Endogenously activated mGlu5 metabotropic glutamate receptors sustain the increase in c-Myc expression induced by leukaemia inhibitory factor in cultured mouse embryonic stem cells

J Neurochem. 2006 Oct;99(1):299-307. doi: 10.1111/j.1471-4159.2006.04038.x.


We have shown that endogenous activation of type 5 metabotropic glutamate (mGlu5) receptors supports the maintenance of a pluripotent, undifferentiated state in D3 mouse embryonic stem cells cultured in the presence of leukaemia inhibitory factor (LIF). Here, we examined the interaction between LIF and mGlu5 receptors using as a read-out the immediate early gene, c-Myc. The selective mGlu5 receptor antagonist, 2-methyl-6-(phenylenthynyl)pyridine (MPEP; 1 mum), reduced the increase in c-Myc protein levels induced by LIF by enhancing c-Myc ubiquitination. A reduction in c-Myc levels was also observed following small interfering RNA-mediated mGlu5 receptor gene silencing. MPEP reduced glycogen synthase kinase-3beta phosphorylation on Ser9, but increased phosphorylation of the phosphatidylinositol-3-kinase (PI-3-K) substrate, AKT. In our hands, activated PI-3-K reduced the stability of c-Myc, because (i) the PI-3-K inhibitor, LY294002, prevented the reduction in c-Myc levels induced by MPEP; and (ii) over-expression of AKT promoted c-Myc ubiquitination. All effects of MPEP were mimicked by protein kinase C (PKC) inhibitors and reversed by the PKC activator, tetradecanoylphorbol-13-acetate. We conclude that endogenous activation of mGlu5 receptors sustains the increase in c-Myc induced by LIF in embryonic stem cells by inhibiting both glycogen synthase kinase-3beta and PI-3-K, both effects resulting from the activation of PKC.

MeSH terms

  • Animals
  • Cells, Cultured
  • Embryo, Mammalian
  • Excitatory Amino Acid Antagonists / pharmacology
  • Gene Expression Regulation, Developmental*
  • Genes, myc*
  • Glycogen Synthase Kinase 3 / metabolism
  • Glycogen Synthase Kinase 3 beta
  • Interleukin-6 / physiology*
  • Leukemia Inhibitory Factor
  • Mice
  • Phosphatidylinositol 3-Kinases / metabolism
  • Pyridines / pharmacology
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate / physiology*
  • Stem Cells / cytology
  • Stem Cells / physiology*


  • Excitatory Amino Acid Antagonists
  • Interleukin-6
  • Leukemia Inhibitory Factor
  • Lif protein, mouse
  • Pyridines
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate
  • 6-methyl-2-(phenylethynyl)pyridine
  • Phosphatidylinositol 3-Kinases
  • GSK3B protein, human
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, mouse
  • Glycogen Synthase Kinase 3