Identification of sterol-independent regulatory elements in the human ATP-binding cassette transporter A1 promoter: role of Sp1/3, E-box binding factors, and an oncostatin M-responsive element.
The ATP-binding cassette transporter A1 (ABCA1) shows a differentiation-, cAMP-, and sterol-dependent up-regulation in human monocytes. As part of an ongoing study, we investigated the proximal promoter regions that are highly conserved between the human and murine ABCA1 genes. Using reporter gene assays, we show here that a TATA box 24 bp upstream of the transcription initiation site is essential for promoter activity in RAW 264.7 and HepG2 cells, whereas further enhancement of transcriptional activity is mediated by the -175 bp promoter region. Gel shift assays revealed in vitro binding of Sp1 to a -91 GnC motif as well as binding of Sp1 and Sp3 to a -157 GnC promoter region. In co-transfection experiments using Drosophila S2 cells, we demonstrate that Sp3 competes with Sp1 for binding to the -157 GnC motif and acts as a repressor. On the other hand, overexpression of Sp1 increased ABCA1 mRNA expression in HeLa cells and enhanced cellular cholesterol and phospholipid efflux in RAW 246.7 macrophages. We also show here that the conserved E-box at position -140 binds upstream stimulatory factors 1 and 2 and hepatic nuclear factor 1alpha and that mutagenesis of the E-box enhanced constitutive ABCA1 expression in RAW 264.7 cells, implying a role for this element in silencing ABCA1 expression. Besides the functional importance for basal gene expression, we have identified that the core promoter region (-175 to +224) is also responsible for the induction of ABCA1 by the cytokine oncostatin M, resulting in a rapid increase in ABCA1 mRNA levels in HepG2 cells. Interestingly, this oncostatin M-induced expression is not dependent on the currently known sequence motifs in the ABCA1 promoter. In conclusion, a functional complex of cis-elements within the proximal human ABCA1 promoter associated with the transcription factors Sp1/3, upstream stimulatory factors 1 and 2, and hepatic nuclear factor 1alpha has been characterized, which allows a subtle tissue-specific regulation of ABCA1 gene expression.
Langmann
Thomas
T
Institute for Clinical Chemistry, University of Regensburg, 93042 Regensburg, Germany, and the Pharma Research Center, Bayer AG, Aprather Wey 18a, D-42096 Wuppertal, Germany.
Porsch-Ozcürümez
Mustafa
M
Heimerl
Susanne
S
Probst
Mario
M
Moehle
Christoph
C
Taher
Mohammed
M
Borsukova
Hana
H
Kielar
Danuta
D
Kaminski
Wolfgang E
WE
Dittrich-Wengenroth
Elke
E
Schmitz
Gerd
G
D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D053683:Oncostatin M; D010455:Peptides / Q000502:physiology; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000502:physiology*; D051705:Sp3 Transcription Factor; D013261:Sterols / Q000378:metabolism*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C508351:OSM protein, human; D010455:Peptides; C497121:SP3 protein, human; D016329:Sp1 Transcription Factor; D013261:Sterols; D014157:Transcription Factors; D053683:Oncostatin M; D051705:Sp3 Transcription Factor