Epithelial-to-mesenchymal transformation (EMT) of tubular cells into a myofibroblastic phenotype is an important mediator of renal scarring in chronic nephropathy. This study examines the role of the renin-angiotensin system (RAS) in this process. NRK-52E cells were exposed to angiotensin (ANG) II and ANG 1-7 in the presence or absence of inhibitors and agonists of RAS signaling. EMT was assessed at 3 days by expression of alpha-smooth muscle actin (alpha-SMA) and E-cadherin and the induction of a myofibroblastic phenotype. Expression of fibrogenic growth factors and matrix proteins was assessed by RT-PCR and immunofluorescence microscopy. To confirm findings in vivo, rats were also infused with ANG 1-7 (24 microg*kg(-1)*h(-1)) or saline via an osmotic minipump for 10 days, and renal fibrogenesis was then assessed. Treatment of NRK-52E cells with ANG II induced characteristic changes of EMT. Selective blockade of the AT(1) receptor or the AT(2) receptor failed to inhibit ANG II-induced EMT. However, blockade of the ANG 1-7 receptor, Mas-1, was able to prevent ANG II-dependent EMT. To confirm these findings, both ANG 1-7 and the selective Mas receptor agonist, AVE-0991, were able to induce NRK-52E cells in a dose-dependent manner. Exposing cells to recombinant ACE2 was also able to induce EMT. In addition, an infusion of ANG 1-7 induced the tubular expression of alpha-SMA and the expression of matrix proteins in the kidney. ANG II is a potent stimulus for EMT, but not through conventional pathways. This study points to the possible limitations of conventional RAS blockade, which not only fails to antagonize this pathway, but also may enhance it via augmenting the synthesis of ANG 1-7.