Regulation of prolactin receptor levels and activity in breast cancer

Dopamine D2 receptor antagonist counteracts hyperglycemia and insulin resistance in diet-induced obese male mice

Obesity leads to insulin resistance (IR) and type 2 diabetes. In humans, low levels of the hormone prolactin (PRL) correlate with IR, adipose tissue (AT) dysfunction, and increased prevalence of T2D. In obese rats, PRL treatment promotes insulin sensitivity and reduces visceral AT adipocyte hypertrophy. Here, we tested whether elevating PRL levels with the prokinetic and antipsychotic drug sulpiride, an antagonist of dopamine D2 receptors, improves metabolism in high fat diet (HFD)-induced obese male mice. Sulpiride treatment (30 days) reduced hyperglycemia, IR, and the serum and pancreatic levels of triglycerides in obese mice, reduced visceral and subcutaneous AT adipocyte hypertrophy, normalized markers of visceral AT function (PRL receptor, Glut4, insulin receptor and Hif-1α), and increased glycogen stores in skeletal muscle. However, the effects of sulpiride reducing hyperglycemia were also observed in obese prolactin receptor null mice. We conclude that sulpiride reduces obesity-induced hyperglycemia by mechanisms that are independent of prolactin/prolactin receptor activity. These findings support the therapeutic potential of sulpiride against metabolic dysfunction in obesity.

Stem Cell-Associated Signatures Help to Predict Diagnosis and Prognosis in Ovarian Serous Cystadenocarcinoma

Ovarian serous cystadenocarcinoma (OV) is a fatal gynecologic cancer with a five-year survival rate of only 46%. Resistance to platinum-based chemotherapy is a prevalent factor in OV patients, leading to increased mortality. The platinum resistance in OV is driven by transcriptome heterogeneity and tumor heterogeneity. Studies have indicated that ovarian cancer stem cells (OCSCs), which are chemoresistant and help in disease recurrence, are enriched by platinum-based chemotherapy. Stem cells have a significant influence on the OV progression and prognosis of OV patients and are key pathology mediators of OV. However, the molecular mechanisms and targets of OV have not yet been fully understood. In this study, systematic research based on the TCGA-OV dataset was conducted for the identification and construction of key stem cell-related diagnostic and prognostic models for the development of multigene markers of OV. A six-gene diagnostic and prognostic model (C19orf33, CBX2, CSMD1, INSRR, PRLR, and SLC38A4) was developed based on the differentially expressed stem cell-related gene model, which can act as a potent diagnostic biomarker and can characterize the clinicopathological properties of OV. The key genes related to stem cells were identified by screening the genes differentially expressed in OV and control samples. The mRNA-miRNA-TF molecular network for the six-gene model was constructed, and the potential biological significance of this molecular model and its impact on the infiltration of immune cells in the OV tumor microenvironment were elucidated. The differences in immune infiltration and stem cell-related biological processes were determined using gene set variation analysis (GSVA) and single-sample gene set enrichment analysis (ssGSEA) for the selection of molecular treatment options and providing a reference for elucidating the posttranscriptional regulatory mechanisms in OV.

Antipsychotic exposure is an independent risk factor for breast cancer: A systematic review of epidemiological evidence

Background

The effect of antipsychotics on breast cancer remains controversial.

Materials and methods

Embase, Scopus, PubMed, Web of Science, Cochrane Library, and Hebei Medical University Library were used for the literature search. Observational studies with original data for the effects of antipsychotics on breast cancer were used. Studies of bed quality, those with inadequate sample size, incomplete follow-up works, or studies that did not meet the criteria were excluded. Meta-analysis was performed using R version 4.1.2. The odds ratio (OR) and its 95% confidence interval (CI) were used to evaluate the proportion of breast cancer in different groups. To detect possible sources of heterogeneity, subgroup and meta-regression analyses were employed.

Results

Pooled data from 11 relevant studies with 1,499,001 participants suggested that individuals exposed to antipsychotics were more likely to suffer from breast cancer than those who were not exposed (OR, 1.23; 95% CI, 1.04-1.47). No significant difference in breast cancer prevalence between the atypical and typical antipsychotic groups was found (OR, 1.23; 95% CI, 0.93-1.63). Prolactin (PRL)-increasing and PRL-sparing antipsychotics posed a similar risk of breast cancer (OR, 1.13; 95% CI, approximately 0.97-1.31). Furthermore, the use of antipsychotics is attributed to increased mortality in patients with breast cancer (OR, 1.54; 95% CI, 1.29-1.82). Those exposed to antipsychotics at the maximum dose were more likely to suffer from breast cancer than those exposed to the minimum dose.

Conclusions

Antipsychotic exposure is an independent risk factor for breast cancer. No significant difference in the risk of breast cancer between typical and atypical antipsychotics was noted. Those exposed to antipsychotics at higher doses are more likely to suffer from breast cancer. Moreover, the use of antipsychotics is attributed to increased mortality in patients with breast cancer. PRL-increasing and PRL-sparing antipsychotics pose a similar risk of breast cancer.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022307624.

The effect of prolactin on immune cell subsets involved in SLE pathogenesis

The higher frequency of autoimmune diseases in the female population compared to males suggests that certain hormones, such as prolactin (PRL), play a role in determining the prevalence of autoimmunity in women, particularly during childbearing age. PRL can act not only as a hormone but also as a cytokine, being able to modulate immune responses. Hyperprolactinemia has been implicated in the pathogenesis of various autoimmune diseases where it may affect disease activity. One of the conditions where PRL has such a role is systemic lupus erythematosus (SLE). PRL regulates the proliferation and survival of both lymphoid and myeloid cells. It also affects the selection of T-cell repertoires by influencing the thymic microenvironment. In autoimmune conditions, PRL interferes with the activity of regulatory T cells. It also influences B cell tolerance by lowering the activation threshold of anergic B cells. The production of CD40L and cytokines, such as interleukin IL-6, are also promoted by PRL. This, in turn, leads to the production of autoantibodies, one of the hallmarks of SLE. PRL increases the cytotoxic activity of T lymphocytes and the secretion of proinflammatory cytokines. The production of proinflammatory cytokines, particularly those belonging to the type 1 interferon (IFN) family, is part of the SLE characteristic genetic signature. PRL also participates in the maturation and differentiation of dendritic cells, promoting the presentation of autoantigens and high IFNα secretion. It also affects neutrophil function and the production of neutrophil traps. Macrophages and dendritic cells can also be affected by PRL, linking this molecule to the abnormal behavior of both innate and adaptive immune responses.This review aimed to highlight the importance of PRL and its actions on the cells of innate and adaptive immune responses. Additionally, by elucidating the role of PRL in SLE etiopathogenesis, this work will contribute to a better understanding of the factors involved in SLE development and regulation.

