Ultrastructural analysis of ESCRT proteins suggests a role for endosome-associated tubular-vesicular membranes in ESCRT function.
The endosomal sorting complex required for transport (ESCRT) is thought to support the formation of intralumenal vesicles of multivesicular bodies (MVBs). The ESCRT is also required for the budding of HIV and has been proposed to be recruited to the HIV-budding site, the plasma membrane of T cells and MVBs in macrophages. Despite increasing data on the function of ESCRT, the ultrastructural localization of its components has not been determined. We therefore localized four proteins of the ESCRT machinery in human T cells and macrophages by quantitative electron microscopy. All the proteins were found throughout the endocytic pathway, including the plasma membrane, with only around 10 and 3% of the total labeling in the cytoplasm and on the MVBs, respectively. The majority of the labeling (45%) was unexpectedly found on tubular-vesicular endosomal membranes rather than on endosomes themselves. The ESCRT labeling was twice as concentrated on early and late endosomes/lysosomes in macrophages compared with that in T cells, where it was twice more abundant at the plasma membrane. The ESCRT proteins were not redistributed on HIV infection, suggesting that the amount of ESCRT proteins located at the budding site suffices for HIV release. These results represent the first systematic ultrastructural localization of ESCRT and provide insights into its role in uninfected and HIV-infected cells.
Welsch
Sonja
S
Department of Virology, Heidelberg University, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany.
Habermann
Anja
A
Jäger
Stefanie
S
Müller
Barbara
B
Krijnse-Locker
Jacomine
J
Kräusslich
Hans-Georg
HG
D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure / Q000821:virology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D015497:HIV-1 / Q000254:growth & development / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008264:Macrophages / Q000378:metabolism / Q000648:ultrastructure / Q000821:virology; D008854:Microscopy, Electron; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure / Q000821:virology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D022161:Transport Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D014771:Virion / Q000378:metabolism; D000099177:Tsg101 Protein
D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; D033921:Vesicular Transport Proteins; D000099177:Tsg101 Protein; C117020:PDCD6IP protein, human; C096164:hepatocyte growth factor-regulated tyrosine kinase substrate; C490304:VPS4B protein, human