51 - The BCR Redox Machinery

Abstract

Through the B cell antigen receptor (BCR), mature B cells recognize the presence of antigens in the external world and adapt their responses. The signaling output from this receptor is tightly controlled so as to prevent its hypo- or hyper-stimulation. Reactive oxygen species (ROS) can amplify BCR signaling, by inhibiting its intracellular negative regulators, i.e. protein tyrosine phosphatases. However, ROS fluxes and signals - most likely dependent on close proximity - have never been systematically studied. We recently showed that the NADPH oxidase complex 2 (NOX2) produces ROS extracellularly in B lymphocytes and that the water channel aquaporin 8 (AQP8) is consequently needed for their passage across the membrane for BCR signal amplification. On aquaporin 8 silencing, indeed, inducible B lymphoma cells respond poorly to BCR stimulation. Their differentiation is severely impaired, as demonstrated by retarded onset of IgM polymerization, low amounts of IgM secretion, and prolonged BCR expression on the cell surface. Thus, efficient induction of B cell activation and differentiation requires intact H 2 O 2 fluxes across the plasma membrane for signal amplification. The following step would be to understand whether there are physical connections between BCR, NOXes and AQPs. Are these connections induced or reinforced by antigen binding? To answer these questions, we are currently characterizing by PLA techniques the spatial organization and interaction of redox-regulators on the plasma membrane of resting and activated B cells.