MicroRNAs (miRNAs) are small, non-coding RNAs that post-transcriptionally regulate gene expression. Aberrant miRNA expression or function have close links with various human diseases. Therefore, therapeutic treatments with disease-associated miRNAs as targets are emerging. However, the intracellular miRNA networks are extremely complicated and poorly understood, which thus hinder the development of miRNA-targeted therapeutics. Small molecules that are able to regulate endogenous miRNAs hold great potential in both elucidation of miRNA networks and treatment of miRNA-related diseases. Herein, we summarize current strategies for discovery of small molecule modifiers of miRNAs, and we highlight aspects of miRNA cellular biology elucidated by using these small molecules and miRNAtargeted therapeutics realized by these small molecules. We envision that this area will expand dramatically in the near future and will ultimately contribute to a better understanding of miRNAinvolved cellular processes and development of therapeutic agents for miRNA-associated diseases.

The zinc finger protein Snail1 is an important factor in the regulation of the epithelial-mesenchymal transition (EMT) of hepatocellular carcinoma (HCC) cells. The present study demonstrated that the expression of Snail1 in HCC tissues was significantly higher compared with its expression in tissues adjacent to primary sites, as determined via western blotting. Furthermore, the results of a dual luciferase assay revealed that hsa-microRNA(miR)199a-5p negatively regulated the protein expression of Snail1 by binding to its 3' untranslated region. However, in a comparative analysis of primary HCC and its metastatic tissues using reverse transcription-quantitative polymerase chain reaction and western blotting, it was demonstrated that the expression of hsa-miR199a-5p and Snail1 in HCC metastatic tissues were significantly higher compared with primary lesions and an association between them identified that hsa-miR199a-5p lost its ability to negatively regulate Snail1. This result is contradictive to the fact that hsa-miR199a-5p inhibits the expression of the Snail1 protein. The present study hypothesized that the aberrant expression of long non-coding RNA was the cause of hsa-miR199a-5p inactivation based on loss of function rather than a reduction in content. The data collected in the present study confirmed the hypothesis that AB209371 binds to hsa-miR199a-5p and weakened the inhibitory effect of hsa-miR199a-5p on Snail1 expression. In addition, an in vitro EMT model was established in the present study by inducing HCC cells with TGF-β1. The results revealed that AB209371 silencing effectively reversed the hsa-miR199a-5p mediated inhibition of EMT by negatively regulating Snail1 protein expression. Therefore, AB209371 silencing in combination with hsa-miR199a-5p expression may serve as an effective means to inhibit EMT in HCC cells. The present study also revealed that hsa-miR199a-5p/Snail1 exhibits a dominant regulatory effect in the EMT of HCC cells via a Snail1 recovery experiment. In conclusion, to the best of our knowledge, the present study confirmed for the first time that the high expression of AB209371 is favorable for the EMT in HCC cells and may be a direct cause of hsa-miR199a-5p inactivation (an HCC metastasis suppressor). Additionally, AB209371 silencing combined with hsa-miR199a-5p overexpression may be an effective means to inhibit the metastasis of HCC and the EMT of HCC cells.

Hepatocellular carcinoma (HCC) is among the most common cancers in the world with a low survival rate. Our previous study showed Short chain enoyl-CoA hydratase (ECHS1) could bind to HBsAg (HBs) and that ECHS1's localization in mitochondria induced HepG2 cell apoptosis. However, the role of the ECHS1 in energy metabolism and autophagy during hepatocellular carcinoma development remains undefined. We aimed to determine what ECHS1 does to energy metabolism and its effects on HCC progression. We performed CCK-8, EdU assays in hepatocellular carcinoma cell lines (HepG2 and HuH7) with stable ECHS1 knock-down. ATP and NADP+/NADPH levels were measured using an colorimetric assay. Our data demonstrated that ECHS1 silencing inhibited cell proliferation and induced autophagy. ECHS1 knockdown did not increase fatty acid synthesis, but decreased cellular ATP. This resulted in AMP-activated protein kinase (AMPK) activation and induced HCC cell autophagy. Our results showed that silencing ECHS1 to attenuate proliferation and induce autophagy may make it a novel cancer therapy target.

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