Functional assessment of ABCG2 (BCRP) gene polymorphisms to protein expression in human placenta.
The aim of the present study was to assess the contribution of polymorphisms in the breast cancer resistance protein/ATP-binding cassette transporter G2 (BCRP/ABCG2) gene to the placental expression from a new perspective, allelic imbalance. Polymorphisms were screened by polymerase chain reaction (PCR)-single-strand conformation polymorphism analysis followed by sequencing with DNA extracted from 100 placentas. To examine whether polymorphisms of the BCRP gene correlate with the placental BCRP expression, we determined mRNA and protein levels by quantitative real-time PCR and Western blotting, respectively. In placentas, G34A (Val(12)Met) and C421A (Gln(141)Lys) were frequently observed (18-36%), but C376T, which creates a stop codon (Gln(126) stop codon), was found with an allelic frequency of 1%. The mean of the BCRP protein level was significantly lower (p < 0.05) in homozygotes for the A421 allele than in those for the C421 allele, and heterozygotes had an intermediate value. To evaluate whether the C421A polymorphism acts as a cis-element in BCRP transcription, allelic imbalance was determined using informative lymphoblasts and 56 samples of placental cDNA. In most of the placental samples we tested, the difference in expression levels between the two alleles was small, and only two samples indicated a monoallelic expression (i.e., preferential expression of one allele). These results suggest that 1) the predominant allelic expression pattern of BCRP in placental samples is biallelic, and 2) the mutation C421A is not a genetic variant acting in cis, but is considered to influence the translation efficiency.
Kobayashi
Daisuke
D
Department of Hospital Pharmacy, Faculty of Medicine, Tottori University, Nishi-machi 36-1, Yonago, 683-8504, Japan.
Ieiri
Ichiro
I
Hirota
Takeshi
T
Takane
Hiroshi
H
Maegawa
Shinji
S
Kigawa
Junzo
J
Suzuki
Hiroshi
H
Nanba
Eiji
E
Oshimura
Mitsuo
M
Terakawa
Naoki
N
Otsubo
Kenji
K
Mine
Kazunori
K
Sugiyama
Yuichi
Y
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics*; D001741:Black or African American / Q000235:genetics; D044466:Asian People / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D005787:Gene Frequency; D006239:Haplotypes; D006801:Humans; D009154:Mutation; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics*; D011110:Polymorphism, Genetic / Q000502:physiology*; D011257:Pregnancy Proteins / Q000096:biosynthesis* / Q000235:genetics*; D044465:White People / Q000235:genetics
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D009363:Neoplasm Proteins; D011257:Pregnancy Proteins