Expression of PTEN was inhibited by GM3S silencing. (a) Relative PTEN expression in GM3S-knockdown 4T1 cells analyzed by real-time RT-PCR. (b) Upper panels: expression and activation of PTEN detected by immunoblotting. Lower panels: quantitation of these blots after normalization with the GAPDH blot. *P < 0.05, **P < 0.01. CMP, cytidine 5'-monophosphate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GM3S, CMP-N-acetylneuraminic acid:lactosylceramide 2,3-sialyltransferase; p-PTEN, phosphor-PTEN Ser380/Thr382/383; PTEN, phosphatase and tensin homolog.