Dopamine induces ERK activation in renal epithelial cells through H2O2 produced by monoamine oxidase

Background. The rat renal proximal tubule cells contain a large amount of m onoamine oxidase, which catalyzes the oxidative deamination of catecholamin es such as dopamine (DA). The aim of this study is to investigate the poten tial role of hydrogen peroxide (H2O2) produced by monoamine oxidase (MAO) i soform on regulation of cell signaling and function. Methods. Primary rat proximal tubular cells, which contain almost exclusive ly MAO-A, and human embryonic kidney 293 (HEK 293) cells stably transfected with human MAO-B cDNA were treated with DA or tyramine in the presence or the absence of some inhibitors. Then, Shc protein tyrosine phosphorylation and extracellular-regulated kinase (ERK) activation were evaluated by immun oprecipitation/immunoblot analysis and cell proliferation by [H-3]thymidine incorporation or cell counting. Results. In rat proximal tubule cells, DA induced tyrosine phosphorylation of Shc, ERK activation, and a significant increase in DNA synthesis. The in volvement of MAO-dependent H2O2 generation induced by DA (5 mu mol/L) was s upported by the demonstration that the DA effects were (1) fully prevented by cell pretreatment with the MAO inhibitor pargyline, the antioxydant N-ac etylcysteine (NAC), and the DA uptake inhibitor GBR 12909; (2) not abrogate d by the D1 and D2 receptor antagonists; (3) observed in HEK 293 MAO-B cell s but not in HEK 293 wild-type cells, which do not express MAO; and (4) sim ilar to those induced by another MAO substrate, tyramine. Conclusions. Taken together, these results show that in addition to the eff ects related to receptor stimulation, DA, and probably the other catecholam ines, may induce some of its effects through the MAO-dependent H2O2 product ion.