Inhibition of IGF-1R-dependent PI3K activation sensitizes colon cancer cells specifically to DR5-mediated apoptosis but not to rhTRAIL.
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.
Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Bodvael
B
Pennarun
Jan H
JH
Kleibeuker
Tjitske
T
Oenema
Janet H
JH
Stegehuis
Elisabeth G E
EG
de Vries
Steven
S
de Jong
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002469:Cell Separation; D003110:Colonic Neoplasms / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D008856:Microscopy, Fluorescence; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D011994:Recombinant Proteins; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*
D000970:Antineoplastic Agents; C501177:NVP-AEW541; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D011758:Pyrroles; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D011994:Recombinant Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1