Proteomic Analysis of the Media Proteins

The proteins obtained from the media as described above were digested with trypsin (1 μg/50 μg protein, Promega) at 37°C overnight. The resulting peptides were purified with a stage tip [12], and re-suspended in 0.5% acetic acid for proteomics analysis, which was accomplished with Q Exactive mass spectrometer (Thermo Fisher Scientific) according to the methods from manufacturer [13]. The spectrum data obtained was searched against human protein database to identify target proteins.