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

• Published in: Oncogene 2021-08, Vol.40 (32), p.5142
• 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: Article
• Language: English
• Subjects: Cancer; Development and progression; Gene expression; Genetic aspects; Health aspects; Neovascularization; Oncology, Experimental; Phosphorylation; Protein kinases; Proto-oncogenes; Transcription factors; Tumors
• ISSN: 0950-9232
• 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-1[alpha] in cancer, irrespective of oxygen tension. PIM1 kinase directly phosphorylates HIF-1[alpha] 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-1[alpha], interrupting its canonical degradation pathway and promoting constitutive transcription of HIF-1 target genes. Moreover, phosphorylation of the analogous site in HIF-2[alpha] (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-[alpha] subunits. In vitro and in vivo models demonstrate that expression of PIM1 is sufficient to stabilize HIF-1[alpha] and HIF-2[alpha] in normoxia and stimulate angiogenesis in a HIF-1-dependent manner. CRISPR mutants of HIF-1[alpha] (Thr455D) promoted increased tumor growth, proliferation, and angiogenesis. Moreover, HIF-1[alpha]-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.