Parathyroid hormone-related protein is produced by cultured endothelial cells: a possible role in angiogenesis

PTHrP treatment of colon cancer cells promotes tumor associated-angiogenesis by the effect of VEGF

We showed that Parathyroid Hormone-related Peptide (PTHrP) induces proliferation, migration, survival and chemoresistance via MAPKs and PI3K/AKT pathways in colorectal cancer (CRC) cells. The objective of this study was to investigate if PTHrP is also involved in tumor angiogenesis. PTHrP increased VEGF expression and the number of structures with characteristics of neoformed vessels in xenografts tumor. Also, PTHrP increased mRNA levels of VEGF, HIF-1α and MMP-9 via ERK1/2 and PI3K/Akt pathways in Caco-2 and HCT116 cells. Tumor conditioned media (TCMs) from both cell lines treated with PTHrP increases the number of cells, the migration and the tube formation in the endothelial HMEC-1 cells, whereas the neutralizing antibody against VEGF diminished this response. In contrast, PTHrP by direct treatment only increased ERK1/2 phosphorylation and the HMEC-1 cells number. These results provide the first evidence related to the mode of action of PTHrP that leads to its proangiogenic effects in the CRC.

Effects of parathyroid hormone-related peptide on the large conductance calcium-activated potassium channel and calcium homeostasis in vascular smooth muscle cells

AIM

To demonstrate the impact of the parathyroid hormone-related peptide (PTHrP) on the large conductance calcium-activated potassium (BKCa) channels in vascular smooth muscle cells (VSMC) and hyperpolarization of the cell membrane and its dependence on calcium.

MATERIALS AND METHODS

VSMC were isolated from rat aorta and further subcultured. Four experiments were conducted in calcium-release measurements and each of them consisted of a control group, PTHrP, chemical substance, and PTHrP + chemical substance. Chemical substances used were: iberiotoxin, xestospongin C, xestospongin D, and thapsigargin, respectively. Fura-2 imaging was used to determine changes in calcium release of VSMC. In membrane-potential experiments, groups were designed similarly to the Fura-2 imaging experiments: iberiotoxin, BAPTA, and xestospongin D were added, in respective order. Changes in the membrane potential were examined using the fluorescence dye (DiBAC).

RESULTS

Given in a dose between 0.01 and 1.0 μmol/L, PTHrP caused a concentration-dependent decrease in fluorescence intensity, with a maximum effect at 0.5 μmol/L. The decrease, therefore, demonstrated a PTHrP-induced hyperpolarization of the VSMC. The effect was blocked by use of iberiotoxin (100 nmol/L), a highly selective inhibitor of BKCa. Furthermore, when the calcium chelator BAPTA (10 μmol/L) was added, there was a significant reduction in PTHrP-induced hyperpolarization. Use of PTHrP (0.5 μmol/L) also decreased the fluorescence intensity of the indicator for intracellular calcium, Fura-2AM (a membrane-permeable derivative of Fura 2). This effect was re-blocked by use of iberiotoxin. Xestospongin C (3 μmol/L) and xestospongin D (6 μmol/L), both inhibitors of the inositol 1,4,5 trisphosphate-triggered calcium release, inhibited the effects of PTHrP. Additionally, thapsigargin (1 μmol/L), a sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor, inhibited the effect of PTHrP.

CONCLUSION

The results of our study show that PTHrP induces hyperpolarization and activates BKCa in VSMC. The activation of BKCa channels is calcium dependent; activation is linked to the inositol 1,4,5 trisphosphate-triggered calcium release and is also dependent on the endo/sarcoplasmic reticulum calcium pump.

Parathyroid hormone-related peptide (PTHrP), parathyroid hormone/parathyroid hormone-related peptide receptor 1 (PTHR1), and MSX1 protein are expressed in central and peripheral giant cell granulomas of the jaws

OBJECTIVE

Parathyroid hormone-related peptide (PTHrP) binds to the parathyroid hormone receptor type 1 (PTHR1), which results in the activation of pathways in osteoblasts that promote osteoclastogenesis through the RANK/RANKL system. RANK/RANKL expression has been shown in central giant cell granuloma of the jaws but PTHrP/PTHR1 has not. MSX1 protein is a classical transcription regulator which promotes cell proliferation and inhibits cell differentiation by inhibiting master genes in tissues such as bone and muscle. It has been implicated in the pathogenesis of cherubism, and its expression has been reported in a single central giant cell granuloma (CGCG) case. We aimed, therefore, to study the expression of those proteins by the different cellular populations of central and peripheral giant cell granulomas (PGCGs) of the jaws.

STUDY DESIGN

Twenty cases of CGCG and 20 cases of PGCG of the jaws were retrospectively examined by immunohistochemistry for the percentage of positively staining cells to antibodies for PTHrP, PTHR1, and MSX1, using a semiquantitative method.

