MiR-137 and miR-34a directly target Snail and inhibit EMT, invasion and sphere-forming ability of ovarian cancer cells.
In ovarian cancer (OC) cells, Snail was reported to induce the epithelial-to-mesenchymal transition (EMT), which is a critical step in OC metastasis. At present little is known about controlling Snail expression in OC cells by using specific microRNAs (miRNAs).



We first used a computational target prediction analysis to identify 6 candidate miRNAs that bind to the 3'-untranslated region (3'-UTR) region of the Snail mRNA. Among these miRNAs, two miRNAs (miR-137 and miR-34a) with a potential to regulate Snail were validated by quantitative real-time PCR, Western blot analysis, and Snail 3'-UTR reporter assays. We assessed the effects of miR-137 and miR-34a on EMT, invasion and sphere formation in OC cells. We also evaluated the expression of miR-137 and miR-34a in OC tissues and adjacent normal tissues and analyzed the relationship between their expression and patient survival.



We report that OC tissues possess significantly decreased levels of miR-137 and miR-34a and increased expression of Snail when compared to their adjacent normal tissues, and lower miR-137 and miR-34a expression correlates with worse patient survival. Using luciferase constructs containing the 3'-UTR region of Snail mRNA combined with miRNA overexpression and mutagenesis, we identified miR-137 and miR-34a as direct suppressors of Snail in OC cells. The introduction of miR-137 and miR-34a resulted in the suppression of Snail at both the transcript and protein levels, and effectively suppressed the EMT phenotype and sphere formation of OC cells. However, the inhibition of miR-137 and miR-34a with antisense oligonucleotides promoted EMT and OC cell invasion. Moreover, ectopic expression of Snail significantly reversed the inhibitory effects of miR-137 and miR-34a on OC cell invasion and sphere formation.



These findings suggest that both miR-137 and miR-34a act as Snail suppressors to negatively regulate EMT, invasive and sphere-forming properties of OC cells.
Department of Women's Health Educational System, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan. dpx1cn@gmail.com.
Peixin
P
Dong
Department of Gynecology, State Key Laboratory of Oncology in South China, Sun Yat-sen University Cancer Center, Guangzhou, 510060, People's Republic of China.
Ying
Y
Xiong
Department of Gynecology, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan. watarih@med.hokudai.ac.jp.
Hidemichi
H
Watari
Department of Women's Health Educational System, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Sharon J B
SJ
Hanley
Department of Gynecology, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Yosuke
Y
Konno
Department of Gynecology, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Kei
K
Ihira
Department of Women's Health Educational System, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Takahiro
T
Yamada
Department of Gynecology, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Masataka
M
Kudo
Department of Pathology and Laboratory Medicine, University of Tennessee Health Science Center, Memphis, TN, 38163, USA. jyue@uthsc.edu.|Center for Cancer Research, University of Tennessee Health Science Center, Memphis, TN, 38163, USA. jyue@uthsc.edu.
Junming
J
Yue
Department of Women's Health Educational System, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.|Department of Gynecology, Hokkaido University School of Medicine, Hokkaido University, N15, W7, Sapporo, 0608638, Japan.
Noriaki
N
Sakuragi
D020413:3' Untranslated Regions; D045744:Cell Line, Tumor; D058750:Epithelial-Mesenchymal Transition; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D035683:MicroRNAs / Q000235:genetics*; D009361:Neoplasm Invasiveness; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D000071250:Snail Family Transcription Factors / Q000235:genetics* / Q000378:metabolism; D018874:Spheroids, Cellular / Q000378:metabolism / Q000473:pathology; D016019:Survival Analysis; D014407:Tumor Cells, Cultured
D020413:3' Untranslated Regions; C545567:MIRN137 microRNA, human; C522425:MIRN34 microRNA, human; D035683:MicroRNAs; C000604407:SNAI1 protein, human; D000071250:Snail Family Transcription Factors
Cancer stemness; EMT; Ovarian cancer; Snail; microRNA-137; microRNA-34a