EXPRESSION OF MDR1 (MULTIDRUG-RESISTANCE) GENE AND ITS PROTEIN IN NORMAL HUMAN KIDNEY

P-glycoprotein (Pgp), the product of the multidrug resistance (MDR) ge ne overexpressed in cancer cells, is present also in normal tissues. I n the kidney, MDR1 Pgp has been found in the proximal tubule and in cu ltured mesangial cells. In situ hybridization and immunohistochemistry were used to determine the complete nephronal localization of MDR mRN A and its product, Pgp, in the human kidney. MDR mRNA expression was s tudied with the use of nonradioactive in situ MDR RNA probes. MDR1 Pgp was immunolocalized using the specific monoclonal antibody MRK16. The presence of MDR mRNA was confirmed in proximal tubules and mesangium, and demonstrated as well in thick limb of Henle's loops and in collec ting ducts. MDR1 Pgp colocalized in the same nephronal segments. This suggests that, in addition to secreting xenobiotics, Pgp may play a ro le in the transport of endogenous substrates or in the regulation of C l- channels.