NGF, cyclic AMP, and phorbol esters regulate oxytocin receptor gene transcription in SK-N-SH and MCF7 cells

Oxytocin as neuro-hormone and neuro-regulator exert neuroprotective properties: A mechanistic graphical review

BACKGROUND

Neurodegeneration is progressive cell loss in specific neuronal populations, often resulting in clinical consequences with significant medical, societal, and economic implications. Because of its antioxidant, anti-inflammatory, and anti-apoptotic properties, oxytocin has been proposed as a potential neuroprotective and neurobehavioral therapeutic agent, including modulating mood disturbances and cognitive enchantment.

METHODS

Literature searches were conducted using the following databases Web of Science, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, and Cochrane from January 2000 to February 2023 for articles dealing with oxytocin neuroprotective properties in preventing or treating neurodegenerative disorders and diseases with a focus on oxidative stress, inflammation, and apoptosis/cell death.

RESULTS

The neuroprotective effects of oxytocin appears to be mediated by its anti-inflammatory properties, inhibition of neuro inflammation, activation of several antioxidant enzymes, inhibition of oxidative stress and free radical formation, activation of free radical scavengers, prevent of mitochondrial dysfunction, and inhibition of apoptosis.

CONCLUSION

Oxytocin acts as a neuroprotective agent by preventing neuro-apoptosis, neuro-inflammation, and neuronal oxidative stress, and by restoring mitochondrial function.

The Role of Endogenous Oxytocin in Anxiolysis: Structural and Functional Correlates

BACKGROUND

Oxytocin is anxiolytic, and administration of synthetic oxytocin in humans reduces amygdala reactivity to negative stimuli. However, it is unknown whether endogenous oxytocin levels-which are heritable and stable across time-attenuate anxiety via similar mechanisms.

METHODS

In this study, we used plasma assays and structural and functional neuroimaging to examine potential anxiolytic effects of endogenous oxytocin in 73 participants.

RESULTS

We found that higher endogenous oxytocin levels are associated with reduced central amygdala volume and blood oxygen level-dependent activity in response to aversive stimuli. In contrast to previous reports, we found that oxytocin was not related to patterns of functional connectivity between the amygdala and other brain regions.

CONCLUSIONS

Together, our results underscore the importance of considering individual differences in participants' endogenous oxytocin with respect to anxiety-related neural activity and neuromorphology.

Effect of pregnancy on endometrial expression of luteolytic pathway components in the mare

Endometrial oxytocin receptors (OXTR) and prostaglandin-endoperoxide synthase 2 (PTGS2) are central components of the luteolytic pathway in cyclic mares, and their suppression is thought to be critical to luteal maintenance during early pregnancy. We examined the effect of pregnancy on endometrial expression of potential regulators of prostaglandin (PG) F2α secretion in mares. Expression of the nuclear progesterone receptor and oestrogen receptor ERα was high during oestrus, and depressed when progesterone was elevated; the opposite applied to the membrane progesterone receptor. PTGS2 was upregulated on Day 14 of dioestrus, but not pregnancy. Although OXTR mRNA expression was not elevated on Day 14 of dioestrus, protein abundance was; this increase in OXTR protein was absent on Day 14 of pregnancy. Intriguingly, gene and protein expression for PTGS2 and OXTR increased markedly between Days 14 and 21 of pregnancy suggesting that, although initial avoidance of luteolysis during pregnancy involves their suppression, this is a transient measure that delays rather than abolishes luteolytic pathway generation. The only oxytocin-PGF2α feedback loop component downregulated on both Days 14 and 21 of pregnancy was the PGF2α receptor we propose that downregulation of the PGF2α receptor uncouples the oxytocin-PGF2α feedback loop, thereby preventing generation of the large PGF2α pulses required for luteolysis.

