Functional interaction between Wnt3 and Frizzled-7 leads to activation of the Wnt/beta-catenin signaling pathway in hepatocellular carcinoma cells

Deregulation of Frizzled Receptors in Hepatocellular Carcinoma

G protein-coupled receptors (GPCRs) have a substantial role in tumorigenesis and are described as a “cancer driver”. Aberrant expression or activation of GPCRs leads to the deregulation of downstream signaling pathways, thereby promoting cancer progression. In hepatocellular carcinoma (HCC), the Wnt signaling pathway is frequently activated and it is associated with an aggressive HCC phenotype. Frizzled (FZD) receptors, a family member of GPCRs, are known to mediate Wnt signaling. Accumulating findings have revealed the deregulation of FZD receptors in HCC and their functional roles have been implicated in HCC progression. Given the important role of FZD receptors in HCC, we summarize here the expression pattern of FZD receptors in HCC and their corresponding functional roles during HCC progression. We also further review and highlight the potential targeting of FZD receptors as an alternative therapeutic strategy in HCC.

Wnt Signaling in Adult Epithelial Stem Cells and Cancer

Wnt/β-catenin signaling is integral to the homeostasis and regeneration of many epithelial tissues due to its critical role in adult stem cell regulation. It is also implicated in many epithelial cancers, with mutations in core pathway components frequently present in patient tumors. In this chapter, we discuss the roles of Wnt/β-catenin signaling and Wnt-regulated stem cells in homeostatic, regenerative and cancer contexts of the intestines, stomach, skin, and liver. We also examine the sources of Wnt ligands that form part of the stem cell niche. Despite the diversity in characteristics of various tissue stem cells, the role(s) of Wnt/β-catenin signaling is generally coherent in maintaining stem cell fate and/or promoting proliferation. It is also likely to play similar roles in cancer stem cells, making the pathway a salient therapeutic target for cancer. While promising progress is being made in the field, deeper understanding of the functions and signaling mechanisms of the pathway in individual epithelial tissues will expedite efforts to modulate Wnt/β-catenin signaling in cancer treatment and tissue regeneration.

Sox9 confers stemness properties in hepatocellular carcinoma through Frizzled-7 mediated Wnt/β-catenin signaling

Sox9, an SRY-related HMG box transcription factor, is a progenitor/precursor cell marker of the liver expressed during embryogenesis and following liver injury. In this study, we investigated the role of Sox9 and its molecular mechanism with reference to stemness properties in hepatocellular carcinoma (HCC). Here, we observed upregulation of Sox9 in human HCC tissues compared with the non-tumorous liver counterparts (p < 0.001). Upregulation of Sox9 transcript level was associated with poorer tumor cell differentiation (p = 0.003), venous invasion (p = 0.026), advanced tumor stage (p = 0.044) and shorter overall survival (p = 0.042). Transcript levels of Sox9 and CD24 were positively correlated. Silencing of Sox9 in HCC cells inhibited in vitro cell proliferation and tumorsphere formation, sensitized HCC cells to chemotherapeutic agents, and suppressed in vivo tumorigenicity. In addition, knockdown of Sox9 suppressed HCC cell migration, invasion, and in vivo lung metastasis. Further studies showed that Sox9 endowed stemness features through activation of Wnt/β-catenin signaling, which was confirmed by the partial rescue effect on tumorigenicity and self-renewal upon transfection of active β-catenin in Sox9 knockdown cells. By ChIP and luciferase promoter assays, Frizzled-7 was identified to be the direct transcriptional target of Sox9. In conclusion, Sox9 confers stemness properties of HCC through Frizzled-7 mediated Wnt/β-catenin pathway.

Down-regulation of the Wnt/β-catenin signaling pathway by Cacnb4

The β4 isoform of the β-subunits of voltage-gated calcium channel regulates cell proliferation and cell cycle progression. Herein we show that coexpression of the β4-subunit with actors of the canonical Wnt/β-catenin signaling pathway in a hepatoma cell line inhibits Wnt-responsive gene transcription and decreases cell division, in agreement with the role of the Wnt pathway in cell proliferation. β4-subunit-mediated inhibition of Wnt signaling is observed in the presence of LiCl, an inhibitor of glycogen synthase kinase (GSK3) that promotes β-catenin translocation to the nucleus. Expression of β4-subunit mutants that lost the ability to translocate to the nucleus has no effect on Wnt signaling, suggesting that β4-subunit inhibition of Wnt signaling occurs downstream from GSK3 and requires targeting of β4-subunit to the nucleus. β4-subunit coimmunoprecipitates with the TCF4 transcription factor and overexpression of TCF4 reverses the effect of β4-subunit on the Wnt pathway. We thus propose that the interaction of nuclear β4-subunit with TCF4 prevents β-catenin binding to TCF4 and leads to the inhibition of the Wnt-responsive gene transcription. Thereby, our results show that β4-subunit is a TCF4 repressor and therefore appears as an interesting candidate for the regulation of this pathway in neurons where β4-subunit is specifically expressed.

Modulation of Wnt signaling pathway by hepatitis B virus

Hepatitis B virus (HBV) has a global distribution and is one of the leading causes of hepatocellular carcinoma. The precise mechanism of pathogenicity of HBV-associated hepatocellular carcinoma (HCC) is not yet fully understood. Viral-related proteins are known to take control of several cellular pathways like Wnt/β-catenin, TGF-β, Raf/MAPK and ROS for the virus's own replication. This affects cellular persistence, multiplication, migration, alteration and genomic instability. The Wnt/FZD/β-catenin signaling pathway plays a significant role in the pathology and physiology of the liver and has been identified as a main factor in HCC development. The role of β-catenin is linked mainly to the canonical pathway of the signaling system. Progression of liver diseases is known to be accompanied by disturbances in β-catenin expression (mainly overexpression), with its cytoplasmic or nuclear translocation. In recent years, studies have documented that the HBV X protein and hepatitis B surface antigen (HBsAg) can act as pathogenic factors that are involved in the modulation and induction of canonical Wnt signaling pathway. In the present review we explore the interaction of HBV genome products with components of the Wnt/β-catenin signaling pathway that results in the enhancement of the pathway and leads to hepatocarcinogenesis.

FZD7 is a novel prognostic marker and promotes tumor metastasis via WNT and EMT signaling pathways in esophageal squamous cell carcinoma

Frizzled (FZD) proteins are receptors for secreted WNT proteins and play a critical role in the malignant progression of various cancers. However, the role of human FZD family members in esophageal squamous cell carcinoma (ESCC) was rarely investigated. In this study, we found that the FZD7 gene was the most commonly up-regulated FZD member in ESCC cell lines compared with other FZDs. TMA studies further validated that FZD7 protein was up-regulated in 165 of 252 (65.5%) informative ESCC patients and significantly correlated with poor overall survival (P=0.001). Additionally, multivariate Cox regression analysis showed that FZD7 overexpression was an independent prognostic factor for ESCC patients. Ectopic expression of FZD7 could promote ESCC cell metastasis both in vitro and in vivo. Under WNT3A stimulation, FZD7 was able to induce the nuclear translocation of β-catenin and activate the downstream targets of WNT/β-catenin signaling, as well as promote epithelial-mesenchymal transition (EMT) potential in ESCC cells. Our study demonstrated for the first time that FZD7 contributes to the malignant progression of ESCC and represents a novel prognostic marker and a potential therapeutic target for ESCC patients.

