REGULATION OF G-PROTEIN MESSENGER-RNA LEVELS BY THYROLIBERIN, VASOACTIVE-INTESTINAL-PEPTIDE AND SOMATOSTATIN IN PROLACTIN-PRODUCING RAT PITUITARY-ADENOMA CELLS

We have investigated the regulation of mRNA levels of alpha- and beta-subunits of guanine nucleotide-binding regulatory proteins (G proteins) by peptide hormones in prolactin producing rat pituitary adenoma cells (GH3 cells) in culture. The cells were treated with thyroliberin (1-mu-M), vasoactive intestinal peptide (1-mu-M) or somatostatin (10-mu-M) for 6 to 48 hours. Thyroliberin and vasoactive intestinal peptide increased the levels of G(s)alpha G0-alpha, G(i-2)alpha, G(i-3)alpha, G(x)alpha, G-beta-36 and G-beta-35 mRNAs. The effect of vasoactive intestinal peptide was however earlier and more pronounced. G(i-2)alpha mRNA levels showed the quantitatively largest alterations. Somatostatin upregulated G(s)alpha and downregulated G(o)alpha and G(i-2) mRNAs. G protein mRNAs for G(i-2)alpha and G(o)alpha were increased by exposure of the cells to a medium devoid of serum. We conclude that G protein mRNA levels are subjected to alterations by hormones that act through the corresponding G proteins in the regulation of prolactin synthesis and secretion.