SLP-65: A New Signaling Component in B Lymphocytes which Requires Expression of the Antigen Receptor for Phosphorylation

TLDR

The B cell antigen receptor (BCR) is a membrane‑bound immunoglobulin with Ig‑α/β signaling subunits that initiates protein tyrosine kinase activation and phosphorylation of several proteins, some of which are induced by antigen or pervanadate/H₂O₂. SLP‑65, a 65‑kDa adaptor protein homologous to T cell SLP‑76, associates with Grb‑2 and Vav in a signaling complex downstream of the BCR. The 65‑kDa adaptor protein SLP‑65 is phosphorylated only when the BCR is expressed and is therefore part of the BCR transducer complex.

Abstract

The B cell antigen receptor (BCR) consists of the membrane-bound immunoglobulin (Ig) molecule as antigen-binding subunit and the Ig-α/Ig-β heterodimer as signaling subunit. BCR signal transduction involves activation of protein tyrosine kinases (PTKs) and phosphorylation of several proteins, only some of which have been identified. The phosphorylation of these proteins can be induced by exposure of B cells either to antigen or to the tyrosine phosphatase inhibitor pervanadate/H2O2. One of the earliest substrates in B cells is a 65-kD protein, which we identify here as a B cell adaptor protein. This protein, named SLP-65, is part of a signaling complex involving Grb-2 and Vav and shows homology to SLP-76, a signaling element of the T cell receptor. In pervanadate/H2O2-stimulated cells, SLP-65 becomes phosphorylated only upon expression of the BCR. These data suggest that SLP-65 is part of a BCR transducer complex.