A new mechanism for prolactin processing into 16K PRL by secreted cathepsin D

The role of prolactin/vasoinhibins in cardiovascular diseases

Prolactin (PRL) is a polypeptide hormone that is mainly synthesized and secreted by the lactotroph cells of the pituitary. There are two main isoforms of PRL: 23-kDa PRL (named full-length PRL) and vasoinhibins (including 5.6-18 kDa fragments). Both act as circulating hormones and cytokines to stimulate or inhibit vascular formation at different stages and neovascularization, including endothelial cell proliferation and migration, protease production, and apoptosis. However, their effects on vascular function and cardiovascular diseases are different or even contrary. In addition to the structure, secretion regulation, and signal transduction of PRL/vasoinhibins, this review focuses on the pathological mechanism and clinical significance of PRL/vasoinhibins in cardiovascular diseases.

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.

A comparative phylogenetic analysis of prolactin cleavage sites for the generation of vasoinhibin in vertebrates

Vasoinhibin is a pleiotropic protein hormone with endocrine, autocrine, and paracrine effects on blood vessel growth, permeability, and dilation, and a role in several human diseases. It is generated by proteolytic cleavage of the pituitary hormone prolactin by cathepsin D. Several isoforms with a variation in the number of amino acids and corresponding molecular mass exist. This in silico study investigated the cathepsin D cleavage sites in prolactin responsible for the generation of vasoinhibin in vertebrate species. Ninety-one prolactin protein sequences from species of the taxa primates, rodents, laurasiatheria, mammals, sauropsida, and fish were retrieved, and a multiple sequence alignment was performed. Each sequence was investigated for the presence of a vasoinhibin-generating cathepsin D cleavage site and its corresponding substrate affinity using a scoring system. Primates demonstrated the highest substrate affinity for the generation of the 15 kDa vasoinhibin isoform, and fish the highest affinity for the 16.8 kDa isoform. In both cases, this associates to the presence of leucine in the cleavage site, which is not present in species of the other taxa. In primate evolution, the presence of leucine in the cleavage site occurs with the emergence of simiiformes 42 million years ago and is conserved in higher primates across all subsequent speciation nodes. The 17.2 kDa vasoinhibin isoform has a constant substrate affinity in all taxa. The presence of leucine in vasoinhibin generating cleavage sites appears as an important feature of the molecular evolution of vasoinhibin.

Vasoinhibin generation and effect on neuronal apoptosis in the hippocampus of late mouse embryos

Morphological and behavioral evidence suggests that vasoinhibin is present in the central nervous system (CNS), triggering neuroendocrine and behavioral responses to stress. Moreover, vasoinhibin reduces neuronal survival and differentiation of primary sensory neurons of the peripheral nervous system. To address the functional role played by vasoinhibin at the CNS, and to better understand the underlying mechanisms involved in its actions, we treated primary cultured hippocampal neurons obtained from embryonic day 16 (E16) mice with a human recombinant vasoinhibin. We examined the resulting cellular changes, focusing on neuronal cell death, and explored the local generation of vasoinhibin within the hippocampus. Our results show that vasoinhibin significantly reduced neuronal cell density and increased immunoreactive activated caspase-3 and TUNEL-positive staining at 72, 16, and 24 h, respectively. Furthermore, vasoinhibin increased the expression of proapoptotic genes BAX, BAD, BIM, and PUMA and decreased that of the antiapoptotic gene BCL-2 at 24 h, as assessed by quantitative real-time reverse transcription-polymerase chain reaction. Vasoinhibin effects were blocked by coincubation with a vasoinhibin antibody or with prolactin. Immunoreactive bands consistent with vasoinhibin were observed in hippocampal extracts by Western blot analysis, and a prolactin standard was cleaved to vasoinhibin by a hippocampal lysate in a heat- and cathepsin D inhibitor pepstatin A-dependent fashion. Taken together, these data support the notion that vasoinhibin is locally produced by cathepsin D within the embryonic mouse hippocampus, a brain region that plays a critical role in emotional regulation, resulting in decreased neuronal cell viability via the activation of the intrinsic apoptosis pathway.

Cathepsins: Potent regulators in carcinogenesis

Cathepsins (CTS) are mainly lysosomal acid hydrolases extensively involved in the prognosis of different diseases, and having a distinct role in tumor progression by regulating cell proliferation, autophagy, angiogenesis, invasion, and metastasis. As all these processes conjunctively lead to cancer progression, their site-specific regulation might be beneficial for cancer treatment. CTS regulate activation of the proteolytic cascade and protein turnover, while extracellular CTS is involved in promoting extracellular matrix degradation and angiogenesis, thereby stimulating invasion and metastasis. Despite cancer regulation, the involvement of CTS in cellular adaptation toward chemotherapy and radiotherapy augments their therapeutic potential. However, lysosomal permeabilization mediated cytosolic translocation of CTS induces programmed cell death. This complex behavior of CTS generates the need to discuss the different aspects of CTS associated with cancer regulation. In this review, we mainly focused on the significance of each cathepsin in cancer signaling and their targeting which would provide noteworthy information in the context of cancer biology and therapeutics.

Long-Term Assessment of AAV-Mediated Zinc Finger Nuclease Expression in the Mouse Brain

Gene editing tools like TALENs, ZFNs and Crispr/Cas now offer unprecedented opportunities for targeted genetic manipulations in virtually all species. Most of the recent research in this area has concentrated on manipulation of the genome in isolated cells, which then give rise to transgenic animals or modified stem cell lines. Much less is known about applicability of genetic scissors in terminally differentiated, non-dividing cells like neurons of the adult brain. We addressed this question by expression of a pair of ZFNs targeting the murine cathepsin D gene in CNS neurons by means of an optimized AAV viral vector. We show that ZFN expression resulted in substantial depletion of cathepsin D from neuronal lysosomes, demonstrating a robust gene deletion. Importantly, long-term ZFN expression in CNS neurons did not impair essential neuronal functionality and did not cause inflammation or neurodegeneration, suggesting that potent genetic scissors can be expressed safely in the mouse brain. This finding opens up new venues to create novel research models for neurodegenerative disorders.

Molecular mechanism of C-reaction protein in promoting migration and invasion of hepatocellular carcinoma cells in vitro

Hepatocellular carcinoma (HCC) is one of most common malignant cancers and is the second leading cause of cancer related deaths. The prognosis and survival of patients are closely related to the degree of tumor metastasis. The mechanism of HCC metastasis is still unclear. In the present study, we investigated the molecular mechanism of C-reaction protein in promoting migration and invasion of hepatocellular carcinoma cells in vitro. We estimated that CRP is overexpressed in liver cancer tissues and that it promotes invasion and metastasis of HCC in vitro. In the present study, we employed iTRAQ-based mass spectrometry to analyze the HepG2 secretory proteins of CRP siRNA-treated cells and negative control siRNA-treated cells. We identified 109 differentially expressed proteins after silencing CRP, of which 45 were upregulated and 64 were downregulated. Some of the differentially expressed proteins were confirmed by western blot analysis and real-time quantitative PCR. Furthermore, we found that knockdown of CRP substantially abrogates HIF-1α expression levels, the luciferase activity of HIF-1α and ERK and Akt phosphorylation in HepG2 cells. The present study provides a novel mechanism by which CRP promotes the proliferation, migration, invasion and metastasis of hepatocellular carcinoma cells. Inhibition of CRP suppressed migration, invasion and healing of hepatoma carcinoma cells by decreasing HIF-1α activity and CTSD.

Prolactin Signaling Stimulates Invasion via Na(+)/H(+) Exchanger NHE1 in T47D Human Breast Cancer Cells

Prolactin (PRL) and its receptor (PRLR) are implicated in breast cancer invasiveness, although their exact roles remain controversial. The Na(+)/H(+) exchanger (NHE1) plays essential roles in cancer cell motility and invasiveness, but the PRLR and NHE1 have not previously been linked. Here we show that in T47D human breast cancer cells, which express high levels of PRLR and NHE1, exposure to PRL led to the activation of Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5), Akt, and ERK1/2 signaling and the rapid formation of peripheral membrane ruffles, known to be associated with cell motility. NHE1 was present in small ruffles prior to PRL treatment and was further recruited to the larger, more dynamic ruffles induced by PRL exposure. In PRL-induced ruffles, NHE1 colocalized with activated Akt, ERK1/2, and the ERK effector p90Ribosomal S kinase (p90RSK), known regulators of NHE1 activity. Stimulation of T47D cells with PRL augmented p90RSK activation, Ser703-phosphorylation of NHE1, NHE1-dependent intracellular pH recovery, pericellular acidification, and NHE1-dependent invasiveness. NHE1 activity and localization to ruffles were attenuated by the inhibition of Akt and/or ERK1/2. In contrast, noncancerous MCF10A breast epithelial cells expressed NHE1 and PRLR at lower levels than T47D cells, and their stimulation with PRL induced neither NHE1 activation nor NHE1-dependent invasiveness. In conclusion, we show for the first time that PRLR activation stimulates breast cancer cell invasiveness via the activation of NHE1. We propose that PRL-induced NHE1 activation and the resulting NHE1-dependent invasiveness may contribute to the metastatic behavior of human breast cancer cells.

Vastatin, an Endogenous Antiangiogenesis Polypeptide That Is Lost in Hepatocellular Carcinoma, Effectively Inhibits Tumor Metastasis

Hepatocellular carcinoma (HCC) is a hypervascular cancer without effective treatment. Here we report that polypeptide of NC1 domain of type VIII collagen (Vastatin) is an endogenous polypeptide expressed in normal liver tissue but lost in the liver of most HCC patients (73.1%). Its expression level is negatively associated with tumor size (P = 0.035) and metastasis (P = 0.016) in HCC patients. To evaluate its potential use as a therapeutic, we constructed a recombinant adeno-associated virus carrying Vastatin (rAAV-Vastatin) to treat HCC in an orthotopic Buffalo rat model. rAAV-Vastatin treatment significantly prolonged the median survival, inhibited tumor growth, and completely prevented metastasis in HCC-bearing rats by decreasing microvessel density and increasing tumor necrosis. No detectable toxicity in nontumor-bearing mice was observed. To investigate its molecular mechanisms, we performed DNA microarray, western blotting assays, and bioinformatic analysis to determine its effect on global gene expression patterns and signal transduction pathways. Our results indicated that rAAV-Vastatin significantly reduced the expressions of Pck1, JAG2, and c-Fos, thus inhibiting the cellular metabolism, Notch and AP-1 signaling pathways, respectively. Hence, we demonstrated for the first time that Vastatin is a novel, safe, and effective antiangiogenic therapeutic and a potential biomarker for HCC.

Vasoinhibins, N-terminal mouse prolactin fragments, participate in mammary gland involution

Vasoinhibins are a family of peptides that act on endothelial cells to suppress angiogenesis and promote apoptosis-mediated vascular regression. Vasoinhibins include the N-terminal fragments from prolactin (PRL), GH, and placental lactogen. One of the vasoinhibins, the N-terminal PRL fragment of 16 kDa, is generated by the lysosomal representative protease cathepsin D (Cath D). Because the normal growth and involution of the mammary gland (MG) are profoundly affected by the expansion and regression of blood vessels and also because PRL stimulates the growth and differentiation of MG, we proposed that intact PRL produced during lactation contributes to MG angiogenesis and increased blood flow, whereas during involution, the N-terminal PRL fragment would have proapoptotic effects on mammary epithelial cells (MECs). Therefore, we investigated the production of the N-terminal PRL fragment and its direct effect on the MG. Mouse PRL (mPRL) was proteolytically cleaved by Cath D between amino acids 148 and 149. N-terminal PRL fragment and Cath D expression increased during MG involution. Furthermore, incubation of MG fragments and MCF7 with recombinant 16 kDa mPRL revealed a proapoptotic effect in MECs. Ectopic mPRL in MECs was cleaved to 16 kDa PRL by Cath D in the MG lysosomal fraction. The majority of PRL derived from pituitary gland was cleaved to 16 kDa PRL in culture medium. Therefore, N-terminal PRL fragment increases during the involution period, has a proapoptotic effect on MECs, and is mainly generated by secreted Cath D in the extracellular space of MG.

