1. The adenosine triphosphate (ATP) binding cassette (ABC) transporters form one 
of the largest protein families encoded in the human genome, and more than 48 
genes encoding human ABC transporters have been identified and sequenced. It has 
been reported that mutations of ABC protein genes are causative in several 
genetic disorders in humans. 2. Many human ABC transporters are involved in 
membrane transport of drugs, xenobiotics, endogenous substances or ions, thereby 
exhibiting a wide spectrum of biological functions. According to the new 
nomenclature of human ABC transporter genes, the 'ABCC' gene sub-family 
comprises three classes involving multidrug resistance-associated proteins 
(MRPs), sulfonylurea receptors (SURs), and a cystic fibrosis transmembrane 
conductance regulator (CFTR). 3. Molecular cloning studies have identified a 
total of ten members of the human MRP class including ABCC11, ABCC12, and ABCC13 
(pseudo-gene) that have recently been characterized. 4. This review addresses 
the historical background and discovery of the ATP-driven xenobiotic export 
pumps (GS-X pumps) encoded by MRP genes, biological functions of ABC 
transporters belonging to the MRP class, and regulation of gene expression of 
MRPs by oxidative stress.