LYSOSOMAL-ENZYME TRAFFICKING BETWEEN PHAGOSOMES, ENDOSOMES, AND LYSOSOMES IN J774 MACROPHAGES - ENRICHMENT OF CATHEPSIN H IN EARLY ENDOSOMES

In this study we take advantage of recently developed methods using J7 74 macrophages to prepare enriched fractions of early endosomes, late endosomes, dense lysosomes, as well as phagosomes of different ages en closing 1-mu m latex beads to investigate the steady state distributio n and trafficking of lysosomal enzyme activity between these organelle s. At steady state these cells appear to possess four different cellul ar structures, in addition to phagolysosomes, where acid hydrolases we re concentrated. The first site of hydrolase concentration was the ear ly endosomes, which contained the bulk of the cellular cathepsin H. Th is enzyme was acquired by phagosomes significantly faster than the oth er hydrolases tested. The second distinct site of lysosomal enzyme con centration was the late endosomes which contain the bulk of cathepsin S. The third and fourth large pools of hydrolases were found in two fu nctionally distinct types of dense lysosomes, only one of which was fo und to be secreted in the presence of chloroquine or bafilomycin, Amon g this secreted pool was soluble furin, generally considered only as a membrane-bound trans-Golgi network resident protein. Thus, the organe lles usually referred to as ''lysosomes'' in fact encompass a growing family of highly dynamic but functionally distinct endocytic organelle s.