The angiostatic protein 16K human prolactin significantly prevents tumor-induced lymphangiogenesis by affecting lymphatic endothelial cells

The 16-kDa angiostatic N-terminal fragment of human prolactin (16K hPRL) has been reported to be a new potent anticancer compound. This protein has already proven its efficiency in several mouse tumor models in which it prevented tumor-induced angiogenesis and delayed tumor growth. In addition to angiogenesis, tumors also stimulate the formation of lymphatic vessels, which contribute to tumor cell dissemination and metastasis. However, the role of 16K hPRL in tumor-induced lymphangiogenesis has never been investigated. We establish in vitro that 16K hPRL induces apoptosis and inhibits proliferation, migration, and tube formation of human dermal lymphatic microvascular endothelial cells. In addition, in a B16F10 melanoma mouse model, we found a decreased number of lymphatic vessels in the primary tumor and in the sentinel lymph nodes after 16K hPRL treatment. This decrease is accompanied by a significant diminished expression of lymphangiogenic markers in primary tumors and sentinel lymph nodes as determined by quantitative RT-PCR. These results suggest, for the first time, that 16K hPRL is a lymphangiostatic as well as an angiostatic agent with antitumor properties.

N-terminal prolactin-derived fragments, vasoinhibins, are proapoptoptic and antiproliferative in the anterior pituitary

The anterior pituitary is under a constant cell turnover modulated by gonadal steroids. In the rat, an increase in the rate of apoptosis occurs at proestrus whereas a peak of proliferation takes place at estrus. At proestrus, concomitant with the maximum rate of apoptosis, a peak in circulating levels of prolactin is observed. Prolactin can be cleaved to different N-terminal fragments, vasoinhibins, which are proapoptotic and antiproliferative factors for endothelial cells. It was reported that a 16 kDa vasoinhibin is produced in the rat anterior pituitary by cathepsin D. In the present study we investigated the anterior pituitary production of N-terminal prolactin-derived fragments along the estrous cycle and the involvement of estrogens in this process. In addition, we studied the effects of a recombinant vasoinhibin, 16 kDa prolactin, on anterior pituitary apoptosis and proliferation. We observed by Western Blot that N-terminal prolactin-derived fragments production in the anterior pituitary was higher at proestrus with respect to diestrus and that the content and release of these prolactin forms from anterior pituitary cells in culture were increased by estradiol. A recombinant preparation of 16 kDa prolactin induced apoptosis (determined by TUNEL assay and flow cytometry) of cultured anterior pituitary cells and lactotropes from ovariectomized rats only in the presence of estradiol, as previously reported for other proapoptotic factors in the anterior pituitary. In addition, 16 kDa prolactin decreased forskolin-induced proliferation (evaluated by BrdU incorporation) of rat total anterior pituitary cells and lactotropes in culture and decreased the proportion of cells in S-phase of the cell cycle (determined by flow cytometry). In conclusion, our study indicates that the anterior pituitary production of 16 kDa prolactin is variable along the estrous cycle and increased by estrogens. The antiproliferative and estradiol-dependent proapoptotic actions of this vasoinhibin may be involved in the control of anterior pituitary cell renewal.

