title: Coordinated epigenetic remodelling of transcriptional networks occurs during early breast carcinogenesis.
abstract: BACKGROUND
  Dysregulation of the epigenome is a common event in malignancy; however, deciphering the earliest cancer-associated epigenetic events remains a challenge. Cancer epigenome studies to date have primarily utilised cancer cell lines or clinical samples, where it is difficult to identify the initial epigenetic lesions from those that occur over time. Here, we analysed the epigenome of human mammary epithelial cells (HMEC) and a matched variant cell population (vHMEC) that have spontaneously escaped senescence and undergone partial carcinogenic transformation. Using this model of basal-like breast carcinogenesis, we provide striking new insights into the very first epigenetic changes that occur during the initial stages of malignancy.
  
  
  RESULTS
  The first phase of malignancy is defined by coordinated changes in the epigenome. At the chromatin level, this is embodied in long-range epigenetic deregulation, which involves the concomitant but atypical acquisition or loss of active and repressive histone modifications across large regional blocks. Changes in DNA methylation also occurs in a highly coordinated manner. We identified differentially methylated regions (DMRs) in the very earliest passages of vHMECs. Notably, we find that differential methylation targets loci regulated by key transcription factors including p53, AHR and E2F family members suggesting that epigenetic deregulation of transcription factor binding is a key event in breast carcinogenesis. Interestingly, DMRs identified in vHMEC are extensively methylated in breast cancer, with hypermethylation frequently encroaching into neighbouring regions. A subset of vHMEC DMRs exhibited a strong basal-like cancer specific hypermethylation.
  
  
  CONCLUSIONS
  Here, we generated epigenome-wide maps of the earliest phase of breast malignancy and show long-range epigenetic deregulation and coordinated DNA hypermethylation targets loci regulated by key transcription factors. These findings support a model where induction of breast cancer occurs through epigenetic disruption of transcription factor binding leading to deregulation of cancer-associated transcriptional networks. With their stability and very early occurrence, vHMECs hypermethylated loci could serve as excellent biomarkers for the initial detection of basal breast cancer.
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Level 5 deLacy Building, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010 Australia.
authors.forename: Warwick J
authors.initials: WJ
authors.lastname: Locke
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Level 5 deLacy Building, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010 Australia.
authors.forename: Elena
authors.initials: E
authors.lastname: Zotenko
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Level 5 deLacy Building, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010 Australia.
authors.forename: Clare
authors.initials: C
authors.lastname: Stirzaker
authors.affiliation: Swiss Institute of Bioinformatics, University of Zurich, Zurich, and Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057 Switzerland.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Robinson
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; Sydney West Cancer Trials Centre, Crown Princess Mary Cancer Centre Westmead, Westmead Hospital, Hawkesbury Road, Westmead, NSW 2145 Australia.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Hinshelwood
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Level 5 deLacy Building, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010 Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Stone
authors.affiliation: Cancer Research Unit, Children's Medical Research Institute, 2145 Hawkesbury Road, Westmead, NSW 2145 Australia ; Sydney Medical School, University of Sydney, Fisher Road, Sydney, NSW 2006 Australia.
authors.forename: Roger R
authors.initials: RR
authors.lastname: Reddel
authors.affiliation: Cancer Research Unit, Children's Medical Research Institute, 2145 Hawkesbury Road, Westmead, NSW 2145 Australia.
authors.forename: Lily I
authors.initials: LI
authors.lastname: Huschtscha
authors.affiliation: Epigenetic Research Laboratory, Genomics and Epigenetic Division, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010 Australia ; St. Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Level 5 deLacy Building, St Vincent's Hospital, Victoria Street, Darlinghurst, NSW 2010 Australia.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Clark
keywords: Basal breast cancer; Biomarker; DNA methylation; Epigenetics; Epigenome sequencing; Methylome