Ya-Qin He

Wnt/β-Catenin Signaling Contributes to Activation of Normal and Tumorigenic Liver Progenitor Cells

Adult hepatic progenitor (oval) cells are facultative stem cells in liver, which participate in a range of human liver diseases, including hepatocellular carcinoma (HCC). However, the molecular pathways regulating the expansion and differentiation of these cells are poorly understood. We show that active Wnt/beta-catenin signaling occurs preferentially within the oval cell population, and forced expression of constitutively active beta-catenin mutant promotes expansion of the oval cell population in the regenerated liver. More importantly, we identify a subpopulation of less differentiated progenitor-like cells in HCC cell lines and primary HCC tissues, which are defined by expression of the hepatic progenitor marker OV6 and endowed with endogenously active Wnt/beta-catenin signaling. These OV6(+) HCC cells possess a greater ability to form tumor in vivo and show a substantial resistance to standard chemotherapy compared with OV6(-) tumor cells. The fraction of tumor cells expressing OV6 is enriched after Wnt pathway activation, whereas inhibition of beta-catenin signaling leads to a decrease in the proportion of OV6(+) cells. In addition, the chemoresistance of OV6(+) HCC progenitor-like cells can be reversed by lentivirus-delivered stable expression of microRNA targeting beta-catenin. These results highlight the importance of the Wnt/beta-catenin pathway in activation and expansion of oval cells in normal rodent models and human HCCs. OV6(+) tumor cells may represent the cellular population that confers HCC chemoresistance, and therapies targeted to the Wnt/beta-catenin signaling may provide a specific method to disrupt this resistance mechanism to improve overall tumor control with chemotherapy.

Endotoxin accumulation prevents carcinogen‐induced apoptosis and promotes liver tumorigenesis in rodents

Increasing evidence suggests that the presence of endotoxemia is of substantial clinical relevance to patients with cirrhosis, but it is unclear whether and how gut‐derived LPS amplifies the tumorigenic response of the liver. We found that the circulating levels of LPS were elevated in animal models of carcinogen‐induced hepatocarcinogenesis. Reduction of LPS using antibiotics regimen in rats or genetic ablation of its receptor Toll‐like receptor 4 (TLR4) in mice prevented excessive tumor growth and multiplicity. Additional investigation revealed that TLR4 ablation sensitizes the liver to carcinogen‐induced toxicity via blocking NF‐κB activation and sensitizing the liver to reactive oxygen species (ROS)‐induced toxicity, but lessens inflammation‐mediated compensatory proliferation. Reconstitution of TLR4‐expressing myeloid cells in TLR4‐deficient mice restored diethylnitrosamine (DEN)‐induced hepatic inflammation and proliferation, indicating a paracrine mechanism of LPS in tumor promotion. Meanwhile, deletion of gut‐derived endotoxin suppressed DEN‐induced cytokine production and compensatory proliferation, whereas in vivo LPS pre‐challenge promotes hepatocyte proliferation. Conclusion: Our data indicate that sustained LPS accumulation represents a pathological mediator of inflammation‐associated hepatocellular carcinoma (HCC) and manipulation of the gut flora to prevent pathogenic bacterial translocation and endotoxin absorption may favorably influence liver function in patients with cirrhosis who are at risk of developing HCC. (Hepatology 2010.)

Hepatitis B virus X (HBx) induces tumorigenicity of hepatic progenitor cells in 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine‐treated HBx transgenic mice

Hepatitis B virus X (HBx) protein is implicated in hepatitis B virus (HBV)‐associated liver carcinogenesis. However, it remains unclear whether HBx‐expressing hepatic progenitor cells (HPCs) are attributed to liver tumor formation. In this study, by using HBx transgenic mice and a 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine (DDC)‐induced liver injury model, the relationship between HBx expression and tumorigenicity of HPCs was analyzed. Compared with control mice, an elevated number of EpCAM+ cells with characteristics of HPCs was observed in HBx mice after 1 month and 4 months of DDC diet feeding. All HBx transgenic mice developed liver tumors characterized by histological features of both hepatocellular carcinoma (HCC) and cholangiocarcinoma after 7 months of DDC feeding. Notably, EpCAM+ HPCs isolated from premalignant HBx mice exposed to a DDC diet for 4 months formed subcutaneous mixed‐lineage tumors (four out of six) in nonobese diabetic/severe‐combined immunodeficient (NOD/SCID) mice, and none of the cells from wildtype (WT) induced tumor, indicating that HBx may induce malignant transformation of HPCs that contributes to tumorigenesis. We also found higher titers of circulating interleukin (IL)‐6, activities of IL‐6/STAT3, and Wnt/β‐catenin signaling pathways in HBx transgenic mice, suggesting HBx may induce intrinsic changes in HPCs by way of the above signaling that enables HPCs with tumorigenicity potential. Finally, clinical evidence showed that high HBx expression in human HBV‐related HCC was statistically associated with expansion of EpCAM+ or OV6+ tumor cells and aggressive clinicopathologic features. Conclusion: HBx induces intrinsic cellular transformation promoting the expansion and tumorigenicity of HPCs in DDC‐treated mice, which may be a possible origin for liver cancer induced by chronic hepatitis infection. (HEPATOLOGY 2012)