Prolactin and its significance in the placenta

Prolactin, a pituitary hormone that was discovered about 80 years ago and is primarily known for its functions in mammary gland development and lactation, is now known to participate in numerous functions across different phylogenetic groups. Fundamentally known for its secretion from lactotroph cells in adenohypophysis region of pituitary gland, newer studies have demonstrated a number of extrapituitary sites which secrete prolactin, where it acts in an autocrine, paracrine, and endocrine manner to regulate essential physiological and biochemical processes. These sites include lymphocytes, epithelial cells of lactating mammary glands, breast cancer cells of epithelial origin, and the placenta. The placenta is one of the most important organs secreting prolactin; however, its role in placental biology has not to date been reviewed comprehensively. This review elaborates upon the various facets of prolactin hormone, including prolactin production and its post-translational modifications and signaling. Major emphasis is placed on placental prolactin and its potential roles, ranging from the role of prolactin in angiogenesis, preeclampsia, maternal diabetes, and anti-apoptosis, among others.

Highlights regarding prolactin in the dentate gyrus and hippocampus

Prolactin (PRL) is a pituitary hormone that has been typically related to lactogenesis in mammals. However, it has been described over 300 roles in the organism of vertebrae and its relationship with the central nervous system (CNS) is yet to be clarified. Mainly secreted by the pituitary gland, the source of prolactin in the CNS remains unclear, where some experiments suggest active transport via an unknown carrier or, on the contrary, PRL being synthesized on the brain. So far, it seems to be involved with neurogenesis, neuroprotection, maternal behavior and cognitive processes in the hippocampus and dentate gyrus, among other regions.

Characterization of prolactin (PRL) and PRL receptor (PRLR) in Chinese soft-shelled turtle: Molecular identification, ligand-receptor interaction and tissue distribution

Prolactin (PRL) plays crucial roles in many physiological and pathological processes through activating its specific membrane-anchored receptor (PRLR). Although this ligand-receptor pair has been extensively studied in mammals, birds and fishes, researches examining their significance is rather scarce in reptiles. Additionally, the interaction mechanism of PRL-PRLR has abortively understood across vertebrates, since two tandem repeated ligand-binding domains of PRLR have been identified in birds and few reptiles. To lay the foundation to clarify their roles and ligand-receptor interaction in reptiles, using Chinese soft-shelled turtle as model, the cDNAs containing open reading frame of PRL and PRLR were cloned. The cloned PRL consisted of 710 bp and encoded a precursor of 228 amino acid (-aa), while PRLR was 2658 bp in length and predicted to generate a 828-aa precursor. Furthermore, the recombinant PRL protein with high-purity was prepared from Escherichia coli (E. coli) strain Rosetta gamiB (DE3) by using cobalt resin. Using the 5 × STAT5-Luciferase reporter system, we found PRLR and PRLR-M2 (the PRLR-mutant lacking membrane-distal ligand-binding domain) could be dose-dependently activated by recombinant PRL, thereby triggering the intracellular JAK2-STAT5 signaling cascade, suggesting PRL-PRLR is functional in Chinese soft-shelled turtle, and the membrane-proximal ligand-binding domain of PRLR is the critical domain involving in PRL-binding. Quantitative real-time PCR revealed that PRL was predominantly and abundantly expressed in pituitary, while PRLR exhibited ubiquitous expression in all of the tissues examined. Collectively, our data indicate the PRL-PRLR pair may function in reptiles including Chinese soft-shelled turtle, in a way similar to that in birds.

Prolactin and prolactin receptor expression in the HPG axis and crop during parental care in both sexes of a biparental bird (Columba livia)

During breeding, multiple circulating hormones, including prolactin, facilitate reproductive transitions in species that exhibit parental care. Prolactin underlies parental behaviors and related physiological changes across many vertebrates, including birds and mammals. While circulating prolactin levels often fluctuate across breeding, less is known about how relevant target tissues vary in their prolactin responsiveness via prolactin receptor (PRLR) expression. Recent studies have also investigated prolactin (PRL) gene expression outside of the pituitary (i.e., extra-pituitary PRL), but how PRL gene expression varies during parental care in non-pituitary tissue (e.g., hypothalamus, gonads) remains largely unknown. Further, it is unclear if and how tissue-specific PRL and PRLR vary between the sexes during biparental care. To address this, we measured PRL and PRLR gene expression in tissues relevant to parental care, the endocrine reproductive hypothalamic-pituitary- gonadal (HPG) axis and the crop (a tissue with a similar function as the mammalian mammary gland), across various reproductive stages in both sexes of a biparental bird, the rock dove (Columba livia). We also assessed how these genes responded to changes in offspring presence by adding chicks mid-incubation, simulating an early hatch when prolactin levels were still moderately low. We found that pituitary PRL expression showed similar increases as plasma prolactin levels, and detected extra-pituitary PRL in the hypothalamus, gonads and crop. Hypothalamic and gonadal PRLR expression also changed as birds began incubation. Crop PRLR expression correlated with plasma prolactin, peaking when chicks hatched. In response to replacing eggs with a novel chick mid-incubation, hypothalamic and gonadal PRL and PRLR gene expression differed significantly compared to mid-incubation controls, even when plasma prolactin levels did not differ. We also found sex differences in PRL and PRLR that suggest gene expression may allow males to compensate for lower levels in prolactin by upregulating PRLR in all tissues. Overall, this study advances our understanding of how tissue-specific changes in responsiveness to parental hormones may differ across key reproductive transitions, in response to offspring cues, and between the sexes.

Prolactin and endocrine therapy resistance in breast cancer: The next potential hope for breast cancer treatment

Breast cancer, a hormone‐dependent tumour, generally includes four molecular subtypes (luminal A, luminal B, HER2 enriched and triple‐negative) based on oestrogen receptor, progesterone receptor and human epidermal growth factor receptor‐2. Multiple hormones in the body regulate the development of breast cancer. Endocrine therapy is one of the primary treatments for hormone‐receptor‐positive breast cancer, but endocrine resistance is the primary clinical cause of treatment failure. Prolactin (PRL) is a protein hormone secreted by the pituitary gland, mainly promoting mammary gland growth, stimulating and maintaining lactation. Previous studies suggest that high PRL levels can increase the risk of invasive breast cancer in women. The expression levels of PRL and PRLR in breast cancer cells and breast cancer tissues are elevated in most ER⁺ and ER⁻ tumours. PRL activates downstream signalling pathways and affects endocrine therapy resistance by combining with prolactin receptor (PRLR). In this review, we illustrated and summarized the correlations between endocrine therapy resistance in breast cancer and PRL, as well as the pathophysiological mechanisms and clinical practices. The study on PRL and its receptor would help explore reversing endocrine therapy‐resistance for breast cancer.

