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

ABSTRACT: Hypoxia-inducible factor (HIF), an ?? dimer, is the master regulator of oxygen homeostasis with hundreds of hypoxia-inducible target genes. Three HIF isoforms differing in the oxygen-sensitive ? 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-3? variants can form ?? dimers that possess transactivation capacity. Here, we show that overexpression of the long HIF-3?2 variant induces the expression of a subset of genes, including the erythropoietin (EPO) gene, while simultaneous downregulation of all HIF-3? 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-3?2 overexpression. Chromatin immunoprecipitation analyses showed that HIF-3?2 binding associated with canonical hypoxia response elements in the promoter regions of EPO. Luciferase reporter assays showed that the identified HIF-3?2 chromatin-binding regions were sufficient to promote transcription by all three HIF-? isoforms. Based on these data, HIF-3?2 is a transcription activator that directly regulates EPO expression.

SUBMITTER: Tolonen JP 

PROVIDER: S-EPMC7452874 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature