Establishment and characterization of two cell lines from N-methyl-N-nitrosourea-induced mouse glandular stomach carcinomas

Established gastric cancer cell lines transplantable into C57BL/6 mice show fibroblast growth factor receptor 4 promotion of tumor growth

Previously no mouse gastric cancer cell lines have been available for transplantation into C57BL/6 mice. However, a gastric cancer model in immunocompetent mice would be useful for analyzing putative therapies. N-Methyl-N-nitrosourea (MNU) was given in drinking water to C57BL/6 mice and p53 heterozygous knockout mice. Only 1 tumor from a p53 knockout mouse could be cultured and the cells s.c. transplanted into a C57BL/6 mouse. We cultured this s.c. tumor, and subcloned it. mRNA expression in the most aggressive YTN16 subline was compared to the less aggressive YTN2 subline by microarray analysis, and fibroblast growth factor receptor 4 (FGFR4) in YTN16 cells was knocked out with a CRISPR/Cas9 system and inhibited by an FGFR4 selective inhibitor, BLU9931. These transplanted cell lines formed s.c. tumors in C57BL/6 mice. Four cell lines (YTN2, YTN3, YTN5, YTN16) were subcloned and established. Their in vitro growth rates were similar. However, s.c. tumor establishment rates, metastatic rates, and peritoneal dissemination rates of YTN2 and YTN3 were lower than for YTN5 and YTN16. YTN16 established 8/8 s.c. tumors, 7/8 with lung metastases, 3/8 with lymph node metastases and 5/5 with peritoneal dissemination. FGFR4 expression by YTN16 was 121-fold higher than YTN2. FGFR4-deleted YTN16 cells failed to form s.c. tumors and showed lower rates of peritoneal dissemination. BLU9931 significantly inhibited the growth of peritoneal dissemination of YTN16. These studies present the first transplantable mouse gastric cancer lines. Our results further indicate that FGFR4 is an important growth signal receptor in gastric cancer cells with high FGFR4 expression.

Establishment of an orthotopic transplantable gastric cancer animal model for studying the immunological effects of new cancer therapeutic modules

Tumor cell growth is influenced by the cellular microenvironment including the presence of immune cells and blood vessels. Currently, no transplantable gastric cancer syngeneic animal models exist; therefore, we set out to establish a mouse gastric carcinoma cell line, which was named mouse gastric carcinoma cell line 3I (MGCC3I), from forestomach carcinoma developed in benzo[a]pyrene-treated ICR mice. MGCC3I cells showed epithelial-like morphology, multinuclear giant cell formation, and retained an intestinal phenotype, which are similar to human gastric cancer carcinoma cells. The expression of gastric cancer markers MUC1, MUC2, and MUC5AC, and oncogenes c-myc, c-met, cyclin E1, and cancer stem cell marker CD44 was determined in MGCC3I cells. MGCC3I cells formed poorly differentiated stomach tumors following orthotopic implantation into the stomachs of syngeneic ICR mice. Histone deacetylase inhibitors are recognized as a new class of anticancer drugs. The immunological therapeutic effects of the histone deacetylase inhibitors sodium butyrate and valproic acid were evaluated in this new animal tumor model. Sodium butyrate inhibited MGCC3I stomach tumor formation in animal models. Increased tumor infiltration by CD8 T cells and neutrophils was observed in mice treated with sodium butyrate or valproic acid. Depletion of CD8 T cells significantly attenuated tumor regression mediated by histone deacetylase inhibitors, which is correlated with enhancement of the MHC class I pathway in MGCC3I cells. Taken together, we have successfully established an orthotopic transplantable gastric tumor animal model and demonstrated its usefulness in revealing the role of CD8 T cells in the therapeutic effects of sodium butyrate.

Nucleolin as cell surface receptor for tumor necrosis factor-alpha inducing protein: a carcinogenic factor of Helicobacter pylori

PURPOSE

Tumor necrosis factor-alpha inducing protein (Tipalpha) is a unique carcinogenic factor released from Helicobacter pylori (H. pylori). Tipalpha specifically binds to cells and is incorporated into cytosol and nucleus, where it strongly induces expression of TNF-alpha and chemokine genes mediated through NF-kappaB activation, resulting in tumor development. To elucidate mechanism of action of Tipalpha, we studied a binding protein of Tipalpha in gastric epithelial cells.

METHODS

Tipalpha binding protein was found in cell lysates of mouse gastric cancer cell line MGT-40 by FLAG-pull down assay and identified to be cell surface nucleolin by flow cytometry using anti-nucleolin antibody. Incorporation of Tipalpha into the cells was determined by Western blotting and expression of TNF-alpha gene was quantified by RT-PCR.

RESULTS

Nucleolin was co-precipitated with Tipalpha-FLAG, but not with del-Tipalpha-FLAG (an inactive mutant). After treatment with Tipalpha-FLAG, incorporated Tipalpha was co-immunoprecipitated with endogenous nucleolin using anti-nucleolin antibody. The direct binding of Tipalpha to recombinant His-tagged nucleolin fragment (284-710) was also confirmed. Although nucleolin is an abundant non-ribosomal protein of the nucleolus, we found that nucleolin is present on the cell surface of MGT-40 cells. Pretreatment with anti-nucleolin antibody enhanced Tipalpha-incorporation into the cells through nucleolin internalization. In addition, pretreatment with tunicamycin, an inhibitor of N-glycosylation, decreased the amounts of cell surface nucleolin and inhibited both internalization of Tipalpha and expression of TNF-alpha gene.

CONCLUSIONS

All the results indicate that nucleolin acts as a receptor for Tipalpha and shuttles Tipalpha from cell surface to cytosol and nuclei. These findings provide a new mechanistic insight into gastric cancer development with Tipalpha.

Nucleolin on the cell surface as a new molecular target for gastric cancer treatment

Nucleolin is an abundant non-ribosomal protein found in nucleolus and a major component of silver-stained nucleolar organizer region (AgNOR), a histopathological marker of cancer which is highly elevated in cancer cells. We recently reported that nucleolin on the cell surface of mouse gastric cancer cells acts as a receptor for tumor necrosis factor-alpha-inducing protein (Tipalpha), a new carcinogenic factor of Helicobacter pylori. In this study, we first examined the localization of nucleolin on cell surface of five gastric cancer cell lines by cell fractionation and flow cytometry: We found that large amounts of nucleolin were present on surface of MKN-45, KATOIII, MKN-74, and AGS cells, with smaller amounts on surface of MKN-1 cells. The membrane fraction of normal epithelial cells of mouse glandular stomach did not contain much nucleolin, suggesting that translocation of nucleolin to the cell surface occurs during carcinogenesis, making for easier binding with Tipalpha. AS1411, a nucleolin targeted DNA aptamer, inhibited growth of gastric cancer cell lines in this order of potency: MKN-45>KATOIII>AGS>MKN-74=MKN-1, associated with induction of S-phase cell cycle arrest. Fluorescein isothiocyanate (FITC)-AS1411 was more rapidly incorporated into MKN-45 and AGS than into MKN-1 cells, based on varying amounts of cell surface nucleolin. We think that AS1411 first binds to nucleolin on the cell surface and that the binding complex is then incorporated into the cells. All results indicate that nucleolin on the cell surface is a new and promising therapeutic target for treatment of gastric cancer.

TNF-alpha-inducing protein, a carcinogenic factor secreted from H. pylori, enters gastric cancer cells

TNF-alpha inducing protein (Tip alpha) is secreted from Helicobacter pylori (H. pylori): it is a potent inducer of TNF-alpha and chemokine genes, mediated through NF-kappaB activation, and it also induces tumor-promoting activity in Bhas 42 cells. To investigate the carcinogenic mechanisms of H. pylori with Tip alpha, we first examined how Tip alpha acts on gastric epithelial cells. We found that fluorescent-Tip alpha specifically bound to, and then entered, the cells in a dose- and temperature-dependent manner, whereas deletion mutant of Tip alpha (del-Tip alpha), an inactive form, neither bound to nor entered the cells, suggesting the presence of a specific binding molecule. Mutagenesis analysis of Tip alpha revealed that a dimer formation of Tip alpha with a disulfide bond is required for both specific binding and induction of TNF-alpha gene expression. A confocal laser scanning microscope revealed some Tip alpha in the nuclei, but del-Tip alpha was not present, which indicated that an active form of Tip alpha can penetrate the nucleus and may be involved in the induction of TNF-alpha gene expression. Examination of Tip alpha production and secretion in 28 clinical isolates revealed that H. pylori obtained from gastric cancer patients secreted Tip alpha in significantly higher amounts than did H. pylori from patients with chronic gastritis, suggesting that Tip alpha is an essential factor in H. pylori inflammation and cancer microenvironment in the human stomach. Tip alpha is thus a new carcinogenic factor of H. pylori that can enter the nucleus through a specific binding molecule, and its mechanism of action is completely different from that of CagA.

