The Lack of WIP Binding to Actin Results in Impaired B Cell Migration and Altered Humoral Immune Responses

Selina Jessica Keppler,Marianne Burbage,Francesca Gasparrini,Lara Hartjes,Shweta Aggarwal,Michel J Massaad,Raif S Geha,Andreas Bruckbauer,Facundo D Batista

doi:10.1016/j.celrep.2018.06.051

Abstract

SummaryWiskott-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 vivo motility, 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.

Highlights

B cells are an integral part of the adaptive immune system
To establish whether WASp-interacting protein (WIP) binding to actin has an effect on humoral immune responses, we generated mixed bone marrow (BM) chimeras by reconstituting lethally irradiated congenic BALB/c CD45.1 animals with a mixture of 50% CD45.1 wild-type (WT) BM and 50% CD45.2 WIPDABD mutant BM (WTWIPDABD), WIP-deficient BM (WT-Wipf1À/À), or WT-WT BM
These mixed chimeras were used to analyze reconstitution and the formation of germinal center (GC) B cells in a competitive environment. During analysis of these mixed chimeras, we found a 50% reduction of CD45.2 Wipf1À/À B cells compared to CD45.1 WT B cells, altering the ratio of CD45.1 to CD45.2 B cells from 50:50 initially to 80:20 in the spleen, similar to what we have described previously (Figure S1A) (Keppler et al, 2015)

Summary

Introduction

B cells are an integral part of the adaptive immune system. correct activation of B cells protects the host against a variety of infections and cancers, aberrant B cell activation has been implicated in the development of autoimmune diseases. The B cell receptor (BCR) is immobilized on the plasma membrane by areas of high-density cortical actin cytoskeleton. Changes in actin organization alone increase BCR diffusion in a ligand-independent manner and trigger signaling similar to BCR crosslinking (Treanor et al, 2010), involving the co-receptor CD19 held in place by its association with the tetraspanin molecule CD81 (Mattila et al, 2013). The actin cytoskeleton organizes and immobilizes the BCR and regulates the BCR proximity to its co-receptors in the plasma membrane (Gasparrini et al, 2016; Mattila et al, 2016; Song et al, 2014; Tolar, 2017) but is needed for the correct reorganization of the plasma membrane surface in response to extracellular clues, thereby regulating intracellular signaling

Results

Discussion

Conclusion