Prolactin and prolactin receptors are expressed and functioning in human prostate

Stat5 induces androgen receptor (AR) gene transcription in prostate cancer and offers a druggable pathway to target AR signaling

Androgen receptor (AR) drives prostate cancer (PC) growth and progression, and targeting AR signaling is the mainstay of pharmacological therapies for PC. Resistance develops relatively fast as a result of refueled AR activity. A major gap in the field is the lack of understanding of targetable mechanisms that induce persistent AR expression in castrate-resistant PC (CRPC). This study uncovers an unexpected function of active Stat5 signaling, a known promoter of PC growth and clinical progression, as a potent inducer of AR gene transcription. Stat5 suppression inhibited AR gene transcription in preclinical PC models and reduced the levels of wild-type, mutated, and truncated AR proteins. Pharmacological Stat5 inhibition by a specific small-molecule Stat5 inhibitor down-regulated Stat5-inducible genes as well as AR and AR-regulated genes and suppressed PC growth. This work introduces the concept of Stat5 as an inducer of AR gene transcription in PC. Pharmacological Stat5 inhibitors may represent a new strategy for suppressing AR and CRPC growth.

PRL-mediated STAT5B/ARRB2 pathway promotes the progression of prostate cancer through the activation of MAPK signaling

Previous study showed that higher expression of prolactin (PRL) was found in CRPC samples compared with hormone-naive prostate cancer (HNPC) and benign prostatic hyperplasia (BPH) samples. We further investigate the function of PRL in prostate cancer (PCa) and explored its downstream effects. We found heterogeneous expression of the PRLR in clinical prostate samples. The VCaP and 22Rv1 cells exhibited PRLR expression. Among the downstream proteins, STAT5B was the dominant subtype in clinical samples and cell lines. Human recombinant PRL stimulation of PCa cells with PRLR expression resulted in increased phosphorylation of STAT5B(pSTAT5B) and progression of PCa in vitro and in vivo, and STAT5B knockdown can suppress the malignant behavior of PCa. To understand the mechanism further, we performed Bioinformatic analysis, ChIP qPCR, and luciferase reporter gene assay. The results revealed that ARRB2 was the transcription target gene of STAT5B, and higher expression of ARRB2 was related to higher aggression and poorer prognosis of PCa. Additionally, Gene set enrichment analysis indicated that higher expression of ARRB2 was significantly enriched in the MAPK signaling pathway. Immunohistochemistry (IHC) demonstrated elevated pSTAT5B, ARRB2, and pERK1/2 expression levels in CRPC tissues compared to HNPC and BPH. Mechanically, ARRB2 enhanced the activation of the MAPK pathway by binding to ERK1/2, thereby promoting the phosphorylation of ERK1/2 (pERK1/2). In conclusion, our study demonstrated that PRL stimulation can promote the progression of PCa through STAT5B/ARRB2 pathway and activation of MAPK signaling, which can be suppressed by intervention targeting STAT5B. Blockade of the STAT5B can be a potential therapeutic target for PCa.

Cell Plasticity in a Mouse Model of Benign Prostate Hyperplasia Drives Amplification of Androgen-Independent Epithelial Cell Populations Sensitive to Antioxidant Therapy

Benign prostate hyperplasia (BPH) is caused by the nonmalignant enlargement of the transition zone of the prostate gland, leading to lower urinary tract symptoms. Although current medical treatments are unsatisfactory in many patients, the limited understanding of the mechanisms driving disease progression prevents the development of alternative therapeutic strategies. The probasin-prolactin (Pb-PRL) transgenic mouse recapitulates many histopathological features of human BPH. Herein, these alterations parallel urodynamic disturbance reminiscent of lower urinary tract symptoms. Single-cell RNA-sequencing analysis of Pb-PRL mouse prostates revealed that their epithelium mainly includes low-androgen signaling cell populations analogous to Club/Hillock cells enriched in the aged human prostate. These intermediate cells are predicted to result from the reprogramming of androgen-dependent luminal cells. Pb-PRL mouse prostates exhibited increased vulnerability to oxidative stress due to reduction of antioxidant enzyme expression. One-month treatment of Pb-PRL mice with anethole trithione (ATT), a specific inhibitor of mitochondrial ROS production, reduced prostate weight and voiding frequency. In human BPH-1 epithelial cells, ATT decreased mitochondrial metabolism, cell proliferation, and stemness features. ATT prevented the growth of organoids generated by sorted Pb-PRL basal and LSCmed cells, the two major BPH-associated, androgen-independent epithelial cell compartments. Taken together, these results support cell plasticity as a driver of BPH progression and therapeutic resistance to androgen signaling inhibition, and identify antioxidant therapy as a promising treatment of BPH.

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.

Rate of castration-induced prostate stroma regression is reduced in a mouse model of benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a non-neoplastic proliferative disease producing lower urinary tract symptoms related to the resulting enlarged prostate. BPH is pathologically characterized by hyperplastic growth in both epithelial and stromal compartments. Androgen signaling is essential for prostate function and androgen blockade is the second-line medical therapy to relieve symptoms of BPH. Here we examined the prostates of probasin promoter-driven prolactin (Pb-PRL) transgenic mice, a robust model of BPH that spontaneously develops prostate enlargement, to investigate prostate regression in response to surgical castration. Serial ultrasound imaging demonstrated very uniform self-limited growth of Pb-PRL prostate volume that is consistent with the benign, limited cellular proliferation characteristic of BPH and that contrasts with the highly variable, exponential growth of murine prostate cancer models. Castration elicited only a partial reduction in prostate volume, relative to castration-induced regression of the normal prostate gland. The anti-androgen finasteride induced a diminished reduction of Pb-PRL prostate volume versus castration. The limited extent of Pb-PRL mouse prostate volume regression correlated with the initial volume of the stromal compartment, suggesting a differential sensitivity of the epithelial and stromal compartments to androgen withdrawal. Indeed, two-dimensional morphometric analyses revealed a distinctly reduced rate of regression for the stromal compartment in Pb-PRL mice. The myofibroblast component of the Pb-PRL prostate stroma appeared normal, but the stromal compartment contained more fibroblasts and extracellular collagen deposition. Like normal prostate, the rate of regression of the Pb-PRL prostate was partially dependent on TGFß and TNF signaling, but unlike the normal prostate, the extent of castration-induced regression was not affected by TGFß or TNF blockade. Our studies show that androgen deprivation can effectively reduce the overall volume of hyperplastic prostate, but the stromal compartment is relatively resistant, suggesting additional therapies might be required to offer an effective treatment for the clinical manifestations of BPH.

Second-Generation Jak2 Inhibitors for Advanced Prostate Cancer: Are We Ready for Clinical Development?

