11106 Background: Several studies suggest the existence of breast cancer-initiating cells (BCIC), responsible for tumor development and progression. Initial reports that only the CD44+CD24−/low subpopulation contains BCIC have been challenged by subsequent studies. We examined the relationship between CD24 and biological properties of breast cancer cells. Methods: MA-11 breast carcinoma cells, originating from bone marrow micrometastases, are CD44+ and have an heterogeneous expression of CD24 (214,000/cell; range 0–1,120,000). We have previously reported that upon in vitro culture as mammospheres under stem cell-like conditions, MA-11 cells acquired increased tumorigenicity and a CD44+CD24−/low phenotype. We have now investigated the relationship between CD24 expression and tumorigenicity in the MA-11 model. Results: Upon passage of MA-11 mammospheres in adherent culture, cells rapidly re-expressed CD 24. The rapid increase in CD24 was consistent with antigen up-regulation, not selection of CD24−/low cells. Exposure of adherent MA-11 cells to imatinib for 72h resulted in a reversible decrease in CD24 from 214,000 to 15,800/cell. CD44+CD24−/low cells, sorted by flow cytometry, generated CD44+CD24high, and CD44+CD24highgenerated CD44+CD24−/low. Immediately after sorting, >90% CD44+CD24−/low cells were in G0/G1. After 24–48 h in culture, cell cycle distribution, growth rate and invasiveness of the sorted cell populations were equivalent. Upon injection and s.c. growth, CD24 expression of CD44+CD24−/low populations and clones increased from 10,000 to 220,000/cell. Similarly, CD44+CD24−/low clones derived from human MCF-7 breast carcinoma cells formed tumors containing >99% CD44+CD24high cells. The average number of CD24 per cell was equivalent for tumors formed upon injection of CD44+CD24−/low, CD44+CD24+, mammosphere-derived cells or parental adherent MA-11 cells. The tumorigenic potentials of sorted CD44+CD24−/low, CD44+CD24−/lowsub-populations and clones in nu/nu mice were equivalent. Conclusions: CD44+CD24−/low breast cancer cells are not associated with increased tumorigenicity; the high CD24 level of mouse xenografts derived from both CD44+CD24−/low and CD44+CD24hi breast cancer cells suggests an important role for CD24 in tumor growth. No significant financial relationships to disclose.
miR-622 is a novel potential biomarker of breast carcinoma and impairs motility of breast cancer cells through targeting NUAK1 kinase
