Induction of distinct phenotypes in clonal and variant GH4 pituitary cells

GH cells are a widely used cell strain for the investigation of mechanisms regulating hormone release and synthesis. This report identifies two inducible phenotypes of the GH4 clone (epithelioid and motile) which may extend studies of this well-characterized cell line to different stages of pituitary cell development. GH4C1 cells treated in suspension with epidermal growth factor plus tetradecanoylphorbol acetate aggregate to form large epithelioid colonies with extensive cell-to-cell and cell-to-substratum adhesion. These cells cease replicating within 48 h, increase 50% in cell volume, and synthesize 40-fold more prolactin. A GH4C1 variant with enhanced substratum adhesion and little or no cell-to-cell adhesion (GH4S1), responds differently to this treatment. These cells cease replicating immediately, show increased cell separation, develop leading lamellae, and display locomotory activity. Each phenotype coexists in mixed cultures of GH4C1 and GH4S1 cells. This indicates that the different inducible response of the variant does not result from autocrine secretion. A molecular basis for cell-to-cell adhesion in GH4 cells was investigated. GH4C1, but not the variant cells, express a 180 kDa immunoreactive protein indistinguishable from an isoform of the neural cell adhesion molecule. Therefore the absence of cell-to-cell adhesion and inability to develop extensive cell-to-cell adhesion characteristic of the epithelioid phenotype may result from altered expression of the neural cell adhesion molecule. These findings are important because they have defined an in vitro approach to investigate genetic and cellular changes associated with the development and progression of pituitary cell phenotype.

Pituitary mammosomatotroph adenomas develop in old mice transgenic for growth hormone-releasing hormone

It has been shown that mice transgenic for human growth hormone-releasing hormone (GRH) develop hyperplasia of pituitary somatotrophs and mammosomatotrophs, cells capable of producing both growth hormone and prolactin, by 8 months of age. We now report for the first time that old GRH-transgenic mice, 16 to 24 months of age, develop pituitary mammosomatotroph adenomas. These findings provide conclusive evidence that protracted stimulation of secretory activity can cause proliferation, hyperplasia and adenoma of adenohypophysial cells.

Interactions of signal peptides with signal-recognition particle

The mechanisms whereby isolated or synthetic signal peptides inhibit processing of newly synthesized prolactin in microsome-supplemented lysates from reticulocytes and wheat-germ were investigated. At a concentration of 5 microM, a consensus signal peptide reverses the elongation arrest imposed by the signal-recognition particle (SRP), and at higher concentrations in addition inhibits elongation of both secretory and non-secretory proteins. A photoreactive form of a synthetic signal peptide cross-links under u.v. illumination to the 54 kDa and 68 kDa subunits of SRP, whereas the major cross-linked protein produced after photoreaction of rough microsomes is of 45 kDa. As SRP-mediated elongation arrest is unlikely to be essential for translocation, it is suggested that signal peptides may interact with components other than SRP in the translation system in vitro.

Changes in a mammalian signal sequence required for efficient protein secretion by yeasts

A plasmid-encoded gene for a hybrid pre-protein containing most of the bovine prolactin signal peptide (SpPRL) fused to the mature sequence of yeast invertase (IVT) was expressed and the product was processed and secreted by yeast. However, the level of IVT activity was reduced about six-fold when compared to that obtained with the wild type (wt) invertase signal peptide (SpIVT). When the 5'-untranslated sequence of the hybrid mRNA was truncated by 29 nucleotides, a 2.5-fold increase in secreted IVT was observed. Replacement of the PRL codons with preferred yeast codons did not result in any improvement in the production of secreted IVT. An increase in IVT activity to the level observed with the wt SpIVT was obtained by replacement of the Gly residue located between the N terminus and the central lipophilic region of the SpPRL by Ala. Since this amino acid replacement results in a higher probability of the SpPRL assuming an alpha-helical conformation, it suggests that the secondary structure of this region is important in recognition by the yeast secretory apparatus.

Expression of biologically active rat prolactin in mammalian COS-1 cells

Rat prolactin (PRL) cDNA was constructed in mammalian expression vector, pSVL. Transient expression of rat PRL was performed in COS-1 cells by the DEAE-dextran method. The production of recombinant rat PRL started within 48 h from the cells and reached the level of 1.0-1.5 micrograms/ml/5 x 10(5) cells. The molecular size of recombinant rat PRL was the same as that of standard rat PRL (Mw: 23,000), suggesting successful removal of the signal peptide. The radioimmunoassay and isoelectric focusing analysis showed that recombinant rat PRL has almost the same immunological and biochemical characteristics as those of standard rat PRL. As biological tests, receptor-binding activity, Nb 2 node lymphoma cell growth activity, and mammary gland stimulating activity were examined. The radioreceptor assay showed that recombinant rat PRL has binding activity to mammary microsomal membrane similar to that of standard rat PRL. Recombinant rat PRL also stimulated the growth of Nb 2 lymphoma cells as standard rat PRL. Finally it was shown that recombinant rat PRL promotes the synthesis of the secretory materials in the lumen of mouse mammary gland with the same potency as that of standard rat PRL. In conclusion, recombinant rat PRL, which was produced in mammalian cells in the present experiment, has immunological, biochemical and biological characteristics similar to those of standard PRL, and has full bioactivity.

Long-term culture of rat mammotrope and somatotrope subpopulations separated on continuous Percoll density gradients: effects of dopamine, TRH, GHRH and somatostatin

Normal adult female rat mammotrope and somatotrope subpopulations were separated on continuous Percoll density gradients according to differences in their density. Viable cells were recovered in 16 fractions. The cells from each fraction were cultured during 7 days after which period 4-h incubations were performed. rPRL secretion per cell increased towards the higher density fractions. No major difference in TRH, dopamine and somatostatin responsiveness was observed between mammotropes that were recovered in the different gradient fractions. In addition, no differences in somatostatin responsiveness between the somatotrope cells in the different gradient fractions were observed. However, somatotropes that were recovered in the highest density region of the gradient appeared to be more responsive to GHRH than the lower density somatotropes. In the various gradient fractions there were no paradoxical effects of TRH and dopamine on rGH release and of GHRH on rPRL release.

CONCLUSIONS

1. In long-term cultures there is no evidence for functionally different subpopulations of mammotropes and somatotropes, separated according to differences in their density, with regard to dopamine and TRH responsiveness and with regard to somatostatin responsiveness, respectively. 2. There is no evidence for a (mammosomatotrope?) subpopulation of cells showing paradoxical responses of PRL or GH release to GHRH and dopamine or TRH, respectively.

Prolactin messenger ribonucleic acid levels, prolactin synthesis, and radioimmunoassayable prolactin during the estrous cycle in the golden Syrian hamster

The purpose of this study was to observe the molecular dynamics of pituitary prolactin (PRL) gene expression during the estrous cycle of the Golden Syrian hamster. PRL messenger ribonucleic acid (mRNA) levels, PRL synthesis (3H-PRL in the incubation media or incubated pituitary after a 3 hr incubation with 3H-leucine), and radioimmunoassayable (RIA) PRL (in the incubation media or incubated pituitary after the 3 hr incubation) were measured in the morning (0930-1100 hr) on each day of the cycle. We observed that all of these PRL indices declined or did not change from Day 2 to Day 3 of the cycle. From Day 3 to Day 4 (proestrus), however, PRL mRNA levels increased 33-38% and media 3H-PRL increased 32-42%, while there were no significant changes in pituitary 3H-PRL, or RIA-PRL in the media or pituitary. From Day 4 to Day 1 (estrus) there was a reciprocal change in the levels of 3H-PRL in the pituitary vs. the media, with the former increasing 37-50% and the latter decreasing 25-32%. Pituitary RIA-PRL also increased 45-64% from Day 4 to Day 1 while media RIA-PRL did not change. These data are consistent with the following hypothesis: On the morning of proestrus (Day 4) in the hamster, PRL mRNA levels are elevated compared to those on Day 3, signaling an increase in PRL synthesis. This newly synthesized PRL is shunted into a "readily releasable" pool on the morning of Day 4 (contributing to the afternoon surge of serum PRL), and into a "preferentially stored" pool by the morning of Day 1 (for release in response to cervical stimulation and use as a luteotrophin to maintain early pregnancy should fertilization occur).

Ontogeny of prolactin mRNA in the rat pituitary gland as evaluated by in situ hybridization

We have studied the ontogeny of prolactin (PRL) messenger RNA (mRNA) in male and female rats. Quantitative in situ hybridization was performed on sections of fixed pituitaries using a 32S-labeled PRL cDNA probe. With this technique, hybridization signal was first detected on day 19 of gestation. The PRL mRNA levels were very low in foetuses and newborn animals. Higher PRL mRNA levels were found in 5-day-old animals. Thereafter, mRNA concentrations regularly increased to reach a plateau at 60 and 90 days of age in males and females, respectively. Sexual dimorphism was first observed in 20-day-old animals, the PRL mRNA levels being higher in the female than in the male. This difference in PRL mRNA became more marked after puberty such that in 90-day-old animals the amounts of PRL mRNA in females were 2.7 times those observed in males. Since sexual dimorphism in PRL mRNA levels occurs well before sexual dimorphism in PRL secretion, which takes place first during puberty, it is suggested that during sexual maturation PRL secretion is regulated translationally as well as transcriptionally.

Hormonal regulation of human endometrial stromal cells in culture: an in vitro model for decidualization

Stromal cells derived from proliferative or secretory human endometria, cultured in the absence of steroid hormones, grew as monolayers that showed only occasional areas of immunoreactive fibronectin and did not produce detectable levels of prolactin (PRL) or laminin. Treatment with physiological doses of estradiol and progesterone induced PRL production and stimulated cell proliferation, resulting in multilayering with an increase of the saturation density. Electron microscopy showed the development of gap junctions, whereas immunofluorescence revealed a dense pericellular matrix containing fibronectin and laminin. These findings show that human endometrial stromal cells in culture respond to physiological doses of ovarian hormones with ultrastructural, proliferative, and biochemical changes that are characteristic of decidualization in vivo. This culture system thus provides an in vitro model for human decidualization.

Calcium regulation of prolactin gene expression: opposing effects of extracellular CaCl2 and Ca2+ ionophores

Previous studies have demonstrated that the high basal level of transcription of the rat PRL gene in pituitary tumor GH3 cells is dependent on [CA2+]e. In the present study, we have extended these findings by examining the effects of the Ca2+ ionophores, A23187 and ionomycin, on [Ca2+]i, and on PRL mRNA levels and glucose-regulated protein (GRP) mRNA levels in GH3 cells cultured in a low Ca2+, serum-free medium (SFM). Using digital imaging microscopy of individual Fura 2-loaded GH3 cells in SFM plus 0.4 mM CaCl2, extranuclear and nuclear [Ca2+] were both about 70 nM. Addition of 600 nM ionomycin increased these levels by 10-fold within minutes, and by about 45-fold after 120 min. As previously published, addition of 0.4 mM CaCl2 to GH3 cells cultured in SFM significantly increased PRL mRNA, and had little or no effect on GRP78 and GRP94 mRNA after 16 h. Addition of 0.4 mM CaCl2 plus 100 nM A23187 significantly increased GRP78 and GRP94 mRNA. Surprisingly, the Ca2+ ionophore significantly inhibited PRL gene expression below that obtained in 0.4 mM CaCl2 without A23187. This same pattern of stimulation of GRP78 gene expression, but inhibition of PRL gene expression, was observed with 125 and 600 nM ionomycin. Both Ca2+ ionophores had no effect on histone 3 mRNA, and A23187 depressed PRL gene expression at a concentration (50 nM) that did not affect protein synthesis. Although A23187 reproducibly lowered PRL mRNA levels, it slightly inhibited its degradation in cells in which RNA synthesis was blocked by actinomycin D.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of prolactin secretion by dopamine and thyrotropin-releasing hormone in lactating rat adenohypophyses: influence of intracellular age of the hormone

