Regulation of prolactin expression in leukemic cell lines and peripheral blood mononuclear cells

Analgesic use in relation to sex hormone and prolactin concentrations in premenopausal women

PURPOSE

Common analgesics (aspirin, non-aspirin NSAIDs, and acetaminophen) may be associated with hormone-related cancers, possibly via effects on sex hormone and prolactin concentrations.

METHODS

Between 1996 and 1999, 29,611 participants in the Nurses' Health Study II (NHSII) provided blood samples; 18,521 provided samples timed in the early follicular and mid-luteal phases of the menstrual cycle, the remainder provided untimed samples. We assessed the cross-sectional relationship between analgesic use and plasma sex hormone and prolactin concentrations among 2,034 premenopausal women, 32-54 years old, who served as controls in nested case-control studies, or participated in a within-person hormone reproducibility study in the NHSII; this included 1,700 timed and 334 untimed samples. Estrogens and progesterone were measured in timed samples; androgens and prolactin were measured in timed and untimed samples.

RESULTS

In multivariable models, non-aspirin NSAIDs were positively associated with follicular free estradiol [13.5 % higher, use ≥4 days/week vs. nonusers (p = 0.04; p trend = 0.11)]; results for follicular total estradiol were similar (13.2 % higher, p = 0.06; p trend = 0.11). Acetaminophen use was inversely associated with prolactin (11.8 % lower, use 2 days/week vs. nonusers, p = 0.01, p trend = 0.04). Acetaminophen was also inversely associated with free testosterone (7.1 % lower, use 2 days/week vs. nonusers, p = 0.04; p trend = 0.04). No other associations were observed with the other hormones, or with aspirin use.

CONCLUSIONS

There were no clear patterns between analgesic use and sex hormones in premenopausal women. Acetaminophen use may be modestly associated with prolactin and free testosterone. Our results do not support that analgesic use influences cancer risk through alterations in premenopausal circulating sex hormones or prolactin.

The prolactin gene: a paradigm of tissue-specific gene regulation with complex temporal transcription dynamics

Transcription of numerous mammalian genes is highly pulsatile, with bursts of expression occurring with variable duration and frequency. The presence of this stochastic or 'noisy' expression pattern has been relatively unexplored in tissue systems. The prolactin gene provides a model of tissue-specific gene regulation resulting in pulsatile transcription dynamics in both cell lines and endocrine tissues. In most cell culture models, prolactin transcription appears to be highly variable between cells, with differences in transcription pulse duration and frequency. This apparently stochastic transcription is constrained by a transcriptional refractory period, which may be related to cycles of chromatin remodelling. We propose that prolactin transcription dynamics result from the summation of oscillatory cellular inputs and by regulation through chromatin remodelling cycles. Observations of transcription dynamics in cells within pituitary tissue show reduced transcriptional heterogeneity and can be grouped into a small number of distinct patterns. Thus, it appears that the tissue environment is able to reduce transcriptional noise to enable coordinated tissue responses to environmental change. We review the current knowledge on the complex tissue-specific regulation of the prolactin gene in pituitary and extra-pituitary sites, highlighting differences between humans and rodent experimental animal models. Within this context, we describe the transcription dynamics of prolactin gene expression and how this may relate to specific processes occurring within the cell.

Peritonitis activates transcription of the human prolactin locus in myeloid cells in a humanized transgenic rat model

Prolactin (PRL) is mainly expressed in the pituitary in rodents, whereas in humans, expression is observed in many extrapituitary sites, including lymphocytes. Due to the lack of adequate experimental models, the function of locally produced PRL in the immune system is largely unknown. Using transgenic rats that express luciferase under the control of extensive human PRL regulatory regions, we characterized immune cell responses to thioglycollate (TG)-induced peritonitis. Resident populations of myeloid cells in the peritoneal cavity of untreated rats expressed barely detectable levels of luciferase. In contrast, during TG-induced peritonitis, cell-specific expression in both neutrophils and monocytes/macrophages in peritoneal exudates increased dramatically. Elevated luciferase expression was also detectable in peripheral blood and bone marrow CD11b(+) cells. Ex vivo stimulation of primary myeloid cells showed activation of the human extrapituitary promoter by TNF-α, lipopolysaccharide, or TG. These findings were confirmed in human peripheral blood monocytes, showing that the transgenic rat provided a faithful model for the human gene. Thus, the resolution of an inflammatory response is associated with dramatic activation of the PRL gene promoter in the myeloid lineage.

