Alternative splicing within the ligand binding domain of the human constitutive androstane receptor.
The human constitutive androstane receptor (hCAR; NR1I3) is a member of the nuclear receptor superfamily. The activity of hCAR is regulated by a variety of xenobiotics including clotrimazole and acetaminophen metabolites. hCAR, in turn, regulates a number of genes responsible for xenobiotic metabolism and transport including several cytochrome P450s (CYP 2B5, 2C9, and 3A4) and the multidrug resistance-associated protein 2 (MRP2, ABCC2). Thus, hCAR is believed to be a mediator of drug-drug interactions. We identified two novel hCAR splice variants: hCAR2 encodes a receptor in which alternative splice acceptor sites are utilized resulting in a 4 amino acid insert between exons 6 and 7, and a 5 amino acid insert between 7 and 8, and hCAR3 encodes a receptor with exon 7 completely deleted resulting in a 39 amino acid deletion. Both hCAR2 and hCAR3 mRNAs are expressed in a pattern similar to the initially described MB67 (hCAR1) with some key distinctions. Although the levels of expression vary depending on the tissue examined, hCAR2 and hCAR3 contribute 6-8% of total hCAR mRNA in liver. Analysis of the activity of these variants indicates that both hCAR2 and hCAR3 lose the ability to heterodimerize with RXR and lack transactivation activity in cotransfection experiments where either full-length receptor or GAL4 DNA-binding domain/CAR ligand binding domain chimeras were utilized. Although the role of hCAR2 and hCAR3 is currently unclear, these additional splice variants may provide for increased diversity in terms of responsiveness to xenobiotics.
Savkur
Rajesh S
RS
Gene Regulation Research, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN 46285, USA.
Wu
Yifei
Y
Bramlett
Kelli S
KS
Wang
Minmin
M
Yao
Sufang
S
Perkins
Douglas
D
Totten
Michelle
M
Searfoss
George
G
Ryan
Timothy P
TP
Su
Eric W
EW
Burris
Thomas P
TP
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D008099:Liver; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation / Q000235:genetics; D015262:Xenobiotics / Q000378:metabolism
D000090702:Constitutive Androstane Receptor; D003577:Cytochrome P-450 Enzyme System; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D015262:Xenobiotics; C000715087:ABCC2 protein, human; C000716327:NR1I3 protein, human