Azide-containing amino acid modulation of cellular transcriptome and proteome composition – implications on click chemistry based secretome analysis

The analysis of the secretome provides important information on cellular communication and on the recruitment and behavior of cells in specific tissues. Especially in the context of tumors, knowledge on the composition of the secretome plays an important role for diagnosis and therapy. Mass spectrometry-based analysis of cell-conditioned media is widely used for the unbiased characterization of cancer secretomes in vitro. Azide-containing amino acid labeling in combination with click chemistry now facilitates this type of analysis without serum starvation. The modified amino acids, however, are less efficiently incorporated into newly synthesized proteins. Utilizing transcriptome and proteome analysis, we describe here in detail the effects of labeling cells with the methionine analog azidohomoalanin (AHA) on the modulation of gene expression and protein composition. We observe that 11% – 34% of the proteins detected in the secretome were affected by AHA labeling regarding their expression levels in the transcriptome and/or proteome. Performing gene ontology analyses, our results provide a detailed view on the AHA-based induction of cellular stress and apoptosis-related pathways and provide first insights on how this might affect the composition of the secretome on a global scale. To describe and understand the effects of AHA on the behaviour of cells in detail, we performed comparative transcriptome analyses of seven different tumor cells grown 20 h in AHA- or methionine-containing media and evaluated the gene expression profiles.