The present study investigated whether transforming growth factor-beta 1 (TGF-β1) exerts an autocrine positive effect on angiotensinogen (ANG) gene expression in rat kidney proximal tubular cells, and delineates its underlying mechanism(s) of action. Rat immortalized renal proximal tubular cells (IRPTCs) and freshly isolated mouse renal proximal tubules were incubated in the absence or presence of active human TGF-β1. IRPTCs were also stably transfected with rat TGF-β1 or p53 tumor suppressor protein (p53) cDNA in sense (S) and antisense (AS) orientations. ANG mRNA and p53 protein expression were assessed by reverse transcription-polymerase chain reaction and Western blotting, respectively. Reactive oxygen species (ROS) generation was quantified by lucigenin assay. Active TGF-β1 evoked ROS generation and stimulated ANG mRNA and p53 protein expression, whereas a superoxide scavenger and inhibitors of nicotinamide adenine dinucleotide oxidase and p38 mitogen-activated protein kinase (p38 MAPK) abolished the TGF-β1 effect. Stable transfer of p53 cDNA (S) enhanced and p53 cDNA (AS) abolished the stimulatory effect of TGF-β1 on ANG mRNA expression in IRPTCs. Our results demonstrate that TGF-β1 stimulates ANG gene expression and its action is mediated, at least in part, via ROS generation, p38 MAPK activation, and p53 expression, suggesting that angiotensin II and TGF-β1 may form a positive feedback loop to enhance their respective gene expression, leading to renal injury.