Multivesicular body morphogenesis requires phosphatidyl-inositol 3-kinase activity.
Multivesicular bodies are endocytic compartments containing multiple small vesicles that originate from the invagination and 'pinching off' of the limiting membrane into the luminal space [1] [2] [3]. The molecular mechanisms responsible for the formation of these compartments are unknown. In the human melanoma cell line Mel JuSo, newly synthesised major histocompatibility complex (MHC) class II molecules accumulate in multivesicular early lysosomes [4]. The phosphatidylinositol (PI) 3-kinase inhibitor wortmannin induced the transient vacuolation of early MHC class II compartments, but also of early and late endosomes. We demonstrate that endocytic membrane influx is required for the wortmannin-induced swelling of vesicles. The wortmannin-induced vacuoles contained a reduced number of intraluminal vesicles that were linked to the limiting membrane by membraneous connections. These data suggest that wortmannin inhibits the invagination and/or pinching off of intraluminal vesicles and provide evidence of a role for PI 3-kinase in multivesicular body morphogenesis. We propose that the wortmannin-induced vacuolation occurs as a result of the inability of multivesicular bodies to store endocytosed membranes as intraluminal vesicles thereby causing the formation of large 'empty' vacuoles.
Fernandez-Borja
M
M
Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121 1066CX, Amsterdam, The Netherlands.
Wubbolts
R
R
Calafat
J
J
Janssen
H
H
Divecha
N
N
Dusseljee
S
S
Neefjes
J
J
D000730:Androstadienes / Q000494:pharmacology; D002678:Chimera / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005802:Genes, MHC Class II; D049452:Green Fluorescent Proteins; D015803:HLA-DR3 Antigen / Q000378:metabolism; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014617:Vacuoles / Q000187:drug effects* / Q000502:physiology; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D049452:Green Fluorescent Proteins; D015803:HLA-DR3 Antigen; D008164:Luminescent Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D000077191:Wortmannin