title: Delivery of internalized ricin from endosomes to cisternal Golgi elements is a discontinuous, temperature-sensitive process.
abstract: Galactose-terminating membrane glycoproteins and glycolipids on two established human breast carcinoma cell lines were tagged at 4 degrees C with a ricin-horseradish peroxidase conjugate (Ri-HRP). The cells were then incubated for various periods of time at 37 or 18 degrees C. After fixation and diaminobenzidine cytochemistry, the compartments reached by Ri-HRP were studied by analyzing thin serial sections. In both cell types a highly pleomorphic endosomal system comprising vacuolar elements as well as smaller, sometimes branched, tubular elements (tubular endosomes) was revealed at both 37 and 18 degrees C. At 37 degrees C Ri-HRP was consistently observed in flattened cisterns of the Golgi region in 30-40% of the Golgi complexes examined after 30-60 min of incubation. However, no Ri-HRP reached such Golgi elements at 18 degrees C, even after incubation for 180 min. Moreover, at 18 degrees C the ability of ricin to inhibit protein synthesis was virtually abolished, whereas the effect of diphtheria toxin was reduced much less. Following incubation with a monovalent transferrin-HRP conjugate or with unconjugated HRP, no labeling of cisternal Golgi elements was detected. These data indicate that delivery of galactose-terminating membrane molecules from endosomes to the Golgi complex is a discontinuous, temperature-sensitive process and that this process may be required for optimal ricin A-chain translocation.
mesh_terms: D001943:Breast Neoplasms; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004167:Diphtheria Toxin / Q000378:metabolism / Q000633:toxicity; D004705:Endocytosis; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006735:Horseradish Peroxidase; D006801:Humans; D009940:Organoids / Q000378:metabolism* / Q000648:ultrastructure; D014176:Protein Biosynthesis; D012276:Ricin / Q000378:metabolism* / Q000633:toxicity; D013696:Temperature
chemical_list: D004167:Diphtheria Toxin; D012276:Ricin; D006735:Horseradish Peroxidase