DNase I hypersensitivity analysis of non-pituitary human prolactin gene expression

The expression of non-pituitary human PRL is initiated at a unique 5' untranslated exon located approximately 5.7 kb upstream of the pituitary-specific transcriptional start site. Unlike pituitary PRL expression, transcriptional regulation from the upstream promoter does not rely on the POU-homeodomain protein Pit-1. We have used DNase I mapping of chromatin from PRL-producing and non-producing human lymphoblastoid cell lines to identify hypersensitive sites unique to the PRL expressing phenotype. Analysis of 22 kb of 5' flanking DNA revealed DNase I hypersensitive sites in intron A-1 separating the pituitary from non-pituitary specific transcription start site which were only detected in the PRL-producing cell line. Transient transfection showed strong transcriptional activity directed by this region only in the antisense orientation and in a non cell-type specific manner. Transfection experiments with deletion mutants of 5259 bp of the non-pituitary PRL promoter region also revealed promoter activity not restricted to the PRL expressing phenotype. These data suggest that non-pituitary PRL gene expression may be regulated by elements located in intron A-1 and that recapitulation of cell-specific expression requires a unique cellular context and chromatin assembly.

The EGF response element in the prolactin promoter

Epidermal growth factor (EGF) increases prolactin gene expression in GH4 cells, but the promoter element(s) required for this response has not been clearly defined. We identified a bipartite element - 96/ - 87, - 76/ - 67 in the rat proximal promoter that is essential for EGF signaling using deletion and linker-scanning mutants of the prolactin promoter. This element was active in either normal or inverted orientation when transferred to a heterologous promoter (mammary-tumor virus). We had previously identified this element as the cAMP/insulin response element of the prolactin promoter. However, the effects of EGF are additive with the responses to insulin or cAMP implying that EGF activated prolactin gene transcription by a mechanism different from insulin or cAMP. The EGF response element of the prolactin promoter is a recognition sequence for the Ets-related family of transcription factors and Ets-related factors have been shown to bind this element. Expression of the DNA-binding domain of c-Ets-1, which acts as a dominant negative inhibitor of Ets-related transcription factors, reduces EGF-increased prolactin-CAT expression 65% in GH4 cells. Thus, both EGF and insulin may signal through Ets-related transcription factors to activate prolactin gene transcription at the same response element in the prolactin proximal promoter.

Absence of prolactin gene expression in colorectal cancer

AIMS

Previous studies documenting hyperprolactinaemia in patients with colorectal cancer have suggested that the tumour is the source of hormone production. The aim of this study was to determine the frequency of hyperprolactinaemia in patients with colorectal cancer before, during, and after surgery, and also to determine whether prolactin is produced by these tumours.

METHODS

Serum prolactin concentrations were measured in 20 patients with colorectal cancer before, during, and after surgical resection of their tumours. Samples taken during surgery included peripheral venous blood and blood taken from the main veins draining the tumour. To determine whether the tumour was responsible for the production of prolactin in these patients, paraffin wax embedded sections of tumour specimens were subjected to immunohistochemistry and western blotting using a monoclonal antibody to prolactin.

RESULTS

Five patients (three women, two men) had preoperative prolactin concentrations above the normal reference range, although this increase was of clinical importance in only two. After surgical resection of their tumours, prolactin concentrations remained high in both patients. All 20 patients had greatly raised prolactin values at the time of surgery, irrespective of whether this was measured in peripheral blood or in blood taken from veins draining the tumour. All 20 colorectal cancer tissue samples, including those with raised preoperative and/or postoperative prolactin concentrations, were negative for prolactin staining. Frozen tissue was also available in four cases. The absence of prolactin gene expression in these four tumours was confirmed both by repeat immunohistochemistry and by western blotting. A further 50 colorectal cancer cases examined by immunohistochemistry alone were also unreactive for prolactin.

CONCLUSIONS

The results of this study suggest that serum prolactin concentrations may occasionally be raised in colorectal cancer patients, but that the tumour is not the source of hormone production.

Regulation of estrogen receptor activation of the prolactin enhancer/promoter by antagonistic activation function-2-interacting proteins