Mapping of Wnt-Frizzled interactions by multiplex CRISPR targeting of receptor gene families

Signaling pathway modules are often encoded by several closely related paralogous genes that can have redundant roles and are therefore difficult to analyze by loss-of-function analysis. A typical example is the Wnt signaling pathway, which in mammals is mediated by 19 Wnt ligands that can bind to 10 Frizzled (FZD) receptors. Although significant progress in understanding Wnt-FZD receptor interactions has been made in recent years, tools to generate systematic interaction maps have been largely lacking. Here we generated cell lines with multiplex mutant alleles of FZD1, FZD2, and FZD7 and demonstrate that these cells are unresponsive to canonical Wnt ligands. Subsequently, we performed genetic rescue experiments with combinations of FZDs and canonical Wnts to create a functional ligand–receptor interaction map. These experiments showed that whereas several Wnt ligands, such as Wnt3a, induce signaling through a broad spectrum of FZD receptors, others, such as Wnt8a, act through a restricted set of FZD genes. Together, our results map functional interactions of FZDs and 10 Wnt ligands and demonstrate how multiplex targeting by clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 can be used to systematically elucidate the functions of multigene families.—Voloshanenko, O., Gmach, P., Winter, J., Kranz, D., Boutros, M. Mapping of Wnt-Frizzled interactions by multiplex CRISPR targeting of receptor gene families.

Downregulated connexin32 promotes EMT through the Wnt/β-catenin pathway by targeting Snail expression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the common malignances in the world and is associated with high mortality and poor prognosis, partly due to early invasion and metastasis. Cx32 has been indicated to be involved in the progression of many cancers including HCC, but its relationship with tumor invasion and metastasis is still controversial. In the present study, the downregulated Cx32 in HCC tissue was found negatively correlated with histological grade and lymph node metastasis. Cx32 regulated HCC migration and invasion in vitro and inhibited tumor metastasis in xenograft models in vivo. We subsequently identified that Cx32 mediated epithelial-mesenchymal transition (EMT) by regulating Snail expression, and the enhanced Snail was due to activation of Wnt/β-catenin signaling in response to Cx32 inhibition. Finally, decreased expression of Cx32 showed strong correlation with loss/reduction of E-cadherin, higher expression of Snail, and nuclear accumulation of β-catenin in HCC tissues. Taken together, our results suggest that Cx32 inhibits HCC invasion and metastasis through Snail-mediated EMT, Cx32 and this signaling pathway molecules may offer potential targets for HCC cancer therapy.

FZD7 regulates BMSCs-mediated protection of CML cells

Inspite of effective treatment with imatinib (IM), chronic myeloid leukemia (CML) is still an incurable disease. Some patients became refractory because of IM resistance. Bone marrow mesenchymal stem cells (BMSCs) have been implicated a role in promoting CML cells' resistance against IM treatment. The detailed molecular mechanisms, however, remain largely unknown. In this study, we found that BMSCs increased the expression of FZD7 and activated Wnt/β-catenin signaling pathway in CML cells. BMSCs from CML patients showed increased efficiency to accelerate CML cell proliferation, enhance the drug resistance of K562 cells and up-regulate the expression of FZD7. Antagonism of FZD7 expression by shRNA significantly suppressed proliferation and increased IM sensitivity of CML cells co-cultured with BMSCs cells. Our findings suggest that FZD7, involved in canonical Wnt signaling pathway, plays a critical role in mediating BMSCs-dependent protection of CML cells, and potentially provide a novel therapeutic target for CML.

MicroRNA-542-3p inhibits the growth of hepatocellular carcinoma cells by targeting FZD7/Wnt signaling pathway

MicroRNAs (miRNA) are relevant regulators of the tumorigenesis of various cancers, such as hepatocellular carcinoma (HCC). Recent studies have suggested that miR-542-3p is a tumor suppressor gene in numerous cancers. However, the role of miR-542-3p in HCC remains unclear. This study showed that miR-542-3p was downregulated in HCC tissues and cell lines. MTT, colony formation, and cell cycle assays revealed that miR-542-3p overexpression inhibited HCC cell growth, whereas miR-542-3p suppression promoted cell growth. Frizzled7 (FZD7), the most important Wnt receptor involved in cancer development and progression, was identified as a functional target of miR-542-3p through dual-luciferase reporter assay, RT-qPCR, and Western blot. The mRNA expression of FZD7 was inversely correlated with miR-542-3p expression in HCC tissues. miR-542-3p overexpression could significantly decrease the activation of Wnt signaling pathway in HCC cells. FZD7 overexpression could significantly reverse the inhibitory effect of miR-542-3p on HCC cell growth and Wnt signaling pathway. Taken together, our study suggests that miR-542-3p inhibits HCC cell growth by targeting FZD7 and inhibiting Wnt signaling pathway. The decreased miR-542-3p expression may also contribute to the progression of HCC and may represent a novel molecular therapeutic target for HCC.

Keratin 18-deficiency results in steatohepatitis and liver tumors in old mice: A model of steatohepatitis-associated liver carcinogenesis

Backround: Steatohepatitis (SH)-associated liver carcinogenesis is an increasingly important issue in clinical medicine. SH is morphologically characterized by steatosis, hepatocyte injury, ballooning, hepatocytic cytoplasmic inclusions termed Mallory-Denk bodies (MDBs), inflammation and fibrosis.

RESULTS

17-20-months-old Krt18-/- and Krt18+/- mice in contrast to wt mice spontaneously developed liver lesions closely resembling the morphological spectrum of human SH as well as liver tumors. The pathologic alterations were more pronounced in Krt18-/- than in Krt18+/- mice. The frequency of liver tumors with male predominance was significantly higher in Krt18-/- compared to age-matched Krt18+/- and wt mice. Krt18-deficient tumors in contrast to wt animals displayed SH features and often pleomorphic morphology. aCGH analysis of tumors revealed chromosomal aberrations in Krt18-/- liver tumors, affecting loci of oncogenes and tumor suppressor genes.

MATERIALS AND METHODS

Livers of 3-, 6-, 12- and 17-20-months-old aged wild type (wt), Krt18+/- and Krt18-/- (129P2/OlaHsd background) mice were analyzed by light and immunofluorescence microscopy as well as immunohistochemistry. Liver tumors arising in aged mice were analyzed by array comparative genomic hybridization (aCGH).

CONCLUSIONS

Our findings show that K18 deficiency of hepatocytes leads to steatosis, increasing with age, and finally to SH. K18 deficiency and age promote liver tumor development in mice, frequently on the basis of chromosomal instability, resembling human HCC with stemness features.