Effects of prolactin on TSC2-null Eker rat cells and in pulmonary lymphangioleiomyomatosis

RATIONALE

Lymphangioleiomyomatosis, a cystic lung disease of women, is characterized by proliferation of smooth muscle-like lymphangioleiomyomatosis cells, which possess mutations in the tuberous sclerosis complex genes, TSC1/TSC2. Growth factors involved in lymphangioleiomyomatosis cell proliferation are unknown. Prolactin, an important reproductive hormone in women, is known to promote cell proliferation and survival in other tissues.

OBJECTIVES

To determine the role of prolactin in signaling and proliferation in lymphangioleiomyomatosis.

METHODS

Prolactin levels in the sera of patients with lymphangioleiomyomatosis were correlated with clinical status. Components of prolactin signal transduction pathways were assessed in lymphangioleiomyomatosis lesions from human lung explants by real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Prolactin effects on proliferation and signaling were quantified in tuberin-deficient and tuberin-expressing rat cells in vitro.

MEASUREMENTS AND MAIN RESULTS

Higher prolactin levels in the sera of patients with lymphangioleiomyomatosis were associated with a faster rate of decline in FEV(1) and an increased history of pneumothorax (P < 0.01). Higher levels of prolactin and prolactin receptor mRNA and immunoreactivity were found in lymphangioleiomyomatosis lesions when compared with vascular smooth muscle cells in the same region of tissue. This was accompanied by evidence of activation of signal transducer and activator of transcription-1 (STAT1), STAT3, p44/42, and p38 mitogen-activated protein kinase. Tsc2(-/-) Eker rat embryonic fibroblasts expressed more prolactin receptor than did Tsc2(+/+) cells, and responded to prolactin with increased proliferation and activation of the same signaling pathways seen in vivo.

CONCLUSIONS

Prolactin may be an important growth factor in the pathogenesis of lymphangioleiomyomatosis.

Estrogen stimulates transcription from the human prolactin distal promoter through AP1 and estrogen responsive elements in T47D human breast cancer cells

Human prolactin (hPRL) is a pleiotropic and versatile hormone that exercises more than 300 biological activities through binding to its cognate receptors. Recently, multiple studies have implicated hPRL in the development of human breast cancer. As a target of hPRL, both normal and neoplastic human breast cells also synthesize and secrete hPRL, which therefore establishes an autocrine/paracrine action loop in the mammary gland. In contrast to the extensive studies of regulation of hPRL expression in the pituitary gland, regulation of hPRL in mammary tissue and human breast cancer cells has not been extensively addressed. Extrapituitary PRL expression is primarily regulated by a distal promoter located 5.8 kb upstream to the pituitary promoter. As a result of alternative promoter usage, extrapituitary PRL is regulated by different signalling pathways and different hormones, cytokines or neuropeptides compared to regulation in the pituitary. Here, we present evidence that shows estrogen directly induces hPRL gene expression in T47D human breast cancer cells. We have identified a functional, non-canonical estrogen responsive element (ERE) and an AP1 site located in the hPRL distal promoter. Gel shift and chromatin immunoprecipitation assays demonstrated that both estrogen receptor (ER)alpha and ERbeta directly bind to the ERE. However, only ERalpha interacts with AP1 proteins that bind to the AP1 site in the hPRL distal promoter. Promoter-reporter gene studies demonstrate that both ERE and AP1 sites are required for full induction of the promoter activity by estradiol. Our studies suggest that the interactions between estrogens, ERs, the ERE and AP1 transcription factors in regulation of autocrine/paracrine PRL in the human breast may be critical for oncogenesis and may contribute to progression of breast cancer.

Prolactin expression is induced in Jurkat T-cells by beta-catenin LEF-1, AP-1 and cAMP

Prolactin (PRL) in humans is produced in the pituitary as well as in extra-pituitary sites. A proximal promoter that requires the Pit-1 transcription factor controls pituitary PRL expression, whereas a distal (upstream) promoter located at 5.8 kb upstream of the pituitary start site regulates extra-pituitary PRL synthesis. We have previously reported that cAMP regulates PRL transcription in Jurkat lymphocytes in part through a cAMP responsive element. Here we demonstrate that additional PRL regulatory elements corresponding to LEF-l and AP-1 transcription factor binding sites appear important for PRL expression, since factor binding by EMSA and reporter gene expression are reduced when these sites are deleted or mutated. Interestingly, over-expression of a constitutively active form of beta-catenin increases PRL expression of Jurkat cells. This effect occurs through both LEF-dependent and -independent pathways. Our studies identify the distal PRL promoter as a target for beta-catenin, and reveal novel pathways regulating extra-pituitary PRL expression.