We studied the effect of dopamine (DA) on the rate of processing of PRL after biosynthesis and, with TRH, on the secretion of PRL of different intracellular ages. In these studies anterior pituitary (AP) PRL of lactating rats was pulse labeled either in vivo with [3H]leucine (3 microCi/g BW, injected iv 0.2, 1, 4, 8, 16, or 24 h before removing the AP for incubation) or in vitro with [3H]- or [14C]leucine (5 microCi/ml Krebs-Ringer bicarbonate buffer for 5 min), followed by a chase period of 15-240 min of AP fragments in medium 199. Also, to determine if endogenous DA influenced PRL synthesis, the rate of [14C]-leucine incorporation into PRL was determined in AP fragments from alpha-methyl-p-tyrosine (alpha MpT)-pretreated (200 mg/kg BW) rats. Tissue and medium PRL levels were quantified by polyacrylamide gel electrophoresis densitometric and liquid scintillation techniques. In APs from alpha MpT-treated animals [14C]-leucine incorporation into PRL increased about 30% above control values after the 5-min pulse period, and the release of labeled PRL from alpha MpT-treated APs was about 80% higher than control values after 4 h of incubation. On the other hand, when DA (50 microM) was present in the incubation medium, AP concentrations and release of in vitro synthesized [3H]PRL were significantly decreased (45-55% compared to control values; P less than 0.001). The [3H]PRL concentration, but not that of total, i.e. unlabeled PRL, fell within the AP as the time from in vivo pulse labeling to removal of the pituitary gland increased from 8 to 24 h, thus suggesting that a loss of labeled hormone occurred as it aged within the gland. Also, it was found that biosynthesis and/or processing of PRL were markedly depressed in APs from rats whose pups were removed for 24 h. Under basal conditions, in vitro secretion of [3H]PRLs during the first 30-60 min of incubation consisted primarily of mature [3H]PRL, i.e. those labeled 4 and 8 h previously, whereas newly synthesized (labeled 0.2 and 1 h previously) and old [3H]PRL (labeled 16 and 24 h previously) were secreted at much lower rates. These data confirm previous in vivo and in vitro results on the sequential release of different age PRLs. DA (17 microM) had a significantly greater inhibitory effect on newly synthesized and older stored PRL than on PRL labeled 4-8 h previously. The converse was true with regard to the PRL stimulatory effects of TRH; it provoked greater stimulation of PRL labeled 4-8 h before incubation, thus suggesting an interdependence of the actions of DA or TRH with intracellular age of the hormone.

Relative importance of newly synthesized and stored hormone to basal secretion by growth hormone and prolactin cells

It is generally accepted that under basal conditions there is preferential release of newly synthesized hormone by a number of endocrine cell type, including those that secrete GH or PRL. However, the cellular basis for this phenomenon along with the relative contribution of stored hormone to basal secretion has yet to be clearly established. In the present study, we employed reverse hemolytic plaque assays to monitor basal and stimulated release of GH and PRL from individual cells in which de novo protein synthesis had been blocked. Monodispersed pituitaries from adult male rats were cultured for 21 h in the absence or presence of maximally effective doses of puromycin (100 microM) or cycloheximide (36 microM) and were then subjected to separate plaque assays for GH or PRL. Treatment with puromycin reduced the percentage of GH or PRL secretors (plaque formers) by about half. Coincubation with stimulatory secretagogues did not increase the percentages of GH or PRL secretors in control cultures, but returned the proportion in puromycin-treated cells to normal, demonstrating that cells which failed to secrete basally could still release hormone from their stored pools when stimulated. Very similar results were obtained when these experiments were repeated with cycloheximide. Taken together, these results demonstrate that only a fraction of the cells that release GH or PRL are dependent upon newly synthesized hormone for basal secretion; the remainder appear capable of mobilizing stored hormone for this purpose even in the absence of stimulation.

Suppression of prolactin gene expression in GH cells correlates with site-specific DNA methylation

Prolactin- (PRL) producing and nonproducing subclones of the GH line of (rat) pituitary tumor cells have been compared to elucidate the regulatory mechanisms of PRL gene expression. Particular emphasis was placed on delineating the molecular basis of the suppressed state of the PRL gene in the prolactin-nonproducing (PRL-) GH subclone (GH(1)2C1). We examined six methylatable cytosine residues (5, -CCGG- and 1, -GCGC-) within the 30-kb region of the PRL gene in these subclones. This analysis revealed that -CCGG-sequences of the transcribed region, and specifically, one in the fourth exon of the PRL gene, were heavily methylated in the PRL-, GH(1)2C1 cells. Furthermore, the inhibition of PRL gene expression in GH(1)2C1 was reversed by short-term treatment of the cells with a sublethal concentration of azacytidine (AzaC), an inhibitor of DNA methylation. The reversion of PRL gene expression by AzaC was correlated with the concurrent demethylation of the same -CCGG- sequences in the transcribed region of PRL gene. An inverse correlation between PRL gene expression and the level of methylation of the internal -C- residues in the specific -CCGG-sequence of the transcribed region of the PRL gene was demonstrated. The DNase I sensitivity of these regions of the PRL gene in PRL+, PRL-, and AzaC-treated cells was also consistent with an inverse relationship between methylation state, a higher order of structural modification, and gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis of the secreted 24 K isoforms of prolactin