RESULTS

In both CGCG and PGCG of the jaws, PTHrP and PTHR1 were abundantly expressed by type I multinucleated giant cells (MGC) and mononucleated stromal cells (MSC) with vesicular nuclei, whereas type II MGC and MSC with pyknotic nuclei expressed those proteins to a lesser extent. In both CGCG and PGCG of the jaws, MSX1 was abundantly expressed by type I MGC and MSC but type II MGC did not express it. A statistically significant difference (P < .05) was observed between CGCG and PGCG in the expression of PTHrP in type II MGC and MSC with pyknotic nuclei and in the expression of PTHR1 in type II MGC.

CONCLUSIONS

We suggest that in CGCG and PGCG of the jaws, PTHrP-positive immature osteoblasts activate PTHR1-positive mature osteoblasts to produce RANKL which interacts with RANK on the PTHrP/PTHR1-positive osteoclast-precursor cells found in abundance in the stroma of giant cell lesions and induces osteoclastogenesis through the classic pathway. Cells of the jawbones, the periodontal ligament, or the dental follicle, originating from the neural crest, may be involved in the pathogenesis of giant cell lesions of the jaws. Further study is required for these suggestions to be proved.

Tumor expressed PTHrP facilitates prostate cancer-induced osteoblastic lesions

Expression of parathyroid hormone-related protein (PTHrP) correlates with prostate cancer skeletal progression; however, the impact of prostate cancer-derived PTHrP on the microenvironment and osteoblastic lesions in skeletal metastasis has not been completely elucidated. In this study, PTHrP overexpressing prostate cancer clones were stably established by transfection of full length rat PTHrP cDNA. Expression and secretion of PTHrP were verified by western blotting and IRMA assay. PTHrP overexpressing prostate cancer cells had higher growth rates in vitro, and generated larger tumors when inoculated subcutaneously into athymic mice. The impact of tumor-derived PTHrP on bone was investigated using a vossicle co-implant model. Histology revealed increased bone mass adjacent to PTHrP overexpressing tumor foci, with increased osteoblastogenesis, osteoclastogenesis and angiogenesis. In vitro analysis demonstrated pro-osteoclastic and pro-osteoblastic effects of PTHrP. PTHrP enhanced proliferation of bone marrow stromal cells and early osteoblast differentiation. PTHrP exerted a pro-angiogenic effect indirectly, as it increased angiogenesis but only in the presence of bone marrow stromal cells. These data suggest PTHrP plays a role in tumorigenesis in prostate cancer, and that PTHrP is a key mediator for communication and interactions between prostate cancer and the bone microenvironment. Prostate cancer-derived PTHrP is actively involved in osteoblastic skeletal progression.

Skeletal metastasis: Established and emerging roles of parathyroid hormone related protein (PTHrP)

Parathyroid hormone related protein (PTHrP) is a well characterized tumor derived product that also has integral functions in normal development and homeostasis. PTHrP is produced by virtually all tumor types that metastasize to bone and numerous studies have demonstrated a correlation between PTHrP expression and skeletal localization of tumors. PTHrP has prominent effects in bone via its interaction with the PTH-1 receptor on osteoblastic cells. Through indirect means, PTHrP supports osteoclastogenesis by upregulating the receptor activator of NFkappaB ligand (RANKL) in osteoblasts. PTHrP also regulates osteoblast proliferation and differentiation in manners that are temporal and dose dependent. Bone turnover has been implicated in the localization of tumors to bone and PTHrP increases bone turnover. Bone turnover results in the release of growth factors such as TGFbeta and minerals such as calcium, both of which impact tumor cell growth and contribute to continued PTHrP production. PTHrP also has anabolic properties and could be in part responsible for osteoblastic type reactions in prostate cancer. Finally, emerging roles of PTH and PTHrP in the support of hematopoietic stem cell development in the bone marrow microenvironment suggest that an interaction between hematopoietic cells and tumor cells warrants further investigation.

N-terminal parathyroid hormone-related peptide hyperpolarizes endothelial cells and causes a reduction of the coronary resistance of the rat heart via endothelial hyperpolarization

Parathyroid hormone-related peptide (PTHrP) is known to be a strong vasorelaxant peptide. The mechanisms by which PTHrP reduces the coronary resistance of the rat heart have not been worked out but seem to be independent of the classical PTH/PTHrP receptor-mediated, cAMP-dependent effect. In this study we hypothesized that PTHrP reduces the coronary resistance of the rat heart via endothelial cell hyperpolarization. Isolated microvascular endothelial cells from rat heart were incubated with PTHrP(1-36), and changes in the membrane potential were recorded via DiBAC fluorescence. Cells exposed to PTHrP showed a hyperpolarization of approximately 7mV. In the isolated Langendorff preparation, PTHrP-dependent vasodilatation of l-nitro-arginine-exposed hearts was abolished under depolarizing conditions (high potassium). Denudation of the endothelial cell layer significantly impaired the vasodilatory effect of PTHrP. In the presence of H89 (a cAMP/protein kinase A pathway antagonist) and indomethacin (a cyclooxygenase inhibitor), PTHrP dilated the vessels. In conclusion, PTHrP exerted a nitric oxide-independent vasodilatory effect that depends on endothelial cell hyperpolarization.

