Abstract 1934: Molecular mechanism of abnormal localization of nucelolin on cell-surface of gastric cancer cells, with regard to Ras signaling pathway

Abstract

Abstract Our intensive study of TNF-α inducing protein (Tipα), a carcinogenic factor secreted from H. pylori, revealed that nucleolin acts as a receptor of Tipα in a mouse gastric cancer cell line (MGT-40). Although nucleolin is a major nucleolar protein, nucleolin was found in the cell membrane by cell fractionation and on the cell-surface by flow cytometrical analysis. We further found that nucleolin shuttles Tipα from cell surface to the cytosol, resulting in expression of TNF-α gene, an endogenous tumor promoter. Moreover, a large amount of nucleolin was found in the membrane fraction of MGT-40 cells, but not in that of mouse normal glandular stomach. These results suggest that abnormal localization of nucleolin occures in gastric cancer, as an associated process of carcinogenesis. In the light of this evidence, we think that the abnormal localization of nucleolin on cell surface produces the optimal carcinogenic environment for Tipα binding in gastric cancer development by H. pylori infection. Experimentally we found that large amounts of nucleolin were expressed on the surface of four human gastric cancer cell lines (MKN-45, MKN-74, AGS, and KATOIII), with smaller amounts on that of another cell line (MKN-1), although the total amounts of nucleolin were almost the same among these five cell lines. It is important to note that the amounts of cell-surface nucleolin are correlated well with those of Ras-GTP form, the active form of Ras protein in these cell lines, and we confirmed that MKN-1 cells had the lowest amounts of Ras-GTP form among the five lines. Moreover, the treatment of AGS cells with okadaic acid, a tumor promoter and inhibitor of protein phosphatases 1 and 2A, reduced the amount of nucleolin localized on cell-surface, indicating that abnormal localization of nucleolin on cell surface can be induced by Ras signaling pathway and post-translational modifications. Thus, we discuss the relationship between the abnormal localization of nucleolin and the disorder in the Ras signaling pathway in gastric cancer development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1934. doi:10.1158/1538-7445.AM2011-1934