ATP-binding cassette sub-family B member 4 (ABCB4)

ATP-binding cassette sub-family B member 4 (ABCB4, also known as multidrug resistance protein 3 or MDR3) is a membrane-associated transporter belonging to the superfamily of ATP-binding cassette proteins. It functions primarily by transporting phosphatidylcholine from hepatocytes into bile—a process essential for protecting biliary epithelium from toxic effects of unbound bile acids and maintaining proper digestion of fats. Loss-of-function mutations cause progressive familial intrahepatic cholestasis type 3 (PFIC3), low-phospholipid associated cholelithiasis syndrome, chronic liver disease, and increase susceptibility to intrahepatic cholestasis during pregnancy. The gene is also implicated in cancer biology through its downregulation in certain neoplastic conditions.

Other names

Multidrug resistance protein 3MDR3P-glycoprotein 3PFIC-3GBD1PGY3ATP-binding cassette, sub-family B (MDR/TAP), member 4ABC21

For drugs targeting this molecule, mechanisms would include modulation of phospholipid transport into bile to restore normal bile composition or reduce toxic effects of unbound bile acids. Inhibitors could theoretically block substrate transport; however, no approved direct inhibitors are currently noted in the search results.