Transcriptional responses to estrogens are controlled by the cell- and gene-specific interactions of the nuclear estrogen receptor (ER) with cofactors and other transcription factors. The pituitary-specific PRL enhancer/promoter is regulated by estrogens only when it is bound by both ER and the pituitary-specific transcription factor, Pit-1. Cooperative ER/Pit-1 activation of the dormant PRL enhancer/promoter in pituitary progenitor cells requires the estrogen-dependent activation function-2 (AF-2) of ER, but is inhibited by one AF-2-interacting cofactor, RIP140. Here, the complex actions of RIP140 and other AF-2-interacting proteins at the PRL enhancer/promoter were shown to operate via ER itself. RIP140 inhibition of ER/Pit-1 activation in the absence of AF-1 and RIP140 inhibition of both ER alpha and ER beta cooperative activation with Pit-1 suggested a conserved ER site for RIP140 action, possibly AF-2. Coexpression of other AF-2-interacting proteins, including the p160 factors, steroid receptor coactivator-1a (SRC-1a) and glucocorticoid receptor interacting protein-1 (GRIP1), had negligible effects on ER alpha/Pit-1 cooperative activation, but partially relieved RIP140 inhibition. Relief of RIP140 inhibition required the AF-2-binding, LXXLL motifs in SRC-1a and GRIP1. An ER AF-2 mutant that selectively blocked ER interaction with p160s, but not RIP140, still cooperated with Pit-1 and was inhibited by RIP140, but was not relieved by SRC-1a or GRIP1 expression. Thus, SRC-1a and GRIP1 binding to AF-2 counteracted the inhibition of ER/Pit-1 activation by another AF-2-interacting protein, RIP140. Complex, sometimes antagonistic, actions of different classes of AF-2-interacting proteins may play an important role in the cell- and gene-specific estrogen regulation of PRL and other genes.

Early embryonic expression of the growth hormone family protein genes in the developing rainbow trout, Oncorhynchus mykiss

In fish, growth hormone (GH), prolactin (PRL) and somatolactin (SL) are three major peptide hormones produced in the pituitary gland. Using reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot analysis of the amplified products, the expression of GH, PRL, and SL genes were determined during the embryonic development in rainbow trout (Oncorhynchus mykiss). The mRNA for GH, PRL and SL were detected not only in embryos prior to or after organogenesis of the pituitary gland but also in mature oocytes as maternal messages. After hatching, all of these three mRNA species were detected at very high levels. Since the ontogenesis of the pituitary gland takes place on embryonic day (ED) 14, these observations suggest that the GH family protein genes are expressed in the developing embryos prior to the formation of the pituitary gland. Using the same RT-PCR assay, PRL mRNA was detected only in the head part of the fry whereas GH and SL mRNA were detected in both the head and trunk. In adult animals, though high levels of GH mRNA were primarily detected in the pituitary gland, brain, gill, and heart, low levels of GH mRNA were also detected in the kidney, liver, pyloric ceaca, and ovary. Results of the current study and those reported by Yang et al. (1997. Gen Comp Endocrinol 106:271-281) suggest that GH and SL genes are also expressed in extrapituitary tissues even after the organogenesis of the pituitary gland. Furthermore, these results suggest that these hormones may play important roles yet to be identified during embryonic development in fish.

Differential regulation and action of estrogen receptors alpha and beta in GH3 cells

The pituitary lactotroph, a well established target for estrogens, expresses estrogen receptor-alpha (ER alpha) and -beta (ER beta). A truncated isoform of ER alpha, named TERP, is expressed in the pituitary, but not in the uterus. In this study we used the somatolactotroph cell line, GH3 cells, to examine 1) the expression of ER alpha, TERP, or ER beta and their regulation by estradiol; 2) the presence of receptor proteins; and 3) the effects of overexpressing ER beta or TERP on estrogen induction of the PRL gene and activation of the estrogen response element (ERE). Incubation of GH3 cells with estradiol (0.1-10 nM) produced dose-dependent increases in messenger RNA levels of ER beta and TERP, but not ER alpha, as determined by quantitative RT-PCR. Cell incubation with 1 nM estradiol resulted in a time-dependent biphasic increase in TERP and a delayed rise in ER beta, suggesting activation by both direct and indirect mechanisms. A polyclonal ER beta antibody directed against an N-terminal synthetic peptide was generated. This antibody detected ER beta-positive cells in ovarian granulosa cells and in many cells throughout the pituitary; its specificity was demonstrated by preabsorption with the synthetic peptide. The antibody detected a 58- to 60-kDa protein by Western blotting of ovarian, pituitary, and GH3 cell extracts. Cotransfection of ER beta and reporter genes (PRL promoter/luciferase or ERE/luciferase) into GH3 cells resulted in a dose-dependent increase in estrogen-induced PRL gene expression, with a lesser activation of the ERE. A 20-kDa TERP protein was undetectable in untreated GH3 cells and was weakly induced by estradiol. Overexpression of TERP had no effect on estrogen induction of either PRL or ERE. We conclude that 1) both ER beta and TERP messenger RNAs in GH3 cells are increased by estradiol in a dose- and time-dependent manner, whereas ER alpha is not altered; 2) a 58-kDa ER beta protein is expressed in both the pituitary and GH3 cells; and 3) overexpression of ER beta increases estrogen-induced PRL gene expression.

