Hypoxia-inducible factor 1 mediates TAZ expression and nuclear localization to induce the breast cancer stem cell phenotype

// Lisha Xiang 1,2,3 , Daniele M. Gilkes 2,3 , Hongxia Hu 2,3 , Naoharu Takano 2,3,5 , Weibo Luo 2,3 , Haiquan Lu 2,3 , John W. Bullen 2,3 , Debangshu Samanta 2,3 , Houjie Liang 1 and Gregg L. Semenza 2,3,4 1 Department of Oncology and Southwest Cancer Center, Southwest Hospital, Third Military Medical University, Chongqing, China 2 Vascular Program, Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 3 McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 4 Departments of Pediatrics, Medicine, Oncology, Radiation Oncology, and Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 5 Department of Biochemistry, School of Medicine, Keio University, Tokyo, Japan Correspondence: Gregg L. Semenza, email: // Keywords : Aldefluor assay, basal-like breast cancer, mammospheres, targeted therapy, triple-negative breast cancer Received : December 11, 2014 Accepted : December 12, 2014 Published : December 18, 2014 Abstract Intratumoral hypoxia, which is associated with breast cancer metastasis and patient mortality, increases the percentage of breast cancer stem cells (BCSCs) but the underlying molecular mechanisms have not been delineated. Here we report that hypoxia-inducible factor 1 (HIF-1) triggers the expression and activity of TAZ, a transcriptional co-activator that is required for BCSC maintenance, through two discrete mechanisms. First, HIF-1 binds directly to the WWTR1 gene and activates transcription of TAZ mRNA. Second, HIF-1 activates transcription of the SIAH1 gene, which encodes a ubiquitin protein ligase that is required for the hypoxia-induced ubiquitination and proteasome-dependent degradation of LATS2, a kinase that inhibits the nuclear localization of TAZ. Inhibition of HIF-1α, TAZ, or SIAH1 expression by short hairpin RNA blocked the enrichment of BCSCs in response to hypoxia. Human breast cancer database analysis revealed that increased expression (greater than the median) of both TAZ and HIF-1 target genes, but neither one alone, is associated with significantly increased patient mortality. Taken together, these results establish a molecular mechanism for induction of the BCSC phenotype in response to hypoxia.