Cathepsin D Processes Human Prolactin into Multiple 16K-Like N-Terminal Fragments: Study of Their Antiangiogenic Properties and Physiological Relevance

Prolactin: A Mammalian Stress Hormone and Its Role in Cutaneous Pathophysiology

The hormone prolactin (PRL) is best recognised for its indispensable role in mammalian biology, specifically the regulation of lactation. Bearing in mind that the mammary gland is a modified sweat gland, it is perhaps unsurprising to discover that PRL also plays a significant role in cutaneous biology and is implicated in the pathogenesis of a range of skin diseases, often those reportedly triggered and/or exacerbated by psychological stress. Given that PRL has been implicated in over 300 biological processes, spanning reproduction and hair growth and thermo- to immunoregulation, a comprehensive understanding of the relationship between PRL and the skin remains frustratingly elusive. In an historical curiosity, the first hint that PRL could affect skin biology came from the observation of seborrhoea in patients with post-encephalitic Parkinsonism as a result of another global pandemic, encephalitis lethargica, at the beginning of the last century. As PRL is now being postulated as a potential immunomodulator for COVID-19 infection, it is perhaps timeous to re-examine this pluripotent hormone with cytokine-like properties in the cutaneous context, drawing together our understanding of the role of PRL in skin disease to illustrate how targeting PRL-mediated signalling may represent a novel strategy to treat a range of skin diseases and hair disorders.

Vasoinhibin's Apoptotic, Inflammatory, and Fibrinolytic Actions Are in a Motif Different From Its Antiangiogenic HGR Motif

Vasoinhibin, a proteolytic fragment of the hormone prolactin, inhibits blood vessel growth (angiogenesis) and permeability, stimulates the apoptosis and inflammation of endothelial cells, and promotes fibrinolysis. The antiangiogenic and antivasopermeability properties of vasoinhibin were recently traced to the HGR motif located in residues 46 to 48 (H46-G47-R48), allowing the development of potent, orally active, HGR-containing vasoinhibin analogues for therapeutic use against angiogenesis-dependent diseases. However, whether the HGR motif is also responsible for the apoptotic, inflammatory, and fibrinolytic properties of vasoinhibin has not been addressed. Here, we report that HGR-containing analogues are devoid of these properties. Instead, the incubation of human umbilical vein endothelial cells with oligopeptides containing the sequence HNLSSEM, corresponding to residues 30 to 36 of vasoinhibin, induced apoptosis, nuclear translocation of NF-κB, expression of genes encoding leukocyte adhesion molecules (VCAM1 and ICAM1) and proinflammatory cytokines (IL1B, IL6, and TNF), and adhesion of peripheral blood leukocytes. Also, intravenous or intra-articular injection of HNLSSEM-containing oligopeptides induced the expression of Vcam1, Icam1, Il1b, Il6, and Tnf in the lung, liver, kidney, eye, and joints of mice and, like vasoinhibin, these oligopeptides promoted the lysis of plasma fibrin clots by binding to plasminogen activator inhibitor-1 (PAI-1). Moreover, the inhibition of PAI-1, urokinase plasminogen activator receptor, or NF-κB prevented the apoptotic and inflammatory actions. In conclusion, the functional properties of vasoinhibin are segregated into 2 different structural determinants. Because apoptotic, inflammatory, and fibrinolytic actions may be undesirable for antiangiogenic therapy, HGR-containing vasoinhibin analogues stand as selective and safe agents for targeting pathological angiogenesis.

Cathepsin D Attenuates the Proliferation of Vascular Smooth Muscle Cells Induced by the AGE/RAGE Pathway by Suppressing the ERK Signal

BACKGROUND

In this study, we aimed to clarify the role and mechanism by which Cathepsin D (CTSD) mediates the advanced glycation end products (AGEs)-induced proliferation of vascular smooth muscle cells (VSMCs).

METHODS

We conducted a Western blotting assay and co-immunoprecipitation assay to detect the expression of target proteins and the interaction between different proteins. Cell Counting Kit-8 (CCK-8) assay and 5- ethynyl-2'-deoxyuridine (EdU) were used to evaluate the proliferation.

RESULTS

AGEs significantly promoted phenotypic switching and proliferation of VSMCs in a concentration-dependent manner. This effect of AGEs was accompanied by inhibition of CTSD. Both the proliferation of VSMCs and inhibition of CTSD induced by AGEs could be attenuated by the specific inhibitor of the receptor for advanced glycation end products (RAGE), FPS-ZM1. Overexpression of CTSD significantly alleviated these effects of AGEs on VSMCs. The mechanism of CTSD action in VSMCs was also explored. Overexpression of CTSD reduced the activation of p-ERK caused by AGEs. By contrast, the knockdown of CTSD, elicited using a plasmid containing short hairpin RNA (shRNA) against CTSD, further increased the activation of p-ERK compared to AGEs alone. Additionally, co-immunoprecipitation studies revealed an endogenous interaction between CTSD, a protease, and p-ERK, its potential substrate.

CONCLUSION

It has been demonstrated that CTSD downregulates the level of phosphorylated ERK by degrading its target, and this interaction plays a critical role in the proliferation of VSMCs induced by the AGE/RAGE axis. These results provide a novel insight into the prevention and treatment of vascular complications in diabetes.

