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 measured for the uptake of [3H]-estrone sulfate (3-min uptake and 0.1 μM estrone sulfate). The data represent uptake into hOAT4-transfected cells minus uptake into mock cells (parental COS-7 cells). Values are mean ± S.E. (n = 3). *P<0.05, NS: statistically not significant.