Hypoxia-Inducible Factor 3 Is an Oxygen-Dependent Transcription Activator and Regulates a Distinct Transcriptional Response to Hypoxia

Abstract

Hypoxia-inducible factors (HIFs) play key roles in the cellular response to hypoxia. It is widely accepted that whereas HIF-1 and HIF-2 function as transcriptional activators, HIF-3 inhibits HIF-1/2α action. Contrary to this idea, we show that zebrafish Hif-3α has strong transactivation activity. Hif-3α is degraded under normoxia. Mutation of P393, P493, and L503 inhibits this oxygen-dependent degradation. Transcriptomics and chromatin immunoprecipitation analyses identify genes that are regulated by Hif-3α, Hif-1α, or both. Under hypoxia or when overexpressed, Hif-3α binds to its target gene promoters and upregulates their expression. Dominant-negative inhibition and knockdown of Hif-3α abolish hypoxia-induced Hif-3α-promoter binding and gene expression. Hif-3α not only mediates hypoxia-induced growth and developmental retardation but also possesses hypoxia-independent activities. Importantly, transactivation activity is conserved and human HIF-3α upregulates similar genes in human cells. These findings suggest that Hif-3 is an oxygen-dependent transcription factor and activates a distinct transcriptional response to hypoxia.

The Role of Hypoxia-Inducible Factors in Cancer Resistance

“…The reasons of this reside not only on the initial discovery of a large array of HIF3α variants which has posed enormous challenges to study HIF3α-mediated physiological roles, but mainly on the prevailing view of HIF3α as a negative regulator of HIF1α and HIF2α actions, on the basis of the initial finding that two of its variants, lacking transactivation domains, act as negative regulators of HIF1α and HIF2α transactivating gene functions [9][10][11]. However, this dogma was refuted in 2014 by Zhang et al [12], which demonstrated that HIF3α functions as a transcriptional activator in zebrafish embryos. They showed that under hypoxia, Hif3α stabilizes and binds to HREs in the promoters of its target genes and upregulates their expression.…”

“…They have distinct or even opposite functions when tested by overexpression approaches [35]. For instance, while the full-length human HIF3α-1 can stimulate HRE-dependent reporter construct activity and upregulate unique target genes [8,12], human HIF3α-4 isoform, a shorter isoform that lacks the TAD domain, inhibits the activity of HIF-1α and HIF-2α [11,60] in a similar manner as mouse IPAS was shown to inhibit HIF-1α activity [9].…”

“…There are distinct groups of HIFα -regulated genes: (1) those that are up-regulated only by each HIFα subunit, (2) [12].…”

“…Inhibitor of NO production Macrophages [97] EPO Erythropoiesis Kidney [98][99][100] , liver [100,101] OCT4 pluripotency Mouse ES [84] , hESC [99] SCGB3A1 Secretoglobin 3A1 NSCLC [103] TGFα Growth Factor RCC [83,104] , HCC (HepG2 [105 , Huh7 [12] cells)…”

“…Involved in mTOR pathway HEK293 cells [12] LC3c Autophagy HEK293 cells [12] SQRDL Metabolism HEK293 cells [12] zp3v2 Embryogenesis Zebrafish [12] isg15* Chemotactic activity towards neutrophils, direction of ligated target proteins to intermediate filaments, cell-to-cell signaling, and antiviral activity during viral infections Zebrafish [12] sqrdl Metabolism: catalyze the conversion of sulfide to persulfides, thereby decreasing toxic concencrations of sulfide Zebrafish [12] EH546362 Zebrafish [12] gcnt7* Metabolism and O-linked glycosylation Zebrafish [12] mcl1b* BCL2 Family Apoptosis Regulator Zebrafish [12] casp8* Signaling pathways of apoptosis, necrosis and inflammation Zebrafish [12] REDD1: DNA Damage Inducible Transcript 4; LC3c (Autophagy-Related Protein LC3 C); SQRDL: Sulfide Quinone Reductase-Like (Yeast); zp3v2: zona pellucida glycoprotein 3d tandem duplicate 2; isg15: Interferon-Stimulated Protein, 15 KDa. *; sqrdl : Sulfide Quinone Reductase-Like; EH546362 (cystatin 14b, tandem duplicate 2); gcnt7: Glucosaminyl (N-Acetyl) Transferase Family Member 7*; mcl1b: myeloid cell leukemia 1b*; casp8: Caspase 8, Apoptosis-Related Cysteine Peptidase*.…”