The cyclolignan PPP induces activation loop-specific inhibition of tyrosine phosphorylation of the insulin-like growth factor-1 receptor. Link to the phosphatidyl inositol-3 kinase/Akt apoptotic pathway

Oncogene. 2004 Oct 14;23(47):7854-62. doi: 10.1038/sj.onc.1208065.


The insulin-like growth factor-1 receptor (IGF-1R) is crucial for many functions in neoplastic cells, for example, antiapoptosis. Recently, we demonstrated that the cyclolignan PPP efficiently inhibited phosphorylation of IGF-1R without interfering with insulin receptor activity. PPP preferentially reduced phosphorylated Akt, as compared to phosphorylated Erk1/2, and caused apoptosis. Now, we aimed to investigate how PPP inhibits the IGF-1R tyrosine kinase (IGF-1RTK) and the PI3K/Akt apoptotic pathway. Using a baculovirus driven IGF-1RTK we found that PPP interfered with tyrosine phosphorylation in the activation loop of the kinase domain. Specifically, it blocked phosphorylation of tyrosine (Y) 1136, while sparing the two others (Y1131 and Y1135). To explore the impact of inhibition of Y1136 on Akt phosphorylation we transfected P6 cells (overexpressing IGF-1R) and malignant melanoma cells with different IGF-1R mutants, including Y1136F (tyrosine replaced by phenylalanine). Y1136F was found to strongly decrease IGF-1 stimulated phosphorylation of Akt. Conversely, Akt phosphorylation was weakly affected in the Y1131F transfectant. Taken together, our data suggest that the preferential inhibition of phosphorylated Akt, after PPP treatment, may be due to specific inhibition of Y1136. PPP was proven not to interfere directly with Akt or any of its downstream molecules in the apoptotic pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / physiology*
  • Caspase 3
  • Caspases / metabolism
  • Cell Line
  • Cell Line, Tumor
  • Cell Survival
  • Fibroblasts
  • Humans
  • Insulin Receptor Substrate Proteins
  • Kinetics
  • Melanoma
  • Mice
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Phosphotyrosine / metabolism
  • Podophyllotoxin / analogs & derivatives*
  • Podophyllotoxin / pharmacology*
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Receptor, IGF Type 1 / antagonists & inhibitors*
  • Receptor, IGF Type 1 / drug effects
  • Receptor, IGF Type 1 / genetics
  • Recombinant Proteins / metabolism
  • Transfection


  • IRS1 protein, human
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, mouse
  • Phosphoproteins
  • Proto-Oncogene Proteins
  • Recombinant Proteins
  • picropodophyllin
  • Phosphotyrosine
  • Receptor, IGF Type 1
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • CASP3 protein, human
  • Casp3 protein, mouse
  • Caspase 3
  • Caspases
  • Podophyllotoxin