Ceramide as a modulator of endocytosis.
The effects of ceramide analogs on the uptake of markers for fluid-phase (horseradish peroxidase, HRP) and receptor-mediated (low density lipoprotein, LDL) endocytosis were studied in Chinese hamster fibroblasts. N-Hexanoyl-D-erythro-sphingosine (C6-Cer) decreased the uptake of HRP in a dose-dependent manner. Internalization was inhibited > 40% with 25 microM C6-Cer, relative to controls, and was apparent within 5 min. Internalization of HRP was also inhibited by other Cer analogs and by treatment with agents that raise levels of endogenous Cer (sphingomyelinase or the glycosphingolipid synthesis inhibitor, 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP)), but not by N-hexanoyl-D-erythrosphinganine (C6-dihydro-Cer) or sphingosine. Internalization of LDL was also inhibited by C6-Cer in a concentration-dependent manner, but was less pronounced than the effect on HRP internalization (10% versus 40% inhibition with 25 microM C6-Cer), suggesting that ceramide might affect fluid-phase and receptor-mediated endocytosis to different extents. C6-Cer also slowed HRP and LDL transport from endosomes to lysosomes as studied by analysis of endocytic vesicles on Percoll density gradients and induced a redistribution of endocytic organelles as determined by fluorescence microscopy of intact cells using appropriate markers. This resulted in decreased degradation of 125I-labeled LDL in the presence of C6-Cer. These results suggest that endogenous ceramide may modulate endocytosis.
Chen
C S
CS
Carnegie Institution of Washington, Baltimore, Maryland 21210, USA.
Rosenwald
A G
AG
Pagano
R E
RE
D000818:Animals; D016466:CHO Cells; D002518:Ceramides / Q000494:pharmacology*; D006224:Cricetinae; D004705:Endocytosis / Q000187:drug effects*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D015388:Organelles / Q000187:drug effects / Q000378:metabolism
D002518:Ceramides; D008077:Lipoproteins, LDL; D006735:Horseradish Peroxidase