Prolactin receptor expression in the developing human prostate and in hyperplastic, dysplastic, and neoplastic lesions

The Involvement of Prolactin in Stress-Related Disorders

The most important and widely studied role of prolactin (PRL) is its modulation of stress responses during pregnancy and lactation. PRL acts as a neuropeptide to support physiological reproductive responses. The effects of PRL on the nervous system contribute to a wide range of changes in the female brain during pregnancy and the inhibition of the hypothalamic-pituitary axis. All these changes contribute to the behavioral and physiological adaptations of a young mother to enable reproductive success. PRL-driven brain adaptations are also crucial for regulating maternal emotionality and well-being. Hyperprolactinemia (elevated PRL levels) is a natural and beneficial phenomenon during pregnancy and lactation. However, in other situations, it is often associated with serious endocrine disorders, such as ovulation suppression, which results in a lack of offspring. This introductory example shows how complex this hormone is. In this review, we focus on the different roles of PRL in the body and emphasize the results obtained from animal models of neuropsychiatric disorders.

Sleep disorders and prostate cancer prognosis: biology, epidemiology, and association with cancer development risk

Sleep is crucial for the maintenance of health and well-being. Sleep disorders can result in physiological consequences and are associated with several health issues, including cancer. Cancer is one of the most significant health problems in the world. In Western countries, prostate cancer is the most prevalent noncutaneous cancer among men. Epidemiological studies showed that one in nine men will have this disease during their life. Many factors influence prostate cancer and the tumor niche, including endogenous hormones, family history, diet, and gene mutations. Disruption of the circadian cycle by sleep disorders or other factors has been suggested as a novel and important risk factor for prostate cancer and its tumorigenesis. This review presents information regarding the epidemiological and biological aspects of prostate cancer, and discusses the impact of sleep physiology and sleep disorders on this type of cancer, highlighting possible associations with risk of cancer development.

Role of corticosteroids in prostate cancer progression: implications for treatment strategy in metastatic castration-resistant patients

Corticosteroid agents (CA) are widely used in the treatment of metastatic castration-resistant prostate cancer (mCRPC) either as concomitant treatment with active agents such as docetaxel, cabazitaxel and abiraterone or in a palliative setting, predominantly due to their anti-inflammatory activity. However, the chronic use of CA has numerous side effects, especially in case of steroid-induced adrenal insufficiency. Furthermore, the latest clinical and preclinical data demonstrate that CA themselves are likely to promote tumour progression in certain populations of patients with mCRPC. Therefore, the role of CA in advanced disease should be carefully weighed for each patient and their withdrawal should be considered in some patients. This is necessary, especially in clinical trials that need good performance status patients to evaluate the activity and the safety of emerging drugs in mCRPC that do not require the concurrent use of CA. In oncology, there is no consensus on an algorithm of gradual steroid tapering and frequently the approach to this procedure is empirical. An algorithm is presented in this article based on clinical observations. Prospective studies are necessary to evaluate the efficacy and safety of the above-proposed algorithm in metastatic castration-resistant prostate cancer.

Phase I Study of the Prolactin Receptor Antagonist LFA102 in Metastatic Breast and Castration-Resistant Prostate Cancer

LESSONS LEARNED

Despite evidence for a role for prolactin signaling in breast and prostate tumorigenesis, a prolactin receptor-binding monoclonal antibody has not produced clinical efficacy.Increased serum prolactin levels may be a biomarker for prolactin receptor inhibition.Results from the pharmacokinetic and pharmacodynamics (PD) studies suggest that inappropriately long dosing intervals and insufficient exposure to LFA102 may have resulted in lack of antitumor efficacy.Based on preclinical data, combination therapy of LFA102 with those novel agents targeting hormonal pathways in metastatic castration-resistant prostate cancer and metastatic breast cancer is promising.Given the PD evidence of prolactin receptor blockade by LFA102, this drug has the potential to be used in conditions such as hyperprolactinemia that are associated with high prolactin levels.

BACKGROUND

Prolactin receptor (PRLR) signaling is implicated in breast and prostate cancer. LFA102, a humanized monoclonal antibody (mAb) that binds to and inhibits the PRLR, has exhibited promising preclinical antitumor activity.

METHODS

Patients with PRLR-positive metastatic breast cancer (MBC) or metastatic castration-resistant prostate cancer (mCRPC) received doses of LFA102 at 3-60 mg/kg intravenously once every 4 weeks. Objectives were to determine the maximum tolerated dose (MTD) and/or recommended dose for expansion (RDE) to investigate the safety/tolerability of LFA102 and to assess pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity.

RESULTS

A total of 73 patients were enrolled at 5 dose levels. The MTD was not reached because of lack of dose-limiting toxicities. The RDE was established at 60 mg/kg based on PK and PD analysis and safety data. The most common all-cause adverse events (AEs) were fatigue (44%) and nausea (33%) regardless of relationship. Grade 3/4 AEs reported to be related to LFA102 occurred in 4% of patients. LFA102 exposure increased approximately dose proportionally across the doses tested. Serum prolactin levels increased in response to LFA102 administration, suggesting its potential as a biomarker for PRLR inhibition. No antitumor activity was detected.

CONCLUSION

Treatment with LFA102 was safe and well tolerated, but did not show antitumor activity as monotherapy at the doses tested.

Prolactin- and testosterone-induced carboxypeptidase-D correlates with increased nitrotyrosines and Ki67 in prostate cancer

BACKGROUND

Carboxypeptidase-D (CPD) cleaves C-terminal arginine for conversion to nitric oxide (NO) by nitric oxide synthase (NOS). Prolactin (PRL) and androgens stimulate CPD gene transcription and expression, which increases intracellular production of NO to promote viability of prostate cancer (PCa) cells in vitro. The current study evaluated whether hormonal upregulation of CPD and NO promote PCa cell viabilty in vivo, by correlating changes in expression of CPD and nitrotyrosine residues (products of NO action) with proliferation marker Ki67 and associated proteins during PCa development and progression.

METHODS

Fresh prostate tissues, obtained from 40 men with benign prostatic hyperplasia (BPH) or PCa, were flash-frozen at the time of surgery and used for RT-qPCR analysis of CPD, androgen receptor (AR), PRL receptor (PRLR), eNOS, and Ki67 levels. Archival paraffin-embedded tissues from 113 men with BPH or PCa were used for immunohistochemical (IHC) analysis of CPD, nitrotyrosines, phospho-Stat5 (for activated PRLR), AR, eNOS/iNOS, and Ki67.

