Roles of epithelial-mesenchymal transition and niche in tumorigenesis of tumor-initiating cells

2015-01-24Abstract Study – 1 (Chapter 2) ❧ BACKGROUND & AIMS: Alcohol and obesity cause steatohepatitis through activation of Toll‐like receptor‐4 (TLR4) signaling and enhance hepatitis C virus (HCV) associated liver carcinogenesis. The HCV NS5A protein ectopoically upregulates TLR4 in hepatocytes, generates TLR4/NANOG dependent liver tumor initiating stem cell‐like cells (TICs), and induces liver tumor in alcohol fed transgenic (Tg) mice. These TICs have robust and selective expression of the leptin receptor, and increased phosphorylation and activation of STAT3. However, whether the TLR4‐NANOG pathway promotes an oncogenic signaling in other etiological mouse models and patients is ambiguous. METHOD: We sought to determine whether a Western diet high in cholesterol, and saturated fat (HCFD) that causes obesity can also synergistically induce liver tumors via TLR4 signaling. RESULTS: We have identified the TLR4‐NANOG oncogenic pathway in the genesis of TICs, and liver tumor in alcohol and/or HCFD fed NS5A Tg mice. A sensitized response in TICs to LPS and/or Leptin resulted in an enchanced Twist1 Promoter activity, which was abrogated by silencing: Tlr4, Nanog or Stat3. We provide evidence of NANOG and STAT3 sharing their binding site on Twist1 promoter to transactive it. CONCLUSION: Taken together, TLR4‐NANOG axis promotes liver tumorigenesis/metastasis through accentuated mesenchymal phenotype with elevated Twist1 expression upon exposure to HCV and alcohol/high‐fat diets. The TLR4 pathway serves as a novel therapeutic target for HCC. ❧ Abstract – Study 2 (Chapter 3) ❧ BACKGROUND & AIMS: Evidence that TLR4/NANOG dependent liver tumor initiating stem cell‐like cells (TICs) induces liver tumor in Western diet high in cholesterol and saturated fat (HCFD)/alcohol fed transgenic (Tg) mice. These TICs have robust characteristics of distal organ metastasis and tumor development (in similar or dissimilar germ line lineage). However, whether this characteristics of TICs is due to their microenvironment (dissimilar lineage) crosstalk in mouse models and patients is obscure. METHOD: We sought to determine whether the Hepatic Progenitor cell’s Niche acts as an intricate factor in regulating the homeostasis of TICs and can also synergistically induce their metastatic characteristics. RESULTS: We have identified the Hepatic Stellate cells (HSCs), and the Kupffer cells (KCs) are involved in the genesis of extremely metastatic TICs via fusion (cytogenetic analysis) between KCs and TICs. A sensitized Fibroblast growth factor 2 (FGF) emanated from the TIC’s Niche acts as a cue for a Cell‐Cell competition between TICs and HSCs leading to HSCs apoptosis. Enhanced expression of CD47 (don’t eat me signal) ligand in TICs ensures cellocytosis with KCs via its receptor SIRP‐α rather undergoing phagocytosis. Abrogation of CD47 or Fibroblast growth factor receptor 2 (FGFR2) in TICs prevented incidence of metastasis and tumor growth. CONCLUSION: Here we provide evidence that the TIC’s Niche serves as an intrinsic factor for its phenotypic trait—an extremely metastatic cell which can develop tumor in diverse germline lineage. The CD47 & FGFR2 pathway serves as a novel therapeutic target for HCC