Prolactin neuroprotective action against excitotoxic insult in the hippocampus of male mice

Prolactin (PRL) is known to exert neuroprotective effects against excitotoxic damage in the hippocampus of female rats, both in vitro and in vivo. It is still unknown whether this effect can be seen in the male hippocampus and intracellular signaling mediating such action. To assess this, adult male CD-1 mice were subjected to excitotoxic damage with kainic acid (KA; i.c.v.), after a) no manipulation (control group), b) treatment with saline, and c) treatment with PRL (8 μg of PRL/100 μl of saline s.c.). Treatments consisted of one daily injection of the mentioned dosage for seven consecutive days until the day of the excitotoxic lesion. Neurodegeneration (Fluoro-Jade C), neuronal survival (NeuN) and astrogliosis (GFAP) markers were identified with immunohistochemistry in the CA1, CA3 and CA4 areas of the dorsal hippocampus, as well as PRL-related protein levels by Western blot in the whole hippocampus 48 h after excitotoxicity. Anatomical measurements revealed a preferential protective effect of PRL against excitotoxic damage in the CA3 hippocampal subfield, with lower levels of cell death and neurodegeneration, compared to controls. In CA4, the results were not conclusive, and no damage was observed in CA1 after KA administration. PRL treatment provoked an upregulation of active Akt, a well-known cell survival pathway, after KA administration. PRL also caused downregulation of active MAPK, independently of the excitotoxic damage. The present results indicate a neuroprotective role for PRL preferentially located in the CA3 area of the hippocampus of male mice, possibly mediated by Akt-related survival mechanisms.

Gene expression profiles for low-dose exposure to diethyl phthalate in rodents and humans: a translational study with implications for breast carcinogenesis

Phthalates are commonly included as ingredients in personal care products such as cosmetics, shampoos and perfumes. Diethyl phthalate (DEP) has been found to be anti-androgenic and linked with adverse reproductive effects on males, but effects on females are poorly understood. We designed an integrative and translational study to experimentally examine the effects of DEP exposure at a human-equivalent dose on the mammary transcriptome in rats and to subsequently examine the DEP gene signature in breast tissues (both pre-malignant and tumor) from a population study. In Sprague-Dawley rats treated orally with DEP from birth to adulthood, we identified a signature panel of 107 genes predominantly down-regulated by DEP exposure. Univariate analysis of this 107 DEP gene signature in pre-malignant breast tissues revealed that six genes (P4HA1, MPZL3, TMC4, PLEKHA6, CA8, AREG) were inversely associated with monoethyl phthalate (MEP; the urinary metabolite of DEP) concentration (p < 0.05) among postmenopausal women; all six genes loaded on to one of seven factors identified by factor analysis. Transcription factor enrichment analysis revealed that genes in this factor were enriched for androgen receptor binding sites. These six genes were also significantly down-regulated in pre-malignant adjacent tissues compared to the corresponding tumor tissues in pair-wise analyses (p < 0.05). Results from our translational study indicate that low level exposure to diethyl phthalate results in measurable genomic changes in breast tissue with implications in breast carcinogenesis.

Two indel variants of prolactin receptor (PRLR) gene are associated with growth traits in goat

Prolactin receptor (PRLR) gene plays a crucial role in the milk production, reproduction and the growth of mammals. To fully characterize the structure of the mutation and to further study the function of the goat PRLR gene, two insertion/deletion (indel) loci (12 bp; 16-bp; 5-bp) were detected in 1038 Shaanbei white cashmere (SBWC) goats. Associated analysis revealed that the 16-bp indel mutation was significantly associated the body length, body height, chest depth (CD), body length index (BLI), heart girth index and cannon circumference index (CCI) (p < 0.05). The polymorphism of 5-bp indel was significantly associated with CD, heart girth, CCI and BLI (p < 0.05). Overall, individuals with genotype DD showed better phenotypic traits than individuals with other genotypes at the two loci of PRLR gene in SBWC goat. These findings suggested that the two novel indels within the caprine PRLR gene could be considered as effective DNA molecular markers and could provide a valuable theoretical basis for the application of marker-assisted selection in the goat industry.

ATM Is Required for the Prolactin-Induced HSP90-Mediated Increase in Cellular Viability and Clonogenic Growth After DNA Damage

Prolactin (PRL) acts as a survival factor for breast cancer cells, but the PRL signaling pathway and the mechanism are unknown. Previously, we identified the master chaperone, heat shock protein 90 (HSP90) α, as a prolactin-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) target gene involved in survival, and here we investigated the role of HSP90 in the mechanism of PRL-induced viability in response to DNA damage. The ataxia-telangiectasia mutated kinase (ATM) protein plays a critical role in the cellular response to double-strand DNA damage. We observed that PRL increased viability of breast cancer cells treated with doxorubicin or etoposide. The increase in cellular resistance is specific to the PRL receptor, because the PRL receptor antagonist, Δ1-9-G129R-hPRL, prevented the increase in viability. Two different HSP90 inhibitors, 17-allylamino-17-demethoxygeldanamycin and BIIB021, reduced the PRL-mediated increase in cell viability of doxorubicin-treated cells and led to a decrease in JAK2, ATM, and phosphorylated ATM protein levels. Inhibitors of JAK2 (G6) and ATM (KU55933) abolished the PRL-mediated increase in cell viability of DNA-damaged cells, supporting the involvement of each, as well as the crosstalk of ATM with the PRL pathway in the context of DNA damage. Drug synergism was detected between the ATM inhibitor (KU55933) and doxorubicin and between the HSP90 inhibitor (BIIB021) and doxorubicin. Short interfering RNA directed against ATM prevented the PRL-mediated increase in cell survival in two-dimensional cell culture, three-dimensional collagen gel cultures, and clonogenic cell survival, after doxorubicin treatment. Our results indicate that ATM contributes to the PRL-JAK2-STAT5-HSP90 pathway in mediating cellular resistance to DNA-damaging agents.

Preclinical Activity of the Novel Anti-Prolactin Receptor (PRLR) Antibody-Drug Conjugate REGN2878-DM1 in PRLR-Positive Breast Cancers

The Prolactin Receptor (PRLR) is a type 1 cytokine receptor that is expressed in a subset of breast cancers and may contribute to its pathogenesis. It is relatively overexpressed in approximately 25% of human breast tumors while expressed at low levels in some normal human tissues including the mammary gland. We developed an anti-PRLR antibody-drug conjugate (ADC), to target PRLR-positive breast cancer. REGN2878-DM1 is comprised of a fully human high-affinity function-blocking anti-PRLR IgG1 antibody (REGN2878) conjugated via a noncleavable SMCC linker to the cytotoxic maytansine derivative DM1. Both unconjugated REGN2878 and conjugated REGN2878-DM1 block PRL-mediated activation in vitro and are rapidly internalized into lysosomes. REGN2878-DM1 induces potent cell-cycle arrest and cytotoxicity in PRLR-expressing tumor cell lines. In vivo, REGN2878-DM1 demonstrated significant antigen-specific antitumor activity against breast cancer xenograft models. In addition, REGN2878-DM1 showed additive activity when combined with the antiestrogen agent fulvestrant. These results illustrate promising antitumor activity against PRLR-positive breast cancer xenografts and support the evaluation of anti-PRLR ADCs as potential therapeutic agents in breast cancer. Mol Cancer Ther; 16(7); 1299-311. ©2017 AACR.

PAK1 translocates into nucleus in response to prolactin but not to estrogen

Tyrosyl phosphorylation of the p21-activated serine-threonine kinase 1 (PAK1) has an essential role in regulating PAK1 functions in breast cancer cells. We previously demonstrated that PAK1 serves as a common node for estrogen (E2)- and prolactin (PRL)-dependent pathways. We hypothesize herein that intracellular localization of PAK1 is affected by PRL and E2 treatments differently. We demonstrate by immunocytochemical analysis that PAK1 nuclear translocation is ligand-dependent: only PRL but not E2 stimulated PAK1 nuclear translocation. Tyrosyl phosphorylation of PAK1 is essential for this nuclear translocation because phospho-tyrosyl-deficient PAK1 Y3F mutant is retained in the cytoplasm in response to PRL. We confirmed these data by Western blot analysis of subcellular fractions. In 30 min of PRL treatment, only 48% of pTyr-PAK1 is retained in the cytoplasm of PAK1 WT clone while 52% re-distributes into the nucleus and pTyr-PAK1 shuttles back to the cytoplasm by 60 min of PRL treatment. In contrast, PAK1 Y3F is retained in the cytoplasm. E2 treatment causes nuclear translocation of neither PAK1 WT nor PAK1 Y3F. Finally, we show by an in vitro kinase assay that PRL but not E2 stimulates PAK1 kinase activity in the nuclear fraction. Thus, PAK1 nuclear translocation is ligand-dependent: PRL activates PAK1 and induces translocation of activated pTyr-PAK1 into nucleus while E2 activates pTyr-PAK1 only in the cytoplasm.

Synergistic Activation of ERα by Estrogen and Prolactin in Breast Cancer Cells Requires Tyrosyl Phosphorylation of PAK1

Serine/threonine kinase PAK1 is activated by estrogen and plays an important role in breast cancer. However, the integration of PAK1 into the estrogen response is not fully understood. In this study, we investigated the mechanisms underlying the hormone-induced activation of estrogen receptor (ERα, ESR1). We show that estrogen activated PAK1 through both the ERα and GPER1 membrane receptors. Estrogen-dependent activation of PAK1 required the phosphorylation of tyrosine residues by Etk/Bmx and protein kinase A (PKA) within an assembled signaling complex comprising pTyr-PAK1, Etk/Bmx, the heterotrimer G-protein subunits Gβ1, Gγ2, and/or Gγ5, PAK-associated guanine nucleotide exchange factor (βPIX, ARHGEF7), and PKA. Moreover, the PKA RIIβ subunit is a direct target of PAK1, and thus in response to estrogen, the activated pTyr-PAK1 complex reciprocally potentiated PKA activity, suggesting a positive feedback mechanism. We also demonstrate that PKA phosphorylated Ser305-ERα in response to estrogen, but pTyr-PAK1 phosphorylated Ser305-ERα in response to prolactin (PRL), implying that maximal ERα phosphorylation is achieved when cells are exposed to both PRL and estrogen. Furthermore, S305-ERα activation led to enhanced phosphorylation of Ser118-ERα and promoted cell proliferation and tumor growth. Together, these data strongly support a critical interplay between PRL and estrogen via PAK1 and suggest that ligand-independent activation of ERα through PRL/PAK1 may impart resistance to anti-estrogen therapies. Cancer Res; 76(9); 2600-11. ©2016 AACR.

Seasonal Expression of Prolactin Receptor in the Scented Gland of Male Muskrat (Ondatra zibethicus)

Prolactin (PRL) has numerous actions in mammalian biological systems including mammary development and biological processes. The aim of this study was to investigate the seasonal changes of prolactin receptor (PRLR) expression in the scented gland of muskrat during the breeding and nonbreeding seasons. Histologically, glandular cells, interstitial cells and excretory tubules were identified in the scented glands in both seasons, whereas epithelial cells were sparse in the nonbreeding season. PRLR was observed in glandular cells of scented glands during the breeding and nonbreeding seasons with stronger immunostaining during the breeding season. Consistent with the immunohistochemical results, both the mean of protein and mRNA levels of PRLR were higher in the scented glands of the breeding season, and relatively lower level in the nonbreeding season. In addition, differential seasonal changes were also detected in the expression profile of microRNAs (miRNAs) in the scented gland of muskrat. Besides, plasma PRL concentration was remarkably higher in the breeding season than that in the nonbreeding season. These results suggested that muskrat scented gland was the direct target organ of PRL, and stronger expression of PRLR in scented glands during the breeding season indicated that PRL may directly regulate scented glandular function of the muskrats.

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.

Dense collagen-I matrices enhance pro-tumorigenic estrogen-prolactin crosstalk in MCF-7 and T47D breast cancer cells

Breast cancers that express estrogen receptor alpha (ERα+) constitute the majority of breast tumors. Estrogen is a major driver of their growth, and targeting ER-mediated signals is a largely successful primary therapeutic strategy. Nonetheless, ERα+ tumors also result in the most breast cancer mortalities. Other factors, including altered characteristics of the extracellular matrix such as density and orientation and consequences for estrogen crosstalk with other hormones such as prolactin (PRL), may contribute to these poor outcomes. Here we employed defined three dimensional low density/compliant and high density/stiff collagen-I matrices to investigate the effects on 17β-estradiol (E2) activity and PRL/E2 interactions in two well-characterized ERα+/PRLR+ luminal breast cancer cell lines in vitro. We demonstrate that matrix density modulated E2-induced transcripts, but did not alter the growth response. However, matrix density was a potent determinant of the behavioral outcomes of PRL/E2 crosstalk. High density/stiff matrices enhanced PRL/E2-induced growth mediated by increased activation of Src family kinases and insensitivity to the estrogen antagonist, 4-hydroxytamoxifen. It also permitted these hormones in combination to drive invasion and modify the alignment of collagen fibers. In contrast, low density/compliant matrices allowed modest if any cooperation between E2 and PRL to growth and did not permit hormone-induced invasion or collagen reorientation. Our studies demonstrate the power of matrix density to determine the outcomes of hormone actions and suggest that stiff matrices are potent collaborators of estrogen and PRL in progression of ERα+ breast cancer. Our evidence for bidirectional interactions between these hormones and the extracellular matrix provides novel insights into the regulation of the microenvironment of ERα+ breast cancer and suggests new therapeutic approaches.

Modeling prolactin actions in breast cancer in vivo: insights from the NRL-PRL mouse

Elevated exposure to prolactin (PRL) is epidemiologically associated with an increased risk of aggressive ER+ breast cancer. To understand the underlying mechanisms and crosstalk with other oncogenic factors, we developed the NRL-PRL mouse. In this model, mammary expression of a rat prolactin transgene raises local exposure to PRL without altering estrous cycling. Nulliparous females develop metastatic, histotypically diverse mammary carcinomas independent from ovarian steroids, and most are ER+. These characteristics resemble the human clinical disease, facilitating study of tumorigenesis, and identification of novel preventive and therapeutic approaches.

Prolactin Promotes Breast Cancer Cell Migration through Actin Cytoskeleton Remodeling

The role of prolactin on breast cancer development and progression is debated. Breast cancer progression largely depends on cell movement and on the ability to remodel the actin cytoskeleton. In this process, actin-binding proteins are requested to achieve fibrillar actin de-polymerization and relocation at the cell membrane. Kinases such as focal adhesion kinase (FAK) are later required to form actin/vinculin-enriched structures called focal adhesion complexes, which mediate firm adhesion to the extracellular matrix. These controllers are regulated by c-Src, which forms multiprotein signaling complexes with membrane receptors and is regulated by a number of hormones, including -prolactin. We here show that breast cancer cells exposed to prolactin display an elevated c-Src expression and phosphorylation. In parallel, increased moesin and FAK expression and phosphorylation are found. These molecular changes are associated to relocation to the plasma membrane of cytoskeletal actin fibers and to increased horizontal cell movement. In conclusion, prolactin regulates actin remodeling and enhances breast cancer cell movement. This finding broadens the understanding of prolactin actions on breast cancer cells, highlighting new pathways that may be relevant to on breast cancer progression.

Eliminative signaling by Janus kinases: role in the downregulation of associated receptors

Activation of cytokine receptor-associated Janus kinases (JAKs) mediates most, if not all, of the cellular responses to peptide hormones and cytokines. Consequently, JAKs play a paramount role in homeostasis and immunity. Members of this family of tyrosine kinases control the cytokine/hormone-induced alterations in cell gene expression program. This function is largely mediated through an ability to signal toward activation of the signal transducer and activator of transcription proteins (STAT), as well as toward some other pathways. Importantly, JAKs are also instrumental in tightly controlling the expression of associated cytokine and hormone receptors, and, accordingly, in regulating the cell sensitivity to these cytokines and hormones. This review highlights the enzymatic and non-enzymatic mechanisms of this regulation and discusses the importance of the ambidextrous nature of JAK as a key signaling node that integrates the combining functions of forward signaling and eliminative signaling. Attention to the latter aspect of JAK function may contribute to emancipating our approaches to the pharmacological modulation of JAKs.

Immunomodulatory effects of sex hormones: requirements for pregnancy and relevance in melanoma

Similarities between the pathologic progression of cancer and the physiologic process of placentation (eg, proliferation, invasion, and local/systemic tolerance) have been recognized for many years. Sex hormones such as human chorionic gonadotropin, estrogens, progesterone, and others contribute to induction of immunologic tolerance at the beginning of gestation. Sex hormones have been shown to play contributory roles in the growth of cancers such as breast cancer, prostrate cancer, endometrial cancer, and ovarian cancer, but their involvement as putative mediators of the immunologic escape of cancer is still being elucidated. Herein, we compare the emerging mechanism by which sex hormones modulate systemic immunity in pregnancy and their potentially similar role in cancer. To do this, we conducted a PubMed search using combinations of the following keywords: "immune regulation," "sex hormones," "pregnancy," "melanoma," and "cancer." We did not limit our search to specific publication dates. Mimicking the maternal immune response to pregnancy, especially in late gestation, might aid in design of better therapies to reconstitute endogenous antitumor immunity and improve survival.

Miz1 deficiency in the mammary gland causes a lactation defect by attenuated Stat5 expression and phosphorylation

Miz1 is a zinc finger transcription factor with an N-terminal POZ domain. Complexes with Myc, Bcl-6 or Gfi-1 repress expression of genes like Cdkn2b (p15^Ink4) or Cdkn1a (p21^Cip1). The role of Miz1 in normal mammary gland development has not been addressed so far. Conditional knockout of the Miz1 POZ domain in luminal cells during pregnancy caused a lactation defect with a transient reduction of glandular tissue, reduced proliferation and attenuated differentiation. This was recapitulated in vitro using mouse mammary gland derived HC11 cells. Further analysis revealed decreased Stat5 activity in Miz1ΔPOZ mammary glands and an attenuated expression of Stat5 targets. Gene expression of the Prolactin receptor (PrlR) and ErbB4, both critical for Stat5 phosphorylation (pStat5) or pStat5 nuclear translocation, was decreased in Miz1ΔPOZ females. Microarray, ChIP-Seq and gene set enrichment analysis revealed a down-regulation of Miz1 target genes being involved in vesicular transport processes. Our data suggest that deranged intracellular transport and localization of PrlR and ErbB4 disrupt the Stat5 signalling pathway in mutant glands and cause the observed lactation phenotype.

Human metastatic melanoma cell lines express high levels of growth hormone receptor and respond to GH treatment

Accumulating evidence implicates the growth hormone receptor (GHR) in carcinogenesis. While multiple studies show evidence for expression of growth hormone (GH) and GHR mRNA in human cancer tissue, there is a lack of quantification and only a few cancer types have been investigated. The National Cancer Institute's NCI60 panel includes 60 cancer cell lines from nine types of human cancer: breast, CNS, colon, leukemia, melanoma, non-small cell lung, ovarian, prostate and renal. We utilized this panel to quantify expression of GHR, GH, prolactin receptor (PRLR) and prolactin (PRL) mRNA with real-time RT qPCR. Both GHR and PRLR show a broad range of expression within and among most cancer types. Strikingly, GHR expression is nearly 50-fold higher in melanoma than in the panel as a whole. Analysis of human metastatic melanoma biopsies confirmed GHR gene expression in melanoma tissue. In these human biopsies, the level of GHR mRNA is elevated in advanced stage IV tumor samples compared to stage III. Due to the novel finding of high GHR in melanoma, we examined the effect of GH treatment on three NCI60 melanoma lines (MDA-MB-435, UACC-62 and SK-MEL-5). GH increased proliferation in two out of three cell lines tested. Further analysis revealed GH-induced activation of STAT5 and mTOR in a cell line dependent manner. In conclusion, we have identified cell lines and cancer types that are ideal to study the role of GH and PRL in cancer, yet have been largely overlooked. Furthermore, we found that human metastatic melanoma tumors express GHR and cell lines possess active GHRs that can modulate multiple signaling pathways and alter cell proliferation. Based on this data, GH could be a new therapeutic target in melanoma.

Hope and fear for interferon: the receptor-centric outlook on the future of interferon therapy

After several decades of intense clinical research, the great promise of Type I interferons (IFN1) as the anticancer wonder drugs that could cure or, at the very least, curb the progression of various oncological diseases has regrettably failed to deliver. Severe side effects and low efficacy of IFN1-based pharmaceutics greatly limited use of these drugs and further reduced the enthusiasm of clinical oncologists for future optimization of IFN1-based therapeutic modalities. Incredibly, extensive clinical studies to assess the efficacy of IFN1 alone or in combination with other anticancer drugs have not been paralleled by an equal scope in defining the determinants that confer cell sensitivity or refractoriness to IFN1. Given that all effects of IFN1 on malignant and benign cells alike are mediated by its receptor, the mechanisms regulating these receptor cell surface levels should play a paramount role in shaping the magnitude and duration of IFN1-elicited effects. These mechanisms and their role in controlling IFN1 responses, as well as an ability of a growing tumor to commandeer these events, are the focus of our review. We postulate that activation of numerous signaling pathways leading to elimination of IFN1 receptor occurs in cancer cells and benign cells that contribute to tumor tissue. We further hypothesize that activation of these eliminative pathways enables the escape from IFN1-driven suppression of tumorigenesis and elicits the primary refractoriness of tumor to the pharmaceutical IFN1.

