Carcinogenesis Advance Access originally published online on January 6, 2009
Carcinogenesis 2009 30(3):449-456; doi:10.1093/carcin/bgp005
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Elevated NCOR1 disrupts a network of dietary-sensing nuclear receptors in bladder cancer cells
Institute of Biomedical Research, Wolfson Drive, University of Birmingham Medical School, Edgbaston, Birmingham B15 2TT, UK
1 Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Elm & Carlton Streets, Buffalo, NY 14263, USA
2 Department of Urology, Queen Elizabeth Hospital, Edgbaston, Birmingham B15 2TH, UK
3 Uro-Oncology Research Group, Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
* To whom correspondence should be addressed. Tel: +716 845 4443; Fax: +716 845 8857; Email: moray.campbell{at}roswellpark.org
Increasingly invasive bladder cancer cells lines displayed insensitivity toward a panel of dietary-derived ligands for members of the nuclear receptor superfamily. Insensitivity was defined through altered gene regulatory actions and cell proliferation and reflected both reduced receptor expression and elevated nuclear receptor corepressor 1 (NCOR1) expression. Stable overexpression of NCOR1 in sensitive cells (RT4) resulted in a panel of clones that recapitulated the resistant phenotype in terms of gene regulatory actions and proliferative responses toward ligand. Similarly, silencing RNA approaches to NCOR1 in resistant cells (EJ28) enhanced ligand gene regulatory and proliferation responses, including those mediated by peroxisome proliferator-activated receptor (PPAR) 
and vitamin D receptor (VDR) receptors. Elevated NCOR1 levels generate an epigenetic lesion to target in resistant cells using the histone deacetylase inhibitor vorinostat, in combination with nuclear receptor ligands. Such treatments revealed strong-additive interactions toward the PPAR, VDR and Farnesoid X-activated receptors. Genome-wide microarray and microfluidic quantitative real-time, reverse transcription–polymerase chain reaction approaches, following the targeting of NCOR1 activity and expression, revealed the selective capacity of this corepressor to govern common transcriptional events of underlying networks. Combined these findings suggest that NCOR1 is a selective regulator of nuclear receptors, notably PPAR and VDR, and contributes to their loss of sensitivity. Combinations of epigenetic therapies that target NCOR1 may prove effective, even when receptor expression is reduced.
Abbreviations: CDCA, chenodeoxycholic acid; ED50, dose required to inhibit cell proliferation by 50%; ETYA, 5,8,11,14-eicosatetraenoic acid; FXR, Farnesoid X-activated receptor; 22-HC, 22-hydroxycholesterol; HDAC, histone deacetylase; HNF4
, hapatocyte nucleur factor; LCA, lithocholic acid; LCOR, ligand-dependent nuclear receptor corepressor; LXR, liver X receptor; mRNA, messenger RNA; NCOR1, nuclear receptor corepressor 1; NCOR2/SMRT, silencing mediator of retinoid and thyroid hormone receptors/nuclear receptor corepressor 2; PPAR, peroxisome proliferator-activated receptor; Q-RT–PCR, quantitative real-time, reverse transcription–polymerase chain reaction; Q-RT–PCRM, microfluidic quantitative real-time, reverse transcription–polymerase chain reaction; RXR, retinoid X receptor; siRNA, silencing RNA; SLIRP, SRA stem loop-interacting RNA-binding protein; VDR, vitamin D receptor; 1,25(OH)2D3, 1,25dihydroxyvitaminD3
Received September 30, 2008; revised December 8, 2008; accepted December 26, 2008.