RT Journal Article SR Electronic T1 Insulin-Like Growth Factor Type-I Receptor-Dependent Phosphorylation of Extracellular Signal-Regulated Kinase 1/2 but not Akt (Protein Kinase B) Can Be Induced by Picropodophyllin JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 930 OP 939 DO 10.1124/mol.107.040014 VO 73 IS 3 A1 Radu Vasilcanu A1 Daiana Vasilcanu A1 Bita Sehat A1 Shucheng Yin A1 Ada Girnita A1 Magnus Axelson A1 Leonard Girnita YR 2008 UL http://molpharm.aspetjournals.org/content/73/3/930.abstract AB The initial event upon binding of insulin-like growth factor 1 to the insulin-like growth factor type-I receptor (IGF-1R) is auto-phosphorylation of tyrosine residues within the activation loop of the kinase domain followed by phosphorylation of other receptor tyrosine residues and the subsequent activation of the intracellular signaling cascades. We found recently that the cyclolignan picropodophyllin (PPP) inhibits phosphorylation of IGF-1R and phosphatidyl-3 kinase/Akt (protein kinase B) signaling molecules without interfering with the highly homologous insulin receptor. Furthermore, PPP causes regression of tumor grafts and substantially prolongs the survival of animals with systemic tumor disease. It is of interest that we show here that short treatments with PPP activate the intracellular extracellular signal-regulated kinase (ERK) signaling. Our data suggest that PPP induces IGF-1R ubiquitination and in turn activates ERK1/2. The PPP-induced ERK activation requires IGF-1R because PPP is not able to induce ERK phosphorylation in IGF-1R-negative cells or in cells in which the receptor is knocked down by small interfering RNA. Moreover, in the absence of Mdm2, an E3 ligase that has been shown previously to be involved in IGF-1R ubiquitination, the phosphorylation of ERK did not occur. Thus, apart from inhibiting the receptor activity, PPP can induce IGF-1R ubiquitination and stimulate ERK in an Mdm2-dependent manner. This response could contribute to the apoptotic effect of PPP. The American Society for Pharmacology and Experimental Therapeutics