Lysosomal localization of GLUT8 in the testis--the EXXXLL motif of GLUT8 is sufficient for its intracellular sorting via AP1- and AP2-mediated interaction.
The class III sugar transport facilitator GLUT8 co-localizes with the lysosomal protein LAMP1 in heterologous expression systems. GLUT8 carries a [D/E]XXXL[L/I]-type dileucine sorting signal that has been postulated to retain the protein in an endosomal/lysosomal compartment via interactions with clathrin adaptor protein (AP) complexes. However, contradictory findings have been described regarding the subcellular localization of the endogenous GLUT8 and the adaptor proteins that interact with its dileucine motif. Here we demonstrate that endogenous GLUT8 is localized in a late endosomal/lysosomal compartment of spermatocytes and spermatids, and that the adaptor complexes AP1 and AP2, but not AP3 or AP4, interact with its N-terminal intracellular domain (NICD). In addition, fusion of the GLUT8 NICD to the tailless lumenal domain of the IL-2 receptor alpha chain (TAC) protein (interleukin-2 receptor a chain) targeted the protein to intracellular membranes, indicating that its N-terminal dileucine signal is sufficient for endosomal/lysosomal targeting of the transporter. The localization and targeting of GLUT8 show striking similarities to sorting mechanisms reported for lysosomal proteins. Therefore, we suggest a potential role for GLUT8 in the so far unexplored substrate transport across intracellular membranes.
Diril
Muhammed Kasim
MK
Institute of Chemistry and Biochemistry, Department of Membrane Biochemistry, Freie Universität & Charité Universitätsmedizin Berlin, Takustrasse 6, Berlin, Germany.
Schmidt
Stefan
S
Krauss
Michael
M
Gawlik
Verena
V
Joost
Hans-Georg
HG
Schürmann
Annette
A
Haucke
Volker
V
Augustin
Robert
R
D033961:Adaptor Protein Complex 1 / Q000235:genetics / Q000378:metabolism*; D033962:Adaptor Protein Complex 2 / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D051379:Mice; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D013737:Testis / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D052118:Lysosomal-Associated Membrane Protein 1
D033961:Adaptor Protein Complex 1; D033962:Adaptor Protein Complex 2; D004268:DNA-Binding Proteins; D051246:Glucose Transport Proteins, Facilitative; D051907:Lysosomal Membrane Proteins; D014157:Transcription Factors; C052255:Lamp1 protein, mouse; D052118:Lysosomal-Associated Membrane Protein 1; C405325:SLC2A8 protein, human; C498628:Slc2a8 protein, mouse; C498629:Slc2a8 protein, rat; C060759:enhancer-binding protein AP-3