Molecular cloning of the bovine prolactin receptor and distribution of prolactin and growth hormone receptor transcripts in fetal and utero-placental tissues

Prolactin role in the bovine uterus during adenomyosis

Adenomyosis is uterine dysfunction defined as the presence of endometrial glands within the myometrium. It is suggested that adenomyosis is estrogen-dependent pathology, and prolactin (PRL) also affects its development. In the uterus of ruminants, PRL stimulates gland proliferation and function. We hypothesized that in the bovine uterus, the expression of PRL and its receptors (PRLRs) during adenomyosis is disturbed and modulated by estradiol (E₂). Uterine tissues were collected postmortem from cows; epithelial, stromal, and myometrial cells were isolated; and cultured and treated with E₂. Material was divided into 2 groups: control (nonadenomyotic) and uteri with adenomyosis. In adenomyotic uterine tissue, PRL and its long-form receptor protein were increased, as determined by Western blotting. Immunohistostaining showed that during adenomyosis, PRL and its receptors are highly expressed in adenomyotic lesions. In cultured myometrial cells, protein expression of PRL and its receptors was increased during adenomyosis. Estradiol decreased PRLRs protein expression in nonadenomyotic stromal cells and in adenomyotic myometrial cells, and increased PRL secretion by adenomyotic myometrial cells. Moreover, PRL secretion was increased in untreated epithelial and stromal cells during adenomyosis. On the other hand, in stromal cells, PRLRs messenger RNA and protein expression was decreased, as determined by real-time PCR and Western blotting, respectively. Obtained results show that significant changes in PRL and PRLRs expression are observed in uterine tissue and cells during adenomyosis, which were also affected by E₂. These data suggest involvement of PRL in adenomyosis development and the link between PRL and E₂ actions during the dysfunction in cows.

Reproductive actions of prolactin mediated through short and long receptor isoforms

Prolactin (PRL) is a polypeptide hormone with a wide range of physiological functions, and is critical for female reproduction. PRL exerts its action by binding to membrane bound receptor isoforms broadly classified as the long form and the short form receptors. Both receptor isoforms are highly expressed in the ovary as well as in the uterus. Although signaling through the long form is believed to be more predominant, it remains unclear whether activation of this isoform alone is sufficient to support reproductive functions or whether both types of receptor are required. The generation of transgenic mice selectively expressing either the short or the long form of PRL receptor has provided insight into the differential signaling mechanisms and physiological functions of these receptors. This review describes the essential finding that both long and short receptor isoforms are crucial for ovarian functions and female fertility, and highlights novel mechanisms of action for these receptors.

Luteal and placental function in the bitch: spatio-temporal changes in prolactin receptor (PRLr) expression at dioestrus, pregnancy and normal and induced parturition

BACKGROUND

Endocrine mechanisms governing canine reproductive function remain still obscure. Progesterone (P4) of luteal origin is required for maintenance of pregnancy. Corpora lutea (CL) are gonadotrop-independent during the first third of dioestrus; afterwards prolactin (PRL) is the primary luteotropic factor. Interestingly, the increasing PRL levels are accompanied by decreasing P4 concentrations, thus luteal regression/luteolysis occurs in spite of an increased availability of gonadotropic support. PRL acts through its receptor (PRLr), the expression of which has not yet been thoroughly investigated at the molecular and cellular level in the dog.

METHODS

The expression of PRLr was assessed in CL of non-pregnant dogs during the course of dioestrus (days 5, 15, 25, 35, 45, 65 post ovulation; p.o.) as well as in CL, the utero/placental compartments (Ut/Pl) and interplacental free polar zones (interplacental sites) from pregnant dogs during the pre-implantation, post-implantation and mid-gestation period of pregnancy and during the normal and antigestagen-induced luteolysis. Expression of PRLr was tested by Real Time PCR, immunohistochemistry and in situ hybridization.

RESULTS

In non-pregnant CL the PRLr expression was significantly upregulated at day 15 p.o. and decreased significantly afterwards, towards the end of dioestrus. CL of pregnancy showed elevated PRLr expression until mid gestation while prepartal downregulation was observed. Interestingly, placental but not interplacental expression of PRLr was strongly time-related; a significant upregulation was observed towards mid-gestation. Within the CL PRLr was localized to the luteal cells; in the Ut/Pl it was localized to the fetal trophoblast and epithelial cells of glandular chambers. Moreover, in mid-pregnant animals treated with an antigestagen, both the luteal and placental, but not the uterine PRLr were significantly downregulated.

CONCLUSIONS

The data presented suggest that the luteal provision of P4 in both pregnant and non-pregnant dogs may be regulated at the PRLr level. Furthermore, a role of PRL not only in maintaining the canine CL function but also in regulating the placental function is strongly suggested. A possible functional interrelationship between luteal P4 and placental and luteal PRLr expression also with respect to the prepartal luteolysis is implied.

Prolactin-dependent modulation of organogenesis in the vertebrate: Recent discoveries in zebrafish

The scientific literature is replete with evidence of the multifarious functions of the prolactin (PRL)/growth hormone (GH) superfamily in adult vertebrates. However, little information is available on the roles of PRL and related hormones prior to the adult stage of development. A limited number of studies suggest that GH functions to stimulate glucose transport and protein synthesis in mouse blastocytes and may be involved during mammalian embryogenesis. In contrast, the evidence for a role of PRL during vertebrate embryogenesis is limited and controversial. Genes encoding GH/PRL hormones and their respective receptors are actively transcribed and translated in various animal models at different time points, particularly during tissue remodeling. We have addressed the potential function of GH/PRL hormones during embryonic development in zebrafish by the temporary inhibition of in vivo PRL translation. This treatment caused multiple morphological defects consistent with a role of PRL in embryonic-stage organogenesis. The affected organs and tissues are known targets of PRL activity in fish and homologous structures in mammalian species. Traditionally, the GH/PRL hormones are viewed as classical endocrine hormones, mediating functions through the circulatory system. More recent evidence points to cytokine-like actions of these hormones through either an autocrine or a paracrine mechanism. In some situations they could mimic actions of developmentally regulated genes as suggested by experiments in multiple organisms. In this review, we present similarities and disparities between zebrafish and mammalian models in relation to PRL and PRLR activity. We conclude that the zebrafish could serve as a suitable alternative to the rodent model to study PRL functions in development, especially in relation to organogenesis.

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Bone morphogenetic protein 1 processes prolactin to a 17-kDa antiangiogenic factor

In addition to classical expression patterns in pituitary and placenta and functions in growth and reproduction, members of the small family of hormones that includes prolactin (PRL), growth hormone (GH), and placental lactogen are expressed by endothelia and have angiogenic effects. In contrast, 16- to 17-kDa proteolytic fragments of these hormones have antiangiogenic effects. Here we show that PRL and GH are bound and processed by members of the bone morphogenetic protein 1 (BMP1) subgroup of extracellular metalloproteinases, previously shown to play key roles in forming extracellular matrix and in activating certain TGFbeta superfamily members. BMP1 has previously been suggested to play roles in angiogenesis, as high throughput screens have found its mRNA to be one of those induced to highest levels in tumor-associated endothelia compared with resting endothelia. PRL and GH cleavage is shown to occur in each hormone at a single site typical of sites previously characterized in known substrates of BMP1-like proteinases, and the approximately 17-kDa PRL N-terminal fragment so produced is demonstrated to have potent antiangiogenic activity. Mouse embryo fibroblasts are shown to produce both PRL and GH and to process them to approximately 17-kDa forms, whereas GH and PRL processing activity is lost in mouse embryo fibroblasts doubly null for two genes encoding BMP1-like proteinases.

