A large fraction of ductal carcinoma in situ (DCIS), a non-invasive precursor lesion of invasive breast cancer, overexpresses the HER2/neu oncogene. The ducts of DCIS are abnormally filled with cells that evade apoptosis, but the underlying mechanisms remain incompletely understood. We overexpressed HER2 in mammary epithelial cells and observed growth factor-independent proliferation. When grown in extracellular matrix as three-dimensional spheroids, control cells developed a hollow lumen, but HER2-overexpressing cells populated the lumen by evading apoptosis. We demonstrate that HER2 overexpression in this cellular model of DCIS drives transcriptional upregulation of multiple components of the Notch survival pathway. Importantly, luminal filling required upregulation of a signaling pathway comprising Notch3, its cleaved intracellular domain and the transcriptional regulator HES1, resulting in elevated levels of c-MYC and cyclin D1. In line with HER2-Notch3 collaboration, drugs intercepting either arm reverted the DCIS-like phenotype. In addition, we report upregulation of Notch3 in hyperplastic lesions of HER2 transgenic animals, as well as an association between HER2 levels and expression levels of components of the Notch pathway in tumor specimens of breast cancer patients. Therefore, it is conceivable that the integration of the Notch and HER2 signaling pathways contributes to the pathophysiology of DCIS.
Bibliographical noteFunding Information:
We thank Amit Zeisel and Sara Lavi for help, Brenda Lilly for the Notch3 reporter, and Powel Brown, Corey Speers and the Kleberg Center for Molecular Markers at MD Anderson Cancer Center (CCSG grant NCI CA16672) for providing tumors for the RPPA analysis. We acknowledge research funding by the National Cancer Institute (CA072981, CA121994-01 and CA120248-01), the Israel Cancer Research Fund, Dr Miriam and Sheldon G Adelson Medical Research Foundation, Kekst Family Institute for Medical Genetics, Kirk Center for Childhood Cancer and Immunological Disorders, the Women’s Health Research Center funded by Bennett-Pritzker Endowment Fund, Marvelle Koffler Program for Breast Cancer Research, Leir Charitable Foundation and the MD. Moross Institute for Cancer Research, the Susan G Komen Foundation (FAS0703849 to AMG, BTH and GBM), and a fellowship for PhD track for specialist medical doctors by the Linda and Michael Jacobs Charitable Trust (WJK). YY is the incumbent of the Harold and Zelda Goldenberg Professorial Chair and ED of the Henry J Leir Professorial Chair.
- breast cancer
- growth factor
- receptor tyrosine kinase
- signal transduction