Multiple cAMP-induced signaling cascades regulate prolactin expression in T cells

Beside its pivotal role in reproduction, the pituitary hormone prolactin (PRL) has been attributed an immunomodulatory function. Here we report that cAMP is an important stimulator of PRL transcription in primary human T lymphocytes. Inhibition of both protein kinase A (PKA) and p38 MAPK partially abrogated cAMP-induced PRL expression. In addition, cAMP-induced phosphorylation of p38 was shown to occur independently of PKA and could be mimicked by a methylated cAMP analogue which specifically activates the recently discovered cAMP receptor EPAC (exchange protein directly activated by cAMP). Our findings suggest that cAMP induces PRL expression in T lymphocytes via cooperation of at least two different signaling pathways: a PKA-dependent pathway leading to the phosphorylation of cAMP response element-binding protein, and a PKA-independent pathway leading to p38 phosphorylation.

Insulin-like growth factor-I augments interleukin-8 promoter activity through induction of activator protein-1 complex formation

We previously established that stimulation by IGF-I of interleukin (IL)-8 expression in leukocytes required activation of extracellular-regulated kinase (ERK) and basal activity of c-Jun N-terminal kinase (JNK). In this study, we tested the hypothesis that IGF-I stimulates IL-8 expression at the transcriptional level through induction of Fos/Jun activator protein (AP)-1 complex formation. Inhibition studies using the transcriptional inhibitor actinomycin D and IL-8 promoter activation studies indicate that IGF-I act at the transcriptional level. Using gel shift assays we demonstrate that IGF-I induces the formation of active c-Jun/c-Fos AP-1 complexes. Promoter activation studies using mutated IL-8 promoter constructs show that the AP-1 response element is required for promoter activation by IGF-I whereas CAAT-enhancer binding protein (C/EBP) and nuclear factor of kappa B (NFkappaB) sites were not essential. These results indicate that IGF-I can augment IL-8 expression through activation of AP-1 independent of other inducible transcription factors which have shown to be involved in IL-8 regulation by immune stimuli. This finding is in agreement with our previous observation that IGF-I is able to enhance basal IL-8 production in peripheral blood mononuclear cells (PBMC) in the absence of other stimuli.

Physiology of the periparturient period and its relation to severity of clinical mastitis

Incidence of clinical mastitis is highest at drying off and during the periparturient period. Intramammary Escherichia coli infection in high-yielding cows can show a severe clinical response during the early post-partum period. Severe clinical mastitis is mainly determined by cow factors, in particular the functionality of the circulating polymorphonuclear leukocytes (PMN) which are recruited to the mammary gland during the inflammatory reaction. There is a co-incidence between the periods of highest incidence of clinical mastitis and specific structural changes in the mammary gland. During the periparturient period, marked changes in various systemic and local hormones are related to the secretory state of the mammary gland epithelium (lactogenesis). Estrogen and progesterone induce proliferation of the mammary epithelium throughout gestation and act as survival factors in different tissues, although conflicting data have been reported on their effect on PMN oxidative burst. Somatotropin (STH), responsible for maintenance of lactation in ruminants, has been shown to positively influence innate immunity and a more rapid recovery in milk production of severely affected animals. The concentration of STH, and as a result also IGF-I levels is, however, quite low during early lactation. IGF-I and its regulating binding proteins are associated with cell survival, modulation of apoptosis and functionality of PMN in humans. During early lactation, bio-availability of IGF-I is decreased, which might reduce its stimulating effects on PMN quality and functionality. PRL, concomitantly known as a lactogenic hormone and an immunoregulatory cytokine, has also been associated with modulation of the immune system. It is expected that in periparturient animals, hormone changes could interfere with the immune response and the clinical response of mastitis.

