ROS and NF-κB but not LXR mediate IL-1β signaling for the downregulation of ATP-binding cassette transporter A1

Abstract

ATP-binding cassette transporter A1 (ABCA1), a pivotal regulator of cholesterol efflux from cells to apolipoproteins, plays an important role in cholesterol homeostasis. As an inflammatory factor, IL-1β has been shown to downregulate ABCA1 in macrophages and facilitates foam cell formation. However, the molecular mechanism underlining the downregulated ABCA1 by IL-1β is still elusive. In the present study, we demonstrated that IL-1β downregulated ABCA1 but not ABCG1 at mRNA and protein levels in a time- and dose-dependent manner in THP-1 and A549 cells. IL-1β attenuated ABCA1 promoter activity through an LXR (liver X receptor)-independent pathway, since IL-1β did not alter the expression and activities of LXRα/β, and deletion of the LXR responsive element from the ABCA1 promoter failed to reverse the IL-1β effect. In contrast, NF-κB inhibition by pyrrolidine dithiocarbamate and MG132 prevented the suppression of ABCA1 by IL-1β. Cotransfection with ABCA1 luciferase reporter and the expression plasmids of Rel A decreased ABCA1 promoter activities. An adenovirus expressing NF-κB inhibitor subunit-α inhibited NF-κB activities and also reversed the IL-1β effect at the promoter activity and protein levels of ABCA1. In addition, IL-1β could induce the production of reactive oxygen species (ROS), and N-acetyl-l-cysteine, a scavenger of ROS, reversed the decreased level of ABCA1 induced by IL-1β. H2O2decreased ABCA1 at the mRNA and protein levels and the promoter activity. Thus our data provide strong evidence that ROS and NF-κB, but not LXR, mediate the IL-1β-induced downregulation of ABCA1 via a novel transcriptional mechanism, which might play an important role of proinflammation in the alteration of lipid metabolism.