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

Oncogene. 2021 Aug;40(32):5142-5152. doi: 10.1038/s41388-021-01915-1. Epub 2021 Jul 2.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Cell Line, Tumor
  • Disease Models, Animal
  • Gene Expression Regulation, Neoplastic
  • Heterografts
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / genetics
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
  • Mice
  • Mutation
  • Neoplasms / etiology*
  • Neoplasms / metabolism*
  • Neoplasms / pathology
  • Neovascularization, Pathologic / etiology*
  • Neovascularization, Pathologic / metabolism*
  • Phosphorylation
  • 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*


  • Basic Helix-Loop-Helix Transcription Factors
  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • endothelial PAS domain-containing protein 1
  • PIM1 protein, human
  • Proto-Oncogene Proteins c-pim-1