Simple Summary

Prostate Cancer (PC) is currently estimated to affect 1 in 9 men and is the second leading cause of cancer in men in the US. While androgen deprivation therapy, which targets the androgen receptor, is one of the front-line therapies for advanced PC and for recurrence of organ-confined PC treated with surgery, lethal castrate-resistant PC develops consistently in patients. PC is a multi-focal cancer with different grade carcinoma areas presenting simultaneously. Jak2-Stat5 signaling pathway has emerged as a potentially highly effective molecular target in PCs with positive areas for activated Stat5 protein. Activated Jak2-Stat5 signaling can be readily targeted by the second-generation Jak2-inhibitors that have been developed for myeloproliferative and autoimmune disorders and hematological malignancies. In this review, we analyze and summarize the Jak2 inhibitors that are currently in preclinical and clinical development.

Abstract

Androgen deprivation therapy (ADT) for metastatic and high-risk prostate cancer (PC) inhibits growth pathways driven by the androgen receptor (AR). Over time, ADT leads to the emergence of lethal castrate-resistant PC (CRPC), which is consistently caused by an acquired ability of tumors to re-activate AR. This has led to the development of second-generation anti-androgens that more effectively antagonize AR, such as enzalutamide (ENZ). However, the resistance of CRPC to ENZ develops rapidly. Studies utilizing preclinical models of PC have established that inhibition of the Jak2-Stat5 signaling leads to extensive PC cell apoptosis and decreased tumor growth. In large clinical cohorts, Jak2-Stat5 activity predicts PC progression and recurrence. Recently, Jak2-Stat5 signaling was demonstrated to induce ENZ-resistant PC growth in preclinical PC models, further emphasizing the importance of Jak2-Stat5 for therapeutic targeting for advanced PC. The discovery of the Jak2V617F somatic mutation in myeloproliferative disorders triggered the rapid development of Jak1/2-specific inhibitors for a variety of myeloproliferative and auto-immune disorders as well as hematological malignancies. Here, we review Jak2 inhibitors targeting the mutated Jak2V617F vs. wild type (WT)-Jak2 that are currently in the development pipeline. Among these 35 compounds with documented Jak2 inhibitory activity, those with potency against WT-Jak2 hold strong potential for advanced PC therapy.

Connections between prolactin and ovarian cancer

Ovarian cancer (OC) is characterized by a high morbidity and mortality, highlighting a great need for a better understanding of biological mechanisms that affect OC progression and improving its early detection methods. This study investigates effects of prolactin (PRL) on ovarian cancer cells, analyzes PRL receptors (PRLR) in tissue micro arrays and relates PRLR expression to survival of ovarian cancer. A database, composed of transcript profiles from OC, was searched for PRLR expression and results were put in relation to survival. Expression of PRLR in OC tissue sections and OC cell lines SKOV3, OV2008 and OVSAHO was assessed using immunohistochemistry, western blots and quantitative real-time PCR. The biological function of PRLR was evaluated by proliferation, colony formation and wound healing assays. Levels of PRLR mRNA are related to survival; in epithelial OC a high PRLR mRNA expression is related to a shorter survival. Analysis of a tissue micro array consisting of 84 OC showed that 72% were positive for PRLR immuno-staining. PRLR staining tended to be higher in OC of high grade tumors compared to lower grades. PRLR mRNA and protein can further be detected in OC cell lines. Moreover, in vitro treatment with PRL significantly activated the JAK/STAT pathway. PRLR expression is associated with OC survivals. PRL and its receptor may play an onco-modulatory role and promote tumor aggressiveness in OC. Alternatively, increased PRLR levels may form a base for the development of PRLR antagonist or PRLR antagonist-drug conjugate to increase selective uptake of anti-cancer drugs.

Prolactin promotes a partial recovery from the atrophy of both male and female gerbil prostates caused by castration

BACKGROUND

The male and female prostates are controlled by steroid hormones, suffering important morphological and physiological changes after castration. Prolactin is involved in the regulation of the male prostate, having already been identified in the tissue, acting through its receptor PRLR. In the Mongolian gerbil, in addition to the male prostate, the female prostate is also well developed and active in its secretion processes. The aim of the present study was to evaluate the effects of exposure to exogenous prolactin in the prostate of both intact and castrated male and female gerbils in order to establish if prolactin administration can sustain prostate cell activity in conditions of sexual hormone deprivation.

METHODS

The morphological analyses were performed by biometric analysis, lesion histological analysis and morphometric-stereological aspects. In addition, immune-cytochemical tests were performed for prolactin and its receptor, as well as for the receptors of androgen and oestrogen and serum prolactin dosage. All data were submitted to ANOVA or Kruskal-Wallis tests for comparison between groups. P < 0.05 was considered to be statistically significant.

RESULTS

The results showed a strong influence of prolactin on the morphology of the prostate, with the development of important epithelial alterations, after only 3 days of administration, and an expressive epithelial cell discard process after 30 days of administration. Prolactin acts in synergy with testosterone in males and mainly with oestrogens in females, establishing different steroid hormonal receptor immunoreactivity according to sex. It was also demonstrated that prolactin can assist in the recovery from some atrophic effects caused in the gland after castration, without causing additional tissue damage.

CONCLUSIONS

The prolactin and its receptor are involved in the maintenance of the homeostasis of male and female gerbils, and also cause distinct histological alterations after exogenous exposure for 3 and 30 days. The effects of prolactin are related to its joint action on androgens and oestrogens and it can also assist in the recovery from the atrophic effects of castration.

An investigation on the relevance of prolactin, insulin-like growth factor-1 and 25-hydroxyvitamin D3 (25-OHD3 ) in canine benign prostatic hyperplasia in a predisposed breed model

Serum concentrations of prolactin (PRL), insulin-like growth factor-1 (IGF-1) and 25 hydroxyvitamin D₃ (25-OHD₃ ) were analysed to investigate their possible involvement in the pathogenesis of benign prostatic hyperplasia (BPH). For this, dogs of the Rhodesian Ridgeback (RR) breed were used because of a verified breed disposition for the development of BPH. Labrador Retrievers (LR) served as controls. The prostate gland status was characterised by the prostate gland volume, clinical signs of BPH (haemospermia and sonographic findings) and the plasma concentration of canine prostate-specific arginine esterase (CPSE). Breed specificity in the RR was expressed by a correlation of PRL with breed (p < 0.05). Similar relationships existed in the dogs with normal CPSE (CPSEn) with respect to the IGF-1 concentrations (LR: p < 0.05). The latter were negatively correlated with prostatic volume and age (both p < 0.05). Concentrations of 25-OHD₃ were tendentially (p = 0.18) lower in the RR with increased CPSE (CPSEi) compared with the CPSEn LR and RR showing clinical signs of BPH. A negative correlation between serum 25-OHD₃ and age (p < 0.05) existed in the CPSEi RR. Proof of 25-OHD₃ in prostatic secretion proved to be a breed specific feature in the RR (p < 0.0001). For all RR dogs showing clinical signs of BPH, a close to significant (p = 0.06) positive correlation with prostate gland volume was found. The results of the present study reveal no clear hints towards the significance of PRL and IGF-1 in the pathogenesis of canine BPH. In the RR breed there were indications of a causal relationship with age-dependent changes in the vitamin D metabolism. The data suggest the possibility of preventing or treating canine BPH by administering vitamin D or substances involved in the intraprostatic vitamin D metabolism.