Helicobacter pylori-secreting protein Tipalpha is a potent inducer of chemokine gene expressions in stomach cancer cells

PURPOSE

Stomach cancer has a high mortality rate in East Asia, and is strongly associated with Helicobacter pylori (H. pylori) infection. H. pylori is known to express chemokine genes in the gastric mucosa, chemokines that are important host immune factors facilitating inflammation and tumor growth. To investigate the mechanism of carcinogenesis in the stomach, it is essential to determine which molecule of H. pylori is involved in induction of chemokines, but this has remained unclear. We previously reported that a tumor necrosis factor-alpha (TNF-alpha) inducing protein (Tipalpha) secreted from H. pylori acts as a tumor promoter in stomach cancer development, and thus started to investigate whether Tipalpha is involved in induction of chemokine genes.

METHODS

Comprehensive gene expression analysis was conducted using DNA microarray and KeyMolnet analyses. The gene expression was quantitatively analyzed by real-time RT-PCR.

RESULTS

Comprehensive and quantitative gene expression analyses revealed that Tipalpha induces gene expression of the chemokines Ccl2, Ccl7, Ccl20, Cxcl1, Cxcl2, Cxcl5 and Cxcl10 extensively and simultaneously in mouse stomach cancer cells, MGT-40. Tipalpha induced high levels of chemokine gene expression, whereas inactive deleted Tipalpha, del-Tipalpha, showed only marginal expression, suggesting a correlation between tumor promotion and chemokine gene expression by Tipalpha. MG-132, a proteasome inhibitor which represses NF-kappaB-activation, inhibited chemokine gene expressions.

CONCLUSION

We report here that Tipalpha of H. pylori gene product is a strong inducer of chemokine gene expressions, providing a new model for stomach cancer development.

New tumor necrosis factor-alpha-inducing protein released from Helicobacter pylori for gastric cancer progression

PURPOSE

To investigate the association between Helicobacter pylori infection and its inflammatory reaction in gastritis, gastric ulcer, and gastric cancer, a new tumor necrosis factor-alpha (TNF-alpha)-inducing protein of H. pylori was studied.

METHODS

The HP0596 gene of H. pylori was identified as the TNF-alpha-inducing protein (Tipalpha) gene from genome sequence of H. pylori strain 26695. Using recombinant Tipalpha (rTipalpha) and deleted Tipalpha (rdel-Tipalpha) proteins, the latter of which lacks six amino acids containing two cysteines in the N-terminal domain, we examined their activities in TNF-alpha gene expression and NF-kappaB activation in both Bhas 42 (v-H-ras transfected BALB/3T3) cells and mouse gastric epithelial cell line MGT-40, and in vitro transformation of Bhas 42 cells.

RESULTS

Tipalpha protein as a homodimer form (38 kDa) was found in both extracts and culture medium of various H. pylori strains. rTipalpha significantly induced TNF-alpha gene expression and NF-kappaB activation in both Bhas 42 cells and MGT-40, and induced in vitro transformation of Bhas 42 cells. However, rdel-Tipalpha did not. Treatment with MG-132, a proteasome inhibitor, inhibited translocation of NF-kappaB p65, and abrogated TNF-alpha induction induced by Tipalpha protein.

CONCLUSION

Tipalpha is a new carcinogenic factor released from H. pylori mediated through NF-kappaB activation.

New tumor necrosis factor-alpha-inducing protein released from Helicobacter pylori for gastric cancer progression

PURPOSE

To investigate the association between Helicobacter pylori infection and its inflammatory reaction in gastritis, gastric ulcer, and gastric cancer, a new tumor necrosis factor-alpha (TNF-alpha)-inducing protein of H. pylori was studied.