Cathepsin D Inhibits Angiogenesis in Pituitary Neuroendocrine Tumors

Prolactin and growth hormone can acquire anti-angiogenic properties after undergoing proteolytic cleavage by Cathepsin D and bone morphogenetic protein 1 (BMP-1) into fragments known as vasoinhibins. Little is known about the effect of vasoinhibins on angiogenesis through the involvement of key cleavage enzymes Cathepsin D and BMP-1 in pituitary neuroendocrine tumors (PitNETs, formerly pituitary adenomas). The purpose of this study was to investigate the mechanism of action of Cathepsin D and BMP-1 on angiogenesis in PitNETs compared with that of pro-angiogenic factors, including vascular endothelial growth factor (VEGF) and basic fibroblast growth factor-2 (FGF2). A total of 43 patients were enrolled in a retrospective analysis and 22 samples were suitable for RNA extraction, including 16 nonfunctional PitNETs and six somatotroph tumors. The mRNA and protein levels of Cathepsin D, BMP-1, VEGF, and FGF2 were compared with those of von Willebrand factor, which was assessed to determine the vascularization of PitNETs. Cathepsin D and FGF2 were significantly correlated with vascularization in PitNETs. Both Cathepsin D and FGF2 are highly involved in angiogenesis in PitNETs, although the effect of Cathepsin D as an anti-angiogenic factor is dominant over that of FGF2 as a pro-angiogenic factor.

New horizons in specific hormone proteolysis

Proteolysis of protein hormones is primarily acknowledged in the context of breakdown and metabolic clearance by hepatorenal elimination. However, less explored is the specific proteolytic processing of large protein hormones, for which canonical signaling pathways were already established [e.g., prolactin (PRL)], to generate unique messengers that impact cellular functions via pathways unrelated to the receptors of their precursor molecules. Yet, the proteolysis of PRL to generate new messengers evolved under positive selection, and cleaved protein hormones regulate essential functions to maintain homeostasis at the organismal, tissue, or organ levels. The cleavage sites at which proteolysis occurs and the proteases with their determinants define a hormone-metabolism junction at which specific proteolytic cleavage, pathological alteration, and hepatorenal elimination occur.

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.

Vasoinhibin is Generated and Promotes Inflammation in Mild Antigen-induced Arthritis

Inflammatory arthritis defines a family of diseases influenced by reproductive hormones. Vasoinhibin, a fragment of the hormone prolactin (PRL), has antiangiogenic and proinflammatory properties. We recently showed that vasoinhibin reduces joint inflammation and bone loss in severe antigen-induced arthritis (AIA) by an indirect mechanism involving the inhibition of pannus vascularization. This unexpected finding led us to hypothesize that a severe level of inflammation in AIA obscured the direct proinflammatory action of vasoinhibin while allowing the indirect anti-inflammatory effect via its antiangiogenic properties. In agreement with this hypothesis, here we show that the intra-articular injection of an adeno-associated virus type-2 vector encoding vasoinhibin reduced joint inflammation in a severe AIA condition, but elevated joint inflammation in a mild AIA model. The proinflammatory effect, unmasked in mild AIA, resulted in joint swelling, enhanced leukocyte infiltration, and upregulation of expression of genes encoding proinflammatory mediators (Il1b, Il6, Inos, Mmp3), adhesion molecule (Icam1), and chemokines (Cxcl1, Cxcl2, Cxcl3, Ccl2). Furthermore, vasoinhibin induced the expression of proinflammatory mediators and chemokines in cultured synovial fibroblasts through nuclear factor-κB. Finally, matrix metalloproteases and cathepsin D, upregulated in the arthritic joint, cleaved PRL to vasoinhibin, and vasoinhibin levels increased in the circulation of mice subjected to AIA. We suggest that vasoinhibin is generated during inflammatory arthritis and acts on synovial fibroblasts and endothelial cells to initially promote and later inhibit inflammation, respectively. These opposite effects may work together to help keep joint inflammation under balance.

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.

Complement Proteins C5/C5a, Cathepsin D and Prolactin in Chondrocytes: A Possible Crosstalk in the Pathogenesis of Osteoarthritis

Introduction: Both increased activity of the complement system (CS) and the role of the pituitary hormone prolactin (PRL) are implicated in osteoarthritis (OA) pathogenesis. Besides, Cathepsin D (CatD) activity is increased in the context of OA and can exert not only proteolytic but also non-proteolytic effects on cells. For the first time, possible crosstalk between two separate humoral systems: the CS and the PRL hormone systems in chondrocytes are examined together. Methods: Primary human articular chondrocytes (hAC) were stimulated with complement protein C5 (10 µg /mL), PRL (25 ng/mL), CatD (100 ng/mL), or anaphylatoxin C5a (25 ng/mL) for 24 h or 72 h, while unstimulated cells served as controls. In addition, co-stimulations of C5 or PRL with CatD were carried out under the same conditions. The influence of the stimulants on cell viability, cell proliferation, and metabolic activity of hAC, the chondrosarcoma cell line OUMS-27, and endothelial cells of the human umbilical cord vein (HUVEC) was investigated. Gene expression analysis of C5a receptor (C5aR1), C5, complement regulatory protein CD59, PRL, PRL receptor (PRLR), CatD, and matrix metal-loproteinases (MMP)-13 were performed using real-time PCR. Also, collagen type (Col) I, Col II, C5aR1, CD59, and PRL were detected on protein level using immunofluorescence labeling. Results: The stimulation of the hAC showed no significant impairment of the cell viability. C5, C5a, and PRL induced cell growth in OUMS-27 and HUVEC, but not in chondrocytes. CatD, as well as C5, significantly reduced the gene expression of CatD, C5aR1, C5, and CD59. PRLR gene expression was likewise impaired by C5, C5a, and PRL+CatD stimulation. On the protein level, CatD, as well as C5a, decreased Col II as well as C5aR1 synthesis. Conclusions: The significant suppression of the C5 gene expression under the influence of PRL+CatD and that of CD59 via PRL+/−CatD and conversely a suppression of the PRLR gene expression via C5 alone or C5a stimulation indicates an interrelation between the two mentioned systems. In addition, CatD and C5, in contrast to PRL, directly mediate possible negative feedback of their own gene expression.