Profound impact of gut homeostasis on chemically-induced pro-tumorigenic inflammation and hepatocarcinogenesis in rats

BACKGROUND & AIMS Due to its anatomic connection, the liver is constantly exposed to gut-derived bacterial products or metabolites. Disruption of gut homeostasis is associated with many human diseases. The aim of this study was to determine the role of gut homeostasis in initiation and progression of hepatocellular carcinoma (HCC). METHODS Disruption of intestinal homeostasis by penicillin or dextran sulfate sodium (DSS) and its restoration by probiotics were applied in a diethylnitrosamine (DEN) model of rat hepatocarcinogenesis. RESULTS Patients with liver cirrhosis and HCC had significantly increased serum endotoxin levels. Chronic DEN treatment of rats was associated with an imbalance of subpopulations of the gut microflora including a significant suppression of Lactobacillus species, Bifidobacterium species and Enterococcus species as well as intestinal inflammation. Induction of enteric dysbacteriosis or intestinal inflammation by penicillin or DSS, respectively, significantly promoted tumor formation. Administration of probiotics dramatically mitigated enteric dysbacteriosis, ameliorated intestinal inflammation, and most importantly, decreased liver tumor growth and multiplicity. Interestingly, probiotics not only inhibited the translocation of endotoxin, which bears pathogen-associated molecular patterns (PAMPs) but also the activation of damage-associated molecular patterns (DAMPs) such as high-mobility group box 1 (HMGB1). As a result, the production of pro- and anti-inflammatory cytokines was skewed in favor of a reduced tumorigenic inflammation in the liver. CONCLUSIONS The data highlights the importance of gut homeostasis in the pathogenesis of HCC. Modulation of the gut microbiota by probiotics may represent a new avenue for therapeutic intervention to treat or prevent HCC development.

OV6 + tumor-initiating cells contribute to tumor progression and invasion in human hepatocellular carcinoma

BACKGROUND & AIMS Accumulating evidence suggests the involvement of tumor-initiating cells (T-ICs) in cancer genesis, but whether liver T-ICs contribute to HCC invasion and metastasis remains unclear. METHODS OV6(+) T-ICs were isolated from SMMC7721 and HuH7 cell lines by magnetic sorting. Characteristics of T-ICs were assessed by in vitro and mouse xenograft assays. Expression of OV6 was determined by immunostaining in specimens from 218 HCC patients, and Kaplan-Meier survival analysis was used to determine the correlation of OV6 expression with prognosis. RESULTS OV6(+) T-ICs isolated from HCC cell lines not only possess a higher capacity to form tumor spheroids in vitro, but also had a greater potential to form tumors when implanted in non-obese diabetic/severe combined immunodeficient mice, suggesting their elevated self-renewal capacity and tumorigenicity. Moreover, OV6(+) T-ICs exhibited more invasive and metastatic potentials both in vitro and in vivo. Patients with more OV6(+) tumor cells were associated with aggressive clinicopathologic features and poor prognosis. CXCR4 is expressed at higher levels in OV6(+) cells. Recombinant stromal cell-derived factor-1 (SDF-1) treatment expanded the OV6(+) HCC T-ICs population, by sustaining the stem cell property of OV6(+) cells. The SDF-1 effect was blocked by a specific CXCR4 inhibitor, AMD3100, or transfection of siRNA targeting CXCR4. CONCLUSIONS OV6(+) HCC cells may represent a subpopulation of T-ICs with augmented invasion and metastasis potential, which contribute to progression and metastasis of HCC. The SDF-1/CXCR4 axis also provides therapeutic targets for elimination of liver T-ICs.