Genetic alterations in hepatocellular carcinoma: An update

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. Although recent advances in therapeutic approaches for treating HCC have improved the prognoses of patients with HCC, this cancer is still associated with a poor survival rate mainly due to late diagnosis. Therefore, a diagnosis must be made sufficiently early to perform curative and effective treatments. There is a need for a deeper understanding of the molecular mechanisms underlying the initiation and progression of HCC because these mechanisms are critical for making early diagnoses and developing novel therapeutic strategies. Over the past decade, much progress has been made in elucidating the molecular mechanisms underlying hepatocarcinogenesis. In particular, recent advances in next-generation sequencing technologies have revealed numerous genetic alterations, including recurrently mutated genes and dysregulated signaling pathways in HCC. A better understanding of the genetic alterations in HCC could contribute to identifying potential driver mutations and discovering novel therapeutic targets in the future. In this article, we summarize the current advances in research on the genetic alterations, including genomic instability, single-nucleotide polymorphisms, somatic mutations and deregulated signaling pathways, implicated in the initiation and progression of HCC. We also attempt to elucidate some of the genetic mechanisms that contribute to making early diagnoses of and developing molecularly targeted therapies for HCC.

Molecular alterations in the carcinogenesis and progression of hepatocellular carcinoma: Tumor factors and background liver factors

Although hepatocellular carcinoma (HCC) is associated with poor prognosis worldwide, the molecular mechanisms underlying the carcinogenesis and progression of this disease remain unclear. Several tumor characteristics have previously been demonstrated to be prognostic factors of survival following hepatic resection, or the recurrence of HCC or other types of cancer. Comparisons of normal tissues and HCC tumor tissues have revealed the presence of numerous molecular alterations in HCC, including genetic and epigenetic mechanisms, particularly mutations in certain genes and DNA methylation in the promoter regions of tumor-suppressor genes. A number of studies have previously used array analysis to detect variations in the expression levels of cancer-associated genes and microRNAs, and in DNA methylation. However, an investigation of HCC tumor tissues may not determine the effect of noncancerous liver tissues (background liver) in patients with HCC. As HCC may recur multicentrically following resection, a damaged or chronically diseased HCC background liver may be considered as a pre-cancerous organ. Therefore, the influence of the background liver on HCC requires further study. Detailed studies regarding the background liver may be essential for the improved understanding of the carcinogenesis and progression of this malignancy; however only a few studies have investigated the microenvironment of the HCC background liver. The present review discusses prior molecular studies of hepatocarcinogenesis that focus on HCC and background liver tissues.

Aberrant regulation of Wnt signaling in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies in the world. Several signaling pathways, including the wingless/int-1 (Wnt) signaling pathway, have been shown to be commonly activated in HCC. The Wnt signaling pathway can be triggered via both catenin β1 (CTNNB1)-dependent (also known as "canonical") and CTNNB1-independent (often referred to as "non-canonical") pathways. Specifically, the canonical Wnt pathway is one of those most frequently reported in HCC. Aberrant regulation from three complexes (the cell-surface receptor complex, the cytoplasmic destruction complex and the nuclear CTNNB1/T-cell-specific transcription factor/lymphoid enhancer binding factor transcriptional complex) are all involved in HCC. Although the non-canonical Wnt pathway is rarely reported, two main non-canonical pathways, Wnt/planar cell polarity pathway and Wnt/Ca(2+) pathway, participate in the regulation of hepatocarcinogenesis. Interestingly, the canonical Wnt pathway is antagonized by non-canonical Wnt signaling in HCC. Moreover, other signaling cascades have also been demonstrated to regulate the Wnt pathway through crosstalk in HCC pathogenesis. This review provides a perspective on the emerging evidence that the aberrant regulation of Wnt signaling is a critical mechanism for the development of HCC. Furthermore, crosstalk between different signaling pathways might be conducive to the development of novel molecular targets of HCC.

Frizzled7: A Promising Achilles' Heel for Targeting the Wnt Receptor Complex to Treat Cancer

Frizzled7 is arguably the most studied member of the Frizzled family, which are the cognate Wnt receptors. Frizzled7 is highly conserved through evolution, from Hydra through to humans, and is expressed in diverse organisms, tissues and human disease contexts. Frizzled receptors can homo- or hetero-polymerise and associate with several co-receptors to transmit Wnt signalling. Notably, Frizzled7 can transmit signalling via multiple Wnt transduction pathways and bind to several different Wnt ligands, Frizzled receptors and co-receptors. These promiscuous binding and functional properties are thought to underlie the pivotal role Frizzled7 plays in embryonic developmental and stem cell function. Recent studies have identified that Frizzled7 is upregulated in diverse human cancers, and promotes proliferation, progression and invasion, and orchestrates cellular transitions that underscore cancer metastasis. Importantly, Frizzled7 is able to regulate Wnt signalling activity even in cancer cells which have mutations to down-stream signal transducers. In this review we discuss the various aspects of Frizzled7 signalling and function, and the implications these have for therapeutic targeting of Frizzled7 in cancer.

Molecular pathogenesis of hepatocellular carcinoma and impact of therapeutic advances

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality and has an increasing incidence worldwide. HCC can be induced by multiple etiologies, is influenced by many risk factors, and has a complex pathogenesis. Furthermore, HCCs exhibit substantial heterogeneity, which compounds the difficulties in developing effective therapies against this highly lethal cancer. With advances in cancer biology and molecular and genetic profiling, a number of different mechanisms involved in the development and progression of HCC have been identified. Despite the advances in this area, the molecular pathogenesis of hepatocellular carcinoma is still not completely understood. This review aims to elaborate our current understanding of the most relevant genetic alterations and molecular pathways involved in the development and progression of HCC, and anticipate the potential impact of future advances on therapeutic drug development.

Characterizing the activation of the Wnt signaling pathway in hilar cholangiocarcinoma using a tissue microarray approach

Hilar cholangiocarcinoma (HCCA) is an invasive hepatic malignancy that is difficult to biopsy; therefore, novel markers of HCCA prognosis are needed. Here, the level of canonical Wnt activation in patients with HCCA, intrahepatic cholangiocarcinoma (IHCC), and congenital choledochal cysts (CCC) was compared to understand the role of Wnt signaling in HCCA. Pathology specimens from HCCA (n=129), IHCC (n=31), and CCC (n=45) patients were used to construct tissue microarrays. Wnt2, Wnt3, β-catenin, TCF4, c-Myc, and cyclin D1 were detected by immunohistochemistry. Parallel correlation analysis was used to analyze differences in protein levels between the HCCA, IHCC, and CCC groups. Univariate and multivariate analyses were used to determine independent predictors of successful resection and prognosis in the HCCA group. The protein levels of Wnt2, β-catenin, TCF4, c-Myc, and cyclin D1 were significantly higher in HCCA compared to IHHC or CCC. Wnt signaling activation (Wnt2+, Wnt3+, nuclear β-catenin+, nuclear TCF4+) was significantly greater in HCCA tissues than CCC tissues. Univariable analyses indicated that expression of cyclin D1 as well as Wnt signaling activation, and partial Wnt activation (Wnt2+ or Wnt3+ and nuclear β-catenin+ or nuclear TCF4+) predicted successful resection, but only cyclin D1 expression remained significant in multivariable analyses. Only partial Wnt activation was an independent predictor of survival time. Proteins in the canonical Wnt signaling pathway were present at higher levels in HCCA and correlated with tumor resecility and patient prognosis. These results suggest that Wnt pathway analysis may be a useful marker for clinical outcome in HCCA.

