Transforming growth factor-ß1 (TGF-ß1) is a pleiotropic factor involved in the regulation of extracellular matrix (ECM) synthesis and remodeling. In search for novel genes mediating the action of TGF-ß1 on vascular ECM, we identified the member of the lysyl oxidase family of matrix remodeling enzymes, lysyl oxidase-like 4 (LOXL4), as a direct target of TGF-ß1 in aortic endothelial cells, and dissected the molecular mechanism of its induction. Deletion mapping and mutagenesis analysis of the LOXL4 promoter demonstrated the absolute requirement of a distal enhancer containing an activator protein-1 (AP-1) site and a Smad binding element for TGF-ß1 to induce LOXL4 expression. Functional cooperation between Smad proteins and the AP-1 complex composed of JunB/Fra2 accounted for the action of TGF-ß1, which involved the extracellular signal-regulated kinase (ERK)-dependent phosphorylation of Fra2. We furthermore provide evidence that LOXL4 was extracellularly secreted and significantly contributed to ECM deposition and assembly. These results suggest that TGF-ß1-dependent expression of LOXL4 plays a role in vascular ECM homeostasis, contributing to vascular processes associated to ECM remodeling and fibrosis.

Read more »