In addition to the role of SSEA-1 as a tumor-initiating marker in glioblastoma multiforme cells [
12], another recent study showed that B3GNT5 was correlated with glioma stem cells, and its expression was significantly downregulated during glioma stem cells differentiation [
8]. Given the importance of B3GNT5 and SSEA-1 in cancer cell stemness, B3GNT5 might be required for the maintenance of breast cancer cell stemness. To verify this notion, we first examined the impact of B3GNT5 expression on proliferation in MDA-MB231, BT549 and SUM159 cells. Knockout of B3GNT5 significantly suppressed the proliferation in these cells, whereas ectopic expression of B3GNT5 remarkably restored the decreased proliferation rate (Figure S
4A). Next, we assessed the effects of B3GNT5 knockout on the mammosphere formation. Strikingly, B3GNT5 knockout dramatically impeded the mammosphere formation in MDA-MB231, BT549 and SUM159 cells, which was partially rescued in MDA-MB231 KO and BT549 KO cells by ectopic expression of B3GNT5 (Fig.
4 A-B and Figure S
4B), whereas ectopic B3GNT5 expression in MCF7 cells led to a remarkable promoted mammosphere formation (Fig.
4D-E). Human breast CSCs are enriched in cells of CD44
high/CD24
low population [
34]. To explore correlation between B3GNT5 expression and breast CSCs, we analyzed the potential changes of CD44
high/CD24
low cells populations by flow cytometry. Similar to the observation in mammosphere formation, B3GNT5 knockout led to a significant reduction of CD44
high/CD24
low populations in MDA-MB231, BT549 and SUM159 cells, whereas ectopic expression of B3GNT5 partially rescued the CD44
high/CD24
low populations in MDA-MB231 KO and BT549 KO cells (Fig.
4 C and Figure S
4C). Consistently, ectopic B3GNT5 expression also increased CD44
high/CD24
low population in MCF7 cells (Fig.
4 F). Subsequent resuspending and replating of cells from the primary and secondary mammospheres showed a similar reduced spheres formation in MDA-MB231 KO and BT549 KO cells compared with wild-type control cells (Fig.
4G). Using
in vitro limiting dilution assay, we observed that MDA-MB231 KO and BT549 KO cells with higher expression of B3GNT5 were consistently more tumorigenic (Fig.
4 H, Figure S
4D and Figure S
4E). These results suggest that B3GNT5 expression is important for stemness maintenance of breast cancer cells.