An intracrine view of angiogenesis

Angiogenesis, the generation of new blood vessels from pre-existing vessels, is an integral component of wound healing, responses to inflammation and other physiologic processes. It is also an essential part of tumor growth; in the absence of new vessel formation, tumors cannot expand beyond a small volume. Although much is known about angiogenesis and its regulation, there is no overall theory that describes or explains this process. It is here suggested that the intracrine hypothesis, which ascribes to certain extracellular signaling peptides (whether hormones, growth factors, DNA-binding proteins or enzymes) a role in both intracellular biology and extracellular signaling, can contribute to a more general understanding of angiogenesis. Intracrine factors participate in angiogenesis in the following ways: (1) they can act within the cells that synthesized them (type I intracrine action), (2) they can be secreted and then taken up by their cell of synthesis to act intracellularly (type II intracrine action ), or (3) they can be secreted and internalized by a distant target cell (type III intracrine action). The parallels between the intracrine growth factor mechanisms cancer cells employ in stimulating their own growth and the mechanisms operative in endothelial cell proliferation during angiogenesis ("intracrine reciprocity") are discussed. Collectively, these explorations lead to testable hypotheses regarding the regulation of normal and pathological angiogenesis, and point to similarities between tumor-induced angiogenesis and tissue differentiation.

Women with palmoplantar pustulosis have disturbed calcium homeostasis and a high prevalence of diabetes mellitus and psychiatric disorders: a case-control study

Palmoplantar pustulosis is characterized by pustule formation in the acrosyringium. Nearly 50% of palmoplantar pustulosis sera produce immunofluorescence of the palmar papillary endothelium from healthy subjects, but also of the endothelium of normal parathyroid gland. With a case-control design the levels of calcium and parathyroid hormone in serum were measured in 60 women with palmoplantar pustulosis and 154 randomly selected population-based control women. One-third of the controls had been smokers, whereas 95% of the cases were or had been smokers. Mean age-adjusted serum calcium was increased in the patients compared with the controls (2.43 vs 2.36 mmol/l; p<0.0001), whereas the parathyroid hormone concentration was suppressed (23.2 vs 31.1 ng/l; p<0.0001). The plasma levels of parathyroid hormone-related protein were normal in patients but there was a strong expression of this protein in the acrosyringium both in palmoplantar pustulosis and control skin. As even a marginal elevation of serum calcium is associated with an increased risk for diabetes, cardiovascular disease and psychiatric disease, we analysed the risk for these disorders in palmoplantar pustulosis patients compared with that in the control group. Both diabetes mellitus and psychiatric disorders were associated with palmoplantar pustulosis with an odds ratio of 8.7 (95% CI 3.3-22.8) and 5.6 (95% CI 2.2-14.4), respectively. Palmoplantar pustulosis is a complex disease with an increased risk for several non-dermatological disorders. The role of the mildly increased serum calcium for the high risk for diabetes and depression deserves to be studied.

Parathyroid hormone-related peptide is induced by stimulation of alpha 1A-adrenoceptors and improves resistance against apoptosis in coronary endothelial cells

Parathyroid hormone-related peptide (PTHrP) is expressed throughout the vascular system, including coronary endothelial cells. The regulation of endothelial PTHrP expression and the role of PTHrP expression in endothelial cells is not clear. This study investigates the question of whether the stimulation of alpha-adrenergic or angiotensin II receptors increases endothelial expression of PTHrP and whether endogenously expressed PTHrP exerts intracrine effects in coronary endothelial cells. We found that the stimulation of alpha 1A-adrenoceptors, but not that of angiotensin II, increases cellular expression of PTHrP in growing, but not in growth-arrested, coronary endothelial cells. Angiotensin II increases the expression of PTHrP in smooth muscle cells but not in endothelial cells. PTHrP enters the nucleus of endothelial cells at the stadium of confluence, which suggests an intracrine effect of PTHrP. It was further investigated whether the down-regulation of endogenous PTHrP expression by transfection with antisense oligonucleotides alters cell proliferation or apoptosis resistance in growing or nongrowing endothelial cells. Down-regulation of PTHrP did not modify cell proliferation, but it increased the amount of UV-induced apoptosis. An increased expression of PTHrP in cells pretreated with an alpha-adrenoceptor agonist reduced the basal rate of apoptosis and improved resistance against UV-induced apoptosis. These results indicate a novel intracrine effect of PTHrP in coronary endothelial cells that improves cell survival. In endothelial cells, its expression is regulated by alpha-adrenoceptor stimulation in a cell-cycle-dependent and cell-type-specific manner.