Prolactin and prolactin receptor expressions in a marine teleost, pufferfish Takifugu rubripes

To investigate the physiological significance of prolactin (PRL) in a marine teleost, pufferfish (or fugu), Takifugu rubripes, we cloned and characterized cDNAs encoding its PRL and PRL receptor (PRLR) from the pituitary and gills, respectively. The fugu PRL cDNA consisted of 995 bp and encoded a protein of 213 amino acids. The PRLR, consisting of 510 amino acids, contained a putative signal peptide, an extracellular domain with two pairs of cysteines, a WSXWS motif, a single transmembrane domain, and a cytoplasmic (intracellular) domain with box 1 and box 2 regions, all of which are characteristic of the cytokine receptor superfamily. Reverse transcription-PCR showed the expression of PRLR mRNA in osmoregulatory organs, such as gills, kidney, and intestine, whereas pufferfish PRL mRNA was detected only in the pituitary. Furthermore, in situ hybridization revealed the expression of pufferfish PRLR in branchial chloride cells, kidney tubule cells, and intestinal epithelia. The PRL-gene expression levels in the pituitary were about five times higher in 25%-diluted seawater than in full-strength seawater. These results suggest that fugu PRL regulates water and electrolyte balances through PRLR expressed in the osmoregulatory organs, as is the case with freshwater-adapted euryhaline species.

Prolactin signals via Stat5 and Oct-1 to the proximal cyclin D1 promoter

Prolactin (PRL) modulates proliferation in the mammary gland and other tissues, in part through inducing transcription of cyclin D1, a key regulator of G(1) phase cell cycle progression. We showed previously that PRL, via Jak2, induces binding of Stat5 to a distal GAS site (GAS1) in the cyclin D1 promoter. However, full promoter activity requires additional regions, and in this paper we explored PRL-induced activity at sites other than GAS1. We defined a second PRL-responsive region spanning -254 to -180 that contains a second GAS site (GAS2) and an Oct-1 binding site. Although mutational analysis indicated independence from GAS2, proximal promoter activity remained Stat5-dependent, suggesting alternative mechanisms. EMSA showed that Oct-1 binds the -254 to -180 region and that PRL decreased Oct-1 binding, leading to increased PRL-responsiveness of the proximal cyclin D1 promoter in multiple cell lines. This suggests a role for Oct-1 in PRL-dependent control of cyclin D1 transcription.

Growth hormone receptor gene expression in the skeletal muscle of normal and double-muscled bovines during foetal development

The expression of the growth hormone receptor (GHR) gene was investigated in semitendinosus muscle during bovine foetal development in both normal and double-muscled Charolais foetuses which differ with respect to muscle development. Northern-blot analysis of foetal muscle RNA preparations with a GHR cDNA probe identified the 4.5 kb GHR mRNA as early as 130 days post-conception. In double-muscled animals, the expression of GHR mRNA increased from 130 to 210 days of gestation while it stayed stable in normal ones. It was significantly higher (P < 0.05) in double-muscled foetuses compared to normal ones from the second third of gestation. Northern-blot analysis of foetal muscle RNA preparations from both genotypes with a beta-actin cDNA probe, revealed lower beta-actin gene expression in double-muscled foetuses than in normal ones, suggesting a delay in the differentiation of muscle cells. In situ hybridisation revealed the localisation of specific GHR mRNA in muscle cells at all gestation stages analysed (130, 170, 210 days post-conception) but not in connective tissue surrounding the muscle cells. At the adult stage, the hybridisation signal was also very high and observed in muscle cells only. These results show the ontogeny of GHR mRNA in bovine muscle and demonstrate a difference between normal and double-muscled animals.

Growth hormone as an early embryonic growth and differentiation factor

In this review we consider the evidence that growth hormone (GH) acts in the embryo as a local growth, differentiation, and cell survival factor. Because both GH and its receptors are present in the early embryo before the functional differentiation of pituitary somatotrophs and before the establishment of a functioning circulatory system, the conditions are such that GH may be a member of the large battery of autocrine/paracrine growth factors that control embryonic development. It has been clearly established that GH is able to exert direct effects, independent of insulin-like growth factor-I (IGF-I), on the differentiation, proliferation, and survival of cells in a wide variety of tissues in the embryo, fetus, and adult. The signaling pathways behind these effects of GH are now beginning to be determined, establishing early extrapituitary GH as a bona fide developmental growth factor.

Placental hormones and fetal–placental development

Production of growth promoting substances by the placenta is regulated differently from the way production of similar compounds is regulated by maternal organs in various cases. Gene duplication is one of the mechanisms that facilitated the evolution of placental specific endocrine activity. Cattle, sheep and goats, although evolutionarily related, differ significantly from each other in the way their placental growth hormone (GH) and prolactin (PRL)-like hormones have evolved. Cattle carry one copy of the GH gene and there is no evidence yet for expression of that single GH gene copy in the placenta. On the other hand, the ovine GH gene has been duplicated and both oGH copies are expressed in the placenta during early stages of gestation. Prolactin gene duplication in ruminants resulted in the formation of specific placental-expressed prolactin-related genes including the placental lactogen (PL) gene. In homologous state, ovine PL manifests PRL activity, but antagonizes GH activity. Ovine PL activity which can be mediated by PRL receptors or by hetero-dimerization of GH and PRL receptors, provide a novel regulatory mechanism for somatogenic activity dependent on the coexistence of both GH and PRL receptors in the same cells. Another mechanism for specific placental endocrine activity is silencing of the alleles through genetic imprinting. Disruption of genetic imprinting of placental genes has been proposed as one of the explanations for the loss of cloned fetuses generated by somatic cell nuclear transfer.

Expression of prolactin receptor mRNA in the abdominal gland of the newt Cynops ensicauda

To further the understanding that the structural development of the Cynops ensicauda abdominal gland and the synthesis of the pheromone silefrin in the gland are under the control of prolactin and androgen, we sought to demonstrate the presence of prolactin receptor (PRLR) mRNA in the gland. Firstly, PRLR cDNA was isolated from an abdominal gland cDNA library. A cDNA consisting of a 415-bp 5'-untranslated region, 1878-bp open reading frame and 175-bp 3'-untranslated region was obtained. The deduced amino acid sequence consisted of 626 amino acids with signal peptide and single transmembrane domain. By Northern blot analysis using partial C. ensicauda PRLR cDNA, two transcripts, of 3 and 10 kb, were detected for PRLR in the brain, liver, kidney, abdominal gland, oviduct and skin. RT-PCR coupled with Southern blot analysis showed that the PRLR gene was transcribed broadly in newt organs and revealed that PRLR mRNA levels in the abdominal gland were much higher in sexually developed newts than in the sexually undeveloped ones. By in situ hybridization, specific signals were detected in the epithelial cells of the abdominal gland of sexually developed newts, but much less in those of the sexually undeveloped ones.

