Proteomic Comparison of the Cytotoxicology of Two Diastereomers of Citreamicin Reveals Differentially Activation of NF-kappa B Pathway

Citreamicin epsilon is a group of antitumor compounds produced by Streptomyces species. Cytotoxicology study of two diastereomers, citreamicin epsilon A and B, showed different apoptotic effects on PtK2 cells with IC50 (half-maximal inhibitory concentration) values of 0.086 and 0.025 mu M, respectively. Thus, we performed an iTRAQ (isobaric tags for relative and absolute quantitation)-based quantitative proteomic analysis to reveal the mechanism of cytotoxicity of citreamicin epsilon A and B in PtK2 cells. A total of 1,079 proteins were identified and quantified, among which 103 and 94 proteins displayed significant changes in expression levels after the treatment of citreamicin epsilon A and B, respectively. These significantly differentially expressed proteins (DEPs) were further annotated by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and protein-protein interaction analysis, which revealed the involvement of eight molecular pathways. Among them, expression trends of proteins involved in the nuclear transcription factor kappa B (NF-kappa B) pathway displayed the opposite between the two diastereomer treatments, indicating different modes of action of these two compounds. Citreamicin epsilon A treatment induced rapid activation of the NF-kappa B pathway, which might promote cell survival and resulted in lower toxicity. Our comparative proteomic analysis provided molecular evidence on the toxicity of two diastereomers compounds to cells, which may shed new light on future mechanism study of these antitumor compounds.