Fig. 1

Screening of differentially expressed cellular membrane proteins between SP and non-SP cells through SILAC. A Strategy for SILAC is shown. Heavy Lys was used to label proteins in SP cells, and light Lys was used to label proteins in non-SP cells. B Differentially expressed proteins in SKOV3 SP cells are shown. Proteins were considered significantly differentially expressed when the P value was less than 0.05 and the fold change (ratio H/L) was more than 1. Proteins were classified through protein function. Most of the upregulated proteins had functions of cell proliferation, transcription regulation and material transport. C. Six proteins, CD59, CDC50A, TMEM109, ATAD3A, CSN6, and ATAD3B, were found to be differentially expressed in SP cells of SKOV3 through SILAC, and five of them exhibited the same expression difference in SP cells of A2780. CD59 and CDC50A were the two proteins expressed on the cellular surface and were increased in both cell lines. D, E Expression of CD59 and CDC50A in SKOV3 and A2780 cells assessed by FACS analysis. CD59 was expressed on nearly all SKOV3 and A2780 cells, whereas CDC50A was expressed on only 0.4–0.6% of them. Based on the reasonable ratio, CDC50A was chosen as the candidate differentially expressed protein in SP cells