Coordinated expression of cyclin D1 and LEF-1/TCF transcription factor is restricted to a subset of hepatocellular carcinoma

Synthetic miR-26a mimics delivered by tumor exosomes repress hepatocellular carcinoma through downregulating lymphoid enhancer factor 1

BACKGROUND

The dysregulation of exosomal microRNAs plays an important role in the progression of hepatocarcinogenesis. In this study, we investigated the therapeutic potential of synthetic exosomal miR-26a against HCC cells and explored the feasibility of tumor-derived exosomes as drug delivery vehicles.

METHODS

Proliferation and migration assays were performed to examine the effects of miR-26a on HCC in vitro. The direct target gene of miR-26a was identified through miRecords analysis and target validation. The transferring efficiency and anti-HCC effect of exosomes with different origin were studied and the optimal miR-26a delivery method was established and verified in vitro and in vivo. In addition, the relationships between prognosis of HCC patients and miR-26a expression in HCC serum and exosomes were retrospectively analyzed.

RESULTS

Here, we found that tumor cell-derived exosomes were taken in preferentially by HCC cells and promoted HCC progression through Wnt pathway by low-density lipoprotein receptor-related protein 6 (LRP6). HCC cells with vacuolar protein sorting-associated protein 35 knocked down were adopted to generate engineered LRP6-exosomes. The engineered HCC-derived exosomes loading miR-26a inhibited HCC progression in vitro and in vivo effectively. Overexpression of miR-26a impaired the growth and migration of HCC by targeting lymphoid enhancer factor 1 (LEF1). Moreover, low expression of exosomal miR-26a was an independent prognostic factor for recurrence and survival in HCC patients.

CONCLUSIONS

Our findings suggested the exosomal miR-26a could serve as a non-invasive prognostic marker for HCC patients. Genetically modified tumor-derived exosomes showed preferable transfection efficiency but reduced Wnt activity, which provides a novel therapeutic strategy for HCC.

Snail Upregulates Transcription of FN, LEF, COX2, and COL1A1 in Hepatocellular Carcinoma: A General Model Established for Snail to Transactivate Mesenchymal Genes

SNA is one of the essential EMT transcriptional factors capable of suppressing epithelial maker while upregulating mesenchymal markers. However, the mechanisms for SNA to transactivate mesenchymal markers was not well elucidated. Recently, we demonstrated that SNA collaborates with EGR1 and SP1 to directly upregulate MMP9 and ZEB1. Remarkably, a SNA-binding motif (TCACA) upstream of EGR/SP1 overlapping region on promoters was identified. Herein, we examined whether four other mesenchymal markers, lymphoid enhancer-binding factor (LEF), fibronectin (FN), cyclooxygenase 2 (COX2), and collagen type alpha I (COL1A1) are upregulated by SNA in a similar fashion. Expectedly, SNA is essential for expression of these mesenchymal genes. By deletion mapping and site directed mutagenesis coupled with dual luciferase promoter assay, SNA-binding motif and EGR1/SP1 overlapping region are required for TPA-induced transcription of LEF, FN, COX2 and COL1A1. Consistently, TPA induced binding of SNA and EGR1/SP1 on relevant promoter regions of these mesenchymal genes using ChIP and EMSA. Thus far, we found six of the mesenchymal genes are transcriptionally upregulated by SNA in the same fashion. Moreover, comprehensive screening revealed similar sequence architectures on promoter regions of other SNA-upregulated mesenchymal markers, suggesting that a general model for SNA-upregulated mesenchymal genes can be established.

Expression of LEF1 and TCF1 (TCF7) proteins associates with clinical progression of nasopharyngeal carcinoma

Aims

Our previous study has demonstrated that β-catenin pathway was abnormally activated in nasopharyngeal carcinoma (NPC). The purposes of the present study are to investigate whether the alterations of LEF1 and TCF1 (TCF7) proteins, the important components of the canonical Wnt/β-catenin pathway, are associated with clinicopathological features and prognostic implications.

Methods

We collected 391 cases of NPC, 53 non-cancerous control nasopharyngeal mucosa and 28 pairs of NPC and their matched metastases, detected expression of LEF1 and TCF1 (TCF7) proteins in these tissues by immunohistochemistry. 

Results

Results showed that there were significantly increased expression of both LEF1 and TCF1 (TCF7) proteins and coexpression of LEF1 and TCF1 (TCF7) in NPC than these in non-cancerous nasopharyngeal mucosa (all p<0.001), as well as LEF1 and coexpression of LEF1 and TCF1 (TCF7) in matched metastasis NPCs than these in the primary NPCs (p=0.003 and p=0.014, respectively). In addition, expression of LEF1 and the coexpression of LEF1 and TCF1 (TCF7) proteins were positively correlated with lymph node metastasis (p=0.001 and p=0.020, respectively), advanced clinical stage (p<0.003 and p=0.027, respectively) and poor survival status of patients with NPC (p<0.001 and p=0.004, respectively). Moreover, multivariate Cox regression analysis identified that the positive expression of LEF1 was the independent poor prognostic factor for overall survival of patients with NPC (p<0.001).

Conclusions

The expression of LEF1 associated positively with TCF1 (TCF7) and clinical progression of NPC, and positive expression of LEF1 protein may act as valuable independent biomarker to predict poor prognosis for patients with NPC.

Positive effects of α-asarone on transplanted neural progenitor cells in a murine model of ischemic stroke

BACKGROUND

Some traditional Oriental herbal medicines, such as Acorus tatarinowii and Acorus gramineus, produce beneficial effects for cognition enhancement. An active compound in rhizomes and the bark of these plants is α-asarone.

PURPOSE

This study investigated the effects of α-asarone on the proliferation and differentiation of neural progenitor cells (NPCs) in a primary culture and a murine model of ischemic stroke.

METHODS

NPCs were isolated from mouse fetal cerebral cortices on embryonic day 15, and all experiments were performed using passage 3 NPCs. We utilized a cell counting kit-8 assay, flow cytometry, western blot, and immunohistochemical analysis to assess proliferation and differentiation of NPCs and employed α-asarone in NPC transplanted ischemic stroke mice to evaluate stroke-related functional recovery using behavioral and immunohistochemical analysis.

RESULT

Treatment with 1 µM, 3 µM, or 10 μM α-asarone induced significant NPC proliferation compared to vehicle treatment. Induced NPCs expressed the neuronal marker neuronal nuclei (NeuN) or the astrocyte marker S100 calcium-binding protein B (S100β). Both immunohistochemistry and flow cytometry revealed that treatment with α-asarone increased the number of NeuN-immunoreactive cells and decreased the number of S100β-immunoreactive cells. Treatment with α-asarone also increased the expression of β-catenin, cyclin D1, and phosphorylated extracellular signal-regulated kinase (ERK) compared to vehicle treatment. In a murine model of ischemic stroke, treatment with α-asarone and transplanted NPCs alleviated stroke-related functional impairments. The corner and rotarod test results revealed that treatment with α-asarone in the NPC transplanted group had greater-than-additive effects on sensorimotor function and motor balance. Moreover, α-asarone treatment promoted the differentiation of transplanted NPCs into NeuN-, glial fibrillary acidic protein (GFAP)-, platelet-derived growth factor-α (PDGFR-α)-, and 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)-immunoreactive cells.

CONCLUSION

α-asarone may promote NPC proliferation and differentiation into neuron-lineage cells by activating β-catenin, cyclin D1, and ERK. Moreover, α-asarone treatment facilitated neurofunctional recovery after NPC transplantation in a murine model of ischemic stroke. Therefore, α-asarone is a potential adjunct treatment to NPC therapy for functional restoration after brain injuries such as ischemic stroke.

Snail collaborates with EGR-1 and SP-1 to directly activate transcription of MMP 9 and ZEB1

The Snail transcription factor plays as a master regulator of epithelial mesenchymal transition (EMT), one of the steps of tumor metastasis. Snail enhances expressions of a lot of mesenchymal genes including the matrix degradation enzyme matrix metalloproteinases 9 (MMP9) and the EMT transcription factor zinc finger E-box binding homeobox 1 (ZEB1), however, the underlying mechanisms are not clarified. Herein, we investigated how Snail upregulated transcription of ZEB1 and MMP9 induced by the tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA) in hepatoma cell HepG2. According to deletion mapping and site directed mutagenesis analysis, the TPA-responsive elements on both MMP9 and ZEB1 promoters locate on a putative EGR1 and SP1 overlapping region coupled with an upstream proposed Snail binding motif TCACA. Consistently, chromatin immunoprecipitation (ChIP) assay showed TPA triggered binding of Snail, EGR1 and SP1 on MMP9 and ZEB1 promoters. Double ChIP further indicated TPA induced association of Snail with EGR1 and SP1 on both promoters. Also, electrophoresis mobility shift assay revealed TPA enhanced binding of Snail with a MMP9 promoter fragment. According to shRNA techniques, Snail was essential for gene expression of both ZEB1 and MMP9. In conclusion, Snail transactivates genes involved in tumor progression via direct binding to a specific promoter region.

Genome-wide genetic and epigenetic analyses of pancreatic acinar cell carcinomas reveal aberrations in genome stability

Pancreatic acinar cell carcinoma (ACC) is an aggressive exocrine tumor with largely unknown biology. Here, to identify potential targets for personalized treatment, we perform integrative genome-wide and epigenome-wide analyses. The results show frequently aberrant DNA methylation, abundant chromosomal amplifications and deletions, and mutational signatures suggesting defective DNA repair. In contrast to pancreatic ductal adenocarcinoma, no recurrent point mutations are detected. The tumor suppressors ID3, ARID1A, APC, and CDKN2A are frequently impaired also on the protein level and thus potentially affect ACC tumorigenesis. Consequently, this work identifies promising therapeutic targets in ACC for drugs recently approved for precision cancer therapy.

Hypoxia stimulates neural stem cell proliferation by increasing HIF‑1α expression and activating Wnt/β-catenin signaling

Evidence indicates that after brain injury, neurogenesis is enhanced in regions such as hippocampus, striatum, and cortex. To study the role of hypoxia-inducible factor-1 (HIF‑1α) and Wnt signaling in cerebral ischemia/hypoxia-induced proliferation of neural stem cells (NSCs), we investigated the proliferation of NSCs, expression of HIF‑1α, and activation of Wnt signaling under conditions of pathologic hypoxia in vitro. NSCs were isolated from 30-day-old Sprague-Dawley rats and subjected to 0.3% oxygen in a microaerophilic incubation system. Cell proliferation was evaluated by measuring the diameter of neurospheres and by bromodeoxyuridine incorporation assays. Real-time quantitative PCR and Western blotting were used to detect mRNA and protein levels of HIF-1α, β-catenin, and cyclin D1 in the NSCs. The results showed that hypoxia increased NSC proliferation and the levels of HIF-1α, β‑catenin, and cyclin D1 (p &lt; 0.05). Blockade of the Wnt signaling pathway decreased hypoxia-induced NSC proliferation, whereas activation of this pathway increased hypoxia-induced NSC proliferation (p &lt; 0.05). Knockdown of HIF-1α with HIF-1α siRNA decreased β‑catenin nuclear translocation and cyclin D1 expression, and inhibited proliferation of NSCs (p &lt; 0.05). These findings indicate that pathologic hypoxia stimulates NSC proliferation by increasing expression of HIF-1α and activating the Wnt/β-catenin signaling pathway. The data suggest that Wnt/β-catenin signaling may play a key role in NSC proliferation under conditions of pathologic hypoxia.

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/Ca²⁺ 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.

Immunohistochemistry panel segregates molecular types of hepatocellular carcinoma in Brazilian autopsy cases

AIM: To assess the distribution of proteins coded by genes reported as relevant for the molecular classification of hepatocellular carcinoma (HCC).

METHODS: In this retrospective cross-sectional study, the following clinicopathological data were analyzed in 80 autopsied HCC patients: sex, age, ethnicity, alcohol intake, infection with hepatitis B and/or C virus, infection with human immunodeficiency virus, prior treatment, basic and immediate causes of death, liver weight, presence of cirrhosis, number and size of nodules, gross pattern, histological grade and variants, architectural pattern, invasion of large veins, and presence and location of extrahepatic metastases. The protein products of genes known to be involved in molecular pathogenesis of HCC, including epidermal growth factor receptor (EGFR), MET, keratin 19 (K19), vimentin, beta-catenin, mechanistic target of rapamycin (mTOR), extracellular signaling-related kinase (ERK)1, ERK2, Ki67, cyclin D1, caspase 3 and p53, were detected by immunohistochemistry on tissue microarrays. The expression levels were scored and statistically assessed for correlation with HCC parameters.

RESULTS: Infection with hepatitis C virus was identified in 49% of the 80 autopsy patients, cirrhosis in 90%, advanced tumors in 95%, and extrahepatic metastases in 38%. Expression of K19, p53 and ERK1 correlated to high-grade lesions. Expression of ERK1, nuclear beta-catenin, cyclin D1 and ERK2 correlated to higher rates of cell proliferation as determined by Ki67. Expression of MET, EGFR (> 0) and caspase 3 correlated with lower histological grades. Expression of EGFR correlated to that of caspase 3, and overexpression of EGFR (≥ 200/300) was observed in low-grade tumors more frequently (grades 1 and 2: 67% vs grade 3: 27% and grade 4: 30%). Expression of ERK1 was associated with that of K19 and vimentin, whereas expression of ERK2 was associated with that of cyclin D1, MET and membrane beta-catenin. Expression of vimentin was strongly correlated with that of K19.

CONCLUSION: Expression of K19, p53, ERK1, ERK2, vimentin and nuclear beta-catenin was related to higher-grade markers, as opposed to expression/overexpression of EGFR, MET and caspase 3.

Characterization of single nucleotide polymorphisms in the promoter region of the bovine paraoxonase 1 (PON1) gene affecting serum enzyme activity in dairy cows

The aim of the present study was to characterize single nucleotide polymorphisms (SNPs) in the promoter region of the bovine paraoxonase 1 (PON1) gene and determine their relationship with PON1 serum activity. Blood samples were collected from 47 Holstein cows during the periparturient period. Serum PON1 was measured and DNA extracted for PCR and sequencing of the promoter region of the PON1 gene. Seven novel SNPs were identified and of these, five SNPs, at positions -105, -221, -392, -611 and -674, upstream of the start of the published mRNA sequence (NM_001046269.2), were found to be associated with variability in serum PON1 activity (P < 0.05). The SNPs at positions -221 and -611 were located in regions predicted to bind to transcription factors linked to the acute phase response.

Crosstalk between beta-catenin and snail in the induction of epithelial to mesenchymal transition in hepatocarcinoma: role of the ERK1/2 pathway

Epithelial to mesenchymal transition (EMT) is an integral process in the progression of many epithelial tumors. It involves a coordinated series of events, leading to the loss of epithelial features and the acquisition of a mesenchymal phenotype, resulting in invasion and metastasis. The EMT of hepatocellular carcinoma (HCC) cells is thought to be a key event in intrahepatic dissemination and distal metastasis. In this study, we used 12-O-tet-radecanoylphorbol-13-acetate (TPA) to dissect the signaling pathways involved in the EMT of HepG2 hepatocarcinoma cells. The spectacular change in phenotype induced by TPA, leading to a pronounced spindle-shaped fibroblast-like cell morphology, required ERK1/2 activation. This ERK1/2-dependent EMT process was characterized by a loss of E-cadherin function, modification of the cytoskeleton, the acquisition of mesenchymal markers and profound changes to extracellular matrix composition and mobility. Snail was essential for E-cadherin repression, but was not sufficient for full commitment of the TPA-triggered EMT. We found that TPA triggered the formation of a complex between Snail and β-catenin that activated the Wnt pathway. This study thus provides the first evidence for the existence of a complex network governed by the ERK1/2 signaling pathway, converging on the coregulation of Snail and the Wnt/β-catenin pathway and responsible for the onset and the progression of EMT in hepatocellular carcinoma cells.

Transcriptional regulators in hepatocarcinogenesis--key integrators of malignant transformation

Hepatocellular carcinoma (HCC) is one of the most frequent human malignancies with poor prognosis and increasing incidence in the Western world. Only for a minority of HCC patients, surgical treatment options offer potential cure and therapeutic success of pharmacological approaches is limited. Highly specific approaches (e.g., kinase inhibitors) did not significantly improve the situation so far, possibly due to functional compensation, genetic heterogeneity of HCC, and development of resistance under selective pressure. In contrast, transcriptional regulators (especially transcription factors and co-factors) may integrate and process input signals of different (oncogenic) pathways and therefore represent cellular bottlenecks that regulate tumor cell biology. In this review, we want to summarize the current knowledge about central transcriptional regulators in human hepatocarcinogenesis and their potential as therapeutic target structures. Genomic and transcriptomic data of primary human HCC revealed that many of these factors showed up in subgroups of HCCs with a more aggressive phenotype, suggesting that aberrant activity of transcriptional regulators collect input information to promote tumor initiation and progression. Therefore, expression and dysfunction of transcription factors and co-factors may gain relevance for diagnostics and therapy of HCC.

Dickkopfs and Wnt/β-catenin signalling in liver cancer

Liver cancer is the fifth and seventh most common cause of cancer in men and women, respectively. Wnt/β-catenin signalling has emerged as a critical player in both the development of normal liver as well as an oncogenic driver in hepatocellular carcinoma (HCC). Based on the current understanding, this article summarizes the possible mechanisms for the aberrant activation of this pathway with specific focus on HCC. Furthermore, we will discuss the role of dickkopfs (DKKs) in regulating Wnt/β-catenin signalling, which is poorly understood and understudied. DKKs are a family of secreted proteins that comprise at least four members, namely DKK1-DKK4, which act as inhibitors of Wnt/β-catenin signalling. Nevertheless, not all members antagonize Wnt/β-catenin signalling. Their functional significance in hepatocarcinogenesis remains to be further characterized for which these studies should provide new insights into the regulatory role of DKKs in Wnt/β-catenin signalling in hepatic carcinogenesis. Because of the important oncogenic roles, there are an increasing number of therapeutic molecules targeting β-catenin and the Wnt/β-catenin pathway for potential therapy of HCC.

Mammalian target of rapamycin regulates expression of β-catenin in hepatocellular carcinoma

Although evidence has shown that both the mammalian target of rapamycin and β-catenin are involved in hepatocellular carcinoma, little is known about their relationship in pathogenesis of hepatocellular carcinoma. To investigate the expression of phosphorylated mammalian target of rapamycin and β-catenin and their prognostic impacts, as well as their relationship in hepatocellular carcinoma, we analyzed 63 human hepatocellular carcinoma samples by immunohistochemistry. Phosphorylated mammalian target of rapamycin cytoplasmic and β-catenin cytoplasmic/nuclear-positive immunoreactivities were observed in 63.5% (40/63) and 55.6% (35/63) of the hepatocellular carcinoma specimens, respectively. Significant associations were found between cytoplasmic β-catenin and phosphorylated mammalian target of rapamycin expression and tumor size (both P < .01) and metastasis (P < .01 and P < .05, respectively). In addition, β-catenin expression in the cytoplasm was closely associated with the expression of phosphorylated mammalian target of rapamycin. To further explore the relationship between mammalian target of rapamycin and β-catenin, hepatocellular carcinoma HepG2 and Hep3B cells were treated with β-catenin siRNA and mammalian target of rapamycin inhibitor, rapamycin; and the expression of phosphorylated mammalian target of rapamycin and β-catenin in cells was then measured by Western blot. The activity of Wnt/β-catenin signaling pathway was also assessed by luciferase reporter assay. The cell viability and proliferation were evaluated by thiazolyl blue tetrazolium bromide assay and [(3)H]-thymidine incorporation assay. The results showed that the level of β-catenin protein expression was markedly decreased by rapamycin in HepG2 and Hep3B cells. The reduction of β-catenin and mammalian target of rapamycin resulted in inhibition of cell viability proliferation, but the combination of reduction of β-catenin and mammalian target of rapamycin did not show a synergistic effect on the inhibition of cell viability and proliferation in HepG2 and Hep3B cells. In conclusion, the present study showed that, for the first time, mammalian target of rapamycin regulated the expression level of β-catenin in hepatocellular carcinoma. Both mammalian target of rapamycin and β-catenin play important roles in the growth, metastasis, and prognosis of hepatocellular carcinoma.

Wnt/beta-catenin is involved in the proliferation of hippocampal neural stem cells induced by hypoxia

BACKGROUND AND AIM

Beta-catenin, as a major effector molecule in the canonical Wnt signaling pathway, could regulate adult neurogenesis. Here, the role of Wnt/β-catenin signaling pathway in the proliferation of hippocampal neural stem cells (NSCs) induced by hypoxia was investigated.

METHODS

The hippocampal NSCs of neonatal green fluorescent protein transgenic mice on day 0 were cultured in hypoxia (5% O(2)) and traditional O(2) (20% O(2)). The expression of β-catenin, p-GSK-3β, and cyclinD1 in NSCs was measured under hypoxia or traditional O(2) by western blotting. NSCs were electroporated with pTOPFLASH reporter in different conditions and the LEF/TCF-dependent luciferase activity was assayed.

RESULTS

Hypoxia increased the proliferation and reduced the apoptosis of hippocampal NSCs. NSCs proliferation was inhibited by transfecting with pAxin, whereas promoted by transfecting with pβ-catenin.

CONCLUSION

Hypoxia could enhance the proliferation of hippocampal NSCs and β-catenin contributed to this action.

Role of hepatitis B surface antigen in the development of hepatocellular carcinoma: regulation of lymphoid enhancer-binding factor 1

Background

There are around 350 million of hepatitis B surface antigen (HBsAg) carriers worldwide, and among them, high risk of developing hepatocellular carcinoma (HCC) has been identified by epidemiological studies. To date, the molecular role of HBsAg in HCC development has not been fully studied. We have previously reported that in cell cultures, HBsAg up-regulated the expression of lymphoid enhancer-binding factor 1 (LEF-1), a key component of the Wnt pathway. In this study we aimed to study this effect of HBsAg on LEF-1 in the development of HCC.

Methods

Expression of HBsAg, LEF-1 and its downstream effector genes were compared among 30 HCCs, their peritumor tissue counterparts and 9 normal control liver tissues by quantitative real-time PCR. In addition, immunohistochemical staining studies on HBsAg and LEF-1 expression were conducted among these samples.

Results

The expression of LEF-1 was compared between 13 HBsAg positive HCC tissues and 17 HBsAg negative HCC tissues. Simultaneous detection of LEF-1 and HBsAg was observed in HBsAg positive HCC tissues and, additionally, the simultaneous detection of HBsAg and LEF-1 was more pronounced in peritumor tissues, compared to that in the tumor tissues. The distribution of cellular LEF-1 in peritumor tissues was predominantly in the cytoplasm; while LEF-1 in the tumor tissues was located either exclusively in the nucleus or both in the nucleus and cytoplasm. By real-time PCR, the expression levels of LEF-1 downstream effector genes cyclin D1 and c-myc were higher in peritumor cells compared to that of the tumor cells. However, a 38 kDa truncated isoform of LEF-1, rather than the 55 kDa wild-type LEF-1, was significantly elevated in the HBsAg positive tumor cells.

Conclusion

Data indicate that deregulation of the Wnt pathway by HBsAg occurred in HBV-associated HCCs, but was more pronounced in the peritumor cells. It is speculated that HBsAg could stimulate proliferation and functional modification of hepatocytes via LEF-1 through the Wnt pathway at the pre-malignant stage.

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

BACKGROUND/AIMS

The canonical Wnt signaling is frequently activated in human hepatocellular carcinoma (HCC). We previously demonstrated that upregulation of Frizzled-7 receptor (FZD7) in HCC was associated with nuclear accumulation of wild-type beta-catenin. Here, we investigated Wnt ligand(s) that may activate the Wnt/beta-catenin pathway through FZD7 in HCC cells.

METHODS

To identify Wnt ligand expression, RT-PCR was performed in HCC cells. To evaluate the function of Wnt3 and FZD7 in HCC, we utilized Wnt3 overexpressing FOCUS HCC cells (FOCUS-Wnt3) and human tumors.

RESULTS

In hepatitis B virus (HBV)-induced HCC, Wnt3 was upregulated in tumor and peritumoral tissues compared to normal liver and downstream beta-catenin target genes were also increased in these samples. Activation of the Wnt/beta-catenin pathway in FOCUS-Wnt3 cells was demonstrated by beta-catenin accumulation, enhanced TCF transcriptional activity and proliferation rate. The activation of Wnt/beta-catenin signaling in FOCUS-Wnt3 was abolished by a knockdown of FZD7 expression by siRNA. More important, a specific Wnt3-FZD7 interaction was observed by co-immunoprecipitation experiments, which suggest that the action of Wnt3 was mediated via FZD7.

CONCLUSIONS

These findings demonstrate a functional interaction between Wnt3 and FZD7 leading to activation of the Wnt/beta-catenin signaling pathway in HCC cells and may play a role during hepatocarcinogenesis.

siRNA-mediated beta-catenin knockdown in human hepatoma cells results in decreased growth and survival

beta-Catenin, the chief oncogenic component of the canonical Wnt pathway, is known to be involved in a variety of cancers, including hepatocellular carcinoma (HCC). Although the mechanism of beta-catenin activation in HCC is multifactorial, it is indisputably implicated at various stages of hepatocarcinogenesis, making it an attractive therapeutic target. Here we investigate the effect of small interfering RNA-mediated beta-catenin knockdown on the growth and survival of human hepatoma cell lines with (HepG2) and without (Hep3B) beta-catenin mutations. Transfection of HepG2 and Hep3B cells with human beta-catenin (CTNNB1) small interfering RNA resulted in a significant beta-catenin decrease, as confirmed by Western blot analyses and immunofluorescence, also leading to decreased expression of known target genes such as cyclin D1 and glutamine synthetase. The decrease in beta-catenin activity was confirmed by TOPflash reporter luciferase assay. The functional impact of diminished beta-catenin was exhibited as temporal decrease in tumor cell viability by the MTT assay. A concomitant decrease in tumor cell proliferation was also evident with [(3)H]thymidine incorporation and verified with soft agar assays. Thus, beta-catenin is essential for the survival and growth of hepatoma cells independent of mutations in the beta-catenin gene and provide a proof of principle for the significance of the therapeutic inhibition of beta-catenin in HCC.

Gene-expression profiles of a hepatitis B small surface antigen-secreting cell line reveal upregulation of lymphoid enhancer-binding factor 1

The genome of hepatitis B virus (HBV) consists of four open reading frames, encoding the envelope proteins (Pre-S/S), the core proteins (Pre-C/C), the polymerase (P) and the transactivating X protein (X). In the sera of HBV-infected patients, hepatitis B surface antigen (HBsAg) particles without the viral genome can outnumber virions by more than 1000-fold. To analyse the interactions between HBsAg and host cells, global gene-expression profiles of a small HBsAg (SHBs)-secreting stable cell line (HepG2-S-G2) and its counterpart control cell line (HepG2-Neo-F4) were compared. Marked upregulation of lymphoid enhancer-binding factor 1 (LEF-1), a transcription factor in the Wnt pathway, was found in SHBs-expressing cells and was confirmed by interference experiments with small interfering RNA. However, compared with the control cells, HepG2-S-G2 did not show higher proliferative competence in culture or increased tumorigenesis in nude mice. A possible mechanism to explain the discrepancy between the upregulation of LEF-1 and the lack of increased tumorigenesis is SHBs expression resulting in altered expression and distribution of LEF-1 protein in cell compartments and upregulation of LEF-1 isoforms that could suppress, rather than enhance, the Wnt pathway.