RAGE-MEDIATED CELLULAR SIGNALING IS TRIGGERED BY THE ALLOSTERIC ACTIVATION OF THE AT1 RECEPTOR

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Objective: We recently identified the physical interaction of a pattern recognition receptor (PRR), lectin-like oxidized LDL receptor with the GPCR, angiotensin II type 1 receptor (AT1) whereby oxLDL allosterically activates AT1. In this study, we investigated if AT1 physically interacts with another PRR, the receptor for AGE (RAGE), and ligands of RAGE could allosterically activate AT1. Design and method: We used normal rat kidney epithelial cells (NRK52E) to investigate the interaction of the endogenous receptors. We also generated five different genetically-engineered CHO cells to individually analyze the G protein and β-arrestin pathways of AT1 activation; CHO cells expressing human RAGE (CHO-RAGE), CHO cells expressing both hRAGE and hAT1 (CHO-RAGE-AT1), CHO cells expressing both hRAGE and mutated hAT1 with impaired ability to activate G protein, and CHO cells expressing both hLOX-1 and mutated hAT1 with impaired ability to activate β-arrestin Results: In NRK52E, AGE-BSA provoked the activation of MAP kinase (ERK) that was inhibited by ARB or siRNA of AT1 or RAGE. Activation of NfκB and Epithelial mesanchmal transition induced by AGE-BSA was inhibited by ARBs as well as RAGE inhibitor. In genetically engineered CHO-cells, in situ PLA assay and immunoprecipitation confirmed the physical interaction of AT1 and RAGE on cellular membrane. HMGB1, a RAGE ligand induced Gαi-dependent inhibition of cAMP production only in the presence of both RAGE and AT1 with intact G protein binding. The effect of HMGB1 on cAMP content was abolished by ARB as well as RAGE inhibitor. HMGB1 did not induce the accumulation of IP1, a downstream of Gαq signaling, in CHO cells expressing both AT1 and RAGE. Real-time imaging of cellular membrane revealed that RAGE induced endocytosis of LOX-1 that depends on the intact β-arrestin pathway of AT1, and the phenomenon was not inhibited by ARB. Conclusions: RAGE ligands mediates cellular signaling via a physical interaction between RAGE and AT1. The activation of AT1 by RAGE ligands is distinct from that by angiotensin II in terms of selective G protein activation and the effect of ARB on G protein pathway but not on β-arrestin pathway.