Human Placental Tissue Contains a Placental Lactogen Derived Vasoinhibin

Hormonal factors affecting the vascular adaptions of the uteroplacental unit in noncomplicated and complicated pregnancies are of interest. Here, 4 human placentas from women with and without preeclampsia (PE) were investigated for the presence of placental lactogen (PL)-derived, antiangiogenic vasoinhibin. Western blotting and mass spectrometry of placental tissue revealed the presence of a 9-kDa PL-derived vasoinhibin, the normal 22-kDa full-length PL, and a 28-kDa immunoreactive protein of undetermined nature. The sequence of the 9-kDa vasoinhibin includes the antiangiogenic determinant of vasoinhibin and could constitute a relevant factor in normal pregnancy and PE.

Pathophysiology and risk factors of peripartum cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a potentially fatal form of idiopathic heart failure with variable prevalence across different countries and ethnic groups. The cause of PPCM is unclear, but environmental and genetic factors and pregnancy-associated conditions such as pre-eclampsia can contribute to the development of PPCM. Furthermore, animal studies have shown that impaired vascular and metabolic function might be central to the development of PPCM. A better understanding of the pathogenic mechanisms involved in the development of PPCM is necessary to establish new therapies that can improve the outcomes of patients with PPCM. Pregnancy hormones tightly regulate a plethora of maternal adaptive responses, including haemodynamic, structural and metabolic changes in the cardiovascular system. In patients with PPCM, the peripartum period is associated with profound and rapid hormonal fluctuations that result in a brief period of disrupted cardiovascular (metabolic) homeostasis prone to secondary perturbations. In this Review, we discuss the latest studies on the potential pathophysiological mechanisms of and risk factors for PPCM, with a focus on maternal cardiovascular changes associated with pregnancy. We provide an updated framework to further our understanding of PPCM pathogenesis, which might lead to an improvement in disease definition.

Dual Roles of Prolactin and Vasoinhibin in Inflammatory Arthritis

The term inflammatory arthritis defines a family of diseases, including rheumatoid arthritis (RA), caused by an overactive immune system, and influenced by host aspects including sex, reproductive state, and stress. Prolactin (PRL) is a sexually dimorphic, reproductive, stress-related hormone long-linked to RA under the general assumption that it aggravates the disease. However, this conclusion remains controversial since PRL has both negative and positive outcomes in RA that may depend on the hormone circulating levels, synthesis by joint tissues, and complex interactions at the inflammatory milieu. The inflamed joint is rich in matrix metalloproteases that cleave PRL to vasoinhibin, a PRL fragment with proinflammatory effects and the ability to inhibit the hyperpermeability and growth of blood vessels. This review addresses this field with the idea that explanatory mechanisms lie within the PRL/vasoinhibin axis, an integrative framework influencing not only the levels of systemic and local PRL, but also the proteolytic conversion of PRL to vasoinhibin, as vasoinhibin itself has dual actions on joint inflammation. In this review, we discuss recent findings from mouse models suggesting the upregulation of endogenous vasoinhibin by the pro-inflammatory environment and showing dichotomous actions and signaling mechanisms of PRL and vasoinhibin on joint inflammation that are cell-specific and context-dependent. We hypothesize that these opposing actions work together to balance the inflammatory response and provide new insights for understanding the pathophysiology of RA and the development of new treatments.

Thrombin Cleaves Prolactin Into a Potent 5.6-kDa Vasoinhibin: Implication for Tissue Repair

Vasoinhibin is an endogenous prolactin (PRL) fragment with profibrinolytic, antivasopermeability, and antiangiogenic effects. The fact that blood clotting, vascular permeability, and angiogenesis are functionally linked during the wound-healing process led us to investigate whether thrombin, a major protease in tissue repair, generates vasoinhibin. Here, we have incubated human PRL with thrombin and analyzed the resulting proteolytic products by Western blot, mass spectrometry, high-performance liquid chromatography purification, recombinant production, and bioactivity. We unveil a main thrombin cleavage site at R48-G49 that rapidly (< 10 minutes) generates a 5.6-kDa fragment (residues 1-48) with full vasoinhibin activity, that is, it inhibited the proliferation, invasion, and permeability of cultured endothelial cells and promoted the lysis of a fibrin clot in plasma with a similar potency to that of a conventional 14-kDa vasoinhibin (residues 1-123). The R48-G49 cleavage site is highly conserved throughout evolution and precedes the intramolecular disulfide bond (C58-C174), thereby allowing the 5.6-kDa vasoinhibin to be released without a reduction step. Furthermore, the 5.6-kDa vasoinhibin is produced by endogenous thrombin during the clotting process. These findings uncover the smallest vasoinhibin known, add thrombin to the list of PRL-cleaving proteases generating vasoinhibin, and introduce vasoinhibin as a thrombin-activated mechanism for the regulation of hemostasis, vasopermeability, and angiogenesis in response to tissue injury.

Plasmin generates vasoinhibin-like peptides by cleaving prolactin and placental lactogen

Vasoinhibin is an antiangiogenic, profibrinolytic peptide generated by the proteolytic cleavage of the pituitary hormone prolactin by cathepsin D, matrix metalloproteinases, and bone morphogenetic protein-1. Vasoinhibin can also be generated when placental lactogen or growth hormone are enzymatically cleaved. Here, it is investigated whether plasmin cleaves human prolactin and placental lactogen to generate vasoinhibin-like peptides. Co-incubation of prolactin and placental lactogen with plasmin was performed and analyzed by gel electrophoresis and Western blotting. Mass spectrometric analyses were carried out for sequence validation and precise cleavage site identification. The cleavage sites responsible for the generation of the vasoinhibin-like peptides were located at K170-E171 in prolactin and R160-T161 in placental lactogen. Various genetic variants of the human prolactin and placental lactogen genes are projected to affect proteolytic generation of the vasoinhibin-like peptides. The endogenous counterparts of the vasoinhibin-like peptides generated by plasmin may represent vasoinhibin-isoforms with inhibitory effects on vasculature and coagulation.

