Effect of Tyr719Phe substitution in c-Kit on PI-3kinase and haptotactic migration in mast cells. Tyrosine-to-phenylalanine substitution at position 719 in c-Kit abrogates the binding of the p85α subunit of PI-3kinase and impairs c-Kit–induced haptotactic migration in mast cells. (A) Lack of association of the p85α subunit of PI-3kinase with the 719 chimeric c-Kit receptor. Cells expressing either the M-CSF/c-Kit or the M-CSF/c-Kit719 receptor were starved and stimulated with M-CSF for indicated times. Equal amounts of protein were subjected to IP with the use of an anti–M-CSF receptor antibody, and Western blot analysis was performed with an anti-p85α antibody. Shown is the position of p85α. (B) Flow cytometric analysis of mast cells expressing M-CSF/c-Kit (left panel) and M-CSF/c-Kit719 (right panel). Solid histogram demonstrates staining using an isotype control antibody. Open histogram indicates the level of expression of the M-CSF receptor. (C) Mast cells expressing either M-CSF/c-Kit or M-CSF/c-Kit719 were subjected to migration in the presence or absence of M-CSF as described in “Materials and methods.” Shown are the mean ± standard deviation (SD) of 3 independent experiments. *P < .05 for M-CSF/c-Kit versus M-CSF/c-Kit719.