Differential signaling pathways of HO-1 gene expression in pulmonary and systemic vascular cells.
Heme oxygenase-1 (HO-1) is induced by oxidative stress and plays an important role in cellular protection against oxidant injury. Increasing evidence also suggests that HO-1 is markedly modulated by hypoxia in vitro and in vivo. Our group has previously demonstrated that the transcription factor hypoxia-inducible factor (HIF)-1 mediates hypoxia-induced HO-1 gene transcription and expression in systemic (aortic) vascular smooth muscle (AoVSM) cells (P. J. Lee, B. -H. Jiang, B. Y. Chin, N. V. Iyer, J. Alam, G. L. Semenza, and A. M. K. Choi. J. Biol. Chem. 272: 5375-5381, 1997). Because the pulmonary circulation is an important target of hypoxia, this study investigated whether HO-1 gene expression in pulmonary arterial vascular smooth muscle was differentially regulated by hypoxia in comparison to AoVSM cells. Interestingly, hypoxia neither induced HO-1 gene expression nor increased HIF-1 DNA binding activity in pulmonary arterial vascular smooth muscle cells. Conversely, pulmonary arterial endothelial cells (PAECs) demonstrated a marked induction of HO-1 gene expression after hypoxia. Electrophoretic mobility shift assays detected an increase in activator protein-1 rather than in HIF-1 DNA binding activity in nuclear extracts of hypoxic PAECs. Analyses of the promoter and 5'-flanking regions of the HO-1 gene were performed by transiently transfecting PAECs with either the hypoxia response element (HIF-1 binding site) or the HO-1 gene distal enhancer element (AB1) linked to a chloramphenicol acetyltransferase reporter gene. Increased chloramphenicol acetyltransferase activity was observed only in transfectants containing the AB1 distal enhancer, and mutational analysis of this enhancer suggested that the activator protein-1 regulatory element was critical for hypoxia-induced HO-1 gene transcription. Collectively, our data demonstrate that the molecular regulation of HO-1 gene transcription during hypoxia differs between the systemic and pulmonary circulations and also provide evidence that hypoxia-induced HO-1 gene expression in PAECs and AoVSM cells is regulated through two discrete signaling pathways.
Hartsfield
C L
CL
Division of Pulmonary and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224, USA.
Alam
J
J
Choi
A M
AM
D000818:Animals; D015152:Blotting, Northern; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology; D004742:Enhancer Elements, Genetic / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics*; D051547:Heme Oxygenase-1; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D011651:Pulmonary Artery / Q000166:cytology / Q000201:enzymology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000235:genetics; D014157:Transcription Factors
D004268:DNA-Binding Proteins; C497444:Hif1a protein, rat; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1