Quantitative interactomics in primary T cells unveils TCR signal diversification extent and dynamics

The activation of T cells by the T cell antigen receptor (TCR) results in the formation of signaling protein complexes (signalosomes), the composition of which has not been analyzed at systems-level. Here, we isolated primary CD4(+) T cells from 15 gene-targeted mice each expressing one tagged-form of a canonical protein of the TCR signaling pathway. Using affinity purification coupled with mass spectrometry, we analyzed the signalosomes assembling around each of the tagged protein over 600 seconds of TCR engagement. We showed that the TCR signal-transduction network comprises at least 277 unique proteins involved in 366 high-confidence interactions, and that TCR signals diversify extensively at the level of the plasma membrane. Integrating the cellular abundance of the interacting proteins and their interaction stoichiometry provided a quantitative and contextual view of each documented interaction permitting to anticipate whether ablation of a single interacting protein can impinge on the whole TCR signal-transduction network.