FRIZZLED7 Is Required for Tumor Initiation and Metastatic Growth of Melanoma Cells

Metastases are thought to arise from cancer stem cells and their tumor initiating abilities are required for the establishment of metastases. Nevertheless, in metastatic melanoma, the nature of cancer stem cells is under debate and their contribution to metastasis formation remains unknown. Using an experimental metastasis model, we discovered that high levels of the WNT receptor, FZD7, correlated with enhanced metastatic potentials of melanoma cell lines. Knocking down of FZD7 in a panel of four melanoma cell lines led to a significant reduction in lung metastases in animal models, arguing that FZD7 plays a causal role during metastasis formation. Notably, limiting dilution analyses revealed that FZD7 is essential for the tumor initiation of melanoma cells and FZD7 knockdown impeded the early expansion of metastatic melanoma cells shortly after seeding, in accordance with the view that tumor initiating ability of cancer cells is required for metastasis formation. FZD7 activated JNK in melanoma cell lines in vitro and the expression of a dominant negative JNK suppressed metastasis formation in vivo, suggesting that FZD7 may promote metastatic growth of melanoma cells via activation of JNK. Taken together, our findings uncovered a signaling pathway that regulates the tumor initiation of melanoma cells and contributes to metastasis formation in melanoma.

MicroRNA-27b suppresses Helicobacter pylori-induced gastric tumorigenesis through negatively regulating Frizzled7

MicroRNAs (miRNAs) are novel tools for cancer therapy. Frizzled7 (FZD7) is an important co-receptor in the WNT signaling pathway. The WNT signaling pathway is aberrantly activated in Helicobacter pylori (H. pylori)‑infected gastric cancer cells. However, the role of FZD7 in H. pylori‑induced gastric tumorigenesis remains unknown. In this study, we investigated the potential role of FZD7 in H. pylori-induced gastric tumorigenesis and validated the possibility that targeting of FZD7 by specific miRNA inhibits H. pylori-induced gastric tumorigenesis. First, we found that FZD7 was significantly induced by H. pylori infection in a dose- and time-dependent manner. Knockdown of FZD7 by FZD7 small interfering RNA effectively inhibited H. pylori infection-induced cell proliferation of gastric cancer cells. We found that microRNA-27b (miR-27b) was the predicted miRNA for FZD7 and that miR-27b negatively regulated FZD7 expression by targeting the 3'-untranslated region of FZD7. Furthermore, miR-27b overexpression significantly inhibited H. pylori infection-induced cell proliferation and WNT signaling pathway activation in gastric cancer cells. Restoration of FZD7 expression significantly attenuated the inhibitory effect of miR-27b overexpression on cell proliferation and WNT signaling pathway activation. Collectively, our study suggests that FZD7 triggered by H. pylori infection contributes to the H. pylori infection-induced cell proliferation that links the WNT. Thus, miR-27b may be a promising molecular target for the treatment of the disease.

Overexpression of Rab25 promotes hepatocellular carcinoma cell proliferation and invasion

Rab25 was reported to be associated with several human cancers and malignant biological behavior of cancer cells. The goal of the present study was to determine its expression pattern and biological function in human hepatocellular carcinoma (HCC). We examined Rab25 protein in 92 cases of HCC tissues and 3 HCC cell lines. The results showed that Rab25 was upregulated in HCC tissues and cells compared with normal liver tissues and cell line. Rab25 overexpression correlated with advanced tumor stage and nodal metastasis. Rab25 small interfering RNA (siRNA) was employed in Bel7402 and SK-Hep-1 cell lines. Cell Counting Kit-8 (CCK-8) assay and colony formation assay showed that Rab25 depletion blocked cell growth rate and inhibited colony formation ability. Transwell assay showed that Rab25 depletion negatively regulated the invading ability of HCC cells. To explore the possible mechanisms, we checked several signaling pathways and found that Rab25 depletion downregulated AKT phosphorylation. In addition, luciferase reporter assay showed that Rab25 depletion inhibited the Wnt signaling pathway and its target genes such as cyclin D1, c-myc, and MMP7. In conclusion, Rab25 is overexpressed in human HCC and contributes to cancer cell proliferation and invasion possibly through regulation of the Wnt signaling pathway.

Frizzled-7 promoter is highly active in tumors and promoter-driven Shiga-like toxin I inhibits hepatocellular carcinoma growth

Frizzled-7 protein plays a significant role in the formation of several malignant tumors. Up regulation of the Frizzled-7 in cancer cell lines is associated with nuclear accumulation of wild-type β-catenin from the Wnt/β-catenin pathway which is frequently activated in tumors. To analyze activity of the Frizzled-7 promoter in tumor cells, we constructed two recombinant plasmid vectors in which the Frizzled-7 promoter was used to drive the expression of green fluorescent protein (GFP) and Shiga-like toxin I (Stx1) (pFZD7-GFP/Stx1) genes. The Frizzled-7 protein was found to be expressed in the cancer cell lines but not in the normal cell lines. The GFP expression was restricted to the cancer cell lines and xenografts in the BALB/C mice but not to normal cell lines. Moreover, cell proliferation and tumor growth decreased significantly after transfection with the pFZD7-Stx1. Results from this study will help determine a highly effective strategy for gene therapy of tumors.

Wnt-/-β-catenin pathway signaling in human hepatocellular carcinoma

The molecular basis of the carcinogenesis of hepatocellular carcinoma (HCC) has not been adequately clarified, which negatively impacts the development of targeted therapy protocols for this overwhelming neoplasia. The aberrant activation of signaling in the HCC is primarily due to the deregulated expression of the components of the Wnt-/-β-catenin. This leads to the activation of β-catenin/T-cell factor-dependent target genes that control cell proliferation, cell cycle, apoptosis, and cell motility. The deregulation of the Wnt pathway is an early event in hepatocarcinogenesis. An aggressive phenotype was associated with HCC, since this pathway is implicated in the proliferation, migration, and invasiveness of cancer cells, regarding the cell’s own survival. The disruption of the signaling cascade Wnt-/-β-catenin has shown anticancer properties in HCC’s clinical evaluations of therapeutic molecules targeted for blocking the Wnt signaling pathway for the treatment of HCC, and it represents a promising perspective. The key to bringing this strategy in to clinical practice is to identify new molecules that would be effective only in tumor cells with aberrant signaling β-catenin.

Structure-based Discovery of Novel Small Molecule Wnt Signaling Inhibitors by Targeting the Cysteine-rich Domain of Frizzled

Frizzled is the earliest discovered glycosylated Wnt protein receptor and is critical for the initiation of Wnt signaling. Antagonizing Frizzled is effective in inhibiting the growth of multiple tumor types. The extracellular N terminus of Frizzled contains a conserved cysteine-rich domain that directly interacts with Wnt ligands. Structure-based virtual screening and cell-based assays were used to identify five small molecules that can inhibit canonical Wnt signaling and have low IC₅₀ values in the micromolar range. NMR experiments confirmed that these compounds specifically bind to the Wnt binding site on the Frizzled8 cysteine-rich domain with submicromolar dissociation constants. Our study confirms the feasibility of targeting the Frizzled cysteine-rich domain as an effective way of regulating canonical Wnt signaling. These small molecules can be further optimized into more potent therapeutic agents for regulating abnormal Wnt signaling by targeting Frizzled.

