Differential sensitivity of P-Rex1 to isoforms of G protein βγ dimers

Abstract

P-Rex1 is a specific guanine nucleotide exchange factor (GEF) for Rac, which is present in high abundance in brain and hematopoietic cells. P-Rex1 is dually regulated by phosphatidylinositol (3,4,5)-trisphosphate and the Gβγ subunits of heterotrimeric G proteins. We examined which of the multiple G protein α and βγ subunits activate P-Rex1-mediated Rac guanine nucleotide exchange using pure, recombinant proteins reconstituted into synthetic lipid vesicles. AlF4- activated G s, Gi, Gq, G12, or G13 α subunits were unable to activate P-Rex1. Gβγ dimers containing Gβ1-4 complexed with γ2 stimulated P-Rex1 activity with EC50 values ranging from 10 to 20 nM. Gβ5γ2 was not able to stimulate P-Rex1 GEF activity. Dimers containing the β1 subunit complexed with a panel of different Gγ subunits varied in their ability to stimulate P-Rex1. The β1γ3, β1γ 7, β1γ10, and β 1γ13HA dimers all activated P-Rex1 with EC 50 values ranging from 20 to 38 nM. Dimers composed of β1γ12 had lower EC50 values (∼12 nM). The farnesylated γ11 subunit is highly expressed in hematopoietic cells; surprisingly, dimers containing this subunit (β1γ11) were also less effective at activating P-Rex1. These findings suggest that the composition of the Gβγ dimer released by receptor activation may differentially activate P-Rex1. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.