Osteopontin is cleaved at multiple sites close to its integrin-binding motifs in milk and is a novel substrate for plasmin and cathepsin D

Osteopontin (OPN) is a highly modified integrin-binding protein present in most tissues and body fluids where it has been implicated in numerous biological processes. A significant regulation of OPN function is mediated through phosphorylation and proteolytic processing. Proteolytic cleavage by thrombin and matrix metalloproteinases close to the integrin-binding Arg-Gly-Asp sequence modulates the function of OPN and its integrin binding properties. In this study, seven N-terminal OPN fragments originating from proteolytic cleavage have been characterized from human milk. Identification of the cleavage sites revealed that all fragments contained the Arg-Gly-Asp(145) sequence and were generated by cleavage of the Leu(151)-Arg(152), Arg(152)-Ser(153), Ser(153)-Lys(154), Lys(154)-Ser(155), Ser(155)-Lys(156), Lys(156)-Lys(157), or Phe(158)-Arg(159) peptide bonds. Six cleavages cannot be ascribed to thrombin or matrix metalloproteinase activity, whereas the cleavage at Arg(152)-Ser(153) matches thrombin specificity for OPN. The principal protease in milk, plasmin, hydrolyzed the same peptide bond as thrombin, but its main cleavage site was identified to be Lys(154)-Ser(155). Another endogenous milk protease, cathepsin D, cleaved the Leu(151)-Arg(152) bond. OPN fragments corresponding to plasmin activity were also identified in urine showing that plasmin cleavage of OPN is not restricted to milk. Plasmin, but not cathepsin D, cleavage of OPN increased cell adhesion mediated by the alpha(V)beta(3)- or alpha(5)beta(1)-integrins. Similar cellular adhesion was mediated by plasmin and thrombin-cleaved OPN showing that plasmin can be a potent regulator of OPN activity. These data show that OPN is highly susceptible to cleavage near its integrin-binding motifs, and the protein is a novel substrate for plasmin and cathepsin D.

Cathepsin D is the primary protease for the generation of adenohypophyseal vasoinhibins: cleavage occurs within the prolactin secretory granules

Vasoinhibins are a family of N-terminal prolactin (PRL) fragments that inhibit blood vessel growth, dilation, permeability, and survival. The aspartyl endoprotease cathepsin D is active at acidic pH and can cleave rat PRL to generate vasoinhibins. We investigated whether and where vasoinhibins could be generated by cathepsin D in the adenohypophysis of rats and mice and whether their production could be gender dependent. Vasoinhibins were detected in primary cultures of rat adenohypophyseal cells by Western blot with antibodies directed against the N terminus of PRL but not the C terminus. Ovariectomized, estrogen-treated females show greater levels of adenohypophyseal vasoinhibins than males. Peptide sequencing analysis revealed that the cleaved form of PRL in rat adenohypophyseal extracts contains the PRL N terminus and a second N terminus starting at Ser(149), the reported cleavage site of cathepsin D in rat PRL. In addition, cathepsin D inhibition by pepstatin A reduced vasoinhibin levels in rat adenohypophyseal cell cultures. Confocal and electron microscopy showed the colocalization of cathepsin D and PRL within rat adenohypophyseal cells and secretory granules, and a subcellular fraction of rat adenohypophysis enriched in secretory granules contained cathepsin D activity able to generate vasoinhibins from PRL. Of note, vasoinhibins were absent in the adenohypophysis of mice lacking the cathepsin D gene but not in wild-type mice. These findings show that cathepsin D is the main protease responsible for the generation of adenohypophyseal vasoinhibins and that its action can take place within the secretory granules of lactotrophs.

