The extracellular levels of lysosomal enzymes have been implicated in the development of uncontrolled cellular growth, tumor invasiveness, and the inflammatory response. Previous work in our laboratory has uncovered a mannosyl/glucosyl-specific receptor system associated with macrophage plasma membranes which mediates adsorptive pinocytosis (uptake) of lysosomal glycosidases and glycoproteins having mannose in the terminal position. The receptor also recognizes glucose and N-acetylglycosamine but not galactose. We are studying the mode and mechanism of uptake of lysosomal enzymes by macrophages. To accomplish this we have developed methods to fractionate macrophages by Percoll gradient sedimentation and to follow the uptake of ligands by electron microscopy. We have identified an intracellular compartment in macrophages which appears to mediate separation of receptor-ligand complexes and recycling of free receptors to the cell surface. The regulation of the receptor will be studied by following ligand binding and by preparing receptor-specific antibody. The interrelationships between ligand and internalization and lysosomal enzyme biosynthesis and turnover are being investigated. (E)
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