Prostaglandin F2α regulates the expression of uterine activation proteins via multiple signalling pathways

Prostaglandin F2α (PGF2A) has multiple roles in the birth process in addition to its vital contractile role. Our previous study has demonstrated that PGF2A can modulate uterine activation proteins (UAPs) in cultured pregnant human myometrial smooth muscle cells (HMSMCs). The objective of this study was to define the signalling pathways responsible for PGF2A modulation of UAPs in myometrium. It was found that PGF2A stimulated the expression of (GJA1) connexin 43 (CX43), prostaglandin endoperoxide synthase 2 (PTGS2) and oxytocin receptor (OTR) in cultured HMSMCs. The inhibitors of phospholipase C (PLC) and protein kinase C (PKC) blocked PGF2A-stimulated expression of CX43. The inhibitors of ERK, P38 and NFκB also blocked the effect of PGF2A on CX43 expression, whereas PI3K and calcineurin/nuclear factor of activated T-cells (NFAT) pathway inhibitors did not reverse the effect of PGF2A on CX43. For PTGS2 and OTR, PLC, PI3K, P38 and calcineurin/NFAT signalling pathways were involved in PGF2A action, whereas PKC and NFκB signalling were not involved. In addition, PGF2A activated NFAT, PI3K, NFκB, ERK and P38 signalling pathways. Our data suggest that PGF2A stimulates CX43, PTGS2 and OTR through divergent signalling pathways.

Cellular arrays for large-scale analysis of transcription factor activity

Identifying molecular mechanisms or therapeutic targets is typically based on large-scale cellular analysis that measures the abundance of mRNA or protein; however, abundance does not necessarily correlate with activity. We report a method for direct large-scale quantification of active pathways that employs a cellular array with parallel gene delivery of constructs that report pathway activity. The reporter constructs encode luciferase, whose expression is influenced by binding of transcription factors (TFs), which are the downstream targets of signaling pathways. Luciferase levels are quantified by bioluminescence imaging (BLI), which allows for rapid, non-invasive measurements. Activity profiles by BLI of 32 TFs were robust, consistent, and reproducible, and correlated with standard cell lysis techniques. The array identified five TFs with differential activity during phorbol-12-myristate-13-acetate (PMA)-induced differentiation of breast cancer cells. A system for rapid, large-scale, BLI quantification of pathway activity provides an enabling technology for mechanistic studies of cellular responses and processes.

Effect of estrogen and tamoxifen on the shell gland AVT and VT3R of scotosensitive and scotorefractory Japanese quail

The neurohypophyseal hormone arginine vasotocin (AVT) found in most vertebrate species is known to modulate different aspects of reproduction in quail. AVT system is sensitive to gonadal steroids. Previous studies have shown that estradiol benzoate stimulates the proliferation of shell gland and increases the AVT and the vasotocin 3 receptor (VT3R) in long day length. This study was undertaken to investigate the effect of estrogen and tamoxifen on AVT as well as its receptor VT3 under the short day condition (6L:18D). Estradiol benzoate (EB) was administered daily in sexually quiescent (scotosensitive) condition for 15days. After the initial period of sexual quiescence, the quail of control group exhibited sexual development (scotorefractory condition). Thereafter, scotorefractory quail were administered with anti-estrogen tamoxifen, which eliminated the reoccurrence of scotosensitivity. Immunohistochemical and in-situ hybridization studies indicate the expression of AVT and VT3R transcripts in both scotosensitive as well as scotorefractory conditions. Administration of EB to scotosensitive female quail produced an increase in AVT and VT3 while tamoxifen suppressed them in scotorefractory quail. The results indicate that in quail myometrium the expression of VT3R is upregulated by estrogen when kept under short day condition.

Characterization of the cyclic adenosine monophosphate target site in the oxytocin receptor gene in rabbit amnion

Oxytocin (OXT) is a potent stimulator of prostaglandin E(2) (PGE(2)) synthesis by rabbit amnion cells obtained near the end of pregnancy. Coincident with a marked increase in sensitivity of PGE(2) synthesis to OXT, the concentration of OXT receptors (OXTRs) is abruptly upregulated about 200-fold at term. This increase can be mimicked in preterm amnion cells in primary culture by the synergistic action of agents that increase cAMP synthesis and by glucocorticoids. To elucidate the mechanism of cAMP action, we cloned the rabbit OXTR gene and isolated a 200-base pair (bp) forskolin-responsive region about 4.7 kilobase upstream from the transcriptional start site using transient transfection assays. This region corresponds to a DNase I-hypersensitive site that appears in amnion tissue only near the end of pregnancy, when OXTRs are upregulated. The effects of forskolin were mediated in part by cAMP response element binding protein (CREB), as coexpression of reporter constructs with dominant negative CREB inhibited reporter expression. In addition, CREB was cross-linked to sites in the 200-bp region only in chromatin isolated from cells near the end of pregnancy, as demonstrated by chromatin immunoprecipitation (ChIP). Because the transient transfection results are consistent with work using tissue extracts (DNase I hypersensitivity and ChIP), we conclude that cAMP, acting through a specific upstream CREB binding site, is critical for the physiological upregulation of OXTRs in the amnion at the end of gestation.

