Abstract: Abstract： Objective To detect the expression of stem-cell related factors Nanog and CD44 in spheroid body-form⁃ ing cells of gastric cancer cell line MKN-45. Methods The gastric cancer cell line MKN-45 was used to culture spheroid bodies in non-adherent condition in a serum-free medium supplemented with epidermal growth factor (EGF) and basic fibro⁃ blast growth factor (bFGF). Using Western blot analysis, immunofluorescence staining and quantitative real time polymerase chain reaction（qRT-PCR）, the expression levels of stem cell-related genes Nanog and CD44 were studied. Results In this study, we observed that MKN45 cells formed spheroid bodies in non-adherent condition in a serum-free medium, and the levels of Nanog and CD44 mRNA expression in spheroid body-forming cells were 2.34±0.22 and 1.18±0.04， respectively, which were higher than those in parental cells (1.00±0.00 and 1.00±0.05). The levels of Nanog and CD44 protein expression in spheroid body-forming cells were 0.18±0.02 and 0.24±0.04, respectively, which were significantly higher than those in pa⁃ rental cells (0.07±0.02 and 0.18±0.01, P＜ 0.05). Nanog protein was positively stained within the perinuclear and cytoplasm of the spheroid body-forming cells, and CD44 was positively stained mainly in the membrane. Dual staining of Nanog/CD44 indicated that the embryonal protein Nanog was co-localized with CD44 in the spheroid body-forming cells. Conclusion Spheroid body-forming cells developed from human gastric cancer cell line MKN-45 in serum-free medium supplemented with EGF and bFGF show characteristics of cancer stem cell (CSC). The cells co-expressed of CD44 and Nanog maybe a phe⁃ notype of gastric CSCs.

Key words: stomach neoplasms, neoplastic stem cells, antigens, CD44, suspension culture, Nanog