Rac1 contributes to TGF-β1–mediated ROS generation via NADP(H) oxidases. A) The composition of different NOX proteins. Rac and p47Phox are common subunits of NOX1 and NOX2, whereas p22Phox is present in NOX1/2/4. Confluent HK-2 cells were stimulated with TGF-β1 for the times indicated with or without the Rac inhibitor EHT 1864 then incubated with 5 μM DCFDA for 15 min prior to scrape harvest. B) Histogram depicts relative DCFDA measurements (mean ± sd) in triplicate studies for each experimental condition. An equal number of cells were used to assess baseline fluorescence in the unstimulated (−) state and in response to TGF-β1; all measurements were done at the same time. *P < 0.05, **P < 0.01. Serum-deprived control shRNA and Rac1 shRNA stable HK-2 transductants were stimulated with TGF-β1 (15 min) for DCFDA analysis. C) Data illustrate relative free radical levels (mean ± sd) for each experimental condition for triplicate cultures. *P < 0.05, **P < 0.01. D) Plot depicts relative DCFDA measurements (mean ± sd) of serum-deprived control shRNA and p22Phox shRNA stably expressing HK-2 cells, which remained untreated (−) or stimulated with TGF-β1 (15 min); data plotted are for triplicate replicates for each condition in each of 3 separate experiments. Con, control. **P < 0.01.