Defective lysosomal exocytosis and plasma membrane repair in Chediak–Higashi/beige cells

Plasma membrane resealing is a Ca²⁺-dependent process that involves the exocytosis of intracellular vesicles next to the wound site. Recent studies revealed that conventional lysosomes behave as Ca²⁺-regulated secretory compartments and play a central role in membrane resealing. These findings raised the possibility that the complex pathology of lysosomal diseases might also include defects in plasma membrane repair. Here, we investigated the capacity for lysosomal exocytosis and membrane resealing of fibroblasts derived from Chediak–Higashi syndrome (CHS) patients, or frombeige-Jmice. By using a sensitive electroporation/fluorescence-activated cell sorter-based assay, we show that lysosomal exocytosis triggered by membrane wounding is impaired in both human Chediak–Higashi and mousebeige-Jfibroblasts. Lysosomal exocytosis increased when the normal size of lysosomes was restored inbeige-Jcells by expression of the CHS/Beige protein. A similar effect was seen when the lysosomal enlargement inbeige-Jcells was reversed by treatment with E64d. In addition, the survival of Chediak–Higashi andbeige-Jfibroblasts after wounding was reduced, indicating that impaired lysosomal exocytosis inhibits membrane resealing in these mutant cells. Thus, the severe symptoms exhibited by CHS patients may also include defects in the ability of cells to repair plasma membrane lesions.