PRL exists within the mammotroph population in a number of different molecular forms. Several of these forms are best described as isoforms, as they have the same mol wt (24 K), but differ in their net charges. In this study we have used in vitro translation assays to ascertain the number of 24 K translation products of normal pituitary messenger RNA (mRNA), and, finding only one, have used both in vitro translation assays and subcellular fractionation to determine the intracellular site of the posttranslational modification of this single translation product. Translation of mRNA from normal pituitary tissue or GH3 cells resulted in the apparent production of a number of pre-PRLs, but in only a single rough microsome-processed form of PRL, 24 K isoform 2. Longer term translation assays utilizing a variety of isotopes failed to show any evidence for rough microsomal posttranslational modification of isoform 2. Subcellular fractionation, using a discontinuous sucrose gradient, however, produced a membrane-bound large secretory granule fraction which, when isolated, contained essentially only isoform 2, and which had the capacity to convert isoform 2 to isoforms 3 and 3' by posttranslational phosphorylation.

Calcium induction of the mRNAs for prolactin and c-fos is independent of protein kinase C activity

Ca2+ is a strong regulator of the expression of a limited number of eukaryotic genes, including prolactin and c-fos. However, little is known about the cellular signal transduction pathways involved in the action of this ion on specific gene expression. The Ca2+-dependent enzyme protein kinase C has been implicated in other transcriptional pathways regulating the prolactin and c-fos genes. We therefore employed down-regulation of protein kinase C in rat pituitary cells to investigate whether this enzyme is involved in Ca2+ regulation of expression of either of these genes. Exposure of Ca2+-deprived GH3 cells to this ion in the presence of the Ca2+ channel modulator Bay K8644 yielded large increases in the mRNAs for both prolactin and c-fos. Incubation of cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) yielded a 7- to 15-fold decrease in the enzymatic activity of C kinase assayed in vitro, but little or no effect on Ca2+ stimulation of cellular levels of either mRNA. The latter observation was apparently not due simply to an inability of TPA to down-regulate the gene-regulatory activity of kinase C in intact GH3 cells, since this phorbol ester blocked the stimulation by platelet-derived growth factor of cellular levels of c-fos mRNA. TPA treatment also yielded no significant effect on the kinetics of the Ca2+-stimulated accumulation of either mRNA, implying that kinase C is not required at any stage of the Ca2+ induction of these two genes.

[Changes in the prolactin level under the effect of pulsatile infusion of gonadotropin releasing hormone]

Plasma prolactin levels were measured in 18 GnRH loading tests and, in 24 cycles involving treatment with GnRH. During 17 GnRH loading tests the prolactin levels production remained virtually unchanged, the individual GnRH pulses not raising the prolactin level. In one case the GnRH loading test led to a considerable rise in prolactin level, which is considered to be a pathological prognostic sign as concerns subsequent GnRH treatment. During unsuccessful pulsatile GnRH treatment, the prolactin secretion in monotonous, while treatment resulting in ovulation, even in hyperprolactinaemia cases, is accompanied by higher prolactin levels in the preovulation and luteal periods than in the early follicular phase.

