Angiotensin II stimulates a novel angiotensin II type 1 receptor-associated protein, GLP gene expression in rat kidney proximal tubular cells

We have recently demonstrated that a novel angiotensin II (Ang II) type 1 receptor-associated protein, GLP induces cellular hypertrophy and Ang II stimulated GLP mRNA expression in a time-, dose-, and AT₁ receptor-dependent manner in rat immortalized renal proximal tubular cells (IRPTCs). The present studies investigated which signaling pathways are involved in Ang II stimulated GLP mRNA expression in IRPTCs. Cellular GLP mRNA expression was determined by reverse transcription polymerase chain reaction. The effect of Ang II was blocked by epidermal growth factor receptor inhibitor, AG1478, PKC inhibitor, GF109203X, MAPK kinase inhibitor, PD98059, antioxidants, taurine and tiron, and NADH/NADPH oxidase inhibitor, DPI, whereas, no effects were observed on Ang II-induced GLP mRNA expression with p38 MAPK inhibitors, SB203580 and PD169316, and Janus kinase 2 inhibitor, AG490. IRPTCs stably expressing GLP gene significantly increased reactive oxygen species (ROS) generation compared to control IRPTCs analyzed by lucigenin assay. Furthermore, NADH/NADPH oxidase inhibitor, DPI, and antioxidants taurine and tiron inhibited GLP-induced total protein content and de novo protein synthesis. These studies demonstrated that the stimulatory action of Ang II on GLP mRNA expression in IRPTCs is mediated by multiple signal mechanisms, transactivation of EGF receptor and subsequent MAPK activation, PKC activation and ROS generation. Furthermore, the cellular hypertrophic effect of GLP gene in IRPTCs is mediated at least in part via ROS generation.