RESULTS

RT-qPCR and IHC analyses showed strong AR and PRLR expression in benign and malignant prostates. CPD mRNA levels increased ∼threefold in PCa compared to BPH, which corresponded to a twofold increase in Ki67 mRNA levels. IHC analysis showed a progressive increase in CPD from 11.4 ± 2.1% in benign to 21.8 ± 3.2% in low-grade (P = 0.007), 40.7 ± 4.0% in high-grade (P < 0.0001) and 50.0 ± 9.5% in castration-recurrent PCa (P < 0.0001). Immunostaining for nitrotyrosines and Ki67 mirrored these increases during PCa progression. CPD, nitrotyrosines, and Ki67 tended to co-localize, as did phospho-Stat5.

CONCLUSIONS

CPD, nitrotyrosine, and Ki67 levels were higher in PCa than in benign and tended to co-localize, along with phospho-Stat5. The strong correlation in expression of these proteins in benign and malignant prostate tissues, combined with abundant AR and PRLR, supports in vitro evidence that the CPD-Arg-NO pathway is involved in the regulation of PCa cell proliferation. It further highlights a role for PRL in the development and progression of PCa.

The prolactin receptor as a therapeutic target in human diseases: browsing new potential indications

INTRODUCTION

Prolactin (PRL) signaling has emerged as a relevant target in breast and prostate cancers. This has encouraged various laboratories to develop compounds targeting the PRL receptor (PRLR). As the latter is widely distributed, it is timely to address whether other conditions could also benefit from such inhibitors.

AREAS COVERED

The authors briefly overview the two classes of PRLR blockers, which involve: i) PRL-core based analogs that have been validated as competitive antagonists in various preclinical models, and ii) anti-PRLR neutralizing antibodies that are currently in clinical Phase I for advanced breast and prostate cancers. The main purpose of this review is to discuss the multiple organs/diseases that may be considered as potential targets/indications for such inhibitors. This is done in light of reports suggesting that PRLR expression/signaling is increased in disease, and/or that systemic or locally elevated PRL levels correlate with (or promote) organ pathogenesis.

EXPERT OPINION

The two immediate challenges in the field are i) to provide the scientific community with potent anti-prolactin receptor antibodies to map prolactin receptor expression in target organs, and ii) to take advantage of the availability of functionally validated PRLR blockers to establish the relevance of these potential indications in humans.

Prolactin and prolactin receptor expression in cervical intraepithelial neoplasia and cancer

Prolactin receptor (PRLR) overexpression could play a role in tumorigenesis. The aim of this study was to determine prolactin (PRL) and PRLR expression in biopsies from patients with precursor lesions and uterine cervical cancer. PRLR expression was analyzed in 63 paraffin-embedded biopsies of uterine cervical tissue. In total, eleven low-grade squamous intraepithelial lesions (LSIL), 23 high-grade squamous intraepithelial lesions (HSIL), 21 uterine cervical cancers (UCC) and 8 normal epithelium (NE) were examined using immunoperoxidase staining and Western blot analysis. Additionally, PRL expression was identified in human cervical cancer serum and tissues. The PRLR expression was found to be significantly increased in cervical cancer in comparison with normal tissue and precursor lesions (P < 0.0003). The presence of the long isoform of the PRLR was observed only in cervical cancer tissues. Serum PRL levels were normal in all samples and local prolactin expression was similar in precursor lesions and cervical cancer by Western blot analysis. Our data suggest a possible role for PRLR in the progression of cervical cancer.

Thyroid autoimmunity in patients with hyperprolactinemia: an observational study

Objective : To establish whether there is a relationship between hyperprolactinemia and primary thyroid disorders, focusing on patients with autoimmune features. Materials and methods : The medical records of 100 patients with hyperprolactinemia (HPRL) were retrospectively examined. Records of thyroid ultrasonography (USG), basal serum levels of thyroid stimulating hormone, circulating free thyroxine, free triiodothyronine, antithyroglobulin (anti-Tg), and antithyroperoxidase (anti-TPO) antibodies were analyzed. In 100 control subjects, matched by age and gender with HPRL patients, thyroid USG, thyroid function tests (TFTs), and autoantibody panel were obtained. Results : The median PRL in patients was 93 ng/mL (range: 37-470). Twenty-five patients (25%) and 22 controls (22%) had positive anti-Tg and/or anti-TPO titers (P = 0.739). The median serum PRL was 98 (37-470) ng/mL in patients with positive thyroid autoantibodies, and 92 (40-470) ng/mL in patients who were negative (P = 0.975). Among the individuals with autoantibody positivity TFTs abnormalities were more frequent in HPRL patients (60%, out of 25 patients, 14 with subclinical hypothyroidism and one with hyperthyroidism) than in controls (9.1%, out of 22 patients, 2 with subclinical hyperthyroidism) (P < 0.001). Twenty-seven patients with HPRL and 31 controls had goiter (27 vs. 31%, P = 0.437). Forty-six patients (46%) and 50 (50%) controls had one or more of the features of thyroid disorder, which were goiter, positive thyroid autoantibody, and thyroid function abnormality (P = 0.888). Conclusion : HPRL may be associated with more severe thyroid dysfunction in patients with thyroid autoimmunity.

High expression of prolactin receptor is associated with cell survival in cervical cancer cells

BACKGROUND

The altered expression of prolactin (PRL) and its receptor (PRLR) has been implicated in breast and other types of cancer. There are few studies that have focused on the analysis of PRL/PRLR in cervical cancer where the development of neoplastic lesions is influenced by the variation of the hormonal status. The aim of this study was to evaluate the expression of PRL/PRLR and the effect of PRL treatment on cell proliferation and apoptosis in cervical cancer cell lines.

RESULTS

High expression of multiple PRLR forms and PRLvariants of 60-80 kDa were observed in cervical cancer cell lines compared with non-tumorigenic keratinocytes evaluated by Western blot, immunofluorecence and real time PCR. Treatment with PRL (200 ng/ml) increased cell proliferation in HeLa cells determined by the MTT assay at day 3 and after 1 day a protective effect against etoposide induced apoptosis in HeLa, SiHa and C-33A cervical cancer cell lines analyzed by the TUNEL assay.

CONCLUSIONS

Our data suggests that PRL/PRLR signaling could act as an important survival factor for cervical cancer. The use of an effective PRL antagonist may provide a better therapeutic intervention in cervical cancer.

Testosterone and prolactin increase carboxypeptidase-D and nitric oxide levels to promote survival of prostate cancer cells

BACKGROUND

Plasma-membrane carboxypeptidase-D (CPD) releases arginine from extracellular substrates. Arginine is converted intracellularly to nitric oxide (NO). This study determined the effects of testosterone (T) and prolactin (PRL) on CPD expression, and the role(s) of CPD in NO production and survival of prostate cancer (PCa) cells.

