Banin S, Truong O, Katz DR, Waterfield MD, Brickell PM, Gout I

Leukaemia Research Fund Centre for Childhood Leukaemia, Molecular Haematology Unit, Institute of Child Health, 30 Guilford Street, LondonWC1N 1EH, UK.

BACKGROUND: Receptor-mediated signal transduction requires the assembly of multimeric complexes of signalling proteins, and a number of conserved protein domains, such as the SH2, SH3 and PH domains, are involved in mediating protein-protein interactions in such complexes. The identification of binding partners for these domains has added considerably to our understanding of signal-transduction pathways, and the purpose of this work was to identify SH3-binding proteins in haematopoietic cells. RESULTS: We performed affinity-chromatography experiments with a panel of GST-SH3 fusion proteins (composed of glutathione-S-transferase appended to various SH3 domains) to search for SH3-binding proteins in a human megakaryocytic cell line. Protein microsequencing identified one of the SH3-binding proteins as WASp, the protein that is defective in Wiskott-Aldrich syndrome (WAS) and isolated X-linked thrombocytopenia. WASp bound preferentially in vitro to SH3 domains from c-Src family kinases, and analysis of proteins expressed in insect cells using a baculovirus vector demonstrated a specific interaction between WASp and the Fyn protein-tyrosine kinase. Finally, in vivo experiments showed that WASp and Fyn physically associate in human haematopoietic cells. CONCLUSIONS: Haematopoietic cells from individuals with WAS exhibit defects in cell morphology and signal transduction, including reduced proliferation and tyrosine phosphorylation in response to stimulatory factors. Members of the c Src family of protein-tyrosine kinases, including Fyn, are involved in a range of signalling pathways - such as those regulating cytoskeletal structure - in both haematopoietic and non-haematopoietic cells. Our data suggest that binding of Fyn to WASp may be a critical event in such signalling pathways in haematopoietic cells.

Mesh Terms:
Blotting, Western, Cell Line, Chromatography, Affinity, Glutathione Transferase, Humans, Protein Binding, Proteins, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-fyn, Recombinant Fusion Proteins, Wiskott-Aldrich Syndrome, Wiskott-Aldrich Syndrome Protein, src Homology Domains, src-Family Kinases

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