Background & Aims: Although a significant amount of regenerating gene (REG) Iα protein is present not only in normal gastric mucosa but also in gastric cancer tissues, its pathophysiologic role in gastric cancer development remains unclear. We investigated REG Iα protein expression in early gastric cancers, and examined whether cytokines are responsible for REG Iα gene expression and whether REG Iα protein has a trophic and/or an antiapoptotic effect on gastric cancer cells. Methods: Early gastric cancer specimens were analyzed histologically using immunohistochemistry for REG Iα protein and proliferating cell nuclear antigen (PCNA). The effects of cytokines on REG Iα promoter activity and its messenger RNA (mRNA) expression in AGS (a kind of gastric cancer cell line) cells were examined by luciferase reporter assay and Northern blot analysis, respectively. Effects of REG Iα protein on cell growth and H2O2-induced apoptosis in AGS cells were examined by 3,-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide (MTT) and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphatase nick-end labeling (TUNEL) assays, respectively. Results: REG Iα-positive early gastric cancers showed a significantly higher PCNA labeling index and more severe inflammatory cell infiltration in adjacent gastric mucosa than the negative cancers. REG Iα gene expression and its promoter activity were enhanced by interferon (IFN)-γ and interleukin (IL)-6. REG Iα protein promoted cell growth and cell resistance to H2O2-induced apoptosis in AGS cells. These effects were abolished by concomitant treatment with anti-REG Iα antibody. REG Iα protein enhanced Akt phosphorylation and Bcl-xL expression in AGS cells. Conclusions: REG Iα gene is inducible by cytokine stimulation and its gene product may function as a mitogenic and/or an antiapoptotic factor in the development of early gastric cancer.
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