Hypoxia-Inducible Factor-3.ALPHA. Functions as an Accelerator of 3T3-L1 Adipose Differentiation

Abstract

Adipose differentiation is a complex process associated with coordinated changes in gene expression, cell morphology, and hormone sensitivity.1) Several transcription factors influence these processes, among which peroxisome proliferator activated receptor g (PPARg) and CCAAT/enhancerbinding protein (C/EBP) family have been extensively studied.2,3) C/EBPb and C/EBPd are induced in the early stage of adipocyte differentiation and then mediate the expression of PPARg and C/EBPa. [4][5][6] In contrast to C/EBPd, C/EBPb is able to induce spontaneous differentiation in 3T3-L1 preadipocytes and enhance the adipogenic potential in NIH-3T3 fibroblasts. 5,6) Highly specific for adipose tissues, PPARg plays a critical role in the expression of most adipocyte-specific genes 7) and is able to convert nonadipogenic mesenchymal cells, such as fibroblasts and myoblasts, to adipocytes. 8,9) On the other hand, although developmentally necessary for adipogenesis, 10) C/EBPa is not always expressed during adipose differentiation and is critical in the establishment of insulin sensitivity. 11)Several recent studies have shown that hypoxia-inducible factor (HIF) is also involved in the regulation of adipose differentiation. [12][13][14] HIF is a transcriptional factor that plays a central role in oxygen homeostasis in mammalian cells by stimulating expression of oxygen-regulated genes related to erythropoiesis, angiogenesis, glucose uptake, and glycolysis. 15,16) HIF is a heterodimer composed of HIF-a and -b, both of which belong to basic helix-loop-helix (bHLH)/Per-ARNT-Sim (PAS) domain transcriptional factors.17) The HIFb subunit is identical to the arylhydrocarbon receptor nuclear translocator (ARNT) that also serves as a heterodimeric partner with the arylhydrocarbon receptor (AhR).18) In contrast, it appears that the HIF-a subunit's sole but critical function is to mediate the response to hypoxia. Under normoxic conditions, HIF-a subunits are hydroxylated at two conserved proline (Pro564 and Pro402 in HIF-1a) residues and one asparagine (Asn803 in HIF-1a) residue by HIF-a prolyl hydroxylases (PHD1, PHD2, and PHD3) and asaparagine hydroxylase FIH-1 (factor inhibiting HIF-1), respectively, and the hydroxylated HIF-a subunit proteins are destabilized and transcriptionally suppressed.19) Deprivation of oxygen by exposing cells to hypoxia prevents HIF hydroxylase activity and then stabilizes and transcriptionally activates HIF-a subunits. The first identified isoform of HIF-a, HIF-1a, was originally discovered as a high-affinity DNA-binding protein localized to the 3Ј hypoxia-responsive element (HRE) on the erythropoietin (EPO) gene. Using a subtraction cloning approach, Imagawa et al. found that HIF-1a mRNA is transiently induced in 3T3-L1 preadipocytes upon treatment with the adipogenic hormone cocktail containing insulin, dexamethasone, and 3-isobutyl-1-methylxanthine.12) Yun et al. found that HIF-1a represses PPARg2 gene expression and then inhibits adipogenesis through the induction of expression of transcriptional repressor DE...

Progress on hypoxia-inducible factor-3: Its structure, gene regulation and biological function (Review)

“…A similar previous study revealed that HIF-1α binds to the hypoxia response element (HRE) in the IPAS promoter and induces the expression of IPAS (36). However, the stabilized form of HIF-1α does not affect the mRNA expression levels of HIF-3α in zebrafish embryos (35) and 3T3-L1 cells (37). This contradictory result may be due to the different cell lines or animal models used in the experiments.…”

“…This contradictory result may be due to the different cell lines or animal models used in the experiments. In addition to HIF-1α, Hatanaka et al (37) observed that the promoter activity of HIF-3α is specifically activated by HIF-2α. HIF-2α specifically binds to the sequence between -251 and -228 in the mHIF-3α promoter, which is essential in response to the activation of HIF-2α (37).…”

“…In addition to HIF-1α, Hatanaka et al (37) observed that the promoter activity of HIF-3α is specifically activated by HIF-2α. HIF-2α specifically binds to the sequence between -251 and -228 in the mHIF-3α promoter, which is essential in response to the activation of HIF-2α (37). In human umbilical venous endothelial cells, the expression of HIF-3α is driven by HIF-1 and HIF-2 (18).…”

Hypoxia-inducible factor 3 biology: complexities and emerging themes

“…An in vivo study in zebrafish embryos showed that overexpression of stabilized Hif-1␣ did not change Hif-3␣ mRNA levels, while it increased the expression of igfbp-1a mRNA, a known Hif-1 target gene (55). It was reported that Hif-2␣ mediated hypoxiainduced Hif-3␣ gene expression in murine 3T3-L1 cells (13). Augstein et al (1) showed that human HIF-3␣2 mRNA expression in human umbilical venous endothelial cells (HUVECs) is induced by hypoxia and this hypoxic induction involves both HIF-1␣, HIF-2␣, and other factors.…”

“…These data suggest that IPAS/HIF-3␣4 negatively regulates tumor progression, likely by inhibiting HIF-1/2␣ activity. In cultured murine 3T3-L1 adipocytes, HIF-3␣ expression was induced during adipose differentiation and overexpression of HIF-3␣ at the early stage of differentiation accelerated 3T3-L1 adipocyte differentiation (13). Yamashita et al (52) disrupted the mouse Hif-3␣ locus using conventional gene knockout technology.…”