Binding of cyclic nucleotides with proteins in malignant and adenosine cyclic 3':5'-monophosphate-induced "differentiated" neuroblastoma cells in culture.

The binding of adenosine cyclic 3':5'-monophosphate (cyclic AMP) with soluble (100,000 X g supernatant), pellet, and total homogenate proteins from cyclic AMP-induced "differentiated" mouse neuroblastoma cells increased by about two-fold. The extent of binding with soluble proteins was higher than that with pellet proteins. The binding of cyclic AMP with soluble proteins from 5'-adenosine monophosphate-treated, serum-free medium-treated, sodium butyrate-treated, 6-thioguanine-treated, or X-irradiated neuroblastoma cells did not significantly change. When the soluble proteins containing bound cyclic [3H]AMP were filtered through a Sephadex G-25 column, the relative amount of protein-bound cyclic [3H]AMP in differentiated cells was greater than that in malignant cells, but the amount of free cyclic [3H]AMP was correspondingly less. The electrophoretic characteristics of cyclic AMP-binding proteins of differentiated and malignant cells were identical. There were two binding peaks, but the extent of binding at each peak was relatively high in differentiated neuroblastoma cells. An increase in cyclic AMP binding occurred 24 hr after treatment of neuroblastoma cells with prostaglandin E1. This increase was completely blocked by cycloheximide but not by actinomycin D. The binding was heat labile and sensitive to protease action. These data indicate that the increase in binding in differentiated cells is due to an elevation in the levels of binding proteins. The binding of cyclic AMP with soluble proteins from rat glial cells and mouse L-cells did not significantly change after treatment with prostaglandin E1 or an inhibitor of cyclic AMP phosphodiesterase. Cyclic AMP and guanosine cyclic 3':5'-monophosphate bind with the same proteins, but cyclic AMP has about 10-fold higher binding affinity than does guanosine cyclic 3':5'-monophosphate.