Gab1 Acts as an Adapter Molecule Linking the Cytokine Receptor gp130 to ERK Mitogen-Activated Protein Kinase

ABSTRACT

Gab1 has structural similarities with Drosophila DOS (daughter of sevenless), which is a substrate of the protein tyrosine phosphatase Corkscrew. Both Gab1 and DOS have a pleckstrin homology domain and tyrosine residues, potential binding sites for various SH2 domain-containing adapter molecules when they are phosphorylated. We found that Gab1 was tyrosine phosphorylated in response to various cytokines, such as interleukin-6 (IL-6), IL-3, alpha interferon (IFN-α), and IFN-γ. Upon the stimulation of IL-6 or IL-3, Gab1 was found to form a complex with phosphatidylinositol (PI)-3 kinase and SHP-2, a homolog of Corkscrew. Mutational analysis of gp130, the common subunit of IL-6 family cytokine receptors, revealed that neither tyrosine residues of gp130 nor its carboxy terminus was required for tyrosine phosphorylation of Gab1. Expression of Gab1 enhanced gp130-dependent mitogen-activated protein (MAP) kinase ERK2 activation. A mutation of tyrosine 759, the SHP-2 binding site of gp130, abrogated the interactions of Gab1 with SHP-2 and PI-3 kinase as well as ERK2 activation. Furthermore, ERK2 activation was inhibited by a dominant negative p85 PI-3 kinase, wortmannin, or a dominant negative Ras. These observations suggest that Gab1 acts as an adapter molecule in transmitting signals to ERK MAP kinase for the cytokine receptor gp130 and that SHP-2, PI-3 kinase, and Ras are involved in Gab1-mediated ERK activation.

ACKNOWLEDGMENTS

The first two authors contributed equally to this work.

We thank T. Matozaki, W. Ogawa, M. Kasuga, M. D. Waterfield, K. Matsuoka, and T. Deng for various reagents. We also thank E. Barsoumian for comments on the manuscript and R. Masuda and T. Kimura for excellent secretarial assistance.

This work was supported in part by a Grant-Aid for COE Research from the Ministry and Education, Science, Sports, and Culture in Japan, the Yamanouchi Foundation for Research on Metabolic Disorders, and the Osaka Foundation for Promotion of Clinical Immunology.