Expression of PTHrP and its cognate receptor in the rheumatoid synovial microcirculation

Parathyroid hormone-related protein (PTHrP), a multifunctional peptide that acts as a vasodilator as well as possible regulator of vascular development, is produced in increased amounts in the rheumatoid synovium. To understand whether PTHrP can contribute to the development and function of the rheumatoid microcirculation, studies were undertaken to identify and compare vascular sites of expression of PTHrP and its cognate receptor in the rheumatoid synovium and/or in cultured rheumatoid synovial endothelial cells. Endothelial cells, including apoptotic cells, as determined by TUNEL staining, were the primary site of vascular PTHrP expression in the rheumatoid synovium, a result confirmed in vitro in rheumatoid synovial microvascular endothelial cells. In contrast, the PTH/PTHrP receptor was primarily located in pericytes and smooth muscle cells within the vasculature. These results are consistent with a possible paracrine pathway for PTHrP action in the synovial microcirculation, wherein PTHrP peptides secreted by the synovial endothelium could act on surrounding PTH1R-positive pericytes and smooth muscle cells.

Parathyroid hormone-related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so-called 'parathyroid hormone-related protein' (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N-terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly-hormone which comprises a family of distinct peptide hormones arising from post-translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N-terminal, mid-region and C-terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1-34) and PTHrP(1-36), is the only cloned receptor so far. PTHrP is a PTH-like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo-vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium-sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

Expression of parathyroid hormone-related protein in human and experimental atherosclerotic lesions: functional role in arterial intimal thickening

We investigated the expression of parathyroid hormone-related protein (PTHrP) in atherosclerotic lesions and the role of PTHrP in the development of arterial neointima formation. Immunohistochemical staining of PTHrP in the neointima of rat aorta produced by balloon injury and of rat femoral artery produced by non-obstructive polyethylene cuff placement, and in the atherosclerotic lesion of human coronary artery was performed using anti-human PTHrP-(1-34) antibody. Anti-muscle actin antibody, HHF-35, and anti-macrophage antibody, HAM-56, were used to identify smooth muscle cells and macrophages, respectively. Immunoreactivity of PTHrP was detected in the thickened intima of rat and human lesions where the predominant cell types were smooth muscle cells or macrophages dependently on the lesion type. In the next series of experiments, we examined the effect of PTHrP on the development of cuff-induced intimal thickening of rat femoral artery. Either PTHrP-(1-34) or PTHrP-(7-34), a PTH/PTHrP receptor antagonist, suspended in pluronic F-127 gel was locally applied around the rat femoral artery. Intimal thickening induced by cuff placement was evaluated 2 weeks later. PTHrP-(1-34) dose-dependently inhibited intimal thickening determined as intima/media ratio and % stenosis whereas PTHrP-(7-34) dose-dependently enhanced that. These results suggest that PTHrP, which is expressed in atherosclerotic lesions, inhibits the development of neointimal formation.

Expression, release, and biological activity of parathyroid hormone-related peptide from coronary endothelial cells

Ventricular cardiomyocytes have previously been identified as potential target cells for parathyroid hormone-related peptide (PTHrP). Synthetic PTHrP peptides exert a positive contractile effect. Because systemic PTHrP levels are normally negligible, this suggests that PTHrP is expressed in the ventricle and acts as a paracrine mediator. We investigated the ventricular expression of PTHrP and its expression in cultured cells isolated from the ventricle, studied the release of PTHrP from hearts and cultures, and investigated whether this authentic PTHrP mimics the biological effects previously described for synthetic PTHrP on ventricular cardiomyocytes. We found PTHrP expressed in ventricles of neonatal and adult rat hearts. In cells isolated from adult hearts, we found PTHrP expression exclusively in coronary endothelial cells but not in cardiomyocytes. The latter, however, are target cells for PTHrP. PTHrP was released from isolated perfused hearts during hypoxic perfusion and from cultured coronary endothelial cells under energy-depleting conditions. This PTHrP was biologically active; ie, it exerted a positive contractile and lusitropic effect on cardiomyocytes. Authentic PTHrP was glycosylated and showed a slightly higher potency than synthetic PTHrP. These results suggest that PTHrP is an endothelium-derived modulator of ventricular function.

