The Survivin-mediated radioresistant phenotype of glioblastomas is regulated by RhoA and inhibited by the green tea polyphenol (-)-epigallocatechin-3-gallate.
BACKGROUND
Glioblastoma multiforme's (GBM) aggressiveness is potentiated in radioresistant tumor cells. The combination of radiotherapy and chemotherapy has been envisioned as a therapeutic approach for GBM. The goal of this study is to determine if epigallocatechin-3-gallate (EGCg), a green tea-derived anti-cancer molecule, can modulate GBMs' response to ionizing radiation (IR) and whether this involves mediators of intracellular signaling and inhibitors of apoptosis proteins.


METHODS
U-87 human GBM cells were cultured and transfected with cDNAs encoding for Survivin, RhoA or Caveolin-1. Mock and transfected cells were irradiated at sublethal single doses. Cell proliferation was analyzed by nuclear cell counting. Apoptosis was detected using a fluorometric caspase-3 assay. Analysis of protein expression was accomplished by Western immunoblotting.


RESULTS
IR (10 Gy) reduced control U-87 cell proliferation by 40% through a caspase-independent mechanism. The overexpression of Survivin induced a cytoprotective effect against IR, while the overexpression of RhoA conferred a cytosensitizing effect upon IR. Control U-87 cells pretreated with EGCg exhibited a dose-dependent decrease in their proliferation rate. The growth inhibitory effect of EGCg was not antagonized by overexpressed Survivin. However, Survivin -transfected cells pretreated with EGCg became sensitive to IR, and their RhoA expression was downregulated. A potential therapeutic effect of EGCg targeting the prosurvival intracellular pathways of cancer cells is suggested to act synergistically with IR.


CONCLUSIONS
The radioresistance of GBM is possibly mediated by a mechanism dependent on Survivin in conjunction with RhoA. The combination of natural anti-cancerous molecules such as EGCg with radiotherapy could improve the efficacy of IR treatments.
McLaughlin
Nancy
N
Laboratoire de Médecine Moléculaire, Centre de Cancérologie Charles-Bruneau, Hôpital Sainte-Justine-UQAM, Québec, Canada.
Annabi
Borhane
B
Bouzeghrane
Mounia
M
Temme
Achim
A
Bahary
Jean-Paul
JP
Moumdjian
Robert
R
Béliveau
Richard
R
D016588:Anticarcinogenic Agents / Q000627:therapeutic use*; D015153:Blotting, Western / Q000379:methods; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives* / Q000627:therapeutic use; D051242:Caveolin 1 / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005455:Fluorescent Antibody Technique / Q000379:methods; D015870:Gene Expression / Q000187:drug effects / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D005909:Glioblastoma / Q000188:drug therapy* / Q000532:radiotherapy*; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D010641:Phenotype; D011336:Probability; D000077022:Survivin; D014162:Transfection / Q000379:methods; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D016588:Anticarcinogenic Agents; C107489:BIRC5 protein, human; D051242:Caveolin 1; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D000077022:Survivin; D002392:Catechin; C045651:epigallocatechin gallate; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D020742:rhoA GTP-Binding Protein