ID: 58. Issue 1 (November 2015) - Hessenkemper, Wiebke
Abstract The timely orchestration of multiple signalling pathways is crucial for the integrity of organisms and therefore tightly controlled. Gab family proteins coordinate signal transduction at the plasma membrane by acting as docking platforms for signalling components involved in various pathways such as MAP kinase (MAPK) and PI3 kinase (PI3K) cascade. The interaction with these components as well as the targeting of the docking platform to the plasma membrane underlies complex spatial and temporal regulatory mechanisms. In this study, we focus on Gab1, which is known to be activated and regulated by PI3K- and MAPK-cascades, but is also regulating these pathways. Previously, we could demonstrate that the presence of PIP3 in the plasma membrane alone, which is generated by PI3K, is not sufficient for constitutive Gab1 membrane recruitment. In addition, MAPK-dependent phosphorylation of Gab1 at serine 552 (Ser552) is vital for Gab1 membrane binding. Here, we confirm our hypothesis that in the absence of MAPK activity or by substituting Ser552 in Gab1 for an alanine an intramolecular interaction within Gab1 prevents binding to the plasma membrane. This interaction is mediated by the Gab1 PH domain and an epitope of Gab1, which encompasses Ser552 as well as two arginine residues (Arg556/Arg560) that are essential for the inhibition of membrane recruitment of Gab1 in the absence of a stimulus. Our data document that Gab1 recruitment to the plasma membrane is highly dynamic and continuous activation of both, PI3K and MAPK are essential for sustained Gab1 membrane localisation and phosphorylation of Gab1.