ABCB11

ATP-binding cassette, sub-family B member 11 (ABCB11), also known as the bile salt export pump (BSEP), is a protein which in humans is encoded by the  gene.

Function
The product of the ABCB11 gene is an ABC transporter named BSEP (bile salt export pump), or sPgp (sister of P-glycoprotein). This membrane-associated protein is a member of 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 MDR/TAP subfamily. Some members of the MDR/TAP subfamily are involved in multidrug resistance. This particular protein is responsible for the transport of taurocholate and other cholate conjugates from hepatocytes (liver cells) to the bile. In humans, the activity of this transporter is the major determinant of bile formation and bile flow.

Clinical significance
ABCB11 is a gene associated with progressive familial intrahepatic cholestasis type 2 (PFIC2). PFIC2 caused by mutations in the ABCB11 gene increases the risk of hepatocellular carcinoma in early life. Benign recurrent intrahepatic cholestasis (BRIC) is associated with episodic cholestatic jaundice and mutations in ATP8B1 or ABCB11.

Bile salts from the cytoplasm of hepatocytes are transported by the bile salt export pump (BSEP) into bile canaliculi. When bile salt export is deficient due to mutation in the ABCB11 gene, this can lead to intrahepatic toxic accumulation of the bile salts. Individuals with such mutations have an increased incidence of hepatocellular carcinoma or cholangiocarcinoma.