Two human osteoblast-like osteosarcoma cell lines show distinct expression and differential regulation of parathyroid hormone-related protein

Parathyroid hormone (PTH)-related protein (PTHrP) acts as a local regulator of osteoblast function via mechanisms that involve PTH/PTHrP receptors linked to protein kinase A (PKA) and C (PKC). However, the regulation of PTHrP production and mRNA expression in human osteoblasts is poorly understood. Here we have characterized alternative PTHrP mRNA 3' splicing variants, encoding PTHrP isoforms of 139, 141, and 173 amino acids, and studied the regulation of PTHrP and its mRNAs by activated PKA and PKC in two human osteoblast-like cell lines (KPDXM and TPXM). Using exon-specific Northern analysis and reverse transcriptase-coupled polymerase chain reaction, we identified mRNAs encoding PTHrP(1-139) and PTHrP(1-141) in both cell lines. PTHrP(1-139) mRNAs predominated in TPXM cells and PTHrP(1-173) mRNAs were only detected in TPXM cells. Activation of PKA or PKC resulted in different effects on PTHrP and its mRNAs in the two cell lines. In TPXM cells, peptide-specific immunoassays detected high basal levels of PTHrP, increasing by 2-fold in cell extracts and 4-fold in culture media at 7 h and 24 h after exposure to forskolin, respectively, paralleling changes in PTHrP mRNA expression. Phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA), a PKC activator, had no effect. In KPDXM cells, PTHrP was not detected in culture media under basal experimental conditions, and barely detectable amounts were present in cell extracts of TPA-treated cells, although the mRNA levels increased substantially in response to TPA. In the responsive cell lines, the effects on mRNA levels were dose dependent, and increased by 6.9- to 10.5-fold and 2.0- to 4.1-fold at 4 h in TPXM and KPDXM cells after exposure to 10 microM forskolin and 150 nM TPA, respectively. PTHrP mRNA levels then declined but were sustained above controls also at 12 h in both cell lines, albeit at considerably higher levels in TPXM cells. The different responsiveness to agents activating PKA- and PKC-dependent pathways may depend on the cellular state of differentiation, or alternatively, cancer cell line-specific defects. Our data demonstrating distinct differences in mRNA species and the amounts of PTHrP produced by the two cell lines as compared with roughly equivalent overall mRNA levels may suggest that post-transcriptional mechanisms play an important role in limiting the production of intracellular and secreted PTHrPs in human osteoblastic cells.

Mechanical stretch increases secretion of parathyroid hormone-related protein by cultured bladder smooth muscle cells

Parathyroid hormone-related protein (PTHrP) immunoreactivity has been detected in the bladder and increases in response to dilatation secondary to obstruction. The hypothesis that PTHrP could be increased solely by stretch rather than other possible in vivo variables was tested by stretching cultured bladder smooth muscle cells and analyzing the culture medium for this protein. In response to mechanical stretch, PTHrP was increased in smooth muscle cell cultures. Immunoradiometric assay revealed maximal rates of secretion for the first eight hours. Comparison of percent change in PTHrP secretion of flexed cells for the various flex parameters revealed a difference (p = .006) when the degree of stretch (i.e. percent elongation) was altered. The protein synthesis inhibitor cycloheximide inhibited basal and stretch-induced PTHrP secretion. PTHrP (1-100 nM) relaxed carbachol-contracted bladder body and base by 15% and 45% respectively. PTHrP did not affect bladder contractions induced by potassium (124 mM) or alpha-beta MeATP (10 microM). Increased PTHrP secretion in response to stretch of smooth muscle raises the possibility of an autocrine action to relax the bladder during filling. PTHrP may also exert a paracrine action on vessels regulating blood flow during bladder filling or it may modulate neural activity.

Mechanical stretch increases secretion of parathyroid hormone-related protein by cultured bladder smooth muscle cells

Parathyroid hormone-related protein (PTHrP) immunoreactivity has been detected in the bladder and increases in response to dilatation secondary to obstruction. The hypothesis that PTHrP could be increased solely by stretch rather than other possible in vivo variables was tested by stretching cultured bladder smooth muscle cells and analyzing the culture medium for this protein. In response to mechanical stretch, PTHrP was increased in smooth muscle cell cultures. Immunoradiometric assay revealed maximal rates of secretion for the first eight hours. Comparison of percent change in PTHrP secretion of flexed cells for the various flex parameters revealed a difference (p = .006) when the degree of stretch (i.e. percent elongation) was altered. The protein synthesis inhibitor cycloheximide inhibited basal and stretch-induced PTHrP secretion. PTHrP (1-100 nM) relaxed carbachol-contracted bladder body and base by 15% and 45% respectively. PTHrP did not affect bladder contractions induced by potassium (124 mM) or alpha-beta MeATP (10 microM). Increased PTHrP secretion in response to stretch of smooth muscle raises the possibility of an autocrine action to relax the bladder during filling. PTHrP may also exert a paracrine action on vessels regulating blood flow during bladder filling or it may modulate neural activity.

