Amplification of B cell antigen receptor signaling by a Syk/ITAM positive feedback loop.
We have established a protocol allowing transient and inducible coexpression of many foreign genes in Drosophila S2 Schneider cells. With this powerful approach of reverse genetics, we studied the interaction of the protein tyrosine kinases Syk and Lyn with the B cell antigen receptor (BCR). We find that Lyn phosphorylates only the first tyrosine whereas Syk phosphorylates both tyrosines of the BCR immunoreceptor tyrosine-based activation motif (ITAM). Furthermore, we show that Syk is a positive allosteric enzyme, which is strongly activated by the binding to the phosphorylated ITAM tyrosines, thus initiating a positive feedback loop at the receptor. The BCR-dependent Syk activation and signal amplification is efficiently counterbalanced by protein tyrosine phosphatases, the activity of which is regulated by H(2)O(2) and the redox equilibrium inside the cell.
Rolli
Véronique
V
Department of Molecular Immunology, Biology III, University of Freiburg and Max-Planck Institute for Immunobiology, Stuebeweg 51, 79108 Freiburg, Germany.
Gallwitz
Maike
M
Wossning
Thomas
T
Flemming
Alexandra
A
Schamel
Wolfgang W A
WW
Zürn
Christa
C
Reth
Michael
M
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D004330:Drosophila; D004792:Enzyme Precursors / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine; D006861:Hydrogen Peroxide; D005982:Glutathione Transferase; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases