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A more recent version of this article appeared on April 1, 2003
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Submitted on June 20, 2002
Revised on November 29, 2002
Accepted on December 9, 2002
1 Department of Medicine, Molecular Oncology Group, McGill University Health Centre, McGill University, Montreal, Quebec, H3A 1A1, Canada
2 Departments of Medicine, Biochemistry and Oncology, Molecular Oncology Group, McGill University Health Centre, McGill University, Montreal, Quebec, H3A 1A1, Canada
* Corresponding author. E-mail address: morag{at}molonc.mcgill.ca.
The hepatocyte growth factor receptor tyrosine kinase, Met, promotes cell dissociation and the inherent morphogenic program of epithelial cells. In a search for substrates downstream from Met, we have previously identified the Grb2-associated binder-1 (Gab1) as critical for the morphogenic program. Gab1 is a scaffold protein that acts to diversify the signal downstream from the Met receptor through its ability to couple with multiple signal transduction pathways. Gab1 contains a pleckstrin homology (PH) domain with specificity for phosphatidylinositol 3,4,5-trisphosphate. The phospholipid binding capacity of the Gab1 PH domain is required for the localiation of Gab1 at sites of cell-cell contact in colonies of epithelial cells and for epithelial morphogenesis, suggesting that PH domain dependent subcellular localization of Gab1 is a prerequisite for function. We have investigated the requirement for membrane localization of Gab1 for biological activity. We show that substitution of the Gab1 PH domain with the myristoylation signal from the c-Src protein is sufficient to replace the Gab1 PH domain for epithelial morphogenesis. The membrane targeting of Gab1, enhances Rac activity in the absence of stimulation and switches a non-morphogenic non-invasive response to EGF to a morphogenic invasive program. These results sugest that the subcellular localization of Gab1 is a critical determinant for epithelial morphogenesis and invasiveness.
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