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 fa ctor (PDGF), regulate cell proliferation is via the receptor tyrosine kinas e/Ras/niitogen-activated protein kinase (MAPK) signaling cascade. The outpu t of this pathway is subjected to tight regulation of both positive and neg ative regulators. One such regulator is p62(dok), the prototype of a newly identified family of adaptor proteins. We recently provided evidence, throu gh the use of p62(dok)-deficient cells, that p62(dok) acts as a negative re gulator of growth factor-induced cell proliferation and the Ras/MAPK pathwa y. 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 essenti al for its function. We also show that the PDGF-triggered plasma membrane t ranslocation of p62(dok) requires activation of phosphoinositide 3-kinase ( PI3-kinase) and binding of its pleckstrin homology (PH) domain to 3 ' -phos phorylated phosphomositides. Furthermore, we demonstrate that p62(dok) can exert its negative effect on the PDGFR/MAPK pathway independently of its ab ility 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 P13-kinase-dependent recruitment of p62(dok) to the pla sma membrane.