Modulation of prolactin expression in human T lymphocytes by cytokines

Besides its pivotal role in reproduction, the polypeptide hormone prolactin (PRL) has immunomodulatory properties. Whereas the bulk of circulating PRL is produced by the pituitary, PRL is also produced by the decidua, the myometrium, the mammary gland and leukocytes. Extrapituitary PRL expression is regulated differently from that in the pituitary, due to the use of an alternative promoter. Here we show for the first time that in T lymphocytes PRL expression is subject to regulation by cytokines. We established that both IL-2 and IL-4 reduced PRL mRNA levels in T lymphocytes to 25 and 28% of control values, respectively. PRL mRNA expression was inhibited to a lesser extent by IL-1beta, which decreased PRL mRNA levels to 58% of control values.

EGF stimulates Pit-1 independent transcription of the human prolactin pituitary promoter in human breast cancer SK-BR-3 cells through its proximal AP-1 response element

Normal and neoplastic human mammary gland cells are targets for the proliferative action of prolactin. These cells also synthesize prolactin, thereby inducing an autocrine/paracrine proliferative loop. We present the first extensive analysis of the transcriptional regulation of the human prolactin gene (hPRL) in human mammary tumor cells, SK-BR-3. We show that the pituitary promoter is functional in these cells in the absence of the pituitary-specific factor Pit-1. Expression of exogenous Pit-1 or epidermal growth factor (EGF) treatment stimulates the transfected hPRL pituitary promoter and the endogenous hPRL expression. EGF stimulation is mediated by increased synthesis of c-fos and c-jun, resulting in AP-1 binding to the proximal hPRL pituitary promoter. This regulation involves the EGF receptor, possibly ErbB2 that is highly expressed in SK-BR-3 cells, and a PI3K/JNK pathway. The stimulation of hPRL gene transcription by EGF in mammary cells may include hPRL in a complex regulatory network controlling growth of human mammary cells.

Multiple, PKA-dependent and PKA-independent, signals are involved in cAMP-induced PRL expression in the eosinophilic cell line Eol-1

Besides its pivotal role in reproduction, the polypeptide hormone prolactin (PRL) has been attributed an immunomodulatory function. Extrapituitary PRL expression is regulated differently from that in the pituitary, due to the use of an alternative promoter. In leukocytes, cAMP is an important regulator of PRL expression. We report that in the human eosinophilic cell line Eol-1, cAMP-induced PRL expression is partially abrogated by two protein kinase A (PKA) inhibitors (H89, PKI) and by the p38 inhibitor SB203580. Phosphorylation of p38 was PKA-independent and could be stimulated by a methylated cAMP analogue, which specifically activates the exchange factor directly activated by cAMP (EPAC). Furthermore, cAMP induced a PKA-dependent phosphorylation of cAMP-responsive element binding protein (CREB). We postulate that cAMP induces PRL expression via two different signalling pathways: a PKA-dependent pathway leading to the phosphorylation of CREB, and a PKA-independent pathway leading to the phosphorylation of p38.

Mechanism of prostaglandin (PG)E2-induced prolactin expression in human T cells: cooperation of two PGE2 receptor subtypes, E-prostanoid (EP) 3 and EP4, via calcium- and cyclic adenosine 5'-monophosphate-mediated signaling pathways

We previously reported that prolactin gene expression in the T-leukemic cell line Jurkat is stimulated by PGE(2) and that cAMP acts synergistically with Ca(2+) or protein kinase C on the activation of the upstream prolactin promoter. Using the transcription inhibitor actinomycin D, we now show that PGE(2)-induced prolactin expression requires de novo prolactin mRNA synthesis and that PGE(2) does not influence prolactin mRNA stability. Furthermore, PGE(2)-induced prolactin expression was inhibited by protein kinase inhibitor fragment 14-22 and BAPTA-AM, which respectively, inhibit protein kinase A- and Ca(2+)-mediated signaling cascades. Using specific PGE(2) receptor agonists and antagonists, we show that PGE(2) induces prolactin expression through engagement of E-prostanoid (EP) 3 and EP4 receptors. We also found that PGE(2) induces an increase in intracellular cAMP concentration as well as intracellular calcium concentration via EP4 and EP3 receptors, respectively. In transient transfections, 3000 bp flanking the leukocyte prolactin promoter conferred a weak induction of the luciferase reporter gene by PGE(2) and cAMP, whereas cAMP in synergy with ionomycin strongly activated the promoter. Mutation of a C/EBP responsive element at -214 partially abolished the response of the leukocyte prolactin promoter to PGE(2), cAMP, and ionomycin plus cAMP.