Sex Differences in Renal Function: Participation of Gonadal Hormones and Prolactin

Kidney pathophysiology is influenced by gender. Evidence suggests that kidney damage is more severe in males than in females and that sexual hormones contribute to this. Elevated prolactin concentration is common in renal impairment patients and is associated with an unfavorable prognosis. However, PRL is involved in the osmoregulatory process and promotes endothelial proliferation, dilatation, and permeability in blood vessels. Several proteinases cleavage its structure, forming vasoinhibins. These fragments have antagonistic PRL effects on endothelium and might be associated with renal endothelial dysfunction, but its role in the kidneys has not been enough investigated. Therefore, the purpose of this review is to describe the influence of sexual dimorphism and gonadal hormones on kidney damage, emphasizing the role of the hormone prolactin and its cleavage products, the vasoinhibins.

Short prolactin isoforms are expressed in photoreceptors of canine retinas undergoing retinal degeneration

Prolactin (PRL) hormone functions as a pleiotropic cytokine with a protective role in the retina. We recently identified by transcriptome profiling that PRL is one of the most highly upregulated mRNAs in the retinas of mutant rcd1 (PDE6B) and xlpra2 (RPGR) dogs at advanced stages of photoreceptor disease. In the present study, we have identified the expression of a short PRL isoform that lacks exon 1 in canine retinas and analyzed the time-course of expression and localization of this isoform in the retinas of these two models. Using laser capture microdissection to isolate RNA from each of the retinal cellular layers, we found by qPCR that this short PRL isoform is expressed in photoreceptors of degenerating retinas. We confirmed by in situ hybridization that its expression is localized to the outer nuclear layer and begins shortly after the onset of disease at the time of peak photoreceptor cell death in both models. PRL protein was also detected only in mutant dog retinas. Our results call for further investigations into the role of this novel PRL isoform in retinal degeneration.

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.

Sequence optimization and glycosylation of vasoinhibin: Pitfalls of recombinant production

Vasoinhibin belongs to a family of proteins with antiangiogenic properties derived by proteolytic cleavage from the hormone prolactin (PRL). Vasoinhibin isoforms range from the first 79 to the first 159 residues of PRL. In an attempt to increase the yield of recombinant vasoinhibin and avoid incorrect intra- and inter-disulfide bond formation, the cDNA sequence comprising the first 123 amino acids of human PRL, in which cysteine 58 was or not mutated to serine, was codon-optimized. The optimized constructs achieved a 6-fold increase in mRNA expression but showed no change in protein production and reduced protein secretion when expressed in human embryo kidney (HEK293T/17) cells. Limited vasoinhibin levels associated with the activation of the unfolded protein response (UPR) and endoplasmic reticulum-associated degradation (ERAD) as revealed by the upregulation of UPR (Bip, Xbp-1, and Chop) and ERAD (Hrd1, Os9, and Sel1l) target genes. Mutation to serine introduced a new N-glycosylation site and associated with increased glycosylation and release of glycosylated vasoinhibin isoforms having reduced antiangiogenic properties. We conclude that overexpression and excessive glycosylation lead to protein degradation and reduced bioactivity, respectively, negatively affecting the production of recombinant vasoinhibin in mammalian cells.

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.

Vasoinhibin Suppresses Nerve Growth Factor-Induced Differentiation and Survival of PC12 Pheochromocytoma Cells

BACKGROUND

Vasoinhibin, a protein derived from prolactin, regulates various vascular functions including endothelial cell survival. Of note, vasoinhibin is present in the central nervous system, where it triggers neuroendocrine and behavioral responses to stress. Moreover, vasoinhibin compromises nerve growth factor (NGF)-induced neurite outgrowth in primary sensory neurons of the peripheral nervous system. Nonetheless, information on the functions of vasoinhibin in developing neurons remains limited. The present study explored whether vasoinhibin affects the neurotrophic actions of NGF by measuring the cell differentiation and survival of PC12 pheochromocytoma cells.

METHODS

The effects of recombinant or lentiviral vector-transduced human vasoinhibin were tested on differentiating PC12 cells. Neurite outgrowth was quantified by measuring their length and density. The MTT assay was employed to assess cell viability, and ELISA was used to quantify DNA fragmentation as an index of apoptosis. Phosphorylated Akt and ERK1/2 were analyzed by Western blotting.

RESULTS

The addition of a human recombinant vasoinhibin, and the transduction of a lentiviral vector carrying a human vasoinhibin sequence, significantly reduced NGF-induced neurite outgrowth, cell survival, and phosphorylation of Akt and ERK1/2, and increased DNA fragmentation and caspase 3 activation in PC12 cells.

CONCLUSIONS

Vasoinhibin downregulates NGF-induced differentiation and survival of PC12 cells, blocking tropomyosin receptor kinase A-triggered signaling pathways and increasing apoptosis. These results establish that vasoinhibin interaction with NGF and other neurotrophins may be critical in mediating pathways involved in neuronal survival and differentiation.

Vasoinhibin comprises a three-helix bundle and its antiangiogenic domain is located within the first 79 residues

Vasoinhibin belongs to a family of angiogenesis inhibitors generated when the fourth α-helix (H4) of the hormone prolactin (PRL) is removed by specific proteolytic cleavage. The antiangiogenic properties are absent in uncleaved PRL, indicating that conformational changes create a new bioactive domain. However, the solution structure of vasoinhibin and the location of its bioactive domain are unknown. Molecular dynamic simulation (MD) showed that the loss of H4 exposes the hydrophobic nucleus of PRL and leads to the compression of the molecule into a three-helix bundle that buries the hydrophobic nucleus again. Compression occurs by the movement of loop 1 (L1) and its interaction with α-helix 1 (H1) generating a new L1 conformation with electrostatic and hydrophobic surfaces distinct from those of PRL, that may correspond to a bioactive domain. Consistent with this model, a recombinant protein containing the first 79 amino acids comprising H1 and L1 of human PRL inhibited the proliferation and migration of endothelial cells and upregulated the vasoinhibin target genes, IL1A and ICAM1. This bioactivity was comparable to that of a conventional vasoinhibin having the 123 residues encompassing H1, L1, Η2, L2, and Η3 of human PRL. These findings extend the vasoinhibin family to smaller proteins and provide important structural information, which will aid in antiangiogenic drug development.

