Reduced SHARPIN and LUBAC Formation May Contribute to CCl₄- or Acetaminophen-Induced Liver Cirrhosis in Mice.

Takeshi Yamamotoya,Midori Fujishiro,Fuminori Tokunaga,Sunao Kaneko,Yusuke Nakatsu,Takako Kikuchi,Tomoichiro Asano,Yasuka Matsunaga,Toshiaki Fukushima,Hiroki Yamazaki,Akifumi Kushiyama,Hideyuki Sakoda

doi:10.3390/ijms18020326

Abstract

Linear ubiquitin chain assembly complex (LUBAC), composed of SHARPIN (SHANK-associated RH domain-interacting protein), HOIL-1L (longer isoform of heme-oxidized iron-regulatory protein 2 ubiquitin ligase-1), and HOIP (HOIL-1L interacting protein), forms linear ubiquitin on nuclear factor-κB (NF-κB) essential modulator (NEMO) and induces NF-κB pathway activation. SHARPIN expression and LUBAC formation were significantly reduced in the livers of mice 24 h after the injection of either carbon tetrachloride (CCl4) or acetaminophen (APAP), both of which produced the fulminant hepatitis phenotype. To elucidate its pathological significance, hepatic SHARPIN expression was suppressed in mice by injecting shRNA adenovirus via the tail vein. Seven days after this transduction, without additional inflammatory stimuli, substantial inflammation and fibrosis with enhanced hepatocyte apoptosis occurred in the livers. A similar but more severe phenotype was observed with suppression of HOIP, which is responsible for the E3 ligase activity of LUBAC. Furthermore, in good agreement with these in vivo results, transduction of Hepa1-6 hepatoma cells with SHARPIN, HOIL-1L, or HOIP shRNA adenovirus induced apoptosis of these cells in response to tumor necrosis factor-α (TNFα) stimulation. Thus, LUBAC is essential for the survival of hepatocytes, and it is likely that reduction of LUBAC is a factor promoting hepatocyte death in addition to the direct effect of drug toxicity.

Highlights

A novel head-to-tail linear type of ubiquitination was shown to play an essential role in nuclear factor-κB (NF-κB) activation [1,2,3,4,5]
Previous reports indicate that NF-κB transcriptional activation leads to increased releases of several inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β in Kupffer cells as observed in non-alcoholic steatohepatitis (NASH) livers [6,7,8,9]
We previously demonstrated that linear ubiquitin assembly complex (LUBAC) formation is severely impaired mainly via markedly reduced SHARPIN expression in the NASH livers of mice fed a methionine choline deficient (MCD) diet for eight weeks [12]

Summary

Introduction

A novel head-to-tail linear type of ubiquitination was shown to play an essential role in nuclear factor-κB (NF-κB) activation [1,2,3,4,5]. LUBAC, which has a molecular weight that is approximately 600 kDa, is assumed to be comprised of SHANK-associated RH domain interacting protein in postsynaptic density (SHARPIN), the longer isoform of heme-oxidized IRP2 ligase-1 (HOIL-1L) and HOIL-1L interacting protein (HOIP) [3,4,5]. Both HOIL-1L and HOIP possess E3 ligase activity, it is HOIP that serves as an E3 ligase for linear polyubiquitination. NF-κB is involved in both inflammation and cell survival

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Discussion

Conclusion