Figure 5. Knockdown of GD3S reduces cell proliferation, mammosphere formation, and tumor initiation in MDA-MB-231 cells.

(A) To measure knockdown of GD3S, vector control, or GD3S-KD-MDA231 cells were analyzed for mRNA expression of GD3S by real-time TaqMan RT-PCR. Relative expression of GD3S is shown. *P < 0.0001. (B) To measure levels of GD2 on the cell surface, vector control or GD3S-KD-MDA231 cells were stained with anti-GD2 antibody and analyzed on an LSR II flow cytometer (BD). GD2 expression is shown on the y axis and FSC on the x axis. (C) Percentage of GD2⁺ cells in vector control and GD3S-KD-MDA231 cells. *P < 0.01. (D) To measure cell migration, vector control and GD3S-KD-MDA231 cells were cultured in the presence or absence of 30% serum in a Transwell migration chamber. The average number of cells per microscopic field is shown. *P < 0.001. (E) Mammosphere formation assay using either vector control or GD3S-KD-MDA231 cells was performed by seeding 1,000 cells per well in 24-well cell culture dishes containing mammosphere growth medium. After 10 days, the mammospheres were counted under a light microscope. Scale bar: 200 μm. Numbers of mammospheres formed from either vector control or GD3S-KD-MDA231 cells are shown. *P < 0.0001. (F) To examine tumor initiation potential, 1 × 10⁶ vector control or GD3S-KD-MDA231 cells were transplanted subcutaneously into flanks of NOD/SCID mice. At the end of the ninth week, mice were shaved to remove excess hair on the tumors, and photographs were taken. (G) The tumors size was measured between 4 and 9 weeks. P < 0.000001.