Early Increase in the Phosphorylation of Liver Chromatin Non-Histone Proteins from Thyroidectomized Rats Treated with Triiodothyronine¹²

Abstract

The effect of triiodothyronine (T3) on the endogenous phosphorylation of chromatin nonhistone proteins (NHP) was investigated. Chromatin NHP were extracted from livers of thyroidectomized rats treated with T3 (30 μg/100 g BW) for varying times, and the preparations were then incubated in vitro in a medium containing [γ-32P]ATP. Moreover, because of the complex heterogeneity of these proteins, we analyzed by disc gel electrophoresis the 32P uptake of the individual major classes of phosphorylated NHP. A marked increase in 32P uptake was found not only in chromatin NHP prepared from rats treated with T3 for 2 or 4 consecutive days, but also in NHP preparations obtained from rats sacrificed 3 h after a single injection of T3, accounting for an early effect of the thyroid hormone. Electrophoretic fractionation of the phosphorylated NHP obtained from T3 treated rats provided evidence that for the most effective hormonal treatments, the increased radioisotope uptake into NHP was more evident in some protein fractions than others, indicating a selective action of T3 on the phosphorylation of acidic proteins. Assuming that the modifications obtained in vitro simulate those occurring in physiological conditions, a connection between enhanced NHP phosphorylation induced by T3 and the regulation of genetic expression is suggested.