20-Hydroxyecdysone induced aggregation of Drosophila S3 cells is inhibited by antibodies to a hormone-dependent extracellular glycoprotein

The S3 cell line of Drosophila exhibits numerous responses to the molting hormone 20-hydroxyecdysone, including mitotic arrest, cell aggregation and extensive changes in cell surface and extracellular glycoproteins. We have produced polyclonal antibodies to a major hormone induced extracellular glycoprotein to investigate the role of this molecule in cell aggregation. This glycoprotein with a molecular weight of 110 kD (P110) is found primarily in the culture medium of hormone-induced cells. Upon reduction, the electrophoretic mobility of P110 is decreased, indicating the presence of internal disulfide bonds. Results from treatment of medium proteins with a cross-linking reagent indicate that the molecule is part of a higher molecular weight oligomer (300–400 kD). Fab fragments of anti P110 effectively inhibit the reaggregation of hormone-treated S3 cells, while preimmune Fab fragments have no effect. On the basis of these results, we propose that the P110 glycoprotein complex in the medium of hormone-treated cells functions in hormone-dependent cell-cell adhesion.