The human prolactin gene upstream promoter is regulated in lymphoid cells by activators of T-cells and by cAMP

Prolactin (PRL) is produced in human thymocytes, T-cells and endometrium. In these extrapituitary tissues, PRL gene transcription is directed by an alternative upstream promoter, and it is thought to act as a locally produced cytokine, with relevance for immune regulation and modulation of T-cell function. We have studied PRL transcriptional regulation in the human T-lymphoblastoid Jurkat cell line transfected with a fragment of the upstream promoter linked to luciferase. A cAMP analogue (cptAMP) increased promoter activity rapidly and dose dependently. This increase was resistant to inhibition by cyclosporin A and thus independent of calcineurin phosphatase (CN). T-cell activation by phorbol myristate acetate (PMA) failed to enhance promoter activity but phytohaemagglutinin (PHA) alone or PHA+PMA increased it, and cptAMP acted in synergy with PMA or PHA to increase it further. H-89, a cAMP-dependent protein kinase A (PKA) inhibitor, inhibited the effect of cptAMP as did transfection with protein kinase inhibitor PKI, an expression vector of the specific inhibitor of PKA. A single point mutation in the CRE (cAMP response element) located at -25 bp in the PRL upstream promoter (TGACGT to TGCCGT) failed to reduce the response to cptAMP, while mutations or deletion of four nucleotides in the CRE to TACTCT diminished the response to cAMP by more than half. We conclude that activity of the human PRL upstream extrapituitary promoter can be induced by activators of T-cells, as well as by a cAMP analogue. The signal is transmitted by PKA and the effect of cAMP is independent of CN. It is partly dependent on an intact proximal CRE motif but a more upstream enhancer may contribute to promoter regulation.

Progestin modulation of c-fos and prolactin gene expression in the human endometrium

OBJECTIVE

To evaluate the influence of the menstrual cycle and the effects of medroxyprogesterone acetate (MPA) on the expression of the protooncogene c-fos and of prolactin (PRL) in the human endometrium in vivo.

DESIGN

Double-blind, placebo-controlled trial.

SETTING

Healthy volunteers in an academic research environment.

PATIENT(S)

Regularly cycling women who were not taking hormonal medication.

INTERVENTION(S)

Medroxyprogesterone acetate (10 mg/d) or placebo was given for 10 days. Endometrial and blood samples were collected 8-12 hours after the last dose.

MAIN OUTCOME MEASURE(S)

Immunohistochemical localization of PRL and c-fos in the endometrium, PRL and c-fos messenger RNA levels in the endometrium, and E2 and progesterone levels in the serum.

RESULT(S)

Immunoreactive c-fos was concentrated in the nucleus of stromal cells and was observed in a higher proportion of proliferative endometrial specimens compared with secretory specimens from placebo or MPA-treated patients. The levels of c-fos messenger RNA were greatly reduced in the secretory endometrium regardless of treatment with placebo or MPA, compared with the proliferative endometrium. The c-fos gene expression correlated positively with the serum E2 levels (r = 0.56) and inversely with the progesterone/E2 ratio (r = -0.56). The endometrial PRL gene expression (messenger RNA and protein) was rare in the proliferative samples, increased from the early to the mid and late secretory samples, and was increased markedly after treatment with MPA compared with placebo.

CONCLUSION(S)

The differentiation of secretory endometrium is accompanied by decreased c-fos and increased PRL gene expression. The inhibition of c-fos gene expression may contribute to the antiproliferative effect of progestins on the endometrium.

Changes in the expression of neurohypophyseal prolactins during the estrous cycle and after estrogen treatment

Estrogens are recognized regulators of the expression of neurohypophyseal hormones and of anterior pituitary prolactin (PRL). Here we have investigated whether the levels of PRL mRNA and of 23 and 14 kDa PRL variants present in the hypothalamo-neurohypophyseal system change during the estrous cycle or in response to estrogen treatment. The reverse transcription polymerase chain reaction (RT-PCR) was performed to examine PRL mRNA expression in isolated paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei. In both nuclei PRL mRNA levels appeared higher in cycling females than in male rats, with the highest level occurring at estrus. This increase may involve estrogen action, since estrogen administration to ovariectomized rats was associated with apparently higher PRL mRNA levels in both the PVN and SON. Expression of the PRL gene at these sites may occur via both transcriptional factor Pit-1-dependent and -independent mechanisms. RT-PCR detected the mRNA for Pit-1 in the PVN but only at estrus. The concentration of the 23 kDa immunoreactive PRL determined in the neurohypophysis was significantly higher during estrus and after estrogen treatment. However, no difference was detected in the levels of the neurohypophyseal 14 kDa PRL-like fragment along the estrous cycle nor after estrogen administration. This lack of parallelism between neurohypophyseal PRLs could relate to an estrogen-induced inhibition of the proteolysis of 23 kDa PRL at this site, since estrogen treatment reduced the activity of neurohypophyseal proteolytic enzymes able to cleave PRL. Altogether our results are consistent with estrogens having a stimulatory effect on PRL gene expression in the hypothalamo-neurohypophyseal system and a concomitant inhibitory action on PRL proteolysis at this site.

Rapid down-regulation of CD63 transcription by progesterone in human endometrial stromal cells

Differentiation of endometrial stromal cells (decidualization) plays a crucial role in embryo implantation and maintenance of pregnancy. While progesterone is a key factor in regulating endometrial cell decidualization, the molecular mechanisms remain unclear. In the present study, we investigated the effect of gene transcription in human endometrial stromal cells (ESC) by progesterone, oestrogen or vehicle using the polymerase chain reaction-based differential display methodology. A transcript which is down-regulated by progesterone, but not by vehicle and oestrogen, was identified from a differential display band and the progesterone sensitivity of its expression was verified in Northern blot analysis. The level of the gene expression in progesterone-treated ESC was approximately 60% of that in the vehicle- and oestrogen-treated ESC. This cDNA was revealed to be human CD63 antigen, a recently identified member of the transmembrane 4 superfamily. The inhibitory effect of progesterone is observed within 30 min after hormone treatment. In human endometrium, CD63 mRNA levels were significantly decreased (P < 0.05) during the secretory phase compared with levels during the proliferative phase. This down-regulation of CD63 in vivo elevated levels of progesterone in the secretory phase. These results suggest that CD63 transcription is down-regulated by progesterone in human endometrium.

Effects of TGF-beta1 on prolactin synthesis and secretion: an in-vitro study

The hypothalamus exerts a predominantly inhibitory influence on prolactin secretion through dopamine. In addition, the expression of anterior pituitary hormone-gene products are regulated by intrapituitary growth factors. In particular, TGF-beta1 produced in the pituitary regulates lactotroph cell proliferation and prolactin gene-expression. This study characterized the regulation of in-vitro prolactin synthesis and secretion by TGF-beta1 using rat anterior pituitary cells in monolayer culture. Furthermore, we studied the interaction of TGF-beta1 with other signals involved in the neuroregulation of prolactin secretion, such as dopamine and TRH, as well as the importance of different signal transduction pathways in this response. TGF-beta1 inhibited prolactin secretion in a time- and concentration-dependent manner, with half-maximal inhibition occurring at the range of 15-30 pM. The inhibitory effect was observed after 4 h, being maximal after 4 days of exposure of the cells to the peptide. This inhibitory effect was mimicked by TGF-beta2 but not by inhibin, and was not influenced by oestrogens, being similar in male, normal female or oestradiol-treated rats. Prolonged pretreatment of the cells with TGF-beta1(4 days) did not modify GH or TSH secretion nor dopamine-induced inhibition of prolactin secretion, and blunted prolactin responses to TRH, Forskolin, But2-cAMP and to the calcium ionophore A23187. The effect observed after long-term treatment (24 h to 4 days) is essentially caused by a decrease in prolactin synthesis, since TGF-beta1 inhibited prolactin mRNA levels and de novo prolactin protein synthesis. However, in the short term (up to 12 h) TGF-beta1 inhibition of prolactin secretion was associated with an increase in intracellular prolactin content, dissecting a dual mechanism of action of TGF-beta1. The short-term TGF-beta1 effect did not modify Erk-2 phosphorylation, basal or TRH-induced increase in intracellular calcium concentration, but blunted basal and forskolin stimulated cAMP levels. But2-cAMP replacement did not revert the inhibition of prolactin secretion. However, pertussis toxin was able to recover a large percentage of TGF-beta1-induced inhibition of prolactin secretion. This study indicates that TGF-beta1 plays a crucial role as a modulator of lactotroph function, inhibiting prolactin biosynthesis after long-term treatment, as well as, after short-term exposure prolactin secretion at the level of the secretory process, through a mechanism pertussis toxin sensitive but independent of Erk-2 phosphorylation, calcium concentrations or intracellular cAMP.

Cloning, expression, and tissue localisation of prolactin in adult sea bream (Sparus aurata)

A major action of prolactin (PRL) in teleost fish is the maintenance of hydromineral balance in euryhaline species in fresh water. The function of PRL in marine teleosts is less certain and unlike euryhaline teleosts, such as tilapia and salmon, there is relatively little information about protein or gene structure. Associated with studies to determine potential functions of PRL, pituitary prolactin cDNA has been cloned and sequenced from sea bream (Sparus aurata), a marine teleost. The sequence obtained spanned 1349 bp and contained an open reading frame encoding a protein of 212 amino acids composed of a putative signal peptide of 24 residues and a mature protein of 188 amino acids. N-terminal sequencing of the native protein confirmed unambiguously the cleavage site, Ala24, Val25, predicted from alignments of the sea bream PRL cDNA with that of other teleosts. The presence of only one form of PRL in sea bream was supported by identification using Northern blots of only a single transcript of 1.35 kb. Reverse transcription and polymerase chain reaction techniques coupled with Southern blot analysis resulted in the detection of PRL in the pituitary but also in the intestine, liver, ovary, and testes.

Is the primitive regulation of pituitary prolactin (tPRL177 and tPRL188) secretion and gene expression in the euryhaline tilapia (Oreochromis mossambicus) hypothalamic or environmental?

We examined the effects of environmental salinity on circulating levels of the two prolactins (tPRL177 and tPRL188) and levels of pituitary tPRL177 and tPRL188 mRNA in the euryhaline tilapia, Oreochromis mossambicus. Fish were sham-operated or hypophysectomized and the rostral pars distalis (RPD) autotransplanted onto the optic nerve. Following post-operative recovery in (1/4) seawater, tilapia were transferred to fresh water (FW), (1/4) seawater (SW) or SW. Serum tPRL177 and tPRL188 levels in sham-operated and RPD-autotransplanted fish were highest in FW and decreased as salinity was increased. tPRL177 and tPRL188 mRNA levels in RPD implants as well as in pituitaries from the sham-operated fish were also highest in FW and decreased with increasing salinity. Serum osmolality increased with salinity, with the highest levels occurring in the seawater groups. We conclude that some plasma factor (probably plasma osmolality), in the absence of hypothalamic innervation, exerts a direct regulatory action on prolactin release and gene expression in the pituitary of O. mossambicus. This regulation is in accord with the actions of the two prolactins in the freshwater osmoregulation of the tilapia.

Expression cloning and characterization of PREB (prolactin regulatory element binding), a novel WD motif DNA-binding protein with a capacity to regulate prolactin promoter activity

Previous studies have implied that a transcription factor(s) other than Pit-1 is involved in homeostatic regulation of PRL promoter activity via Pit-1-binding elements. One such element, 1P, was employed to clone from a rat pituitary cDNA expression library a novel 417-amino acid WD protein, designated PREB (PRL regulatory element binding) protein. PREB contains two PQ-rich potential transactivation domains, but no apparent DNA-binding motif, and exhibits sequence-specific binding to site 1P, to a site nonidentical to that for Pit-1. The PREB gene (or a related gene) is conserved, as an apparently single copy, in rat, human, fly, and yeast. A single approximately 1.9-kb PREB transcript accumulates in GH3 rat pituitary cells, to levels similar to Pit-1 mRNA. PREB transcripts were detected in all human tissues examined, but the observation of tissue-specific multiple transcript patterns suggests the possibility of tissue-specific alternative splicing. RT-PCR analysis of human brain tumor RNA samples suggested region-specific expression of PREB transcripts in brain. Western and immunocytochemical analysis implied that PREB accumulates specifically in GH3 cell nuclei. Transient transfection employing PREB-negative C6 rat glial cells showed that PREB is as active as, and additive with, Pit-1 in transactivation of a PRL promoter construct, and that PREB, but not Pit-1, can mediate transcriptional activation by protein kinase A (PKA). Expression in GH3 cells of a GAL4-PREB fusion protein both strongly transactivated a 5XGAL indicator construct and yielded a further stimulation of expression of this construct by coexpressed PKA, implying that PREB can mediate both basal and PKA-stimulated transcriptional responses in pituitary cells. These observations imply that PREB will prove to play a significant transcriptional regulatory role, both in the pituitary and in other organs in which transcripts of its gene are expressed.

Is gonadotrope expression of the gonadotropin releasing hormone receptor gene mediated by autocrine/paracrine stimulation of an activin response element?

Expression of the FSHbeta subunit and GnRH receptor (GnRHR) genes in gonadotropes is stimulated by activin. We sought to identify the cis-acting element(s) in the murine GnRHR gene promoter which confer activin responsiveness. We established that 600 bp of 5'flanking sequence from the murine GnRHR gene were sufficient to confer activin responsiveness in the gonadotrope-derived alphaT3-1 cell line. Since alphaT3-1 cells, like gonadotropes, secrete activin, we examined the ability of follistatin, an activin binding protein, to block the activin response. Increasing concentrations of follistatin from 0 to 100 ng/ml resulted in a dose dependent decrease in activity of the -600 promoter. Contained within this region are three elements important for expression in alphaT3-1 cells: a Steroidogenic Factor-1 binding site (SF-1), an Activator Protein-1(AP-1) element, and an element termed the GnRH receptor activating sequence or GRAS. A block mutation of GRAS inhibited the ability of the promoter to respond to follistatin. A more refined analysis using a series of two-bp mutations which scan GRAS and flanking sequence revealed exact convergence of GRAS with activin/follistatin responsiveness. Finally, a construct consisting of 3 copies of GRAS placed upstream of a heterologous minimal promoter (3xGRAS-PRL-LUC) was responsive to both activin stimulation and follistatin inhibition in alphaT3-1 cells. Thus, autocrine/paracrine stimulation of gonadotropes by activin illustrates a unique mechanism for cell-specific gene expression.