Somatolactogens and diabetic retinopathy

IMPORTANCE

Diabetic retinopathy (DR) is one of the most common of all diabetic complications. The number of people with DR in the United States is expected to increase to 16 million by 2050. DR is the leading cause of blindness among working-age adults in many different countries, including the United States. In later DR stages, neovascularization is associated with extensive retinal capillary non-perfusion and vitreo-proliferation leading to retinal detachment. This neovascularization is orchestrated by an imbalance of growth factors in the retina from which somatolactogens (pituitary growth hormone, GH-N; placental growth hormone, GH-V; prolactin, PRL; and placental lactogen, PL, also referred as chorionic somatomammotropin, CSH), may play an important role.

OBSERVATIONS

Somatolactogens are a group of hormones that share many structural and functional features. They are important for physiological changes in pregnancy, for adequate development of the fetus, and in the case of GH-N, for promoting growth after birth. GH-N is synthesized by the anterior pituitary, GH-V and PL are secreted by the placenta, whereas, PRL is synthesized by the anterior pituitary and uterine decidua. However, in recent years the expression of GH-N and PRL and their receptors have been detected in other tissues including the retina, acting as neuroprotective and pro-angiogenic agents. The relationship of GH-N and diabetic retinopathy (DR) was established many years ago when it was observed that its deficiency was related to regression of DR while an increase in serum levels of GH-N, GH-V, and PL promoted DR. While more studies are needed to define the potential implications of GH-V and PL in DR pathogenesis, it has been demonstrated that GH-N and PRL participate in DR by enhancing neovascularization. Some PRL isoforms, however, have shown an anti-angiogenic activity rather than pro-angiogenesis and appears to be PRL's main role in the regulation of retinal vasculature.

CONCLUSIONS

Somatolactogens are a group of hormones with a significant role in neuroprotection and angiogenesis regulation in the eye. Understanding the mechanisms of angiogenesis regulation by somatolactogens will potentially lead to the development of new drugs for DR.

16 kDa vasoinhibin binds to integrin alpha5 beta1 on endothelial cells to induce apoptosis

Many functions of vasoinhibins have been reported, but its receptor has not been clarified yet. Vasoinhibins, 11-18 kDa N-terminal fragments of prolactin, have anti-angiogenic activity and act on endothelial cells to induce apoptosis and to inhibit migration and proliferation, which are opposite to the effects of prolactin. Although vasoinhibins bind to the prolactin receptor, its binding activity is very weak compared to prolactin. Therefore, in this study, we evaluated the binding activity between 16 kDa vasoinhibin and integrin beta1, alpha5 beta1, alpha1 beta1 and alphaV beta3 to identify a specific receptor for vasoinhibins. Moreover, we examined whether 16 kDa vasoinhibin induced apoptosis through integrin beta1 and alpha5 beta1 in endothelial cells. In this study, binding assays and co-immunoprecipitation experiments demonstrated that 16 kDa vasoinhibin could bind strongly to integrin beta1 and alpha5 beta1. Moreover, neutralizing with integrin beta1 and alpha5 beta1 antibody could inhibit 16 kDa vasoinhibin-induced apoptosis in endothelial cells. These findings suggest that vasoinhibins can act on endothelial cells through integrin alpha5 beta1 to induce apoptosis.

Higher prolactin and vasoinhibin serum levels associated with incidence and progression of retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity (ROP) is a potentially blinding, retinal neovascular disease. Systemic prolactin accesses the retina to regulate blood vessels. Prolactin is proangiogenic and can be cleaved to antiangiogenic vasoinhibins. We investigated whether circulating prolactin and vasoinhibins associate with incidence and progression of ROP.

METHODS

A prospective, longitudinal, case-control study covering postnatal weeks 1 to 9 measured serum prolactin, vasoinhibins, and vascular endothelial growth factor (VEGF) weekly in 90 premature infants diagnosed as ROP or control.

RESULTS

Prolactin levels were higher in ROP than in control patients before (106.2 ± 11.3 (SEM) vs. 64.7 ± 4.9 ng/ml, postnatal week 1) and during (120.6 ± 10 vs. 84.7 ± 7.5ng/ml, postnatal week 5) ROP diagnosis. Prolactin, but not gestational age, birth weight, Apgar score, sepsis, or ventilation time, correlated with ROP. The relative risk (RR) of developing ROP increased if Prolactin (PRL) levels were higher than thresholds of 80 ng/ml (RR = 1.55, 95% CI: 1.06-2.28), 100 ng/ml (RR = 1.63, 95% CI: 1.14-2.34), or 120 ng/ml (RR = 1.95, 95% CI: 1.41-2.68). Vasoinhibin levels were 39.7% higher (95% CI: 4.5-77.5) in the circulation of ROP than in control patients at postnatal week 1 and similar thereafter, whereas VEGF serum levels were always similar.

CONCLUSION

High serum prolactin and vasoinhibin levels predict and may impact ROP progression.

