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.