Silencing of microRNA-21 confers radio-sensitivity through inhibition of the PI3K/AKT pathway and enhancing autophagy in malignant glioma cell lines.
Radiation is a core part of therapy for malignant glioma and is often provided following debulking surgery. However, resistance to radiation occurs in most patients, and the underlying molecular mechanisms of radio-resistance are not fully understood. Here, we demonstrated that microRNA 21 (miR-21), a well-known onco-microRNA in malignant glioma, is one of the major players in radio-resistance. Radio-resistance in different malignant glioma cell lines measured by cytotoxic cell survival assay was closely associated with miR-21 expression level. Blocking miR-21 with anti-miR-21 resulted in radio-sensitization of U373 and U87 cells, whereas overexpression of miR-21 lead to a decrease in radio-sensitivity of LN18 and LN428 cells. Anti-miR-21 sustained γ-H2AX DNA foci formation, which is an indicator of double-strand DNA damage, up to 24 hours and suppressed phospho-Akt (ser473) expression after exposure to γ-irradiation. In a cell cycle analysis, a significant increase in the G₂/M phase transition by anti-miR-21 was observed at 48 hours after irradiation. Interestingly, our results showed that anti-miR-21 increased factors associated with autophagosome formation and autophagy activity, which was measured by acid vesicular organelles, LC3 protein expression, and the percentage of GFP-LC3 positive cells. Furthermore, augmented autophagy by anti-miR-21 resulted in an increase in the apoptotic population after irradiation. Our results show that miR-21 is a pivotal molecule for circumventing radiation-induced cell death in malignant glioma cells through the regulation of autophagy and provide a novel phenomenon for the acquisition of radio-resistance.
Specific Organs Cancer Branch, Research Institute and Hospital, National Cancer Center, Goyang, Korea.
Ho-Shin
HS
Gwak
Tae Hoon
TH
Kim
Guk Heui
GH
Jo
Youn-Jae
YJ
Kim
Hee-Jin
HJ
Kwak
Jong Heon
JH
Kim
Jinlong
J
Yin
Heon
H
Yoo
Seung Hoon
SH
Lee
Jong Bae
JB
Park
D017209:Apoptosis / Q000528:radiation effects; D001343:Autophagy / Q000235:genetics*; D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor / Q000469:parasitology; D002470:Cell Survival; D005720:Gamma Rays; D020868:Gene Silencing; D005910:Glioma / Q000235:genetics* / Q000473:pathology; D006657:Histones / Q000235:genetics; D006801:Humans; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics / Q000528:radiation effects
C468783:H2AX protein, human; D006657:Histones; C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt