LAPTM4α is targeted from the Golgi to late endosomes/lysosomes in a manner dependent on the E3 ubiquitin ligase Nedd4-1 and ESCRT proteins.
Lysosome-associated protein transmembrane 4α (LAPTM4α) is a four transmembrane-spanning protein primarily localized in endosomes and lysosomes and has several putative lysosomal targeting signals at its C-terminal cytoplasmic domain, including tyrosine-based motifs (YxxΦ) and PY motifs (L/PxxY). LAPTM4α has been previously shown to be ubiquitinated by the E3 ubiquitin ligase Nedd4-1 through binding to its PY motifs and sorted to lysosomes, however, the molecular mechanisms underlying the localization of LAPTM4α to endosomes/lysosomes have not yet been fully elucidated. In the present study, we show that LAPTM4α binds Nedd4-1 in a manner dependent on PY motifs, while the PY motifs and Nedd4-1 are not necessarily required for LAPTM4α ubiquitination. The binding of LAPTM4α with Nedd4-1, however, is necessary for an effective sorting of LAPTM4α from the Golgi to late endosomes/lysosomes. An unexpected finding is that LAPTM4α is localized in the lumen, but not in the limiting membrane, of late endosomes, and degraded in lysosomes over time. Interestingly, we further found that siRNA knockdown of endosomal sorting complexes required for transport (ESCRT) components that mediate sorting of ubiquitinated membrane proteins into intralumenal vesicles (ILVs) of endosomes selectively blocks the transport of LAPTM4α to endosomes. Collectively, these results suggest that trafficking of LAPTM4α from the Golgi to endosomes is promoted by the interaction with Nedd4-1, which further requires ESCRT components. Furthermore, our findings highlight a novel function for ESCRT proteins in mediating protein and/or vesicle trafficking from the Golgi to endosomes/lysosomes.
['Hirota|Yuko|Y|', 'Hayashi|Masaharu|M|', 'Miyauchi|Yuu|Y|', 'Ishii|Yuji|Y|', 'Tanaka|Yoshitaka|Y|', 'Fujimoto|Keiko|K|']
D000595:Amino Acid Sequence D000818:Animals D019556:COS Cells D002522:Chlorocebus aethiops D056827:Endosomal Sorting Complexes Required for Transport D011992:Endosomes D006056:Golgi Apparatus D006367:HeLa Cells D006801:Humans D008247:Lysosomes D026901:Membrane Transport Proteins D000075702:Nedd4 Ubiquitin Protein Ligases D011485:Protein Binding D021381:Protein Transport D054875:Ubiquitination
Ubiquitination Nedd4-1 ESCRT Lysosomal membrane