A UROKINASE RECEPTOR MESSENGER-RNA BINDING-PROTEIN MESSENGER-RNA INTERACTION REGULATES RECEPTOR EXPRESSION AND FUNCTION IN HUMAN PLEURAL MESOTHELIOMA CELLS

Human pleural malignant mesothelioma (MS-1) or mesothelial (MeT5A) cel ls express the multifunctional urokinase receptor (uPAR) which influen ces neoplastic propagation via contributions to cellular proteolysis, migration, and mitogenesis. Recently, we reported that a 51-nucleotide fragment of the uPAR mRNA coding region contains regulatory informati on for uPAR message stability and that a cytoplasmic uPAR mRNA binding protein (uPAR mRNABp) specifically bound to this sequence in temporal association with uPAR mRNA destabilization in MS-1 cells. To determin e if the uPAR mRNA-uPAR mRNABp interaction is a determinant of uPAR me ssage stability as well as uPAR expression, me further characterized t his cis-trans interaction and created stable transfected cell lines de signed to exploit the interaction and to increase uPAR at the cell sur face. The uPAR mRNABp was purified from MS-1 cells, has an apparent mo lecular mass of 50 kDa, selectively binds to the 51-nt fragment of the uPAR coding region, and does not degrade uPAR mRNA, To determine the role of the uPAR mRNABp on receptor expression, we overexpressed a chi meric beta-globin/uPAR/beta-globin mRNA containing the 51-nt binding f ragment of uPAR mRNA in MS-1 cells and found that uPAR at the cell sur face increased by twofold as measured by [I-125]uPA binding or ligand blotting, Cellular proliferation of uPA-treated cells and invasiveness was similarly increased, The increase in cell surface uPAR was due to commensurately increased uPAR mRNA, The results suggest that competit ion between the overexpressed 51-nt fragment of the uPAR coding region and the wildtype uPAR mRNA transcript for uPAR mRNABp binding enables the cells to translate and express more uPAR at the cell surface. The interaction between the uPAR mRNABp and uPAR mRNA regulates message s tability as well as uPAR expression by MS-1 cells. (C) 1998 Academic P ress.