METHODS

LNCaP cells were treated with T and/or PRL. CPD expression was measured. Regulation by T (low doses) was determined using transfected cells overexpressing 5α-reductase type-1 (5αR1), which converts T to the more potent dihydrotestosterone. The effects of siRNAs targeting CPD (siCPDs) on NO production, cell viability, and apoptosis were determined using DAF2-DA, MTS, and Annexin-V assays. The effects of PRL/T on CPD/NO levels in PC-3, MDA-PCa-2b, and 22Rv1 cells were also evaluated.

RESULTS

In LNCaP cells, 10 nM T and 10 ng/ml PRL-upregulated CPD mRNA/protein levels. In pTRE-transfectants, 1 nM T-upregulated CPD mRNA levels by ∼2-fold over controls, whereas 0.1 nM T caused similar upregulation in pTRE-5αR1-transfectants. In LNCaP cells cultured in arginine-free medium, addition of furylacryloyl-Ala-Arg (FAR; CPD substrate) increased NO levels. NO production, with FAR, was enhanced by PRL and/or T. siCPDs decreased NO production and cell viability, but increased apoptosis. QPCR analysis showed T/PRL-upregulation of CPD in 22Rv1, MDA-PCa-2b, and PC-3 cells. NO production was doubled by T/PRL in 22Rv1 cells, tripled by T in MDA-PCa-2b cells, and marginally increased by PRL in MDA-PCa-2b and PC-3 cells.

CONCLUSIONS

T and PRL upregulate CPD and NO levels in PCa cells. CPD increases NO production to promote PCa cell survival.

Increased expression of the prolactin receptor is associated with malignant laryngeal tumors

The altered expression of the prolactin receptor (PRLR) has been associated with the development of various types of cancer, particularly breast, prostate and endometrial cancer. However, in laryngeal tumors, the expression of PRLR has not yet been documented. The aim of this study was to determine the expression and localization of PRLR in laryngeal cancer (LC) in comparison with recurrent respiratory papillomatosis (RRP). PRLR expression was analyzed in 48 paraffin-embedded tissues (18 RRP and 30 laryngeal cancer tissues) by immunoperoxidase staining. Furthermore, PRLR expression was evaluated in ten samples from each group by Western blot analysis and quantitative real-time PCR. PRLR was observed in all laryngeal tumors at different intensities. PRLR overexpression was significantly associated (P<0.005) with LC. The staining pattern was homogeneous, mainly cytoplasmic, and confined to the tumor area. We found increased expression of different isoforms in LC in comparison with RRP. Our results suggest a possible role of PRL/PRLR in the development of LC. PRLR may be useful as a target for further investigations in laryngeal tissues.

Prolactin regulation of the prostate gland: a female player in a male game

Prolactin is best known for its actions on the mammary gland. However, circulating prolactin is also detected in males and its receptor (PRLR) is expressed in the prostate, suggesting that the prostate is a target of prolactin. Germline knockout of prolactin or its receptor has failed to reveal a key role for prolactin signaling in mouse prostate physiology. However, several studies involving rodent models and human prostate cell lines and specimens have supported the contribution of the canonical PRLR-Jak2-Stat5a/b pathway to prostate cancer tumorigenesis and progression. Increased expression of prolactin in the prostate itself (rather than changes in circulating prolactin levels) and crosstalk with androgen receptor (AR) signaling are potential mechanisms for increased Stat5a/b signaling in prostate cancer. In the mouse prostate, prolactin overexpression results in disorganized expansion of the basal/stem cell compartment, which has been proposed to house putative prostate tumor-initiating cells. These findings provide new insight into the molecular and cellular targets by which locally produced prolactin could contribute to prostate cancer initiation and progression. A number of pharmacological inhibitors targeting various levels of the PRLR-Jak2-Stat5a/b pathway have been developed and are entering clinical trials for advanced prostate cancer.

Estrogens and prostate cancer: etiology, mediators, prevention, and management

The mainstay targets for hormonal prostate cancer (PCa) therapies are based on negating androgen action. Recent epidemiologic and experimental data have pinpointed the key roles of estrogens in PCa development and progression. Racial and geographic differences, as well as age-associated changes, in estrogen synthesis and metabolism contribute significantly to the etiology. This article summarizes how different estrogens/antiestrogens/estrogen mimics contribute to prostate carcinogenesis, the roles of the different mediators of estrogen in the process, and the potentials of new estrogenic/antiestrogenic compounds for prevention and treatment of PCa.

Unexploited therapies in breast and prostate cancer: blockade of the prolactin receptor

Breast and prostate cancers are hormone-sensitive malignancies that afflict millions of women and men. Although prolactin (PRL) is known as a survival factor that supports tumor growth and confers chemoresistance in both cancers, its precise role in these tumors has not been studied extensively. Growth hormone and placental lactogen also bind PRL receptor (PRLR) and mimic some of the actions of PRL. Blockade of the PRLR represents a novel treatment for patients with advanced breast or prostate cancer with limited therapeutic options. This review discusses different approaches for generating PRLR antagonists. Emphasis is placed on technological advances which enable high-throughput screening for small molecule inhibitors of PRLR signaling that could serve as oral medications.

Research resource: estrogen-driven prolactin-mediated gene-expression networks in hormone-induced prostatic intraepithelial neoplasia

Cotreatment with testosterone (T) and 17β-estradiol (E2) is an established regimen for inducing of prostatic intraepithelial neoplasia (PIN) and prostate cancer in rodent models. We previously used the pure antiestrogen ICI 182,780 (ICI) and bromocriptine, a dopamine receptor agonist, to inhibit PIN induction and systemic hyperprolactinemia in Noble rats and found that the carcinogenic action of T+E2 is mediated directly by the effects of E2 on the prostate and/or indirectly via E2-induced hyperprolactinemia. In this study, we delineate the specific action(s) of E2 and prolactin (PRL) in early prostate carcinogenesis by an integrated approach combining global transcription profiling, gene ontology, and gene-network mapping. We identified 2504 differentially expressed genes in the T+E2-treated lateral prostate. The changes in expression of a subset of 1990 genes (∼80%) were blocked upon cotreatment with ICI and bromocriptine, respectively, whereas those of 262 genes (∼10%) were blocked only by treatment with ICI, suggesting that E2-induced pituitary PRL is the primary mediator of the prostatic transcriptional response to the altered hormone milieu. Bioinformatics analyses identified hormone-responsive gene networks involved in immune responses, stromal tissue remodeling, and the ERK pathway. In particular, our data suggest that IL-1β may mediate, at least in part, hormone-induced changes in gene expression during PIN formation. Together, these data highlight the importance of pituitary PRL in estrogen-induced prostate tumorigenesis. The identification of both E2- and pituitary PRL-responsive genes provides a comprehensive resource for future investigations of the complex mechanisms by which changes in the endocrine milieu contribute to prostate carcinogenesis in vivo.

