Induction of E6AP by microRNA-302c dysregulation inhibits TGF-\u03b2-dependent fibrogenesis in hepatic stellate cells

Ji Young Kim,Keon Wook Kang,Su Jung Park,Seung Jung Kim,Kyu Min Kim,Sam Seok Cho,Gum Hwa Lee,Jin Won Yang,Sang‐Gun Ahn,Sung Chul Lim,Ji Hye Yang,Sung Hwan Ki

doi:10.1038/s41598-019-57322-w

Ji Young Kim, Keon Wook Kang + Show 10 more

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https://doi.org/10.1038/s41598-019-57322-w

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Abstract

Hepatic stellate cells (HSCs) are essential for liver fibrosis. E6 associated protein (E6AP) is one of the E3-ubiquitin-protein ligase and has been studied in proliferation and cellular stress. Currently, no information is available on the role of E6AP on transforming growth factor-β (TGF-β) signaling and hepatic fibrogenesis. This study examined whether E6AP is overexpressed in activated HSCs, and if so, its effect on hepatic fibrogenesis and the molecular mechanism. E6AP was expressed higher in HSCs than hepatocytes, and was up-regulated in activated HSCs, HSCs from the livers of carbon tetrachloride-injected mice, or TGF-β-treated LX-2 cells. The TGF-β-mediated E6AP up-regulation was not due to altered mRNA level nor protein stability. Thus, we performed microRNA (miRNA, miR) analysis and found that miR-302c was dysregulated in TGF-β-treated LX-2 cells or activated primary HSCs. We revealed that miR-302c was a modulator of E6AP. E6AP overexpression inhibited TGF-β-induced expression of plasminogen activator inhibitor-1 in LX-2 cells, albeit it was independent of Smad pathway. Additionally, E6AP inhibited TGF-β-mediated phosphorylation of mitogen-activated protein kinases. To conclude, E6AP overexpression due to decreased miR-302c in HSCs attenuated hepatic fibrogenesis through inhibition of the TGF-β-induced mitogen-activated protein kinase signaling pathway, implying that E6AP and other molecules may contribute to protection against liver fibrosis.

Highlights

Liver fibrosis, derived from a variety of etiologies, such as hepatitis B or C virus infection, chronic alcohol abuse, non-alcoholic steatohepatitis, cholestasis, and autoimmune hepatitis, can advance to fibrosis and cirrhosis, which are major causes of morbidity and mortality worldwide[1]
These results suggest that E6 associated protein (E6AP) is overexpressed in activated hepatic stellate cells (HSCs) during liver fibrogenesis
E3 ligases can interact with various substrates which are associated with Transforming growth factor-β (TGF-β) signaling and regulate their expression levels[29]

Summary

Introduction

Liver fibrosis, derived from a variety of etiologies, such as hepatitis B or C virus infection, chronic alcohol abuse, non-alcoholic steatohepatitis, cholestasis, and autoimmune hepatitis, can advance to fibrosis and cirrhosis, which are major causes of morbidity and mortality worldwide[1]. The liver undergoes a wound-healing response, leading to the accumulation of excessive deposition of extracellular matrix (ECM) and impaired organ function[2]. During this process, hepatic stellate cells (HSCs) trans-differentiate from quiescent cells with vitamin A, to highly proliferative myofibroblastic cells, and these activated cells are crucial sources for fiber accumulation and contribute to liver fibrosis[3]. Because the ubiquitin-proteasomal degradation pathway tightly regulates TGF-β signaling[15,16,17], the mainly involved in HSC activation and ECM accumulation, E3 ligase may have profound effects on the progression of liver fibrosis

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