Pituitary immediate release pools of growth hormone and prolactin are preferentially refilled by new rather than stored hormone

Pituitary stores of rat GH (rGH) and PRL (rPRL) are divisible into immediately releasable and more stable compartments representing either compartmentalized hormone within individual cells of a homogeneous population or responses of specialized cell subsets in a functionally heterogeneous population. In addition, newly synthesized rGH and rPRL can be processed either into intracellular storage or toward direct release. Fractional assignment of new hormone to these two paths can be influenced in the somatotroph by GHRH and may also represent either intracellular processes or functional heterogeneity of cells. We investigated the source, newly synthesized or stored, of hormone refilling the somatotroph and lactotroph immediately releasable pools (IRP) after their discharge by 21 mM potassium ion, 1 mM (Bu)2cAMP, 3 nM human GHRH-44, or 3 microM prostaglandin E1. Experiments were performed using perifused pituitary fragments exposed sequentially to [14C]- and [3H]leucine in association with stimulation by two 30-min pulses of the same secretagogue. Therefore, only [14C]hormone was available for release by the first stimulus, whereas both [14C]- and [3H]hormone were available for release by the second stimulus. Analysis was by specific immunoprecipitation. The first episode of stored [14C]rGH release exceeded the second episode of stored [14C]rGH release in response to each secretagogue. However, release of newly synthesized [3H]rGH in response to the second episode of stimulation exceeded the simultaneous release of stored [14C]rGH while matching or exceeding the [14C]rGH release that had occurred in the same experiment in response to the first episode of stimulation. Refilling both GH and PRL IRP stores drew primarily upon newly synthesized hormone, but with different secretagogue-specific patterns. These data confirm differential handling of new and stored rGH and rPRL within the pituitary. They are consistent with either (1) the enhanced shunting of newly synthesized hormone to IRPs within cells that are capable of compartmentalized intracellular hormone storage, or (2) the relatively complete discharge of a subset of somatotrophs and lactotrophs that are specialized to deliver pulsed hormone release, after which they are refilled by newly synthesized hormone.

Absence of progestational activity of oral spironolactone

Menstrual irregularity is a recognized side effect of spironolactone when used as a treatment for hirsutism in women. This effect has been attributed to the progestational activity of spironolactone observed in animal models. However, when oral spironolactone was given to women with appropriately estrogen-primed endometrium, secretory transformation of the endometrium was absent in comparison with control cycles. When control cycles were repeated with the addition of spironolactone, a decidualized endometrial response was seen. These findings suggest that spironolactone at clinically used dosages does not act as a progestin or an antiprogestin on the human endometrium.

Expression of biologically active recombinant-derived chicken prolactin in Escherichia coli

The putative chicken prolactin (chPRL) cDNA clone PRL101 was manipulated in vitro and cloned into the Escherichia coli expression vector pKK2332 to produce a plasmid coding for recombinant-derived mature chPRL (R-chPRL). Expression of this manipulated cDNA sequence in E. coli resulted in the production of a 23 kDa protein which cross-reacted with specific chPRL antisera in Western blots. The partially purified protein stimulated ring dove crop sac mucosa to proliferate in a PRL bioassay, demonstrating that the R-chPRL was biologically active. R-chPRL was expressed at a level of approximately 1.5% of total cell protein.

Cell-specific expression of the prolactin gene in transgenic mice is controlled by synergistic interactions between promoter and enhancer elements

Prolactin gene expression is restricted to the lactotrophic and somatomammotrophic cells of the anterior pituitary. In transgenic mice, a fusion gene consisting of 3 kb of prolactin 5'-flanking region fused to a firefly luciferase or human growth hormone (hGH) reporter gene is expressed at high levels with the strict tissue and cell-type specificity that is characteristic of the endogenous prolactin gene. High levels of expression require two cis-acting regions: a distal enhancer (-1.8 to -1.5 kb) and a proximal region (-422 to +33 bp). Each of these regions alone can direct low levels of fusion gene expression to prolactin-producing cell types in transgenic mice, but a synergistic interaction between these regions is necessary for high levels of expression. The ontogeny of the prolactin transgene expression closely follows the appearance of high levels of a POU homeo-domain transcription factor, Pit-1, that has been shown previously to bind structurally related sequences in both the distal enhancer and proximal regions and to activate the expression of the prolactin gene in vitro. Unexpectedly, transgenes containing the distal enhancer removed from its normal context are expressed in both the prolactin-producing lactotrophs and the thyroid-stimulating hormone (TSH)-producing thyrotrophs, thereby suggesting that sequences flanking this enhancer are necessary to restrict expression to the correct cell type within the pituitary. These data indicate that distinct processes of gene activation and restriction are necessary for the fidelity of cell-type-specific expression within an organ.

