The two mannose 6-phosphate receptors have almost identical subcellular distributions in U937 monocytes.
Using a semiquantitative immunogold technique on ultrathin cryosections, the in situ subcellular distributions of the cation-dependent, 46-kDa mannose 6-phosphate receptor (small MPR) and of the cation-independent, 270-kDa mannose 6-phosphate receptor (large MPR) were for the first time compared. U937 cells were chosen because of their relatively high content of both receptor species. Of each receptor, about 12% occurred at the cell surface, 2% in the Golgi stack, and about 25% in vacuoles resembling endosomal vacuoles. About half of both receptors was found in tubules, presumably belonging to endosomes and trans-Golgi reticulum. It was concluded that the distribution of the small and large MPR were roughly similar. The only exception was formed by electron-dense vesicles occurring in the trans-Golgi region and surrounding endosomes. Dense vesicles contained significantly less small MPR (7%) than large MPR (12%).
Bleekemolen
J E
JE
Laboratory for Cell Biology, Medical School, State University of Utrecht, The Netherlands.
Stein
M
M
von Figura
K
K
Slot
J W
JW
Geuze
H J
HJ
D002478:Cells, Cultured; D006801:Humans; D007150:Immunohistochemistry; D002479:Inclusion Bodies / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000379:methods; D009000:Monocytes / Q000648:ultrastructure*; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000648:ultrastructure*
D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface