DIFFERENTIAL EXPRESSION OF P-GLYCOPROTEIN GENES IN PRIMARY RAT HEPATOCYTE CULTURE

The multidrug resistance (MDR)-associated protein, P-glycoprotein (Pgp ), is expressed on the bile canalicular surface of hepatocytes, where it is thought to function in the detoxification of xenobiotics or in t he transport of specific metabolites. Several studies have shown that Pgp expression in rat liver can be perturbed in vivo and in vitro; how ever, it is not known which of the 3 Pgp genes (class I, II, or III) a re involved. In rodents, the class I and II Pgp genes have been shown to mediate MDR while the class III gene apparently does not. In this r eport, we have used gene-specific probes generated from the 3'-untrans lated regions of the three rat Pgp genes (Deuchars et al.: Biochim. Bi ophys. Acta, 1130:157-165, 1992) to investigate Pgp gene expression in primary rat hepatocytes. We observed that the class II Pgp mRNA, the least abundant in the intact liver, is dramatically increased in cultu re over a 48 h period, while the class I Pgp showed only a modest incr ease in mRNA level. In contrast, the class III Pgp mRNA, which is the most abundant in the intact liver, exhibited a gradual decline. In rat liver hepatocytes, different culture conditions, as well as drugs suc h as cytochalasin D and colchicine, appear to affect the level of the class II Pgp gene expression. Moreover, under all these conditions, th ere is a strong correlation between the level of the class II Pgp and cytoskeletal (actin and tubulin) mRNAs. Thus, there may be a common me chanism regulating the expression of cytoskeletal protein genes and th e class II Pgp gene. These findings have implications for our understa nding of the regulation of Pgp gene expression in normal and malignant tissues. (C) 1993 Wiley-Liss, Inc.