Contribution of individual histidines to the global stability of human prolactin

A member of the family of hematopoietic cytokines human prolactin (hPRL) is a 23k kDa polypeptide hormone, which displays pH dependence in its structural and functional properties. The binding affinity of hPRL for the extracellular domain of its receptor decreases 500-fold over the relatively narrow, physiologic pH range from 8 to 6; whereas, the affinity of human growth hormone (hGH), its closest evolutionary cousin, does not. Similarly, the structural stability of hPRL decreases from 7.6 to 5.6 kcal/mol from pH 8 to 6, respectively, whereas the stability of hGH is slightly increased over this same pH range. hPRL contains nine histidines, compared with hGH's three, and they are likely responsible for hPRL's pH-dependent behavior. We have systematically mutated each of hPRL's histidines to alanine and measured the effect on pH-dependent global stability. Surprisingly, a vast majority of these mutations stabilize the native protein, by as much as 2-3 kcal/mol. Changes in the overall pH dependence to hPRL global stability can be rationalized according to the predominant structural interactions of individual histidines in the hPRL tertiary structure. Using double mutant cycles, we detect large interaction free energies within a cluster of nearby histidines, which are both stabilizing and destabilizing to the native state. Finally, by comparing the structural locations of hPRL's nine histidines with their homologous residues in hGH, we speculate on the evolutionary role of replacing structurally stabilizing residues with histidine to introduce pH dependence to cytokine function.

The role of cathepsins in involution and breast cancer

Cysteine cathepsins are proteolytic enzymes that reside in endolysosomal vesicles. Some are expressed constitutively while others are transcriptionally regulated. However, the expression and subcellular localization of cathepsins changes during cancer progression and cathepsins have been shown to be causally involved in various aspects of tumorigenesis including metastasis. The use of mouse models of breast cancer genetically ablated for cathepsin B has shown that both the growth of the primary tumor and the extend of lung metastasis is reduced by the loss of cathepsin B. The role of cathepsins in involution of the mammary gland has received little attention although it is clear that cathepsins are involved in tissue remodeling in the second phase of involution. We discuss here the roles of cathepsins and their endogenous inhibitors in breast tumorigenesis and post-lactational involution.

Cathepsin D--many functions of one aspartic protease

For years, it has been held that cathepsin D (CD) is involved in rather non-specific protein degradation in a strongly acidic milieu of lysosomes. Studies with CD knock-out mice revealed that CD is not necessary for embryonal development, but it is indispensable for postnatal tissue homeostasis. Mutation that abolishes CD enzymatic activity causes neuronal ceroid lipofuscinosis (NCL) characterized by severe neurodegeneration, developmental regression, visual loss and epilepsy in both animals and humans. In the last decade, however, an increasing number of studies demonstrated that enzymatic function of CD is not restricted solely to acidic milieu of lysosomes with important consequences in regulation of apoptosis. In addition to CD enzymatic activity, it has been shown that apoptosis is also regulated by catalytically inactive mutants of CD which suggests that CD interacts with other important molecules and influences cell signaling. Moreover, procathepsin D (pCD), secreted from cancer cells, acts as a mitogen on both cancer and stromal cells and stimulates their pro-invasive and pro-metastatic properties. Numerous studies found that pCD/CD level represents an independent prognostic factor in a variety of cancers and is therefore considered to be a potential target of anti-cancer therapy. Studies dealing with functions of cathepsin D are complicated by the fact that there are several simultaneous forms of CD in a cell-pCD, intermediate enzymatically active CD and mature heavy and light chain CD. It became evident that these forms may differently regulate the above-mentioned processes. In this article, we review the possible functions of CD and its various forms in cells and organisms during physiological and pathological conditions.

Analysis of site-specific histidine protonation in human prolactin

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

Urinary prolactin as a reliable marker for preeclampsia, its severity, and the occurrence of adverse pregnancy outcomes

CONTEXT

It has been proposed that preeclampsia may result from of an imbalance in angiogenic factors. Although prolactin (PRL) is mainly related to lactation, it is also involved in other biological functions, including angiogenesis.

OBJECTIVE

Our objective was to determine the relationship among preeclampsia, serum and urinary PRL (uPRL) levels, and excretion of antiangiogenic PRL fragments in urine.

STUDY DESIGN

Using a cross-sectional design, uPRL and serum PRL levels, and the presence of PRL isoforms were determined in 546 pregnant women: 207 healthy pregnant, 124 with gestational hypertension, 48 with mild preeclampsia, and 167 with severe preeclampsia (sPE).