Prolactin cooperates with loss of p53 to promote claudin-low mammary carcinomas

TP53 is one of the most commonly mutated genes in cancer. In breast cancer, it is mutated in about 40% of primary clinical tumors and is associated with poor survival. The mammotrophic hormone, prolactin (PRL), and/or its receptor are also expressed in many breast cancers, and accumulating epidemiologic data link PRL to breast cancer development and progression. Like TP53 mutations, evidence for PRL activity is evident across several molecular cancer subtypes, and elevated PRL expression and loss of p53 have been observed in some of the same clinical tumors. In order to examine the interaction of these factors, we used genetically modified mouse models of mammary-specific p53 loss and local overexpression of PRL. We demonstrated that mammary PRL decreased the latency of tumors in the absence of p53, and increased the proportion of triple-negative claudin-low carcinomas, which display similarities to human clinical metaplastic carcinomas. Moreover, PRL/p53(-/-) carcinomas displayed higher rates of proliferation and more aggressive behavior. Transcripts associated with cell cycle progression, invasion and stromal reactivity were differentially expressed in carcinomas that developed in the presence of elevated PRL. PRL/p53(-/-) carcinomas also exhibited selectively altered expression of activating protein-1 components, including higher levels of c-Jun and FosL1, which can drive transcription of many of these genes and the epithelial-mesenchymal transition. The ability of PRL to promote claudin-low carcinomas demonstrates that PRL can influence this subset of triple-negative breast cancers, which may have been obscured by the relative infrequency of this cancer subtype. Our findings suggest novel therapeutic approaches, and provide a preclinical model to develop possible agents.

The prolactin receptor transactivation domain is associated with steroid hormone receptor expression and malignant progression of breast cancer

The polypeptide hormone prolactin (PRL) stimulates breast epithelial cell growth, differentiation, and motility through its cognate receptor, PRLr. PRLr is expressed in most breast cancers; however, its exact role remains elusive. Our laboratory previously described a novel mode of PRLr signaling in which Stat5a-mediated transcription is regulated through ligand-induced phosphorylation of the PRLr transactivation domain (TAD). Herein, we used a PRLr transactivation-deficient mutant (PRLrYDmut) to identify novel TAD-specific target genes. Microarray analysis identified 120 PRL-induced genes up-regulated by wild type but not PRLrYDmut. Compared with control, PRLr expression significantly induced expression of approximately 4700 PRL-induced genes, whereas PRLrYDmut ablated induction of all but 19 of these genes. Ingenuity pathway analysis found that the PRLr TAD most profoundly affected networks involving cancer and proliferation. In support of this, PRLrYDmut expression reduced anchorage-dependent and anchorage-independent growth. In addition, pathway analysis identified a link between the PRLr TAD and the estrogen and progesterone receptors (ERα/PR). Although neither ERα nor PR was identified as a PRL target gene, a TAD mutation significantly impaired ERα/PR expression and estrogen responsiveness. TMA analysis revealed a marked increase in nuclear, but not cytoplasmic, PRLr TAD phosphorylation as a function of neoplastic progression. We propose that PRLr TAD phosphorylation contributes to breast cancer pathogenesis, in part through regulation of ERα and PR, and has potential utility as a biomarker in this disease.

Prolactin signaling mechanisms in ovary

Prolactin is a hormone that is essential for normal reproduction and signals through two types of receptors. Not only is the classical long form of the prolactin receptor identified, but so are many short form receptors in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of prolactin family, providing compelling evidence that the different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary gland and ovarian follicles. This review summarizes our current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Prolactin promotes mammary pathogenesis independently from cyclin D1

Epidemiological and experimental studies have revealed an important role for prolactin (PRL) in breast cancer. Cyclin D1 is a major downstream target of PRL in lobuloalveolar development during pregnancy and is amplified and/or overexpressed in many breast carcinomas. To examine the importance of cyclin D1 in PRL-induced pathogenesis, we generated transgenic mice (NRL-PRL) that overexpress PRL in mammary epithelial cells, with wild-type, heterozygous, or genetically ablated cyclin D1 in the FVB/N genetic background. Although loss of one cyclin D1 allele did not affect PRL-induced mammary lesions in nonparous females, the complete absence of cyclin D1 (D1(-/-)) markedly decreased tumor incidence. Nevertheless, NRL-PRL/D1(-/-) females developed significantly more preneoplastic lesions (eg, epithelial hyperplasias and mammary intraepithelial neoplasias) than D1(-/-) females. Moreover, although lack of cyclin D1 reduced proliferation of morphologically normal mammary epithelium, transgenic PRL restored it to rates of wild-type females. PRL posttranscriptionally increased nuclear cyclin D3 protein in D1(-/-) luminal cells, indicating one compensatory mechanism. Consistently, pregnancy induced extensive lobuloalveolar growth in the absence of cyclin D1. However, transcripts for milk proteins were reduced, and pups failed to survive, suggesting that mammary differentiation was inadequate. Together, these results indicate that cyclin D1 is an important, but not essential, mediator of PRL-induced mammary proliferation and pathology in FVB/N mice and is critical for differentiation and lactation.

Prolactin receptor in primary hyperparathyroidism--expression, functionality and clinical correlations

Background

Primary hyperparathyroidism (PHPT) is an endocrine disorder most commonly affecting women, suggesting a role for female hormones and/or their receptors in parathyroid adenomas. We here investigated the prolactin receptor (PRLr) which is associated with tumours of the breast and other organs.

Methodology/Principal Findings

PRLr expression was investigated in a panel of 37 patients with sporadic parathyroid tumours and its functionality in cultured parathyroid tumour cells. In comparison with other tissues and breast cancer cells, high levels of prolactin receptor gene (PRLR) transcripts were demonstrated in parathyroid tissues. PRLr products of 60/70 kDa were highly expressed in all parathyroid tumours. In addition varying levels of the 80 kDa PRLr isoform, with known proliferative activity, were demonstrated. In parathyroid tumours, PRLr immunoreactivity was observed in the cytoplasm (in all cases, n = 36), cytoplasmic granulae (n = 16), the plasma membrane (n = 12) or enlarged lysosomes (n = 4). In normal parathyroid rim (n = 28), PRLr was uniformly expressed in the cytoplasm and granulae. In in vitro studies of short-term cultured human parathyroid tumour cells, prolactin stimulation was associated with significant transcriptional changes in JAK/STAT, RIG-I like receptor and type II interferon signalling pathways as documented by gene expression profiling. Moreover, PRLR gene expression in parathyroid tumours was inversely correlated with the patients’ plasma calcium levels.

Conclusions

We demonstrate that the prolactin receptor is highly abundant in human parathyroid tissues and that PRLr isoforms expression and PRLr subcellular localisation are altered in parathyroid tumours. Responsiveness of PRLr to physiological levels of prolactin was observed in the form of increased PTH secretion and altered gene transcription with significant increase of RIG-I like receptor, JAK-STAT and Type II interferon signalling pathways. These data suggest a role of the prolactin receptor in parathyroid adenomas.

