Inhibition of STAT3 and ErbB2 suppresses tumor growth, enhances radiosensitivity, and induces mitochondria-dependent apoptosis in glioma cells.
OBJECTIVE
Constitutively activated signal transducer and activator of transcription 3 (STAT3) and ErbB2 are involved in the pathogenesis of many tumors, including astrocytoma. Inactivation of these molecules is reported to result in radiosensitization. The purpose of this study was to investigate whether inhibition of STAT3, ErbB2, or both could enhance radiotherapy in the human glioma model (U251 and U87 cell lines).


METHODS
The RNAi plasmids targeting STAT3 or ErbB2 were constructed, and their downregulatory effects on target proteins were examined by immunoblotting. After combination treatment of RNAi with or without irradiation, the cell viability was determined using 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and clonogenic assays. The in vivo effect of combined treatment was determined using the U251 xenograft model. The apoptosis caused by the inhibition of STAT3 and ErbB2 was detected, and the mechanism involved in the apoptosis was investigated, including increases in caspase proteins, mitochondrial damage, and the expression of key modulating protein of different apoptosis pathways.


RESULTS
Transfection of U251 cells with STAT3 or ErbB2 siRNA plasmids specifically reduced their target gene expressions. Inhibition of STAT3 or ErbB2 greatly decreased glioma cell survival after 2, 4, or 6 Gy irradiation. Inhibition of STAT3 and ErbB2 also enhanced radiation-induced tumor growth inhibition in the U251 xenograft model. Furthermore, the suppression of either STAT3 or ErbB2 could induce U251 cell apoptosis, which was related primarily to the mitochondrial apoptotic pathway.


CONCLUSIONS
These results indicated that simultaneous inhibition of STAT3 and ErbB2 expression can promote potent antitumor activity and radiosensitizing activity in human glioma.
Gao
Ling
L
Department of Experimental Therapy of ARS, Beijing Institute of Radiation Medicine, Beijing, China.
Li
Fengsheng
F
Dong
Bo
B
Zhang
Junquan
J
Rao
Yalan
Y
Cong
Yue
Y
Mao
Bingzhi
B
Chen
Xiaohua
X
D000818:Animals; D017209:Apoptosis; D001253:Astrocytes / Q000166:cytology; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000235:genetics / Q000528:radiation effects; D015536:Down-Regulation; D004789:Enzyme Activation; D005910:Glioma / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000502:physiology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D011836:Radiation Tolerance; D051381:Rats; D017208:Rats, Wistar; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D020169:Caspases; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D050796:STAT3 Transcription Factor; C508053:ERBB2 protein, human