Estrogen and antiestrogen effects on neonatal ovine uterine development

Postnatal development of the ovine uterus between birth and Postnatal Day (PND) 56 involves differentiation of the endometrial glandular epithelium from the luminal epithelium followed by tubulogenesis and branching morphogenesis. These critical events coincide with expression of estrogen receptor alpha (ERalpha) by nascent endometrial glands and stroma. To test the working hypothesis that estrogen and uterine ERalpha regulate uterine growth and endometrial gland morphogenesis in the neonatal ewe, ewes were treated daily from birth (PND 0) to PND 55 with 1) saline and corn oil as a vehicle control (CX), 2) estradiol-17 beta (E2) valerate (EV), an ERalpha agonist, 3) EM-800, an ERalpha antagonist, or 4) CGS 20267, a nonsteroidal aromatase inhibitor. On PND 14, ewes were hemihysterectomized, and the ipsilateral oviduct and ovary were removed. The remaining uterine horn, oviduct, and ovary were removed on PND 56. Treatment with CGS 20267 decreased plasma E2 levels, whereas EM-800 had no effect compared with CX ewes. Uterine horn weight and length were not affected by EM-800 or CGS 20267 but were decreased in EV ewes on PND 56. On PND 14 and PND 56, treatment with EV decreased endometrial thickness but increased myometrial thickness. The numbers of ductal gland invaginations and endometrial glands were not affected by CGS but were lower in EM-800 ewes on PND 56. Exposure to EV completely inhibited endometrial gland development and induced luminal epithelial hypertrophy but did not alter uterine cell proliferation. Exposure to EV substantially decreased expression of ERalpha, insulin-like growth factor (IGF) I, and IGF-II in the endometrium. Results indicate that circulating E2 does not regulate endometrial gland differentiation or development. Although ERalpha does not regulate initial differentiation of the endometrial glandular epithelium, results indicate that ERalpha does regulate, in part, coiling and branching morphogenesis of endometrial glands in the neonatal ewe. Ablation of endometrial gland genesis by EV indicates that postnatal uterine development is extremely sensitive to the detrimental effects of inappropriate steroid exposure.

Ovine placental lactogen specifically binds to endometrial glands of the ovine uterus

A hormonal servomechanism has been proposed to regulate differentiation and function of the endometrial glandular epithelium (GE) in the ovine uterus during pregnancy. This mechanism involves sequential actions of estrogen, progesterone, ovine interferon tau (IFNtau), placental lactogen (oPL), and placental growth hormone (oGH). The biological actions of oPL in vitro are mediated by homodimerization of the prolactin receptor (oPRLR) and heterodimerization of the oPRLR and oGH receptor. The objectives of the study were to determine the effects of intrauterine oPL, oGH, and their combination on endometrial histoarchitecture and gene expression and to localize and characterize binding sites for oPL in the ovine uterus in vivo using an in situ ligand binding assay. Intrauterine infusion of oPL and/or oGH following IFNtau into ovariectomized ewes treated with progesterone daily differentially affected endometrial gland number and expression of uterine milk proteins and osteopontin. However, neither hormone affected PRLR, insulin-like growth factor (IGF)-I, or IGF-II mRNA levels in the endometrium. A chimeric protein of placental secretory alkaline phosphatase (SEAP) and oPL was used to identify and characterize binding sites for oPL in frozen sections of interplacentomal endometrium from pregnant ewes. Specific binding of SEAP-oPL was detected in the endometrial GE on Days 30, 60, 90, and 120 of pregnancy. In Day 90 endometrium, SEAP-oPL binding to the endometrial GE was displaced completely by oPL and prolactin (oPRL) but only partially by oGH. Binding experiments using the extracellular domain of the oPRLR also showed that iodinated oPL binding sites could be competed for by oPRL and oPL but not by oGH. Collectively, results indicate that oPL binds to receptors in the endometrial glands and that oPRL is more effective than oGH in competing for these binding sites. Thus, effects of oPL on the endometrial glands may be mediated by receptors for oPRL and oGH.

Preparation and expression of biologically active prolactin and growth hormone receptors and suppressor of cytokine signaling proteins 1, 2, 3, and 6 tagged with cyan and yellow fluorescent proteins

To prepare reagents for a study of the interactions of prolactin (PRL) and growth hormone (GH) receptors (Rs) with suppressor of cytokine signaling (SOCS) proteins in living cells by fluorescence resonance energy transfer methodology, the respective proteins were tagged with cyan (CFP) or yellow (YFP) fluorescent protein. Constructs encoding ovine (o)PRLR-YFP, oPRLR-CFP, oGHR-YFP, and oGHR-CFP tagged downstream of the receptor DNA were prepared in the plasmid pcDNA plasmid and tested for biological activity in HEK 293T cells transiently cotransfected with those constructs and the reporter gene encoding luciferase. All four constructs were biologically active and as potent as their untagged counterparts. Cells transfected with those proteins exhibited fluorescence in the cytoplasm and the membrane. Constructs encoding DNA tagged with YFP or CFP upstream of SOCS1, SOCS2, SOCS3, and SOCS6 were prepared in pECFP-C1 and pEYFP-C1 plasmids. The biological activities of SOCS1 and SOCS3 tagged at their amino termini were assayed by their ability to inhibit placental lactogen (PL)- or GH-induced activation of JAK2/STAT5-mediated luciferase transcription in HEK 293T cells; the activity of SOCS2 was assayed by its ability to abolish SOCS1-induced inhibition. The tagged proteins exhibited biological activity that was equal to or even more potent than their untagged counterparts. The biological activities of CFP-SOCS2 and YFP-SOCS2 were also assayed using GST-GHR binding assay. Their interaction with the cytosolic domain of GHR was equivalent to their respective untagged counterparts. The biological activity of the construct encoding SOCS6 was not tested because of lack of a suitable assay. Cells transfected with eight of these tagged constructs expressed the fluorescent proteins in both the nucleus and cytosol; the tagged SOCS2 was localized mostly in the latter compartment.

The role of growth hormone in fetal development

Studies across several species, particularly the mouse, show that growth hormone (GH, somatotrophin) is an important determinant of litter size, and to a lesser extent, of birth length. GH acts at all stages of development, from ovulation through preimplantation development to the late fetus, with actions on both embryo/fetus and mother contributing to successful fetal development. The fact that these are not more obvious in vivo is likely a result of redundancy of cytokine hormone action, particularly in relation to prolactin, which shares common actions and receptor locations with GH.

