Direct interaction between mortalin and HIF‐1α at the mitochondria inhibits apoptosis by blocking recruitment of Bax

• Published in: The FEBS journal 2023-08, Vol.290 (15), p.3764-3780
• Main Authors: Yfantis, Angelos, Mylonis, Ilias, Simos, George
• Format: Article
• Language: English
• Subjects: Apoptosis; Bax; BAX protein; Binding sites; Cell death; HIF‐1α; Hypoxia; Immunoprecipitation; Localization; Lymphoma; Mitochondria; mortalin; Natural products; p53 Protein; Phosphorylation; Protein B; Protein interaction; Proteins
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.16762

Hypoxia‐inducible factor‐1, a heterodimer of alpha (HIF‐1α) and beta (HIF‐1β or ARNT) subunits, is a major regulator of the transcriptional response to hypoxia. However, HIF‐1α, the oxygen‐regulated subunit, also exerts nontranscriptional functions through interaction with proteins other than ARNT. We have previously shown that the subcellular localization and protein interactions of HIF‐1α are controlled by ERK‐mediated phosphorylation at Ser641/643. When HIF‐1α is modified at these sites, it is nuclear, binds to ARNT, interacts with nucleophosmin 1 (NPM1) and activates transcription of hypoxia‐target genes. On the contrary, unmodified HIF‐1α is bound by chromosomal region maintenance 1 (CRM1), exits the nucleus and, via its association with mortalin, is targeted to the mitochondria to form an antiapoptotic complex. To further characterize the latter function, recombinant fragments of HIF‐1α and mortalin were used for in vitro binding assays and immunoprecipitation experiments to map the respective binding sites and show that their interaction is direct and functional. We could also show that embelin, a natural product and known inhibitor of the mortalin‐p53 interaction, also disrupts the mortalin‐HIF‐1α association and, furthermore, removes unmodified HIF‐1α from mitochondria. Mitochondrial dissociation of HIF‐1α, either by embelin or overexpression of a HIF‐1α peptide harbouring the mortalin binding site, under stress conditions leads to mitochondrial localization of the pro‐apoptotic protein B‐cell lymphoma 2‐associated X protein (Bax) and induction of apoptosis. We suggest that when ERK activity is low under hypoxia, binding of HIF‐1α to mortalin inhibits mitochondrial recruitment of Bax and protects cells from apoptotic cell death. When hypoxia is combined with extracellular signal‐regulated kinase 1/2 (ERK1/2) inactivation, direct interaction between the ERK1/2‐targeted domain of HIF‐1α (HIF‐1α‐ETD) and the substrate‐binding domain‐variable domain of mortalin (mortalin‐SBD‐VD) targets HIF‐1α to mitochondria, blocks B‐cell lymphoma 2‐associated X protein (Bax) mitochondrial recruitment and inhibits apoptosis. Overexpressed HIF‐1α lacking ERK1/2‐mediated phosphorylation acts likewise in etoposide‐treated normoxic cells. Treatment with embelin or overexpression of HIF‐1α‐ETD or mortalin‐SBD‐VD disrupts the mortalin/HIF‐1α interaction, removes HIF‐1α from mitochondria, allows Bax mitochondrial recruitment and induces apoptosis.