M6PR and melanoma: Human melanoma MNT-1 cells were treated with 50 mM sucrose, and we analyzed the morphology of the intracellular organelles by immunofluorescence staining with the following antibodies: early endosome antigen 1 (EEA1) for early endosomes, M6PR for late endosomes and lysosomal membrane protein 1 (LAMP1) for lysosomes.