Insulin-like growth factor-I decreased etoposide-induced apoptosis in glioma cells by increasing bcl-2 expression and decreasing CPP32 activity.
OBJECTIVE
In a variety of tumors, the susceptibility of the tumor cells to apoptotic cell death following chemotherapy is a major determinant of therapeutic outcome. Gliomas are resistant to most chemotherapeutic agents, and its mechanism is not known in detail. In an attempt to understand the mechanism of chemo-resistance, we investigated the roles of insulin-like growth factor-I (IGF-I), IGF-I receptors (IGF-IR), and their relationship with the apoptotic response of two glioma cell lines to etoposide, a chemotherapeutic agent for malignant gliomas.


METHODS
Two human glioma cell lines, U-87MG and KNS-42, were used. Etoposide-induced cell growth inhibition was quantified using a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide), colorimetric assay. Hoechst 33258 staining, DNA fragmentation assay, and western blot were used for the evaluation of apoptosis. ApoAlert caspase assay was used for measuring the activity of caspase-3 (CPP32) and interleukin-1 beta -converting enzyme (ICE) protease. In addition, the effect of IGF-IR antisense was tested in U-87MG and KNS-42 glioma cell lines.


RESULTS
Etoposide inhibited the growth of U-87MG and KNS-42 cells in a concentration-dependent manner. Etoposide increased the expression of wild-type p53, activated CPP32 (but not ICE) activity, and induced apoptosis in these cells. IGF-I prevented etoposide-induced apoptosis by increasing the expression of bcl-2 and decreasing the activity of CPP32. IGF-IR antisense enhanced the apoptotic effect of etoposide.


CONCLUSIONS
IGF-I decreased etoposide-induced apoptosis in glioma cells by increasing the expression of bcl-2 and decreasing the activity of CPP32. The antisense of IGF-IR increased etoposide-induced apoptosis. The anti-apoptotic effect of IGF-I and IGF-IR might be related to the chemo-resistance of glioma to chemotherapeutic agents.
Yin
Dali
D
Department of Neurosurgery, University of Mississippi Medical Center, Jackson, Mississippi, USA.
Tamaki
Norihiko
N
Parent
Andrew D
AD
Zhang
John H
JH
D017209:Apoptosis / Q000187:drug effects*; D001562:Benzimidazoles; D015139:Blotting, Southern; D015153:Blotting, Western / Q000379:methods; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002452:Cell Count / Q000379:methods; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003124:Colorimetry / Q000379:methods; D019938:Cyclin D1 / Q000378:metabolism*; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D010450:Endopeptidases / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D005910:Glioma; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D020319:Oligodeoxyribonucleotides, Antisense / Q000096:biosynthesis; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis; D013778:Tetrazolium Salts; D013844:Thiazoles; D013997:Time Factors; D014162:Transfection / Q000379:methods
D001562:Benzimidazoles; D053148:Caspase 3; D020169:Caspases; D019938:Cyclin D1; D010450:Endopeptidases; D005047:Etoposide; D007334:Insulin-Like Growth Factor I; D009419:Nerve Tissue Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D020319:Oligodeoxyribonucleotides, Antisense; D017526:Receptor, IGF Type 1; D013778:Tetrazolium Salts; D013844:Thiazoles; C447680:hoechst 32258; C505407:CASP3 protein, human; C022616:thiazolyl blue; C505410:Casp3 protein, rat