Oxytocin: the great facilitator of life

Oxytocin (Oxt) is a nonapeptide hormone best known for its role in lactation and parturition. Since 1906 when its uterine-contracting properties were described until 50 years later when its sequence was elucidated, research has focused on its peripheral roles in reproduction. Only over the past several decades have researchers focused on what functions Oxt might have in the brain, the subject of this review. Immunohistochemical studies revealed that magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei are the neurons of origin for the Oxt released from the posterior pituitary. Smaller cells in various parts of the brain, as well as release from magnocellular dendrites, provide the Oxt responsible for modulating various behaviors at its only identified receptor. Although Oxt is implicated in a variety of "non-social" behaviors, such as learning, anxiety, feeding and pain perception, it is Oxt's roles in various social behaviors that have come to the fore recently. Oxt is important for social memory and attachment, sexual and maternal behavior, and aggression. Recent work implicates Oxt in human bonding and trust as well. Human disorders characterized by aberrant social interactions, such as autism and schizophrenia, may also involve Oxt expression. Many, if not most, of Oxt's functions, from social interactions (affiliation, aggression) and sexual behavior to eventual parturition, lactation and maternal behavior, may be viewed as specifically facilitating species propagation.

Medial preoptic area interactions with dopamine neural systems in the control of the onset and maintenance of maternal behavior in rats

The medial preoptic area (MPOA) and dopamine (DA) neural systems interact to regulate maternal behavior in rats. Two DA systems are involved: the mesolimbic DA system and the incerto-hypothalamic DA system. The hormonally primed MPOA regulates the appetitive aspects of maternal behavior by activating mesolimbic DA input to the shell region of the nucleus accumbens (NAs). DA action on MPOA via the incerto-hypothalamic system may interact with steroid and peptide hormone effects so that MPOA output to the mesolimbic DA system is facilitated. Neural oxytocin facilitates the onset of maternal behavior by actions at critical nodes in this circuitry. DA-D1 receptor agonist action on either the MPOA or NAs can substitute for the effects of estradiol in stimulating the onset of maternal behavior, suggesting an overlap in underlying cellular mechanisms between estradiol and DA. Maternal memory involves the neural plasticity effects of mesolimbic DA activity. Finally, early life stressors may affect the development of MPOA-DA interactions and maternal behavior.

Estrogen regulates transcription of the ovine oxytocin receptor gene through GC-rich SP1 promoter elements

Establishment of pregnancy in ruminants results from paracrine signaling by interferon tau (IFNT) from the conceptus to uterine endometrial luminal epithelia (LE) that prevents release of luteolytic prostaglandin F(2alpha) pulses. In cyclic and pregnant ewes, progesterone down-regulates progesterone receptor (PGR) gene expression in LE. In cyclic ewes, loss of PGR allows for increases in estrogen receptor alpha (ESR1) and then oxytocin receptor (OXTR) gene expression followed by oxytocin-induced prostaglandin F(2alpha) pulses. In pregnant ewes, IFNT inhibits transcription of the ESR1 gene, which presumably inhibits OXTR gene transcription. Alternatively, IFNT may directly inhibit OXTR gene transcription. The 5' promoter/enhancer region of the ovine OXTR gene was cloned and found to contain predicted binding sites for activator protein 1, SP1, and PGR, but not for ESR1. Deletion analysis showed that the basal promoter activity was dependent on the region from -144 to -4 bp that contained only SP1 sites. IFNT did not affect activity of the OXTR promoter. In cells transfected with ESR1, E2, and ICI 182,780 increased promoter activity due to GC-rich SP1 binding sites at positions -104 and -64. Mutation analyses showed that the proximal SP1 sites mediated ESR1 action as well as basal activity of the promoter. In response to progesterone, progesterone receptor B also increased OXTR promoter activity. SP1 protein was constitutively expressed and abundant in the LE of the ovine uterus. These results support the hypothesis that the antiluteolytic effects of IFNT are mediated by direct inhibition or silencing of ESR1 gene transcription, thereby precluding ESR1/SP1 from stimulating OXTR gene transcription.

