Evidence for a Preformed Transducer Complex Organized by the B Cell Antigen Receptor

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 15; pp. 7865 - 7870
• Main Authors: Wienands, Jürgen, Larbolette, Oliver, Reth, Michael
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 23-07-1996; National Acad Sciences; National Academy of Sciences
• Subjects: Animals; Antibodies; B cell antigen receptors; B lymphocytes; Cell Line; Cell lines; Cells; Crosslinking; Detergents; Drugs; Enzyme Inhibitors - pharmacology; Glycosylphosphatidylinositols; Hydrogen Peroxide - pharmacology; Immunity (Disease); Immunoglobulin D - biosynthesis; Immunoglobulin M - biosynthesis; Kinetics; Molecules; Multiple Myeloma; Phosphoproteins - isolation & purification; Phosphoproteins - metabolism; Phosphorylation; Point Mutation; Protein Tyrosine Phosphatases - antagonists & inhibitors; Protein-Tyrosine Kinases - metabolism; Proteins; Receptors; Receptors, Antigen, B-Cell - biosynthesis; Receptors, Antigen, B-Cell - immunology; Receptors, Antigen, B-Cell - physiology; Recombinant Proteins - biosynthesis; Recombinant Proteins - immunology; Signal Transduction; Transducers; Vanadates - pharmacology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.15.7865

The B cell antigen receptor (BCR) consists of the membrane-bound immunoglobulin (mIg) molecule and the Ig-α /Ig-β heterodimer, which functions as signaling subunit of the receptor. Stimulation of the BCR activates protein tyrosine kinases (PTKs) that phosphorylate a number of substrate proteins, including the Ig-α /Ig-β heterodimer of the BCR itself. How the PTKs become activated after BCR engagement is not known at present. Here, we show that BCR-negative J558L cells treated with the protein tyrosine phosphatase inhibitor pervanadate/H2O2 display only a weak substrate phosphorylation. However, in BCR-positive transfectants of J558L, treatment with pervanadate/H2O2 induces a strong phosphorylation of several substrate proteins. Treatment with pervanadate/H2O2 does not result in receptor crosslinking, yet the pattern of protein phosphorylation is similar to that observed after BCR stimulation by antigen. The response requires cellular integrity because tyrosine phosphorylation of most substrates is not visible in cell lysates. Cells that express a BCR containing an Ig-α subunit with a mutated immunoreceptor tyrosine-based activation motif display a delayed response. The data suggest that, once expressed on the surface, the BCR organizes protein tyrosine phosphatases, PTKs, and their substrates into a transducer complex that can be activated by pervanadate/H2O2 in the absence of BCR crosslinking. Assembly of this preformed complex seems to be a prerequisite for BCR-mediated signal transduction.