Methylation in MIRLET7A3 Gene Induces the Expression of IGF-II and Its mRNA Binding Proteins IGF2BP-2 and 3 in Hepatocellular Carcinoma.

Amr A Waly,Nada El-Ekiaby,Mohamed M Abdelrahman,Reem A Assal,Gamal Esmat,Ahmed I Abdelaziz,Hend M El Tayebi,Kai Breuhahn,Karim A Hosny

doi:10.3389/fphys.2018.01918

Abstract

miR-let-7a is a tumor suppressor miRNA with reduced expression in most cancers. Methylation of MIRLET7A3 gene was reported to be the cause of this suppression in several cancers; however, it was not explicitly investigated in hepatocellular carcinoma (HCC). We aimed at investigating miR-let-7a expression and molecular mode in HCC, identifying drug-targetable networks, which might be affected by its abundance. Our results illustrated a significant repression of miR-let-7a, which correlated with hypermethylation of its gene of origin MIRLRT7A3. This was further supported by the induction of miR-let-7a expression upon treatment of HCC cells with a DNA-methyltransferase inhibitor. Using a computational approach, insulin-like growth factor (IGF)-II and IGF-2 mRNA binding proteins (IGF2BP)-2/-3 were identified as potential targets for miR-let-7a that was further confirmed experimentally. Indeed, miR-let-7a mimics diminished IGF-II as well as IGF2BP-2/-3 expression. Direct binding of miR-let-7a to each respective transcript was confirmed using a luciferase reporter assay. In conclusion, this study suggests that DNA hypermethylation leads to epigenetic repression of miR-let-7a in HCC cells, which induces the oncogenic IGF-signaling pathway.

Highlights

MicroRNA lethal-7, has been identified as the second earliest discovered microRNA in the development of the nematode Caenorhabditis elegans, the organism where miRs were first discovered (Reinhart et al, 2000)
These results would suggest that the miR-let-7a is repressed in hepatocellular carcinoma (HCC) cells on the transcriptional level via MIRLET7A3 gene hypermethylation
HCC is characterized by dysregulation of many oncogenic signaling pathways including the insulin-like growth factor (IGF) axis

Summary

Introduction

MicroRNA lethal-7 (miR-let-7), has been identified as the second earliest discovered microRNA (miR) in the development of the nematode Caenorhabditis elegans, the organism where miRs were first discovered (Reinhart et al, 2000). In this study we first show that DNA methylation is one possible mode of negative miR-let-7a regulation in HCC cells. Genomic DNA was extracted from Huh7 cells, HCC and healthy liver tissues using the QIAamp DNA Mini Kit (Qiagen) according to the manufacturer’s protocol. Low Expression Level of miR-let-7a in HCC Cells Is Regulated by Genomic Hypermethylation

Results

Conclusion