Biosynthesis of the D2-cell adhesion molecule: post-translational modifications, intracellular transport, and developmental changes.
Posttranslational modifications and intracellular transport of the D2-cell adhesion molecule (D2-CAM) were examined in cultured fetal rat neuronal cells. Developmental changes in biosynthesis were studied in rat forebrain explant cultures. Two D2-CAM polypeptides with Mr of 187,000-210,000 (A) and 131,000-158,000 (B) were synthesized using radiolabeled precursors in cultured neurons. A and B were found to contain only N-linked complex oligosaccharides, and both polypeptides appeared to be polysialated as determined by [14C]mannosamine incorporation and precipitation with anti-polysialic acid antibody. The two polypeptides were sulfated in the trans-Golgi compartment and phosphorylated at the plasma membrane. D2-CAM underwent rapid intracellular transport, appearing at the cell surface within 35 min of synthesis. A and B were shown to be integral membrane proteins as seen by radioiodination by photoactivation employing a hydrophobic labeling reagent. In rat forebrain explant cultures, D2-CAM was synthesized as four polypeptides: A (195,000 Mr), B (137,000 Mr), C (115,000 Mr), and a group of polypeptides in the high molecular weight region (HMr) between 250,000 and 350,000. Peptide maps of the four polypeptides yielded similar patterns. Biosynthesis of C and HMr increased with age, relative to A and B. A and B were sulfated in embryonic brain, however, sulfation was not noticeable at postnatal ages. Phosphorylation, on the other hand, of A and B was observed at all ages examined. We suggest that D2-CAM function may be modified during development by changes in the relative synthesis of the different polypeptides, as well as by changes in their glycosylation and sulfation.
D000818:Animals; D000954:Antigens, Surface / Q000235:genetics* / Q000302:isolation & purification; D001692:Biological Transport; D001921:Brain / Q000166:cytology / Q000196:embryology*; D015815:Cell Adhesion Molecules; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000196:embryology; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008970:Molecular Weight; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D009924:Organ Culture Techniques; D011499:Protein Processing, Post-Translational; D051381:Rats
D000954:Antigens, Surface; D015815:Cell Adhesion Molecules