RESULTS

uPRL concentrations were significantly (P < 0.001) higher in preeclampsia (11.99 ng/mg creatinine) than in healthy pregnancy (0.20 ng/mg creatinine) and gestational hypertension (0.19 ng/mg creatinine), and were even higher in sPE compared with mild preeclampsia (21.20 vs. 2.77 ng/mg creatinine, respectively; P < 0.001). Antiangiogenic PRL fragments (14-16 kDa) were detected in 21.6% of urine samples from women with sPE but in none from other groups. Patients with hemolysis, elevated liver enzymes, low platelet count syndrome, and/or eclampsia, placental abruption, acute renal failure, and pulmonary edema exhibited highest uPRL concentrations (P < or = 0.028) and frequency of antiangiogenic PRL fragments in urine (P < or = 0.036). High-serum PRL levels were associated with sPE independently of gestational age, proteinuria, and prolactinuria (P = 0.032).

CONCLUSIONS

Preeclampsia is characterized by increased uPRL excretion. uPRL concentrations and their isoforms appear to be suitable markers to assess the severity of preeclampsia and occurrence of adverse outcomes. PRL and and/or its isoforms might be involved in the pathophysiology of preeclampsia.

Role of prolactin and vasoinhibins in the regulation of vascular function in mammary gland

The formation of new blood vessels has become a major focus of mammary gland research stimulated by the therapeutic opportunities of controlling angiogenesis in breast cancer. Normal growth and involution of the mammary gland are profoundly affected by the expansion and regression of blood vessels, whereas dysregulation of angiogenesis is characteristic of breast cancer growth and metastasis. Prolactin stimulates the growth and differentiation of the mammary gland under normal conditions, but its role in breast cancer is controversial. Its action is complicated by the fact that prolactin itself is angiogenic, but proteases cleave prolactin to generate vasoinhibins, a family of peptides that act on endothelial cells to suppress angiogenesis and vasodilation and to promote apoptosis-mediated vascular regression. This review summarizes our current knowledge about the vascular effects of prolactin and the generation and action of vasoinhibins, and discusses their possible contribution to the regulation of blood vessels in the normal and malignant mammary gland.

Hyperprolactinemia and prolactinomas

Any process interfering with dopamine synthesis, its transport to the pituitary gland, or its action at the level of lactotroph dopamine receptors can cause hyperprolactinemia. As described in this article, considering the complexity of prolactin regulation, many factors could cause hyperprolactinemia, and hyperprolactinemia can have clinical effects not only on the reproductive axis. Once any drug effects are excluded, prolactinomas are the most common cause of hyperprolactinemia. The most frequent symptom is hypogonadism in both genders. Medical and surgical therapies generally have excellent results, and most prolactinomas are well controlled or even cured in some cases.

What can we learn from rodents about prolactin in humans?

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.

16-kDa prolactin inhibits endothelial cell migration by down-regulating the Ras-Tiam1-Rac1-Pak1 signaling pathway

Angiogenesis plays a key role in promoting tumorigenesis and metastasis. The 16-kDa fragment of prolactin (16k PRL) is an NH(2)-terminal natural breakdown fragment of the intact 23-kDa prolactin and has been shown to have potent antiangiogenic and antitumor activities. The mechanism(s) involved in the action of 16k PRL in endothelial cells remains unclear. In this study, we showed that 16k PRL reduced rat aortic endothelial cell (RAEC) migration in a wound-healing assay and in a Matrigel tube formation assay, suggesting that 16k PRL inhibits endothelial cell migration, an important activity involved in angiogenesis and tumorigenesis. We further investigated how 16k PRL attenuates endothelial cell migration. We first showed that RAEC migration is mediated through the Rho GTPase Rac1, as Rac1 inhibition by the Rac1-specific inhibitor NSC27366 or Rac1 knockdown by small interfering RNA both blocked RAEC migration. We next showed that 16k PRL reduced the activation of Rac1 in a concentration-dependent manner. Furthermore, 16k PRL inhibition of Rac1 is mediated through the suppression of T lymphoma invasion and metastasis 1 (Tiam1) and its upstream activator Ras in a phosphoinositide-3-kinase-independent manner. 16k PRL also down-regulated the phosphorylation of the downstream effector of Rac1, p21-activating kinase 1 (Pak1), and inhibited its translocation to the leading edge of migrating cells. Thus, 16k PRL inhibits cell migration by blocking the Ras-Tiam1-Rac1-Pak1 signaling pathway in endothelial cells.