Structure and tissue distribution of prolactin receptor mRNA in Japanese flounder (Paralichtys olivaceus): conserved and preferential expression in osmoregulatory organs

In diadromous and euryhaline teleosts, it has been established that prolactin (PRL) is a major hormone regulating the maintenance of water and electrolyte homeostasis by acting on its receptor (PRLR) expressed in the osmoregulatory organs. To investigate the major physiological role of PRL in a marine teleost, cDNA for the Japanese flounder (Paralichtys olivaceus) prolactin receptor (fPRLR) has been cloned and characterized. The predicted fPRLR is composed of 636 amino acids conserving common structural features, such as the WSXWS motif and box 1, that are observed in the members of the cytokine receptor superfamily. By Northern blot analysis, 3.5-kb transcripts for fPRLR were clearly detected in the gill, kidney, and intestine. By RNase protection assay, similarly high levels of mRNA expression were detected in these osmoregulatory organs and lower expression levels were seen in the brain for both males and females. Interestingly, a distinct expression level of fPRLR mRNA was observed in the testis, but not in the ovary. The present results suggest that PRL may play an important role in the control of water and electrolyte balance through PRLR expressed in the osmoregulatory organs in the marine teleost the Japanese flounder as well as in other teleosts. Furthermore, PRL may differentially regulate gonadal functions in males and females of Japanese flounder.

Growth Hormone (GH)/GH Receptor Expression and GH-Mediated Effects During Early Bovine Embryogenesis1

Pituitary growth hormone (GH) stimulates postnatal growth and metabolism. The role of GH and its receptor (GHR) during prenatal development, however, is still controversial. As shown by reverse transcription polymerase chain reaction (RT-PCR), bovine in vitro fertilization embryos synthesized the transcript of GHR from Day 2 of embryonic life onwards. Real time RT-PCR revealed that synthesis of GHR mRNA was increased 5.9-fold in 6-day-old embryos compared with 2-day-old embryos. Using in situ hybridization, the mRNA encoding GHR was predominantly localized to the inner cell mass of blastocysts. The GHR protein was first visualized 3 days after fertilization. GH-specific transcripts were first detected in embryos on Day 8 of in vitro culture. As shown by transmission electron microscopy, GH treatment resulted in elimination of glycogen storage in 6- to 8-day-old embryos and an increase in exocytosis of lipid vesicles. These results suggest that a functional GHR able to modulate carbohydrate and lipid metabolism is synthesized during preimplantation development of the bovine embryo and that this GHR may be subject to activation by embryonic GH after Day 8.

Dysregulation of mammary Stats 1,3 and 5 and PRL receptors by overexpression of TGFalpha

Mammary TGFalpha overexpression results in delayed involution and eventually mammary cancer in transgenic mice. We hypothesized that STATs and PRL receptors (PRLR), critical regulators of mammary function, are altered in these animals and may contribute to this phenotype. We examined these factors late in the first pregnancy (d.18) and during normal involution (d.4 post-lactation) in WAP-TGFalpha transgenic mice and non-transgenic controls. Long form PRLR mRNA in WAP-TGFalpha glands at both pregnant d.18 and d.4 post-lactation was significantly reduced compared to controls, and PRLR-S3 failed to rise during involution. Total and pTyr STAT 1,3,5a and 5b also were altered. STAT 3 was higher at both times in WAP-TGFalpha glands. STAT 5a and 5b were lower at late pregnancy, but higher post-lactation; however, pTyr(694) STAT 5 was abnormally low at both times. Thus overexpression of TGFalpha has direct or indirect effects on both STATs and PRL responsiveness in vivo, which may reflect mechanisms of TGFalpha-induced mammary epithelial abnormalities.

Evidence of rainbow trout prolactin interaction with its receptor through unstable homodimerisation

This study aims to characterise Prolactin receptor (PRLR) in rainbow trout for which no information is available despite the availability of Salmonid PRL preparations. By screening a freshwater rainbow trout intestine cDNA library with a probe corresponding to the extracellular domain (ECD) of tilapia PRLR, we have cloned a 2.5 kb insert coding for the PRLR. The mature protein of 614 amino acid residues is similar to PRLR isolated in tilapia and also the long form of mammalian PRLR. Analysis of PRLR gene expression in osmoregulatory organs revealed the presence of a unique transcript, thus confirming the involvement of this hormone in the control of osmoregulation in this fish species. By using surface plasmon resonance (SPR) technology, kinetic measurement of interaction between trout PRL and its receptor ECD was studied. This approach allowed us to demonstrate the formation of a transient, unstable homodimeric complex. This unstability could explain the inability to perform binding experiments using homologous PRL. In contrast, heterologous lactogenic ligands were able to interact through a more stable complex. Whether these characteristics of PRL-receptor interaction in rainbow trout are different to what occurs in tilapia where a homologous radioreceptor assay was developed would require further studies.

Neonatal ovine uterine development involves alterations in expression of receptors for estrogen, progesterone, and prolactin

Effects of age on uterine histoarchitecture, cell proliferation, and hormone receptor expression were determined for neonatal ewe lambs from birth (Postnatal Day [PND] 0) to PND 56. Uteri were histologically evaluated and proliferating cell nuclear antigen (PCNA), estrogen receptor alpha (ER-alpha), progesterone receptor (PR), and prolactin receptor (PRL-R) expression were characterized by in situ hybridization (ISH), immunohistochemistry, or both. The most striking feature of neonatal uterine development was the genesis and development of glands in the intercaruncular areas of endometrium. After birth, endometrial glandular epithelium (GE) budded and differentiated into the underlying stroma from the luminal epithelium (LE) between PNDs 1 and 7. Between PNDs 14 and 56, extensive coiling and branching morphogenesis of nascent endometrial glands occurred. By PND 56, the uterine wall appeared to be histoarchitecturally mature. At birth, nuclear PCNA protein was strongly detected in LE. Between PNDs 7 and 56, high levels of PCNA, ER-alpha, and PR gene expression were detected in both nascent and developing GE. Higher levels of PCNA and ER-alpha expression were detected in GE at the tips of developing glands as well as in the surrounding stroma. Progesterone was below detectable limits in serum. Serum estradiol-17beta levels were high on PND 1, increased from PNDs 14 to 28, and declined from PND 42 to PND 56. Serum PRL levels increased from PNDs 1 to 14 and declined thereafter. Using ISH and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, expression of mRNAs for short and long forms of the ovine PRL-R were first detected in nascent GE on PND 7 and increased between PNDs 7 and 56 in proliferating and differentiating GE. These results indicate that 1) uterine gland genesis is initiated between PNDs 1 and 7 after birth and is essentially completed by PND 56; 2) neonatal uterine morphogenesis involves temporal and spatial alterations in cell proliferation and ER-alpha, PR, and PRL-R gene expression; 3) PRL-R expression is a unique marker of GE differentiation and proliferation; and 4) serum estradiol-17beta and PRL levels increase during the onset of GE tubular branching morphogenesis. Results support the hypothesis that neonatal ovine uterine development involves epithelial PRL-R and ER-alpha activation to stimulate and maintain endometrial gland genesis and branching morphogenesis.

