Regulation of elastin promoter by lysyl oxidase and growth factors: Cross control of lysyl oxidase on TGF-β1 effects

Abstract

Lysyl oxidase (LOX) plays a key role in the maturation of the extra-cellular matrix, by inducing the formation of lysyl cross-links in collagen and elastin molecules. Beside its enzymic activity, LOX is able to regulate the promoter of collagen III, one of its natural substrates. In this paper we demonstrated that LOX regulates also the promoter of elastin, inducing an important activation of its activity. In order to define the pathways used by LOX to achieve its effect, we activated some of the main fibrogenic signal pathways and studied the consequences on LOX effects on the promoter. TGF-β1 activated most of the elastin promoter constructs that we studied, except for an inhibitory region contained in the region between − 1500 and − 1000 bp. The treatment with TGF-β1 abolished completely the activation induced by LOX. LOX-over-expression coupled with TGF treatment abolished both effects in the − 500 bp region. The treatment with CTGF also inhibited LOX effect, although to a lesser extent. However, CTGF behaved quite differently from TGF-β1 suggesting that it is not necessarily the mediator of TGF effects. Basic FGF, the other fibrogenic factor that we tested, again abolished LOX-dependent activation, but by itself did not affect elastin promoter activity. Because TGF-β1 activating effects, we used EMSA to examine the transcription factor binding patterns in presence of LOX, TGF-β1 or both. The study showed that LOX reverted the patterns of several DNA–protein complexes along the 1.5 kb of the studied promoter region. Most were affected by both LOX and TGF-β1, while on some only TGF-β1 was effective. LOX presence mostly inhibited the TGF-regulated complexes. Many of those included SMAD transcription factors. Two more restricted regions binding AP1 and SMAD were identified as mediators of LOX effects and of LOX and TGF-β1 cross-inhibition.