HIF-1α Hydroxyprolines Modulate Oxygen-Dependent Protein Stability Via Single VHL Interface With Comparable Effect on...

Area of Science:

• Molecular Biology
• Cellular Regulation
• Biophysics

Background:

• The von Hippel-Lindau (VHL) E3 ubiquitin ligase targets hypoxia-inducible factor alpha (HIF-1α) for degradation under normoxia.
• Oxygen-dependent regulation of HIF-1α involves prolyl hydroxylation of conserved proline residues (P402, P564) in the oxygen-dependent degradation domain (ODD).
• The precise functional significance of having one versus two hydroxylated prolines for VHL binding and subsequent ubiquitination remains unclear.

Purpose of the Study:

• To investigate the biophysical and cellular implications of single versus dual proline hydroxylation in the HIF-1α ODD.
• To elucidate the role of proline hydroxylation in VHL binding affinity, ubiquitination rates, and intracellular stability of HIF-1α.
• To determine the contribution of proline hydroxylation to the oxygen-dependent stability profile of HIF-1α.

Main Methods:

• Biophysical analyses (e.g., binding assays) to assess VHL-HIF-1α ODD interactions.
• In vitro ubiquitination assays using purified VHL E3 ligase and modified HIF-1α ODD.
• Intracellular stability assays to evaluate the impact of proline hydroxylation on HIF-1α levels under varying oxygen conditions.

Main Results:

• Both single and dual hydroxyprolines bind to the same VHL interface with comparable affinity.
• VHL binding affinity and in vitro ubiquitination rates are similar for ODD with one or two hydroxyprolines.
• Dual hydroxyprolines can accommodate two VHL molecules, and distinct contributions to intracellular HIF-1α ODD stability were observed.
• The graduated stability of HIF-1α across oxygen levels is not solely due to VHL binding or ubiquitination.

Conclusions:

• The number of hydroxylated prolines in HIF-1α ODD does not significantly alter VHL binding affinity or ubiquitination efficiency per VHL molecule.
• Distinct roles of the two hydroxyprolines in regulating intracellular HIF-1α stability suggest a more nuanced mechanism than previously understood.
• The oxygen-dependent stability profile of HIF-1α is likely governed by the preceding prolyl hydroxylase activity rather than the VHL-mediated degradation step itself.