Sequence and functional characterisation of the marmoset monkey (Callithrix jacchus) prolactin receptor: comparative homology with the human long-form prolactin receptor

This study demonstrates the cloning and in-vitro characterisation of the marmoset monkey (Callithrix jacchus) prolactin receptor cDNA. The marmoset prolactin receptor cDNA was generated by reverse transcription-polymerase chain reaction using adrenal RNA and primers designed from prolactin receptor conserved regions. Sequence analysis predicts a mature protein of 598 amino acids exclusive of the 24 amino acid signal peptide. The marmoset prolactin receptor cDNA shares 93 and 61% base pair, and 89 and 61% amino acid sequence homologies with the long form human and rat prolactin receptor cDNA, respectively. The marmoset prolactin receptor cDNA sequence retains all the receptor sequences that have been shown previously to be essential for ligand binding, structural integrity and signal transduction. Transfection of human 293 fibroblast cells with the marmoset prolactin receptor cDNA (three independent experiments) confirmed the expression of a receptor that has high binding affinity to human growth hormone (K(a)=3.6+/-0.07 nM(-1) and B(max)=7.55+/-2.06x10(-11) M) and human prolactin (K(a)=3.1+/-0.12 nM(-1) and B(max)=2.87+/-0.66x10(-11) M). Functionality of the receptor was assessed by co-transfection of 293 fibroblast cells with marmoset prolactin receptor cDNA and the Jak2 cDNA, or marmoset prolactin receptor and a Stat5 responsive element linked to the luciferase coding sequence. Incubation of the cells with 18 nM ovine prolactin resulted in rapid phosphorylation of Jak2 as ascertained by Western blotting. In addition, the marmoset prolactin receptor cDNA led to 9.06+/-0.47-fold induction of luciferase gene activity. This was comparable with the induction observed following transfection with the human prolactin receptor cDNA (8.55+/-0. 5-fold). In-vivo prolactin receptor expression in the marmoset monkey was assessed by ribonuclease protection assay and detected in a number of tissues including female reproductive organs. These data confirm the cloning and functionality of the marmoset prolactin receptor cDNA. The marmoset prolactin receptor shares a high sequence homology with the long-form human prolactin receptor, and both receptors bind hormones with comparable affinity and confer a similar intracellular response. The marmoset monkey may provide a useful tool to investigate the role of prolactin in primate reproduction.

Prolactin receptor and uterine milk protein expression in the ovine endometrium during the estrous cycle and pregnancy

Lactogenic hormones regulate epithelial proliferation, differentiation, and function in a variety of epitheliomesenchymal organs. During pregnancy, the ovine uterus is a potential site for endocrine and paracrine actions of lactogenic hormones in the form of pituitary prolactin (PRL) and placental lactogen (PL). These studies determined temporal and spatial alterations in PRL receptor (PRL-R) and expression of uterine milk proteins (UTMP), a marker of endometrial secretory activity, in the ovine endometrium during the estrous cycle and pregnancy. Slot-blot hybridization analysis indicated that steady-state levels of endometrial PRL-R mRNA increased during pregnancy. In situ hybridization and immunohistochemical analyses indicated that PRL-R mRNA and protein were exclusively expressed in the endometrial glandular epithelium (GE). No PRL-R mRNA expression was detected in luminal epithelium, stroma, myometrium, or conceptus trophectoderm. Reverse transcription-polymerase chain reaction analyses determined that the endometrial GE expressed both long and short alternative splice forms of the ovine PRL-R gene. Slot-blot hybridization analysis indicated that steady-state levels of intercaruncular endometrial UTMP mRNA increased about 3-fold between Days 20 and 60, increased another 3-fold between Days 60 and 80, and then declined slightly to Day 120. In pregnant ewes, UTMP mRNA expression was restricted to the endometrial GE in the stratum spongiosum (sGE), increased substantially between Days 15 and 17, and, between Days 17 to 50 of gestation, was markedly higher in upper than lower sGE. After Day 50, hyperplasia of the sGE was accompanied by increased UTMP mRNA expression by all sGE. Collectively, results indicate that 1) endometrial sGE is a primary target for actions of lactogenic hormones and 2) UTMP mRNA expression is correlated with PL production by the trophectoderm and state of sGE differentiation during pregnancy. It is proposed that activation of PRL-R signal transduction pathways by PRL and PL plays a major role in endometrial GE remodeling and differentiated function during pregnancy in support of conceptus growth and development.

Molecular cloning and expression studies of a prolactin receptor in goldfish (Carassius auratus)

A full-length cDNA clone, of a size of 4.6 kb, for the goldfish prolactin receptor has been isolated. This cDNA clone encodes a protein of 600 amino acids homologous to prolactin receptors of other species. A Kyte-Doolittle hydropathy analysis of the receptor indicates that the translated protein consists of a signal peptide of 22 amino acids, an extracellular domain of 228 amino acids, a single transmembrane domain of 24 amino acids, and an intracellular domain of 346 amino acids. Several characteristic landmarks of prolactin receptor could be identified in this clone. These include the four conserved cysteine residues and the WS motif within the extracellular domain, and the box 1 and box 2 regions of the intracellular domain. Among all the prolactin receptor sequences known to date, this clone bears the closest resemblance to the tilapia prolactin receptor, although homology between these two fish prolactin receptors is rather low. There are only 57.4% of nucleotide and 48.3% of amino acid sequence identities between these two fish receptors. This receptor cDNA was transfected into CHO-K1 cells for functional analysis. RT-PCR analysis with a pair of gene specific primers indicate that the receptor was transcribed in the transfected cells. Using a cell proliferation assay based on the reduction of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, the receptor transfected CHO-K1 cells can be stimulated to proliferate upon the addition of ovine prolactin in the culture medium. The tissue distribution of the prolactin receptor in goldfish was studied by RT-PCR/Southern analysis and by Northern analysis. The results indicated that the receptor is expressed mostly in the kidney, the gill and the intestine of goldfish, corroborating with the osmoregulatory role of prolactin in fish. In addition, an appreciable level of the receptor is also found in the brain and gonads of goldfish. Northern analysis showed that there are two transcript sizes, a major 4.6 kb and a minor 3.5 kb mRNAs, in the kidney, gill and intestine.

Functional heterodimerization of prolactin and growth hormone receptors by ovine placental lactogen

Although homo- or heterodimerization are common mechanisms for activation of cytokine receptors, cross-talk between two distinct receptors in this superfamily has been never shown. Here we show a physiologically relevant example indicating that such an interaction does occurs, thus raising the hypothesis that heterodimerization between distinct cytokine receptors may be a novel mechanism contributing to the diversity of cytokine signaling. These findings were documented using both surface plasmon resonance and gel filtration experiments and show that ovine placental lactogen (PL) heterodimerizes the extracellular domains (ECDs) of ruminant growth hormone receptor (GHR) and prolactin receptor (PRLR). We also show that PL or PL analogues that exhibit little or no activity in cells transfected with PRLRs and no activity in cells transfected with ovine GHRs exhibit largely enhanced activity in cells cotransfected with both PRLRs and GHRs. Furthermore, chimeric receptors consisting of cytosolic and transmembrane part of ovine GHR or ovine PRLR and ECDs of human granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) alpha or beta were constructed. Upon transfection into Chinese hamster ovary cells along with reporter luciferase gene and stimulation by GM-CSF, a significant increase in luciferase activity occurred when GM-CSFR-alpha-PRLR and GM-CSFR-beta-GHR or GM-CSFR-alpha-GHR and GM-CSRR-beta-PRLR were cotransfected. In conclusion, we show that ovine PL is capable of functional heterodimerization of GHR and PRLR and that when their cytosolic parts, coupled to the ECD of GM-CSF receptors, are heterodimerized by GM-CSF, they are capable of transducing biological signal.

