(a). COS-7 cells were transfected with hOAT4, CA-sgk2 and control vector, or with hOAT4, CA-sgk2 and Nedd4-2, or with hOAT4, CA-sgk2 and ubiquitin ligase-dead Nedd4-2 mutant (Nedd4-2/C821A). Transfected cells were labeled with biotin. Biotinylated/cell surface proteins were separated with streptavidin beads, followed by immunoblotting (IB) with an anti-myc antibody. (b) COS-7 cells were transfected with hOAT4, CA-sgk2 and control vector, or with hOAT4, CA-sgk2 and Nedd4-2, or with hOAT4, CA-sgk2 and ubiquitin ligase-dead Nedd4-2 mutant (Nedd4-2/C821A). Transfected cells were then lysed, followed by immunoblotting with anti-actin antibody, anti-sgk2 antibody or anti-Nedd4-2 antibody, respectively. (c). Densitometry plot of results from Fig. 7a, as well as from other experiments. The values are mean ± S.E. (n = 3). *P<0.05, NS: statistically not significant.