Proliferative disorders of the aging human prostate: involvement of protein hormones and their receptors

The majority of elderly men is affected by benign and malignant diseases of the prostate. Both proliferative disorders, i.e., benign hyperplasia of the prostate (BPH) and prostate cancer (PCa)-which has recently emerged as the most common male malignancy in industrialized countries-seem to be governed by endocrine factors such as sex steroid hormones, but auto/paracrine factors are involved as well. Age-related changes in levels and ratios of endocrine factors as androgens, estrogens, gonadotropins, and prolactin (PRL) and changes in the balance between auto/paracrine growth-stimulatory and growth-inhibitory factors such as insulin-like growth factors (IGFs), epidermal growth factor (EGF), nerve growth factor (NGF), IGF-binding proteins (IGFBPs), and transforming growth factor beta (TGFbeta) are meant to be responsible for abnormal prostatic growth. We investigated the existence of putative local regulatory circuits involving the protein hormones, human growth hormone (hGH), human placental lactogen (hPL), and hPRL, and their corresponding receptors in prostatic tissue specimens (transurethral resections of the prostate, TURP; n = 11), in the prostatic cancer cell lines PC3, Du145, LnCap, a virus-transformed BPH cell line (BPH-1), and in a normal healthy prostate by RT-PCRs and highly specific and sensitive immunofluorometric assays (IFMA). Neither hPRL nor hGH was detected at the mRNA or protein levels in prostatic tissue and cell lines, with the exception of 2 of 11 prostatic TURP-samples, which showed weak expression of the PL-A/B genes. PRL- and GH-receptors were expressed in all normal and pathological prostatic specimens. Surprisingly, PRL-receptor expression was not detectable in prostatic cancer cell lines. The trophic effects of exogenous hGH, hPL, and hPRL were investigated by cell proliferation assays (WST-I) in prostatic primary cell cultures and PCa cell lines. hGH significantly (p < 0.005) increased cell proliferation up to 138+/-3.2% (1 nM hGH), while hPL and hPRL revealed only moderate effects. Our data suggest that local auto/paracrine networks of protein hormone actions are not involved in the pathology of BPH or prostatic cancer. On the other hand, systemic pituitary-derived hGH can increase the proliferative response of BPH and PCa, acting directly on the target organ prostate, via the hGH-R. In this case, envisaged GH substitution in elderly people must be viewed at with caution because age-related declines in GH/IGF-I could act as a protective mechanism against abnormal cell growth.

N5 endometrial stromal cell line: a model system to study decidual prolactin gene expression

Prolactin gene expression in extrapituitary tissues, such as decidua and lymphocytes, is regulated by a distinct promoter approximately 6 kb upstream of the pituitary prolactin gene transcription start site. Here we describe studies in a human endometrial stromal cell line, N5, that was immortalized by transfection with an SV40 mutant and which expresses the prolactin gene driven by the extrapituitary promoter. The N5 cells have phenotypic features of primary cultures of decidualized human endometrial stromal cells and secrete low levels of prolactin and insulin-like growth factor binding protein-1 (IGFBP-1), both of which are markers of decidualized endometrial stromal cells. As in primary cultures of endometrial stromal cells, treatment of N5 cells with progesterone and estradiol alone or in combination with prostaglandin E2 stimulated the synthesis and release of prolactin. Transient transfection of the N5 cells with an expression vector containing - 2927/ + 66 bp of the decidual prolactin promoter coupled to a luciferase reporter gene resulted in a 20 to 25-fold increase in luciferase activity, a magnitude similar to that which occurs in primary cultures of endometrial stromal cells decidualized in vitro by treatment with progesterone and estradiol. Luciferase expression levels were similar in untreated N5 cells and N5 cells treated with progesterone and estradiol. Taken together, these results indicate that the N5 human endometrial stromal cell line has phenotypic characteristics of normal decidualized stromal cells and is a useful model to study regulation of decidual prolactin gene expression.

