N-WASP Is Essential for the Negative Regulation of B Cell Receptor Signaling

• DOI: 10.1371/journal.pbio.1001704
• Publication Date: 2013-11-05T21:55:58Z
• Authors: Chaohong Liu; Xiaoming Bai; Junfeng Wu; Shruti Sharma; Arpita Upadhyaya; Carin I. M. Dahlberg; Lisa S. Westerberg; Scott B. Snapper; Xiaodong Zhao; Wenxia Song
• Keywords: 0301 basic medicine; 570; Mice, 129 Strain; QH301-705.5; 610; Receptors, Antigen, B-Cell; Wiskott-Aldrich Syndrome Protein, Neuronal; Mice; 03 medical and health sciences; Animals; Humans; Biology (General); Antigens; Cells, Cultured; Autoantibodies; Mice, Knockout; B-Lymphocytes; Actins; Wiskott-Aldrich Syndrome; Mice, Inbred C57BL; Protein Transport; Antibodies, Antinuclear; Leukocytes, Mononuclear; Mice, Inbred CBA; Wiskott-Aldrich Syndrome Protein; Research Article; Signal Transduction

Negative regulation of receptor signaling is essential for controlling cell activation and differentiation. In B-lymphocytes, the down-regulation of B-cell antigen receptor (BCR) signaling is critical for suppressing the activation of self-reactive B cells; however, the mechanism underlying the negative regulation of signaling remains elusive. Using genetically manipulated mouse models and total internal reflection fluorescence microscopy, we demonstrate that neuronal Wiskott-Aldrich syndrome protein (N-WASP), which is coexpressed with WASP in all immune cells, is a critical negative regulator of B-cell signaling. B-cell-specific N-WASP gene deletion causes enhanced and prolonged BCR signaling and elevated levels of autoantibodies in the mouse serum. The increased signaling in N-WASP knockout B cells is concurrent with increased accumulation of F-actin at the B-cell surface, enhanced B-cell spreading on the antigen-presenting membrane, delayed B-cell contraction, inhibition in the merger of signaling active BCR microclusters into signaling inactive central clusters, and a blockage of BCR internalization. Upon BCR activation, WASP is activated first, followed by N-WASP in mouse and human primary B cells. The activation of N-WASP is suppressed by Bruton's tyrosine kinase-induced WASP activation, and is restored by the activation of SH2 domain-containing inositol 5-phosphatase that inhibits WASP activation. Our results reveal a new mechanism for the negative regulation of BCR signaling and broadly suggest an actin-mediated mechanism for signaling down-regulation.