Week 10 - HIF

Question 1

How do HIF subunits respond to hypoxia?

Answer 1

• Hypoxia-Inducible Factor
• β subunits always present in nucleus
• alpha subunits sensitive to oxygen levels in cytoplasm
• its stability regulated by hydroxylation of asparagine and proline
• no ligand binding site makes it a transcription factor
• not nuclear receptor

Question 2

How does HIF work during normoxia?

Answer 2

• Prolyl Hydroxylase Domain (PHD) enzyme adds hydroxyl groups to HIF-1α N-terminus proline
• requires O₂ as substrate
• Fe²⁺ and 2 Oxide Glutamates (OG) as co-factors
• pVHL will target the hydroxylated proline
• adds ubiquitin for degradation by proteasome
• FIH hydroxylates C-terminus asparagine
• prevents DNA binding

Question 3

How does HIF work in hypoxia?

Answer 3

• lack of oxygen stops PHD from working
• most oxygen sensitive
• stops HIF-1α degradation
• only partial gene expression
• due to FIH still stopping DNA binding
• oxygen concentration decreases further
• HIF-1α can translocate to nucleus
• bind to HIF-1β
• recruits CBP and p300 co-activators