Title : C-terminal prenylation of the
CLN3 membrane
glycoprotein is required for efficient endosomal sorting to lysosomes
Abstract :
- Mutations in the polytopic lysosomal membrane glycoprotein CLN3 result in a severe neurodegenerative disorder
- Previous studies identified two cytosolic signal structures contributing to lysosomal targeting
- We now examined the role of glycosylation and the C-terminal CAAX motif in lysosomal transport of CLN3 in non-neuronal and neuronal cells
- Mutational analysis revealed that in COS7 cells, CLN3 is glycosylated at asparagine residues 71 and 85
- Both partially and non-glycosylated CLN3 were transported correctly to lysosomes
- Mevalonate incorporation and farnesyltransferase inhibitor studies indicate that CLN3 is prenylated most likely at cysteine 435
- Substitution of cysteine 435 reduced the steady-state level of CLN3 in lysosomes most likely because of impaired sorting in early endosomal structures, particularly in neuronal cells
- Additionally, the cell surface expression of CLN3 was increased in the presence of farnesyltransferase inhibitors
- Alteration of the spacing between the transmembrane domain and the CAAX motif or the substitution of the entire C-terminal domain of CLN3 with cytoplasmic tails of mannose 6-phosphate receptors have demonstrated the importance of the C-terminal domain of proper length and com position for exit of the endoplasmic reticulum
- The data suggest that co-operative signal structures in different cytoplasmic domains of CLN3 are required for efficient sorting and for transport to the lysosome