From Bench to Bedside: Translating the Prolactin/Vasoinhibin Axis

The prolactin/vasoinhibin axis defines an endocrine system, in which prolactin (PRL) and vasoinhibins regulate blood vessel growth and function, the secretion of other hormones, inflammatory and immune processes, coagulation, and behavior. The core element of the PRL/vasoinhibin axis is the generation of vasoinhibins, which consists in the proteolytic cleavage of their precursor molecule PRL. Vasoinhibins can interact with multiple different partners to mediate their effects in various tissues and anatomical compartments, indicating their pleiotropic nature. Based on accumulating knowledge about the PRL/vasoinhibin axis, two clinical trials were initiated, in which vasoinhibin levels are the target of therapeutic interventions. One trial investigates the effect of levosulpiride, a selective dopamine D2-receptor antagonist, on retinal alterations in patients with diabetic macular edema and retinopathy. The rationale of this trial is that the levosulpiride-induced hyperprolactinemia resulting in increased retinal vasoinhibins could lead to beneficiary outcomes in terms of a vasoinhibin-mediated antagonization of diabetes-induced retinal alterations. Another trial investigated the effect of bromocriptine, a dopamine D2-receptor agonist, for the treatment of peripartum cardiomyopathy. The rationale of treatment with bromocriptine is the inhibition of vasoinhibin generation by substrate depletion to prevent detrimental effects on the myocardial microvascularization. The trial demonstrated that bromocriptine treatment was associated with a high rate of left ventricular recovery and low morbidity and mortality. Therapeutic interventions into the PRL/vasoinhibin axis bear the risk of side effects in the areas of blood coagulation, blood pressure, and alterations of the mental state.

Human Prolactin Point Mutations and Their Projected Effect on Vasoinhibin Generation and Vasoinhibin-Related Diseases

BACKGROUND

A dysregulation of the generation of vasoinhibin hormones by proteolytic cleavage of prolactin (PRL) has been brought into context with diabetic retinopathy, retinopathy of prematurity, preeclampsia, pregnancy-induced hypertension, and peripartum cardiomyopathy. Factors governing vasoinhibin generation are incompletely characterized, and the composition of vasoinhibin isoforms in human tissues or compartments, such as the circulation, is unknown. The aim of this study was to determine the possible contribution of PRL point mutations to the generation of vasoinhibins as well as to project their role in vasoinhibin-related diseases.

METHODS

Prolactin sequences, point mutations, and substrate specificity information about the PRL cleaving enzymes cathepsin D, matrix metalloproteinases 8 and 13, and bone-morphogenetic protein 1 were retrieved from public databases. The consequences of point mutations in regard to their possible effect on vasoinhibin levels were projected on the basis of a score indicating the suitability of a particular sequence for enzymatic cleavage that result in vasoinhibin generation. The relative abundance and type of vasoinhibin isoforms were estimated by comparing the relative cleavage efficiency of vasoinhibin-generating enzymes.

RESULTS

Six point mutations leading to amino acid substitutions in vasoinhibin-generating cleavage sites were found and projected to either facilitate or inhibit vasoinhibin generation. Four mutations affecting vasoinhibin generation in cancer tissues were found. The most likely composition of the relative abundance of vasoinhibin isoforms is projected to be 15 > 17.2 > 16.8 > 17.7 > 18 kDa vasoinhibin.

CONCLUSION

Prolactin point mutations are likely to influence vasoinhibin levels by affecting the proteolysis efficiency of vasoinhibin-generating enzymes and should be monitored in patients with vasoinhibin-related diseases. Attempts to characterize vasoinhibin-related diseases should include the 15, 17.2, 16.8, 17.7, and 18 kDa vasoinhibin isoforms.

Principles of the prolactin/vasoinhibin axis

The hormonal family of vasoinhibins, which derive from the anterior pituitary hormone prolactin, are known for their inhibiting effects on blood vessel growth, vasopermeability, and vasodilation. As pleiotropic hormones, vasoinhibins act in multiple target organs and tissues. The generation, secretion, and regulation of vasoinhibins are embedded into the organizational principle of an axis, which integrates the hypothalamus, the pituitary, and the target tissue microenvironment. This axis is designated as the prolactin/vasoinhibin axis. Disturbances of the prolactin/vasoinhibin axis are associated with the pathogenesis of retinal and cardiac diseases and with diseases occurring during pregnancy. New phylogenetical, physiological, and clinical implications are discussed.

A positive feedback loop between prolactin and STAT5 promotes angiogenesis

The signal transduction events that orchestrate cellular activities required for angiogenesis remain incompletely understood. We and others recently described that proangiogenic mediators such as fibroblast growth factors can activate members of the signal transducers and activators of transcription (STAT) family. STAT5 activation is necessary and sufficient to induce migration, invasion and tube formation of endothelial cells. STAT5 effects on endothelial cells require the secretion of the prolactin (PRL) family member proliferin-1 (PLF1) in mice and PRL in humans. In human endothelial cells, PRL activates the PRL receptor (PRLR) resulting in MAPK and STAT5 activation, thus closing a positive feedback loop. In vivo, endothelial cell-derived PRL is expected to combine with PRL of tumor cell and pituitary origin to raise the concentration of this polypeptide hormone in the tumor microenvironment. Thus, PRL may stimulate tumor angiogenesis via autocrine, paracrine, and endocrine pathways. The disruption of tumor angiogenesis by interfering with PRL signaling may offer an attractive target for therapeutic intervention.

Prolactin-Stat5 signaling in breast cancer is potently disrupted by acidosis within the tumor microenvironment

INTRODUCTION

Emerging evidence in estrogen receptor-positive breast cancer supports the notion that prolactin-Stat5 signaling promotes survival and maintenance of differentiated luminal cells, and loss of nuclear tyrosine phosphorylated Stat5 (Nuc-pYStat5) in clinical breast cancer is associated with increased risk of antiestrogen therapy failure. However, the molecular mechanisms underlying loss of Nuc-pYStat5 in breast cancer remain poorly defined.

METHODS

We investigated whether moderate extracellular acidosis of pH 6.5 to 6.9 frequently observed in breast cancer inhibits prolactin-Stat5 signaling, using in vitro and in vivo experimental approaches combined with quantitative immunofluorescence protein analyses to interrogate archival breast cancer specimens.