Activation of signal transduction pathways during hepatic oncogenesis

BACKGROUND AND AIMS

Understanding the molecular pathogenesis of hepatocellular carcinoma (HCC) is essential to identify therapeutic targets. A hepatitis B virus (HBV) related double transgenic murine model was developed.

METHODS

Liver specific expression of HBV X protein (HBx) and insulin receptor substrate 1 (IRS1) was achieved and transgenic mice were followed from birth to age 21 months. Liver and tumor tissue were assessed for histologic changes as well as activation of signal transduction pathways by qRT-PCR and multiplex ELISA protein assays.

RESULTS

Overexpression of HBx and IRS1 stimulates liver cell proliferation in the double transgenic mice. Only the male mice developed HCC starting at age 15-18 months. The IN/IGF1/IRS1/MAPK/ERK and IN/IGF1/IRS1/PI3K/AKT/GSK3β cascades were activated early (6-9 months) in the liver followed by WNT/β-catenin and Notch signaling. Aspartate β-hydroxylase (ASPH) was found to link these upstream growth factor signaling pathways to downstream Notch activation in tumor tissues.

CONCLUSIONS

Sustained overexpression of HBx and IRS1 led to constitutive activation of a tripartite growth factor signal transduction cascade in the liver and was necessary and sufficient to promote HCC development and progression.

Modulating the expression level of secreted Wnt3 influences cerebellum development in zebrafish transgenics

The boundaries of brain regions are associated with the tissue-specific secretion of ligands from different signaling pathways. The dynamics of these ligands in vivo and the impact of its disruption remain largely unknown. Using light and fluorescence microscopy for the overall imaging of the specimen and fluorescence correlation spectroscopy (FCS) to determine Wnt3 dynamics, we demonstrated that Wnt3 regulates cerebellum development during embryogenesis using zebrafish wnt3 transgenics with either tissue-specific expression of an EGFP reporter or a functionally active fusion protein, Wnt3EGFP. The results suggest a state of dynamic equilibrium of Wnt3EGFP mobility in polarized neuroepithelial-like progenitors in the dorsal midline and cerebellar progenitors on the lateral side. Wnt3EGFP is secreted from the cerebellum as shown by measurements of its mobility in the ventricular cavity. The importance of Wnt secretion in brain patterning was validated with the Porcn inhibitor Wnt-C59 (C59), which, when applied early, reduced membrane-bound and secreted fractions of Wnt3EGFP and led to a malformed brain characterized by the absence of epithalamus, optic tectum and cerebellum. Likewise, interference with Wnt secretion later on during cerebellar development negatively impacted cerebellar growth and patterning. Our work, supported by quantitative analysis of protein dynamics in vivo, highlights the importance of membrane-localized and secreted Wnt3 during cerebellum development.

Conceptual models for the initiation of hepatitis B virus-associated hepatocellular carcinoma

Although chronic hepatitis B virus (HBV) infection is a known risk factor for the development of hepatocellular carcinoma (HCC), the steps involved in the progression from normal liver to HCC are poorly understood. In this review, we apply five conceptual models, previously proposed by Vineis et al. to explain carcinogenesis in general, to explore the possible steps involved in the initiation and evolution of HBV-associated HCC. Available data suggest that the most suitable and inclusive model is based on evolution of hepatocyte subpopulations. In this evolutionary model, HCC-associated changes are driven by selection and subsequent clonal expansion of phenotypically altered hepatocyte subpopulations in the microenvironment of the HBV-infected liver. This model can incorporate the wide range of mechanisms proposed to play a role in the initiation of HCC including oncogenic HBV proteins, integration of HBV DNA and chronic inflammation of the liver. The model may assist in the early prevention, detection and treatment of HCC and may guide future studies of the initiation of HBV-associated HCC.

β-Catenin Signaling and Roles in Liver Homeostasis, Injury, and Tumorigenesis

β-catenin (encoded by CTNNB1) is a subunit of the cell surface cadherin protein complex that acts as an intracellular signal transducer in the WNT signaling pathway; alterations in its activity have been associated with the development of hepatocellular carcinoma and other liver diseases. Other than WNT, additional signaling pathways also can converge at β-catenin. β-catenin also interacts with transcription factors such as T-cell factor, forkhead box protein O, and hypoxia inducible factor 1α to regulate the expression of target genes. We discuss the role of β-catenin in metabolic zonation of the adult liver. β-catenin also regulates the expression of genes that control metabolism of glucose, nutrients, and xenobiotics; alterations in its activity may contribute to the pathogenesis of nonalcoholic steatohepatitis. Alterations in β-catenin signaling may lead to activation of hepatic stellate cells, which is required for fibrosis. Many hepatic tumors such as hepatocellular adenomas, hepatocellular cancers, and hepatoblastomas have mutations in CTNNB1 that result in constitutive activation of β-catenin, so this molecule could be a therapeutic target. We discuss how alterations in β-catenin activity contribute to liver disease and how these might be used in diagnosis and prognosis, as well as in the development of therapeutics.

Frizzled7 functions as a Wnt receptor in intestinal epithelial Lgr5(+) stem cells

The mammalian adult small intestinal epithelium is a rapidly self-renewing tissue that is maintained by a pool of cycling stem cells intermingled with Paneth cells at the base of crypts. These crypt base stem cells exclusively express Lgr5 and require Wnt3 or, in its absence, Wnt2b. However, the Frizzled (Fzd) receptor that transmits these Wnt signals is unknown. We determined the expression profile of Fzd receptors in Lgr5(+) stem cells, their immediate daughter cells, and Paneth cells. Here we show Fzd7 is enriched in Lgr5(+) stem cells and binds Wnt3 and Wnt2b. Conditional deletion of the Fzd7 gene in adult intestinal epithelium leads to stem cell loss in vivo and organoid death in vitro. Crypts of conventional Fzd7 knockout mice show decreased basal Wnt signaling and impaired capacity to regenerate the epithelium following deleterious insult. These observations indicate that Fzd7 is required for robust Wnt-dependent processes in Lgr5(+) intestinal stem cells.

