Transcriptional Regulation of the Hypoxia Inducible Factor-2 a ( HIF-2 a ) Gene during Adipose Differentiation in 3 T 3L 1 Cells

EPAS1, HLF, or MOP2, is a basic-helix-loop-helix/PAS domain transcription factor that is expressed preferentially in vascular endothelial cells, the organ of Zuckerland I, and adipocytes. HIF-2a regulates the expression of several genes including vascular endothelial growth factor and is involved in the mature vessel construction. Although HIF2a was originally identified as a factor responsible for hypoxia responses, a study using HIF-2a knockout mice revealed that, even under normoxia conditions, HIF-2a plays a role in several physiologic events such as hematopoiesis, catecholamine homeostasis and maintenance of the reactive oxygen species levels. We recently demonstrated that HIF-2a expression is induced during adipose differentiation in vivo and in vitro. Adipose differentiation is regulated by the sequential activation of several transcription factors including the peroxisome proliferator-activated receptor (PPAR) g2 and the CCAAT/ enhancer-binding proteins (C/EBP). PPARg2 plays a leading role in synthesis and accumulation of lipid droplets in adipocytes. On the other hand, C/EBPa is critical in the establishment of insulin sensitivity. Like C/EBPa , HIF-2a regulates cellular insulin sensitivity and promotes adipogenesis via the direct transcriptional activation of Glut1, Glut4, and IRS3 genes. Overexpression of dominant negative form of HIF-2a results in suppression of adipogenesis. Also, adipose tissues in HIF-2a KO mice are smaller than those in control mice (Garcia, J. A., personal communication). Therefore, induction of HIF-2a expression is necessary for execution of adipose differentiation program. Despite better understanding of the HIF-2a functions in adipocytes, the mechanism by which the expression of HIF2a gene is up-regulated during adipose differentiation is still poorly understood. Therefore, in this study, we analyzed HIF-2a promoter activity during adipose differentiation in 3T3-L1 cells. We here showed that the sequence –478/–445 is responsible for the up-regulation of HIF-2a expression during adipose differentiation and that the activity of this region is controlled by Sp1 and Sp3.