The expression of prolactin and its cathepsin D-mediated cleavage in the bovine corpus luteum vary with the estrous cycle

In the corpus luteum (CL), blood vessels develop, stabilize, and regress. This process depends on the ratio of pro- and antiangiogenic factors, which change during the ovarian cycle. The present study focuses on the possible roles of 23,000 (23K) prolactin (PRL) in the bovine CL and its antiangiogenic NH(2)-terminal fragments after extracellular cleavage by cathepsin D (Cath D). PRL RNA and protein were demonstrated in the CL tissue, in luteal endothelial cells, and in steroidogenic cells. Cath D was detected in CL tissue, cell extracts, and corresponding cell supernatants. In the intact CL, 23K PRL levels decreased gradually, whereas Cath D levels concomitantly increased between early and late luteal stages. In vitro, PRL cleavage occurred in the presence of acidified homogenates of CL tissue, cells, and corresponding cell supernatants. Similar fragments were obtained with purified Cath D, and their appearance was inhibited by pepstatin A. The aspartic protease specific substrate MOCAc-GKPILF~FRLK(Dnp)-D-R-NH(2) was cleaved by CL cell supernatants, providing further evidence for Cath D activity. The 16,000 PRL inhibited proliferation of luteal endothelial cells accompanied by an increase in cleaved caspase-3. In conclusion, 1) the bovine CL is able to produce PRL and to process it into antiangiogenic fragments by Cath D activity and 2) PRL cleavage might mediate angioregression during luteolysis.

Reproductive role of prolactin

The biological actions of prolactin (PRL), a polypeptide hormone, are mostly related to lactation and reproduction. These actions have been clarified by studies of PRL and PRL-deficient receptor mice, which have a clear phenotype of reproductive failure at multiple sites. This review aims to summarize current knowledge about PRL and its receptor, role in reproductive axis and presents information of hyperprolactinemia in reproductive medicine. Our understanding of the physiology and transduction pathway of PRL has largely increased in the past 20 years with the cloning of PRL and its receptor gene.

Bone morphogenetic protein 1 processes prolactin to a 17-kDa antiangiogenic factor

In addition to classical expression patterns in pituitary and placenta and functions in growth and reproduction, members of the small family of hormones that includes prolactin (PRL), growth hormone (GH), and placental lactogen are expressed by endothelia and have angiogenic effects. In contrast, 16- to 17-kDa proteolytic fragments of these hormones have antiangiogenic effects. Here we show that PRL and GH are bound and processed by members of the bone morphogenetic protein 1 (BMP1) subgroup of extracellular metalloproteinases, previously shown to play key roles in forming extracellular matrix and in activating certain TGFbeta superfamily members. BMP1 has previously been suggested to play roles in angiogenesis, as high throughput screens have found its mRNA to be one of those induced to highest levels in tumor-associated endothelia compared with resting endothelia. PRL and GH cleavage is shown to occur in each hormone at a single site typical of sites previously characterized in known substrates of BMP1-like proteinases, and the approximately 17-kDa PRL N-terminal fragment so produced is demonstrated to have potent antiangiogenic activity. Mouse embryo fibroblasts are shown to produce both PRL and GH and to process them to approximately 17-kDa forms, whereas GH and PRL processing activity is lost in mouse embryo fibroblasts doubly null for two genes encoding BMP1-like proteinases.