Insulin stimulates the synthesis and release of prolactin from human decidual cells

Insulin-like growth factor I (IGF-I) and insulin have been implicated in the regulation of differentiated functions in many cells. We have reported that IGF-I stimulates the release of decidual PRL, acting through the type I IGF receptor (1). To determine whether insulin regulates the synthesis and secretion of decidual PRL, monolayer cultures of human decidual cells were exposed to insulin at concentrations ranging from 10 ng to 10 micrograms/ml for up to 5 days. Insulin stimulated a dose-dependent increase in PRL release (half-maximal concentration, 50 ng/ml), beginning 48 h after initial exposure. Insulin-exposed cells released 62 +/- 2% (mean +/- SEM), 97 +/- 3% and 82 +/- 6% more PRL than control cultures on days 3, 4, and 5, respectively. Insulin also stimulated de novo PRL synthesis. During the final 24-h culture period, insulin-exposed cells released 73 +/- 7% more immunoprecipitable [35S]-methionyl PRL than control cells, comparable to the 60 +/- 7% increase in PRL (by RIA) during the same period. Insulin effects were relatively specific to PRL, since insulin had a much smaller effect on the synthesis of total trichloroacetic acid-precipitable proteins. Additionally, insulin had no significant effect on cell number, total DNA, or total cellular protein. Specific and saturable insulin-binding sites were observed in decidual cells, and polyclonal antibodies to the insulin receptor acted as insulin agonists, stimulating an increase in PRL release comparable to that produced by insulin alone. These observations suggest that the responses to insulin are mediated through the insulin receptor. Furthermore, our studies suggest that insulin may have a role in the regulation of PRL synthesis and release from human decidua.

Regulation of prolactin gene expression during early pregnancy in rats

We have shown that administration of estrogen which increases prolactin (PRL) synthesis in the rat may be mediated by an increase in poly [adenosine diphosphate ribose (ADP-ribose)] synthesis. Present investigation was attempted to study whether poly (ADP-ribose) synthesis is involved in rat PRL gene expression during early pregnancy. Anterior pituitaries were obtained on days 0, 2, 4, 6, 8, 10 and 12 of pregnancy (group C). Another group of pregnant rats was given nicotinamide, an inhibitor of poly (ADP-ribose) synthesis twice a day intra-peritoneally from day 0 to the day of sacrifice (group N). Serum estradiol (E2) concentration was determined by radioimmunoassay. PRL mRNA was measured by cytoplasmic dot hybridization using 32P-labeled cDNA. Poly (ADP-ribose) synthesis was assessed by incubating purified nuclei with 14C-nicotinamide adenine dinucleotide. The serum concentration of E2 increased between days 2 and 4, and on day 6 it decreased to the level of day 0. It remained low until day 12. No difference in the serum E2 level was observed in groups C and N. In group C, PRL mRNA increased from day 2 and remained high until day 8. In group C, poly (ADP-ribose) synthesis increased between days 2 and 4, decreased on day 6 to the level of day 0, and thereafter gradually increased until day 10. Administration of nicotinamide abolished the increase in poly (ADP-ribose) synthesis observed in group C during early pregnancy. In group N, the increase in PRL mRNA was completely suppressed. It is suggested that the increase in PRL mRNA in early pregnancy may be mediated by increased poly (ADP-ribose) synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Observation of production of immunoactive prolactin by normal human connective tissue in cell culture

Data from our in vitro studies indicate a new source of prolactin (PRL)-like activity, normal human connective tissue. Fascial cells from primary culture and subsequent passages produced an extracellular antigen which specifically reacted in a radioimmunoassay RIA developed to detect human pituitary PRL. An initial peak or first surge of fascial PRL-like activity occurred between 4 and 15 d in primary culture. Ibuprofen, cytotoxic levels of 0.01% azide, or 7.5 mM EDTA and medium lacking serum [fetal bovine serum (FBS)] significantly (P less than or equal to 0.05) reduced PRL-like activity levels, whereas female steroids, 257 to 342 milliosmolarity, 1 to 3.6 mg/ml glucose, 2 to 20% FBS, and dialyzed FBS (MWCO approximately 1 kDa) were without effect. Optimum production of PRL-like activity occurred at pH 7.3. A second surge began after 18 d and continued until passage indicating that perhaps two populations of cells produced PRL-like activity in primary culture. Production of PRL-like activity by cells from early passages (1 and 2) became detectable at confluence, was serum-dependent, showed two patterns (tonic, rising to plateau), and averaged 3.2 fg.cell-1.3 d-1 feed interval. Cells from late passages showed morphologic damage from repetitive trypsinization, aging, and reduced production of PRL-like activity with aberrant production pattern. Production of PRL-like activity was maintained in an unusual long-term culture. These in vitro studies demonstrate the most recently recognized and ubiquitous source of human extrapituitary PRL or PRL-like activity, normal connective tissue (fascia).