Cytokine-induced expression of parathyroid hormone-related peptide in cultured human vascular endothelial cells

Parathyroid hormone-related peptide (PTHrP) is a potent vasodilatory peptide whose expression has been demonstrated in various tissues. The present study was undertaken to examine the regulation of PTHrP expression in cultured endothelial cells derived from human umbilical vein. Immunoradiometric assay revealed that the amount of PTHrP in the conditioned medium was increased by both tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) in both a time- and a dose-dependent manner. The induction of PTHrP mRNA was also observed, with a peak after 2 hours of incubation with both TNF-alpha and IL-1beta. Angiotensin II, endothelin-1, and arginine vasopressin had no affect on PTHrP production. Our results suggest that PTHrP produced in vascular endothelial cells in response to cytokines may modulate vascular function as a local factor.

Expression of parathyroid hormone/parathyroid hormone-related protein receptor in vascular endothelial cells

The parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor has been reported to be expressed in many tissues, including vascular smooth-muscle cells (VSMCs), but it has not been identified in vascular endothelial cells. To determine whether vascular endothelial cells can express the PTH/PTHrP receptor, its gene expression was examined in simian virus 40-transformed rat lung vascular endothelial cells (TRLECs) by the reverse-transcription polymerase chain reaction (RT-PCR). Results in TRLEC, with rat VSMCs and kidney as controls, showed identical 741-bp products. Furthermore, incubation with PTHrP[1-34] reduced the thrombin-stimulated endothelin-1 (ET-1) expression in TRLECs. Our results demonstrate that vascular endothelial cells can express the PTH/PTHrP receptor and therefore are also a target tissue for PTHrP.

Amino-terminal fragment (1-34) of parathyroid hormone-related protein inhibits migration and proliferation of cultured vascular smooth muscle cells

We investigated the effects of amino-terminal fragment (1-34) of parathyroid hormone-related protein [PTHrP-(1-34)] on the migration and proliferation of vascular smooth muscle cells (VSMCs). Cultured VSMCs (5-9th passage) obtained from the aortas of male Wistar rats were used in this study. Migration of VSMCs was assessed using a modified Boyden's chamber. Proliferation of VSMCs was evaluated by measuring [3H]thymidine incorporation and counting cell numbers. PTHrP-(1-34) inhibited 10% fetal bovine serum (FBS)-induced increase in migration of VSMCs (61% of control at 1 micromol/l) in a concentration-dependent manner. PTHrP-(1-34) also inhibited 5% FBS-induced increase in [3H]thymidine incorporation (37% of control at 1 micromol/l) and cell number of VSMCs (33% of control at 1 micromol/l) in a concentration-dependent manner. Parathyroid hormone (PTH)-(1-34) inhibited the migration and DNA synthesis of VSMCs to a similar extent. PTHrP-(7-34), a PTH/PTHrP receptor antagonist, significantly inhibited these effects of PTHrP and PTH. PTHrP-(1-34) also inhibited platelet-derived growth factor-BB (5 ng/ml)-induced migration and DNA synthesis of VSMCs. These findings suggest that PTHrP-(1-34) inhibits the migration and proliferation of VSMCs through PTH/PTHrP receptors.

Cardiovascular actions of parathyroid hormone and parathyroid hormone-related peptide

Cardiovascular cells (cardiomyocytes and smooth muscle cells) are target cells for parathyroid hormone (PTH) and the structurally related peptide parathyroid hormone-related peptide (PTH-rP). PTH activates protein kinase C (PKC) of cardiomyocytes via a PKC activating domain previously identified on chondrocytes. Activation of PKC leads to hypertrophic growth and re-expression of fetal type proteins in cardiomyocytes. This hypertrophic effect of PTH might contribute to left ventricular hypertrophy in hemodialysis patients with secondary hyperparathyroidism. PTH-rP is expressed in cardiovascular cells (endothelial cells and smooth muscle cells). It does not mimic the above described actions of PTH but exerts effects of its own on cardiomyocytes. These effects involve activation of protein kinase A, via a N-terminal domain distinct from that identified on PTH, and activation of PKC, via a C-terminally located domain distinct from that found on PTH. On smooth muscle cells PTH and PTH-rP reduce the influence of extracellular calcium, through cAMP-dependent mechanisms. These inhibitory effects on voltage-dependent L-type calcium channels of smooth muscle cells cause vasorelaxation. Present studies concerning cardiovascular actions of either PTH and PTH-rP suggest that increased plasma levels of PTH and PTH-rP influence cardiomyocyte and smooth muscle cell physiology. It can be assumed that PTH-rP acts as a paracrine or autocrine modulator in heart and vessels.

