Dysregulation of the Hedgehog pathway in human hepatocarcinogenesis

Correlation analysis of liver tumor-associated genes with liver regeneration

AIM: To study at transcriptional level the similarities and differences of the physiological and biochemical activities between liver tumor (LT) and regenerating liver cells.

METHODS: LT-associated genes and their expression changes in LT were obtained from databases and scientific articles, and their expression profiles in rat liver regeneration (LR) were detected using Rat Genome 230 2.0 array. Subsequently their expression changes in LT and LR were compared and analyzed.

RESULTS: One hundred and twenty one LT-associated genes were found to be LR-associated. Thirty four genes were up-regulated, and 14 genes were down-regulated in both LT and regenerating liver; 20 genes up-regulated in LT were down-regulated in regenerating liver; 21 up-regulated genes and 16 down-regulated genes in LT were up-regulated at some time points and down-regulated at others during LR.

CONCLUSION: Results suggested that apoptosis activity suppressed in LT was still active in regenerating liver, and there are lots of similarities and differences between the LT and regenerating liver at the aspects of cell growth, proliferation, differentiation, migration and angiogenesis.

Hepatocellular carcinoma: epidemiology and molecular carcinogenesis

Primary liver cancer, which consists predominantly of hepatocellular carcinoma (HCC), is the fifth most common cancer worldwide and the third most common cause of cancer mortality. HCC has several interesting epidemiologic features including dynamic temporal trends; marked variations among geographic regions, racial and ethnic groups, and between men and women; and the presence of several well-documented environmental potentially preventable risk factors. Moreover, there is a growing understanding on the molecular mechanisms inducing hepatocarcinogenesis, which almost never occurs in healthy liver, but the cancer risk increases sharply in response to chronic liver injury at the cirrhosis stage. A detailed understanding of epidemiologic factors and molecular mechanisms associated with HCC ultimately could improve our current concepts for screening and treatment of this disease.

Selective down-regulation of glioma-associated oncogene 2 inhibits the proliferation of hepatocellular carcinoma cells

The sonic hedgehog (Shh) pathway contributes to the initiation and progression of tumors with various origins when aberrantly activated. In this study, we investigated if the Shh pathway is important for the proliferation of hepatocellular carcinoma (HCC) cells and also began to identify which components of the pathway play a pivotal role in the biology of HCC. Expression levels of components in the pathway were measured, and glioma-associated oncogene (Gli) 2 levels were found to be considerably higher in human HCC lines compared with normal liver. Gli2 levels were also higher in tumor tissue from HCC patients compared with normal liver. Antisense oligonucleotides (ASO) were used to specifically down-regulate Gli2, and this led to decreased proliferation of various HCC cell lines. However, inhibition of Gli1 and Gli3 with ASOs did not decrease proliferation in most HCC cell lines and inhibitors targeting the upstream components of the pathway, including smoothened (Smo), displayed antiproliferative effects in only a subset of HCC cell lines. Moreover, in cancer cells harboring Smo mutations or unresponsive to the Smo inhibitor 3-keto-N-aminoethylaminoethylcaproyldihydrocinnamoyl cyclopamine, the Gli2 ASO was still able to inhibit proliferation. The importance of Gli2 in HCC proliferation was further confirmed by the changes in expression levels of genes, such as Bcl-2, c-Myc, and p27, following suppression of Gli2 expression. Taken together, these results suggest that, among the Gli transcription factors, Gli2 plays a predominant role in the proliferation of HCC cells and the suppression of Gli2 expression may provide a useful therapeutic option for the treatment of HCC.

Bile ductules and stromal cells express hedgehog ligands and/or hedgehog target genes in primary biliary cirrhosis

Indian Hedgehog (Ihh) regulates tissue morphogenesis. Hedgehog (Hh) activity has been demonstrated in human cholangiocarcinoma and hepatocellular carcinoma lines, and in myofibroblasts and progenitors from adult rodent livers. We evaluated Hh pathway involvement in the response to biliary injury in primary biliary cirrhosis (PBC). Liver sections from 3 PBC patients and 3 controls without liver disease were studied. Immunohistochemistry was used to determine if cells that accumulate in PBC livers express Ihh or Hh-target genes including the Hh-receptor, Patched (Ptc), and the Hh-transcriptional activator glioblastoma (Gli) 2. Positive cells were further identified by costaining for cytokeratin (CK) 19, a biliary marker, or OV6, a hepatic progenitor marker. In all subjects, Gli2 and Ptc expression localized in portal areas. The numbers of Gli2- or Ptc-expressing cells/portal triad were each 10-fold greater in patients with PBC than in controls (P<0.05). In PBC livers, some CK19+ cells coexpressed Gli2 or Ptc. Many stromal fibroblastic cells were also Gli2+. Strong Ihh expression was detected in most bile ductular cells. Scattered stromal cells also expressed Ihh. The number of Ihh+ cells/portal triad was 6-fold greater in PBC livers than controls (P<0.05). OV6+ progenitors increased significantly in PBC livers, and some of these cells coexpressed Ihh, Ptc, and/or Gli2.

CONCLUSION

This is the first direct evidence that noncancerous, adult human livers harbor several types of cells that produce and/or respond to Hh ligands. Such Hh-responsive cells accumulate during the fibroproliferative response to chronic cholestatic liver injury, suggesting a role for Hh signaling in this process.

Hedgehog-mediated mesenchymal-epithelial interactions modulate hepatic response to bile duct ligation

In bile duct-ligated (BDL) rodents, as in humans with chronic cholangiopathies, biliary obstruction triggers proliferation of bile ductular cells that are surrounded by fibrosis produced by adjacent myofibroblastic cells in the hepatic mesenchyme. The proximity of the myofibroblasts and cholangiocytes suggests that mesenchymal-epithelial crosstalk promotes the fibroproliferative response to cholestatic liver injury. Studying BDL mice, we found that bile duct obstruction induces activity of the Hedgehog (Hh) pathway, a system that regulates the viability and differentiation of various progenitors during embryogenesis. After BDL, many bile ductular cells and fibroblastic-appearing cells in the portal stroma express Hh ligands, receptor and/or target genes. Transwell cocultures of an immature cholangiocyte line that expresses the Hh receptor, Patched (Ptc), with liver myofibroblastic cells demonstrated that both cell types produced Hh ligands that enhanced each other's viability and proliferation. Further support for the concept that Hh signaling modulates the response to BDL was generated by studying PtcLacZ mice, which have an impaired ability to constrain Hh signaling due to a heterozygous deficiency of Ptc. After BDL, PtcLacZ mice upregulated fibrosis gene expression earlier than wild-type controls and manifested an unusually intense ductular reaction, more expanded fibrotic portal areas, and a greater number of lobular necrotic foci. Our findings reveal that adult livers resurrect developmental signaling systems, such as the Hh pathway, to guide remodeling of the biliary epithelia and stroma after cholestatic injury.

Genome-wide molecular profiles of HCV-induced dysplasia and hepatocellular carcinoma

Although HCC is the third-leading cause of cancer-related deaths worldwide, there is only an elemental understanding of its molecular pathogenesis. In western countries, HCV infection is the main etiology underlying this cancer's accelerating incidence. To characterize the molecular events of the hepatocarcinogenic process, and to identify new biomarkers for early HCC, the gene expression profiles of 75 tissue samples were analyzed representing the stepwise carcinogenic process from preneoplastic lesions (cirrhosis and dysplasia) to HCC, including 4 neoplastic stages (very early HCC to metastatic tumors) from patients with HCV infection. We identified gene signatures that accurately reflect the pathological progression of disease at each stage. Eight genes distinguish between control and cirrhosis, 24 between cirrhosis and dysplasia, 93 between dysplasia and early HCC, and 9 between early and advanced HCC. Using quantitative real-time reverse-transcription PCR, we validated several novel molecular tissue markers for early HCC diagnosis, specifically induction of abnormal spindle-like, microcephaly-associated protein, hyaluronan-mediated motility receptor, primase 1, erythropoietin, and neuregulin 1. In addition, pathway analysis revealed dysregulation of the Notch and Toll-like receptor pathways in cirrhosis, followed by deregulation of several components of the Jak/STAT pathway in early carcinogenesis, then upregulation of genes involved in DNA replication and repair and cell cycle in late cancerous stages.

CONCLUSION

These findings provide a comprehensive molecular portrait of genomic changes in progressive HCV-related HCC.

Rab23 is a potential biological target for treating hepatocellular carcinoma

AIM: To elucidate the role of Rab23 in hepatocellular carcinoma (HCC) by assessing the expression of Rab23 in HCC tissue and in HCC cell lines.

METHODS: Primary tumors (n = 100) were stained with Rab23 antibodies using immunohistochemistry and in situ hybridization in tissue microarrays. Relationships between gene expression and pathology parameters were analysed. The biological significance of Rab23 in Hep-3B cells was examined by knocking down Rab23 gene expression. We designed a pair of double-stranded RNAs against human rab23 and transfected siRNA into Hep-3B cells. Rab23 expression in these cells was examined using RT-PCR and Western blots. We investigated cell growth by MTT assays and fluorescence-activated cell sorting.

RESULTS: High cytoplasmic and nuclear expression of Rab23 was found in 38 of 71 (53.5%) and in 49 of 68 HCC patients (72%) respectively, which correlated with tumor size. HCC cell lines expressed Rab23. In Hep3B cells, siRNA for Rab23 decreased Rab23 mRNA by 4.5-fold and protein expression by 2-fold. Survival rates at 24 and 48 h for Hep-3B cells transfected with siRNA were lower and about 30% Hep-3B cells were apoptotic. Knocking down rab23 suppressed Hep3B cell growth, suggesting that rab23 could play an important role in Hep3B cell growth.

CONCLUSION: Rab23 is overexpressed and/or activated in HCC. Rab23 may be both a HCC predictor and a target for treating HCC.

Increased expression of nucleophosmin/B23 in hepatocellular carcinoma and correlation with clinicopathological parameters

Nucleophosmin (NPM, B23, numatrin, NO38) is an abundant nucleolar phosphoprotein involved in multiple cellular functions. Previous evidence indicates that high-level expression of NPM causes uncontrolled cell growth and suggests that NPM may have oncogenic potential. In this study, we examined NPM expression in 103 paired cases of hepatocellular carcinoma (HCC), 12 cases of hepatic focal nodular hyperplasia, 17 cases of liver tissue adjacent to a hepatic haemangioma, and series of array tissues from normal human organs and malignancies using a monoclonal antibody against NPM and reverse transcription-PCR techniques, Western blot analysis, immunohistochemistry, and immunocytofluorescence. Our data indicated that NPM expression was significantly higher in HCC than in the non-malignant hepatocytes (P<0.001). Nucleophosmin was weakly expressed in hepatocytes from a 5-month-old embryo and in stationary hepatocytes of healthy adults. Moreover, enhanced expression of NPM in HCC correlated with the level of PCNA (R(2)=0.5639) and with the clinical prognostic parameters such as serum alpha fetal protein level, tumour pathological grading, and liver cirrhosis (P<0.05). Our results suggest that NPM may play an important role in the progression of tumorigenesis and that NPM may serve as a potential marker for HCC.

Suppressing Wnt signaling by the hedgehog pathway through sFRP-1

The hedgehog (Hh) signaling pathway is essential for embryonic development and carcinogenesis. Activation of Hh signaling has been identified in several types of gastrointestinal cancers, including esophageal, gastric, pancreatic, and liver cancers. Several recent studies suggest that Hh signaling activation can inhibit Wnt signaling. However, the molecular basis underlying this inhibition remains unclear. As transcription factors in the Hh signaling pathway, Gli molecules transform cells in culture, and their expression are associated with cancer development. Here we report that expression of a secreted frizzled-related protein-sFRP-1 in mouse embryonic fibroblasts is dependent on Gli1 and Gli2. In human gastric cancer cells, inhibition of Hh signaling reduces the level of sFRP-1 transcript, whereas ectopic expression of Gli1 increases the level of sFRP-1 transcript. Results from chromatin immunoprecipitation indicate that Gli1 is involved in transcriptional regulation of sFRP-1. In 293 cells with Gli1 expression, Wnt-1-mediated beta-catenin accumulation in the cytosol and DKK1 expression are all abrogated, which can be reversed by inhibiting sFRP-1 expression. Furthermore, while SIIA cells do not respond to Wnt-1-conditioned medium, inhibition of Hh signaling by smoothened (SMO) antagonist KAAD-cyclopamine (keto-N-aminoethylaminocaproyldihydrocinnamoylcyclopamine) leads to Wnt1-mediated beta-catenin accumulation in the cytosol. These data indicate that sFRP-1, a target gene of the hedgehog pathway, is involved in cross-talk between the hedgehog pathway and the Wnt pathway.