Increase of a surface glycoprotein by cyclic AMP in Chinese hamster ovary cells. Dependence on cell-cell interaction.

Cell surface proteins and glycoproteins of the CHO-K1 clone of Chinese hamster ovary cells were radiolabeled by surface-specific reactions as well as by metabolic incorporation of glycoprotein precursors. After the proteins were separated by two-dimensional gel electrophoresis, they were quantified according to the amount of radioactivity which was associated with individual proteins spots. A glycoprotein of 133,000 daltons (P133-11) wa found to increase severalfold by the elevation of the cytoplasmic level of adenosine 3':5'-cyclic monophosphate. In this paper, we report that the increase of P133-11 was more efficient in dense cultures than in sparse cultures. The use of conditioned medium or frequent medium changes during the treatment with the cyclic nucleotide did not influence the efficiency of the increase of the glycoprotein, indicating that the enrichment or exhaustion of diffusible materials was not responsible for this density-dependent phenomenon. The same conclusion was drawn from an experiment in which the amount of P133-11 was compared between homogeneously plated sparse cultures and cultures containing the same number of cells in the form of colonies with well contacted cells at an average density of 400 cells/colony. The increase of the protein was higher in the latter type of cell cultures. We, therefore, propose that the interaction of surface components upon cell-cell contact plays a role in the expression of P133-11 surface glycoprotein.