The AKT kinase signaling network is rewired by PTEN to control proximal BCR signaling in germinal center B cells.

B cell antigen receptor (BCR) and CD40 signaling are rewired in germinal center (GC) B cells (GCBCs) to optimize selection for high-affinity B cells. In GCBC， BCR signals are constrained， but the mechanisms are not well understood. Here we describe a GC-specific， AKT-kinase-driven negative feedback loop that attenuates BCR signaling. Mass spectrometry revealed that AKT target activity was altered in GCBCs compared with naive B cells. Retargeting was linked to differential AKT T308 and S473 phosphorylation， in turn controlled by GC-specific upregulation of phosphoinositide-dependent protein kinase PDK1 and the phosphatase PTEN. In GCBCs， AKT preferentially targeted CSK， SHP-1 and HPK1， which are negative regulators of BCR signaling. We found that phosphorylation enhances enzymatic activity of these proteins， creating a negative feedback loop that dampens upstream BCR signaling. AKT inhibition relieved this negative feedback and enhanced activation of BCR-proximal kinase LYN， as well as downstream BCR signaling molecules in GCBCs.