Phosphorylation of an acid-soluble nuclear protein in response to catecholamine in cultured rat cardiocytes

Effect of norepinephrine on the phosphorylation of nuclear proteins was examined in cultured rat cardiocytes. Differential effects of phorbol esters, endothelin and platelet activating factor on the phosphorylation of a nuclear acid soluble fraction were evaluated. A specific phosphorylated nuclear acid soluble protein was identified in response to norepinephrine. The increase in phosphorylation in the norepinephrine-treated cardiocytes is significantly greater than 8 fold (p < 0.001) as compared to the control group. This nuclear acid soluble protein has a high content of serine (> 12%) as well as acidic amino acids (> 20%) which is distinctively different from the histones as analyzed by amino acid composition. The specific phosphorylation of this nuclear protein (Mr 31 Kda) can be induced by norepinephrine within 5 minutes, indicating of an early gene activation event which modulates nucleosomal structure by phosphorylation.