Cloning and sequence analysis of the extracellular region of the polar bear (Ursus maritimus) luteinizing hormone receptor (LHr), follicle stimulating hormone receptor (FSHr), and prolactin receptor (PRLr) genes and their expression in the testis of the black bear (Ursus americanus)

Male black bears undergo seasonal changes in testicular activity. The testes are fully functional from May through July, regress from July through December, and recrudesce from January until May. The mechanisms responsible for the initiation of testicular recrudescence in the bear are unknown. The objectives of this study were to: (1) clone and sequence a substantial fragment of the extracellular portion of the luteinizing hormone receptor (LHr: 646 bp) and follicle stimulating hormone receptor (FSHr: 852 bp), and the extracellular/transmembrane portion of the prolactin receptor (PRLr: 680 bp) in the bear using reverse transcription-polymerase chain reaction (RT-PCR); and (2) determine whether the expression of LH-, FSH-, and PRL-receptor mRNA transcripts differs between the beginning and terminal stages of testicular recrudescence. Comparisons of the partial cDNA and predicted amino acid sequences of ursine receptors with the corresponding sequences from the pig, cow, human, and rat suggest that the LHr and FSHr are highly conserved (LHr: 87.1-93.7%; FSHr: 86.0-92.7%) whereas the PRLr is less well conserved (81-87%). Testicular LHr mRNA was more abundant during the breeding season in May than during the non-breeding season (early stage of recrudescence) in January. In contrast, testicular FSHr mRNA abundance was greater in January than in May. Testicular PRLr mRNA appeared equally abundant in January and May; however, two additional transcripts were present during the breeding season in May. This study provides molecular tools for future investigations of the control of testicular recrudescence in the black bear and demonstrates that the expression of testicular gonadotropin and PRL receptor mRNA is seasonally regulated. Mol. Reprod. Dev. 55:136-145, 2000.

Evaluation of the somatogenic activity of bovine placental lactogen with cell lines transfected with the bovine somatotropin receptor

Studies have shown that bovine placental lactogen (bPL) has partial somatogenic activity in vivo even though binding results clearly indicate bPL does not cause homodimerization of the bovine somatotropin receptor (bST-R). To help understand the receptor binding versus biological activity of bovine somatotropin (bST) and bPL we have developed a homologous model system. Full length bST-R was stably transfected into a murine lymphoid cell line, Ba/F3 and a hamster kidney cell line, BHK. From both transfected cell lines, clones were isolated (Ba/F3-C1 and BHK-24) which demonstrated specific binding of bST and, or bPL. Bovine ST stimulated proliferation of the Ba/F3-C1 clonal line over a dose range of 10 to 3000 pM with an EC50 of 100 pM. A bST variant (des 1-4 bST) and porcine ST (pST) which both have approximately 10% of the binding affinity for bST-R as native bST were 1 and 10% as potent as bST in this bioassay, respectively. This suggests that affinity and biological activity are correlated for this system. Proliferation was initiated through the bST-R because addition of a monoclonal antibody which recognizes the extracellular domain of bST-R and inhibits binding of bST to its receptor, inhibited bST-stimulated mitosis. However, even though the affinity of bPL for the bST-R is similar to that of bST, bPL antagonized the proliferative action of bST with an IC50 of 1 nM. Components of the somatogenic signal transduction pathway were also evaluated in both cell lines. Addition of bST to the cell cultures increased phosphorylation of JAK2 in Ba/F3-C1 and BHK-24 cells in a dose-responsive manner but bPL failed to increase phosphorylation of JAK2 in either cell line. In summary, these data support the hypothesis that ST-R homodimerization is necessary for bioactivity in this model system but fail to explain apparent somatogenic activity of bPL in vivo.

Expression of growth hormone and its receptor in the placental and feto-maternal environment during early pregnancy in sheep

In a previous study we showed the existence of GH in the ovine placenta. We now supplement the information available on placental GH and describe the presence and distribution of GH receptor (GH-R) messenger RNA (mRNA) in uterine, fetal, and placental tissues during early pregnancy. GH mRNA was not detected in the placenta before day 27 (d27). Its expression peaked between d40 and d45 and fell after d55. GH mRNA was localized in the trophectoderm and syncytium. During the d35-d50 period, concentrations of GH in the maternal circulation were not increased. In umbilical blood, however, GH was detected from d35 and was presumed to be of placental origin, because GH mRNA was not detected in the fetal pituitary gland on d40. We report on GH-R mRNA expression in the placenta between d20-d120. The relative abundance of GH-R transcripts increased significantly between d25-d43. In the endometrium, GH-R mRNA was detected from d8-d120 of pregnancy and from d4-d16 of the cycle. GH-R mRNA was localized in the trophectoderm, fetal mesoderm, and maternal uterine stroma. In the fetal liver, GH-R mRNA was first detectable on d35. The results of this study indicate that between d35-d50 of pregnancy, the endometrium, placenta, and fetus are all potential targets for the placental GH.

The prolactin receptor from the brushtail possum (Trichosurus vulpecula): cDNA cloning, expression and functional analysis

A full length, prolactin receptor cDNA clone has been isolated from the brushtail possum (Trichosurus vulpecula). This clone encodes a 625 amino acid protein which shares 60-70 and 54% sequence identity with prolactin receptor (long form) sequences from mammalian and avian species, respectively. Sequence similarity was highest in the extra-cellular, hormone-binding domain and in specific regions of the intracellular domain which regulates prolactin receptor signalling in cells. Prolactin receptor mRNA was detected in a wide range of possum tissues and in the mammary gland the PRL-R gene was differentially expressed during lactation with peak mRNA levels being detected during the first 6 days of lactation and after day 115 throughout late lactation. This pattern of PRL-R mRNA expression in the mammary gland is similar to that observed for circulating prolactin in the lactating possum. In CHO cells transiently transfected with the possum prolactin receptor, expression of a beta-lactoglobulin promoter/reporter gene construct was increased 3-fold by adding prolactin. The possum prolactin receptor is therefore capable of binding ovine prolactin and activating the Jak2/Stat5 signalling cascade. This provides evidence for the highly conserved nature of the prolactin signalling pathway in mammalian evolution.

Cellular localization and evolution of prolactin receptor mRNA in ovine endometrium during pregnancy

In this study, we have investigated the expression of the prolactin receptor gene in ovine endometrium during oestrus cycle and pregnancy. Using reverse transcription-PCR analysis, we provided evidence that the prolactin receptor gene is specifically transcribed in this tissue. As shown by Northern blot analysis, the level of the prolactin receptor transcripts increased dramatically during late pregnancy. In situ hybridization experiments revealed that prolactin receptor mRNA was specifically expressed in the glandular compartment and confirmed the dramatic increase of its expression that occurs at the end of pregnancy. Taken together, these findings are consistent with a putative role of prolactin and/or related molecules in the regulation of the proliferation of the glandular compartment and/or in the control of the secretory activity of the endometrium.

