Mammalian tumor suppressor Int6 specifically targets hypoxia inducible factor 2 alpha for degradation by hypoxia- and pVHL-independent regulation.

Abstract

The hypoxia-inducible factors HIF-1 alpha and HIF-2 alpha are structurally similar as regards their DNA-binding and dimerization domains, but differ in their transactivation domains and, as is shown by experiments using hif-1 alpha(-/-) and hif-2 alpha(-/-) mice, in their functions. This implies that HIF-1 alpha and HIF-2 alpha may have unique target genes. To address this discrepancy and identify HIF-2 alpha-specific target genes, we performed yeast two-hybrid analysis and identified the tumor suppressor Int6/eIF3e/p48 as a novel target gene product involved in HIF-2 alpha regulation. The int6 gene was first identified from a screen in which the mouse mammary tumor virus was employed as an insertional mutagen to identify genes whose functions are critical for breast tumor formation. Here, by using two-hybrid analysis, immunoprecipitation in mammalian cells, and HRE-reporter assays, we report the specific interaction of HIF-2 alpha (but not HIF-1 alpha or HIF-3 alpha) with Int6. The results indicate that the direct interaction of Int6 induces proteasome inhibitor-sensitive HIF-2 alpha degradation. This degradation was clearly observed in renal cell carcinoma 786-O cells, and was found to be both hypoxia- and pVHL-independent. Furthermore, Int6 protein knockdown by int6-siRNA vectors or the dominant-negative mutant Int6-Delta C increased endogenous HIF-2 alpha expression, even under normoxia, and induced sets of critical angiogenic factors comprising vascular endoplasmic growth factor, angiopoietin, and basic fibroblast growth factor mRNA. These results indicate that Int6 is a novel and critical determinant of HIF-2 alpha-dependent angiogenesis as well as cancer formation, and that int6-siRNA transfer may be an effective therapeutic strategy in pathological conditions such as heart and brain ischemia, hepatic cirrhosis, and obstructive vessel diseases.

• Authors: Li Chen, Kazuyo Uchida, Alexander Endler, Futoshi Shibasaki
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 282 Issue 17 Pg. 12707-16 (Apr 27 2007) ISSN: 0021-9258 [Print] United States
• PMID: 17324924 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Basic Helix-Loop-Helix Transcription Factors
• Eukaryotic Initiation Factor-3
• Intercellular Signaling Peptides and Proteins
• endothelial PAS domain-containing protein 1
• Von Hippel-Lindau Tumor Suppressor Protein

Topics

• Animals
• Basic Helix-Loop-Helix Transcription Factors (genetics, metabolism)
• Cell Hypoxia
• Eukaryotic Initiation Factor-3 (antagonists & inhibitors, metabolism)
• HeLa Cells
• Humans
• Intercellular Signaling Peptides and Proteins (biosynthesis, genetics)
• Mice
• Mice, Knockout
• Neoplasms (drug therapy, metabolism)
• Neovascularization, Pathologic (drug therapy, metabolism)
• Von Hippel-Lindau Tumor Suppressor Protein (metabolism)