THE GIANT ORGANELLES IN BEIGE AND CHEDIAK-HIGASHI FIBROBLASTS ARE DERIVED FROM LATE ENDOSOMES AND MATURE LYSOSOMES

Chediak-Higashi Syndrome (CHS) is an autosomal recessive disease affec ting secretory granules and lysosome-like organelles. In CHS fibroblas ts, acidic organelles are abnormally large and clustered in the perinu clear area. We have analyzed fibroblast cell lines from a CHS patient and from the murine model for CHS, the beige mouse, to determine which lysosome-like compartments are affected. Uptake of neutral red showed that in both beige and CHS cell lines, the acidic organelles were mar kedly clustered in the perinuclear region of the cells. Giant organell es (>4 mum) were observed in a fraction of the cells, and these were m ore dramatic in the beige fibroblasts than in the CHS fibroblasts. The total dye uptake of both mutant cell lines was similar to their respe ctive wild type fibroblasts, suggesting that the overall volume of aci dic compartments is unaffected by the disorder. Histochemistry and imm unofluorescence showed that the giant organelles in both beige and CHS fibroblasts were positive for cathepsin D, lysosome-associated membra ne protein (LAMP) 1, LAMP 2, and a 120-kD lysosomal glycoprotein, all marker proteins for late endosomes and lysosomes. The giant organelles were also negative for transferrin receptor and mannose-6-phosphate r eceptor, and most of them were also negative for rab 7. This distribut ion of marker proteins shows that the giant organelles in both beige a nd CHS are derived from late compartments of the endocytic pathway. Th is conclusion was confirmed using endocytic tracers. BSA was transport ed to the giant organelles, but only after long incubation times, and only at 37-degrees-C. Alpha2-macroglobulin was taken up and degraded a t similar rates by CHS or beige cells and their respective wild type c ontrol cells. Taken together, our results indicate that the mutation i n CHS specifically affects late endosomes and lysosomes, with little o r no effect on early endosomes. Although the mutation clearly causes m islocalization of these organelles, it appears to have little effect o n their endocytic and degradative functions.