Phosphoinositide 3-Kinase–Dependent Membrane Recruitment of P62^dok Is Essential for Its Negative Effect on Mitogen-Activated Protein (Map) Kinase Activation

A major pathway by which growth factors, such as platelet-derived growth factor (PDGF), regulate cell proliferation is via the receptor tyrosine kinase/Ras/mitogen-activated protein kinase (MAPK) signaling cascade. The output of this pathway is subjected to tight regulation of both positive and negative regulators. One such regulator is p62^dok, the prototype of a newly identified family of adaptor proteins. We recently provided evidence, through the use of p62^dok-deficient cells, that p62^dok acts as a negative regulator of growth factor–induced cell proliferation and the Ras/MAPK pathway. We show here that reintroduction of p62^dok into p62^dok−^/− cells can suppress the increased cell proliferation and prolonged MAPK activity seen in these cells, and that plasma membrane recruitment of p62^dok is essential for its function. We also show that the PDGF-triggered plasma membrane translocation of p62^dok requires activation of phosphoinositide 3-kinase (PI3-kinase) and binding of its pleckstrin homology (PH) domain to 3′-phosphorylated phosphoinositides. Furthermore, we demonstrate that p62^dok can exert its negative effect on the PDGFR/MAPK pathway independently of its ability to associate with RasGAP and Nck. We conclude that p62^dok functions as a negative regulator of the PDGFR/Ras/MAPK signaling pathway through a mechanism involving PI3-kinase–dependent recruitment of p62^dok to the plasma membrane.