Direct phosphorylation and stabilization of HIF-1α by PIM1 kinase drives angiogenesis in solid tumors

• Published in: Oncogene Vol. 40; no. 32; pp. 5142 - 5152
• Main Authors: Casillas, Andrea L., Chauhan, Shailender S., Toth, Rachel K., Sainz, Alva G., Clements, Amber N., Jensen, Corbin C., Langlais, Paul R., Miranti, Cindy K., Cress, Anne E., Warfel, Noel A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12-08-2021; Nature Publishing Group
• Subjects: 13/1; 13/106; 13/51; 13/95; 14/5; 14/63; 38/77; 59/5; 631/67/2328; 631/80/458/1733; 64/60; 82/58; Angiogenesis; Animals; Apoptosis; Basic Helix-Loop-Helix Transcription Factors - metabolism; Cell Biology; Cell Line, Tumor; CRISPR; Cytotoxicity; Degradation; Disease Models, Animal; Gene Expression Regulation, Neoplastic; Heterografts; Human Genetics; Humans; Hypoxia; Hypoxia-inducible factor 1; Hypoxia-Inducible Factor 1, alpha Subunit - genetics; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Hypoxia-inducible factor 1a; Internal Medicine; Kinases; Medicine; Medicine & Public Health; Mice; Mutation; Neoplasms - etiology; Neoplasms - metabolism; Neoplasms - pathology; Neovascularization, Pathologic - etiology; Neovascularization, Pathologic - metabolism; Oncology; Oxygen tension; Phosphorylation; Post-translation; Protein Binding; Protein Stability; Proto-Oncogene Proteins c-pim-1 - antagonists & inhibitors; Proto-Oncogene Proteins c-pim-1 - genetics; Proto-Oncogene Proteins c-pim-1 - metabolism; Solid tumors; Therapeutic targets; Threonine; Transcription; Tumors; Xenografts
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/s41388-021-01915-1

Angiogenesis is essential for the sustained growth of solid tumors. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of angiogenesis and constitutive activation of HIF-1 is frequently observed in human cancers. Therefore, understanding the mechanisms governing the activation of HIF-1 is critical for successful therapeutic targeting of tumor angiogenesis. Herein, we establish a new regulatory mechanism responsible for the constitutive activation of HIF-1α in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1α at threonine 455, a previously uncharacterized site within its oxygen-dependent degradation domain. This phosphorylation event disrupts the ability of prolyl hydroxylases to bind and hydroxylate HIF-1α, interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Moreover, phosphorylation of the analogous site in HIF-2α (S435) stabilizes the protein through the same mechanism, indicating post-translational modification within the oxygen-dependent degradation domain as a mechanism of regulating the HIF-α subunits. In vitro and in vivo models demonstrate that expression of PIM1 is sufficient to stabilize HIF-1α and HIF-2α in normoxia and stimulate angiogenesis in a HIF-1-dependent manner. CRISPR mutants of HIF-1α (Thr455D) promoted increased tumor growth, proliferation, and angiogenesis. Moreover, HIF-1α-T455D xenograft tumors were refractory to the anti-angiogenic and cytotoxic effects of PIM inhibitors. These data identify a new signaling axis responsible for hypoxia-independent activation of HIF-1 and expand our understanding of the tumorigenic role of PIM1 in solid tumors.