Prolactin (PRL) induction of cyclooxygenase 2 (COX2) expression and prostaglandin (PG) production in hamster Leydig cells

Serum prolactin (PRL) variations play a crucial role in the photoperiodic-induced testicular regression-recrudescence transition in hamsters. We have previously shown that cyclooxygenase 2 (COX2), a key enzyme in the biosynthesis of prostaglandins (PGs), is expressed mostly in Leydig cells of reproductively active hamsters with considerable circulating and pituitary levels of PRL. In this study, we describe a stimulatory effect of PRL on COX2/PGs in hamster Leydig cells, which is mediated by IL-1β and prevented by P38-MAPK and JAK2 inhibitors. Furthermore, by preparative isoelectric focusing (IEF), we isolated PRL charge analogues from pituitaries of active [isoelectric points (pI): 5.16, 4.61, and 4.34] and regressed (pI: 5.44) hamsters. More acidic PRL charge analogues strongly induced COX2 expression, while less acidic ones had no effect. Our studies suggest that PRL induces COX2/PGs in hamster Leydig cells through IL-1β and activation of P38-MAPK and JAK2. PRL microheterogeneity detected in active/inactive hamsters may be responsible for the photoperiodic variations of COX2 expression in Leydig cells.

Hypothesis: prolactin is tumorigenic to human breast: dispelling the myth that prolactin-induced mammary tumors are rodent-specific

The commonly held assumption that rodent mammary tumors resulting from elevated prolactin are species-specific, or not biologically relevant to humans, is incorrect. Substantial epidemiological, clinical, and biological evidence now exists confirming the role of prolactin in human breast cancer. This evidence is evaluated and the argument presented that the tumorigenic risk from prolactin is therefore not species-specific to rodents but directly applies to humans. Further, as the mechanisms of prolactin-induced mammary tumor promotion and development appear analogous between rodents and humans, mammary tumorigenic findings in rodent carcinogenicity bioassays are both predictive and biologically relevant to the human response. Toxicologists and regulators need to consider this in carcinogenicity risk assessments.

Evaluation of prolactin receptor (PRLR) as candidate gene for male fertility in Hanoverian warmblood horses

Stallion fertility has increasing importance as the artificial insemination is employed in horses more intensely. Molecular genetic markers may be useful tools to evaluate the stallion fertility before breeding. The prolactin receptor gene (PRLR) was chosen as a candidate for stallion fertility because of its influence on testicular and accessory sex gland function. Screening the equine PRLR gene for polymorphisms in Hanoverian stallions revealed two single nucleotide polymorphisms (SNPs). Association and haplotype analyses were performed in 162 Hanoverian warmblood stallions for these intragenic SNPs using the least square means (LSM) of the pregnancy rate per oestrus for stallions and the paternal component and embryonic component of the breeding values (BV) of the pregnancy rate per oestrus. The two SNPs (BIEC2-589441, BIEC2-560860) showed significant associations using single marker and haplotype analysis with the embryonic and paternal component of BV and one SNP (BIEC2-560860) was also significantly associated with the LSM of the pregnancy rate per oestrus. This is the first report on an association of PRLR-associated genetic markers with fertility traits in stallions.

Prolactin-stimulated activation of ERK1/2 mitogen-activated protein kinases is controlled by PI3-kinase/Rac/PAK signaling pathway in breast cancer cells

There is strong evidence that deregulation of prolactin (PRL) signaling contributes to pathogenesis and chemoresistance of breast cancer. Therefore, understanding cross-talk between distinct signal transduction pathways triggered by activation of the prolactin receptor (PRL-R), is essential for elucidating the pathogenesis of metastatic breast cancer. In this study, we applied a sequential inhibitory analysis of various signaling intermediates to examine the hierarchy of protein interactions within the PRL signaling network and to evaluate the relative contributions of multiple signaling branches downstream of PRL-R to the activation of the extracellular signal-regulated kinases ERK1 and ERK2 in T47D and MCF-7 human breast cancer cells. Quantitative measurements of the phosphorylation/activation patterns of proteins showed that PRL simultaneously activated Src family kinases (SFKs) and the JAK/STAT, phosphoinositide-3 (PI3)-kinase/Akt and MAPK signaling pathways. The specific blockade or siRNA-mediated suppression of SFK/FAK, JAK2/STAT5, PI3-kinase/PDK1/Akt, Rac/PAK or Ras regulatory circuits revealed that (1) the PI3-kinase/Akt pathway is required for activation of the MAPK/ERK signaling cascade upon PRL stimulation; (2) PI3-kinase-mediated activation of the c-Raf-MEK1/2-ERK1/2 cascade occurs independent of signaling dowstream of STATs, Akt and PKC, but requires JAK2, SFKs and FAK activities; (3) activated PRL-R mainly utilizes the PI3-kinase-dependent Rac/PAK pathway rather than the canonical Shc/Grb2/SOS/Ras route to initiate and sustain ERK1/2 signaling. By interconnecting diverse signaling pathways PLR may enhance proliferation, survival, migration and invasiveness of breast cancer cells.

Mutations in the exon 10 of prolactin receptor gene change the egg production performance in Wanjiang white goose

To select the molecular genetic markers related to egg performance of Wanjiang white goose, prolactin receptor gene (PRLR) was adopted to be a candidate gene in our study. Five pairs of primers (P1-P5) were designed to detect the SNPs of PRLR gene by PCR-SSCP method. The results revealed that polymorphisms were discovered in the PCR products amplified with P4 primers in PRLR exon 10, three genotypes were found: AA, AB and AC. The sequence of AB genotype is the same as original sequence (DQ660982) in NCBI. There are five mutations in AA genotype: C→A at 840 bp, C→T at 862 bp, T→C at 875 bp, T→A at 963 bp, A→T at 989 bp, resulting in amino acid mutations: His→Asn, Thr→Ile, Asn→Lys, Thr→Ser, and synonymous mutation at 875 bp. Sequencing revealed five mutations in AC genotype: G→T at 816 bp, A→T at 861 bp, C→T at 862 bp, T→C at 875 bp, A→G at 948 bp, causing amino acid mutations of Val→Phe, Thr→Phe, synonymous mutations at 875 and 963 bp. Besides, there are an N-glycosylation site (NQSR), three casein kinase II phosphorylation sites including SIIE, SKTE, and SLMD in AA genotype; three casein kinase II phosphorylation sites including SIIE, SKTE, and TLMD in AB genotype; three casein kinase II phosphorylation sites including SIFE, SKTE, and TLMD in AC genotype. The annual egg yielding of AB genotype geese are significantly more than those of AA and AC genotype geese on the average (P<0.05). It is suggested for the first time that PRLR is a promising candidate gene that can affect egg performance in Wanjiang white goose.

Lactogens and estrogens in breast cancer chemoresistance

Tumor resistance to chemotherapy in advanced breast cancer is a major impediment to treatment success. Resistance can be induced by the drugs themselves or result from the action of internal factors. The role of hormones in chemoresistance has received little attention. This article focuses on two classes of hormones: lactogens and estrogens. Lactogens include prolactin, growth hormone and placental lactogen, all of which can activate the prolactin receptor. Estrogens include endogenous steroids and nonsteroidal compounds from the environment termed endocrine disruptors, all of which can activate 'classical' estrogen receptors (ERα and ERβ), as well as other types of receptors. Both lactogens and estrogens antagonize cytotoxicity of multiple chemotherapeutic agents through complementary mechanisms. The implications of chemoresistance by these hormones to patients with breast cancer, and the potential benefits of developing combinatorial anti-lactogen/anti-estrogen treatment regimens, are discussed.

