Submitted on August 7, 2007
Accepted on April 1, 2008
RAGE: Developmental Expression and Positive Feedback Regulation by Egr-1 During Cigarette Smoke Exposure in Pulmonary Epithelial Cells
Paul R Reynolds1*, Stephen D. Kasteler1, Manuel G. Cosio2, Anne Sturrock1, Tom P. Huecksteadt1, and John R Hoidal1
1 Internal Medicine: Pulmonary, University of Utah, Salt Lake City, Utah, United States
2 Meakins-Christie Laboratories, McGill University, Montreal, Canada
* To whom correspondence should be addressed. E-mail: paul.reynolds{at}hsc.utah.edu.
The receptor for advanced glycation end-products (RAGE) is a member of the immunoglobin superfamily of multiligand receptors. Following ligand binding, mechanisms associated with host defense, tissue remodeling, and inflammation are activated. RAGE is highly expressed in pulmonary epithelium transitioning from alveolar type II (ATII) to ATI cells and is up-regulated in the presence of ligand; however, the regulation and function of RAGE during development are less clear. Herein, immunohistochemistry demonstrated a temporal-spatial pattern of RAGE expression in pulmonary epithelial cells from E17.5 to PN10. Co-transfection experiments revealed that the mouse RAGE promoter was activated by Egr-1 and inhibited by TTF-1 via interaction with specific regulatory elements. A rat ATI cell line (R3/1) with endogenous RAGE expression also differentially regulated RAGE when transfected with TTF-1 or Egr-1. Since Egr-1 is markedly induced in pulmonary epithelial cells exposed to cigarette smoke extract (CSE, 28), we sought to investigate RAGE induction by CSE. Employing RT-PCR and Western blotting, RAGE and common ligands (HMGB-1 and S100A12) were up-regulated in epithelial (R3/1 and A-549) and macrophage (RAW) cell lines following exposure to CSE. Immunostaining for RAGE in cells similarly exposed and in lungs from mice exposed to cigarette smoke for six months revealed elevated RAGE expression in pulmonary epithelium. After the addition of GO-BSA, an advanced glycation end-product (AGE) that binds RAGE, real time RT-PCR detected a 200-fold increase in Egr-1. These results indicate that Egr-1 regulates RAGE expression during development and the likelihood of positive feedback involving Egr-1 and RAGE in cigarette smoke-related disease.
