Nontranscriptional activation of PI3K by GR. (a) Nontranscriptional activation of PI3K and Akt kinase by GR: The upper panels show PI3K and Akt kinase assays in COS7 cells transfected with expression plasmids encoding GRα (GRSB) or dimerization-defective GR (A458T). Lysates were immunoblotted against GR. The lower panel shows GRE-reporter activity of COS7 cells cotransfected with either GRSB or A458T expression plasmid with GRE-luc and stimulated with dexamethasone (100 nM). (b) MEFs obtained from wild-type, GR^–/–, and dimerization-defective GR^dim mice were assayed for Akt activity and expression of GR by Western blotting. (c) Dexamethasone activates the PI3K/Akt pathway through GR. The upper panel shows immunoprecipitation of ERα, GR, or MR followed by PI3K assay or immunoblotting against ERα, GR, and MR. (d) Akt kinase assay in COS7 cells transfected with expression plasmids encoding ER, GR or MR. Lysates of mock-transfected or receptor-transfected cells were immunoblotted against ER, GR, or MR. Representative experiments are shown; m, mock transfected. WB, Western blot; P-GSK-3, phospho-GSK-3.