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- Title
Differentiation of Hypoxia-Inducible Factor (HIF)-1α and HIF-2α Functions by the Use of RNA Interference: Erythropoietin Is a HIF-2α Target Gene.
- Authors
Warnecke, C.; Zaborowska, Z.; Kurreck, J.; Erdmann, V.; Frei, U.; Wiesener, M.; Eckardt, K. -U.
- Abstract
Objective: Hypoxia-inducible transcription factor (HIF) mediates cellular and systemic adaptations to an insufficient oxygen supply, stimulating the transcription of, e.g., glycolytic enzymes, angiogenic factors and erythropoietin (EPO). HIF is a heterodimer which consists of an oxygen-regulated β subunit and a constitutively expressed α subunit. The two alternative HIFα subunits, HIF-1α and HIF-2α, are differentially expressed in vivo. Overexpression experiments in vitro suggested a partial functional redundancy. Methods: Here, we used RNA interference in various human cell lines to determine the relative contribution of HIF-1α versus HIF-2α to the hypoxic gene induction. Results: We found that in HeLa and Hep3B cells the hypoxic induction of most HIF target genes was responsive to HIF-1α knockdown, but not to HIF-2α knock-down. The same applied for the activation of reporter genes driven by hypoxia responsive elements (HREs). Surprisingly, EPO was the only gene investigated which showed responsiveness only to HIF-2α knock-down, as observed in Hep3B and neuroblastoma Kelly cells. In contrast to the EPO-HRE reporter, the complete EPO enhancer displayed dependency on HIF-2α regulation, indicating that cis-acting elements other than the HRE contribute to the HIF-2α effect. We also found that overexpression of the HIFα subunits led to a loss of target gene specificity. Conclusions: In conclusion, EPO is the only HIF-2α target gene identified so far. The fact that renal peritubular fibroblasts, the major source of EPO in the adult, express HIF-2α but not HIF-1α protein, supports our finding. The hypoxic induction of the EPO gene seems to require the interaction of HIF-2α with other DNA-binding factors.
- Subjects
HYPOXEMIA; TRANSCRIPTION factors; GENE expression; GENETIC regulation; FIBROBLASTS
- Publication
Kidney & Blood Pressure Research, 2004, Vol 27, Issue 5/6, p302
- ISSN
1420-4096
- Publication type
Article