Simplification of the purification of heat stable recombinant low molecular weight proteins and peptides from GST-fusion products

The synthesis and purification of peptides of importance in the fields of research and medicine continue to be a challenging task. Chemical synthesis of oligopeptides, especially those greater than 25 amino acids, is cost prohibitive. On the other hand, several bottlenecks exist in the production of recombinant short peptides in heterologous expression hosts such as Escherichia coli (E. coli). In this study, a rapid, cost-effective, and reliable method for the production and single-step-purification of peptides and small proteins was developed. Five peptides and small proteins were overexpressed in E. coli as GST-fusion products in high yields. The recombinant peptides or proteins were successfully purified after enzymatic cleavage with selective heat-induced precipitation of the GST-affinity tag. Qualitative and quantitative analysis using SDS-PAGE and mass spectrometric methods suggest that the recombinant peptides/ proteins were purified to greater than 95% homogeneity. Results of biophysical experiments, including multi-dimensional NMR spectroscopy, show that the purified proteins/ peptides retain their native conformation. Isothermal titration calorimetry studies indicate no significant change in the binding affinity of the heat-treated purified product to their interacting partner(s) compared to the recombinant peptides purified by conventional chromatographic procedures without subjecting to heat treatment. In our opinion, the results reported render the purification of recombinant proteins/ peptides of biomedical relevance using our proposed method easy and reliable.

S179D Prolactin Sensitizes Human PC3 Prostate Cancer Xenografts to Anti-tumor Effects of Well-Tolerated Doses of Calcitriol

Calcitriol has been shown to have multiple anti-prostate cancer effects both in vitro and in xenograft models, and associations between low levels of calcitriol and more aggressive forms of prostate cancer have been observed clinically. However, the concentrations of calcitriol required to have a substantive anti-cancer effect in vivo are toxic. In previous work, we had observed that the selective prolactin receptor modulator, S179D PRL, sensitized prostate cancer cells in vitro to physiological concentrations of calcitriol through an ability to increase expression of the vitamin D receptor. Here, we have investigated whether administration of S179D PRL would likewise sensitize androgen-insensitive human PC3 xenografts in vivo and do so without inducing tissue damage akin to hypervitaminosis D. Using low concentrations of both S179D PRL (250 ng/h) and calcitriol (up to 220 pg/h), we found no effect of each alone or in combination on the growth rate of tumors. However, there was increased central tumor death with their combination that was more than additive at 250 ng S179D PRL and 220 pg calcitriol per hour. Both S179D PRL and calcitriol alone were antiangiogenic, but their antiangiogenic effects were not additive. Also, both S179D PRL and calcitriol alone increased the number of apoptotic cells in tumor sections, but their combination reduced the number, suggesting more effective clearance of apoptotic cells. Histopathology of the livers and kidneys showed no changes consistent with hypervitaminosis D. We conclude that dual therapy holds promise as a means to harness the anti-tumor effects of well-tolerated doses of calcitriol.

Effects of hormones and hormone therapy on breast tissue in transgender patients: a concise review

PURPOSE

Hormone replacement therapy (HRT) has become a mainstay medical treatment option for management of gender dysphoria in transgender patients of both biologic sexes. Very little is known about the long-term effects of steroid hormone modulation on breast tissue in this population. Most of the data available on the effects of HRT on breast and reproductive tissues come from studies of postmenopausal cisgender women. Therapeutic regimens are often provider-dependent, and there, are no uniform guidelines in place for cancer surveillance in transgender patients. In this review, we present what forms of hormone therapy and hormone modulation are available to transgender patients, what is known about their effects on male and female breast tissue, and what other endogenous and exogenous factors contribute to the macroscopic and cellular changes observed.

METHODS

A search for the existing literature focusing on therapeutic regimens and the effects of HRT on breast tissue provided the most current information available for this review. Recent evidence-based reports (since the year 2000) and reviews were given priority over anecdotal evidence and expert opinions when conflicting information was encountered. Older resources were considered when primary sources were needed. Given the paucity of available articles on this subject, all resources were given careful consideration.

RESULTS

Information about the risks associated with HRT in the current literature and in this setting is limited and often conflicting, due to a scarcity of long-term studies tracking breast pathology among transgender men and women.

CONCLUSIONS

We conclude that the long-term effects of off-label pharmaceutical use for modulation of hormone levels and sexual characteristics in transgender patients have not been well studied. The tendency of steroid hormones to promote the growth of certain cancers also raises questions about the safety of differing doses and drug combinations. Further clinical and laboratory study is needed to better establish safety and dosing guidelines in transgender patients.

Enzalutamide-Induced Feed-Forward Signaling Loop Promotes Therapy-Resistant Prostate Cancer Growth Providing an Exploitable Molecular Target for Jak2 Inhibitors

The second-generation antiandrogen, enzalutamide, is approved for castrate-resistant prostate cancer (CRPC) and targets androgen receptor (AR) activity in CRPC. Despite initial clinical activity, acquired resistance to enzalutamide arises rapidly and most patients develop terminal disease. Previous work has established Stat5 as a potent inducer of prostate cancer growth. Here, we investigated the significance of Jak2-Stat5 signaling in resistance of prostate cancer to enzalutamide. The levels of Jak2 and Stat5 mRNA, proteins and activation were evaluated in prostate cancer cells, xenograft tumors, and clinical prostate cancers before and after enzalutamide therapy. Jak2 and Stat5 were suppressed by genetic knockdown using lentiviral shRNA or pharmacologic inhibitors. Responsiveness of primary and enzalutamide-resistant prostate cancer to pharmacologic inhibitors of Jak2-Stat5 signaling was assessed in vivo in mice bearing prostate cancer xenograft tumors. Patient-derived prostate cancers were tested for responsiveness to Stat5 blockade as second-line treatment after enzalutamide ex vivo in tumor explant cultures. Enzalutamide-liganded AR induces sustained Jak2-Stat5 phosphorylation in prostate cancer leading to the formation of a positive feed-forward loop, where activated Stat5, in turn, induces Jak2 mRNA and protein levels contributing to further Jak2 activation. Mechanistically, enzalutamide-liganded AR induced Jak2 phosphorylation through a process involving Jak2-specific phosphatases. Stat5 promoted prostate cancer growth during enzalutamide treatment. Jak2-Stat5 inhibition induced death of prostate cancer cells and patient-derived prostate cancers surviving enzalutamide treatment and blocked enzalutamide-resistant tumor growth in mice. This work introduces a novel concept of a pivotal role of hyperactivated Jak2-Stat5 signaling in enzalutamide-resistant prostate cancer, which is readily targetable by Jak2 inhibitors in clinical development.