Biological significance of prolactin in gynecologic cancers

There is increasing evidence that prolactin (PRL), a hormone/cytokine, plays a role in breast, prostate, and colorectal cancers via local production or accumulation. Elevated levels of serum PRL in ovarian and endometrial cancers have been reported, indicating a potential role for PRL in endometrial and ovarian carcinogenesis. In this study, we show that serum PRL levels are significantly elevated in women with a strong family history of ovarian cancer. We show dramatically increased expression of PRL receptor in ovarian and endometrial tumors as well as in endometrial hyperplasia, signifying the importance of PRL signaling in malignant and premalignant conditions. PRL mRNA was expressed in ovarian and endometrial tumors, indicating the presence of an autocrine loop. PRL potently induced proliferation in several ovarian and endometrial cancer cell lines. Binding of PRL to its receptor was followed by rapid phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, mitogen-activated protein kinase/ERK kinase 1, signal transducer and activator of transcription 3, CREB, ATF-2, and p53 and activation of 37 transcription factors in ovarian and endometrial carcinoma cells. PRL also activated Ras oncogene in these cells. When human immortalized normal ovarian epithelial cells were chronically exposed to PRL, a malignant transformation occurred manifested by the acquired ability of transformed cells to form clones, grow in soft agar, and form tumors in severe combined immunodeficient-beige mice. Transformation efficiency was diminished by a Ras inhibitor, providing proof that PRL-induced transformation uses the Ras pathway. In summary, we present findings that indicate an important role for PRL in ovarian and endometrial tumorigenesis. PRL may represent a risk factor for ovarian and endometrial cancers.

Analysis of site-specific histidine protonation in human prolactin

The structural and functional properties of human prolactin (hPRL), a 23 kDa protein hormone and cytokine, are pH-dependent. The dissociation rate constant for binding to the extracellular domain of the hPRL receptor increases nearly 500-fold over the relatively narrow and physiologic range from pH 8 to 6. As the apparent midpoint for this transition occurs around pH 6.5, we have looked toward histidine residues as a potential biophysical origin of the behavior. hPRL has a surprising number of nine histidines, nearly all of which are present on the protein surface. Using NMR spectroscopy, we have monitored site-specific proton binding to eight of these nine residues and derived equilibrium dissociation constants. During this analysis, a thermodynamic interaction between a localized triplet of three histidines (H27, H30, and H180) became apparent, which was subsequently confirmed by site-directed mutagenesis. After consideration of multiple potential models, we present statistical support for the existence of two negative cooperativity constants, one linking protonation of residues H30 and H180 with a magnitude of approximately 0.1 and the other weaker interaction between residues H27 and H30. Additionally, mutation of any of these three histidines to alanine stabilizes the folded protein relative to the chemically denatured state. A detailed understanding of these complex protonation reactions will aid in elucidating the biophysical mechanism of pH-dependent regulation of hPRL's structural and functional properties.

The cooked meat derived genotoxic carcinogen 2-amino-3-methylimidazo[4,5-b]pyridine has potent hormone-like activity: mechanistic support for a role in breast cancer

The cooked meat-derived heterocyclic amine 2-amino-3-methylimidazo[4,5-b]pyridine (PhIP) is activated by CYP1A2 to the N-hydroxy metabolite, then esterified by acetyl transferase and sulfur transferase into unstable DNA-reactive products that can lead to mutation. The genotoxicity of PhIP has been implicated in its carcinogenicity. Yet, CYP1A2-null mice are still prone to PhIP-mediated cancer, inferring that alternative mechanisms must be operative in tumor induction. PhIP induces tumors of the breast, prostate, and colon in rats and lymphoma in mice. This profile of carcinogenicity is indicative of hormonal involvement. We recently reported that PhIP has potent estrogenic activity inducing transcription of estrogen (E2)-regulated genes, proliferation of E(2)-dependent cells, up-regulation of progesterone receptor, and stimulation of mitogen-activated protein kinase signaling. In this report, we show for the first time that PhIP at doses as low as of 10(-11) mol/L has direct effects on a rat pituitary lactotroph model (GH3 cells) and is able to induce cell proliferation and the synthesis and secretion of prolactin. This PhIP-induced pituitary cell proliferation and synthesis and secretion of prolactin can be attenuated by an estrogen receptor (ER) inhibitor, implying that PhIP effects on lactotroph responses are ERalpha mediated. In view of the strong association between estrogen, progesterone, prolactin, and breast cancer, the PhIP repertoire of hormone-like activities provides further mechanistic support for the tissue-specific carcinogenicity of the chemical. Furthermore, the recent epidemiology studies that report an association between consumption of cooked red meat and premenopausal and postmenopausal human breast cancer are consonant with these observations.

S179D prolactin sensitizes human prostate cancer cells such that physiological concentrations of 1, 25 dihydroxy vitamin D3 result in growth inhibition and cell death

BACKGROUND

S179D Prolactin (PRL) is a molecular mimic of naturally phosphorylated human PRL which has been shown to inhibit the growth of human prostate cancer cells both in vitro and when grown as tumors in nude mice.

METHODS

In the current study, we have investigated the potential interplay between S179D PRL and 1,25 dihydroxy vitamin D3 (1,25D) in the inhibition of prostate cancer cell growth by incubating cells under circumstances where each hormone alone has no effect.

RESULTS

Incubation of DU145 or PC3 cells in 100 pM 1,25D or 10 nM S179D PRL for 3 days showed no effect of each alone on expression of the vitamin D receptor (VDR), or the cell cycle regulatory protein p21, or on cell number. Incubation in both together increased expression of the VDR and p21 two to threefold. This co-operative effect was reproduced when activation of the p21 promoter was analyzed using a p21-luciferase (p21-luc) construct. Elimination of the VDR response element from p21-luc eliminated response to the hormone combination, showing that the effect on p21 was through the VDR. Most importantly, S179D PRL sensitized the cells to 1,25D such that there was a concentration-related reduction in cell number versus controls between 40 and 160 pM. At least part of this effect was via the induction of cell death.

CONCLUSIONS

These results suggest that combined anti-tumor therapy may be very efficacious and that the dose of 1,25D required may be below the range that results in hypercalcemia.

The kinetics of binding human prolactin, but not growth hormone, to the prolactin receptor vary over a physiologic pH range

A member of the family of hematopoietic cytokines, human prolactin (hPRL) serves a dual role both as an endocrine hormone and as an autocrine/paracrine cytokine or growth factor. During investigation of the solution structural properties of hPRL, we have noted a surprising pH dependence of its structural stability over a range from approximately pH 6.0 to pH 8.0. An analysis of backbone atom NMR chemical shift changes and backbone amide hydrogen-deuterium exchange rates due to titration of the solution pH over this same range, along with calculations of protein surface electrostatic potential, suggests the possible involvement of a localized cluster of three His residues (27, 30, and 180), which comprise a portion of the high-affinity receptor-binding epitope. Surface plasmon resonance analysis of the interaction between hPRL and the extracellular domain (ECD) of the hPRL receptor reveals a selective 500-fold change in the dissociation rate between pH 8.3 and pH 5.8. In comparison, the interaction of hGH with the same receptor ECD did not demonstrate any significant dependence on pH. We also present an initial investigation of the pH dependence of hPRL function in rat Nb2 cell proliferation assays and a STAT5 luciferase gene reporter assay in the T47D human breast cancer cell line, whose results are consistent with our biophysical studies. The potential implications of this variation in hPRL's structural stability and receptor-binding kinetics over this physiologic range of pH are discussed.

