BACKGROUNDTo study the difference in gene expression between the EBV associated gastric carcinoma (EBVaGC) tissues. To explore the mechanism of gastric carcinoma pathogenesis initiated by EBV.

METHODSIn situ hybridization was used to study the frequencies of EBV small RNA expression in 155 cases of gastric carcinoma tissues. The expression levels of P53 protein and P21WAF1 protein were detected by immunohistochemistry in all gastric carcinoma tissues.

RESULTSThe expression of EBV small RNA was positive in 10 out of 155 cases (6.45%). The expression of P53 protein was weakly positive in 4 of the 10 cases. The expression level of P53 protein in EBVaGC was much lower than that in EBVnGC and was weakly positive in 30 of 145 cases with EBVnGC). P21WAF1 expression was detected in 7 of 10 cases with EBVaGC, but in 55 out of 145 cases with EBVaGC, P21WAF1 expression in EBVaGC was much higher than that in EBVnGC.

CONCLUSIONThere seems existing a special mechanism of pathogenesis in EBVaGC. In which P53 gene mutation may not play an important role.

Epstein-Barr Virus Infections ; metabolism ; pathology ; virology ; Herpesvirus 4, Human ; genetics ; physiology ; Host-Pathogen Interactions ; Humans ; Immunohistochemistry ; In Situ Hybridization ; Proto-Oncogene Proteins c-met ; metabolism ; RNA, Viral ; genetics ; Stomach Neoplasms ; metabolism ; pathology ; virology ; Tumor Suppressor Protein p53 ; metabolism

The C-terminal fragment of the c-Met receptor tyrosine kinase is present in the nuclei of some cells irrespective of ligand stimulation, but the responsible nuclear localization signal (NLS) has not been previously reported. Here, we report that two histidine residues separated by a 10-amino-acid spacer (H1068-H1079) located in the juxtamembrane region of c-Met function as a putative novel NLS. Deletion of these sequences significantly abolished the nuclear translocation of c-Met, as did substitution of the histidines with alanines. This substitution also decreased the association of c-Met fragment with importin beta. The putative NLS of c-Met is unique in that it relies on histidines, whose positive charge changes depending on pH, rather than the lysines or arginines, commonly found in classical bipartite NLSs, suggesting the possible 'pH-dependency' of this NLS. Indeed, decreasing the cytosolic pH either with nigericin, an Na+/H+ exchanger or pH 6.5 KRB buffer significantly increased the level of nuclear c-Met and the interaction of the c-Met fragment with importin beta, indicating that low pH itself enhanced nuclear translocation. Consistent with this, nigericin treatment also increased the nuclear level of endogenous c-Met in HeLa cells. The putative aberrant bipartite NLS of c-Met seems to be the first example of what we call a 'pH-dependent' NLS.
Active Transport, Cell Nucleus ; Amino Acid Sequence ; HeLa Cells ; Humans ; Hydrogen-Ion Concentration ; Molecular Sequence Data ; *Nuclear Localization Signals ; Protein Structure, Tertiary ; Proto-Oncogene Proteins c-met/*analysis/genetics/*metabolism ; Sequence Deletion

Met tyrosine kinase receptor, the receptor of hepatocyte growth factor/scatter factor (HGF/SF), is present in mouse tissues as two major isoforms differing by a 47-aminoacid segment in the juxtamembrane domain via alternative splicing of exon 14. We found that the smaller isoform of Met (Sm-Met) was highly transformable in both in vitro and in vivo tumorigenesis assays. In this report, close examination of the transforming activity of the Sm-Met showed that the expression of Sm-Met conferred the cells serum independence and anti- apoptotic property when treated with doxorubicin. These properties of Sm-Met seemed to be originated from its far longer maintenance of tyrosine kinase activity after the binding of HGF/SF. Interestingly, the longer maintenance of activated status was accompanied with more increase of tyrosine phosphorylation of Stat3 protein. Moreover, we have tried to find (an) animal tumorigenesis model(s) showing the increase in the expression of this transforming variant of Met. In gamma-ray-induced mouse thymic lymphoma model, the expression of the mRNAs for Sm-Met was significantly increased as well as those of wild type Met and HGF/SF, suggesting a possible role of the Sm-Met in tumorigenesis in vivo.
Animals ; *Apoptosis ; Cell Proliferation ; Cell Survival ; *Cell Transformation, Neoplastic ; DNA-Binding Proteins/metabolism ; Doxorubicin/pharmacology ; Hepatocyte Growth Factor/pharmacology ; Lymphoma/*etiology/genetics/metabolism ; Mice ; NIH 3T3 Cells ; Phosphorylation ; Protein Isoforms/genetics/metabolism ; Proto-Oncogene Protein c-met/genetics/*metabolism ; RNA, Messenger/analysis/metabolism ; Research Support, Non-U.S. Gov't ; Serum/metabolism ; Thymus Gland ; Trans-Activators/metabolism

Autocrine stimulation via coexpression of hepatocyte growth factor (HGF) and its receptor (Met) has been reported in many human sarcomas, but few in carcinomas. In this report, we found that one gastric cancer cell line, SNU-484, among 11 gastric cell lines tested has an autocrine HGF- Met stimulation. RT-PCR, ELISA and scattering assay using MDCK cells revealed that SNU-484 cells secreted a significant amount of active HGF (about 1.25 +/- 0.41 ng/24 h/106 cells) into conditioned medium. Resultantly, Met in this cell line was constitutively phosphorylated. Neutralizing antibodies against HGF reduced the tyrosine phosphorylation of Met, resulting in the inhibition of cell proliferation and migration (P <0.005). To the best of our knowledge, this is the first report on autocrine HGF-Met signaling in a gastric cancer cell line. Our observations with SNU-484 cells suggest that HGF is involved in the development and/or progression of some gastric carcinoma through an autocrine mechanism.
Animals ; Antibodies, Neoplasm/immunology ; *Autocrine Communication ; *Cell Movement ; Cell Proliferation ; Culture Media, Conditioned/pharmacology ; Dogs ; Enzyme-Linked Immunosorbent Assay ; Hepatocyte Growth Factor/immunology/*pharmacology ; Neutralization Tests ; Phosphorylation ; Proto-Oncogene Protein c-met/genetics/*metabolism ; Research Support, Non-U.S. Gov't ; Reverse Transcriptase Polymerase Chain Reaction ; Stomach Neoplasms/*immunology/metabolism/pathology ; Tumor Cells, Cultured ; Tyrosine/metabolism