Transporter Associated with Antigen Processing-Like (ABCB9) Stably Expressed in Chinese Hamster Ovary-K1 Cells Is Sorted to the Microdomains of Lysosomal Membranes

Abstract

The carboxyl terminus of a human ATP-binding cassette (ABC) transporter, transporter associated with antigen processing (TAP)-like (TAPL), was tagged with green fluorescence protein (GFP), and the resulting fusion protein (TAPL-GFP) was stably expressed in Chinese hamster ovary (CHO)-K1 cells. The GFP signal was co-localized with that of LysoTracker but not that of MitoTracker, as visualized under a microscope. TAPL-GFP was co-sedimented with lysosomal marker cathepsin D on Percoll density gradient centrifugation. These results indicated that TAPL is a lysosomal ABC transporter but not a mitochondrial one. It was not solubilized completely with a non-ionic detergent under ice-cold conditions, and was co-sedimented with flotillin-1 on sucrose density gradient centrifugation. A similar result was obtained with high pH-treatment. Furthermore, treatment with methyl-β-cyclodextrin resulted in an altered distribution of TAPL-GFP. These results suggest that TAPL may be localized to the microdomains (lipid rafts) of lysosomal membranes enriched in cholesterol.