Molecular mechanisms governing microRNA-125a expression in human hepatocellular carcinoma cells

Nicoletta Potenza,Nicola Mosca,Marta Panella,Aniello Russo,Filomena Castiello,Elena Amendola

doi:10.1038/s41598-017-11418-3

Abstract

MicroRNA-125a-5p (miR-125a) is a vertebrate homolog of lin-4, the first discovered microRNA, and plays a fundamental role in embryo development by downregulating Lin-28 protein. MiR-125a is also expressed in differentiated cells where it generally acts as an antiproliferative factor by targeting membrane receptors or intracellular transductors of mitogenic signals. MiR-125a expression is downregulated in several tumors, including hepatocellular carcinoma (HCC) where it targets sirtuin-7, matrix metalloproteinase-11, VEGF-A, Zbtb7a, and c-Raf. In this study, we have isolated the transcription promoter of human miR-125a and characterized its activity in HCC cells. It is a TATA-less Pol II promoter provided with an initiator element and a downstream promoter element, located 3939 bp upstream the genomic sequence of the miRNA. The activity of the promoter is increased by the transcription factor NF-kB, a master regulator of inflammatory response, and miR-125a itself was found to strengthen this activation through inhibition of TNFAIP3, a negative regulator of NF-kB. This finding contributes to explain the increased levels of miR-125a observed in the liver of patients with chronic hepatitis B.

Highlights

MicroRNAs are small non-coding RNAs that play crucial roles in regulating gene expression in a variety of physiological processes by affecting both translation and stability of complementary mRNAs1, 2
We considered the possibility that the 869 segment may contain both the SPACA6 transcription promoter and the translation start site; its cloning in the luciferase reporter plasmid would have directed the transcription of a chimeric mRNA whose translation couldn’t be initiated at the luciferase start site but 100–150 bp upstream, leading to translation frameshift and/ or production of an inactive fusion protein
Lin-4/miR-125a plays a fundamental role during development in controlling the expression of Lin-28 protein promoting phase transitions and cell differentiation in Nematodes, Insects and Mammals[17,18,19,20]

Summary

Introduction

MicroRNAs (miRNAs) are small non-coding RNAs that play crucial roles in regulating gene expression in a variety of physiological processes by affecting both translation and stability of complementary mRNAs1, 2. Several studies have been devoted to quantitative and qualitative assessment of miRNA expression, showing that miRNA abundance is tightly regulated during development and across tissues. Dicer expression often increases during cell differentiation[9,10,11] In this field, a growing body of evidence indicates that dysregulated expression of specific miRNAs plays a causative role, since miRNAs can function as either tumor suppressors by down-regulating oncogenic targets, or tumor promoters by negatively regulating oncosuppressor proteins[12,13,14]. The role of miR-125a during the carcinogenesis is object of extensive research, the mechanisms governing miR-125a expression are still largely unexplored

Methods

Results

Conclusion