Differential effects of cyclic adenosine-3′, 5′-monophosphate on phosphorylation of rat liver nuclear acidic proteins

Abstract

The effects of cyclic AMP on the phosphorylation of different acidic proteins of rat liver nuclei were examined in vivo and in vitro. N 6,O 2′-dibutyryl cyclic AMP selectively stimulated in vivo phosphorylation of specific nuclear proteins more than twofold within 15 min after injection. Cyclic AMP caused only a small stimulation of phosphorylation of acidic proteins in isolated nuclei but the stimulation was selective for specific proteins. When isolated nuclear acidic proteins were incubated with a soluble cyclic AMP-dependent protein kinase, the cyclic nucleotide stimulated total phosphorylation about 1.7-fold. These results support the view that the regulatory effects of cyclic AMP may involve phosphorylation of acidic proteins associated with DNA in the chromatin.