title: Cyclic AMP enhances gene expression, synthesis and release of newly synthesized alpha and luteinizing hormone beta subunits in cultured rat anterior pituitary cells.
abstract: We have previously demonstrated that GnRH stimulates the synthesis of both the ? and LH? polypeptide chains, an effect which was reproduced in a non additive manner by direct activation of protein kinases A and C, and abolished by actinomycin D. In the present study, we examined the effects in monolayer cultures from rat anterior pituitary cells of 8-Br-cAMP and cholera toxin, on ? and LH? subunit mRNA levels and in parallel the synthesis and release of the subunits. RNA blot hybridization analysis with cDNA probes demonstrated that ? and LH? mRNA levels increased by 8.9- and 4.7-fold, respectively, after a 5 h-incubation in the presence of 6 nM cholera toxin and 7.1- and 2.9-fold in the presence of 1.5 mM 8-Br-cAMP. Under the same conditions, [(35)S]methionine incorporation into ? and LH? subunits was optimally stimulated, by 2.8-fold and 1.7 to 2.2-fold, respectively, whether the cAMP analogue 8-Br-cAMP or cholera toxin, an endogenous cAMP generator, were employed. Further, in addition to synthesis, 8-Br-cAMP appeared to increase release of neosynthesized ? and LH? polypeptides, and in this respect, 8-Br-cAMP was more effective than GnRH. In contrast, 8-Br-cAMP had a weak, non significant effect compared to GnRH on the release of total radioimmunoassayable LH in the cell media. These data provide the first direct evidence for a stimulation of ? and LH? gene expression by cyclic AMP, which accounts for an increase in subunit synthesis. They suggest that cAMP, as previously shown for diacylglycerols, is a potent candidate for an intracellular mediator of the GnRH effects on subunit synthesis and that it is largely responsible for sustained (protein synthesis-dependent) LH release.
authors.affiliation: Laboratoire des Hormones Polypeptidiques, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France.
authors.forename: A
authors.initials: A
authors.lastname: Starzec
authors.forename: M
authors.initials: M
authors.lastname: Moumni
authors.forename: G
authors.initials: G
authors.lastname: D'Angelo-Bernard
authors.forename: Y
authors.initials: Y
authors.lastname: Lerrant
authors.forename: M
authors.initials: M
authors.lastname: Jutisz
authors.forename: R
authors.initials: R
authors.lastname: Counis