Uptake of human urinary trypsin inhibitor by the kidney epithelial cell line, LLC-PK1.

Abstract

We investigated the uptake of human urinary trypsin inhibitor (UTI) by the kidney epithelial cells, LLC-PK1. Indirect immunogold techniques with an electron microscope demonstrated the localization of UTI within the cells after an incubation during which UTI was added to the apical side. Immunoreactivities were found in endocytic vesicles, vacuoles and lysosomes. Subsequently, we tried to characterize the property of the uptake of UTI using the fluorescein isothiocyanate-labelled UTI (FITC-UTI). FITC-UTI uptake was decreased by an incubation with an excess of unlabelled UTI and showed concentration-dependent saturation. This process was markedly suppressed during the incubation at 4 degrees C. The uptake was significantly lessened with 2,4-dinitrophenol and antimycin A, inhibitors of oxidative phosphorylation, and colchicine, a microtubule-depolymerizing agent. These results indicate that exogenous UTI is internalized by LLC-PK1 cells through an endocytic pathway. From uptake studies, it is suggested that an adsorptive process is partially involved in the mechanisms of endocytosis.