RESULTS

Moderate acidosis at pH 6.8 potently disrupted signaling by receptors for prolactin but not epidermal growth factor, oncostatin M, IGF1, FGF or growth hormone. In breast cancer specimens there was mutually exclusive expression of Nuc-pYStat5 and GLUT1, a glucose transporter upregulated in glycolysis-dependent carcinoma cells and an indirect marker of lactacidosis. Mutually exclusive expression of GLUT1 and Nuc-pYStat5 occurred globally or regionally within tumors, consistent with global or regional acidosis. All prolactin-induced signals and transcripts were suppressed by acidosis, and the acidosis effect was rapid and immediately reversible, supporting a mechanism of acidosis disruption of prolactin binding to receptor. T47D breast cancer xenotransplants in mice displayed variable acidosis (pH 6.5 to 6.9) and tumor regions with elevated GLUT1 displayed resistance to exogenous prolactin despite unaltered levels of prolactin receptors and Stat5.

CONCLUSIONS

Moderate extracellular acidosis effectively blocks prolactin signaling in breast cancer. We propose that acidosis-induced prolactin resistance represents a previously unrecognized mechanism by which breast cancer cells may escape homeostatic control.

Placental ischemia induces changes in gene expression in chorionic tissue

Preeclampsia is a serious and common hypertensive complication of pregnancy, affecting ~5 to 8 % of pregnancies. The underlying cause of preeclampsia is believed to be placental ischemia, which causes secretion of pathogenic factors into the maternal circulation. While a number of these factors have been identified, it is likely that others remain to be elucidated. Here, we have utilized a relevant preclinical rodent model of placental ischemia-induced hypertension, the reduced uterine perfusion pressure (RUPP) model, to determine the effect of chronic placental ischemia on the underlying chorionic tissue and placental villi. Tissue from control and RUPP rats were isolated on gestational day 19 and mRNA from these tissues was subjected to microarray analysis to determine differential gene expression. At a statistical cutoff of p < 0.05, some 2,557 genes were differentially regulated between the two groups. Interestingly, only a small subset (22) of these genes exhibited changes of greater than 50 % versus control, a large proportion of which were subsequently confirmed using qRT-PCR analysis. Network analysis indicated a strong effect on inflammatory pathways, including those involving NF-κB and inflammatory cytokines. Of the most differentially expressed genes, the predominant gene classes were extracellular remodeling proteins, pro-inflammatory proteins, and a coordinated upregulation of the prolactin genes. The functional implications of these novel factors are discussed.

Preparation of human serum for prolactin measurement by multiple reaction monitoring mass spectrometry

The measurement of the protein hormone prolactin (PRL) in biological samples has developed over the years into a routine clinical assay aiding the diagnosis of multiple medical conditions. PRL is known to exist in multiple isoforms circulating throughout the body. Current methodologies for measuring the PRL levels typically involve a variety of immunoassays. However, most of these tests are not capable of distinguishing between the different isoforms. To address this need, we have developed a highly specialized method employing multiple reaction monitoring mass spectrometry (MRM-MS) capable of monitoring seven distinct peptides from two of the most common prolactin isoforms (the 23 kDa PRL and its 16 kDa N-terminal cleavage product). Since serum is the main source of clinical specimen for the measurement of prolactin isoforms, the method described in this chapter is focused on the approach to processing whole serum samples for prolactin analysis via reversed-phase liquid chromatography (RPLC) and MRM-MS.

Prolactin actions

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

STAT5 and prolactin participate in a positive autocrine feedback loop that promotes angiogenesis

We have shown previously that the murine prolactin/growth hormone family member proliferin plays a pivotal role in angiogenesis induced by the FGF2/STAT5 signaling cascade. To delineate the signaling pathway downstream of STAT5 in the human system, where proliferin does not exist, we expressed constitutively active (CA) or dominant-negative (DN) mutant STAT5A in hCMEC/D3 human brain endothelial cells. We found that conditioned medium from CA-STAT5A- but not from DN-STAT5A-overexpressing endothelial cells (EC) is sufficient to induce EC migration and tube formation but not proliferation, indicating that STAT5A regulates the secretion of autocrine proangiogenic factors. We identified prolactin (PRL) as a candidate autocrine factor. CA-STAT5A expression stimulates PRL production at the RNA and protein level, and STAT5A binds to the PRL promoter region, suggesting direct transcriptional regulation. Medium conditioned by CA-STAT5A-overexpressing EC induces phosphorylation of the PRL receptor and activates MAPK. Knockdown of PRL expression by shRNA or blocking of PRL activity with neutralizing antibodies removed the CA-STAT5A-dependent proangiogenic activity from the conditioned medium of EC. The addition of recombinant PRL restores this activity. STAT5A-induced PRL in the conditioned medium can activate STAT5, STAT1, and to a lesser extent STAT3 in hCMEC/D3 cells, suggesting the existence of a positive feedback loop between STAT5 and PRL that promotes angiogenesis. Furthermore, we find that VEGF, a potent proangiogenic factor, is induced by activation of STAT5A, and VEGF induction depends on PRL expression. These observations demonstrate a STAT5/PRL/VEGF signaling cascade in human brain EC and implicate PRL and VEGF as autocrine regulators of EC migration, invasion, and tube formation.