METHODS

The HP0596 gene of H. pylori was identified as the TNF-alpha-inducing protein (Tipalpha) gene from genome sequence of H. pylori strain 26695. Using recombinant Tipalpha (rTipalpha) and deleted Tipalpha (rdel-Tipalpha) proteins, the latter of which lacks six amino acids containing two cysteines in the N-terminal domain, we examined their activities in TNF-alpha gene expression and NF-kappaB activation in both Bhas 42 (v-H-ras transfected BALB/3T3) cells and mouse gastric epithelial cell line MGT-40, and in vitro transformation of Bhas 42 cells.

RESULTS

Tipalpha protein as a homodimer form (38 kDa) was found in both extracts and culture medium of various H. pylori strains. rTipalpha significantly induced TNF-alpha gene expression and NF-kappaB activation in both Bhas 42 cells and MGT-40, and induced in vitro transformation of Bhas 42 cells. However, rdel-Tipalpha did not. Treatment with MG-132, a proteasome inhibitor, inhibited translocation of NF-kappaB p65, and abrogated TNF-alpha induction induced by Tipalpha protein.

CONCLUSION

Tipalpha is a new carcinogenic factor released from H. pylori mediated through NF-kappaB activation.

Growth regulation of gastric epithelial cells by Runx3

RUNX3: is expressed by gastric epithelial cells throughout development. Mice whose Runx3 gene has been knocked out died soon after birth. In the knockout mouse, gastric epithelia exhibited hyperplasia and epithelial apoptosis was suppressed. Analysis using a primary culture system for the epithelial cells suggested that this is caused by the reduced sensitivity of Runx3-/- gastric epithelial cells to the growth-inhibiting and apoptosis-inducing activities of TGF-beta. In human and mouse gastric cancer cell lines, RUNX3/Runx3 was silenced due to hypermethylation of CpG islands in the promoter region. Exogenous expression of RUNX3 in the cells that do not express the endogenous gene caused an inhibition of growth both in vivo and in vitro. These observations indicate that Runx3 is a major growth regulator of gastric epithelial cells, and that it is deeply involved in gastric tumorigenesis in both humans and mice.

An optimal therapeutic expression level is crucial for suicide gene therapy for hepatic metastatic cancer in mice

The most serious problem in current gene therapy is discrepancies between experimental data and actual clinical outcomes, which may be due to insufficient analyses and/or inappropriate animal models. We have explored suicide gene therapy by using various clinically relevant animal models and doubt the clinical use of maximal suicide gene expression, which has been generally recommended. To explore this subject further, we studied what expression level of suicide gene and what promoter led to the maximal clinical benefit in the case of hepatic metastatic cancer in mice. Therapeutic and adverse side effects of 4 adenoviral vectors that express herpes simplex virus thymidine kinase (HSV-tk) under different promoters were scrupulously investigated in 2 mouse models of hepatic metastasis of gastric cancer that possess clinical characteristics. Surprisingly, increases in HSV-tk expression beyond a certain point, achieved by the Rous sarcoma virus long terminal repeat promoter, not only enhanced the adverse side effects of lethal hepatotoxicity and ganciclovir-independent cytotoxicity but also failed to further increase therapeutic potential. Moreover, the carcinoembryonic antigen (CEA) tumor-specific promoter, the therapeutic potential of which had been underestimated, was much more useful-even in the case of low CEA-producing cancer-than had been previously reported. In conclusion, the optimal therapeutic expression level of a suicide gene is a novel concept and a crucial factor for successful cancer gene therapy. The present results, which contradict those of previous studies, alert researchers about possible problems with ongoing and future clinical trials that lack this concept.

Inhibition of growth of mouse gastric cancer cells by Runx3, a novel tumor suppressor

We reported recently that the silencing of RUNX3 is causally related to gastric cancer in humans. Here we report that in three of four cell lines derived from N-methyl-N-nitrosourea-induced mouse glandular stomach carcinomas, Runx3 is silenced due to hypermethylation of CpG islands in the promoter region, as we also observed for human gastric cancer cells. Although two of the sites we tested in the promoter of the fourth line were not methylated, in all four cases the silencing of Runx3 could be reversed by treatment of the cells with 5'-azacytidine and trichostatin A. Interestingly, the exogenous expression of RUNX3 in cell lines that do not express the endogenous gene caused an inhibition of growth in soft agar, suggesting that anchorage-independent growth could be used as an assay of RUNX3 activity in vitro. These observations suggest that the mouse system described here may be useful as a model for the study of human gastric carcinogenesis.