A spatiotemporal map of co-receptor signaling networks underlying B cell activation

The B cell receptor (BCR) signals together with a multi-component co-receptor complex to initiate B cell activation in response to antigen binding. Here, we take advantage of peroxidase-catalyzed proximity labeling combined with quantitative mass spectrometry to track co-receptor signaling dynamics in Raji cells from 10 s to 2 h after BCR stimulation. This approach enables tracking of 2,814 proximity-labeled proteins and 1,394 phosphosites and provides an unbiased and quantitative molecular map of proteins recruited to the vicinity of CD19, the signaling subunit of the co-receptor complex. We detail the recruitment kinetics of signaling effectors to CD19 and identify previously uncharacterized mediators of B cell activation. We show that the glutamate transporter SLC1A1 is responsible for mediating rapid metabolic reprogramming and for maintaining redox homeostasis during B cell activation. This study provides a comprehensive map of BCR signaling and a rich resource for uncovering the complex signaling networks that regulate activation. [Display omitted] •Proteins and phosphoproteins near CD19 are tracked after B cell activation•Recruitment dynamics of signaling effectors, such as PI3K, to CD19 are profiled•Potential novel regulators of B cell receptor signaling are identified•SLC1A1 mediates metabolic reprogramming during B cell activation in Raji cells Susa et al. develop an unbiased, cell-based system to profile the proteins recruited to the B cell co-receptor, CD19, throughout B cell activation. The recruitment dynamics of known and previously uncharacterized regulators are profiled, providing a rich resource for uncovering the complex signaling networks that regulate activation.