Prolactin stimulates prostate cell proliferation by increasing endoplasmic reticulum content due to SERCA 2b over-expression

Prolactin (PRL) has been shown to be involved in the differentiation and proliferation of numerous tissues, including the prostate gland. Moreover, variations in [Ca2+]ER (calcium concentration within the endoplasmic reticulum) may play a role in cell growth. However, few studies have focused on the regulation of calcium homoeostasis by prolactin. The present study evaluates the regulation of calcium pools as well as the possible role of [Ca2+]ER variations as a signal for growth modulation by PRL. We show that PRL stimulates the proliferation of normal SV40 immortalized epithelial prostate (PNT1A) cells with a maximum effect at a dose of 100 ng/ml. We also show that 100 ng/ml PRL increases the [Ca2+]ER when measured either by indirect quantification with Fura-2AM after application of 1 mM thapsigargin or by direct quantification with Mag-Fura-2AM within the endoplas-mic reticulum. Western blot analysis shows that the SERCA 2b (sarcoendoplasmic calcium ATPase 2b) is over-expressed in PNT1A cells treated with 100 ng/ml PRL for 24 h. A small inter-fering RNA SERCA 2a/b, used to down-regulate endogenous SERCA 2b expression, reduced both PNT1A cell proliferation and [Ca2+]ER. We thus identify [Ca2+]ER and SERCA 2b as protagonists in PRL-induced proliferation.

Drug Insight: prolactin-receptor antagonists, a novel approach to treatment of unresolved systemic and local hyperprolactinemia?

Prolactin is a polypeptide hormone whose major biological actions are related to normal lactation and reproduction. Abnormally high prolactin levels, referred to as hyperprolactinemia, can result in various reproductive disorders. Currently, therapeutic management of hyperprolactinemia relies on dopamine agonists, since dopamine is the primary physiological suppressor of pituitary prolactin production. Epidemiologic studies have shown that prolactin levels in the high-normal range, as well as medications that interfere with dopamine action (e.g. certain antipsychotic drugs), might correlate with increased breast cancer risk. In addition to circulating prolactin, it is now well established that prolactin is also produced locally within various tissues, including breast and prostate. Increasing evidence, mainly from animal studies at present, suggests that excess locally produced prolactin may promote the growth of breast and prostate tumors via an autocrine or paracrine mechanism. These findings have renewed the interest in finding alternative strategies to suppress prolactin actions when dopamine agonists are ineffective. Our studies of the relationship between prolactin structure and function have resulted in the development of pure prolactin-receptor antagonists. These molecules prevent endogenous prolactin from exerting its actions via a competitive mechanism for receptor binding. In this review, we discuss the possible future therapeutic utility of this novel class of compounds.

Estrogens and Antiestrogens as Etiological Factors and Therapeutics for Prostate Cancer

Mounting evidence supports a key role played by estrogen or estrogen in synergy with an androgen, in the pathogenesis of prostate cancer (PCa). New experimental data suggest that this process could begin as early as prenatal life. During adulthood, estrogen carcinogenicity is believed to be mediated by the combined effects of hormone-induced, unscheduled cell proliferation and bioactivation of estrogens to genotoxic carcinogens. Increased bioavailability of estrogen through age-dependent increases in conversion from androgen could also be a contributing factor. Individual variations and race-/ethnic-based differences in circulating or locally formed estrogens or in tissue estrogen responsiveness may explain differential PCa risk among individuals or different populations. Estrogen receptor (ER)-alpha and ER-beta are the main mediators of estrogen action in the prostate. However, ER-beta is the first ER subtype expressed in the fetal prostate. During cancer development, ER-beta expression is first lost as tumors progress into high grade in the primary site. Yet, its reexpression occurs in all metastatic cases of PCa. A change in cytosine methylation in a regulatory CpG island located in the proximal promoter of ER-beta may constitute an "on/off" switch for reversible regulation of ER-beta expression. A variety of estrogenic/antiestrogenic/selective estrogen receptor modulator (SERM)-like compounds have been shown to use non-ERE pathways, such as tethering of ER-beta to NF-kappaB binding proteins, Sp2, or Ap1 for gene transactivation. These findings open new avenues for drug design that now focuses on developing a new generation of estrogen-based PCa therapies with maximal proapoptotic action but few or no side effects.

Signal transducers and activators of transcription 1 and 3 in prostate: Effect of sexual activity

The signal transducers and activators of transcription (Stat) are effector molecules downstream of cytokine receptors. Ligand occupancy of these receptors results in the tyrosine phosphorylation, dimerization and nuclear translocation of the Stat family of transcription factors and by these means regulate gene expression. Prolactin receptors as members of the cytokine-hematopoietin receptor superfamily, are linked to Stat activation. Sexual stimulation leads to an increase in prolactin secretion that might be involved in long-term changes in the protein repertoire associated to prostate hyperplasia. In order to gain insight into this phenomenon, we analyzed the tyrosine phosphorylation and DNA binding activity of two members of the Stat family in the prostate of sexual experienced rats after different number of ejaculations. A significant increase in Stat-1 and Stat-3 tyrosine phosphorylation was found after three ejaculations. Concomitantly an increase in Stat-1 and Stat-3 DNA-binding activity is detected after two and three ejaculation series. These results, favor the notion that ejaculation-induced prolactin secretion activates its prostate receptors resulting in Stat-1 and Stat-3 nuclear translocation, event likely to be associated to the so-called benign prostate hyperplasia.

Hyperinsulinemia and dyslipidemia in non-diabetic benign prostatic hyperplasia

BACKGROUND

BPH is a multifactorial disease. Several studies have elucidated the role of hormones and growth factors in its etiology. Insulin is a growth-stimulating hormone. Previous studies have reported the association between hyperinsulinemia, dyslipidemia and BPH in patients with metabolic disorders like diabetes. We evaluated insulin and lipid profile parameters in non-diabetic BPH cases and correlated it with prostate size.

METHODS

50 symptomatic BPH cases and 38 controls were included in this study. Fasting serum insulin concentrations were measured by radioimmunoassay. Insulin resistance was assessed by HOMA. Fasting glucose, total cholesterol and triglycerides were quantified by enzymatic methods. HDL-cholesterol was quantified by phosphotungstate magnesium chloride method. LDL-cholesterol was calculated by Friedwald's formula.