STAT5a/b Deficiency Delays, but does not Prevent, Prolactin-Driven Prostate Tumorigenesis in Mice

The canonical prolactin (PRL) Signal Transducer and Activator of Transcription (STAT) 5 pathway has been suggested to contribute to human prostate tumorigenesis via an autocrine/paracrine mechanism. The probasin (Pb)-PRL transgenic mouse models this mechanism by overexpressing PRL specifically in the prostate epithelium leading to strong STAT5 activation in luminal cells. These mice exhibit hypertrophic prostates harboring various pre-neoplastic lesions that aggravate with age and accumulation of castration-resistant stem/progenitor cells. As STAT5 signaling is largely predominant over other classical PRL-triggered pathways in Pb-PRL prostates, we reasoned that Pb-Cre recombinase-driven genetic deletion of a floxed Stat5a/b locus should prevent prostate tumorigenesis in so-called Pb-PRL^ΔSTAT5 mice. Anterior and dorsal prostate lobes displayed the highest Stat5a/b deletion efficiency with no overt compensatory activation of other PRLR signaling cascade at 6 months of age; hence the development of tumor hallmarks was markedly reduced. Stat5a/b deletion also reversed the accumulation of stem/progenitor cells, indicating that STAT5 signaling regulates prostate epithelial cell hierarchy. Interestingly, ERK1/2 and AKT, but not STAT3 and androgen signaling, emerged as escape mechanisms leading to delayed tumor development in aged Pb-PRL^ΔSTAT5 mice. Unexpectedly, we found that Pb-PRL prostates spontaneously exhibited age-dependent decline of STAT5 signaling, also to the benefit of AKT and ERK1/2 signaling. As a consequence, both Pb-PRL and Pb-PRL^ΔSTAT5 mice ultimately displayed similar pathological prostate phenotypes at 18 months of age. This preclinical study provides insight on STAT5-dependent mechanisms of PRL-induced prostate tumorigenesis and alternative pathways bypassing STAT5 signaling down-regulation upon prostate neoplasia progression.

Autocrine actions of prolactin contribute to the regulation of lactotroph function in vivo

Prolactin (PRL), whose principal role is regulation of lactation, is mainly synthesized and secreted by lactotroph anterior pituitary cells. Its signaling is exerted via a transmembrane PRL receptor (PRLR) expressed in a wide variety of tissues, including the anterior pituitary. Dopamine, which is secreted by tuberoinfundibular hypothalamic neurons, is the major inhibitory regulator of prolactin secretion. Although PRL is well established to stimulate hypothalamic dopamine secretion, thereby exerting a negative feedback regulation on its own release, autocrine or paracrine actions of PRL on lactotroph cells have also been suggested. Within the pituitary, PRL may inhibit both lactotroph proliferation and secretion, but in vivo evaluation of these putative functions is limited. To determine whether the autocrine actions of prolactin have a significant role in the physiologic function of lactotrophs in vivo, we examined the consequences of conditional deletion of Prlr in lactotroph cells using a novel mouse line with loxP sites flanking the Prlr gene ( Prlr^lox/lox) and Cre-recombinase (Cre) expressed under the control of the pituitary-specific Prl promoter. Prlr^lox/lox/Prl-Cre mice have normal PRL levels and did not develop any pituitary lactotroph adenoma, even at 20 mo of age. Nevertheless, Prlr^lox/lox/Prl-Cre mice displayed an increased dopaminergic inhibitory tone compared with control Prlr^lox/lox mice. These results elegantly confirm an autocrine/paracrine feedback of PRL on lactotroph cells in vivo, which can be fully compensated by an intact hypothalamic feedback system.-Bernard, V., Lamothe, S., Beau, I., Guillou, A., Martin, A., Le Tissier, P., Grattan, D., Young, J., Binart, N. Autocrine actions of prolactin contribute to the regulation of lactotroph function in vivo.

Influence of postnatal prolactin modulation on the development and maturation of ventral prostate in young rats

Besides androgenic dependence, other hormones also influence the prostate biology. Prolactin has been described as an important hormone associated with maintenance of prostatic morphophysiology; however, there is a lack of information on the involvement of prolactin during prostate development and growth. This study aimed to evaluate whether perinatal prolactin modulation interferes with rat ventral prostate (VP) development and maturation. Therefore, prolactin or bromocriptine (an inhibitor of prolactin release from the pituitary) were administered to Sprague Dawley rats from postnatal Day (PND) 12 to PND 21 or 35. Animals were then killed and serum hormonal quantification, VP morphological-stereological and immunohistochemical analyses and western blotting reactions were employed. Our results demonstrate that prolactin blockage increased serum testosterone on PND 21, which reflected an increase in anogenital distance. Although prolactin modulation did not interfere with VP weight, it modified VP morphology by dilating the acinar lumen and reducing epithelial cell height. Prolactin activated the signal transducer and activator of transcription (STAT) downstream pathway, increased androgen receptor expression and epithelial proliferation. In addition, prolactin and bromocriptine also increased expression of cytokeratin 18, a marker of luminal-differentiated cells. In conclusion, the VP responds to prolactin modulation through a mechanism of increasing the epithelial proliferative response and dynamics of cell differentiation, especially in animals treated for a more prolonged period.

Androgen receptor-dependent and -independent mechanisms driving prostate cancer progression: Opportunities for therapeutic targeting from multiple angles

Despite aggressive treatment for localized cancer, prostate cancer (PC) remains a leading cause of cancer-related death for American men due to a subset of patients progressing to lethal and incurable metastatic castrate-resistant prostate cancer (CRPC). Organ-confined PC is treated by surgery or radiation with or without androgen deprivation therapy (ADT), while options for locally advanced and disseminated PC include radiation combined with ADT, or systemic treatments including chemotherapy. Progression to CRPC results from failure of ADT, which targets the androgen receptor (AR) signaling axis and inhibits AR-driven proliferation and survival pathways. The exact mechanisms underlying the transition from androgen-dependent PC to CRPC remain incompletely understood. Reactivation of AR has been shown to occur in CRPC despite depletion of circulating androgens by ADT. At the same time, the presence of AR-negative cell populations in CRPC has also been identified. While AR signaling has been proposed as the primary driver of CRPC, AR-independent signaling pathways may represent additional mechanisms underlying CRPC progression. Identification of new therapeutic strategies to target both AR-positive and AR-negative PC cell populations and, thereby, AR-driven as well as non-AR-driven PC cell growth and survival mechanisms would provide a two-pronged approach to eliminate CRPC cells with potential for synthetic lethality. In this review, we provide an overview of AR-dependent and AR-independent molecular mechanisms which drive CRPC, with special emphasis on the role of the Jak2-Stat5a/b signaling pathway in promoting castrate-resistant growth of PC through both AR-dependent and AR-independent mechanisms.

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.

Jak2-Stat5a/b Signaling Induces Epithelial-to-Mesenchymal Transition and Stem-Like Cell Properties in Prostate Cancer

Active Stat5a/b predicts early recurrence and disease-specific death in prostate cancer (PC), which both typically are caused by development of metastatic disease. Herein, we demonstrate that Stat5a/b induces epithelial-to-mesenchymal transition (EMT) of PC cells, as shown by Stat5a/b regulation of EMT marker expression (Twist1, E-cadherin, N-cadherin, vimentin, and fibronectin) in PC cell lines, xenograft tumors in vivo, and patient-derived PCs ex vivo using organ explant cultures. Jak2-Stat5a/b signaling induced functional end points of EMT as well, indicated by disruption of epithelial cell monolayers and increased migration and adhesion of PC cells to fibronectin. Knockdown of Twist1 suppressed Jak2-Stat5a/b-induced EMT properties of PC cells, which were rescued by re-introduction of Twist1, indicating that Twist1 mediates Stat5a/b-induced EMT in PC cells. While promoting EMT, Jak2-Stat5a/b signaling induced stem-like properties in PC cells, such as sphere formation and expression of cancer stem cell markers, including BMI1. Mechanistically, both Twist1 and BMI1 were critical for Stat5a/b induction of stem-like features, because genetic knockdown of Twist1 suppressed Stat5a/b-induced BMI1 expression and sphere formation in stem cell culture conditions, which were rescued by re-introduction of BMI1. By using human prolactin knock-in mice, we demonstrate that prolactin-Stat5a/b signaling promoted metastases formation of PC cells in vivo. In conclusion, our data support the concept that Jak2-Stat5a/b signaling promotes metastatic progression of PC by inducing EMT and stem cell properties in PC cells.

Rapatar, a nanoformulation of rapamycin, decreases chemically-induced benign prostate hyperplasia in rats

Benign prostatic hyperplasia (BPH) is the most common age-related disease in men. Here we tested the efficacy of Rapatar, a micellar nanoformulation of rapamycin, in two rat models of BPH: testosterone-induced and sulpiride-induced hyperplasia in ventral lobes and lateral/dorsal lobes, respectively. We found that Rapatar prevented hypertrophic and hyperplastic abnormalities and degenerative alterations in both BPH models. Rapatar normalized weight of the lateral lobes in sulpiride-induced BPH, the most relevant animal model of human BPH. Unlike Finasteride, a standard therapy of BPH, Rapatar reduced inflammation caused by sulpiride. No obvious side effects of Rapatar were detected. Our data provide a rationale for clinical trials of Rapatar in patients suffering from BPH.

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 role of prolactin in andrology: what is new?

Prolactin (PRL) has been long deemed as a hormone involved only in female reproduction. However, PRL is a surprising hormone and, since its identification in the 1970s, its attributed functions have greatly increased. However, its specific role in male health is still widely unknown. Recently, low PRL has been associated with reduced ejaculate and seminal vesicle volume in infertile subjects. In addition, in men consulting for sexual dysfunction, hypoprolactinemia has been associated with erectile dysfunction and premature ejaculation, findings further confirmed in the general European population and infertile men. Several metabolic derangements, recapitulating metabolic syndrome, have also been associated with low PRL both in men with sexual dysfunction and from the general European population. In men with sexual dysfunction, followed-up for more than 4 years, low PRL was identified as an independent predictor of the incidence of major adverse cardiovascular events. Finally, an association with anxiety or depressive symptoms has been found in men with sexual dysfunction and from the general European population. While a direct role for impaired PRL function in the pathogenesis of these reproductive, sexual, metabolic and psychological disorders is conceivable, the possibility that low PRL is a mirror of an increased dopaminergic or a decreased serotonergic tone cannot be ruled-out. Hyperactivity of the dopaminergic system can explain only a few of the aforementioned findings, whereas a hypo-serotonergic tone fits well with the clinical features associated with low PRL, and there is significant evidence supporting the hypothesis that PRL could be a mirror of serotonin in the brain.

Structure-Based Screen Identifies a Potent Small Molecule Inhibitor of Stat5a/b with Therapeutic Potential for Prostate Cancer and Chronic Myeloid Leukemia

Bypassing tyrosine kinases responsible for Stat5a/b phosphorylation would be advantageous for therapy development for Stat5a/b-regulated cancers. Here, we sought to identify small molecule inhibitors of Stat5a/b for lead optimization and therapy development for prostate cancer and Bcr-Abl-driven leukemias. In silico screening of chemical structure databases combined with medicinal chemistry was used for identification of a panel of small molecule inhibitors to block SH2 domain-mediated docking of Stat5a/b to the receptor-kinase complex and subsequent phosphorylation and dimerization. We tested the efficacy of the lead compound IST5-002 in experimental models and patient samples of two known Stat5a/b-driven cancers, prostate cancer and chronic myeloid leukemia (CML). The lead compound inhibitor of Stat5-002 (IST5-002) prevented both Jak2 and Bcr-Abl-mediated phosphorylation and dimerization of Stat5a/b, and selectively inhibited transcriptional activity of Stat5a (IC50 = 1.5μmol/L) and Stat5b (IC50 = 3.5 μmol/L). IST5-002 suppressed nuclear translocation of Stat5a/b, binding to DNA and Stat5a/b target gene expression. IST5-002 induced extensive apoptosis of prostate cancer cells, impaired growth of prostate cancer xenograft tumors, and induced cell death in patient-derived prostate cancers when tested ex vivo in explant organ cultures. Importantly, IST5-002 induced robust apoptotic death not only of imatinib-sensitive but also of imatinib-resistant CML cell lines and primary CML cells from patients. IST5-002 provides a lead structure for further chemical modifications for clinical development for Stat5a/b-driven solid tumors and hematologic malignancies.

New insights in prolactin: pathological implications

Prolactin is a hormone that is mainly secreted by lactotroph cells of the anterior pituitary gland, and is involved in many biological processes including lactation and reproduction. Animal models have provided insights into the biology of prolactin proteins and offer compelling evidence that the different prolactin isoforms each have independent biological functions. The major isoform, 23 kDa prolactin, acts via its membrane receptor, the prolactin receptor (PRL-R), which is a member of the haematopoietic cytokine superfamily and for which the mechanism of activation has been deciphered. The 16 kDa prolactin isoform is a cleavage product derived from native prolactin, which has received particular attention as a result of its newly described inhibitory effects on angiogenesis and tumorigenesis. The discovery of multiple extrapituitary sites of prolactin secretion also increases the range of known functions of this hormone. This Review summarizes current knowledge of the biology of prolactin and its receptor, as well as its physiological and pathological roles. We focus on the role of prolactin in human pathophysiology, particularly the discovery of the mechanism underlying infertility associated with hyperprolactinaemia and the identification of the first mutation in human PRLR.

