mTORC2 regulates hedgehog pathway activity by promoting stability to Gli2 protein and its nuclear translocation

Cell Death Dis. 2017 Jul 13;8(7):e2926. doi: 10.1038/cddis.2017.296.

Abstract

mTORC2 is aberrantly activated in cancer and therefore is considered to be an important therapeutic target. The hedgehog pathway, which is also often hyperactivated, regulates transcription of several genes associated with angiogenesis, metastasis, cellular proliferation and cancer stem cell (CSC) regeneration. However, the contribution of mTORC2 toward hedgehog pathway activity has not been explored yet. Here we have addressed the molecular cross talk between mTORC2 and hedgehog pathway activities in the context of glioblastoma multiforme, a malignant brain tumor using as a model system. We observed that higher mTORC2 activity enhanced the expression of a few hedgehog pathway molecules (Gli1, Gli2 and Ptch1) and amplified its target genes (Cyclin D1, Cyclin D2, Cyclin E, Snail, Slug and VEGF) both in mRNA and protein levels as corroborated by increased metastasis, angiogenesis, cellular proliferation and stem cell regeneration. Inhibition of mTORC2 formation decreased hedgehog pathway activity and attenuated all these above-mentioned events, suggesting their cross talk with each other. Further investigations revealed that mTORC2 inhibited ubiquitination of Gli2 by inactivating GSK3β, and thus it promotes stability to Gli2 and its nuclear translocation. Moreover, enhanced mTORC2 activity led to the increased clonogenic properties and CD133+ cells, indicating its role in CSC regeneration. mTORC2 inhibitor directed the reduction of hedgehog pathway proteins and also reduced CSCs. Thus, our observations support a role for elevated mTORC2 activity in regulating angiogenesis, metastasis, cellular proliferation and CSC regeneration via hedgehog pathway activity. Taken together, it provides a rationale for including the mTOR2 inhibitor as part of the therapeutic regimen for CSCs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbazoles / pharmacology
  • Cell Line, Tumor
  • Cell Movement / drug effects
  • Cell Nucleus / metabolism*
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Cyclin E / genetics
  • Cyclin E / metabolism
  • Glioblastoma / metabolism
  • Glioblastoma / pathology
  • Glycogen Synthase Kinase 3 beta / antagonists & inhibitors
  • Glycogen Synthase Kinase 3 beta / metabolism
  • Hedgehog Proteins / metabolism*
  • Humans
  • Mechanistic Target of Rapamycin Complex 2 / antagonists & inhibitors
  • Mechanistic Target of Rapamycin Complex 2 / metabolism*
  • Neoplastic Stem Cells / cytology
  • Neoplastic Stem Cells / drug effects
  • Neoplastic Stem Cells / metabolism
  • Nuclear Proteins / antagonists & inhibitors
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Rapamycin-Insensitive Companion of mTOR Protein / antagonists & inhibitors
  • Rapamycin-Insensitive Companion of mTOR Protein / genetics
  • Rapamycin-Insensitive Companion of mTOR Protein / metabolism
  • Signal Transduction* / drug effects
  • Snail Family Transcription Factors / genetics
  • Snail Family Transcription Factors / metabolism
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism
  • Zinc Finger Protein GLI1 / genetics
  • Zinc Finger Protein GLI1 / metabolism
  • Zinc Finger Protein Gli2 / antagonists & inhibitors
  • Zinc Finger Protein Gli2 / genetics
  • Zinc Finger Protein Gli2 / metabolism*

Substances

  • Carbazoles
  • Cyclin E
  • GLI1 protein, human
  • GLI2 protein, human
  • Hedgehog Proteins
  • Nuclear Proteins
  • RICTOR protein, human
  • Rapamycin-Insensitive Companion of mTOR Protein
  • SNAI1 protein, human
  • Snail Family Transcription Factors
  • Vascular Endothelial Growth Factor A
  • Zinc Finger Protein GLI1
  • Zinc Finger Protein Gli2
  • mahanine
  • Glycogen Synthase Kinase 3 beta
  • Mechanistic Target of Rapamycin Complex 2