ligands. NCOR2/SMRT genomic binding overlapped with AR and pioneering factor FOXA1, and modulated androgen responses in LNCaP-C42. Ongoing data integration efforts are dissecting NCOR2/SMRT methylome-cistrome-transcriptome relationships within and across models.

Using clinical cohorts we revealed that NCOR2/SMRT-regulated miRNA are significantly altered in men progressing to PCa from high grade PIN, and elevated NCOR2/SMRT expression on a 700 case TMA associated with worse disease free survival (P< 0.04; Log-rank (Mantel-Cox) test). To define NCOR2/SMRT actions in vivo, we stably knocked down NCOR2/SMRT in the CWR22 xenograft model. This model simulates androgen dependent primary growth and regression upon androgen deprivation therapy (ADT). NCOR2 loss had no effect on primary tumor growth rate or size of tumor at ADT but significantly reduced regression in response to ADT and tumors recurred significantly quicker (P=0.0044). Therefore loss of NCOR2/SMRT during ADT results in more aggressive tumors.

These findings suggest NCOR2/SMRT profoundly regulates the methylome, but the consequences are divergent. At early stages, elevated expression may suppress antiproliferative signals from PPARg but during ADT NCOR2/SMRT loss and mutation drives PCa progression.