Minireview: prolactin regulation of adult stem cells

Adult stem/progenitor cells are found in many tissues, where their primary role is to maintain homeostasis. Recent studies have evaluated the regulation of adult stem/progenitor cells by prolactin in various target tissues or cell types, including the mammary gland, the prostate, the brain, the bone marrow, the hair follicle, and colon cancer cells. Depending on the tissue, prolactin can either maintain stem cell quiescence or, in contrast, promote stem/progenitor cell expansion and push their progeny towards differentiation. In many instances, whether these effects are direct or involve paracrine regulators remains debated. This minireview aims to overview the current knowledge in the field.

An SH2 domain model of STAT5 in complex with phospho-peptides define "STAT5 Binding Signatures"

The signal transducer and activator of transcription 5 (STAT5) is a member of the STAT family of proteins, implicated in cell growth and differentiation. STAT activation is regulated by phosphorylation of protein monomers at conserved tyrosine residues, followed by binding to phospho-peptide pockets and subsequent dimerization. STAT5 is implicated in the development of severe pathological conditions, including many cancer forms. However, nowadays a few STAT5 inhibitors are known, and only one crystal structure of the inactive STAT5 dimer is publicly available. With a view to enabling structure-based drug design, we have: (1) analyzed phospho-peptide binding pockets on SH2 domains of STAT5, STAT1 and STAT3; (2) generated a model of STAT5 bound to phospho-peptides; (3) assessed our model by docking against a class of known STAT5 inhibitors (Müller et al. in ChemBioChem 9:723-727, 2008); (4) used molecular dynamics simulations to optimize the molecular determinants responsible for binding and (5) proposed unique "Binding Signatures" of STAT5. Our results put in place the foundations to address STAT5 as a target for rational drug design, from sequence, structural and functional perspectives.

Prolactin induces apoptosis of lactotropes in female rodents

Anterior pituitary cell turnover occurring during female sexual cycle is a poorly understood process that involves complex regulation of cell proliferation and apoptosis by multiple hormones. In rats, the prolactin (PRL) surge that occurs at proestrus coincides with the highest apoptotic rate. Since anterior pituitary cells express the prolactin receptor (PRLR), we aimed to address the actual role of PRL in the regulation of pituitary cell turnover in cycling females. We showed that acute hyperprolactinemia induced in ovariectomized rats using PRL injection or dopamine antagonist treatment rapidly increased apoptosis and decreased proliferation specifically of PRL producing cells (lactotropes), suggesting a direct regulation of these cell responses by PRL. To demonstrate that apoptosis naturally occurring at proestrus was regulated by transient elevation of endogenous PRL levels, we used PRLR-deficient female mice (PRLRKO) in which PRL signaling is totally abolished. According to our hypothesis, no increase in lactotrope apoptotic rate was observed at proestrus, which likely contributes to pituitary tumorigenesis observed in these animals. To decipher the molecular mechanisms underlying PRL effects, we explored the isoform-specific pattern of PRLR expression in cycling wild type females. This analysis revealed dramatic changes of long versus short PRLR ratio during the estrous cycle, which is particularly relevant since these isoforms exhibit distinct signaling properties. This pattern was markedly altered in a model of chronic PRLR signaling blockade involving transgenic mice expressing a pure PRLR antagonist (TGΔ1-9-G129R-hPRL), providing evidence that PRL regulates the expression of its own receptor in an isoform-specific manner. Taken together, these results demonstrate that i) the PRL surge occurring during proestrus is a major proapoptotic signal for lactotropes, and ii) partial or total deficiencies in PRLR signaling in the anterior pituitary may result in pituitary hyperplasia and eventual prolactinoma development, as observed in TGΔ1-9-G129R-hPRL and PRLRKO mice, respectively.

Carboxypeptidase-D is elevated in prostate cancer and its anti-apoptotic activity is abolished by combined androgen and prolactin receptor targeting

BACKGROUND

Carboxypeptidase-D (CPD) cleaves C-terminal arginine for nitric oxide (NO) production. CPD and NO levels are upregulated by testosterone (T) and prolactin (PRL) to promote survival of prostate cancer (pCa) cells. This study evaluated CPD immunostaining and T/PRL regulation of CPD and NO levels in benign and malignant prostate tissues/cells to determine the role of CPD in pCa.

METHODS

Immunohistochemistry (IHC) and tissue microarrays (TMA) were used to determine CPD immunostaining in prostate specimens. QPCR and immunoblotting were used to quantify CPD mRNA/protein expression in prostate cells. NO production was measured using 4,5-diaminofluorescein diacetate assay.

RESULTS

CPD staining increased from 8.9 ± 3.8% (Mean ± SEM, n = 15) of benign epithelial cell area to 30.9 ± 2.9% (n = 30) of tumor cell area in one set of TMAs (P = 0.0008) and from 5.9 ± 0.9% (n = 45) of benign epithelial cell area to 18.8 ± 1.9% (n = 55) of tumor area in another (P < 0.0001). IHC of prostate tissues (≥50 mm(2)) confirmed increased CPD staining, from 13.1 ± 2.9% in benign (n = 16) to 29.5 ± 4.4% in pCa (n = 31, P = 0.0095). T and/or PRL increased CPD expression in several pCa but not benign cell lines. T and PRL acted synergistically to increase NO production, which was abolished only when receptor antagonists flutamide and Δ1-9-G129R-hPRL were used together.

CONCLUSIONS

CPD immunostaining and T/PRL-stimulated CPD expression were higher in pCa than benign tissues/cells. Elevated CPD increased NO production, which was abolished when both AR and PRLR were inhibited. Our study implicates a critical role for the T/PRL-stimulated CPD-Arg-NO pathway in pCa progression, and suggests that AR+PRLR inhibition is a more effective treatment for pCa.

Minireview: Extrapituitary prolactin: an update on the distribution, regulation, and functions

Prolactin (PRL) is an important hormone with many diverse functions. Although it is predominantly produced by lactrotrophs of the pituitary there are a number of other organs, cells, and tissues in which PRL is expressed and secreted. The impact of this extrapituitary PRL (ePRL) on localized metabolism and cellular functions is gaining widespread attention. In 1996, a comprehensive review on ePRL was published. However, since this time, there have been a number of advancements in ePRL research. This includes a greater understanding of the components of the control elements located within the superdistal promoter of the ePRL gene. Furthermore, several new sites of ePRL have been discovered, each under unique control by a range of transcription factors and elements. The functional role of ePRL at each of the expression sites also varies widely leading to gender and site bias. This review aims to provide an update to the research conducted on ePRL since the 1996 review. The focus is on new data concerning the sites of ePRL expression, its regulation, and its function within the organs in which it is expressed.

Prolactin actions

Molecular genetics and other contemporary approaches have contributed to a better understanding of prolactin (PRL) actions at the cellular and organismal levels. In this review, several advances in knowledge of PRL actions are highlighted. Special emphasis is paid to areas of progress with consequences for understanding of human PRL actions. The impacts of these advances on future research priorities are analyzed.

