Multidrug Resistance Protein 3 (MDR3), also known as ATP-binding cassette sub-family B member 4 (ABCB4), is a crucial protein primarily expressed in the canalicular membrane of hepatocytes. It functions as a phosphatidylcholine translocase, transporting this phospholipid from the inner to the outer leaflet of the membrane bilayer and into bile. This process is essential for forming mixed micelles with bile salts, protecting the biliary tree from the detergent-like toxicity of bile salts. MDR3 plays a significant role in bile formation and preventing cholestasis. Mutations in the ABCB4 gene can lead to severe liver disorders, such as Progressive Familial Intrahepatic Cholestasis type 3 (PFIC3), characterized by early-onset cholestasis, liver fibrosis, and eventual liver failure. Additionally, MDR3 dysfunction has been linked to drug-induced liver injury (DILI) due to its inhibition by certain drugs or their metabolites.
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