Establishment and characterization of a rat pepsin-producing gastric cell line (OUMS-37)

SOX2 is frequently downregulated in gastric cancers and inhibits cell growth through cell-cycle arrest and apoptosis

SOX transcription factors are essential for embryonic development and play critical roles in cell fate determination, differentiation and proliferation. We previously reported that the SOX2 protein is expressed in normal gastric mucosae but downregulated in some human gastric carcinomas. To clarify the roles of SOX2 in gastric carcinogenesis, we carried out functional characterisation of SOX2 in gastric epithelial cell lines. Exogenous expression of SOX2 suppressed cell proliferation in gastric epithelial cell lines. Flow cytometry analysis revealed that SOX2-overexpressing cells exhibited cell-cycle arrest and apoptosis. We found that SOX2-mediated cell-cycle arrest was associated with decreased levels of cyclin D1 and phosphorylated Rb, and an increased p27^Kip1 level. These cells exhibited further characteristics of apoptosis, such as DNA laddering and caspase-3 activation. SOX2 hypermethylation signals were observed in some cultured and primary gastric cancers with no or weak SOX2 expression. Among the 52 patients with advanced gastric cancers, those with cancers showing SOX2 methylation had a significantly shorter survival time than those without this methylation (P=0.0062). Hence, SOX2 plays important roles in growth inhibition through cell-cycle arrest and apoptosis in gastric epithelial cells, and the loss of SOX2 expression may be related to gastric carcinogenesis and poor prognosis.

Frequent epigenetic silencing of the bone morphogenetic protein 2 gene through methylation in gastric carcinomas

Recently, it was reported that exogenous bone morphogenetic protein (BMP)-2 acted as an antiproliferative agent in a variety of cell lines, including normal and cancerous gastric cell lines, indicating that BMP-2 plays an important role during cell growth. However, despite the loss of BMP-2 expression in several cancers, the underlying mechanism remains unknown. Epigenetic silencing through DNA methylation is one of the key steps during carcinogenesis. In this study, we found, through analysis by the methylation-specific polymerase chain reaction technique, CpG island methylation of the BMP-2 promoter region in gastric and colon cancer cell lines. BMP-2 mRNA was found to be activated after 5-aza-2'-deoxycytidine treatment of the methylation-positive cells. Moreover, 24 of the 56 (42.9%) gastric cancer tissues exhibited promoter methylation. Immunohistochemical staining revealed that 18 of the 24 (75%) gastric cancer tissues without methylation signals exhibited BMP-2 expression, whereas among 20 cancer tissues with strong methylation signals only four (20%) expressed BMP-2 (P = 0.0003). These findings indicate that BMP-2 methylation is strongly associated with the loss of BMP-2 protein expression in the primary gastric carcinomas. BMP-2 methylation was more often observed in diffuse type (60.7%) than in intestinal type (25%) gastric carcinomas (P = 0.007). Thus, aberrant BMP-2 methylation and the resultant loss of BMP-2 expression may be related to gastric carcinogenesis, particularly in the diffuse type.

BMP-2 modulates the proliferation and differentiation of normal and cancerous gastric cells

Bone morphogenetic protein 2 (BMP-2), a member of the transforming growth factor beta super-family, has been shown to act as an antiproliferative agent for a variety of cell lines by activating signaling cascades that cause cell cycle arrest. However, the biological effect and mechanism of action of BMP-2 on gastric cells remain unknown. In the present study, we showed that recombinant human BMP-2 dose-dependently inhibited the growth of OUMS37 rat gastric cells and MKN74 human gastric cancer cells. The antiproliferation seems to be due to cell cycle arrest in the G1-phase, which was revealed by flow cytometric assays. BMP-2 increased the level of p21/WAF1/CIP1, suggesting that BMP-2-mediated inhibition of cell proliferation may be induced through p21/WAF1/CIP1. In addition, BMP-2 increased the expression of pepsinogen II, a differentiation marker of the stomach, in MKN74 cells. These results indicate that BMP-2 plays important roles in modulating the proliferation and differentiation of gastric epithelial cells.

Development and characterization of conditionally immortalized gastric epithelial cell lines from transgenic rats harboring temperature-sensitive simian virus 40 large T-antigen gene

Conditionally immortalized gastric epithelial cell lines were established from transgenic rats harboring temperature-sensitive simian virus 40 (tsSV40) large T-antigen gene. Gastric mucosal cells and epithelial tissues isolated from the stomach of the transgenic rats were cultured at permissive temperature (33 degrees C), and proliferative cells were cloned by colony formation. Six cell lines (designated as RGE1-01, RGE1-02, RGE1-03, RGE1-21, RGE1-22 and RGE2-01) showing epithelial-like morphology have been established. All cells grew at 33 degrees C, but did not at nonpermissive temperature (39 degrees C). High expression level of large T-antigen in the nuclei was observed at 33 degrees C, whereas the expression level was gradually decreased in a time-dependent manner at 39 degrees C. These results suggest that the temperature-sensitive growth characteristics arise as a result of a function of the tsSV40 large T-antigen. None of the cell lines were transformed as judged by anchorage-independent growth assay. Immunocytochemical findings indicated that all cells expressed epithelial cell markers including cytoskeletal (cytokeratin and actin), basement membrane (laminin and collagen type IV) and junctional complex (ZO-1 and desmoplakin I+II) proteins at 33 degrees C. All cells expressed mRNA of cathepsin E, a pit cell marker. Moreover, transepithelial resistance was observed between apical and basolateral sides in the cells. RGE1-22 cells produced prostaglandin E(2). Levels of mRNA for cathepsin E, transepithelial resistance and prostaglandin E(2) were influenced by the nonpermissive temperature. Thus, these conditionally immortalized gastric cell lines which preserve some epithelial cell characteristics will provide a useful in vitro model of gastric epithelium.