The membrane-associated protein encoded by this gene is included in the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the White subfamily. Alternatively referred to as the Breast Cancer Resistance Protein, this protein functions as a xenobiotic transporter which may play a role in multi-drug resistance to chemotherapeutic agents including mitoxantrone and camptothecin analogues. Early observations of significant ABCG2-mediated resistance to anthracyclines were subsequently attributed mutations encountered in vitro but not in nature or the clinic. Significant expression of this protein has been observed in the placenta, and it has been shown to have a role in protecting the fetus from xenobiotics in the maternal circulation. The transporter has also been shown to play protective roles in blocking absorption at the apical membrane of the intestine, and at the blood-testis barrier, the blood–brain barrier, and the membranes of hematopoietic progenitor and other stem cells. At the apical membranes of the liver and kidney, it enhances excretion of xenobiotics. In the lactating mammary gland, it has a role in excreting vitamins such as riboflavin and biotin into milk.
^Allikmets R, Gerrard B, Hutchinson A, Dean M (Feb 1997). "Characterization of the human ABC superfamily: isolation and mapping of 21 new genes using the expressed sequence tags database". Hum Mol Genet5 (10): 1649–55. doi:10.1093/hmg/5.10.1649. PMID8894702.
^Doyle LA, Yang W, Abruzzo LV, Krogmann T, Gao Y, Rishi AK, Ross DD (Jan 1999). "A multidrug resistance transporter from human MCF-7 breast cancer cells". Proc Natl Acad Sci U S A95 (26): 15665–70. doi:10.1073/pnas.95.26.15665. PMC28101. PMID9861027.
^ abcdVlaming, M. L. H.; Lagas, J. S.; Schinkel, A. H. (2008-12-07). "Physiological and pharmacological roles of ABCG2 (BCRP): Recent findings in Abcg2 knockout mice". Advanced Drug Delivery Reviews (Elsevier) 61 (1): 14–25. doi:10.1016/j.addr.2008.08.007. PMID19118589.|accessdate= requires |url= (help)
Sugimoto Y, Tsukahara S, Ishikawa E, Mitsuhashi J (2005). "Breast cancer resistance protein: molecular target for anticancer drug resistance and pharmacokinetics/pharmacodynamics.". Cancer Sci.96 (8): 457–65. doi:10.1111/j.1349-7006.2005.00081.x. PMID16108826.
Ishikawa T, Tamura A, Saito H, et al. (2006). "Pharmacogenomics of the human ABC transporter ABCG2: from functional evaluation to drug molecular design.". Naturwissenschaften92 (10): 451–63. doi:10.1007/s00114-005-0019-4. PMID16160819.