Detection of prolactin receptor gene expression in the sheep pituitary gland and visualization of the specific translation of the signal in gonadotrophs

In sheep, as in other mammalian species, the pronounced reduction in GnRH and gonadotropin secretion that characterizes stages of infertility is normally associated with a conspicuous increase in the secretion of PRL. A possible role of PRL in modulating gonadotropin release implies the presence and activation of specific receptors in target tissues (i.e. pituitary, hypothalamus). In this study, we investigated the expression of PRL receptor (PRL-R) messenger RNA (mRNA) in the sheep pituitary and the distribution of the translated product in specific pituitary cell types. Using primers designed to flank different regions of the extracellular and cytoplasmic domains of the PRL-R, two complementary DNA (cDNA) fragments, one of which was specific for the long-form PRL-R, were amplified by reverse transcriptase-PCR. Sequencing revealed more than 95% identity with nucleotides 267-1272 of the bovine PRL-R cDNA. When these cDNA fragments were used as probes for the detection of PRL-R mRNA expression by Northern analysis, three major transcripts of approximately 13, 10, and 3.5 kb were identified in the pituitary. Both probes detected identical transcripts, suggesting that primarily the long form of PRL-R is expressed in the sheep pituitary gland. No difference in the abundance of pituitary PRL-R mRNA transcripts was observed between anestrous and breeding season ewes (P > 0.05). Additional RT-PCR studies revealed the existence of a cDNA variant bearing a 39-bp insert with a premature stop codon. Translation of the PRL-R mRNA was confirmed by Western blot analysis. The identification of PRL-R in specific pituitary cell types was carried out by immunocytochemistry. Double immunofluorescent staining, using antibodies to the rat liver PRL-R and specific monoclonal antibodies to the LHbeta-subunit, FSHbeta-subunit, free alpha-subunit, PRL, or GH, revealed that in both the pars distalis and pars tuberalis, all pituitary cells expressing PRL-R immunoreactivity were positive for LHbeta, although only 53% of LHbeta-positive cells expressed PRL-R. A small proportion (2%) of gonadotrophs expressing PRL-R immunoreactivity were negative for FSHbeta, indicating the specific localization of PRL-R in LH (or LH/FSH) secreting cells. Further, a selective cytological association was detected in the pars distalis where LH gonadotrophs appeared surrounded by lactotrophs. In contrast to these observations, PRL-R immunoreactivity was completely absent in lactotrophs and in the vast majority (>98%) of somatotrophs. In conclusion, here we show the expression of PRL-R mRNA in the sheep pituitary and the specific translation of the signal in LH (or LH/FSH) gonadotrophs. These results support the hypothesis that PRL may be involved in the regulation of gonadotropin secretion through a paracrine mechanism within the pituitary gland and that this action does not seem to be mediated by changes in PRL-R mRNA expression.

Developmental changes in the expression of the growth hormone receptor messenger ribonucleic acid and protein in the bovine ovary

By reverse transcription-polymerase chain reaction, the transcript of the growth hormone receptor (GHR) was demonstrated in oocytes, follicular cells, and corpus luteum of the bovine ovary. Immunoblotting using the monoclonal antibody mAb 263 resulted in a distinct protein band at 120 kDa, confirming that translation of the mRNA takes place in the same cells. Nonradioactive in situ hybridization revealed that distribution of the mRNA encoding GHR was correlated with the developmental stage of the follicle. Whereas in primordial and primary follicles the oocyte showed distinct amounts of the transcript encoding GHR, in tertiary follicles the mRNA was predominantly localized in the cells of the cumulus oophorus. GHR mRNA was also expressed in the large granulosa lutein cells, in the germinal epithelium, and in the endothelial cells of ovarian vessels. Colocalization of the GHR protein showed a distribution pattern identical to that of the mRNA. In calves, oocyte and follicle cells changed GHR expression in the same way as in the adult ovary. During embryonic development of the ovary, distinct amounts of the mRNA encoding GHR were found in primordial follicles shortly before birth. Our results imply that the GHR is involved in ovarian ontogenesis, especially in early folliculogenesis.

Luteotropic hormone receptors in the ovary of the mink (Mustela vison) during delayed implantation and early-postimplantation gestation

The reproductive cycle of the mink displays rigid seasonality and obligate embryonic diapause. After ovulation, the corpus luteum (CL) involutes, and it secretes basal progesterone until activated prior to implantation. To study changes in the relative abundance of luteal prolactin and LH receptor mRNA through gestation, ovaries and serum were collected from pregnant female mink at 2-day intervals (n = 3 per date) through embryonic diapause and CL activation (March 19-31) and at 5-day intervals through implantation and early-postimplantation gestation (March 31-April 15). To determine the effect of endogenous prolactin, mink received Alzet osmotic minipumps releasing 2 mg/day 2-bromo-alpha-ergocryptine (bromocriptine) or saline on March 19. Ovaries and serum were taken from 3 animals every 2 days until March 31. Prolactin receptor mRNA in ovaries was low during CL activation but increased 3-fold through embryo implantation. Its abundance correlated with prolactin binding to ovarian membranes and with circulating prolactin. Bromocriptine suppressed endogenous prolactin levels and prevented the increase in prolactin receptor mRNA. There was a transient peak in LH receptor mRNA in the ovaries at March 19-23, which declined to basal levels by March 25 and remained constant through midgestation. Bromocriptine prevented the preimplantation peak in LH receptor mRNA and reduced its abundance below pretreatment levels. The results suggest that prolactin up-regulates its receptor and maintains the LH receptor in the mink CL. The pattern of LH receptor mRNA argues for a role for LH in CL reactivation and termination of embryonic diapause in mink.

Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Growth hormone. A paracrine growth factor?

A number of tissues, including the brain, pituitary, immune system, placenta, mammary gland, and testis, may be self-contained units of GH regulation, production, and action. The production of GH and GH-releasing factors outside the hypothalamo-pituitary axis complements, rather than replaces, the traditional endocrine interactions between GH-releasing factors, GH, and its target tissues.

Interleukin-1 receptor mRNA expression in activated bovine leukocytes in vitro

Interleukin-1 (IL-1) is a key player in inflammation and the immune response. To better understand the complex interactions of IL-1 and its receptors in inflammation, we need to investigate how type I and type II IL-1 receptors (IL-1RI and IL-1RII) are regulated by cytokines and other mediators. Using semiquantitative reverse transcriptase PCR and Northern analysis, we examined the regulation of IL-1RI and IL-1RII mRNA levels in bovine polymorphonuclear leukocytes (PMNs) (i.e., neutrophils) and peripheral blood mononuclear cells (PBMCs) in vitro. IL-1RI mRNA levels were up-regulated in PBMCs by recombinant bovine IL-1beta (rBoIL-1beta), recombinant bovine granulocyte-macrophage colony-stimulating factor (rBoGM-CSF), rBoIL-4, recombinant bovine gamma interferon (rBoIFN-gamma), and dexamethasone. IL-1RI mRNA was increased in bovine PMNs exposed to rBoGM-CSF, rBoIL-4, and dexamethasone but was down-regulated by rBoIL-1beta and rBoIFN-gamma. IL-1RII mRNA was increased in bovine PBMCs and PMNs after exposure to rBoIL-1beta, rBoGM-CSF, rBoIL-4, and dexamethasone. In contrast, rBoIFN-gamma down-regulated the expression of bovine IL-1RII mRNA in PBMCs. These findings suggest that the expression of bovine IL-1RI and IL-1RII mRNAs is regulated differently by certain soluble stimuli (e.g., IFN-gamma) in PMNs and PBMCs.

