PREFERENTIAL EXPRESSION OF THE MULTIDRUG-RESISTANCE ASSOCIATED PROTEIN (MRP) IN ADENOCARCINOMA OF THE LUNG

The expression of multidrug-resistance-associated protein (MRP) was as sessed in various types of untreated lung cancer using an immunohistoc hemical technique. MRP was abundantly expressed in 28 of 59 adenocarci noma specimens (47%) and its expression was associated with the degree of glandular differentiation of the tumor. MRP expression in well-dif ferentiated adenocarcinomas (56%) was higher than in poorly differenti ated adenocarcinomas (22%) (P < 0.01). In contrast, MRP expression in other cancer types was lower-20% in squamous-cell carcinomas, 20% in l arge-cell carcinomas and 0% in small-cell carcinomas and carcinoids. R T-PCR showed that the MRP-positive adenocarcinomas and squamous-cell c arcinomas expressed mrp mRNA significantly. Immunoelectron microscopic ally, MRP was localized in the plasma membrane and rough endoplasmic r eticulum. It is thus important to take MRP into account when consideri ng chemotherapy for lung cancers because levels of mdr I gene product, another multidrug-resistance gene family, are low in untreated lung c ancers. (C) 1995 Wiley-Liss, Inc.