Up–Regulation of Basolateral Multidrug Resistance Protein 3 (Mrp3) in Cholestatic Rat Liver

Abstract

Cholestasis induces down–regulation of multidrug resistance protein 2 (Mrp2, symbol Abcc2), which is localized to the canalicular membrane. Given the overlapping substrate specificities of Mrp2 and multidrug resistance protein 3 (Mrp3, symbol Abcc3), we examined the hypothesis of a different subcellular and lobular localization of these members of the Mrp family in rat liver after bile duct ligation. We raised a polyclonal antibody against rat Mrp3 and detected this protein in the basolateral plasma membrane of hepatocytes surrounding the central veins and of cholangiocytes. The Mrp3 protein level was less than 2% of the expression observed after 72 hours of obstructive cholestasis. After 48 hours of bile duct ligation, the Mrp3 protein was increased and was further enhanced after 72 hours. In 72–hour–cholestatic rat liver Mrp3 was expressed, in addition, in periportal hepatocytes. However, there was a preponderance of Mrp3 in the pericentral area of the liver lobule. In Mrp2–deficient mutant rat liver, the Mrp3 protein expression was most enhanced and its zonation was lost. The Mrp3 immunostaining of cholangiocytes was preserved in cholestatic and in Mrp2–deficient mutant liver. Canalicular Mrp2 decreased and amounted to 34% of normal after bile duct ligation for 72 hours. We conclude that the hepatocellular up–regulation of Mrp3 in cholestasis together with cholangiocellular Mrp3 may compensate for the biliary obstruction and impaired canalicular Mrp2 function by clearing cholephilic anionic substances into the blood.