ABCG2

ATP-binding cassette sub-family G member 2 is a is_associated_with::protein that in humans is encoded by the ABCG2 is_associated_with::gene. ABCG2 has also been designated as CDw338 (is_associated_with::cluster of differentiation w338).

Function
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 is_associated_with::placenta, and it has been shown to have a role in protecting the fetus from is_associated_with::xenobiotics in the maternal circulation. The transporter has also been shown to play protective roles in blocking absorption at the is_associated_with::apical membrane of the intestine, and at the is_associated_with::blood-testis barrier, the is_associated_with::blood–brain barrier, and the membranes of hematopoietic progenitor and other is_associated_with::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 on excreting vitamins such as is_associated_with::riboflavin and is_associated_with::biotin into milk.