Abstract
Activation of very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (apoER2) results in either pro- or anti-atherogenic effects depending on the ligand. Using reelin and apoE as ligands, we studied the impact of VLDLR- and apoER2-mediated signaling on the expression of ATP binding cassette transporter A1 (ABCA1) and cholesterol efflux using RAW264.7 cells. Treatment of these mouse macrophages with reelin or human apoE3 significantly increased ABCA1 mRNA and protein levels, and apoAI-mediated cholesterol efflux. In addition, both reelin and apoE3 significantly increased phosphorylated disabled-1 (Dab1), phosphatidylinositol 3-kinase (PI3K), protein kinase Cζ (PKCζ), and specificity protein 1 (Sp1). This reelin- or apoER2-mediated up-regulation of ABCA1 expression was suppressed by 1) knockdown of Dab1, VLDLR, and apoER2 with small interfering RNAs (siRNAs), 2) inhibition of PI3K and PKC with kinase inhibitors, 3) overexpression of kinase-dead PKCζ, and 4) inhibition of Sp1 DNA binding with mithramycin A. Activation of the Dab1-PI3K signaling pathway has been implicated in VLDLR- and apoER2-mediated cellular functions, whereas the PI3K-PKCζ-Sp1 signaling cascade has been implicated in the regulation of ABCA1 expression induced by apoE/apoB-carrying lipoproteins. Taken together, these data support a model in which activation of VLDLR and apoER2 by reelin and apoE induces ABCA1 expression and cholesterol efflux via a Dab1-PI3K-PKCζ-Sp1 signaling cascade.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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ATP Binding Cassette Transporter 1
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ATP-Binding Cassette Transporters / biosynthesis*
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ATP-Binding Cassette Transporters / genetics
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Adaptor Proteins, Signal Transducing / genetics
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Adaptor Proteins, Signal Transducing / metabolism
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Animals
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Apolipoprotein E3 / genetics
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Apolipoprotein E3 / metabolism
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Cell Adhesion Molecules, Neuronal / genetics
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Cell Adhesion Molecules, Neuronal / metabolism*
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Cell Line
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Cholesterol / genetics
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Cholesterol / metabolism
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Extracellular Matrix Proteins / genetics
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Extracellular Matrix Proteins / metabolism*
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Gene Knockdown Techniques
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Humans
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LDL-Receptor Related Proteins / genetics
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LDL-Receptor Related Proteins / metabolism*
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Macrophages / metabolism*
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Mice
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism*
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Protein Kinase C-epsilon / genetics
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Protein Kinase C-epsilon / metabolism
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Receptors, LDL / genetics
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Receptors, LDL / metabolism*
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Reelin Protein
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Serine Endopeptidases / genetics
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Serine Endopeptidases / metabolism*
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Signal Transduction / physiology*
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Sp1 Transcription Factor / genetics
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Sp1 Transcription Factor / metabolism
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Up-Regulation / physiology*
Substances
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ABCA1 protein, human
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ATP Binding Cassette Transporter 1
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ATP-Binding Cassette Transporters
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Adaptor Proteins, Signal Transducing
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Apolipoprotein E3
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Cell Adhesion Molecules, Neuronal
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DAB1 protein, human
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Dab1 protein, mouse
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Extracellular Matrix Proteins
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LDL-Receptor Related Proteins
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Nerve Tissue Proteins
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Receptors, LDL
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Reelin Protein
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Sp1 Transcription Factor
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VLDL receptor
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low density lipoprotein receptor-related protein 8
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Cholesterol
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Prkce protein, mouse
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Protein Kinase C-epsilon
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RELN protein, human
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Reln protein, mouse
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Serine Endopeptidases