Promoter characterization and genomic organization of the human breast cancer resistance protein (ATP-binding cassette transporter G2) gene

The breast cancer resistance protein (BCRP) gene, formally known as ATP-bin ding cassette transporter G2 (ABCG2) gene, encodes an ABC half transporter that causes resistance to certain cancer chemotherapeutic drugs when transf ected and expressed in drug sensitive cancer cells. Here we report the orga nization of the BCRP gene, and the initial characterization of the BCRP pro moter. We identified the genomic sequence of BCRP and its promoter by scree ning a human genomic lambda phage library, as well as a BAC library, and by searching the human genome database. The BCRP gene spans over 66 kb and co nsists of 16 exons and 15 introns. The exons range in size from 60 to 532 b p. The translational start site is found in the second exon. The first exon contains the majority of the 5' UTR. Promoter activity was characterized b y a luciferase reporter assay using transient transfection of the human bre ast cancer cell line MCF7, and the human choriocarcinoma cell lines JAR, Be Wo and JEG-3, which we find to have high endogenous expression of BCRP. The BCRP gene is transcribed by a TATA-less promoter with several putative Sp1 sites. which are downstream from a putative CpG island. The sequence 312 b p directly upstream from the BCRP transcriptional start site conferred basa l promoter activity. The 5' region upstream of the basal promoter is charac terized by both positive and negative regulatory domains. (C) 2001 Publishe d by Elsevier Science B.V.