Alix regulates cortical actin and the spatial distribution of endosomes.
Alix/AIP1 is a proline-rich protein that has been implicated in apoptosis, endocytic membrane trafficking and viral budding. To further elucidate the functions of Alix, we used RNA interference to specifically suppress its expression. Depletion of Alix caused a striking redistribution of early endosomes from a peripheral to a perinuclear location. The redistribution of endosomes did not affect transferrin recycling or degradation of endocytosed epidermal growth factor receptors, although the uptake of transferrin was mildly reduced when Alix was downregulated. Quantitative immunoelectron microscopy showed that multivesicular endosomes of Alix-depleted cells contained normal amounts of CD63, whereas their levels of lysobisphosphatidic acid were reduced. Alix depletion also caused an accumulation of unusual actin structures that contained clathrin and cortactin, a protein that couples membrane dynamics to the cortical actin cytoskeleton. Our results suggest that Alix functions in the actin-dependent intracellular positioning of endosomes, but that it is not essential for endocytic recycling or for trafficking of membrane proteins between early and late endosomes in non-polarised cells.
Cabezas
Alicia
A
Department of Biochemistry, the Norwegian Radium Hospital, Montebello, Oslo.
Bache
Kristi G
KG
Brech
Andreas
A
Stenmark
Harald
H
D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015703:Antigens, CD / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002966:Clathrin / Q000737:chemistry / Q000378:metabolism; D051356:Cortactin; D015536:Down-Regulation; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D066246:ErbB Receptors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes; D008246:Lysophospholipids / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D050178:Monoglycerides; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D060149:Tetraspanin 30; D014168:Transferrin / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
D000199:Actins; D015703:Antigens, CD; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002966:Clathrin; D051356:Cortactin; D056827:Endosomal Sorting Complexes Required for Transport; D066246:ErbB Receptors; D008246:Lysophospholipids; D008840:Microfilament Proteins; D050178:Monoglycerides; D010980:Platelet Membrane Glycoproteins; D034741:RNA, Small Interfering; D060149:Tetraspanin 30; D014168:Transferrin; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C554586:CD63 protein, human; C495868:CTTN protein, human; C117020:PDCD6IP protein, human; C012786:bis(monoacylglyceryl)phosphate