Molecular signalling in hepatocellular carcinoma: Role of and crosstalk among WNT/ß-catenin, Sonic Hedgehog, Notch and Dickkopf-1

Hepatocellular carcinoma is the sixth most common cancer worldwide. In the majority of cases, there is evidence of existing chronic liver disease from a variety of causes including viral hepatitis B and C, alcoholic liver disease and nonalcoholic steatohepatitis. Identification of the signalling pathways used by hepatocellular carcinoma cells to proliferate, invade or metastasize is of paramount importance in the discovery and implementation of successfully targeted therapies. Activation of Wnt/β-catenin, Notch and Hedgehog pathways play a critical role in regulating liver cell proliferation during development and in controlling crucial functions of the adult liver in the initiation and progression of human cancers. β-catenin was identified as a protein interacting with the cell adhesion molecule E-cadherin at the cell-cell junction, and has been shown to be one of the most important mediators of the Wnt signalling pathway in tumourigenesis. Investigations into the role of Dikkopf-1 in hepatocellular carcinoma have demonstrated controversial results, with a decreased expression of Dickkopf-1 and soluble frizzled-related protein in various cancers on one hand, and as a possible negative prognostic indicator of hepatocellular carcinoma on the other. In the present review, the authors focus on the Wnt⁄β-catenin, Notch and Sonic Hedgehog pathways, and their interaction with Dikkopf-1 in hepatocellular carcinoma.

Chronic Ethanol-Induced Impairment of Wnt/β-Catenin Signaling is Attenuated by PPAR-δ Agonist

BACKGROUND

The Wnt/β-catenin pathway regulates liver growth, repair, and regeneration. Chronic ethanol (EtOH) exposure blunts normal liver regenerative responses, in part by inhibiting insulin/IGF signaling, and correspondingly, previous studies showed that EtOH-impaired liver regeneration could be restored by insulin sensitizer (proliferator-activated receptor [PPAR]-δ agonist) treatment. As Wnt/β-catenin functions overlap and cross talk with insulin/IGF pathways, we investigated the effects of EtOH exposure and PPAR-δ agonist treatment on Wnt pathway gene expression in relation to liver regeneration.

METHODS

Adult male Long Evans rats were fed with isocaloric liquid diets containing 0 or 37% EtOH for 8 weeks and also treated with vehicle or a PPAR-δ agonist during the last 3 weeks of the feeding regimen. The rats were then subjected to 70% partial hepatectomy (PH) and livers harvested at various post-PH time points were used to quantitate expression of 19 Wnt pathway genes using Quantigene 2.0 Multiplex Assay.

RESULTS

EtOH broadly inhibited expression of Wnt/β-catenin signaling-related genes, including down-regulation of Wnt1, Fzd3, Lef1, and Bcl9 throughout the post-PH time course (0 to 72 hours), and suppression of Wnt7a, Ccnd1, Fgf4, Wif1, Sfrp2, and Sfrp5 at 18- and 24-hour post-PH time points. PPAR-δ agonist treatments rescued the EtOH-induced suppression of Wnt1, Wnt7a, Fzd3, Lef1, Bcl9, Ccnd1, and Sfrp2 gene expression in liver, corresponding with the improvements in DNA synthesis and restoration of hepatic architecture.

CONCLUSIONS

Chronic high-dose EtOH exposures inhibit Wnt signaling, which likely contributes to the impairments in liver regeneration. Therapeutic effects of PPAR-δ agonists extend beyond restoration of insulin/IGF signaling mechanisms and are mediated in part by enhancement of Wnt pathway signaling. Future studies will determine the degree to which targeted restoration of Wnt signaling is sufficient to improve liver regeneration and remodeling in the context of chronic EtOH exposure.

MicroRNA-184 modulates canonical Wnt signaling through the regulation of frizzled-7 expression in the retina with ischemia-induced neovascularization

Aberrant activation of Wnt signaling contributes to ischemia-induced retinal neovascularization in oxygen-induced retinopathy (OIR), although the underlying mechanism is so far unclear. Here, we show that microRNA-184 (miR-184) is significantly down-regulated in the retina of OIR mice, and miR-184 negatively modulates Wnt signaling both in vivo and in vitro. Furthermore, we show that the Wnt receptor, frizzled-7, is a downstream target of miR-184, and delivery of miR-184 mimic inhibits Wnt signaling in the OIR retina. These results suggest that decreased levels of miR-184 are responsible, at least in part, for the aberrant activation of Wnt signaling in ischemia-induced retinal neovascularization.

WNT/Frizzled signalling: receptor-ligand selectivity with focus on FZD-G protein signalling and its physiological relevance: IUPHAR Review 3

The wingless/int1 (WNT)/Frizzled (FZD) signalling pathway controls numerous cellular processes such as proliferation, differentiation, cell-fate decisions, migration and plays a crucial role during embryonic development. Nineteen mammalian WNTs can bind to 10 FZDs thereby activating different downstream pathways such as WNT/β-catenin, WNT/planar cell polarity and WNT/Ca(2+) . However, the mechanisms of signalling specification and the involvement of heterotrimeric G proteins are still unclear. Disturbances in the pathways can lead to various diseases ranging from cancer, inflammatory diseases to metabolic and neurological disorders. Due to the presence of seven-transmembrane segments, evidence for coupling between FZDs and G proteins and substantial structural differences in class A, B or C GPCRs, FZDs were grouped separately in the IUPHAR GPCR database as the class FZD within the superfamily of GPCRs. Recently, important progress has been made pointing to a direct activation of G proteins after WNT stimulation. WNT/FZD and G protein coupling remain to be fully explored, although the basic observation supporting the nature of FZDs as GPCRs is compelling. Because the involvement of different (i) WNTs; (ii) FZDs; and (iii) intracellular binding partners could selectively affect signalling specification, in this review we present the current understanding of receptor/ligand selectivity of FZDs and WNTs. We pinpoint what is known about signalling specification and the physiological relevance of these interactions with special emphasis on FZD-G protein interactions.

MiR-199a regulates cell proliferation and survival by targeting FZD7

A growing amount of evidence indicates that miRNAs are important regulators of multiple cellular processes and, when expressed aberrantly in different types of cancer such as hepatocellular carcinoma (HCC), play significant roles in tumorigenesis and progression. Aberrant expression of miR-199a-5p (also called miR-199a) was found to contribute to carcinogenesis in different types of cancer, including HCC. However, the precise molecular mechanism is not yet fully understood. The present study showed that miR-199a is frequently down-regulated in HCC tissues and cells. Importantly, lower expression of miR-199a was significantly correlated with the malignant potential and poor prognosis of HCC, and restoration of miR-199a in HCC cells led to inhibition of the cell proliferation and cell cycle in vitro and in vivo. Furthermore, Frizzled type 7 receptor (FZD7), the most important Wnt receptor involved in cancer development and progression, was identified as a functional target of miR-199a. In addition, these findings were further strengthened by results showing that expression of FZD7 was inversely correlated with miR-199a in both HCC tissues and cells and that over-expression of miR-199a could significantly down-regulate the expression of genes downstream of FZD7, including β-catenin, Jun, Cyclin D1 and Myc. In conclusion, these findings not only help us to better elucidate the molecular mechanisms of hepatocarcinogenesis from a fresh perspective but also provide a new theoretical basis to further investigate miR-199a as a potential biomarker and a promising approach for HCC treatment.

Wnt signaling pathway and hepatic carcinogenesis

The disturbance of signal transduction often occurs in tumor, and the Wnt signaling pathway is one of the most studied signaling pathways in tumorigenesis. Some studies have shown that the Wnt signaling pathway is related to the occurrence and development of hepatocellular carcinoma (HCC). Elucidation of the interactions between factors in the Wnt signaling pathway is important for understanding the pathogenesis of HCC, which can provide a theoretical basis for more effective diagnosis and treatment of this malignancy.

