title: Inhibition of IGF-1R-dependent PI3K activation sensitizes colon cancer cells specifically to DR5-mediated apoptosis but not to rhTRAIL.
abstract: BACKGROUND
  Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) initiates apoptosis in tumor cells upon binding to its cognate agonistic receptors, death receptors 4 and 5 (DR4 and DR5). The activity of the insulin-like growth factor 1 (IGF-1) survival pathway is often increased in cancer, influencing both cell proliferation and apoptosis. We hypothesized that inhibiting the IGF-1 receptor (IGF-1R) using NVP-AEW541, a small molecular weight tyrosine kinase inhibitor of the IGF-1R, could increase death receptor (DR)-mediated apoptosis in colon cancer cells.
  
  
  METHODS
  The analyses were performed by caspase assay, flow cytometry, Western blotting, immunoprecipitation and fluorescent microscopy.
  
  
  RESULTS
  Preincubation with NVP-AEW541 surprisingly decreased apoptosis induced by recombinant human TRAIL (rhTRAIL) or an agonistic DR4 antibody while sensitivity to an agonistic DR5 antibody was increased. NVP-AEW541 could inhibit IGF-1-induced activation of the phosphatidylinositol 3-kinase (PI3K) pathway. The effects of the PI3K inhibitor LY294002 on TRAIL-induced apoptosis were similar to those of NVP-AEW541, further supporting a role for IGF-1R-mediated activation of PI3K. We show that PI3K inhibition enhances DR5-mediated caspase 8 processing but also lowers DR4 membrane expression and DR4-mediated caspase 8 processing. Inhibition of PI3K reduced rhTRAIL sensitivity independently of the cell line preference for either DR4- or DR5-mediated apoptosis signaling.
  
  
  CONCLUSIONS
  Our study indicates that individual effects on DR4 and DR5 apoptosis signaling should be taken into consideration when combining DR-ligands with PI3K inhibition.
authors.affiliation: Department of Medical Oncology, University Medical Center Groningen, University of Groningen, the Netherlands.
authors.forename: Bodvael
authors.initials: B
authors.lastname: Pennarun
authors.forename: Jan H
authors.initials: JH
authors.lastname: Kleibeuker
authors.forename: Tjitske
authors.initials: T
authors.lastname: Oenema
authors.forename: Janet H
authors.initials: JH
authors.lastname: Stegehuis
authors.forename: Elisabeth G E
authors.initials: EG
authors.lastname: de Vries
authors.forename: Steven
authors.initials: S
authors.lastname: de Jong
mesh_terms: D000912:Antibodies, Neoplasm / Q000276:immunology; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000201:enzymology / Q000473:pathology*; D053418:Death Domain Receptor Signaling Adaptor Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011743:Pyrimidines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000276:immunology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*
chemical_list: D000912:Antibodies, Neoplasm; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053181:Caspase 8; D053418:Death Domain Receptor Signaling Adaptor Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011743:Pyrimidines; D011758:Pyrroles; D017526:Receptor, IGF Type 1; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D011994:Recombinant Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C506386:CFLAR protein, human; C501177:NVP-AEW541