TLR4-dependent tumor-initiating stem cell-like cells (TICs) in alcohol-associated hepatocellular carcinogenesis

Abstract

Alcohol abuse predisposes individuals to the development of hepatocellular carcinoma (HCC) and synergistically heightens the HCC risk in patients infected with hepatitis C virus (HCV). The mechanisms of this synergism have been elusive until our recent demonstration of the obligatory role of ectopically expressed TLR4 in liver tumorigenesis in alcohol-fed HCV Ns5a or Core transgenic mice. CD133+/CD49f+ tumor-initiating stem cell-like cells (TICs) isolated from these models are tumorigenic in a manner dependent on TLR4 and NANOG. TICs' tumor-initiating activity and chemoresistance are causally associated with inhibition of TGF-β tumor suppressor pathway due to NANOG-mediated expression of IGF2BP3 and YAP1. TLR4/NANOG activation causes p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncoprotein TBC1D15. Nutrient deprivation reduces overexpressed TBC1D15 in TICs via autophagy-mediated degradation, suggesting a possible role of this oncoprotein in linking metabolic reprogramming and self-renewal.

Fig. 8.1

Synergistically increased risk for HCV-mediated HCC by alcohol abuse or/and obesity. Comorbidity such as alcohol abuse and obesity synergistically heightens the risk of developing HCC by 6- to 8-fold in HCV-infected patients. As such HCV-infected, alcoholic or obese patients have 40–60 times higher HCC risk compared to healthy subjects

Fig. 8.2

TICs’ tumorigenic activity is dependent on TLR4 and NANOG. CD133+/CD49f+ TICs isolated from liver tumors of alcohol-fed Ns5a Tg mice or alcoholic HCV patients were transplanted subcutaneously into NOG mice following lentiviral transduction of EGFP to allow a whole animal imaging for assessment of tumor growth for a period of 80 days. To test the dependence on TLR4 and NANOG, they were respectively knocked down by lentiviral expression of specific or control shRNA prior to transplantation. Tumor volume was calculated by three dimensional assessment of the tumor image, and final tumor weights were also compared at the end of the experiment. Note TLR4 (a) or NANOG (b) knockdown significantly attenuates tumor growth derived from mouse and patient TICs. Immunoblotting of cell lysates collected 10 days after the transplantation confirms expression of NANOG in the TICs and knockdown of this protein with specific shRNA. *p < 0.05 (Reproduced from the published figure of the reference [32] with permission)

Fig. 8.3

TLR4-NANOG oncogenic pathway activated by alcohol, obesity, and HCV. TLR4 is ectopically activated in the liver by alcohol abuse, obesity, or/and HCV infection. This results in expression of the stem cell factor NANOG to mediate the genesis of TICs and tumorigenesis via antagonism of the TGF-β tumor suppressor pathway and degradation of p53 mediated by the oncoprotein TBC1D15. Upregulated NANOG and TBC1D15 and conversely suppressed p53 also contribute to anabolic metabolic reprogramming that is associated with the cancer stem cell fate regulation of TICs