Characterization of Δ7/11, a functional prolactin-binding protein

Prolactin is essential for normal mammary gland development and differentiation, and has been shown to promote tumor cell proliferation and chemotherapeutic resistance. Soluble isoforms of the prolactin receptor (PrlR) have been reported to regulate prolactin bioavailability by functioning as 'prolactin-binding proteins'. Included in this category is Δ7/11, a product of alternate splicing of the PrlR primary transcript. However, the direct interactions of prolactin with Δ7/11, and the resulting effect on cell behavior, have not been investigated. Herein, we demonstrate the ability of Δ7/11 to bind prolactin using a novel proximity ligation assay and traditional immunoprecipitation techniques. Biochemical analyses demonstrated that Δ7/11 was heavily glycosylated, similar to the extracellular domain of the primary PrlR, and that glycosylation regulated the cellular localization and secretion of Δ7/11. Low levels of Δ7/11 were detected in serum samples of healthy volunteers, but were undetectable in human milk samples. Expression of Δ7/11 was also detected in six of the 62 primary breast tumor biopsies analyzed; however, no correlation was found with Δ7/11 expression and tumor histotype or other patient demographics. Functional analysis demonstrated the ability of Δ7/11 to inhibit prolactin-induced cell proliferation as well as alter prolactin-induced rescue of cell cycle arrest/early senescence events in breast epithelial cells. Collectively, these data demonstrate that Δ7/11 is a novel regulatory mechanism of prolactin bioavailability and signaling.

16-kDa prolactin and bromocriptine in postpartum cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening heart disease emerging toward the end of pregnancy or in the first postpartal months in previously healthy women. Recent data suggest a central role of unbalanced peri-/postpartum oxidative stress that triggers the proteolytic cleavage of the nursing hormone prolactin (PRL) into a potent antiangiogenic, proapoptotic, and proinflammatory 16-kDa PRL fragment. This notion is supported by the observation that inhibition of PRL secretion by bromocriptine, a dopamine D2-receptor agonist, prevented the onset of disease in an animal model of PPCM and by first clinical experiences where bromocriptine seem to exert positive effects with respect to prevention or treatment of PPCM patients. Here, we highlight the current state of knowledge on diagnosis of PPCM, provide insights into the biology and pathophysiology of 16-kDa PRL and bromocriptine, and outline potential consequences for the clinical management and treatment options for PPCM patients.

Effects of prokinetic drugs on the abdominal wall wound healing of rats submitted to segmental colectomy and colonic anastomosis

PURPOSE

To assess the effect of prokinetic agents on abdominal wall wound healing in rats submitted to segmental colectomy and colonic anastomosis.

METHODS

Sixty rats were randomly allocated into three groups according to the agents they would receive in the postoperative period: M (metoclopramide); B (bromopride); and C (control, saline 0.9%). Surgical procedures were performed identically in all animals, and consisted of a midline laparotomy followed by resection of a 1-cm segment of large bowel with end-to-end anastomosis. The abdominal wall was closed in two layers with running stitches. Abdominal wall samples were collected on the 3rd or 7th postoperative day for measurement of breaking (tensile) strength and histopathological assessment.

RESULTS

There were no statistically significant differences in tensile strength of the abdominal wall scar between groups M, B, and C, nor between the three and seven days after surgery subgroups. On histopathological assessment, there were no statistically significant between-group differences in collagen deposition or number of fibroblasts at the wound site

CONCLUSION

Use of the prokinetic drugs metoclopramide or bromopride had no effect on abdominal wall healing in rats submitted to segmental colectomy and colonic anastomosis.

16 kDa prolactin reduces angiogenesis, but not growth of human breast cancer tumors in vivo

Prolactin (PRL) is a peptide hormone necessary for normal growth and development of the human breast. In addition, high levels of PRL in plasma correlate with increased risk of breast cancer, especially among postmenopausal women. Several isoforms of PRL exist in human circulation, including a 16 kDa isoform that is an N-terminal fragment of the full-length 23 kDa PRL. 16 kDa PRL has been shown to be anti-angiogenic in vitro and in vivo, and to reduce formation of tumors from prostate, colon and melanoma cancer cell lines. Here we explore the effect of 16 kDa PRL expression in vitro and in vivo using two breast cancer cell line models (MCF-7 and MDA-MB-231) and also the HCT-116 colon cancer cell line. In all three cell lines, 16 kDa PRL expression inhibited cell proliferation in vitro compared to empty vector controls. In vivo results were markedly different between the two types of cell lines. HCT-116 cells expressing 16 kDa PRL exhibited reduced vascularization and tumor formation, consistent with published results. The breast cancer cell lines expressing 16 kDa PRL also exhibited inhibition of angiogenesis in vivo but no reduction in tumor size or formation. These results suggest that the effects of 16 kDa PRL on tumor formation may vary across tissue types. The unique sensitivity of breast cancer to PRL as a mitogen and/or additional factors in the mammary gland environment (e.g. local hormone/mitogen concentration) may play a dominant role in tumor formation in vivo, thus outweighing the anti-angiogenesis effects and in vitro reduction in cell proliferation induced by 16 kDa PRL.

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.

Cleaved bovine prolactin-related protein-I stimulates vascular endothelial cell proliferation

Prolactin-related protein-I (PRP1) is a member of a non-classical prolactin (PRL)/growth hormone family in cattle. However, its function is still unknown. PRL, when cleaved by cathepsin D and matrix metalloproteinases (MMPs), resulted in cleaved N-terminal 16kDa fragments (16K-PRL) that have antiangiogenetic properties in human and rodents. We examined the possibility of similar activity of bovine PRP1. PRP1 (normally 33kDa) was cleaved by cathepsins (CTSs), MMPs, and bovine cotyledonary-conditioned medium (BCCM), and generated mainly 26kDa N-terminal fragments. Two specific enzyme families, CTSs and MMPs cleaved intact PRP1, and BCCM also contained PRP1 cleavage activity. Bioactivity for pro- or anti-angiogenesis of the cleaved PRP1 was examined in a cell proliferation assay using bovine brain vascular endothelial cells. The cleaved PRP1 proliferated the endothelial cells in vitro. The endothelial cell proliferation activity of cleaved PRP1 may be shared in specific bovine placentomal angiogenesis.

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.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.