Defective retinoic acid regulation of the Pit-1 gene enhancer: a novel mechanism of combined pituitary hormone deficiency

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Pit-1 contains two protein domains, termed POU-specific and POU-homeo, which are both necessary for DNA binding and activation of the GH and PRL genes and regulation of the PRL, TSH-beta subunit (TSH-beta), and Pit-1 genes. Pit-1 is also necessary for retinoic acid induction of its own gene during development through a Pit-1-dependent enhancer. Combined pituitary hormone deficiency is caused by defective transactivation of target genes in the anterior pituitary. In the present report, we provide in vivo evidence that retinoic acid induction of the Pit-1 gene can be impaired by a Pit-1 gene mutation, suggesting a new molecular mechanism for combined pituitary hormone deficiency in man.

The prolactin gene is expressed in the mouse kidney

BACKGROUND

Prolactin (PRL), originally identified as an anterior pituitary hormone exhibiting lactogenic activity, is now recognized as a versatile hormone expressed in a wide variety of tissues.

METHODS

In this study, the expression of PRL in the mouse kidney was investigated by solution-phase and in situ reverse transcription-polymerase chain reaction (RT-PCR) methods and immunohistochemistry.

RESULTS

Mouse PRL (mPRL) transcript and protein are localized in the parietal epithelial cells of Bowman's capsule. Pit-1 is a positive transcription factor for the expression of the PRL gene. The presence of Pit-1 transcript in the kidney was also assessed by RT-PCR methods. The localization of Pit-1 mRNA coincided well with that of PRL. Immunoreactivity to mouse PRL receptor (mPRL-R) is distributed on the luminal membrane of the proximal tubule cells and the parietal epithelial cells of Bowman's capsule.

CONCLUSION

These data indicate that the parietal epithelial cells of Bowman's capsule synthesize PRL de novo and suggest that Pit-1 contributes to the transcriptional regulation of PRL gene expression in the kidney, and PRL expressed in this tissue functions in an autocrine/paracrine fashion.

Prolactin receptor expression in the testis of the ram: localisation, functional activation and the influence of gonadotrophins

The present study investigated the pattern and site of expression of the prolactin receptor gene in the testis of the seasonally breeding Soay sheep. In experiment 1, Northern blot analysis confirmed expression of the prolactin receptor gene in the testis which was encoded by RNA transcripts of approximately 3.6, 11.2, 12.6, and 14.1 kb. In situ hybridisation localised expression of the receptor within the interstitial and seminiferous tubule compartments of the testis and immunohistochemistry localised expression of the receptor to Leydig cells and to pachytene spermatocytes, round and elongating spermatids. In experiment 2, phosphorylation of Jak2, Stat1 and Stat5 proteins in response to prolactin was investigated by Western blotting following incubation of testicular samples with 100 ng/ml ovine prolactin. Jak2 and Stat1 phosphorylation were induced by prolactin within 10 min and Stat5 within 30 min. In experiment 3, intact and hypothalamo-pituitary disconnected (HPD) rams were transferred from a short to a long day photoperiod regimen for a period of 8 weeks. By week 8, testicular diameter had declined in intact rams (52.71+/-1.06 cm vs. 48.00+/-0.49 cm for weeks 1 and 8 after transfer respectively, P<0.01, n = 3) and increased in HPD rams (27.00+/-0.45 cm and 29.66+/-0.99 cm for weeks 1 and 8 after transfer respectively, P<0.05, n = 3). RT-PCR using RNA extracted from intact and HPD rams confirmed expression of the prolactin receptor in the testis of both groups. Immunohistochemistry localised prolactin receptor expression in Leydig cells and in pachytene spermatocytes, round and elongating spermatids of intact sheep testis. In HPD rams, prolactin receptor expression was localised in Leydig cells and germ cells which were arrested predominantly at the pachytene spermatocyte stage. These data demonstrate expression of functional prolactin receptors in the testis of Soay rams. The site and pattern of expression of the receptor gene suggest a role for prolactin in the regulation of steroidogenesis and spermatogenesis.

Interaction between estrogen receptor and Pit-1 protein is influenced by estrogen in pituitary cells

The estrogen responsiveness of the rat prolactin gene expression requires the presence of both the estrogen receptor (ER) and the tissue-specific transcription factor, Pit-1 protein. We performed protein interaction assays using anti-rat Pit-1 antiserum (a-rPit-1) to investigate the physical interactions which occur between ER and Pit-1 proteins following estrogen treatment. After fusing maltose binding protein (MBP) and Pit-1 protein, we used the resulting MBP Pit-1 fusion protein to prepare a-rPit-1. Our results show that the estrogen receptor readily co-precipitated with the Pit-1 protein drawn from the lysates of two prolactin-expressing pituitary cell lines GH3 and PR1. The rate of precipitation appears to be both estrogen- and time-dependent. Cellular levels of estrogen receptors and Pit-1 proteins did not show significant changes during the time of estrogen treatment. We therefore suggest that an estrogen-dependent physical interaction between ER and Pit-1 protein exists in vivo, and that this interaction may play an important role in the regulation of prolactin gene expression.

