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Phosphorylation of a Group of Proteins Related to the Physiological, Multihormonal Regulations of the Various Cell Types in the Anterior Pituitary Gland^*

INSERM U153 - CNRS URA 614 75005 Paris France
INSERM U159 75014 Paris, France

Address requests for reprints to: Dr. Laura Beretta, INSERM U. 153,17 rue du fer a Moulin, 75005 Paris, France.

Abstract

We previously identified a group of cytoplasmic phosphoproteins whose phosphorylation could be related to the multihormonal regulation of PRL in the homogeneous tumorderived GH cell lines (set of proteins 1–11) and in heterogeneous normal anterior pituitary cells in culture (set of proteins 1–15). In normal cells, a mixture of hypothalamic hormones induced, like the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, stronger phosphorylation changes than TRH alone. Proteins of the set 1-15 are therefore likely to be present also in the nonmammotrophic anterior pituitary cell types, where their phosphorylation can be regulated by the hormones specific of the cell type considered. This interpretation is confirmed by the presence of the same proteins in cells of the corticotroph-like AtT-20/D16 cell line and the regulation of their phosphorylation by CRF.

The same phosphoproteins were also detected in non dissociated anterior pituitary tissue from ovariectomized rats. Their phosphorylation was regulated by various hormones and other extracellular agents in a way similar to their regulation in anterior pituitary cells in culture. A 5-day estradiol implant pretreatment of the ovariectomized rats, which stimulates the anterior pituitary gland both directly and indirectly, resulted in a very high level of basal phosphorylation of proteins 1–15. Only very little further stimulation was achieved by the addition of exogenous hypothalamic hormones, indicating that the actual physiological regulatory pathways are the same as those unraveled in the various cell culture model systems.

In conclusion, phosphorylation of proteins 1–15 1) can be related to the multihormonal regulation of the various anterior pituitary cell types in culture and 2) corresponds to intracellular molecular mechanisms actually involved in the physiological regulations of pituitary functions in the intact anterior pituitary gland.

Footnotes

^* This work was supported by funds from the Institut National de la Sante et de la Recherche Medicale, the Centre National de la Recherche Scientifique, the Ministere de la Recherche et de la Technologie, and the Association Francaise contre les Myopathies.

Received April 10, 1989.

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