CHARACTERIZATION OF ENDOGENOUS HYPDXIA-INDUCED TRANSCRIPTIONAL REPRESSOR HIF-3ALPHA

点击翻译按钮获取中文摘要

Hypoxia-inducible factor (HIF) is an important transcriptional factor that is activated when mammalian cells experience hypoxia, a tumor microenvironmental condition that plays a pivotal role in tumor progression and treatment. HIF consists of oxygen-sensitive HIF-α and constitutively expressed HIF-β subunits. The recently identified third member of the human HIF-α, HIF-3α, produces multiple splicing variants. Here we cloned cDNA for one of the splicing variants of human HIF-3α, HIF-3α2, from human kidney and examined its characteristics. HIF-3α2, as well as the first identified HIF-3α variant HIF-3α1, localized in the nucleus and was stabilized under hypoxia when ectopically expressed in COS-7 cells. However, reporter gene analysis showed that HIF-3α2 failed to activate HIF-mediated transcription and conversely suppressed it, although HIF-3a1 with an N-terminal domain identical to HIF-3α2 had the ability to activate it. C-terminal deletion analysis revealed that the C-terminal moiety of HIF-3α2 masked its own transcriptional activity. We further showed that overexpression of HIF-3α2 in renal carcinoma VMRC inhibited both hypoxia-inducible gene expression in vitro and growth as xenografts in vivo. These results indicated that HIF-3α2, which is stabilized under hypoxia, functions as a negative regulator of hypoxia-inducible gene expression in a novel feedback mechanism.