Poster Presentation 28th Lorne Cancer Conference 2016

Characterising the molecular function of Inhibitor of Differentiation 4 in basal-like breast cancer (#114)

Laura Baker 1 2 , Simon Junankar 1 2 , Christoph Krisp 3 4 5 , Hisham Mohammed 6 , Daniel Roden 1 2 , Radhika Nair 1 2 , Sunil Lakhani 7 , Sandra O'Toole 1 2 8 9 , Mark Molloy 3 5 , Jason Carroll 6 , Alexander Swarbrick 1 2
  1. The Kinghorn Cancer Center and Cancer Research Division, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, NSW, Australia
  3. Australian Proteome Analysis Facility (APAF), Macquarie University, Sydney, NSW, Australia
  4. Department of Analytical Chemistry, Biomolecular Mass Spectrometry, Ruhr-University Bochum, Bochum, Germany
  5. Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW, Australia
  6. Cancer Research UK, Cambridge Research Institute, Li Ka Shing Centre, Cambridge, United Kingdom
  7. The University of Queensland, UQ Centre for Clinical Research, School of Medicine and Pathology Queensland, The Royal Brisbane and Women’s Hospital, Brisbane, QLD, Australia
  8. Department of Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia
  9. Sydney Medical School, University of Sydney, Sydney, NSW, Australia

Basal-like breast cancer (BLBC) is a heterogeneous aggressive disease. Patients are diagnosed at an earlier age, with high-grade tumours and often relapse soon after diagnosis. Poor survival outcome is compounded by a lack of targeted treatments. Detailed understanding of the molecular mechanisms underpinning this subtype of breast cancer is essential to the design of better therapeutic options for BLBC. In this study, we show that Inhibitor of Differentiation 4 (ID4), a transcriptional regulator of stem cell homeostasis and mammary development, is amplified and overexpressed in a subset of BLBCs, identifying patients with poor short-term survival and response to chemotherapy. Through loss of function approaches in vitro and in vivo, we show that ID4 is required for proliferation and survival in Id4+ BLBC, demonstrating Id4 to be a bone fide proto-oncogene in BLBC.

The molecular mechanisms through which ID4 controls this phenotype are not known. Conventional models of Id protein function predict cytosolic sequestration of HLH factors by ID4, however we have identified a predominant chromatin association of Id4. We are currently using chromatin immunoprecipitation and sequencing (ChIP-seq), to identify regions of ID4 enrichment in the BLBC genome. Furthermore, using an unbiased technique termed Rapid Immunoprecipitation and Mass Spectrometry of Endogenous proteins (RIME), we comprehensively characterise ID4 protein-protein interactions in BLBC and identify novel protein interactors, including known chromatin-associated proteins. One such protein is a member of the BRCA1-mediated DNA damage response (DDR) pathway.

We have identified a subset of BLBC patients who have aggressive, poor-prognosis disease, marked by ID4 protein overexpression. We have identified a novel ID4 protein interactor, a member of the BRCA1 DDR pathway. Future directions of this project are to determine whether ID4 marks sensitivity to BRCA1-specific therapies and chemotherapy. By further understanding the molecular mechanism of action of ID4 we aim to understand how ID4 is mediating a poor prognosis phenotype in women, and how we can tailor treatment to increase overall survival.