Reproductive actions of prolactin mediated through short and long receptor isoforms

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

Completely humanizing prolactin rescues infertility in prolactin knockout mice and leads to human prolactin expression in extrapituitary mouse tissues

A variety of fundamental differences have evolved in the physiology of the human and rodent prolactin (PRL) systems. The PRL gene in humans and other primates contains an alternative promoter, 5.8 kbp upstream of the pituitary transcription start site, which drives expression of PRL in "extrapituitary" tissues, where PRL is believed to exert local, or paracrine, actions. Several of these extrapituitary PRL tissues serve a reproductive function (eg, mammary gland, decidua, prostate, etc), consistent with the hypothesis that local PRL production may be involved in, and required for, normal reproductive physiology in primates. Rodent research models have generated significant findings regarding the role of PRL in reproduction. Specifically, disruption (knockout) of either the PRL gene or its receptor causes profound female reproductive defects at several levels (ovaries, preimplantation endometrium, mammary glands). However, the rodent PRL gene differs significantly from the human, most notably lacking the alternative promoter. Understanding of the physiological regulation and function of extrapituitary PRL has been limited by the absence of a readily accessible experimental model, because the rodent PRL gene does not contain the alternative promoter. To overcome these limitations, we have generated mice that have been "humanized" with regard to the structural gene and tissue expression of PRL. Here, we present the characterization of these animals, demonstrating that the human PRL transgene is responsive to known physiological regulators both in vitro and in vivo. More importantly, the expression of the human PRL transgene is able to rescue the reproductive defects observed in mouse PRL knockout (mPRL(-)) females, validating their usefulness in studying the function or regulation of this hormone in a manner that is relevant to human physiology.

Pharmacologic inhibition of Jak2-Stat5 signaling By Jak2 inhibitor AZD1480 potently suppresses growth of both primary and castrate-resistant prostate cancer

PURPOSE

Progression of prostate cancer to the lethal castrate-resistant stage coincides with loss of responsiveness to androgen deprivation and requires development of novel therapies. We previously provided proof-of-concept that Stat5a/b is a therapeutic target protein for prostate cancer. Here, we show that pharmacologic targeting of Jak2-dependent Stat5a/b signaling by the Jak2 inhibitor AZD1480 blocks castrate-resistant growth of prostate cancer.

EXPERIMENTAL DESIGN

Efficacy of AZD1480 in disrupting Jak2-Stat5a/b signaling and decreasing prostate cancer cell viability was evaluated in prostate cancer cells. A unique prostate cancer xenograft mouse model (CWR22Pc), which mimics prostate cancer clinical progression in patients, was used to assess in vivo responsiveness of primary and castrate-resistant prostate cancer (CRPC) to AZD1480. Patient-derived clinical prostate cancers, grown ex vivo in organ explant cultures, were tested for responsiveness to AZD1480.

RESULTS

AZD1480 robustly inhibited Stat5a/b phosphorylation, dimerization, nuclear translocation, DNA binding, and transcriptional activity in prostate cancer cells. AZD1480 reduced prostate cancer cell viability sustained by Jak2-Stat5a/b signaling through induction of apoptosis, which was rescued by constitutively active Stat5a/b. In mice, pharmacologic targeting of Stat5a/b by AZD1480 potently blocked growth of primary androgen-dependent as well as recurrent castrate-resistant CWR22Pc xenograft tumors, and prolonged survival of tumor-bearing mice versus vehicle or docetaxel-treated mice. Finally, nine of 12 clinical prostate cancers responded to AZD1480 by extensive apoptotic epithelial cell loss, concurrent with reduced levels of nuclear Stat5a/b.

CONCLUSIONS

We report the first evidence for efficacy of pharmacologic targeting of Stat5a/b as a strategy to inhibit castrate-resistant growth of prostate cancer, supporting further clinical development of Stat5a/b inhibitors as therapy for advanced prostate cancer.

STAT5A/B gene locus undergoes amplification during human prostate cancer progression

The molecular mechanisms underlying progression of prostate cancer (PCa) to castrate-resistant (CR) and metastatic disease are poorly understood. Our previous mechanistic work shows that inhibition of transcription factor Stat5 by multiple alternative methods induces extensive rapid apoptotic death of Stat5-positive PCa cells in vitro and inhibits PCa xenograft tumor growth in nude mice. Furthermore, STAT5A/B induces invasive behavior of PCa cells in vitro and in vivo, suggesting involvement of STAT5A/B in PCa progression. Nuclear STAT5A/B protein levels are increased in high-grade PCas, CR PCas, and distant metastases, and high nuclear STAT5A/B expression predicts early disease recurrence and PCa-specific death in clinical PCas. Based on these findings, STAT5A/B represents a therapeutic target protein for advanced PCa. The mechanisms underlying increased Stat5 protein levels in PCa are unclear. Herein, we demonstrate amplification at the STAT5A/B gene locus in a significant fraction of clinical PCa specimens. STAT5A/B gene amplification was more frequently found in PCas of high histologic grades and in CR distant metastases. Quantitative in situ analysis revealed that STAT5A/B gene amplification was associated with increased STAT5A/B protein expression in PCa. Functional studies showed that increased STAT5A/B copy numbers conferred growth advantage in PCa cells in vitro and as xenograft tumors in vivo. The work presented herein provides the first evidence of somatic STAT5A/B gene amplification in clinical PCas.

Use of prolactin receptor antagonist to better understand prolactin regulation of pituitary homeostasis

The anterior pituitary is permanently regulated by processes of apoptosis and proliferation in order to maintain tissue homeostasis. Several factors have been implicated in this regulation and lately, prolactin (PRL) has been included into that list. However, since PRL is secreted by anterior pituitary lactotropes, the actual outcome of its autocrine/paracrine actions on pituitary cells has remained difficult to assess. The availability of the pure PRL receptor antagonist Del1-9-G129R-hPRL has been helpful to circumvent this problem. While PRL has been traditionally associated with increased cell proliferation, recent studies revealed that this hormone actually induces apoptosis and decreases proliferation of anterior pituitary cells, by mechanisms involving the PRL receptor. The aim of this short review is to overview our current understanding of the regulation of pituitary homeostasis by PRL. Moreover, studies involving Del1-9-G129R-hPRL have helped anticipate to what extent future treatments involving PRL receptor inhibitors may interfere with processes regulated by PRL at the central level.