Prolactin-induced mouse mammary carcinomas model estrogen resistant luminal breast cancer

Introduction

Tumors that express estrogen receptor alpha (ERα+) comprise 75% of breast cancers in women. While treatments directed against this receptor have successfully lowered mortality rates, many primary tumors initially or later exhibit resistance. The paucity of murine models of this "luminal" tumor subtype has hindered studies of factors that promote their pathogenesis and modulate responsiveness to estrogen-directed therapeutics. Since epidemiologic studies closely link prolactin and the development of ERα+ tumors in women, we examined characteristics of the aggressive ERα+ and ERα- carcinomas which develop in response to mammary prolactin in a murine transgenic model (neu-related lipocalin- prolactin (NRL-PRL)). To evaluate their relationship to clinical tumors, we determined phenotypic relationships among these carcinomas, other murine models of breast cancer, and features of luminal tumors in women.

Methods

We examined a panel of prolactin-induced tumors for characteristics relevant to clinical tumors: histotype, ERα/progesterone receptor (PR) expression and estrogen responsiveness, Activating Protein 1 (AP-1) components, and phosphorylation of signal transducer and activator of transcription 5 (Stat5), extracellular signal regulated kinase (ERK) 1/2 and AKT. We compared levels of transcripts in the ERα-associated "luminal" signature that defines this subtype of tumors in women and transcripts enriched in various mammary epithelial lineages to other well-studied genetically modified murine models of breast cancer. Finally, we used microarray analyses to compare prolactin-induced ERα+ and ERα- tumors, and examined responsiveness to estrogen and the anti-estrogen, Faslodex, in vivo.

Results

Prolactin-induced carcinomas were markedly diverse with respect to histotype, ERα/PR expression, and activated signaling cascades. They constituted a heterogeneous, but distinct group of murine mammary tumors, with molecular features of the luminal subtype of human breast cancer. In contrast to morphologically normal and hyperplastic structures in NRL-PRL females, carcinomas were insensitive to ERα-mediated signals. These tumors were distinct from mouse mammary tumor virus (MMTV)-neu tumors, and contained elevated transcripts for factors associated with luminal/alveolar expansion and differentiation, suggesting that they arose from physiologic targets of prolactin. These features were shared by ERα+ and ERα- tumors, suggesting a common origin, although the former exhibited transcript profiles reflecting greater differentiation.

Conclusions

Our studies demonstrate that prolactin can promote diverse carcinomas in mice, many of which resemble luminal breast cancers, providing a novel experimental model to examine the pathogenesis, progression and treatment responsiveness of this tumor subtype.

Characterization of ductal and lobular breast carcinomas using novel prolactin receptor isoform specific antibodies

BACKGROUND

Prolactin is a polypeptide hormone responsible for proliferation and differentiation of the mammary gland. More recently, prolactin's role in mammary carcinogenesis has been studied with greater interest. Studies from our laboratory and from others have demonstrated that three specific isoforms of the prolactin receptor (PRLR) are expressed in both normal and cancerous breast cells and tissues. Until now, reliable isoform specific antibodies have been lacking. We have prepared and characterized polyclonal antibodies against each of the human PRLR isoforms that can effectively be used to characterize human breast cancers.

METHODS

Rabbits were immunized with synthetic peptides of isoform unique regions and immune sera affinity purified prior to validation by Western blot and immunohistochemical analyses. Sections of ductal and lobular carcinomas were stained with each affinity purified isoform specific antibody to determine expression patterns in breast cancer subclasses.

RESULTS

We show that the rabbit antibodies have high titer and could specifically recognize each isoform of PRLR. Differences in PRLR isoform expression levels were observed and quantified using histosections from xenografts of established human breast cancer cells lines, and ductal and lobular carcinoma human biopsy specimens. In addition, these results were verified by real-time PCR with isoform specific primers. While nearly all tumors contained LF and SF1b, the majority (76%) of ductal carcinoma biopsies expressed SF1a while the majority of lobular carcinomas lacked SF1a staining (72%) and 27% had only low levels of expression.

CONCLUSIONS

Differences in the receptor isoform expression profiles may be critical to understanding the role of PRL in mammary tumorigenesis. Since these antibodies are specifically directed against each PRLR isoform, they are valuable tools for the evaluation of breast cancer PRLR content and have potential clinical importance in treatment of this disease by providing new reagents to study the protein expression of the human PRLR.

Prolactin inhibits activity of pyruvate kinase M2 to stimulate cell proliferation

Mitogenic and prosurvival effects underlie the tumorigenic roles of prolactin (PRL) in the pathogenesis of breast cancer. PRL signaling is mediated through its receptor (PRLr). A proteomics screen identified the pyruvate kinase M2 (PKM2), a glycolytic enzyme known to play an important role in tumorigenesis, as a protein that constitutively interacts with PRLr. Treatment of cells with PRL inhibited pyruvate kinase activity and increased the lactate content in human cells in a manner that was dependent on the abundance of PRLr, activation of Janus kinase 2, and tyrosine phosphorylation of the intracellular domain of PRLr. Knockdown of PKM2 attenuated PRL-stimulated cell proliferation. The extent of this proliferation was rescued by the knock-in of the wild-type PKM2 but not of its mutant insensitive to PRL-mediated inhibition. We discuss a hypothesis that the inhibition of PKM2 by PRL contributes to the PRL-stimulated cell proliferation.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSIONS

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

Amplification of the prolactin receptor gene in mammary lobular neoplasia

The identification of lobular carcinoma in situ (LCIS) in a patient's specimen confers an appreciable increased risk of development of future invasive mammary carcinoma. However, the study of LCIS presents a challenge as it is usually only recognized in fixed specimens. Recent advances in high throughput genomics have made possible comprehensive copy number analysis of lesions such as this. Using array comparative genomic hybridization (aCGH), we characterized eight cases of lobular carcinoma (four invasive and four non-invasive) from microdissected samples of archival specimens and validated our results by quantitative real-time PCR (qRT-PCR). Immunohistochemistry (IHC) was performed on an independent set of 80 in situ ductal (DCIS) and lobular breast lesions to confirm our results. Amplification of the prolactin receptor gene (PRLr) was identified in 4/4 cases of LCIS by aCGH. We confirmed this amplification by qRT-PCR and demonstrated PRLr expression in 29/40 (73%) cases of lobular neoplasia by IHC. Amplification of PRLr was neither detected in 10 cases of DCIS nor in 5 areas of normal breast tissue by qRT-PCR and only 14/40 (35%) cases of DCIS showed PRLr expression by IHC (P = 0.0008). Our study suggests the prolactin receptor gene is a molecular target that may be important in the pathogenesis and progression of lobular neoplasia. Investigation of the status of this gene in cases of DCIS has indicated that it may not be as important in the progression of this type of breast cancer, supporting the view that lobular and ductal carcinomas may evolve along separate pathways.