Aim: To determine whether the CD55(hig); expression (CD55(hig);) cells in side population (SP) of the cell line MCF-7 possess characteristics of cancer stem cells.
Methods: Breast cancer cell line MCF-7 was cultured and the nucleic acid dye Hoechst33342 and Verapami were added. Flow cytometry (FCM) was employed to isolate the cells of SP and mian population (MP), the cells were then labeled with CD55 mAb; mean values of fluorescence intensity of CD55 in SP and MP cells were measured. CD55 mAb was used to mark the unsorted MCF-7 cells, the proportion of CD55(hig); cells was determined, and then CD55(hig); cells were sorted and collected, to observe biological characteristics, such as cell morphology, adherence rate, colony formation and cell cycle distribution as well as nude mice implantation.
Results: Mean value of fluorescence intensity of CD55 in SP cells was 100.85±4.57, and mean value of fluorescence intensity of CD55 in MP cells was 50.51±4.75; the proportion of CD55(hig); cell in MCF-7 cells was 2.12%; adherent rate of CD55(hig); cells in 24 h was lower than that in CD55(low); cells and 24 h after inoculation adherent rates of both cells had no significant difference (P>0.05); CD55(hig); cells were mostly spherical and kept in a suspended state at 12 hours after inoculation and culture; CD55(hig); cells had the ability of colony formation, the clone-forming rate of CD55(hig); cells was (20.04±1.07)% when the cells were cultured for one week, it was lower than the rate of (27.14±1.07)% in CD55(low); cells (P<0.01); the ratio of G0/G1 resting cells in CD55(hig); cells was (85.4±3.37)% which was higher than that in CD55(low); cells (58.6±2.55)% and in MCF-7 cells (70.73±4.21)%, which had a statistically significant difference (P<0.05). All nude mice implanted with CD55(hig); cells developed the tumor, and the pathological examination of the transplanted tumor had the properties of malignant cells.
Conclusion: A few CD55(hig); cells were found in breast cancer MCF-7 cells, and most of CD55(hig); cells were quiescent, non-adherent as well as being in a suspended state and being hereditary after cloning, so CD55(hig); cells had biological characteristics of cancer stem cells.