Toll-like receptor 4 mediates synergism between alcohol and HCV in hepatic oncogenesis involving stem cell marker Nanog

Abstract

Alcohol synergistically enhances the progression of liver disease and the risk for liver cancer caused by hepatitis C virus (HCV). However, the molecular mechanism of this synergy remains unclear. Here, we provide the first evidence that Toll-like receptor 4 (TLR4) is induced by hepatocyte-specific transgenic (Tg) expression of the HCV nonstructural protein NS5A, and this induction mediates synergistic liver damage and tumor formation by alcohol-induced endotoxemia. We also identify Nanog, the stem/progenitor cell marker, as a novel downstream gene up-regulated by TLR4 activation and the presence of CD133/Nanog-positive cells in liver tumors of alcohol-fed NS5A Tg mice. Transplantation of p53-deficient hepatic progenitor cells transduced with TLR4 results in liver tumor development in mice following repetitive LPS injection, but concomitant transduction of Nanog shorthairpin RNA abrogates this outcome. Taken together, our study demonstrates a TLR4-dependent mechanism of synergistic liver disease by HCV and alcohol and an obligatory role for Nanog, a TLR4 downstream gene, in HCV-induced liver oncogenesis enhanced by alcohol.

The role of lipopolysaccharide/toll-like receptor 4 signaling in chronic liver diseases

“…Machida et al [50] found that HCV, through the action of its NS5A protein, induces expression of TLR4 on the surface of B cells, leading to enhanced IFN-b and IL-6 production and secretion, particularly in response to LPS. Machida et al [22] also provided evidence that hepatocyte-specific transgenic expression of the HCV nonstructural protein NS5A upregulates TLR4 expression and signaling. They demonstrated enhanced TAK-1-TRAF-6 and TAK-1-IRAK-1 interactions and phosphorylation of JNK and Ij-Ba (downstream mediators of TLR4 signaling) in NS5A mice given LPS.…”

“…Hepatocytes express mRNA for TLR4 and respond to TLR4 ligands although there are contradictory data about the amount of TLR4 mRNA expression and the level of responsiveness to LPS [21,22].…”

“…Machida et al [22] demonstrated that, in a murine model, synergism between alcohol and HCV in liver damage and tumor formation is mediated by sustained activation of LPS/ TLR4 signaling, which results from HCV NS5A-induced hepatic TLR4 expression and alcohol-induced endotoxemia. Recently, in a gene centric functional genome scan in patients with chronic hepatitis C virus, a major CC allele of TLR4 encoding a threonine at amino acid 399 (p.T399I) emerged as the second single nucleotide polymorphism (SNP) with highest ability to predict the risk of developing cirrhosis, indicating a protective role in fibrosis progression of its c.1196C_T (rs4986791) variant at this location (p.T399I), along with another highly cosegregated c.896A_G (rs4986790) SNP located at coding position 299 (p.D299G) [54].…”

“…A recent study provided evidence that TLR4 mediates the synergism between alcohol and HCV in hepatic oncogenesis. Machida et al [22] studied the molecular mechanism of synergism between alcohol and HCV, using mice with hepatocyte-specific transgenic expression of the HCV nonstructural protein NS5A, which is known to have a cryptic trans-acting activity for cellular gene promoters. They demonstrated that NS5A and alcohol synergistically induce hepatocellular damage and transformation via accentuated and/or sustained activation of TLR4 signaling, which results from HCV NS5A-induced hepatic TLR4 expression and alcohol-induced endotoxemia.…”

TLR4-Dependent Tumor-Initiating Stem Cell-Like Cells (TICs) in Alcohol-Associated Hepatocellular Carcinogenesis

“…As endotoxin-TLR4 pathway is established in the pathogenesis of ALD [ 29 , 30 ], a synergism between alcohol-mediated endotoxemia and NS5A-induced TLR4 overexpression was predicted. Indeed, alcohol feeding to the Ns5a mice results in aggravated liver damage with severe hepatitis induced in some mice [ 31 ]. This pathology is dependent on TLR4 as it is abrogated in alcohol-fed Ns5a:Tlr4−/− mice.…”