Roles of RhoA and phospholipase A2 in the elevation of intracellular H2O2 by transforming growth factor-beta in Swiss 3T3 fibroblasts.

We have investigated the mechanisms by which transforming growth factor-beta (TGF-beta) increased intracellular H2O2 in Swiss 3T3 fibroblasts. Increase of intracellular H2O2 by TGF-beta was maximal at 30 min and blocked by catalase from Aspergillus niger. Scrape-loading of C3 transferase, which down-regulated RhoA, inhibited the production of H2O2 in response to TGF-beta. TGF-beta stimulated release of arachidonic acid, which was completely inhibited by mepacrine, a phospholipase A2 inhibitor. Mepacrine also blocked the increase of H2O2 by TGF-beta. In addition, arachidonic acid increased intracellular H2O2. Furthermore, TGF-beta stimulated stress fibre formation, which was blocked by catalase, without membrane ruffling. Catalase also inhibited stimulation of thymidine incorporation by TGF-beta. These results suggested that TGF-beta increased intracellular H2O2 through RhoA and phospholipase A2, and also suggested that intracellular H2O2 was required for the stimulation of stress fibre formation and DNA synthesis in response to TGF-beta.