Hypoxia-associated induction of early growth response-1 gene expression.
The paradigm for the response to hypoxia is erythropoietin gene expression; activation of hypoxia-inducible factor-1 (HIF-1) results in erythropoietin production. Previously, we found that oxygen deprivation induced tissue factor, especially in mononuclear phagocytes, by an early growth response (Egr-1)-dependent pathway without involvement of HIF-1 (Yan, S.-F., Zou, Y.-S., Gao, Y., Zhai, C., Mackman, N., Lee, S., Milbrandt, J., Pinsky, D., Kisiel, W., and Stern, D. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 8298-8303). Now, we show that cultured monocytes subjected to hypoxia (pO2 approximately 12 torr) displayed increased Egr-1 expression because of de novo biosynthesis, with a approximately 10-fold increased rate of transcription. Transfection of monocytes with Egr-1 promoter-luciferase constructs localized elements responsible for hypoxia-enhanced expression to -424/-65, a region including EBS (ets binding site)-SRE (serum response element)-EBS and SRE-EBS-SRE sites. Further studies with each of these regions ligated to the basal thymidine kinase promoter and luciferase demonstrated that EBS sites in the element spanning -424/-375 were critical for hypoxia-enhanceable gene expression. These data suggested that an activated ets factor, such as Elk-1, in complex with serum response factor, was the likely proximal trigger of Egr-1 transcription. Indeed, hypoxia induced activation of Elk-1, and suppression of Elk-1 blocked up-regulation of Egr-1 transcription. The signaling cascade preceding Elk-1 activation in response to oxygen deprivation was traced to activation of protein kinase C-betaII, Raf, mitogen-activated protein kinase/extracellular signal-regulated protein kinase kinase and mitogen-activated protein kinases. Comparable hypoxia-mediated Egr-1 induction and activation were observed in cultured hepatoma-derived cells deficient in HIF-1beta and wild-type hepatoma cells, indicating that the HIF-1 and Egr-1 pathways are initiated independently in response to oxygen deprivation. We propose that activation of Egr-1 in response to hypoxia induces a different facet of the adaptive response than HIF-1, one component of which causes expression of tissue factor, resulting in fibrin deposition.
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology; D015687:Cell Hypoxia / Q000235:genetics*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051766:Early Growth Response Protein 1; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D007527:Isoenzymes / Q000502:physiology; D048728:MAP Kinase Kinase Kinase 1; D009687:Nuclear Proteins / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D064546:Protein Kinase C beta; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*