Abrogation of Local Cancer Recurrence After Radiofrequency Ablation by Dendritic Cell-based Hyperthermic Tumor Vaccine

Local recurrence is a therapeutic challenge for radiofrequency ablation (RFA) in treatment of small solid focal malignancies. Here we show that RFA induced heat shock proteins (HSPs) expression and high mobility group box-1 (HMGB1) translocation in xenografted melanoma, which might create a proinflammatory microenvironment that favors tumor antigen presentation and activation of the effector T cells. On this basis, we investigate whether a prime-boost strategy combining a prime with heat-shocked tumor cell lysate-pulsed dendritic cell (HT-DC) followed by an in situ boost with radiofrequency thermal ablation can prevent local tumor recurrence. The combination treatment with HT-DC and RFA showed potent antitumor effects, with >or=90% of tumor recurrence abrogated following RFA treatment. By contrast, prevaccination with unheated tumor lysate-pulsed DC had little effect on tumor relapse. Analysis of the underlying mechanism revealed that splenocytes from mice treated with HT-DC plus RFA contained significantly more tumor-specific, IFN-gamma-secreting T cells compared with control groups. Moreover, adoptive transfer of splenocytes from successfully treated tumor-free mice protected naive animals from tumor recurrence following RFA, and this was mediated mainly by CD8(+) T cells. Therefore, the optimal priming for the DC vaccination before RFA is important for boosting antigen-specific T cell responses and prevention of cancer recurrence.

Gut-Derived Lipopolysaccharide Promotes T-Cell–Mediated Hepatitis in Mice through Toll-Like Receptor 4

Robust clinical and epidemiologic data support the role of inflammation as a key player in hepatocellular carcinoma (HCC) development. Our previous data showed that gut-derived lipopolysaccharide (LPS) promote HCC development by activating Toll-like receptor 4 (TLR4) expressed on myeloid-derived cells. However, the effects of gut-derived LPS on other types of liver injury models are yet to be studied. The purpose of this study was to determine the importance of gut-derived LPS and TLR4 signaling in a T-cell–mediated hepatitis—Con A–induced hepatitis model, which mimic the viral hepatitis. Reduction of endotoxin using antibiotics regimen or genetic ablation of TLR4 in mice significantly alleviate Con A–induced liver injury by inhibiting the infiltration of T lymphocytes into the liver and the activation of CD4+ T lymphocytes as well as the production of T helper 1 cytokines; in contrast, exogenous LPS can promote Con A–induced hepatitis and CD4+ T cells activation in vivo and in vitro. Reconstitution of TLR4–expressing myeloid cells in TLR4-deficient mice restored Con A–induced liver injury and inflammation, indicating the major cell target of LPS. In addition, TLR4 may positively regulate the target hepatocellular apoptosis via the perforin/granzyme B pathway. These data suggest that gut-derived LPS and TLR4 play important positive roles in Con A–induced hepatitis and modulation of the gut microbiotia may represent a new avenue for therapeutic intervention to treat acute hepatitis induced by hepatitis virus infection, thus to prevent hepatocellular carcinoma. Cancer Prev Res; 5(9); 1090–102. ©2012 AACR.

Structural basis of interaction between protein tyrosine phosphatase PCP-2 and β-catenin

PCP-2 is a member of receptor-like protein tyrosine phosphatase of the MAM domain family. To investigate which part of PCP-2 was involved in its interaction with β-catenin, we constructed various deletion mutants of PCP-2. These PCP-2 mutants and wild-type PCP-2 were co-transfected into BHK-21 cells with β-catenin individually. Anin vivo binding assay revealed that the expression of wild-type PCP-2, PCP-2 ΔC1C2 (deleted PCP-2 without both PTP domains) and PCP-2 ΔC2 (deleted PCP-2 without the second PTP domain) could be immunoprecipitated by anti-catenin antibody in every co-transfection, but PCP-2 EXT (deleted PCP-2 without the juxtamembrane region and both PTP domains) was missing, which implied that PCP-2 and β-catenin could associate directly and the juxtamembrane region in PCP-2 was sufficient for the process.

Signal Transduction of Hepatocellular Carcinoma

Signal transduction pathways involve a large number of molecules and govern the behavior of cells. When disrupted, these signaling pathways can lead to developmental defects, cancer and other diseases.