Figure 1.

Low CD24 expression defines a radio- and chemo-resistant subpopulation of HMLE cells. CD24^−/low subpopulation was defined as the 10% of cells expressing the lowest fluorescence in control cells. (A) Percentage of dead and CD24^−/low HMLE cells at five days following high dose irradiation (4–10 Gy). Percentage of dead and CD24^−/low HMLE cells following three day exposure to high concentrations of (B) 5-fluorouracil (5FU), (C) cisplatin and (D) paclitaxel. Data are presented as the mean ± SD of 3 independent experiments. Significant differences (compared with untreated cells) were analyzed by one-way ANOVA followed by Dunnett's multiple comparisons correction test. *P<0.05, **P<0.01, ***P<0.001 and ****P<0.0001. ns, not significant. (E) CD24^−/low and CD24⁺ HMLE cell subpopulations were analyzed by flow cytometry following CD24/CD44 staining. CD24 expression was analyzed by reverse transcription-quantitative PCR. (F) Percentage of CD24^−/low and CD24⁺ dead cells five days after 4 and 6 Gy irradiation and following three day exposure to 400 µM 5FU, 15 µM cisplatin and 10 nM paclitaxel. Data are presented as the mean ± SD of 3 independent experiments. Significant differences (compared with untreated cells) were analyzed by 2 way ANOVA followed by Sidak's multiple comparisons correction test. *P<0.05, **P<0.01, ***P<0.001 and ****P<0.0001. ns, not significant.