Differential activation of the connexin 43 promoter by dimers of activator protein-1 transcription factors in myometrial cells

The expression of activator protein-1 (AP-1) transcription factors is increased in the myometrium at term and may therefore regulate the expression of genes, such as connexin 43 (Cx43), required for the onset of labor. The region upstream of the mouse, rat, and human Cx43 genes contains two consensus AP-1 binding sequences, a proximal AP-1, located close to the TATA box, and a distal AP-1, 1 kb upstream. A transient transfection system was developed in which Syrian hamster myometrial cells were transfected with Cx43 promoter-luciferase constructs in combination with expression vectors for the AP-1 family. Transfection with c-Jun or JunB had no effect on transcription from the Cx43 promoter, whereas transfection with JunD or combinations of Jun and Fos family members led to significant increases in transcription. Deletion of the distal AP-1 site did not abrogate transcription driven by Fos/Jun, whereas a 2-bp mutation in the proximal AP-1 site significantly reduced pCx43 transactivation by AP-1 dimers. Dimers comprising Fos/Jun proteins conferred greater transcriptional activity than Jun dimmers, with Fra-2/JunB combination conferring greatest activity. These data suggest that increased expression of Fos family members in the myometrium at term drives the increase in Cx43 transcription and expression during labor. Because expression of Fra-2 increases earlier than other Fos family members and confers the highest transcriptional drive to the Cx43 promoter, our data suggest that Fra-2 is a central component in the regulation of Cx43 expression during labor.

Mechanical stretch and progesterone differentially regulate activator protein-1 transcription factors in primary rat myometrial smooth muscle cells

During pregnancy, stretch of the uterus, imposed by the growing fetus, is an important signal for the induction of genes involved in the onset of labor. In this study, the expression of activator protein-1 (AP-1) family mRNAs in response to in vitro stretch was investigated in myometrial cells. Rat primary myometrial smooth muscle cells were plated onto collagen I-coated Flex I culture plates and subjected to 25% static stretch on day 4 of culture. Static stretch induced an increase in the expression of c-fos, fosB, fra-1, c-jun, and junB. The expression of both c-fos and junB was maximally induced at 30 min by static stretch. The peak induction for fosB and c-jun occurred at 1 h, whereas the peak of fra-1 induction occurred between 1 and 2 h after application of stretch. Treatment of myometrial cells with progesterone (100 nM, 400 nM, 1 microM) for 1 or 6 h before the application of static stretch did not affect the magnitude of the c-fos response. However, 24 h of progesterone exposure reduced the magnitude of c-fos and fosB stretch induction at both the 400 nM and 1 microM doses. These data indicate that several members of the AP-1 family are stretch-responsive genes in myometrial smooth muscle cells. This response can be attenuated by pretreatment with progesterone; however, the requirement for longer pretreatment times suggests that the inhibitory actions of progesterone do not occur through a direct action of the progesterone receptor within the promoter regions of AP-1 genes.

Oxytocin inhibits the progression of human ovarian carcinoma cells in vitro and in vivo

The neurohypophyseal nonapeptide oxytocin (OT) is involved in many biologic functions and regulation of cell proliferation under both physiologic and neoplastic conditions. In some cases, OT exhibits an oxytocin receptor (OTR)-mediated antiproliferative effect on cancer cells. In this study, we examined the effects of OT on ovarian carcinoma progression in vitro and in vivo. We investigated the inhibitory effects of OT on cell growth, invasion and migration in vitro. Furthermore, we examined the OT effects in vivo ovarian carcinoma model. We demonstrated OTR expressions in the large majority of ovarian carcinoma tissues, and OT inhibited not only proliferation but also migration and invasion in ovarian carcinoma cells in vitro. Furthermore, we examined the mechanisms of the antiinvasive ability of OT. Secretion of matrix metalloproteinase 2 was slightly inhibited by 10(-7) M OT, while treatment with 10(-7) M OT for 24 hr remarkably enhanced the expression of E-cadherin. In addition, our in vivo study showed that intraperitoneal administration of OT resulted in the reduction of intraperitoneal dissemination of ovarian carcinoma cells. Mean tumor burden in the OT-treated group (0.2 +/- 0.11 g) was significantly (p < 0.05) less than that of physiologic saline-treated group (0.5 +/- 0.54 g). This evidence implies that OT may functionally suppress peritoneal dissemination in ovarian carcinoma.

