Processing inhibition of N-linked sugar chains associated with induction of Fc receptor-mediated phagocytosis in the mouse monocytoid cells.

The concanavalin A staining of cellular glycoproteins and the direct analysis of their sugar chains released by hydrazinolysis revealed that the processing of N-linked sugar chains of some glycoproteins is suppressed by exposure of mouse monocytoid cells P388D1 to dimethyl sulphoxide, which can induce Fc receptor-mediated phagocytosis. To elucidate the significance of altered glycosylation in inducing phagocytosis, the effects of exposure of the cells to processing inhibitors (swainsonine and castanospermine) were examined and it was found that the cells are induced to acquire an ability to ingest IgG-coated sheep red blood cells, depending on the dose of the inhibitors and incubation time. Analysis of the N-linked sugar chains liberated from cellular glycoproteins by hydrazinolysis confirmed that the processing of the sugar chains is suppressed by the two inhibitors as expected. Since no significant alteration was induced in protein synthesis and DNA synthesis after exposure to the inhibitors, it is suggested that the altered glycosylation of cellular glycoproteins may have some direct role in the induction of Fc receptor-mediated phagocytosis. The inhibitors did not affect the binding of the IgG-coated red blood cells to Fc receptors on the cells, non-specific phagocytosis of latex beads, and the contents of lysosomal enzymes, beta-glucuronidase and acid phosphatase. These results suggest that the glycosylation status of cellular glycoproteins influences some specific processes involved in the ingestion of the ligands bound to Fc receptors.