WASP family proteins regulate the mobility of the B cell receptor during signaling activation

Ivan Rey-Suarez,Wenxia Song,Arpita Upadhyaya,Simon Mochrie,Brittany A Wheatley,Hari Shroff,Anshuman Bhanja,Peter Koo,Zhou Shu

doi:10.1038/s41467-020-14335-8

Abstract

Regulation of membrane receptor mobility tunes cellular response to external signals, such as in binding of B cell receptors (BCR) to antigen, which initiates signaling. However, whether BCR signaling is regulated by BCR mobility, and what factors mediate this regulation, are not well understood. Here we use single molecule imaging to examine BCR movement during signaling activation and a novel machine learning method to classify BCR trajectories into distinct diffusive states. Inhibition of actin dynamics downstream of the actin nucleating factors, Arp2/3 and formin, decreases BCR mobility. Constitutive loss or acute inhibition of the Arp2/3 regulator, N-WASP, which is associated with enhanced signaling, increases the proportion of BCR trajectories with lower diffusivity. Furthermore, loss of N-WASP reduces the diffusivity of CD19, a stimulatory co-receptor, but not that of FcγRIIB, an inhibitory co-receptor. Our results implicate a dynamic actin network in fine-tuning receptor mobility and receptor-ligand interactions for modulating B cell signaling.

Highlights

Regulation of membrane receptor mobility tunes cellular response to external signals, such as in binding of B cell receptors (BCR) to antigen, which initiates signaling
We used interference reflection microscopy (IRM) to visualize the spreading and contraction of B cells on supported lipid bilayers (Fig. 1a, top panels), and total internal reflection fluorescence (TIRF) microscopy to analyze the clustering of BCR and coalescence of BCR clusters during cell contraction (Fig. 1a, bottom panels)
We found that Wiskott–Aldrich Syndrome protein (WASP) deletion results in a reduction of BCR diffusivity (Fig. 4e). perturbation-expectation maximization (pEM) analysis of BCR tracks in WASP KO mice (WKO) B cells again led to the identification of eight distinct states similar to control and conditional N-WASP KO mice (cNKO) cells, with the population fraction of each state relatively constant over time (Supplementary Fig. 4b)

Summary

Introduction

Regulation of membrane receptor mobility tunes cellular response to external signals, such as in binding of B cell receptors (BCR) to antigen, which initiates signaling. Our results implicate a dynamic actin network in fine-tuning receptor mobility and receptor-ligand interactions for modulating B cell signaling. The submembrane actin cytoskeleton modulates the concentration of inhibitory co-receptors[16,17] in the vicinity of BCR microclusters, thereby ensuring the rapid inhibition of activated BCRs. A consensus picture that emerges from these studies is that in resting B cells, the actin network serves as a structural barrier for BCRs, regulating their mobility by steric interactions. A consensus picture that emerges from these studies is that in resting B cells, the actin network serves as a structural barrier for BCRs, regulating their mobility by steric interactions Beyond this structural role, considerable evidence points to a role for dynamic actin in regulating BCR signaling and activation. Our findings reveal a role for actin dynamics in modulating nanoscale receptor diffusion, highlighting the importance of the dynamic actin network in regulating receptor mobility and signaling

Methods

Results

Conclusion