Differential expression of activator protein-1 transcription factors in pregnant rat myometrium

While the AP-1 (activator protein-1) genes c-fos and c-jun have been implicated in the expression of myometrial genes associated with the onset of labor, there are no data concerning the role of other members of this family of transcription factors. To address this issue, we defined the expression and hormonal regulation of AP-1 genes in the rat myometrium during pregnancy and labor. Tissue was collected on Days 12, 15, 17, 19, 21, 22, and 23 (labor) and 1 day postpartum. Expression of c-fos, fosB, fra-1, fra-2, and junB was low during early gestation, with a 5- to 10-fold increase on Day 23 during labor, and returned to low levels 1 day postpartum. In contrast, the levels of c-jun and junD remained relatively constant throughout gestation. Administration of progesterone (P4; 16 mg/kg s.c./day) beginning on Day 20 (to maintain elevated plasma P4 levels) prevented the onset of labor and blocked the expected rise in c-fos, fosB, fra-1, fra-2, and junB expression on Day 23. In contrast, administration of the progesterone receptor antagonist RU486 (10 mg/kg s.c.) on Day 19 induced preterm labor and a premature increase in mRNA levels of c-fos, fra-1, fra-2, and junB. In unilaterally pregnant rats, stretch imposed by the growing fetus was found to increase the expression of c-fos, fosB, fra-1, fra-2, and junB only in the gravid horn on the day of labor. These data raise the possibility that AP-1 transcription factors integrate endocrine and mechanical signals, leading to myometrial gene expression required for uterine remodeling and the initiation of labor.

Neurons modulate oxytocin receptor expression in rat cultured astrocytes: involvement of TGF-beta and membrane components

We examined the effect of neurons on oxytocin (OT) receptors (OTR) and OTR gene expression in cultured astrocytes. The addition of neuron-conditioned medium induced an increase of both OTR binding and OTR mRNA level. This effect was enhanced after the medium was boiled or acidified. As it is known that transforming growth factor-beta (TGF-beta) can be released from carrier proteins by acid or heat, TGF-beta1 and 2 were tested and found to induce an increase of OTR binding. Furthermore, TGF-beta antibody abolished the stimulatory effect of normal or acidified neuron-conditioned medium. Neurons added to cultured astrocytes without contact mimicked the stimulatory effect of the conditioned medium. In contrast, neurons added with contact, induced a decrease in OTR binding and an increase of mRNA level, whereas neuronal membranes induced a decrease of both OTR binding and mRNA levels. In conclusion, the present data demonstrate that in vitro, neurons are able to modulate astrocytic OTR expression at the level of both protein and mRNA. They stimulate this expression through their release of TGF-beta and inhibit it by the action of unknown membrane components.

CNS region-specific oxytocin receptor expression: importance in regulation of anxiety and sex behavior

The oxytocin receptor (OTR) is differentially expressed in the CNS. Because there are multiple mechanisms by which the OTR can be transcriptionally induced, we hypothesized that differences in OTR expression may be explained by activation of distinct signal transduction pathways and may be critical for the control of anxiety and sex behaviors. To determine the regulation and functional significance of this expression, we infused female rats with modifiers of protein kinases before assaying for behavior and oxytocin receptor binding. In the ventromedial nucleus of the hypothalamus (VMH), estrogen-dependent induction of oxytocin receptors required protein kinase C activation, and oxytocin infused here promoted female sex behavior but had no effect on anxiety. In contrast, dopamine controlled tonic oxytocin receptor expression in the central nucleus of the amygdala (cAmyg) through activation of protein kinase A, and oxytocin infused here was anxiolytic but had no effect on female sex behavior. Therefore, we have identified brain region-specific regulation of the OTR in the VMH and cAmyg. Distinct signal transduction pathways regulating receptor expression and binding in each brain region may mediate in part the ability of oxytocin to exert these differential behavioral effects.

