Role of HIF-1alpha in proton-mediated CXCR4 down-regulation in endothelial cells.
OBJECTIVE
Acidification is associated with a variety of pathological and physiological conditions. In the present study, we aimed at investigating whether acidic pH may regulate endothelial cell (EC) functions via the chemokine receptor CXCR4, a key modulator of EC biological activities.


RESULTS
Exposure of ECs to acidic pH reversibly inhibited mRNA and protein CXCR4 expression, CXCL12/stromal cell-derived factor (SDF)-1-driven EC chemotaxis in vitro, and CXCR4 expression and activation in vivo in a mouse model. Further, CXCR4 signalling impaired acidosis-induced rescue from apoptosis in ECs. The inhibition of CXCR4 expression occurred transcriptionally and was hypoxia-inducible factor (HIF)-1alpha-dependent as demonstrated by both HIF-1alpha and HIF-1alpha dominant negative overexpression, by HIF-1alpha silencing, and by targeted mutation of the -29 to -25 hypoxia response element (HRE) in the -357/-59 CXCR4 promoter fragment. Moreover, chromatin immunoprecipitation (ChIP) analysis showed endogenous HIF-1alpha binding to the CXCR4 promoter that was enhanced by acidification.


CONCLUSIONS
The results of the present study identify CXCR4 as a key player in the EC response to acidic pH and show, for the first time, that HRE may function not only as an effector of hypoxia, but also as an acidosis response element, and raise the possibility that this may constitute a more general mechanism of transcriptional regulation at acidic pH.
Melchionna
Roberta
R
Laboratorio di Patologia Vascolare, Istituto Dermopatico dell'Immacolata-IRCCS, Via Monti di Creta 104, 00167 Rome, Italy.
Romani
Marta
M
Ambrosino
Valeria
V
D'Arcangelo
Daniela
D
Cencioni
Chiara
C
Porcelli
Daniele
D
Toietta
Gabriele
G
Truffa
Silvia
S
Gaetano
Carlo
C
Mangoni
Antonella
A
Pozzoli
Ombretta
O
Cappuzzello
Claudia
C
Capogrossi
Maurizio C
MC
Napolitano
Monica
M
D000138:Acidosis / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D000643:Ammonium Chloride; D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D015687:Cell Hypoxia; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000378:metabolism; D002633:Chemotaxis; D047369:Chromatin Immunoprecipitation; D004195:Disease Models, Animal; D015536:Down-Regulation; D042783:Endothelial Cells / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D009154:Mutation; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014158:Transcription, Genetic; D014162:Transfection
C527276:CXCR4 protein, human; C514936:CXCR4 protein, mouse; D054377:Chemokine CXCL12; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D019718:Receptors, CXCR4; D000643:Ammonium Chloride