BIOSYNTHESIS AND POLARIZED DISTRIBUTION OF NEUTRAL ENDOPEPTIDASE IN PRIMARY CULTURES OF KIDNEY PROXIMAL TUBULE CELLS

When cultured in defined medium, kidney proximal convoluted tubule (PC T) cells form a homogeneous population and retain a number of differen tiated functions. To characterize this cell system further as a functi onal model of epithelial polarity, we investigated the biogenic pathwa y of neutral endopeptidase (NEP), one of the most abundant microvillar membrane proteins in intestinal and kidney cells. We showed that, in contrast with some tumoral cell lines, RNA extracted from PCT cells sh ows the presence of a single mRNA species encoding NEP. Pulse-chase st udies followed by selective immunoprecipitation of NEP molecules prese nt either at the eel surface or in intracellular cell compartments sho wed that newly synthesized NEP molecules reached the cell surface as e arly as 30 min after the beginning of the chase with maximum cell surf ace expression at 60 min. When grown on semipermeable supports, PCT ce lls were found to target NEP exclusively to the apical plasma membrane . Similar results have been described using MDCK cells to study target ing of recombinant NEP. Thus primary cultures of PCT cells represent a new model with which to investigate the biogenic pathway of endogenou s proteins in native epithelial cells.