Search

CARD protein–BCL-10–MALT1 (CBM) signalosomes are multiprotein signalling platforms that control immune and inflammatory pathways in most tissues. After exposure to distinct immune triggers, these molecules form self-organizing filaments with MALT1 protease activity to regulate canonical nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signalling pathways and the degradation of mRNA-binding proteins, which provides two layers of control of inflammatory gene expression. These CBM-regulated mechanisms are essential for host defence and tissue homeostasis, and numerous genetic alterations in CBM signalling components have been implicated in inherited and acquired immune-mediated diseases. This Review discusses the regulation and signalling of CBM complexes, their physiological roles and their pathophysiological functions in human immunodeficiency diseases, inflammatory disorders and cancers of the immune system.

Wiskott-Aldrich syndrome protein (WASp) is a main cytoskeletal regulator in B cells. WASp-interacting protein (WIP) binds to and stabilizes WASp but also interacts with actin. Using mice with a mutated actin binding domain of WIP (WIPΔABD), we here investigated the role of WIP binding to actin during B cell activation. We found an altered differentiation of WIPΔABD B cells and diminished antibody affinity maturation after immunization. Mechanistically, WIPΔABD B cells showed impaired B cell receptor (BCR)-induced PI3K signaling and actin reorganization, likely caused by diminished CD81 expression and altered CD19 dynamics on the B cell surface. WIPΔABD B cells displayed reduced in vivomotility, concomitantly with impaired chemotaxis and defective F-actin polarization, HS1 phosphorylation, and polarization of HS1 to F-actin-rich structures after CXCL12 stimulation in vitro. We thus concluded that WIP binding to actin, independent of its binding to WASp, is critical for actin cytoskeleton plasticity in B cells.