Differential regulation of nonsteroidal anti-inflammatory drug-activated gene in normal human tracheobronchial epithelial and lung carcinoma cells by retinoids

In this study, we analyze the effect of several retinoids on the expression of nonsteroidal anti-inflammatory drug-activated gene (NAG-1) in normal human tracheobronchial epithelial (HTBE) cells and several lung carcinoma cell lines. The retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (AHPN) greatly enhances the expression of NAG-1 mRNA and protein in a time- and dose-dependent manner in human lung adenocarcinoma H460 cells and several other carcinoma cell lines. This induction was specific for AHPN because retinoic acid, a retinoic acid receptor-, and a retinoid X receptor pan-agonist were unable to induce NAG-1, suggesting that this induction is not mediated through activation of retinoid receptors. Although NAG-1 is a p53-responsive gene, AHPN-induced NAG-1 expression does not require p53. The induction of NAG-1 expression by AHPN is caused at least in part by an 8-fold increase in the stability of NAG-1 mRNA. In contrast to carcinoma cells, NAG-1 expression is effectively induced by retinoic acid and the RAR-selective pan-agonist in normal HTBE cells and accompanies the inhibition of squamous differentiation and the initiation of normal differentiation. In vivo, NAG-1 expression was observed in the normal tracheobronchial epithelium, whereas no expression was found in either squamous metaplastic tracheal epithelium or in sections of human lung tumors. Our results suggest that the induction of NAG-1 expression by retinoids in normal HTBE and lung carcinoma cells is regulated by distinct mechanisms and is associated with different biological processes. The linkage between AHPN treatment and NAG-1 expression revealed in this study provides a new mechanism for the antitumorigenic activity of AHPN.