Hypoxia-induced expression of RTEF-1 (related transcriptional enhancer factor-1) in endothelial cells is independent of HIF-1 (hypoxia-inducible factor-1)

Area of Science:

• Molecular Biology
• Cell Biology
• Physiology

Background:

• Related transcriptional enhancer factor-1 (RTEF-1) regulates angiogenic genes in hypoxic endothelial cells.
• The precise mechanisms of RTEF-1 induction during hypoxia remain unclear.

Purpose of the Study:

• To investigate the role of hypoxia-inducible factor-1 (HIF-1) in the hypoxia-induced upregulation of RTEF-1.
• To elucidate the function of RTEF-1 in endothelial cell angiogenesis under hypoxic conditions.

Main Methods:

• Western blot and quantitative PCR to measure RTEF-1 levels in bovine aortic endothelial cells (BAEC) under hypoxia.
• Experiments using HIF-1 deficient and positive hepatoma cell lines exposed to hypoxia.
• Immunofluorescence and Western blotting to assess RTEF-1 protein expression.
• HIF-1alpha promoter activity assays and siRNA-mediated RTEF-1 knockdown in BAEC.
• Assessment of BAEC proliferation and tubule formation.

Main Results:

• Hypoxia significantly increased both RTEF-1 mRNA and protein levels in BAEC.
• RTEF-1 upregulation by hypoxia occurred independently of HIF-1.
• RTEF-1 overexpression enhanced HIF-1alpha promoter activity (3.6-fold).
• RTEF-1 promoted BAEC proliferation and tubule formation, which were attenuated by RTEF-1 knockdown.

Conclusions:

• HIF-1 is not required for the hypoxic induction of RTEF-1.
• RTEF-1 acts as a regulator of HIF-1, influencing its expression.
• RTEF-1 is a critical regulator of angiogenesis in response to hypoxia, potentially acting through HIF-1.