FUNCTIONAL ASSESSMENT OFABCG2(BCRP) GENE POLYMORPHISMS TO PROTEIN EXPRESSION IN HUMAN PLACENTA

Abstract

ABSTRACT: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)-singlestrand conformation polymorphism analysis followed by sequencing with DNA extracted from 100 placentas. 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.Breast cancer resistance protein (BCRP), also called mitoxantroneresistant protein, is the second member of the G family of ATPbinding cassette transporters (ABCG2) (Allikmets et al., 1998;Doyle et al., 1998;Miyake et al., 1999;Doyle and Ross, 2003). The BCRP gene is located at 4q22 and encodes a 72-kDa membrane protein composed of 655 amino acids (Allikmets et al., 1998;Doyle et al., 1998;Allen et al., 1999;Bailey-Dell et al., 2001). In contrast to many other ABC transporters, BCRP has only one ATP-binding region and one transmembrane domain. Therefore, BCRP is referred to as a half-transporter, and its homodimerization may be necessary to transport substrates .In normal human tissues, BCRP is highly expressed in the placenta, colon, small intestine, and liver (Maliepaard et al., 2001). On the basis of its tissue distribution and findings in knockout mice, BCRP is speculated to have a major influence on the pharmacokinetic and pharmacodynamic profiles of certain xenobiotics and endogenous substrates. For example, inhibition of mouse Bcrp 1 by GF120918, a dual inhibitor for BCRP and P-glycoprotein, has been demonstrated to increase the bioavailability of topotecan when GF120918 was administered orally to mdr1a/1b(Ϫ/Ϫ) mice (Jonker et al., 2000). In a clinical study, coadministration of GF120918 was also associated with a marked increase in the bioavailability of and systemic exposure to topotecan (Kruijtzer et al., 2002).Recent clinical studies indicate that the large interindividual variability in drug response occurs as a result of molecular alterations to various proteins such as drug-metabolizing enzymes, drug targets and receptors, and drug transporters. Most studies on molecular alterations have focused on the impact of single-nucleotide polymorphisms (SNPs) on the expression and function of these proteins (Evans and Relling, 1999;Evans and Johnson, 2001). Several groups have reported naturally occurring SNPs in the BCRP gene. G34A and C421A occur at relative...

Influence of CYP3A5 and drug transporter polymorphisms on imatinib trough concentration and clinical response among patients with chronic phase chronic myeloid leukemia

“…This is particularly pertinent, given the fact that the Japanese and Han Chinese populations have markedly higher ABCG2 421C4A allele frequencies (30.7 and 28.9%, respectively) than do Caucasian (11.7%) and African-American populations (2.3%). [47][48][49] Our group is currently pursuing a prospective clinical study to validate this prediction formula.…”

“…Similarly, ABCC2 (À24C4T (rs717620)) and ABCB1 (1236T4C (rs1128503), 2677G4T/A (rs2032582) and 3435T4C (rs1045642)) were genotyped as described by Naesens et al, 35 Wu et al, 36 Tanaka et al 37 and Cascorbi et al, 38 respectively. ABCG2 421C4A (rs2231142) was genotyped as described by Kobayashi et al, 39 and SLCO1B3 (334T4G (rs4149117)) as described by Tsujimoto et al 40 All genotype frequencies were tested for Hardy-Weinberg equilibrium.…”

Excretion of biliary compounds during intrauterine life

“…BCRP transports a broad variety of conjugated or non-conjugated organic anions, but from a physiological point of view it is probably involved in the elimination of endogenous sulphate conjugates [150] . Substantial variations in BCRP expression have been observed in human placenta [151] , suggesting that considerable variability could exist in the ability of the placenta to protect the fetus from exposure to drugs, xenobiotics and metabolites. Such variable expression and/or activity has been suggested to be due to genetic polymorphisms in the BCRP gene [151] .…”

“…Substantial variations in BCRP expression have been observed in human placenta [151] , suggesting that considerable variability could exist in the ability of the placenta to protect the fetus from exposure to drugs, xenobiotics and metabolites. Such variable expression and/or activity has been suggested to be due to genetic polymorphisms in the BCRP gene [151] .…”

A dose-ranging study of the pharmacokinetics and pharmacodynamics of the selective apoptotic antineoplastic drug (SAAND), OSI-461, in patients with advanced cancer, in the fasted and fed state

“…Additionally, the ABCG2 gene encodes for the breast cancer resistance protein, BCRP and has been associated with chemotherapy drug resistance [6]. Mutations in this gene confer lower protein expression leading to lower drug resistance [10,14]. Pharmacogenetic samples were obtained on Day 1 at baseline and 1 h post-dose, from all patients in fed cohort who signed a written amendment to the informed consent.…”