Receptor for advanced glycation end-products signals through Ras during tobacco smoke-induced pulmonary inflammation

We previously demonstrated up-regulation of the receptor for advanced glycation end-products (RAGE) and its ligands by cigarette smoke extract (CSE) in rat R3/1 cells, a type I-like alveolar epithelial cell line. However, RAGE-mediated intracellular signaling pathways that lead to pulmonary inflammation remained unclear. Using ELISAs, we demonstrate that alveolar epithelial cell lines exposed to 25% CSE for 2 hours induce the activation of Ras, a small GTPase that functions as a molecular switch in the control of several intracellular signaling networks. Conversely, cells treated with siRNA for RAGE (siRAGE) resulted in decreased Ras activation. Furthermore, Ras was significantly diminished in lungs from RAGE null mice exposed to chronic tobacco smoke when compared with smoke-exposed wild-type mice. The use of a luciferase reporter containing NF-κB binding sites also demonstrated elevated NF-κB activation in R3/1 cells after CSE stimulation and decreased NF-κB activation in cells transfected with siRAGE before CSE exposure. ELISA revealed an increase in the secretion of IL-1β and CCL5 by R3/1 cells, two cytokines induced by NF-κB and associated with leukocyte chemotaxis. Furthermore, real-time RT-PCR and ELISAs revealed decreased cytokine secretion in RAGE null mouse lung exposed to tobacco smoke compared with lungs from smoke-exposed wild-type animals. These results support the conclusion that CSE-induced RAGE expression functions in pathways that involve Ras-mediated NF-κB activation and cytokine elaboration. This RAGE-Ras-NF-κB axis likely contributes to inflammation associated with several smoking-related inflammatory lung diseases.