A long hypoxia-inducible factor 3 isoform 2 is a transcription activator that regulates erythropoietin

• Published in: Cellular and molecular life sciences : CMLS Vol. 77; no. 18; pp. 3627 - 3642
• Main Authors: Tolonen, Jussi-Pekka, Heikkilä, Minna, Malinen, Marjo, Lee, Hang-Mao, Palvimo, Jorma J., Wei, Gong-Hong, Myllyharju, Johanna
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.09.2020; Springer Nature B.V
• Subjects: Alternative splicing; Apoptosis Regulatory Proteins - antagonists & inhibitors; Apoptosis Regulatory Proteins - genetics; Apoptosis Regulatory Proteins - metabolism; Binding; Biochemistry; Biomedical and Life Sciences; Biomedicine; Bone Morphogenetic Protein 6 - genetics; Bone Morphogenetic Protein 6 - metabolism; C-Reactive Protein - genetics; C-Reactive Protein - metabolism; Cell Biology; Cell Hypoxia; Cell Line, Tumor; Chromatin; Chromatin - metabolism; chromatin immunoprecipitation; Dimerization; Dimers; Down-regulation; Erythropoietin; Erythropoietin - analysis; Erythropoietin - genetics; Erythropoietin - metabolism; Genes; Glucose Transporter Type 1 - genetics; Glucose Transporter Type 1 - metabolism; Homeostasis; Humans; Hypoxia; Immunoprecipitation; Isoforms; Life Sciences; luciferase; Original; Original Article; Oxygen; Promoter Regions, Genetic; Protein Binding; Protein Isoforms - antagonists & inhibitors; Protein Isoforms - genetics; Protein Isoforms - metabolism; Regulatory sequences; Repressor Proteins - antagonists & inhibitors; Repressor Proteins - genetics; Repressor Proteins - metabolism; RNA Interference; RNA Splicing; RNA, Small Interfering - metabolism; Serum Amyloid P-Component - genetics; Serum Amyloid P-Component - metabolism; siRNA; Splicing; Transcription factors; Transcriptional Activation; Vertebrates; Chromatin immunoprecipitation; Hypoxia-inducible factor 3 isoform; Transcription activator; Erythropoietin; Hypoxia response; Hypoxia response element
• DOI: 10.1007/s00018-019-03387-9
• ISSN: 1420-682X; 1420-9071

Hypoxia-inducible factor (HIF), an αβ dimer, is the master regulator of oxygen homeostasis with hundreds of hypoxia-inducible target genes. Three HIF isoforms differing in the oxygen-sensitive α subunit exist in vertebrates. While HIF-1 and HIF-2 are known transcription activators, HIF-3 has been considered a negative regulator of the hypoxia response pathway. However, the human HIF3A mRNA is subject to complex alternative splicing. It was recently shown that the long HIF-3α variants can form αβ dimers that possess transactivation capacity. Here, we show that overexpression of the long HIF-3α2 variant induces the expression of a subset of genes, including the erythropoietin ( EPO ) gene, while simultaneous downregulation of all HIF-3α variants by siRNA targeting a shared HIF3A region leads to downregulation of EPO and additional genes. EPO mRNA and protein levels correlated with HIF3A silencing and HIF-3α2 overexpression. Chromatin immunoprecipitation analyses showed that HIF-3α2 binding associated with canonical hypoxia response elements in the promoter regions of EPO . Luciferase reporter assays showed that the identified HIF-3α2 chromatin-binding regions were sufficient to promote transcription by all three HIF-α isoforms. Based on these data, HIF-3α2 is a transcription activator that directly regulates EPO expression.