Inflammatory signaling pathways regulating ApoE gene expression in macrophages.
The atheroprotective role of apolipoprotein E (apoE) is well established. During inflammation, expression of apoE in macrophages is reduced leading to enhanced atheromatous plaque development. In the present study, we investigated the signaling pathways involved in the repression of apoE gene expression in response to lipopolysaccharide (LPS) treatment, a condition that mimics the inflammatory stress, in mouse macrophages RAW 264.7. We identified Tpl-2 and MEKK1 as the kinases that are primarily responsible for the down-regulation of apoE promoter activity by LPS. Using a dominant negative form of IkappaB, we established that Tpl-2 and MEKK1 signaling pathways converge to NF-kappaB acting on the apoE core promoter -55/+73. In addition to NF-kappaB activation, LPS also activated c-Jun via its phosphorylation by JNK. The activity of the apoE promoter was repressed by c-Jun, whereas small interference RNA-mediated inhibition of endogenous c-Jun expression reversed the inhibitory effect of Tpl-2 on the apoE promoter. Transfection experiments and DNA binding assays showed that the binding site for c-Jun is in the -55/+73 region of the apoE promoter. Finally, we showed that LPS inhibited apoE gene expression via activation of the Tpl-2/MEK/ERK pathway acting on a different apoE promoter region. In summary, LPS represses apoE gene expression in macrophages via signaling pathways that involve the upstream kinases Tpl-2 and MEKK1, the intermediate mitogen-activated protein kinases ERK and JNK, and the downstream transcription factors AP-1 and NF-kappaB that inhibit the apoE promoter activity via distinct regions.
Gafencu
Anca V
AV
Institute of Cellular Biology and Pathology Nicolae Simionescu, Bucharest, Romania. anca.gafencu@icbp.ro
Robciuc
Marius R
MR
Fuior
Elena
E
Zannis
Vassilis I
VI
Kardassis
Dimitris
D
Simionescu
Maya
M
D000818:Animals; D001057:Apolipoproteins E / Q000235:genetics*; D002460:Cell Line; D002467:Cell Nucleus / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007249:Inflammation / Q000503:physiopathology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009000:Monocytes / Q000187:drug effects / Q000502:physiology; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D015398:Signal Transduction / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection
D001057:Apolipoproteins E; D008070:Lipopolysaccharides; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C489843:Map3k8 protein, mouse