A cross-talk between hypoxia and TGF-beta orchestrates erythropoietin gene regulation through SP1 and Smads.
Erythropoietin (Epo) is the humoral regulator of red blood-cell production. Low oxygen tension increases the Epo levels by enhancing transcription, through the hypoxia-inducible factor (HIF)-1, a transcriptional modulator in oxygen-regulated gene expression. In the present work, a cooperative interaction between hypoxia, mediated by the HIF-1 complex, and transforming growth factor-beta (TGF-beta), mediated by Smad3/4, was revealed in the Epo gene. This cooperation is due to physical interaction between Smad3/4 and HIF-1alpha. The Smad3/4 binding site is located within the 3' Epo enhancer, downstream from the HRE consensus, and immediately adjacent to the orphan hepatic nuclear factor receptor (HNF-4). HNF-4 is interacting also with Smad3 and the HIF-1 complex, to potentiate further the cooperative effect between both factors. Moreover, Sp1 has been identified as the factor binding the promoter necessary for the full hypoxia inducibility of the EPO gene. However, this full induction is achieved only if the TGF-beta pathway is mediating a cross-talk between promoter (Sp1) and enhancer (HIF-1alpha) regions through Smad3. We show that Sp1 binding to the proximal promoter is relevant for Epo transcription, and contributes to the Epo induction by hypoxia. A functional cooperation among the transcription factors mediating hypoxia (HIF-1, Sp1), the TGF-beta pathway (Smad3/4), and tissue-specific HNF-4 is proposed for the regulation of the Epo gene. In this model, the physical contact between the upstream promoter and the 3' downstream enhancer is mediated by Sp1 and Smad3 factors, and would occur upon bending of the DNA intervening sequences. Thus, Sp1 would reinforce the promoter/enhancer contact, while Smad3 would stabilize the multifactorial complex by interacting with HIF-1/Sp1/HNF-4 and the coactivator CBP/p300. This model may be extended to other genes where collaboration between TGF-beta and hypoxia takes place.
Sánchez-Elsner
Tilman
T
Centro de Investigaciones Biológicas, CSIC Ramiro de Maeztu, 9, Madrid 28040, Spain.
Ramírez
Jose R
JR
Sanz-Rodriguez
Francisco
F
Varela
Elisa
E
Bernabéu
Carmelo
C
Botella
Luisa M
LM
Rodriguez-Sanz
Francisco
F
D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D004921:Erythropoietin / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D015398:Signal Transduction / Q000502:physiology; D051900:Smad3 Protein; D051901:Smad4 Protein; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D004921:Erythropoietin