Network-directed cis-mediator analysis of normal prostate tissue expression profiles reveals downstream regulatory associations of prostate cancer susceptibility loci

// Nicholas B. Larson 1 , Shannon K. McDonnell 1 , Zach Fogarty 1 , Melissa C. Larson 1 , John Cheville 2 , Shaun Riska 1 , Saurabh Baheti 1 , Alexandra M. Weber 3 , Asha A. Nair 1 , Liang Wang 4 , Daniel O’Brien 1 , Jaime Davila 1 , Daniel J. Schaid 1 and Stephen N. Thibodeau 5 1 Division of Biomedical Statistics and Informatics, Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA 2 Division of Anatomic Pathology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA 3 Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, USA 4 Department of Pathology, Medical College of Wisconsin, Milwaukee, WI, USA 5 Division of Laboratory Genetics, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA Correspondence to: Nicholas B. Larson, email: Larson.nicholas@mayo.edu Keywords: prostate cancer, genetic risk, expression quantitative trait loci, mediation Received: April 26, 2017 Accepted: July 29, 2017 Published: September 08, 2017 ABSTRACT Large-scale genome-wide association studies have identified multiple single-nucleotide polymorphisms associated with risk of prostate cancer. Many of these genetic variants are presumed to be regulatory in nature; however, follow-up expression quantitative trait loci (eQTL) association studies have to-date been restricted largely to cis -acting associations due to study limitations. While trans -eQTL scans suffer from high testing dimensionality, recent evidence indicates most trans -eQTL associations are mediated by cis -regulated genes, such as transcription factors. Leveraging a data-driven gene co-expression network, we conducted a comprehensive cis -mediator analysis using RNA-Seq data from 471 normal prostate tissue samples to identify downstream regulatory associations of previously identified prostate cancer risk variants. We discovered multiple trans -eQTL associations that were significantly mediated by cis -regulated transcripts, four of which involved risk locus 17q12, proximal transcription factor HNF1B , and target trans -genes with known HNF response elements ( MIA2 , SRC , SEMA6A , KIF12 ). We additionally identified evidence of cis -acting down-regulation of MSMB via rs10993994 corresponding to reduced co-expression of NDRG1 . The majority of these cis -mediator relationships demonstrated trans -eQTL replicability in 87 prostate tissue samples from the Gene-Tissue Expression Project. These findings provide further biological context to known risk loci and outline new hypotheses for investigation into the etiology of prostate cancer.