Characterization of the Human ABCG1 Gene

Liver X Receptor Activates AN Internal Promoter That Produces A Novel Transcript Encoding AN Alternate Form of the Protein

Matthew A. Kennedy, Asha Venkateswaran, Paul T. Tarr, Loannis Xenarios, Jun Kudo, Nobuyoshi Shimizu, Peter A. Edwards

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

The human ABCG1 gene encodes a member of the ATPbinding cassette (ABC) superfamily of transporter proteins and is highly induced when macrophages are incubated with oxysterols. Using mRNA from oxysterol-treated human THP-1 cells together with 5′-rapid amplification of cDNA ends and polymerase chain reaction, we identified a novel ABCG1 transcript that encodes a putative protein of 786 residues containing a new ammo terminus of 203 amino acids. Characterization of the genomic organization and structure of the human ABCG1 gene demonstrates that: (i) the gene consists of 23 exons spanning 98 kilobase pairs (kb) on chromosome 21q22.3, (ii) the 203 amino acids are encoded on three previously unidentified exons, 8-10, and (iii) a promoter, containing a TATA box and two liver X receptor (LXR) a response elements (LXREs), is located upstream of exon 8. Northern analysis using exon-specific probes confirms that oxysterol treatment results in > 10fold induction of ABCG1 transcripts that are derived from either exons 8-23 or exons 5, 7, and 11-23. Electromobility shift assays demonstrate that LXRα and retinoid X receptor α bind to the two LXREs in intron 7. Cells were transiently transfected with reporter luciferase constructs under the control of either (i) 9 kb of genomic DNA corresponding to intron 7 and part of exon 8 and containing either wild-type or mutant LXREs or (ii) two copies of the wild-type or mutant LXRE. In all cases, the wild-type construct was regulated in an LXR- and oxysterol-dependent manner, and this regulation was attenuated when the LXREs were mutated. In conclusion, the human ABCG1 gene contains multiple promoters, spans more than 98 kb and comprises 23 exons that give rise to alternative transcripts encoding proteins with different amino-terminal sequences. Elucidation of the various roles of different ABCG1 isoforms will be important for our understanding of mammalian cholesterol homeostasis.

Original languageEnglish
Pages (from-to)39448-39454
Number of pages7
JournalJournal of Biological Chemistry
Volume276
Issue number42
DOIs
Publication statusPublished - 2001

Fingerprint

Liver
Exons
Genes
Response Elements
Proteins
Introns
Retinoid X Receptors
Amino Acids
TATA Box
Liver X Receptors
Macrophages
Polymerase chain reaction
Chromosomes
Luciferases
Amplification
Assays
Protein Isoforms
Homeostasis
Complementary DNA
Cholesterol

ASJC Scopus subject areas

  • Biochemistry

Cite this

Characterization of the Human ABCG1 Gene : Liver X Receptor Activates AN Internal Promoter That Produces A Novel Transcript Encoding AN Alternate Form of the Protein. / Kennedy, Matthew A.; Venkateswaran, Asha; Tarr, Paul T.; Xenarios, Loannis; Kudo, Jun; Shimizu, Nobuyoshi; Edwards, Peter A.

In: Journal of Biological Chemistry, Vol. 276, No. 42, 2001, p. 39448-39454.

Research output: Contribution to journalArticle

Kennedy, Matthew A. ; Venkateswaran, Asha ; Tarr, Paul T. ; Xenarios, Loannis ; Kudo, Jun ; Shimizu, Nobuyoshi ; Edwards, Peter A. / Characterization of the Human ABCG1 Gene : Liver X Receptor Activates AN Internal Promoter That Produces A Novel Transcript Encoding AN Alternate Form of the Protein. In: Journal of Biological Chemistry. 2001 ; Vol. 276, No. 42. pp. 39448-39454.
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abstract = "The human ABCG1 gene encodes a member of the ATPbinding cassette (ABC) superfamily of transporter proteins and is highly induced when macrophages are incubated with oxysterols. Using mRNA from oxysterol-treated human THP-1 cells together with 5′-rapid amplification of cDNA ends and polymerase chain reaction, we identified a novel ABCG1 transcript that encodes a putative protein of 786 residues containing a new ammo terminus of 203 amino acids. Characterization of the genomic organization and structure of the human ABCG1 gene demonstrates that: (i) the gene consists of 23 exons spanning 98 kilobase pairs (kb) on chromosome 21q22.3, (ii) the 203 amino acids are encoded on three previously unidentified exons, 8-10, and (iii) a promoter, containing a TATA box and two liver X receptor (LXR) a response elements (LXREs), is located upstream of exon 8. Northern analysis using exon-specific probes confirms that oxysterol treatment results in > 10fold induction of ABCG1 transcripts that are derived from either exons 8-23 or exons 5, 7, and 11-23. Electromobility shift assays demonstrate that LXRα and retinoid X receptor α bind to the two LXREs in intron 7. Cells were transiently transfected with reporter luciferase constructs under the control of either (i) 9 kb of genomic DNA corresponding to intron 7 and part of exon 8 and containing either wild-type or mutant LXREs or (ii) two copies of the wild-type or mutant LXRE. In all cases, the wild-type construct was regulated in an LXR- and oxysterol-dependent manner, and this regulation was attenuated when the LXREs were mutated. In conclusion, the human ABCG1 gene contains multiple promoters, spans more than 98 kb and comprises 23 exons that give rise to alternative transcripts encoding proteins with different amino-terminal sequences. Elucidation of the various roles of different ABCG1 isoforms will be important for our understanding of mammalian cholesterol homeostasis.",
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