Oxysterol and 9-cis-retinoic acid stimulate the group IIA secretory phospholipase A2 gene in rat smooth-muscle cells

Abstract

The inflammation that occurs during rheumatoid arthritis or atherosclerosis is characterized by the release of large amounts of sPLA(2) (group IIA secretory phospholipase A(2)). We have shown previously that the sPLA(2) promoter in SMC (smooth-muscle cells) is activated by interleukin-1beta and cAMP-signalling pathways, through the interplay of multiple transcription factors [Antonio, Brouillet, Janvier, Monne, Bereziat, Andreani, and Raymondjean (2002) Biochem. J. 368, 415-424]. In the present study, we have investigated the regulation of sPLA(2) gene expression in rat aortic SMCs by oxysterols. We found that oxysterol ligands that bind to the LXR (liver X receptor), including 25-HC (25-hydroxycholesterol) and 22( R )-HC, cause the accumulation of sPLA(2) mRNA and an increased enzyme activity. Transient transfection experiments demonstrated that the sPLA(2) promoter is synergistically activated by 22( R )-HC in combination with 9- cis -retinoic acid, a ligand for the LXR heterodimeric partner RXR (retinoid X receptor). Promoter activity was also increased in a sterol-responsive fashion when cells were co-transfected with LXRalpha/RXRalpha or LXRbeta/RXRalpha. Mutagenesis studies and gel mobility-shift assays revealed that LXR/RXR heterodimers regulate sPLA(2) transcription directly, by interacting with a degenerated LXRE (LXR response element) at position [-421/-406] of the sPLA(2) promoter. Chromatin immunoprecipitation revealed the in vivo occupancy of LXR on the sPLA(2) promoter. In addition, the orphan nuclear receptor LRH-1 (liver receptor homologue-1) potentiated the sterol-dependent regulation of the sPLA(2) promoter by binding to an identified promoter element (TCAAGGCTG). Finally, we have demonstrated that oxysterols act independent of interleukin-1beta and cAMP pathways to activate the sPLA(2) promoter. In the present study, we have identified a new pathway activating sPLA(2) gene expression in SMCs.

Side effects of oxysterols: cytotoxicity, oxidation, inflammation, and phospholipidosis

“…In U937 and THP-1 cells, stimulation of the secretion of various chemokines involved in the recruitment of immunocompetent cells at the subendothelial level, namely MCP-1, MIP-1ß, TNF-α, IL-1ß and IL-8, was also reported, mainly in the presence of 7ß-hydroxycholesterol and 25-hydroxycholesterol (54). Treatment of aortic rat smooth muscle cells with 25-hydroxycholesterol or 22R-hydroxycholesterol causes the accumulation of group IIA secretory phospholipase A(2) and increases enzyme activity (55). However, under certain conditions, anti-inflammatory effects of oxysterols have also been reported.…”

The liver X-receptor alpha controls hepatic expression of the human bile acid-glucuronidating UGT1A3 enzyme in human cells and transgenic mice

“…Protein-DNA cross-linking, nuclear extracts preparation, and sonication were performed as reported. 25 A volume of lysate equivalent of 20 ϫ 10 6 cells was immunoprecipitated using 4 g anti-LXR␣/␤ (Santa-Cruz, sc1201) 26 or anti-RXR␣ (Santa-Cruz, sc553) antibodies, or with 4 g of an anti-UGT2B antibody as negative control. The same lysate volume was either kept without immunoprecipitation for subsequent purification of input genomic DNA or was incubated in the presence of protein Asepharose alone.…”

“…Chromatin immunoprecipitation assays were performed according to the method of Forsberg et al, 25 as modified by Antonio et al 26 Briefly, 20 ϫ 10 7 HepG2 cells were grown to 60% confluence and serum-starved for 16 hours. Cells were subsequently treated with either DMSO (vehicle) or T0901317 (5 mol/L) for 90 minutes.…”

Inhibition of Interleukin-1β-Induced Group IIA Secretory Phospholipase A2 Expression by Peroxisome Proliferator-Activated Receptors (PPARs) in Rat Vascular Smooth Muscle Cells: Cooperation between PPARβ and the Proto-Oncogene BCL-6

“…The enzyme was reported to have other proatherogenic properties linked to its ability to hydrolyze phospholipid monolayers of high-and low-density lipoproteins (21). Previously, our laboratory demonstrated the interplay of various transcription factors (NF-B, C/EBP␤, ETS, and liver X receptor) that bind on the proximal part of the sPLA2 promoter and, more recently, has provided evidence that sPLA2-IIA could stimulate its own production in VSMCs through positive feedback (2,3,22). Then a better understanding of the molecular mechanisms involved in the regulation of sPLA2-IIA gene expression, in an inflammatory context, may allow the development of new inhibitors.…”