Transcriptional regulation of oxytocin receptor by interleukin-1beta and interleukin-6

The up-regulation of oxytocin (OT) receptors in late pregnancy results principally from increased synthesis of messenger RNA. The 5'-flanking region of the human OT receptor gene contains several putative binding sites for nuclear factor-interleukin-6 (NF-IL6), also known as CAAT/enhancer binding protein-beta. This trans-acting factor modulates the expression of genes involved in acute inflammatory responses. Proinflammatory cytokines, such as IL-1beta or IL-6, have been implicated as mediators in both preterm and term labor, particularly in association with intrauterine infection. We hypothesized that IL-1beta and IL-6 induce OT receptor gene expression in human myometrial cells, and this is mediated by NF-IL6 and cognate response elements in the 5'-flanking region of the OT receptor gene. Contrary to the hypothesis, both IL-1beta and IL-6 treatment resulted in a significant decrease in OT receptor messenger RNA measured by ribonuclease protection analysis. Using electrophoretic mobility shift assay, we have shown that NF-IL6 is present at low levels that appear to be increased after treatment with either IL-1beta or IL-6. Using deletion analysis and functional transfection studies in HeLa cells, we demonstrated that the OT receptor gene promoter displays constitutive basal activity and is negatively regulated by both IL-1beta and IL-6. This suppressive ability of IL-1beta and IL-6 depends on the -1203/-722 region of the OT receptor promoter, which contains binding sites for NF-IL6, acute phase response element, and NF-kappaB. Our findings suggest a role for IL-1beta and IL-6 in the transcriptional regulation of the human OT receptor gene.

The oxytocin receptor system: structure, function, and regulation

The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via G(q) proteins to phospholipase C-beta. The high-affinity receptor state requires both Mg(2+) and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has been characterized by mutagenesis and molecular modeling and is different from the antagonist binding site. The function and physiological regulation of the OT system is strongly steroid dependent. However, this is, unexpectedly, only partially reflected by the promoter sequences in the OT receptor gene. The classical actions of OT are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation. While the essential role of OT for the milk let-down reflex has been confirmed in OT-deficient mice, OT's role in parturition is obviously more complex. Before the onset of labor, uterine sensitivity to OT markedly increases concomitant with a strong upregulation of OT receptors in the myometrium and, to a lesser extent, in the decidua where OT stimulates the release of PGF(2 alpha). Experiments with transgenic mice suggest that OT acts as a luteotrophic hormone opposing the luteolytic action of PGF(2 alpha). Thus, to initiate labor, it might be essential to generate sufficient PGF(2 alpha) to overcome the luteotrophic action of OT in late gestation. OT also plays an important role in many other reproduction-related functions, such as control of the estrous cycle length, follicle luteinization in the ovary, and ovarian steroidogenesis. In the male, OT is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. OT receptors have also been identified in other tissues, including the kidney, heart, thymus, pancreas, and adipocytes. For example, in the rat, OT is a cardiovascular hormone acting in concert with atrial natriuretic peptide to induce natriuresis and kaliuresis. The central actions of OT range from the modulation of the neuroendocrine reflexes to the establishment of complex social and bonding behaviors related to the reproduction and care of the offspring. OT exerts potent antistress effects that may facilitate pair bonds. Overall, the regulation by gonadal and adrenal steroids is one of the most remarkable features of the OT system and is, unfortunately, the least understood. One has to conclude that the physiological regulation of the OT system will remain puzzling as long as the molecular mechanisms of genomic and nongenomic actions of steroids have not been clarified.

Functional oxytocin receptors in a human endometrial cell line

OBJECTIVE

Our goal was to demonstrate expression and functionality of oxytocin receptors in a human endometrial cell line. This cell line could then be used for further investigation of the role of oxytocin in reproductive function at the cellular level.

STUDY DESIGN

Oxytocin receptor messenger ribonucleic acid expression was determined by reverse transcriptase-polymerase chain reaction deoxyribonucleic acid amplification with ribonucleic acid from confluent Ishikawa cells. Ligand binding to whole cells was evaluated by nonlinear regression analysis with an iodinated oxytocin antagonist. The coupling of the oxytocin receptor to signaling pathways was evaluated by measuring oxytocin-stimulated increases in intracellular calcium concentration, phosphorylation of ERK2 (extracellular-regulated protein kinase 2) mitogen-activated protein kinase, and prostaglandin E(2) release.