Long-term effects of progestin and RU 486 on prolactin production and synthesis in human endometrial stromal cells

Previous studies have shown that the production of prolactin (PRL) is increased in human endometrial stromal cells cultured with medroxyprogesterone acetate (MPA) for 3-5 days. In the present study, we have investigated the effect of prolonged treatment of progestin and anti-progestin, RU 486, on the production and synthesis of PRL. Stromal cells were isolated from human endometrium obtained from non-pregnant women and cultured for 20-30 days in medium RPMI 1640 with 2% fetal calf serum or supplemented with MPA, RU 486, alone or in sequence. The PRL content in medium was measured by radioimmunoassay. The production rate was estimated from the PRL content in medium accumulated in 24 h. The PRL production rate was progressively increased in stromal cells continuously treated with MPA for 30 days (greater than 100-fold over the control value, i.e. 0-0.01 microgram/0.1 mg cell DNA/day). RU 486 alone had no effect on the production of PRL. However, the production of PRL was increased by MPA in stromal cells pretreated with RU 486 indicating that the effect of RU 486 is reversible. When stromal cells were treated with MPA and RU 486 sequentially, RU 486 stimulated the PRL production (approximately 2-fold over the MPA-treated cells) for 2-3 days and then reduced to basal levels over a 5-day period. The stimulatory and inhibitory effects of RU 486 on PRL production in stromal cells pretreated with progestin was also observed in the rate of synthesis of PRL estimated by incubating the stromal cells with [35S]methionine and immuno-isolating the [35S]PRL with anti-PRL.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of secretion of luteinizing hormone subunits and free alpha, and effects of gonadotropin releasing hormone

While GnRH is known to stimulate release of pituitary gonadotropins, its acute effects on the kinetics of secretion of the various hormones and subunits are not well characterized. Pulse-chase experiments were therefore performed to compare the time course of secretion of newly synthesized LH subunits and free alpha from rat pituitary quarters, and to study the effects of GnRH. After a 1-h pulse labeling with [35S]cysteine in the presence or absence of 10(-8) M GnRH, cultures were chased with excess unlabeled cysteine for 1, 2, 4, 8, or 20 h. Tissue lysates and media were immunoprecipitated sequentially with antisera to PRL, GH, LH beta and LH alpha, and the products were analyzed by gel electrophoresis. Labeled LH alpha was completely secreted by 4 h of chase without GnRH, and by 2 h with GnRH, as shown by its appearance in media and depletion from pituitary. Newly synthesized LH beta was depleted only at 8 h with GnRH from pituitary, suggesting much slower secretion. Incorporation of 35S into LH beta was approximately half that into LH alpha. Newly synthesized free alpha subunit was secreted between 4 and 20 h without GnRH, and by 8 h with GnRH. Free alpha incorporated a similar amount of radioactivity as LH beta. GnRH had no effect on the timing of the secretion of labeled total protein, PRL, GH, or TSH subunits. The amount of label incorporated during the pulse was greatest for PRL, approximately 15% of total protein label. GH incorporated approximately 20% as much label as PRL, with the glycoprotein subunits somewhat lower. The total amount of 35S incorporated into each protein studied was not affected by GnRH. The data indicate that short term in vitro GnRH exposure during a 1-h pulse labeling and chase acts to accelerate early secretion of LH alpha, LH beta and free alpha but does not affect overall protein synthesis. The peptide hormones PRL and GH incorporated the greatest amount of label and were the most briskly secreted hormones, while LH alpha led the glycoprotein subunits in the amount of incorporation and rapidity of secretion.