ABCC4 is a member of the ATP-binding Cassette (ABC) transporter family. ABC proteins transport various molecules across cellular membranes by utilizing the energy generated from ATP hydrolysis. There are seven subfamilies of ABC proteins: ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, and White (1). ABCC4 belongs to the MRP subfamily, which is involved in multi-drug resistance, hence it is also named MRP4. ABCC4 is widely expressed in cells and tissues including prostate, kidney proximal tubules, astrocytes and capillary endothelial cells of the brain, platelets, and many cancer cell lines (2-4). ABCC4 mediates efflux transport of a wide variety of endogenous and xenobiotic organic anionic compounds (5). The diversity of substrates determines the biological functions of ABCC4. It regulates cAMP levels in human leukemia cells, thereby controlling the proliferation and differentiation of leukemia cells (6). ABCC4 also enables COX deficient pancreatic cancer cells to obtain exogenous prostagladins (7). Researchers have shown that ABCC4 expression is elevated in drug resistant cancer cells, which makes it a potential target for cancer therapy (8,9). ABCC4 localizes to both plasma membrane and intracellular membranous structures (10). Investigators have also implicated ABCC4 in the pathogenesis of Kawasaki desease, a genetic childhood disease characterized by vasculitis (11).