Essential Roles of RNA-binding Protein HuR in Activation of Hepatic Stellate Cells Induced by Transforming Growth Factor-β1

Sci Rep. 2016 Feb 25:6:22141. doi: 10.1038/srep22141.

Abstract

RNA-binding protein HuR mediates transforming growth factor (TGF)-β1-induced profibrogenic actions. Up-regulation of Sphingosine kinase 1 (SphK1) is involved in TGF-β1-induced activation of hepatic stellate cells (HSCs) in liver fibrogenesis. However, the molecular mechanism of TGF-β1 regulates SphK1 remains unclear. This study was designed to investigate the role of HuR in TGF-β1-induced SphK1 expression and identify a new molecular mechanism in liver fibrogenensis. In vivo, HuR expression was increased, translocated to cytoplasm, and bound to SphK1 mRNA in carbon tetrachloride- and bile duct ligation-induced mouse fibrotic liver. HuR mRNA expression had a positive correlation with mRNA expressions of SphK1 and fibrotic markers, α-smooth muscle actin (α-SMA) and Collagen α1(I), respectively. In vitro, up-regulation of SphK1 and activation of HSCs stimulated by TGF-β1 depended on HuR cytoplasmic accumulation. The effects of TGF-β1 were diminished when HuR was silenced or HuR cytoplasmic translocation was blocked. Meanwhile, overexpression of HuR mimicked the effects of TGF-β1. Furthermore, TGF-β1 prolonged half-life of SphK1 mRNA by promoting its binding to HuR. Pharmacological or siRNA-induced SphK1 inhibition abrogated HuR-mediated HSC activation. In conclusion, our data suggested that HuR bound to SphK1 mRNA and played a crucial role in TGF-β1-induced HSC activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Animals
  • ELAV-Like Protein 1 / metabolism*
  • Female
  • Hepatic Stellate Cells / physiology*
  • Humans
  • Liver Cirrhosis / pathology
  • Male
  • Mice, Inbred ICR
  • Middle Aged
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism*
  • RNA-Binding Proteins / metabolism*
  • Transforming Growth Factor beta1 / metabolism*

Substances

  • ELAV-Like Protein 1
  • ELAVL1 protein, human
  • Elavl1 protein, mouse
  • RNA-Binding Proteins
  • Transforming Growth Factor beta1
  • Phosphotransferases (Alcohol Group Acceptor)
  • sphingosine kinase