Figure 6
Retinoic acid represses TNF-α-induced inflammatory response by induction of LXN. (A) Time-dependent and dose-dependent effect of retinoic acid on LXN expression in HIEC cells as determined by qPCR. (B) Time-dependent effects of retinoic acid (500 nM) on LXN expression was determined by Western blot analysis. (C) 48 h after transfection of LXN siRNA, cells were treated with retinoic acid (500 nM) for 24 h. Before harvested, the cells were stimulated with TNF-α (20 ng/mL) for 30 min, and protein samples were subjected to immunoprecipitation with anti-IκBα antibody followed by immunoblot analysis with anti-ubiquitin antibody to detect ubiquitylation of IκBα. (D) Effect of retinoic acid and LXN on the expression of cytokines in HIEC cells, determined by qPCR. (E) Proposed model for LXN mediating the anti-inflammatory process. TNF-α induces inflammatory response, as well as, promotes the interaction of Rps3 and HECTD1, which enhances the ubiquitylation of IκBα and further activation of NF-κB; retinoic acid increases LXN expression, and the expression of LXN competitively binds with Rps3 and dissociates the interaction between Rps3 and HECTD1, which leads to decreasing the ubiquitylation of IκBα, and eventually inhibits the inflammatory response.