FZD7 drives in vitro aggressiveness in Stem-A subtype of ovarian cancer via regulation of non-canonical Wnt/PCP pathway

Ovarian cancer (OC) can be classified into five biologically distinct molecular subgroups: epithelial-A (Epi-A), Epi-B, mesenchymal (Mes), Stem-A and Stem-B. Among them, Stem-A expresses genes relating to stemness and is correlated with poor clinical prognosis. In this study, we show that frizzled family receptor 7 (FZD7), a receptor for Wnt signalling, is overexpressed in the Stem-A subgroup. To elucidate the functional roles of FZD7, we used an RNA interference gene knockdown approach in three Stem-A cell lines: CH1, PA1 and OV-17R. Si-FZD7 OC cells showed reduced cell proliferation with an increase in the G0/G1 sub-population, with no effect on apoptosis. The cells also displayed a distinctive morphologic change by colony compaction to become more epithelial-like and polarised with smaller internuclear distances and increased z-axis height. Immunofluorescence (IF) staining patterns of pan-cadherin and β-catenin suggested an increase in cadherin-based cell–cell adhesion in si-FZD7 cells. We also observed a significant rearrangement in the actin cytoskeleton and an increase in tensile contractility in si-FZD7 OC cells, as evident by the loss of stress fibres and the redistribution of phospho-myosin light chain (pMLC) from the sites of cell–cell contacts to the periphery of cell colonies. Furthermore, there was reciprocal regulation of RhoA (Ras homolog family member A) and Rac1 (Ras-related C3 botulinum toxin substrate 1 (Rho family, small GTP-binding protein Rac1)) activities upon FZD7 knockdown, with a significant reduction in RhoA activity and a concomitant upregulation in Rac1 activity. These changes in pMLC and RhoA, as well as the increased TopFlash reporter activities in si-FZD7 cells, suggested involvement of the non-canonical Wnt/planar cell polarity (PCP) pathway. Selected PCP pathway genes (cadherin EGF LAG seven-pass G-type receptor 3 (CELSR3), prickle homolog 4 (Drosophila) (PRICKLE4), dishevelled-associated activator of morphogenesis 1 (DAAM1), profilin 2 (PFN2), protocadherin 9 (PCDH9), protocadherin α1 (PCDHA1), protocadherin β17 pseudogene (PCDHB17), protocadherin β3 (PCDHB3), sprouty homolog 1 (SPRY1) and protein tyrosine kinase 7 (PTK7)) were found to be more highly expressed in Stem-A than non Stem-A subgroup of OC. Taken together, our results suggest that FZD7 might drive aggressiveness in Stem-A OC by regulating cell proliferation, cell cycle progression, maintenance of the Mes phenotype and cell migration via casein kinase 1ɛ-mediated non-canonical Wnt/PCP pathway.

Aberrant DNA methylation in hepatocellular carcinoma tumor suppression (Review)

Aberrant DNA methylation leads to altered gene expression, resulting in cancerous features. Numerous tumor suppressor genes are silenced by DNA methylation during hepatocarcinogenesis. Promoter CpG island hypermethylation is an important mechanism for inactivating tumor suppressor genes in hepatocellular carcinoma (HCC). Hypermethylation of CpG islands in the p16 (INK4a) and p15 (INK4b) promoters may increase the risk of developing HCC, particularly hepatitis B virus-related HCC. Environmental factors can lead to geographic variations in the methylation status of CpG islands. Aberrant DNA methylation of CpG islands is catalyzed by DNA methyltransferases (DNMTs). Thus, abnormal variations of DNMTs can contribute to hepatocarcinogenesis. In hepatitis-related HCC, microRNAs participate in hepatocarcinogenesis by directly targeting DNMTs, during which hepatitis B virus X acts as a regulator. DNA methylation may also contribute to HCC tumorigenesis by regulating the cell cycle. Based on the importance of DNA methylation in tumor suppression of HCC, certain DNA methylations may predict the risk of tumor development, tumor staging, patient survival and HCC recurrence.

Genetic variants of the Wnt signaling pathway as predictors of recurrence and survival in early-stage non-small cell lung cancer patients

Early-stage non-small cell lung cancer (NSCLC) is potentially curative. Nevertheless, many patients will show disease recurrence after curative treatment. The Wnt signaling pathway is a developmental and stem cell pathway that plays an important role in tumorigenesis and may affect cancer progression. We hypothesize that genetic variants of the Wnt pathway may influence clinical outcome in early-stage NSCLC patients. We genotyped 441 functional and tagging single nucleotide polymorphisms (SNPs) from 54 genes of the Wnt pathway in 535 early-stage NSCLC patients treated with curative intent therapy including surgery and chemotherapy. For validation, 4 top SNPs were genotyped in 301 early-stage NSCLC patients from the Mayo Clinic. Cox proportional hazard model and combined SNP analyses were performed to identify significant SNPs correlated with recurrence-free and overall survival. Results from discovery group showed a total of 40 SNPs in 20 genes correlated with disease recurrence (P < 0.05). After correction for multiple comparisons, rs2536182 near Wnt16 remained significant (q < 0.1), which was validated in the replication population. Thirty-nine SNPs in 16 genes correlated with overall survival (P < 0.05) in the discovery group, and seven remained significant after multiple comparisons were considered (q < 0.1). In patients receiving surgery-only treatment, rs10898563 of FZD4 gene was associated with both recurrence-free and overall survival. Joint SNP analyses identified predictive markers for recurrence stratified by treatment. Our findings suggest inherited genetic variation in the Wnt signaling pathway may contribute to variable clinical outcomes for patients with early-stage NSCLC.

β-catenin is overexpressed in hepatic fibrosis and blockage of Wnt/β-catenin signaling inhibits hepatic stellate cell activation

β-catenin, a core component of Wnt/β-catenin signaling, has been shown to be an important regulator of cellular proliferation and differentiation. Abnormal activation of Wnt/β-catenin signaling promotes tissue fibrogenesis. In the present study, the role of β-catenin during liver fibrogenesis was analyzed and the functional effects of β-catenin gene silencing in hepatic stellate cells (HSCs) using small interfering (si)RNA were investigated. The expression of β-catenin in human hepatic fibrosis tissues of different grades and normal human hepatic tissues was examined using immunohistochemistry. To inhibit the Wnt/β-catenin signaling pathway, siRNA for β-catenin was developed and transiently transfected into HSC-T6 cells using Lipofectamine 2000. β-catenin expression was evaluated by quantitative polymerase chain reaction (qPCR) and western blot analysis. The expression of collagen types Ⅰ and Ⅲ was evaluated by qPCR and immunofluorescent staining. Cellular proliferation and the cell cycle were analyzed using a methyl thiazolyl tetrazolium assay. Apoptosis was assessed by Annexin V staining. A higher expression level of β-catenin was identified in the patients with high-grade hepatic fibrosis in comparison with that of the normal controls. Additionally, β-catenin siRNA molecules were successfully transfected into HSCs and induced inhibition of β-catenin expression in a time-dependent manner. β-catenin siRNA treatment also inhibited synthesis of collagen types Ⅰ and Ⅲ in transfected HSCs. Furthermore, compared with those of the control group, siRNA-mediated knockdown of β-catenin in HSC-T6 cells inhibited cell proliferation and resulted in cell apoptosis. This study suggests a significant functional role for β-catenin in the development of liver fibrosis and demonstrates that downregulation of the Wnt/β-catenin signaling pathway inhibits HSC activation. Thus, this study provides a novel strategy for the treatment of hepatic fibrosis.