RESULTS

Fasting serum insulin, HOMA, total cholesterol, and LDL-cholesterol were significantly higher and HDL-cholesterol was significantly lower in cases as compared to controls. Insulin was significantly associated with prostate size, cholesterol, triglycerides, VLDL-cholesterol and LDL-cholesterol in BPH cases. Stepwise regression analysis showed insulin as an independent risk factor in the development of BPH.

CONCLUSIONS

Hyperinsulinemia associated with insulin resistance is an independent risk factor in the development of BPH.

Prolactin inhibits apoptosis of ovarian carcinoma cells induced by serum starvation or cisplatin treatment

Prolactin, a peptide hormone essential for the development and function of reproductive organs, is involved in development of breast, prostate and colorectal cancers. However, the role of prolactin on the carcinogenesis of ovarian carcinomas is unclear. In this study, we show that mRNA of prolactin receptor is expressed in 5 out of 9 ovarian carcinoma cell lines, 15 out of 17 cases of surgical samples and all of normal ovarian surface epithelium, while prolactin transcript is detected only in 1 ovarian carcinoma cell line and in 1 of the surgical samples. For the prolactin receptor-positive ovarian carcinoma cells, exogenous prolactin did not affect the proliferation but markedly inhibited apoptosis. Therefore, actual cell growth was enhanced by prolactin in a dose-dependent manner. The blocking of prolactin receptor by antibody severely impaired the antiapoptotic and growth-promoting effects of prolactin. Interestingly, the cisplatin-induced cell death of the prolactin receptor-positive cells was significantly inhibited by pretreatment with prolactin. These findings indicate a responsiveness of ovarian carcinomas to prolactin and suggest that the prolactin/prolactin receptor system may be a new therapeutic target of ovarian carcinomas.

Development and potential clinical uses of human prolactin receptor antagonists

There is a large body of literature showing that prolactin (PRL) exerts growth-promoting activities in breast cancer, and possibly in prostate cancer and prostate hyperplasia. In addition, increasing evidence argues for the involvement of locally produced (autocrine) PRL, perhaps even more than pituitary-secreted (endocrine) PRL, in tumor growth. Because dopamine analogs are unable to inhibit PRL production in extrapituitary sites, alternative strategies need investigation. To that end, several PRL receptor antagonists have been developed by introducing various mutations into its natural ligands. For all but one of these analogs, the mechanism of action involves a competition with endogenous PRL for receptor binding. Such compounds are thus candidates to counteract the undesired actions of PRL, not only in tumors, but also in dopamine-resistant prolactinomas. In this review, we describe the different versions of antagonists that have been developed, with emphasis on the controversies regarding their characterization, and the limits for their potential development as a drug. The most recently developed antagonist, Delta1-9-G129R-hPRL, is the only one that is totally devoid of residual agonistic activity, meaning it acts as pure antagonist. We discuss to what extent this new molecule could be considered as a lead compound for inhibiting the actions of human PRL in the above-mentioned diseases. We also speculate on the multiple questions that could be addressed with respect to the therapeutic use of PRL receptor antagonists in patients.

Aging-associated changes in gene expression in the ACI rat prostate: Implications for carcinogenesis

BACKGROUND

Prostate cancer is the most frequently diagnosed neoplasm and the second leading cause of cancer-related mortality in men. Although the incidence of prostate cancer increases with age, the link between aging and prostate cancer is poorly understood.

METHODS

Affymetrix oligonucleotide microarrays were used to analyze the mRNA expression levels in the dorsolateral prostates from 6- and 18-month-old ACI rats. Real-time RT-PCR and immunohistochemistry was performed to validate microarray data in a select set of genes.

RESULTS

Microarray analysis revealed changes in gene expression associated with inflammation, oxidative stress, tissue remodeling, and energy metabolism. Most of these changes have been related to increased proliferative status of the prostate, anti-apoptosis, activated stroma, and alteration of the energy metabolism.

CONCLUSIONS

Age-associated alterations in the gene expression profile may put the aging prostate in risk for the initiation, promotion, and progression of neoplastic transformation in both our animal model and humans.

Prostate cancer and the met hepatocyte growth factor receptor

The hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, the Met protein tyrosine kinase, form a classic ligand-receptor system for epithelial-mesenchymal communications in the normal and cancerous prostate. This review illustrates the expression and activities of HGF/SF and Met during prostate development, homeostasis, and carcinogenesis. The participation of HGF/SF in the morphogenetic program of rodent prostate development, the role of Met in normal human prostate epithelium, and underlying mechanisms of deregulated Met expression in localized and metastatic prostate cancer are discussed. On the basis of the commonly observed overexpression of Met in metastatic prostate cancer, HGF/SF-Met-targeted imaging and therapeutic agents can now be applied toward diagnosis and treatment.

Activation of signal transducer and activator of transcription 5 in human prostate cancer is associated with high histological grade

We have recently identified signal transducer and activator of transcription 5 (Stat5) as a critical survival factor for prostate cancer cells. We now report that activation of Stat5 is associated with high histological grade of human prostate cancer. Specifically, immunohistochemical analysis demonstrated a strong positive correlation with activation of Stat5 and high Gleason score in 114 human prostate cancers. To investigate the mechanisms underlying constitutive activation of Stat5 in prostate cancer, a dominant-negative mutant of Janus kinase 2 (Jak2) was delivered by adenovirus to CWR22Rv cells. Dominant-negative-Jak2 effectively blocked the activation of Stat5 whereas wild-type Jak2 enhanced activation, indicating that Jak2 is the main kinase that phosphorylates Stat5 in human prostate cancer cells. A ligand-induced mechanism for activation of Stat5 in prostate cancer was suggested by the ability of prolactin (Prl) to stimulate activation of both Jak2 and Stat5 in CWR22Rv human prostate cancer cells and in CWR22Rv xenograft tumors. In addition, Prl restored constitutive activation of Stat5 in five of six human prostate cancer specimens in ex vivo long-term organ cultures. Finally, Prl protein was locally expressed in the epithelium of 54% of 80 human prostate cancer specimens with positive correlation with high Gleason scores and activation of Stat5. In conclusion, our data indicate that increased activation of Stat5 was associated with more biologically aggressive behavior of prostate cancer. The results further suggest that Jak2 is the principal Stat5 tyrosine kinase in human prostate cancer, possibly activated by autocrine/paracrine Prl.

