Inhibition of c-FLIPL expression by miRNA-708 increases the sensitivity of renal cancer cells to anti-cancer drugs
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Eun-Ae Kim1,*, Sang-Woo Kim2,*, Jehyun Nam2, Eon-Gi Sung1, In-Hwan Song1, Joo-Young Kim1, Taeg Kyu Kwon3, Tae-Jin Lee1
1Department of Anatomy, College of Medicine, Yeungnam University, Nam-gu, Daegu, Republic of Korea
2Department of Biological Sciences, Pusan National University, Busan, Republic of Korea
3Department of Immunology, School of Medicine, Keimyung University, Dalseo-Gu, Daegu, Republic of Korea
*These authors have contributed equally to this work
Tae-Jin Lee, email: firstname.lastname@example.org
Keywords: c-FLIP, miR-708, RCC, doxorubicin
Received: May 04, 2015 Accepted: January 23, 2016 Published: February 03, 2016
Dysregulation of the anti-apoptotic protein, cellular FLICE-like inhibitory protein (c-FLIP), has been associated with tumorigenesis and chemoresistance in various human cancers. Therefore, c-FLIP is an excellent target for therapeutic intervention. MicroRNAs (miRNAs) are small non-coding RNAs that are involved in tumorigenesis, tumor suppression, and resistance or sensitivity to anti-cancer drugs. However, whether miRNAs can suppress c-FLIPL expression in cancer cells is unclear. The aim of this study was to identify miRNAs that could inhibit the growth of renal cancer cells and induce cell death by inhibiting c-FLIPL expression. We found that MiRNA-708 and c-FLIPL expression were inversely correlated. While c-FLIPL expression was upregulated, miRNA-708 was rarely expressed in renal cancer cells. Luciferase reporter assays demonstrated that miRNA-708 negatively regulated c-FLIPL expression by binding to the miRNA-708 binding site in the 3’ untranslated region (3’UTR) of c-FLIPL. Ectopic expression of miRNA-708 increased the accumulation of sub-G1 populations and cleavage of procaspase-3 and PARP, which could be prevented by pretreatment with the pan-caspase inhibitor, Z-VAD. Ectopic expression of miRNA-708 also increased the sensitivity to various apoptotic stimuli such as tumor necrosis factor-related apoptosis-inducing ligand, doxorubicin (Dox), and thapsigargin in Caki cells. Interestingly, miRNA-708 specifically repressed c-FLIPL without any change in c-FLIPs expression. In contrast, inhibition of endogenous miRNA-708 using antago-miRNAs resulted in an increase in c-FLIPL protein expression. The expression of c-FLIPL was upregulated in renal cell carcinoma (RCC) tissues compared to normal tissues. In contrast, miRNA-708 expression was reduced in RCC tissues. Finally, miRNA-708 enhanced the tumor-suppressive effect of Dox in a xenograft model of human RCC. In conclusion, miRNA-708 acts as a tumor suppressor because it negatively regulates the anti-apoptotic protein c-FLIPL and regulates the sensitivity of renal cancer cells to various apoptotic stimuli.
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