A mimic of phosphorylated prolactin induces apoptosis by activating AP-1 and upregulating p21/waf1 in human prostate cancer PC3 cells

A mimic of phosphorylated prolactin (S179D PRL) has been demonstrated to inhibit prostate cancer cell growth in vitro and in vivo; however, the mechanisms involved in this process remain unknown. In this study, we identified that a four-day treatment of S179D PRL (1 μg/ml) in human prostate PC3 cancer cells activated JNK, c-fos and c-jun, and led to apoptosis. We also demonstrated that p21/waf1 was upregulated in cells transfected with the human PRL receptor (S1b) following a four-day incubation with S179D PRL (1 μg/ml). Once the cells were cotransfected with S1b and either c-fos, c-jun or the c-fos/c-jun constructs for 24 h, S17D PRL activated JNK, c-fos and c-jun, and induced apoptosis in the c-fos/c-jun transfected cells. Additionally, S179D PRL upregulated p21 luciferase activity in the cells transfected with the S1b, activating protein-1 (AP-1) (7x) Luc or p21 Luc constructs. SP600125 (25 μM), a JNK blocker, inhibited the upregulation of AP-1 Luc and p21 Luc in the c-fos/c-jun transfected cells. These results demonstrate that S179D PRL activates JNK and AP-1, which leads to p21 upregulation and apoptosis in human prostate PC3 cancer cells.

The prolactin receptor mediates HOXA1-stimulated oncogenicity in mammary carcinoma cells

The HOX genes are a highly conserved subgroup of homeodomain-containing transcription factors that are crucial to normal development. Forced expression of HOXA1 results in oncogenic transformation of immortalized human mammary cells with aggressive tumour formation in vivo. Microarray analysis identified that the prolactin receptor (PRLR) was significantly upregulated by forced expression of HOXA1 in mammary carcinoma cells. To determine prolactin (PRL) involvement in HOXA1‑induced oncogenicity in mammary carcinoma cells (MCF-7), we examined the effect of human prolactin (hPRL)-initiated PRLR signal transduction on changes in cellular behaviour mediated by HOXA1. Forced expression of HOXA1 in MCF-7 cells increased PRLR mRNA and protein expression. Forced expression of HOXA1 also enhanced hPRL-stimulated phosphorylation of both STAT5A/B and p44/42 MAPK, and increased subsequent transcriptional activity of STAT5A and STAT5B, and Elk-1 and Sap1a, respectively. Moreover, forced expression of HOXA1 in MCF-7 cells enhanced the hPRL‑stimulated increase in total cell number as a consequence of enhanced cell proliferation and cell survival, and also enhanced hPRL-stimulated anchorage-independent growth in soft agar. Increased anchorage-independent growth was attenuated by the PRLR antagonist ∆1-9-G129R‑hPRL. In conclusion, we have demonstrated that HOXA1 increases expression of the cell surface receptor PRLR and enhances PRLR-mediated signal transduction. Thus, the PRLR is one mediator of HOXA1‑stimulated oncogenicity in mammary carcinoma cells.

Nuclear Stat5a/b predicts early recurrence and prostate cancer-specific death in patients treated by radical prostatectomy

There is an urgent need for reliable markers to identify patients whose prostate cancer (PCa) will recur after initial therapy and progress to lethal disease. Gleason score (GS) is considered the most accurate predictive marker for disease-specific mortality after primary treatment of localized PCa. Most PCas cluster into groups of GS 6 and 7 with considerable variation in the disease recurrence and disease-specific death. In preclinical PCa models, Stat5a/b promotes PCa growth and progression. Stat5a/b is critical for PCa cell viability in vitro and for tumor growth in vivo and promotes metastatic dissemination of cancer in nude mice. Here, we analyzed the predictive value of high nuclear Stat5a/b protein levels in 2 cohorts of PCas: Material I (n = 562) PCas treated by radical prostatectomy (RP), and Material II (n = 106) PCas treated by deferred palliative therapy. In intermediate GS PCas treated by radical prostatectomy, high levels of nuclear Stat5a/b predicted both early recurrence (univariable analysis; P < .0001, multivariable analysis; HR = 1.82, P = .017) and early PCa-specific death (univariable analysis; P = .028). In addition, high nuclear Stat5a/b predicted early disease recurrence in both univariable (P < .0001) and multivariable (HR = 1.61; P = .012) analysis in the entire cohort of patients treated by RP regardless of the GS. Patients treated by deferred palliative therapy, elevated nuclear Stat5a/b expression was associated with early PCa-specific death by univariable Cox regression analysis (HR = 1.59; 95% CI = [1.04, 2.44]; P = .034). If confirmed in future prospective studies, nuclear Stat5a/b may become a useful independent predictive marker of recurrence of lethal PCa after RP for intermediate GS PCas.

Relationship between serum sex hormones levels and degree of benign prostate hyperplasia in Chinese aging men

Benign prostatic hyperplasia (BPH) is one of the most common medical conditions in middle aged and older men. This study investigated the relationship between serum levels of sex hormones and measures of BPH in the aging male population of China. Prostate symptoms were assessed as part of a free health screening program for men ≥ 40 years of age. The examination included digital rectal examination, determination of serum prostate-specific antigen levels, International Prostate Symptom Score (IPSS) and transrectal ultrasonography. Serum levels of total testosterone (TT), sex hormone binding globulin (SHBG), free testosterone (FT), luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL) and estradiol (E(2)) were evaluated. The men also completed a health and demographics questionnaire and received a detailed physical examination. The final study population consisted of 949 men with a mean age of 58.9 years. Pearson correlation analysis indicated that there were significant correlations between age and levels of all sex hormones except TT, and between age and prostate volume (PV; r=0.243; P<0.01) or IPSS (r=0.263; P<0.01). Additional significant correlations were found between IPSS and serum levels of LH (r=0.112; P<0.01) and FSH (r=0.074; P<0.05), but there were no significant correlations between sex hormone levels and PV. Multivariate linear regression analysis showed significant correlations between age and body mass index (BMI) with PV (P<0.0001). In addition, there was a significant correlation between age and PV with IPSS (P<0.0001). Serum sex hormone levels did not correlate with PV or IPSS. The effects of endocrine changes on measures of BPH in aging men require further investigation in longitudinal and multicenter studies that include patients with all severities of BPH.

The WSXWS motif in cytokine receptors is a molecular switch involved in receptor activation: insight from structures of the prolactin receptor

The prolactin receptor (PRLR) is activated by binding of prolactin in a 2:1 complex, but the activation mechanism is poorly understood. PRLR has a conserved WSXWS motif generic to cytokine class I receptors. We have determined the nuclear magnetic resonance solution structure of the membrane proximal domain of the human PRLR and find that the tryptophans of the motif adopt a T-stack conformation in the unbound state. By contrast, in the hormone bound state, a Trp/Arg-ladder is formed. The conformational change is hormone-dependent and influences the receptor-receptor dimerization site 3. In the constitutively active, breast cancer-related receptor mutant PRLR(I146L), we observed a stabilization of the dimeric state and a change in the dynamics of the motif. Here we demonstrate a structural link between the WSXWS motif, hormone binding, and receptor dimerization and propose it as a general mechanism for class 1 receptor activation.

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.