Dysregulated expression of dickkopfs for potential detection of hepatocellular carcinoma

The prognosis for hepatocellular carcinoma (HCC) remains dismal due to the lack of diagnostic markers for early detection. This review will discuss the clinical potential of the dickkopf (DKK) family members as diagnostic and/or prognostic markers for HCC. In comparison to serum α-fetoprotein (AFP) level, which remains the gold standard for HCC diagnosis, high serum DKK1 levels have higher diagnostic value for HCC, especially for AFP-negative HCC, and can distinguish HCC from non-malignant chronic liver diseases. Additionally, the combination of serum DKK1 and AFP levels enhances diagnostic accuracy for HCC compared to serum DKK1 or AFP levels alone. Although DKK1 offers potential for its use in HCC diagnosis this review will discuss the challenges facing DKK1 and also shed some light on recent developments on the remaining DKK family members: DKK2, DKK3 and DKK4.

Involvement of DNA damage response pathways in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has been known as one of the most lethal human malignancies, due to the difficulty of early detection, chemoresistance, and radioresistance, and is characterized by active angiogenesis and metastasis, which account for rapid recurrence and poor survival. Its development has been closely associated with multiple risk factors, including hepatitis B and C virus infection, alcohol consumption, obesity, and diet contamination. Genetic alterations and genomic instability, probably resulted from unrepaired DNA lesions, are increasingly recognized as a common feature of human HCC. Dysregulation of DNA damage repair and signaling to cell cycle checkpoints, known as the DNA damage response (DDR), is associated with a predisposition to cancer and affects responses to DNA-damaging anticancer therapy. It has been demonstrated that various HCC-associated risk factors are able to promote DNA damages, formation of DNA adducts, and chromosomal aberrations. Hence, alterations in the DDR pathways may accumulate these lesions to trigger hepatocarcinogenesis and also to facilitate advanced HCC progression. This review collects some of the most known information about the link between HCC-associated risk factors and DDR pathways in HCC. Hopefully, the review will remind the researchers and clinicians of further characterizing and validating the roles of these DDR pathways in HCC.

β-catenin is overexpressed in hepatic fibrosis and blockage of Wnt/β-catenin signaling inhibits hepatic stellate cell activation

β-catenin, a core component of Wnt/β-catenin signaling, has been shown to be an important regulator of cellular proliferation and differentiation. Abnormal activation of Wnt/β-catenin signaling promotes tissue fibrogenesis. In the present study, the role of β-catenin during liver fibrogenesis was analyzed and the functional effects of β-catenin gene silencing in hepatic stellate cells (HSCs) using small interfering (si)RNA were investigated. The expression of β-catenin in human hepatic fibrosis tissues of different grades and normal human hepatic tissues was examined using immunohistochemistry. To inhibit the Wnt/β-catenin signaling pathway, siRNA for β-catenin was developed and transiently transfected into HSC-T6 cells using Lipofectamine 2000. β-catenin expression was evaluated by quantitative polymerase chain reaction (qPCR) and western blot analysis. The expression of collagen types Ⅰ and Ⅲ was evaluated by qPCR and immunofluorescent staining. Cellular proliferation and the cell cycle were analyzed using a methyl thiazolyl tetrazolium assay. Apoptosis was assessed by Annexin V staining. A higher expression level of β-catenin was identified in the patients with high-grade hepatic fibrosis in comparison with that of the normal controls. Additionally, β-catenin siRNA molecules were successfully transfected into HSCs and induced inhibition of β-catenin expression in a time-dependent manner. β-catenin siRNA treatment also inhibited synthesis of collagen types Ⅰ and Ⅲ in transfected HSCs. Furthermore, compared with those of the control group, siRNA-mediated knockdown of β-catenin in HSC-T6 cells inhibited cell proliferation and resulted in cell apoptosis. This study suggests a significant functional role for β-catenin in the development of liver fibrosis and demonstrates that downregulation of the Wnt/β-catenin signaling pathway inhibits HSC activation. Thus, this study provides a novel strategy for the treatment of hepatic fibrosis.

Role of Wnt/β-catenin pathway in activation and proliferation of hepatic stellate cells

Liver fibrosis refers to a pathological state in which a variety of pathogenic factors lead to hepatocyte inflammation and necrosis, the imbalance between degradation and deposition of collagen and other extracellular matrix (ECM) molecules, and the abnormal proliferation of liver connective tissue. In the process of the formation of hepatic fibrosis, hepatic stellate cells are the major contributor. Activated hepatic stellate cells secrete extracellular matrix components, and excessive deposition of extracellular matrix is the central event in liver fibrosis. Currently, there have been many articles reporting that the Wnt/β-catenin signaling pathway is involved in organ fibrosis and liver fibrosis, but the underlying mechanism has not been clearly clarified. Some studies have also confirmed that there is a certain relationship between the Wnt/β-catenin pathway and activation of hepatic stellate cells in liver fibrosis.

Characterization of hepatocellular carcinoma related genes and metabolites in human nonalcoholic fatty liver disease

BACKGROUND

The worldwide prevalences of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are estimated to range from 30 to 40 % and 5-17 %, respectively. Hepatocellular carcinoma (HCC) is primarily caused by hepatitis B infection, but retrospective data suggest that 4-29 % of NASH cases will progress to HCC. Currently the connection between NASH and HCC is unclear.

AIMS

The purpose of this study was to identify changes in expression of HCC-related genes and metabolite profiles in NAFLD progression.

METHODS

Transcriptomic and metabolomic datasets from human liver tissue representing NAFLD progression (normal, steatosis, NASH) were utilized and compared to published data for HCC.

RESULTS

Genes involved in Wnt signaling were downregulated in NASH but have been reported to be upregulated in HCC. Extracellular matrix/angiogenesis genes were upregulated in NASH, similar to reports in HCC. Iron homeostasis is known to be perturbed in HCC and we observed downregulation of genes in this pathway. In the metabolomics analysis of hepatic NAFLD samples, several changes were opposite to what has been reported in plasma of HCC patients (lysine, phenylalanine, citrulline, creatine, creatinine, glycodeoxycholic acid, inosine, and alpha-ketoglutarate). In contrast, multiple acyl-lyso-phosphatidylcholine metabolites were downregulated in NASH livers, consistent with observations in HCC patient plasma.

CONCLUSIONS

These data indicate an overlap in the pathogenesis of NAFLD and HCC where several classes of HCC related genes and metabolites are altered in NAFLD. Importantly, Wnt signaling and several metabolites are different, thus implicating these genes and metabolites as mediators in the transition from NASH to HCC.