The Use of Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC) to Study Ivermectin-Mediated Molecular Pathway Changes in Human Ovarian Cancer Cells

Abstract

Stable isotope labeling with amino acids in cell culture (SILAC) was to use isotopic essential amino acids to replace the original amino acids for cell culture and passage for 8–10 generations, followed by mass spectrometry to identify proteins and the isotopic abundance difference to quantify proteins. SILAC can be used to characterize proteomic changes, and analyze protein turnover, protein interactions, and dynamic changes with quantitative accuracy, and high reproducibility. For this study, SILAC “light” (L-Lysine-2HCl [12C6, 14N2], L-Arginine-HCl [12C6, 14N4])- or “heavy” (L-Lysine-2HCl [13C6, 15N2], L-Arginine-HCl [13C6, 15N4])-labeling RPMI 1640 medium was used to culture human ovarian cancer TOV-21G cells for 10 passages, followed by the treatment of 0.1% dimethylsulfoxide for 24 h and 20 µM ivermectin for 24 h, respectively. The light- and heavy-isotope-labeled proteins were equally mixed (1:1) for digestion with trypsin. The tryptic peptide mixture was fractionated with liquid chromatography and analyzed with tandem mass spectrometry. In total, 4,447 proteins were identified in ivermectin-treated TOV-21G cells in relation to controls. Those proteins were enriched in 89 statistically significant signaling pathways and 62 statistically significant biological processes. These findings clearly demonstrated that SILAC quantitative proteomics was a useful and reliable method to study ivermectin-related proteomic changes in cancer cells, which in combination with molecular pathway networks and biological processes enrichments provided more comprehensive insights into molecular mechanisms of ivermectin in inhibiting TOV-21G cells.