RESULTS

Polyacrylamide gel electrophoresis of the reverse transcriptase-polymerase chain reaction products demonstrated the presence of oxytocin receptor messenger ribonucleic acid in Ishikawa cells. Ligand-binding analysis of these cells demonstrated a single class of noninteracting sites, with a B(max) (maximal number of binding sites) of 77.7 fmol/mg deoxyribonucleic acid and an apparent dissociation constant of 8.3 x 10(-11) mol/L. Stimulation with 100-nmol/L oxytocin caused a rapid transient increase in intracellular free calcium concentration, which was blocked by 1-micromol/L oxytocin antagonist. Treatment of cells with oxytocin for 10 minutes resulted in a marked increase in the phosphorylation of ERK2, as determined by Western blot analysis, and a 5-fold increase in prostaglandin E(2) release.

CONCLUSION

This study is the first to demonstrate functional oxytocin receptors in an established human endometrial cell line. This cell line will be useful in elucidating the mechanisms of action of oxytocin in the reproductive tract at the molecular level.

Demonstration of functional oxytocin receptors in human breast Hs578T cells and their up-regulation through a protein kinase C-dependent pathway

Oxytocin (OT) receptors (OTRs) have been demonstrated in a number of human breast tumors and tumor cells, but it was not clear whether the receptors were functional. We examined the regulation and function of OTR in a tumor cell line, Hs578T, derived from human breast. These cells expressed moderate levels of OTR when cultured in 10% FBS, as demonstrated by RT-PCR and binding analyses. Serum deprivation resulted in the loss of OTRs, with no effect on cell viability. Restoration of serum and addition of 1 microM dexamethasone (DEX) increased OTR levels by about 9-fold. Up-regulation was blocked by the addition of phospholipase C and PKC inhibitors. Serum/DEX treatment also increased steady state OTR messenger RNA levels. OT increased intracellular Ca2+ in a time- and dose-responsive manner, and the effects of OT were lost when OTRs were down-regulated by serum starvation. Serum/DEX up-regulation of OTR restored the responsiveness to OT. OT also stimulated ERK-2 (extracellular signal-regulated protein kinase) phosphorylation and PGE2 synthesis in Hs578T cells. In addition to showing that OTRs in the breast tumor cells are functional, these studies show that Hs578T cells can be used to study molecular regulation of OTR gene expression and intracellular signaling pathways stimulated by OT.

Effect of oxytocin receptor and beta2-adrenoceptor blockade on myometrial oxytocin receptors in parturient rats

It has been proposed that the rise in myometrial oxytocin receptor (OTR) concentrations at term triggers parturition. In the present study, we have shown that in vivo infusion of the beta2-adrenoceptor (beta2AR) antagonist ICI-118.551 in late pregnant rats prevents the rise in myometrial OTR binding normally seen during delivery. A reduced contractile responsiveness of uterine strips isolated from rats in labor when challenged with oxytocin (OT) and a slight shortening of gestation accompanied this effect. OTR mRNA levels were, however, unaltered after the treatment, suggesting that the effect of beta2AR blockade on myometrial OTR was posttranscriptional or due to influences on extra-myometrial tissue. Infusion of the OTR antagonist atosiban down-regulated OTR binding sites in the parturient myometrium and resulted in an impaired contractile response to OT without affecting gestational length. OTR gene expression did not change, as seen from unchanged OTR mRNA values. Neither atosiban nor ICI-118.551 infusions alone changed fetal mortality. A significant increase in the incidence of fetal deaths was found, however, when rats were treated with a combination of atosiban and ICI-118.551. This treatment also down-regulated myometrial OTR and weakened the contractile response to OT, but it did not change gestational length. We conclude that the timing and onset of a normal parturition as well as a favorable outcome seem to be independent of a rise in OTR. This fact cannot exclude the possibility that an increase in OTR is of importance in the genesis of preterm labor. We suggest that beta2 stimulation up-regulates OTR during delivery. This effect may partly be responsible for the tachyphylaxis seen after the use of beta2 agonists to control preterm labor. We further suggest that OTR stimulation up-regulates OTR during labor. The OTR down-regulation seen after atosiban treatment adds to the direct relaxing effect of atosiban on the myometrium. In view of this, atosiban may prove to be a more useful tocolytic than the traditionally used beta2 agonists.