PMID: 6411711Sep 10, 1983Paper

Distinct patterns of cytoplasmic protein phosphorylation related to regulation of synthesis and release of prolactin by GH cells.

The Journal of Biological Chemistry
A Sobel, A H Tashjian

Abstract

The actions of thyrotropin-releasing hormone (TRH) on protein phosphorylation in the GH4C1 clonal strain of rat pituitary cells were examined by two-dimensional polyacrylamide gel electrophoresis and related to the ability of this tripeptide to stimulate prolactin (PRL) synthesis and release, respectively. Between 2 and 10 min after addition of the hormone, TRH increased the rate of phosphorylation of a small number of specific cytoplasmic proteins. The dose-response characteristics for TRH-induced protein phosphorylation were closely similar to those for its biological actions (ED50 congruent to 2 nM). TRH did not stimulate protein phosphorylation in the related GH12C1 cell strain which lacks TRH receptors. The proteins modified by TRH treatment were present in low amounts in the cell; they were not detectable by silver staining of the gels, except for protein 1 (Mr = 80,000) whose TRH-induced conversion from its unphosphorylated to its more acidic phosphorylated form was observed directly on silver-stained gels. Two distinct sets of phosphoproteins were identified among the seven affected by TRH: set I, five proteins whose phosphorylation was increased only by agents which stimulated PRL synthesis; and set II, two proteins wh...Continue Reading

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