ABSTRACT
β1Pix is a guanine nucleotide exchange factor (GEF) for the small GTPases Rac and Cdc42 which has been shown to mediate signaling pathways leading to cytoskeletal reorganization. In the present study, we show that the basal association between endogenous βPix and endogenous 14-3-3β was increased after forskolin stimulation and significantly inhibited by protein kinase A inhibitor. However, forskolin stimulation failed to increase the interaction between 14-3-3β and a β1Pix mutant that is insensitive to protein kinase A phosphorylation, β1Pix(S516A, T526A). We present evidence indicating that forskolin-induced binding of 14-3-3β to β1Pix results in inhibition of Rac1 GTP loading in 293 cells and in vitro. Furthermore, we show that deletion of 10 amino acid residues within the leucine zipper domain is sufficient to block β1Pix homodimerization and 14-3-3β binding and modulates β1Pix-GEF activity. These residues also play a crucial role in β1Pix intracellular localization. These results indicate that 14-3-3β negatively affects the GEF activity of dimeric β1Pix only. Altogether, these results provide a mechanistic insight into the role of 14-3-3β in modulating β1Pix-GEF activity.
Dematin interacts with the Ras-guanine nucleotide exchange factor Ras-GRF2 and modulates mitogen-activated protein kinase pathways