Parathyroid hormone-related protein upregulates interleukin-1beta-induced nitric oxide synthesis

The effect of parathyroid hormone-related protein on interleukin-1beta-induced nitric oxide production was studied in rat vascular smooth muscle cells. Interleukin-1beta time- and dose-dependently enhanced the production of nitrite, a stable metabolite of nitric oxide. Parathyroid hormone-related protein(1-34) alone up to 10(-7) mol/L had no obvious effect, but significantly increased the cytokine-induced nitrite production. RNA analysis revealed that the synergistic effect of parathyroid hormone-related protein(1-34) resulted from a potentiation of the expression of inducible nitric oxide synthase and GTP-cyclohydrolase I, the rate-limiting enzyme in the synthesis of tetrahydrobiopterin, which is a cofactor of nitric oxide synthase. The increased nitric oxide release induced by interleukin-1beta or interleukin-1beta with parathyroid hormone-related protein(1-34) was completely inhibited by coincubation with 3x10(-3) mol/L N(G)-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthase, or with 10(-3) mol/L 2,4-diamino-6-hydroxypyrimidine, an inhibitor of GTP-cyclohydrolase I. Endothelin-1 potentiated interleukin-1beta induction of nitric oxide, which might be mediated by endogenous parathyroid hormone-related protein. Neutralization of exogenous or endogenous parathyroid hormone-related protein with antibody attenuated the synergistic effect of parathyroid hormone-related protein, but did not affect interleukin-1beta induction of nitric oxide. These results suggest that locally produced parathyroid hormone-related protein acts as a synergistic regulator upregulating interleukin-1beta-induced nitric oxide synthesis in the cardiovascular system, and thereby may affect vascular tone and/or vascular remodeling after vascular injury in some pathological processes such as atherosclerosis and hypertension.

Vascular effects of PTHrP (1-34) and PTH (1-34) in the human fetal-placental circulation

The aim of this study was to examine the vasodilatory effects of parathyroid hormone-related protein (PTHrP) (1-34) and parathyroid hormone (PTH) (1-34) on the human fetal-placental circulation utilising an in vitro placental perfusion model. In all experiments, the vasculature of an isolated human placental cotyledon was pre-constricted with the thromboxane A2 mimetic U46619. A simple dose of PTHrP (1-34) or PTH (1-34) (1.7-300 nM) was then infused into the fetal-placental circulation of the cotyledon. In other experiments, cotyledons were repeatedly infused with PTHrP (1-34) or PTH (1-34) (51.3 nM). Vasodilatory responses were significantly reduced in response to repeated exposure to PTHrP (1-34) (P < 0.001), indicating that this peptide desensitizes the fetal-placental vasculature. PTHrP (1-34) and PTH (1-34) equipotently stimulated a significant vasodilation of the fetal-placental circulation (P < 0.0001). The PTHrP receptor antagonist [Asn10, Leu 11]PTHrP (7-34) (102 nM) was infused in U46619-constricted placentae in the presence and absence of PTHrP (1-34) (10.2 nM). The PTHrP antagonist alone had no significant effect in the fetal-placental circulation. The antagonist significantly attenuated the response to PTHrP (1-34) (P < 0.015). Based on the data obtained in this study it is suggested that locally produced PTHrP (1-34) may be involved in the regulation of normal human fetal-placental vascular tone in autocrine and/or paracrine fashion.

Parathyroid hormone-related protein inhibits indothelin-1 production

The effect of human parathyroid hormone-related protein, a powerful vasodilator, on endothelin-1 production in cultured bovine pulmonary arterial endothelial cells was studied. Treatment with parathyroid hormone-related protein(1-34) at concentrations of 10(-9) to 10(-6) mol/L for 24 hours caused dose-dependent suppression of the secretion of endothelin-1, with maximal suppression at 10(-7) mol/L to 74% of the control value. This inhibitory effect was completely abolished by coincubation with 100 ng/mL pertussis toxin, an inhibitor of GTP binding protein. Furthermore, addition of Ng-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, at 10(-3) mol/L significantly blocked the suppressive effect of parathyroid hormone-related protein (1-34) on endothelin-1 secretion, and further addition of 5x10(-3) mol/L L-arginine significantly attenuated the blocking effect of N(G)-monomethyl-L-arginine. Parathyroid hormone-related protein (1-34) at 10(-7) mol/L resulted in an approximately fivefold increase in intracellular cGMP level. Northern blot analysis revealed that parathyroid hormone-related protein (1-34) inhibited both basal and thrombin-induced endothelin-1 gene expression. These findings suggest that the vasodilating property of parathyroid hormone-related protein may be mediated in part through its inhibitory effect on endothelin-1 production, which is probably mediated through nitric oxide and cGMP in endothelial cells. Thus, a feedback regulatory mechanism may exist between parathyroid hormone-related protein and endothelin-1 in the vascular wall.