Cyclic adenosine 3',5'-monosphosphate mediate prolactin regulation of mitochondrial aconitase in human prostate carcinoma cells

Mitochondrial aconitase (mACON) is regarded as the key enzyme for citrate oxidation in human prostatic epithelial cells. The results of RT-PCR and immunoblot assays indicated that human prostatic carcinoma cells (PC-3 cells) express the long-form of the prolactin receptor. In vitro studies determined that prolactin upregulates mACON enzymatic activity and cell proliferation of PC-3 cells. Immunoblot assay revealed that prolactin treatments increase the gene expression of mACON. Transient gene expression assay indicated that the regulation by prolactin of mACON gene expression depends on the presence of the cyclic adenosine 3',5'-monosphosphate (cAMP) response element on the promoter of the mACON gene. Both prolactin and dibutyryl-cAMP doubled the promoter activity of the mACON gene; however, adding H-89, a specific protein kinase A inhibitor, suppressed the prolactin response. The intracellular cAMP levels, but not the cGMP levels, increased after treatment with prolactin. This study showed that prolactin regulates the expression of the mACON gene via the cAMP signal pathway in human prostatic carcinoma cells.

High-grade prostatic intraepithelial neoplasia

High-grade prostatic intraepithelial neoplasia (PIN) is now accepted as the most likely preinvasive stage of adenocarcinoma, almost two decades after its first formal description. PIN has a high predictive value as a marker for adenocarcinoma, and its identification warrants repeat biopsy for concurrent or subsequent invasive carcinoma. The only method of detection is biopsy; PIN does not significantly elevate serum prostate-specific antigen (PSA) concentration or its derivatives and cannot be detected by current imaging techniques, including ultrasound. Most patients with PIN will develop carcinoma within 10 years. PIN is associated with progressive abnormalities of phenotype and genotype, which are similar to cancer rather than normal prostatic epithelium, indicating impairment of cell differentiation with advancing stages of prostatic carcinogenesis. Androgen deprivation therapy decreases the prevalence and extent of PIN, suggesting that this form of treatment may play a role in chemoprevention.

Prostate cancer in African American men is associated with downregulation of zinc transporters

In the United States, prostate cancer is the most commonly diagnosed male cancer and the second leading cause of all male cancer deaths. Furthermore, incidence rates are higher in African Americans than in any other racial group. Our laboratory is attempting to decipher the environmental and molecular mechanisms involved in the development of prostate cancer in African Americans. Because Africa is a mineral-rich continent, and the zinc levels in the water and diet are high, it is hypothesized that Africans may have genetically downregulated their zinc absorption capacity; otherwise, they would absorb abnormally high levels of zinc, resulting in various serious neurodegenerative and biochemical disorders. It is therefore possible that people of African origin may have a lower capacity to absorb zinc when compared with other racial groups because of their inherent downregulation of zinc transporters. Extensive research has shown that low serum levels of zinc are associated with the increased incidence of prostate cancer. We have evaluated 58 prostate cancer tissues in 2 major racial groups (30 from whites and 28 from African Americans) for their ability to express 2 major human zinc transporters, hZIP1 and hZIP2. In all 30 prostate cancer specimens obtained from white people, the degree of expression of these 2 zinc receptors was high when compared with age-matched and Gleason score-matched specimens obtained from African American patients. We also found a significant downregulation of these 2 zinc transporters in normal prostate tissues from African American men when compared with age-matched white men. The loss of the unique ability to retain normal intracellular levels of zinc may be an important factor in the development and progression of prostate cancer. Our observation that the uptake of zinc may be different in racial groups is intriguing and relevant. Once these data are confirmed in larger groups, this finding could have significant application as a preventive maneuver for at least for some people. Because dietary zinc supplements are relatively nontoxic, any efficacy trial would be low-risk.

The survival effect of prolactin on PC3 prostate cancer cells

OBJECTIVES

Recent studies suggest a paracrine/autocrine loop involving prolactin (PRL) within the human prostate. The aims of this study were to determine the effects of PRL on the growth and survival of prostate cancer cells and the intracellular signalling mechanisms underlying such effects.

METHODS

The effect of PRL on proliferation of LNCaP, PC3 and DU145 was assessed by Coulter counting. The effect of PRL on TRAIL-, staurosporine- and flavopiridol-induced apoptosis was assessed by Timelapse microscopy and Annexin V binding. The status of the PRL receptor (PRL-R) and Akt/PKB (protein kinase B) activity were assessed by Western blotting.

RESULTS

All three cell lines expressed both the short and long forms of the PRL receptor. Although, no significant effect of PRL on the proliferation of these cells was found, PRL partially inhibited TRAIL-induced apoptosis in PC3 cells. PRL also enhanced the phosphorylation of Akt/PKB in these cells.

CONCLUSIONS

PRL had no significant effect on the proliferation of PC3, DU145 and LNCaP, but inhibited TRAIL-induced apoptosis in PC3 cells, possibly via enhanced Akt/PKB phosphorylation in PC3 cells. Further investigations are underway to determine the survival effect of PRL on the other two prostate cancer cell line.

Prolactin as an autocrine/paracrine growth factor in human cancer

Prolactin (PRL) has a dual function -- as a circulating hormone and as a cytokine. This understanding is based on PRL production and distinct regulation in extrapituitary sites, its binding to membrane receptors of the cytokine receptor superfamily, and activation of signaling pathways that promote cell growth and survival. There is increasing evidence that PRL plays a role in several types of cancer in reproductive and non-reproductive tissues via local production or accumulation. The expression of both PRL and its receptor in human cancer cell lines of diverse origin lends further support to its action as an autocrine/paracrine growth factor. Establishment of PRL as an active participant in tumorigenesis should inspire the development of novel therapies aimed at reducing tumor growth by suppressing PRL production or by blocking its receptors.

PRL signal transduction in the epithelial compartment of rat prostate maintained as long-term organ cultures in vitro

Using long-term organ cultures of rat prostate tissue explants, we previously demonstrated that PRL both stimulates proliferation and acts as an androgen-independent suppressor of apoptosis in prostate epithelial cells, leading to epithelial hyperplasia. In this work we delineate intracellular signaling molecules activated by PRL in prostate tissue to identify candidate signaling proteins that are responsible for maintaining survival and proliferation of prostate epithelium in androgen-deprived growth environment. We now show that signal transducer and activator of transcription-5a (Stat5a) and Stat5b become tyrosine phosphorylated in response to PRL stimulation in rat prostate using prostate organ culture as an experimental model. Stat5 was translocated to the nuclei of epithelial cells of prostate tissue as demonstrated by immunohistochemistry. Furthermore, EMSA showed PRL-inducible binding of Stat5a homodimers and Stat5a/5b heterodimers to the PRL response element of the beta-casein gene promoter. Signaling molecules Stat3, Stat1, MAPK, or protein kinase B, which can be activated by PRL in other target cells, were not activated by PRL in prostate tissue. Furthermore, we show that Stat5a and Stat5b are continuously phosphorylated in rat prostate in vivo, although they are expressed to varying degree in separate lobes of rat prostate. Collectively, our results suggest that PRL signaling in rat prostate tissue is primarily transduced via Stat5a and Stat5b. The Stat5 pathway represents one candidate signaling mechanism, used by PRL and possibly other growth factors and cytokines, that supports the viability of prostate epithelial cells during long-term androgen deprivation.

Upregulation of lymphocyte apoptosis as a strategy for preventing and treating autoimmune disorders: a role for whole-food vegan diets, fish oil and dopamine agonists

Induced apoptosis of autoreactive T-lymphocyte precursors in the thymus is crucial for the prevention of autoimmune disorders. IGF-I and prolactin, which are lymphocyte growth factors, may have the potential to suppress apoptosis in thymocytes and thus encourage autoimmunity; conversely, dietary fish oil rich in omega-3 fats appears to upregulate apoptosis in lymphocytes. Since whole-food vegan diets may downregulate systemic IGF-I activity, it is proposed that such a diet, in conjunction with fish oil supplementation and treatment with dopamine agonists capable of suppressing prolactin secretion, may have utility for treating and preventing autoimmune disorders. This prediction is consistent with the extreme rarity of autoimmune disorders among sub-Saharan black Africans as long as they followed their traditional quasi-vegan lifestyles, and with recent ecologic studies correlating risks for IDDM and for multiple sclerosis mortality with animal product and/or saturated fat consumption. Moreover, there is evidence that vegan or quasi-vegan diets are useful in the management of rheumatoid arthritis, multiple sclerosis, and possibly SLE. The dopamine agonist bromocryptine exerts anti-inflammatory effects in rodent models of autoimmunity, and there is preliminary evidence that this drug may be clinically useful in several human autoimmune diseases; better tolerated D2-specific agonists such as cabergoline may prove to be more practical for use in therapy. The moderate clinical utility of supplemental fish oil in rheumatoid arthritis and certain other autoimmune disorders is documented. It is not unlikely that extra-thymic anti-inflammatory effects contribute importantly to the clinical utility of vegan diets, bromocryptine, and fish oil in autoimmunity. The favorable impact of low latitude or high altitude on autoimmune risk may be mediated by superior vitamin D status, which is associated with decreased secretion of parathyroid hormone; there are theoretical grounds for suspecting that parathyroid hormone may inhibit apoptosis in thymocytes. Androgens appear to up-regulate thymocyte apoptosis, may be largely responsible for the relative protection from autoimmunity enjoyed by men, and merit further evaluation for the management of autoimmunity in women. It will probably prove more practical to prevent autoimmune disorders than to reverse them once established; a whole-food vegan diet, coupled with fish oil and vitamin D supplementation, may represent a practical strategy for achieving this prevention, while concurrently lowering risk for many other life-threatening 'Western' diseases.

Identification and characterization of the prolactin-binding protein in human serum and milk

The actions of prolactin (PRL) are mediated by its receptor, a member of the superfamily of single transmembrane cytokine receptors. High affinity binding proteins for the closely related growth hormone have been found in the sera of several species including humans and are generated by alternative splicing or proteolysis of the growth hormone receptor extracellular domain (ECD). In contrast, no conclusive evidence has been presented that an analogous prolactin-binding protein (PRLBP) is expressed in human serum. Using both monoclonal and polyclonal antibodies generated against hPRL and the ECD of the human prolactin receptor, co-immunoprecipitation analyses of human serum identified a 32-kDa hPRLBP capable of binding both hPRL and human growth hormone. A measurable fraction of circulating PRL (36%) was associated with the hPRLBP. Despite well documented sex differences in serum hPRL levels, there were no significant differences in the levels of hPRLBP found in the sera of normal adult males and females (15.3 +/- 1.3 ng/ml versus 13.4 +/- 0.8 ng/ml, respectively (mean +/- S.E.)). Immunoprecipitation studies also detected the PRLBP in human milk albeit at lower concentrations than found in sera. Deglycosylation did not alter its electrophoretic mobility, indicating an absence of carbohydrate moieties and suggesting that the hPRLBP spans most of the PRLR ECD, a result confirmed by limited proteolysis and mass spectrometry. The potential function of this serum chaperone was assessed in vitro by the addition of recombinant hPRLBP to the culture medium of the PRL-dependent Nb2 T-cell line. These studies revealed that the hPRLBP antagonizes PRL action, inhibiting PRL-driven growth in a dose-dependent manner.

Elevated androgens and prolactin in aromatase-deficient mice cause enlargement, but not malignancy, of the prostate gland

Although androgens are the main steroids controlling the growth of the mammalian prostate, increasing evidence demonstrates that estrogens also regulate prostate development and growth. This study describes the effects of estrogen deficiency using aromatase knockout mice (ArKO) with targeted disruption of the cyp19 gene. Serum and tissue testosterone and 5alpha-dihydrotestosterone as well as serum PRL levels are significantly (P < 0.05) elevated in mature male ArKO mice. Histological, stereological, and immunohistochemical studies demonstrated enlargement of the ventral, anterior, and dorsolateral lobes of the prostate in young and older ArKO mice. Hyperplasia of the epithelial, interstitial, and luminal compartments was identified and associated with up-regulation of androgen receptors. There was no evidence of malignancy as the animals aged (up to 56 weeks). The changes observed in the prostates of ArKO mice were unaffected by maintaining mice on regular or soy-free diets. It is concluded in ArKO mice that, despite the long-term elevation of androgens and PRL, the absence of estrogen in these animals does not result in induction of malignancy in the prostate gland.

Plasma prolactin and prostate cancer risk: A prospective study

Prolactin, a pituitary peptide hormone with multiple effects, stimulates prostate growth in experimental models. In humans, prolactin receptors are present in the prostate and are particularly abundant in pre-cancerous lesions. This suggests that prolactin could also be involved in the development of prostate cancer. In this study, we tested the hypothesis that elevated levels of circulating prolactin are associated with an increase in prostate cancer risk. We conducted a case-control study nested within the Northern Sweden Health and Disease Cohort using plasma samples collected from 29,560 men at a health survey. We measured prolactin in plasma from 144 men who had a diagnosis of prostate cancer after a median follow-up time of 4 years after health survey and from 289 controls matched for age and date of recruitment. Risk was not associated with plasma prolactin levels in univariate regression analysis. Odds ratios of prostate cancer for increasing quartiles of prolactin were 1.0, 0.92 (95% CI 0.51-1.65), 0.82 (0.45-1.51) and 0.85 (0.49-1.47). Relative risk estimates remained unchanged after adjustments for height and weight or for plasma levels of testosterone, sex hormone-binding globulin, IGF-I and IGF-binding protein-3. Elevated circulating levels of prolactin were not related to an increase in prostate cancer risk, indicating that high circulating prolactin is not associated with development of prostate cancer.