V. Claus et al., LYSOSOMAL-ENZYME TRAFFICKING BETWEEN PHAGOSOMES, ENDOSOMES, AND LYSOSOMES IN J774 MACROPHAGES - ENRICHMENT OF CATHEPSIN H IN EARLY ENDOSOMES, The Journal of biological chemistry, 273(16), 1998, pp. 9842-9851
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.