Distribution and functions of parathyroid hormone-related protein in vertebrate cells

Parathyroid hormone-related protein (PTHrP) was isolated from tumors and identified as the agent of humoral hypercalcemia of malignancy (HHM) in 1987. Since then its gene structure in several mammalian and an avian species has been analyzed and its gene expression demonstrated in many adult and embryonic tissues derived from all three germ layers. The composition and structure of PTHrP peptide depends on both differential gene splicing and posttranslational processing, which result in a range of peptides of potentially diverse functions. This chapter describes the distribution of PTHrP in both normal and neoplastic adult and embryonic tissues. PTHrP is of fundamental importance to cell survival because the absence of the gene is fatal; this aspect of PTHrP function in cell physiology becomes overwhelmingly important in neoplasia. Intracrine or paracrine actions for PTHrP seem to be most likely in mammalian and avian physiology, but in fishes high circulating levels suggest classic endocrine functions as well. Much remains to be learned of the biology of this fascinating protein.

Inhibition of processing of parathyroid hormone-related peptide by anti-sense furin: effect in vitro and in vivo on rat Leydig (H-500) tumor cells

To attain full biological activity, the precursor pro-parathyroid hormone-related peptide (ProPTHRP) must be converted to the mature peptide PTHRP. We have examined the effect of inhibiting expression of the pro-hormone convertase furin in H-500 rat Leydig tumor cells on PTHRP production and action in vitro and in vivo. H-500 Leydig tumor cells were stably transfected with a mammalian expression plasmid containing furin cDNA in an anti-sense orientation. This resulted in inhibition of endogenous furin mRNA expression and of protein production as assessed by immunocytochemistry. These experimental cells secreted extended NH2-terminal PTHRP forms with reduced adenylate cyclase-stimulating activity. This was associated with a marked decrease in the proliferation of these tumor cells in vitro. Transfected and control cells were then implanted into male Fischer rats. Animals implanted with control cells became hypercalcemic. In contrast, animals implanted with experimental cells maintained near normal levels of plasma calcium. Experimental cells inoculated in vivo developed into tumors of significantly decreased volume compared to control cells and animal survival time was prolonged. Our results indicate that alteration of the processing of PTHRP can diminish the hypercalcemic endocrine actions of PTHRP and can reduce autocrine/paracrine effects of PTHRP on tumor cell growth both in vitro and in vivo. Furin may also exert a broader role in processing other factors required for tumor proliferation. Consequently, anti-sense modulation of furin activity may be a potential modality for understanding the mechanism of neoplastic growth and progression.

Interleukin-1 beta and interleukin-4 increase parathyroid hormone-related protein secretion by human umbilical vein endothelial cells in culture

OBJECTIVE

Our purpose was to learn whether cytokines such as interleukin-1 beta and related (or antagonistic) cytokines, hormones, and growth factors could regulate secretion of the vasorelaxant parathyroid hormone-related protein in human umbilical vein endothelial cells in culture.

STUDY DESIGN

Secondary cultures of human umbilical vein endothelial cells were grown to confluence and treated with interleukin-1 beta, an array of factors with possible regulatory actions (cytokines, growth factors, vasoactive peptides, and steroids), and a phorbol ester as a stimulatory control. After 24 hours immunoreactive parathyroid hormone-related peptide in the media was measured by a two-site sandwich radioimmunoassay. The mechanism of interleukin-1 beta action was probed with interleukin-1 beta receptor antagonist and selected inhibitors.

RESULTS

Interleukin-1 beta (10 ng/ml) produced up to an eightfold increase in parathyroid hormone-related peptide secretion from human umbilical vein endothelial cells in culture (p < 0.01). Half-maximal stimulation was seen at 0.23 ng/ml. Interleukin-1 receptor antagonist, cycloheximide, and actinomycin D blocked the effects of interleukin-1 beta (p < 0.05). Interleukin-4 at 10 ng/ml and phorbol 12-myristate 13-acetate at 10(-7) mol/L significantly increased the secretion of parathyroid hormone-related peptide by human umbilical vein endothelial cells (p < 0.05). The time course of each interleukin showed an effect beyond 12 hours. The effects of interleukin-1 beta and interleukin-4 appeared to be specific, because a large series of related interleukins and other growth factors and cytokines were without effect.

CONCLUSION

Interleukin-1 beta and interleukin-4 increase parathyroid hormone-related protein secretion in human umbilical vein endothelial cells in culture. Because interleukin-1 beta messenger ribonucleic acid has been found in umbilical cord endothelial cells, we propose that the umbilical cord has a novel vasorelaxant regulatory system that uses interleukin-1 beta endothelial action and secretion of the vasorelaxant parathyroid hormone-related peptide.