Abstract
In vivo effects of dexamethasone and cycloheximide on the phosphorylation of nucleolar proteins and the activities of nucleolar protein kinases of rat livers were studied. Phosphorylation of nucleolar proteins was accomplished by incubation of isolated nucleoli with [gamma-32P]ATP at 37 degrees C for 10 min followed by electrophoretic separation and autoradiographic demonstration of phosphorylated proteins. Of several nucleolar phosphoproteins observed in the liver of adrenalectomized rats, the incorporation of 32P into nucleolar 110-kDa proteins was rapidly increased, reaching about 1.8-fold of the adrenalectomized level at 12 h after administration of dexamethasone. In addition, the activities of liver nucleolar protein kinases which were measured using casein or phosvitin as substrates were stimulated similarly by the administration of dexamethasone. It was found by DEAE-Sephadex column chromatography that nucleolar protein kinases were separated into NI and NII, the activities being increased about 35 and 80% by dexamethasone treatment (12 h), respectively, and that the enhancements were completely abolished by 1-h treatment of cycloheximide. The injection of cycloheximide also suppressed the hormone-induced enhancement of 32P incorporation into 110-kDa proteins but did not reduce the amount of the proteins at least until 2 h. Evidence was obtained indicating that the phosphorylation of the nucleolar 110-kDa proteins is accomplished primarily by protein kinase NII. These results suggest that continuous synthesis of protein(s) is necessary for glucocorticoid-induced enhancement of phosphorylation of 110-kDa proteins of liver nucleoli and that the nucleolar protein kinase NII is involved in the glucocorticoid-induced short-lived protein(s).
Highlights
In vivo effects of dexamethasone andcycloheximide this problem
The activities in rat prostates,we have recently found that administration of liver nucleolar protein kinases which were meas- of androgen to castrated rats resulteidn an increase of phosured using caseinor phosvitin as substrates were stim- phorylation of nucleolar 110-kDa proteins as well as RNA
Ulated by the administration of dexametha- polymerase I activity and that the enhancemweanst abolished sone. It was found by DEAE-Sephadex column chro- by the administration of cycloheximide a few hours before matography thatnucleolar protein kinases weresepa- death (Suzuki et al, 1984, 1985). This raised the possibility rated into NI and NII, the activities being increased that short-lived protein(s) is responsiblefor the hormoneabout 35 and 80%by dexamethasone treatment (12 h), induced phosphorylation of the nucleolar 110-kDa proteins respectively, and that the enhancements were com- which is presumably related to the hormone-dependent synpletely abolished by l - h treatment of cycloheximide. thesis of pre-rRNA (Suzuki et al, 1985)
Summary
In vivo effects of dexamethasone andcycloheximide this problem. Some groups of the workers are of the opinion on the phosphorylation of nucleolar proteins and the that glucocorticoids can directly stimulate the transctiption activities of nucleolar protein kinaseosf rat livers wereof rDNA’ (Frey and Seifart, 1982; Scheidereit et al, 1986), studied. The activities in rat prostates,we have recently found that administration of liver nucleolar protein kinases which were meas- of androgen to castrated rats resulteidn an increase of phosured using caseinor phosvitin as substrates were stim- phorylation of nucleolar 110-kDa proteins as well as RNA ulated by the administration of dexametha- polymerase I activity and that the enhancemweanst abolished sone. It was found by DEAE-Sephadex column chro- by the administration of cycloheximide a few hours before matography thatnucleolar protein kinases weresepa- death (Suzuki et al, 1984, 1985). These resultsuggest that continuous synthesisof protein(s) is necessary for glucocorticoid-induced enhancement of phosphorylation of 110-kDa proteins of liver nucleoli and that thenucleolar protein kinase NII is involvedin the glucocorticoid-induced short-
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