Cloning and heterologous expression of the ovine (Ovis aries) P‐glycoprotein (Mdr1) in Madin–Darby canine kidney (MDCK) cells

Zahner, D., Alber, J., Petzinger, E. Cloning and heterologous expression of the ovine (Ovis aries) P‐glycoprotein (Mdr1) in Madin–Darby canine kidney (MDCK) cells. J. vet. Pharmacol. Therap. 33 , 304–311. P‐glycoprotein (P‐gp) plays a crucial role in the multidrug resistance of pathogenic helminths in sheep (Ovis aries) as well as in antiparasitic drug pharmacokinetics in the host. We cloned sheep P‐gp cDNA and expressed it stably in Madin–Darby canine kidney (MDCK) cells. The open reading frame consists of 3858 nucleotides coding for a 1285 amino acids containing protein. The sequence shows high homology to the orthologs of other mammalian species, especially cattle. Both ruminant DNA sequences show a 9 bp insertion that is lacking in all other investigated sequences. Expressed in MDCK cells, the protein displays a size of 170 kDa on Western analysis. Transfection of MDCK cells with sheep P‐gp resulted in 10‐ to 50‐fold resistance to the cytotoxic P‐gp substrates colchicin and daunorubicin, and in reduced digoxin accumulation.