Interleukin-2 inhibits the synthesis and release of prolactin from human decidual cells

PRL is synthesized and released by several extrapituitary tissues, including decidualized endometrial stromal cells. As interleukin-2 (IL-2) stimulates the synthesis and release of pituitary PRL, and decidual stromal cells have receptors for IL-2, we examined whether IL-2 also regulates the release of decidual PRL. Exposure of primary cultures of human decidual cells (10(6) cells/well) from term pregnancies to IL-2 (50 ng/mL) inhibited PRL release beginning 48 h after exposure. The inhibition by IL-2 was dose dependent, and the maximal inhibition of PRL release after 5 days of exposure to IL-2 was 71.0 +/- 0.9% (mean +/- SE). IL-2, however, had no effect on decidual cell viability. The inhibitory effect of IL-2 on PRL release was secondary to inhibition of PRL synthesis. Decidualized human endometrial stromal cells transfected with 3 kb of the extrapituitary PRL (exon 1a) promoter coupled to a luciferase expression vector responded to IL-2 (10 ng/mL) with a significant decrease in luciferase activity. These findings strongly suggest that IL-2 inhibits the synthesis and release of decidual PRL and provide further support for a critical role of cytokines in the regulation of decidual PRL gene expression.

Reconstitution of the protein kinase A response of the rat prolactin promoter: differential effects of distinct Pit-1 isoforms and functional interaction with Oct-1

PRL gene transcription is primarily regulated by dopamine, which lowers cAMP levels and inhibits protein kinase A (PKA) activity. Current data indicate that the cAMP/PKA response maps to the most proximal Pit-1/Pit-1beta binding site footprint I (FP I) on the rat PRL (rPRL) promoter. Pit-1, a POU-homeo domain transcription factor, is specifically expressed in the anterior pituitary and is required both for the normal development of anterior pituitary cell types, somatotrophs, lactotrophs, and thyrotrophs, and for the expression of their hormones: GH, PRL, and TSHbeta. Pit-1 has been shown to functionally interact, via FP I, with several transcription factors, including Oct-1, a ubiquitous homeobox protein, and thyrotroph embryonic factor, which is found in lactotrophs, to activate basal rPRL promoter activity. Pit-1beta/GHF-2, a distinct splice isoform of Pit-1, acts to inhibit Ras-activated transcription from the rPRL promoter, which is mediated by a functional interaction between Pit-1 and Ets-1 at the most distal Pit-1 binding site (FP IV). In this manuscript we show 1) that the Pit-1beta isoform not only fails to block PKA activation, but is, in fact, a superior mediator of the PKA response; 2) that the PKA response requires intact POU-specific and POU-homeo domains of Pit-1; and 3) that Oct-1, but not thyrotroph embryonic factor, functions as a Pit-1-interacting factor to mediate an optimal PKA response.

Expression, folding, and characterization of small proteins with increasing disulfide complexity by a pT7-7-derived phagemid

The expression, folding, and characterization of a series of small proteins with increasingly complex disulfide bond patterns were characterized. A phagemid was prepared from the pT7-7 plasmid to facilitate mutagenic studies with these proteins. cDNAs coding for bovine, rat, and human prolactin; human growth hormone; and bovine alpha-lactalbumin were amplified by PCR using primers that inserted restriction sites at the 5' and 3' ends and reduced the coding sequence to the mature methionyl protein with bacterially preferred codons in the 5' region. The expressed proteins were folded and oxidized by methods that allowed disulfide bond formation to occur either during or following folding. The effectiveness of the folding procedures was determined for each protein by electrophoresis, absorption spectroscopy, and functional studies. The redox conditions required for folding functional proteins varied as the number of disulfide bonds per unit molecular weight increased. Human growth hormone, 22 kDa; human prolactin, 23 kDa; and bovine prolactin, 23 kDa, contain two, three, and three disulfides, respectively, and are folded correctly by air oxidation performed during renaturation under alkaline conditions. Proper disulfide bond formation of rat prolactin, 23 kDa, containing three disulfide bonds required the addition of a reducing agent at the initiation of renaturation. Bovine alpha-lactalbumin, 14 kDa with four disulfide bonds, required complete renaturation prior to the removal of a reducing agent. SDS-gel electrophoresis under nonreducing conditions provided information regarding the proper folding of these proteins. The absorption of 250-nm light by disulfide bonds also provided information regarding the proper folding of rat prolactin and bovine alpha-lactalbumin.