Journal of Hepatology 1994; 21 : 754-763 Printed in Demnark . All rights reserved Munksgaard. Copenhagen Copyright©JounmlofHepatology 1994 Journal of Hepatology ISSN 0168-8278 Effect of colchicine and heat shock on multidrug resistance gene and P-glycoprotein expression in rat fiver Valeska Vollrath ~, Ana M. Wielandt ~, Cecilia Acufia ~, Ignacio Duarte-', Leonardo Andrade 2 and Jose Chianale t Departments of IGastroenterology and "Pathology, School of Medicble, Catholic University of Chile, Santiago, Chile (Received 31 August 1993) The multidrug resistance genes encode plasma membrane glycoproteins named P-glycoproteins, that act as an ATP- dependent drug efflux pump and decrease the cytosolic concentration of chemotherapeutic agents. It has been hypo- thesized that in rat liver, this protein may have a physiological role as a biliary transporter of xenobiotics and endobiotics. Some human tumor cell lines turn on the human multidrug resistance gene in response to high temperature and after exposure to toxic chemicals. Accordingly, it has been proposed that the human multidrug resistance gene is a heat shock gene. We have assessed whether two environmental stresses, heat shock or acute exposure to cytotoxic drugs (colchicine, vincristine, vinblastine and daunomycin), induce changes in the expression of multidrug resistance genes in the rat. Total cellular RNA extracted from rat liver was hybridized to a labeled human multidrug resistance gene cDNA probe. Tem- perature upshift did not increase the steady-state of mdr mRNA levels in the tissues studied, suggesting that the mdr genes are not activated as part of a heat shock response. The mdr mRNA levels increased in rat liver as early as 3 h after a single injection of colchicine, reached a peak (500%; p<0.05) after around 24 h and returned to constitutive levels after 48 h. Changes in the relative content of mdr mRNA were not detected in kidney, adrenal gland and small bowel, sug- gesting that the in vivo induction of the mdr gene in the liver is a tissue-specific response. The other cytotoxic drugs that were tested did not increase the steady-state of mdr mRNA levels. Using specific PCR-generated mouse mdr cDNA probes, we found that only the mdr 2 gene is overexpressed in the liver of colchicine-treated mouse. The mdr gene induction was followed at 48-72 h by a stronger immunostaining in rat liver of its encoded product, suggesting that the newly synthesized protein was incorporated into the canalicular domain of hepatocytes. This is the first evidence of modulation of marl" expression gene in rodent liver in response to colchicine, a substrate of P-glycoprotein in multidrug resistant cells. © Journal of Hepatology. Key words: Colchicine; Heat shock; Induction; mdr gene family; P-glycoprotein; Xenobiotics Mammalian tumor cell lines frequently show cross-re- sistance to several structurally unrelated chemothera- peutic agents (1-3). This phenotype, defined as multidrug resistance (MDR), occurs in a variety of tumors and ma- lignant cell lines and may prevent successful chemo- therapy (4). This phenotype has been related to the over- expression or amplification of one or more members of the multidrug resistance gene family (5,6). The MDR1 and MDR2 genes constitute the human and nonhuman primate multidrug resistance gene family (7,8), whereas three genes (mdrla, lb and 2) have been characterized in rats and mice (9-12). The multidrug resistance genes en- code plasma membrane glycoproteins (Gp 170). The hu- man MDR1 gene and the mdrla and mdrlb genes of the mice encode related P-glycoproteins that act as an ATP- dependent drug efflux pump and decrease the cytosolic concentration of chemotherapeutic agents (13). Most of the known substrates of P-glycoprotein are cytotoxic hydrophobic natural compounds (13). It has recently been hypothesized that the mouse mdr2 P-glycoprotein may be Correspondence to: Jos6 Chianale, MD, Department of Gastroenterology, Catholic University of Chile, Casilla I I4-D, Santiago, Chile.