Multidrug resistance related molecules in human and murine lung

Abstract

Aims: Transporter proteins known to mediate multidrug resistance (MDR) in tumour cells--MDR1 P-glycoprotein (P-gp) and multidrug resistance related protein 1 (MRP1)--are thought to be involved in protecting the lungs against inhaled toxic pollutants. Recently, several new transporter family members have been identified--for example, MRP2, MRP3, and breast cancer resistance protein (BCRP). To study the possible contribution of these proteins and the earlier defined MDR1 and MDR3 P-gp molecules, MRP1, and the major vault protein (MVP) to lung functioning, their expression was analysed in normal lung tissue of humans and several animal species.

Methods: Frozen sections of normal lung tissues were examined for the expression of the multidrug resistance associated proteins, using an extended panel of monoclonal antibodies that specifically detect these proteins in immunohistochemical techniques.

Results: In line with earlier reports, the expression of MDR1 P-gp and MRP1 was readily detected in the apical and basolateral membranes, respectively, of the epithelial cell layers of the lungs. In addition, prominent cytoplasmic MVP staining was detected in these layers. In contrast, the recently discovered transporters were either undetectable or they were present at very low values in lung tissue. Immunohistochemical staining in tissues from mice, rats, and guinea pigs points to a strong evolutionary conservation for these transporter proteins.

Conclusions: These results show that the "classic" MDR related molecules, MDR1 P-gp, MRP1, and MVP, should be considered the most important transporters in normal lung physiology. It will be of great interest to investigate differences in expression of both classic and newly defined transporters between normal individuals and-for example, patients with various bronchopulmonary pathological conditions.

Figure 1

Expression of MDR related proteins in frozen sections of normal human lung tissue as detected with (A) C219 (anti-MDR1 P-gp), (B) P₃II-26 (anti MDR3 P-gp), (C) MRPr1 (anti-MRP1), (D1) M2II-12 (anti MRP2), (D2) M2III-6 (anti MRP2), (E) M₃II-9 (anti-MRP3), (F) LRP-56 (anti-MVP), (G) BXP-34 (anti-BCRP), and (H) control monoclonal antibody. MDR1 P-gp is present in the apical membrane of the bronchial and bronchiolar epithelial layer. MRP1 is present at the basolateral membrane of the bronchial and bronchiolar layer. Abberant MRP2 staining is only seen with M₂III-6. MVP is present in the cytoplasm of the bronchial and bronchiolar epithelial cells. Slides were stained with HRP labelled rabbit antimouse, FITC labelled tyramine, HRP labelled rabbit anti-FITC, and aminoethylcarbazole. BCRP, breast cancer resistance protein; FITC, fluorescein isothiocyanate; HRP, horseradish peroxidase; MDR, multidrug resistance; MRP, multidrug resistance protein; MVP, major vault protein; P-gp, P-glycoprotein.

Figure 2

Expression of MDR related proteins in normal human liver tissue. (A) MDR1 P-gp, MDR3 P-gp, MRP2, and BCRP show similar staining at the canalicular membranes of the hepatocytes (example of staining with M₂I-4). (B) MRP3 is present in the bile ducts and the basolateral membranes of the hepatocytes (staining with M₃II-9). (C) negative control. Slides were stained with HRP labelled rabbit antimouse, FITC labelled tyramine, HRP labelled rabbit anti-FITC, and aminoethylcarbazole. BCRP, breast cancer resistance protein; FITC, fluorescein isothiocyanate; HRP, horseradish peroxidase; MDR, multidrug resistance.

Figure 3

Expression of MRP1 as detected with the rat MRPr1 monoclonal antibody in different types of lung tissue. (A) MRP1 staining in alveolar macrophages in frozen sections of normal human lung. (B) MRP1 staining in a seromucinous gland in a frozen section of the upper part of the lung. (C) MRP1 staining in formalin fixed, paraffin wax embedded normal human lung tissue. (D) mrp1 staining in frozen sections of mouse lung tissue. Slides were stained with HRP labelled rabbit antimouse, FITC labelled tyramine, HRP labelled rabbit anti-FITC, and aminoethylcarbazole. FITC, fluorescein isothiocyanate; HRP, horseradish peroxidase; MRP, multidrug resistance protein.