Growth hormone and Pit-1 expression in bovine fetal lymphoid cells

Bovine fetal lymphoid cells were examined for growth hormone (GH) and the transcription factor Pit-1/GHF-1 mRNA. GH and Pit-1/GHF-1 transcripts were detected in thymocytes and splenocytes from fetuses at 60, 90, 120, and 270 d of gestation using reverse transcription-polymerase chain reaction (RT-PCR). Northern analysis indicated that the lymphoid GH mRNA was approximately 350 nucleotides larger than in the pituitary. RT-PCR analysis demonstrated that the coding regions as well as 3' untranslated region of the lymphocyte GH and pituitary transcripts were the same. Analysis of the 5'-untranslated region of the lymphocyte GH mRNA showed that transcription began upstream from the start site in the pituitary gland, suggesting differences in regulation in these tissues. Fetal thymocytes and splenocytes expressed Pit-1/GHF-1 mRNA; however, they contained only the 2.5-kb transcript. The GH and Pit-1/GHF-1 mRNA in fetal lymphoid cells supports the hypothesis that lymphocyte-derived GH may function as an autocrine and/or paracrine factor during the development and maturation of the bovine fetal immune system.

Differential expression of the growth hormone receptor and its transcript in bovine uterus and placenta

By reverse transcription-polymerase chain reaction (RT-PCR) the transcript of the growth hormone receptor (GHR) was proved in bovine placentae of different gestational stages. Using non-radioactive in situ hybridization (ISH) the mRNA encoding GHR was localized in the uterine epithelium, glands, vessels and amniochorion of the placenta from the sixth week until the ninth month of gestation. Production of mRNA was low during the first trimester, significantly increased in the second trimester and peaked at the end of the sixth month of pregnancy. No transcript of GHR was found in the endometrium of non-pregnant uteri. The colocalization of the protein using a monoclonal antibody showed the same distribution pattern as the mRNA. Immunoblotting revealed a protein with a molecular weight of 120 kDa in the endometrium of pregnant cows which was not found in non-pregnant uteri. Our results imply that growth hormone is involved in placental metabolism and embryonic development from the early beginning of pregnancy until birth.

Regulation of interleukin (IL)-1alpha, IL-1beta, and IL-6 expression by growth hormone and prolactin in bovine thymic stromal cells

Growth hormone (GH) and prolactin (PRL) have been implicated in T-cell development, but relatively little is known about the mechanism(s) of their actions on the multiple cell types in this complex tissue. Here, we investigated the effects of GH and PRL on the expression of interleukin (IL)-1alpha, IL-1beta and IL-6 in thymic stromal cells (TSC). These cytokine mRNAs were increased by GH, PRL and placental lactogen (PL) in primary cultures prepared from mid-gestational fetuses in a dose-dependent manner. IL-1 receptor antagonist (IL-1ra) abolished the hormone-induced IL-6 expression, suggesting that the induction of IL-6 was secondary to IL-1 activity. To examine the effects of these hormones on an individual cell type and develop a system in which signalling mechanisms can be studied, we generated immortalized cell lines using a strategy of conditional transformation. In the cell line, TSC-936, which displayed vimentin-positive staining and morphological characteristics of mesenchymal cells, both GH and PRL increased levels of steady-state mRNAs for IL-1alpha and IL-1beta. Nuclear run-on analysis revealed that the transcription rate of the IL-1beta gene was significantly increased by GH and PRL at 30 and 60 min, respectively, but that for IL-1alpha was not significantly changed, suggesting the possibility of an alternative mechanism mediating this response. These data suggest that modulation of cytokine gene expression is one mechanism by which GH and PRL facilitate thymic development and T-cell maturation.

Prolactin signal transduction to milk protein genes: carboxy-terminal part of the prolactin receptor and its tyrosine phosphorylation are not obligatory for JAK2 and STAT5 activation

In this study, we have developed several Chinese Hamster ovary (CHO) cell clones stably expressing various deletion mutant forms of the rabbit prolactin receptor (rbPRL-R) to better define the domains of the receptor involved in JAK2 kinase interaction, STAT5 activation, and to assess the role of tyrosine phosphorylation of the PRL-R in signal transduction. We observed that the box 1 region of the receptor was critical for productive interaction with JAK2 and its tyrosine phosphorylation after PRL stimulation. However, this region appeared to require the presence of additional cytoplasmic domain region(s), such as box 2, to exert its complete effect. In addition, we found that a mutant form lacking the 141 C-terminal residues lost the capacity to be tyrosine phosphorylated in response to PRL but remained able to activate JAK2 kinase and STAT5 transcription factor, indicating that it contained the minimal sequence required for STAT5 activation. The absence of tyrosine phosphorylation of this C-terminal rbPRL-R mutant upon PRL stimulation indicated that the phosphorylation of the PRL-R normally occured in the last 141 animo acids (aa) containing three tyrosines and was not absolutely necessary for induction of these early events in PRL signal transduction. Transfectant cell lines expressing wild type (WT) PRL-R and this C-terminal mutant form were able to induce CAT activity upon PRL stimulation when transiently transfected with the ovine-beta-lactoglobulin promoter, containing STAT5 recognition sites, fused to the CAT reporter gene. The comparison between transcriptional activity of these two receptor forms leads to the conclusion that the C-terminal region of the rbPRL-R, containing the physiological sites for tyrosine phosphorylation, is probably responsible for an amplification of the PRL signal to milk protein genes.

Purification and properties of placental prolactin-related protein-I

We used sucrose density gradient centrifugation, size exclusion chromatography, and high-pressure reversed-phase chromatography in the purification of bovine prolactin-related protein-I (bPRP-I) to homogeneity from a secretory granule-enriched fraction of fetal cotyledon. Amino terminal sequence was unambiguous, consistent with the nucleic acid sequence of the cDNA 50 codons distal to the initial AUG in the open reading frame, and began with the residues: RKSFTDRFMNAASLSHDFY. This is distinct from the signal peptide cleavage site predicted by the algorithm of von Heijne (1986) as well as that expected by comparison with other members of the growth hormone/prolactin family of hormones. The level of bPRP-I in uterine fluid was sufficient to detect by Western blot of unfractionated material and estimated as at least 0.65 microM. In contrast, bPRP-I was undetectable in the serum by this method. Interaction of [125I]-bPRP-I with high molecular weight serum components interfered with its measurement by radio-immunoassay, and could be replicated with purified alpha 2-macroglobulin with an apparent KD of about 0.41 microM. Thus, the bPRP-I gene product is processed secreted and distributed in a manner consistent with a paracrine action at the materno-fetal interface.