Disruption of NF-κB signaling by fluoxetine attenuates MGMT expression in glioma cells.
BACKGROUND
Resistance to temozolomide (TMZ) in glioma is modulated by the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). This study aimed to examine the effects of fluoxetine (FLT) on MGMT expression in glioma cells and to investigate its underlying mechanisms.


METHODS
Expression of MGMT, GluR1, or IκB kinase β (IKKβ) was attenuated using short hairpin RNA-mediated gene knockdown. The 3-(4,5-dimethylthiazol -2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to evaluate the growth inhibition induced by FLT or TMZ. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) was conducted to detect apoptotic cells. Western blotting was conducted to analyze the protein expression of MGMT, IKKβ, and NF-κB/p65 following FLT treatment. The murine subcutaneous xenograft model was used to evaluate the combinational effect of TMZ and FLT.


RESULTS
FLT markedly reduced MGMT expression in glioma cells, which was independent of GluR1 receptor function. Further, FLT disrupted NF-κB/p65 signaling in glioma cells and consequently attenuated NF-κB/p65 activity in regulating MGMT expression. Importantly, FLT sensitized MGMT-expressing glioma cells to TMZ, as FLT enhanced TMZ's ability to impair the in vitro tumorigenic potential and to induce apoptosis in glioma cells. Knockdown of MGMT or IKKβ expression abolished the synergistic effect of FLT with TMZ in glioma cells, which suggested that FLT might sensitize glioma cells to TMZ through down-regulation of MGMT expression. Consistently, TMZ combined with FLT markedly attenuated NF-κB/p65 activity, reduced MGMT expression, and suppressed in vivo tumor growth in the murine subcutaneous xenograft model.


CONCLUSIONS
Our findings demonstrated that FLT attenuated MGMT expression by disrupting NF-κB signaling and sensitized glioma cells to TMZ, which may warrant further investigation toward possible clinical application in MGMT-expressing glioma.
Department of Neurosurgery, Xiangya Hospital, Central South University, Jishou, People's Republic of China.
Tao
T
Song
Department of Immunology and Microbiology, Medical School of Jishou University, Jishou, People's Republic of China.
Hui
H
Li
Department of Neurosurgery, The Hospital of Xiangxi Autonomous Prefecture, Jishou, People's Republic of China.
Zhiliang
Z
Tian
Department of Oncology, The Hospital of Xiangxi Autonomous Prefecture, Jishou, People's Republic of China.
Chaojiu
C
Xu
Department of Neurosurgery, Xiangya Hospital, Central South University, Jishou, People's Republic of China.
Jingfang
J
Liu
Department of Neurosurgery, Xiangya Hospital, Central South University, Jishou, People's Republic of China.
Yong
Y
Guo
MGMT; fluoxetine; glioma