PI3K-mTORC2 but not PI3K-mTORC1 regulates transcription of HIF2A/EPAS1 and vascularization in neuroblastoma

Cancer Res. 2015 Nov 1;75(21):4617-28. doi: 10.1158/0008-5472.CAN-15-0708. Epub 2015 Oct 2.

Abstract

Hypoxia-inducible factor (HIF) is a master regulator of cellular responses to oxygen deprival with a critical role in mediating the angiogenic switch in solid tumors. Differential expression of the HIF subunits HIF1α and HIF2α occurs in many human tumor types, suggesting selective implications to biologic context. For example, high expression of HIF2α that occurs in neuroblastoma is associated with stem cell-like features, disseminated disease, and poor clinical outcomes, suggesting pivotal significance for HIF2 control in neuroblastoma biology. In this study, we provide novel insights into how HIF2α expression is transcriptionally controlled by hypoxia and how this control is abrogated by inhibition of insulin-like growth factor-1R/INSR-driven phosphoinositide 3-kinase (PI3K) signaling. Reducing PI3K activity was sufficient to decrease HIF2α mRNA and protein expression in a manner with smaller and less vascularized tumors in vivo. PI3K-regulated HIF2A mRNA expression was independent of Akt or mTORC1 signaling but relied upon mTORC2 signaling. HIF2A mRNA was induced by hypoxia in neuroblastoma cells isolated from metastatic patient-derived tumor xenografts, where HIF2A levels could be reduced by treatment with PI3K and mTORC2 inhibitors. Our results suggest that targeting PI3K and mTORC2 in aggressive neuroblastomas with an immature phenotype may improve therapeutic efficacy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Animals
  • Antigens, CD / genetics
  • Antigens, CD / metabolism
  • Basic Helix-Loop-Helix Transcription Factors / biosynthesis
  • Basic Helix-Loop-Helix Transcription Factors / genetics*
  • Cell Line, Tumor
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / biosynthesis
  • Mechanistic Target of Rapamycin Complex 1
  • Mechanistic Target of Rapamycin Complex 2
  • Mice
  • Mice, Nude
  • Multiprotein Complexes / metabolism*
  • Neovascularization, Pathologic / genetics*
  • Neovascularization, Pathologic / pathology
  • Neuroblastoma / blood supply*
  • Neuroblastoma / genetics
  • Neuroblastoma / pathology
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism
  • RNA Interference
  • RNA, Messenger / biosynthesis
  • RNA, Small Interfering
  • Receptor, IGF Type 1
  • Receptor, IGF Type 2 / genetics
  • Receptor, Insulin / genetics
  • Receptor, Insulin / metabolism
  • Receptors, Somatomedin / genetics
  • Receptors, Somatomedin / metabolism
  • Regulatory-Associated Protein of mTOR
  • Signal Transduction / physiology
  • TOR Serine-Threonine Kinases / metabolism*
  • Transcription, Genetic / genetics

Substances

  • Adaptor Proteins, Signal Transducing
  • Antigens, CD
  • Basic Helix-Loop-Helix Transcription Factors
  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • IGF1R protein, human
  • Multiprotein Complexes
  • Phosphoinositide-3 Kinase Inhibitors
  • RNA, Messenger
  • RNA, Small Interfering
  • RPTOR protein, human
  • Receptor, IGF Type 2
  • Receptors, Somatomedin
  • Regulatory-Associated Protein of mTOR
  • endothelial PAS domain-containing protein 1
  • INSR protein, human
  • Receptor, IGF Type 1
  • Receptor, Insulin
  • AKT1 protein, human
  • Mechanistic Target of Rapamycin Complex 1
  • Mechanistic Target of Rapamycin Complex 2
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases