Role of ETS transcription factors in the hypoxia-inducible factor-2 target gene selection

• Published in: Cancer research (Chicago, Ill.) Ill.), 2006-06, Vol.66 (11), p.5641-5647
• Main Authors: Aprelikova, Olga, Wood, Matthew, Tackett, Sean, Chandramouli, Gadisetti V R, Barrett, J Carl
• Format: Article
• Language: English
• Subjects: Basic Helix-Loop-Helix Transcription Factors; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Cell Hypoxia - genetics; Cell Line, Tumor; ets-Domain Protein Elk-1 - antagonists & inhibitors; ets-Domain Protein Elk-1 - biosynthesis; ets-Domain Protein Elk-1 - genetics; Gene Expression Regulation, Neoplastic; Gene Silencing; Humans; Hypoxia-Inducible Factor 1, alpha Subunit - antagonists & inhibitors; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Oligonucleotide Array Sequence Analysis; Promoter Regions, Genetic; Proto-Oncogene Proteins c-ets - genetics; Proto-Oncogene Proteins c-ets - physiology; RNA Interference; Transcription Factors - antagonists & inhibitors; Transcription Factors - genetics; Transcriptional Activation
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-05-3345

Tumor hypoxia often directly correlates with aggressive phenotype, metastasis progression, and resistance to chemotherapy. Two transcription factors [hypoxia-inducible factor-1alpha (HIF-1alpha) and HIF-2alpha] are dramatically induced in hypoxic areas and regulate the expression of genes necessary for tumor adaptation to the conditions of low oxygen; however, the relative contribution of these factors is controversial. We used RNA interference-mediated inactivation of HIF-1alpha or HIF-2alpha followed by microarray analysis to identify genes specifically regulated by either HIF-1 or HIF-2 in hypoxia. We found that, in the MCF7 cell line, the vast majority of hypoxia-responsive genes (>80%) were dependent on the presence of HIF-1alpha. However, a small group of genes were preferentially regulated by HIF-2alpha. Promoter analysis for this group of genes revealed that all of them have putative binding sites for ETS family transcription factors, and 10 of 11 HIF-2alpha-dependent genes had at least one potential hypoxia-responsive element (HRE) in proximity to an ETS transcription factor binding site. Knockdown of ELK-1, the most often represented member of ETS family, significantly reduced hypoxic induction of the HIF-2alpha-dependent genes. Physical and functional interaction between ELK-1 and HIF-2alpha were supported by coimmunoprecipitation of these two proteins, luciferase reporter assay using CITED2 promoter, and binding of ELK-1 protein to the promoters of CITED2 and WISP2 genes in proximity to a HRE. These data suggest that the choice of the target genes by HIF-1 or HIF-2 depends on availability and cooperation of HIFs with other factors recognizing their cognate elements in the promoters.