title: Functional analysis of six human aryl hydrocarbon receptor variants in a Japanese population.
abstract: Aryl hydrocarbon receptor (AhR) is an important transcriptional regulator involved in the induction of CYP1A1, CYP1A2, CYP1B1, UGT1A1, and UGT1A6. In this study, functional properties of four novel naturally occurring human AhR variants (K401R, N487D, I514T, and K17T/R554K) were examined along with the single variants K17T and R554K. The luciferase reporter assay using the CYP1A1 promoter reporter in HeLa cells treated with beta-naphthoflavone or 3-methylcholanthrene, which are known as typical agonists for AhR, showed that reporter activities of the K401R and N487D variants were reduced to 40 to 58% of those of wild-type (WT) but not of the other variants. Similarly, the K401R and N487D variants also reduced the omeprazole-induced reporter activities to approximately 56 and 74% of those of the WT, respectively. The reduced activities of the two variants were probably caused by the reduced protein expression levels, since the protein levels of the K401R and N487D variants were approximately 52 and 47% of the WT, respectively, without any changes in their mRNA levels. The reduced protein levels were recovered by treatment with a proteasome inhibitor MG132 [N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal], suggesting that the reduced protein levels were caused by the accelerated proteasomal degradation by a proteasome. Together, the current data demonstrate that the K401R and N487D variants reduce their apparent transcriptional activities, both ligand-induced and omeprazole-induced activation, probably through reduced protein expression. Thus, these two variants may influence drug metabolism through reduced induction of CYP1A1 and other target enzymes.
authors.affiliation: Project Team for Pharmacogenetics, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan. skoyano@nihs.go.jp
authors.forename: Satoru
authors.initials: S
authors.lastname: Koyano
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Saito
authors.forename: Hiromi
authors.initials: H
authors.lastname: Fukushima-Uesaka
authors.forename: Seiichi
authors.initials: S
authors.lastname: Ishida
authors.forename: Shogo
authors.initials: S
authors.lastname: Ozawa
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Kamatani
authors.forename: Hironobu
authors.initials: H
authors.lastname: Minami
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ohtsu
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hamaguchi
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Shirao
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Yoshida
authors.forename: Nagahiro
authors.initials: N
authors.lastname: Saijo
authors.forename: Hideto
authors.initials: H
authors.lastname: Jinno
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Sawada
mesh_terms: D017930:Genes, Reporter; D006239:Haplotypes / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D007564:Japan; D007976:Leupeptins / Q000494:pharmacology; D008156:Luciferases / Q000235:genetics; D016133:Polymerase Chain Reaction; D061988:Proteasome Inhibitors; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D007976:Leupeptins; D061988:Proteasome Inhibitors; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D008156:Luciferases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde