Contribution of HIF-1alpha or HIF-2alpha to erythropoietin expression: in vivo evidence based on chromatin immunoprecipitation.
Circulating erythropoietin (EPO) is mainly produced by the kidneys and mediates erythrogenesis in bone marrow and nonhematopoietic cell survival. EPO is also produced in other tissues where it functions as a paracrine. Moreover, the hypoxic induction of EPO is known to be mediated by HIF-1alpha and HIF-2alpha, but it remains obscure as to which of these two mediators mainly contributes to EPO expression. Thus, we designed in vivo experiments to evaluate the contributions made by HIF-1alpha and HIF-2alpha to EPO expression. In mice exposed to mild whole body hypoxia, HIF-1alpha and HIF-2alpha were both induced in all tissues examined. However, EPO mRNA was expressed in kidney and brain, but not in liver and lung. Likewise, chromatin immunoprecipitation (CHIP) analyses demonstrated that HIF-1alpha or HIF-2alpha binding to the EPO gene increased under hypoxic conditions only in kidney and brain. A comparison of CHIP data and EPO mRNA levels suggested that, during mild hypoxia, renal EPO transcription is induced equally by HIF-1alpha and HIF-2alpha, but that brain EPO is mainly induced during hypoxia by HIF-2alpha. Thus, HIF-1alpha and HIF-2alpha appear to contribute to EPO expression tissue specifically.
Yeo
Eun-Jin
EJ
Department of Pharmacology, College of Medicine, Seoul National University, 28 Yongon-dong, Chongno-gu, Seoul, 110-799, South Korea.
Cho
Young-Suk
YS
Kim
Myung-Suk
MS
Park
Jong-Wan
JW
D000818:Animals; D047369:Chromatin Immunoprecipitation; D004921:Erythropoietin / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009928:Organ Specificity; D012333:RNA, Messenger / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics
C485502:HIF-2 protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D014157:Transcription Factors; D004921:Erythropoietin