C421A polymorphism in the human breast cancer resistance protein gene is associated with low expression of Q141K protein and low-level drug resistance.

Abstract	Breast cancer resistance protein (BCRP) confers multidrug resistance to cancer cells against agents such as SN-38 (an active metabolite of irinotecan), mitoxantrone, and topotecan. Among 59 human tumor cell lines tested, 6 cell lines, A549, NCI-H460, KM-12, HT-29, OVCAR-5, and RPMI8226, showed high BCRP expression. BCRP cDNA was isolated from 11 cancer cell lines and three variant cDNAs [G34A substituting Met for Val-12 (V12M), C421A substituting Lys for Gln-141 (Q141K), and 944-949 deletion lacking Ala-315 and Thr-316 (delta315-6)] were identified. G34A and C421A variants were polymorphisms, and 944-949 deletion was a splicing variant. C421A BCRP-transfected PA317 cells showed markedly decreased protein expression and low-level drug resistance compared with wild-type BCRP-transfected cells when transfectants expressed similar levels of BCRP mRNA. G34A or 944-949-deleted BCRP-transfected PA317 cells showed similar or somewhat lower protein expression and drug resistance compared with wild-type BCRP-transfected cells. Of 124 healthy Japanese volunteers, 67 were wild-type, 48 were heterozygous, and 9 were homozygous for the C421A allele. These results suggest that some people possess the C421A polymorphic BCRP gene and express low amounts of Q141K BCRP. In addition to that, C376T polymorphism in exon 4 substituting stop codon for Gln-126 was found in 3 of the 124 general Japanese population. This C376T polymorphism may also have high impact because active BCRP protein will not be expressed from the C376T allele. Therefore, people with C376T and/or C421A polymorphisms may express low amounts of BCRP, and this low BCRP expression might result in hypersensitivity of normal cells to such anticancer drugs as irinotecan and mitoxantrone.
Authors	Yasuo Imai, Minoru Nakane, Kumie Kage, Satomi Tsukahara, Etsuko Ishikawa, Takashi Tsuruo, Yoshio Miki, Yoshikazu Sugimoto
Journal	Molecular cancer therapeutics (Mol Cancer Ther) Vol. 1 Issue 8 Pg. 611-6 (Jun 2002) ISSN: 1535-7163 [Print] United States
PMID	12479221 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	ABCG2 protein, human ATP Binding Cassette Transporter, Subfamily G, Member 2 ATP-Binding Cassette Transporters Antineoplastic Agents Antineoplastic Agents, Phytogenic DNA, Complementary Neoplasm Proteins RNA, Messenger Irinotecan Topotecan Mitoxantrone Camptothecin
Topics	ATP Binding Cassette Transporter, Subfamily G, Member 2 ATP-Binding Cassette Transporters (genetics) Alternative Splicing Animals Antineoplastic Agents (pharmacology) Antineoplastic Agents, Phytogenic (pharmacology) Base Sequence Blotting, Northern Blotting, Western Camptothecin (analogs & derivatives, pharmacology) DNA, Complementary (metabolism) Dose-Response Relationship, Drug Drug Resistance, Neoplasm Fibroblasts (metabolism) Heterozygote Homozygote Irinotecan Mice Mitoxantrone (pharmacology) Molecular Sequence Data Mutation Neoplasm Proteins Polymorphism, Genetic RNA, Messenger (metabolism) Sequence Analysis, DNA Topotecan (pharmacology) Transfection Tumor Cells, Cultured

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