Cloning and mRNA expression analysis of an ABCG2 (BCRP) efflux transporter in rainbow trout (Oncorhynchus mykiss) liver and primary hepatocytes.

As has been recently demonstrated in mammals, apart from the P-glycoprotein (Pgp, ABCB) and the MRP-like proteins (MRPs, ABCC), another efflux transporter - the BCRP (ABCG2) - expressed in polarized epithelial cells of different tissues, is involved in regulation of intestinal absorption and biliary excretion of potentially toxic xenobiotics. However, no study has been directed towards identification of BCRP (ABCG2) in fish species. In the present study we have cloned the full ABCG2 transcript from rainbow trout (Oncorhynchus mykiss) liver, showing a high sequence identity (60%) to human ABCG2 gene. Using Real-Time PCR we measured relative expression of ABCG2 in trout liver and primary hepatocytes and compared these expression levels to the expression of other ABC transporters expressed in apical membrane of hepatocytes (ABCB1, ABCB11 and ABCC2). ABCG2 expression was 6-fold higher than ABCC2 and almost 42 fold higher than ABCB1, indicating that the ABCG2 probably plays a significant role in the overall disposition and excretion of xenobiotics in fish.