Glucocorticoid regulation of parathyroid hormone-related peptide gene transcription in a human neuroendocrine cell line

A Case of Hypercalcemia from PTHrP-Producing Fibromyxoid Sarcoma Responsive to Glucocorticoid Therapy

The treatment of parathyroid hormone-related protein (PTHrP)-mediated hypercalcemia of malignancy includes treating the malignancy, intravenous fluids, and anti-resorptive therapies such as zoledronic acid or denosumab. PTHrP-mediated hypercalcemia has been reported in benign conditions such as systemic lupus erythematous (SLE) and sarcoidosis and appears to be responsive to glucocorticoids. We report a case of PTHrP-induced hypercalcemia due to a malignancy-low grade fibromyxoid sarcoma-that responded to glucocorticoid treatment. This is the first report of glucocorticoids controlling PTHrP-mediated hypercalcemia of malignancy. Immunohistochemistry of the surgical pathology localized PTHrP staining to the vascular endothelial cells within the tumor. Further studies are needed to elucidate the mechanism of glucocorticoid action in the treatment of PTHrP-mediated hypercalcemia of malignancy.

Wild-type and specific mutant androgen receptor mediates transcription via 17β-estradiol in sex hormone-sensitive cancer cells

We previously encountered regulatory processes wherein dihydrotestosterone (DHT) exerted its inhibitory effect on parathyroid hormone‐related protein (PTHrP) gene repression through the estrogen receptor (ER)α, but not the androgen receptor (AR), in breast cancer MCF‐7 cells. Here, we investigated whether such aberrant ligand‐nuclear receptor (NR) interaction is present in prostate cancer LNCaP cells. First, we confirmed that LNCaP cells expressed large amounts of AR at negligible levels of ERα/β or progesterone receptor. Both suppression of PTHrP and activation of prostate‐specific antigen genes were observed after independent administration of 17β‐estradiol (E2), DHT, or R5020. Consistent with the notion that the LNCaP AR lost its ligand specificity due to a mutation (Thr‐Ala877), experiments with siRNA targeting the respective NR revealed that the AR monopolized the role of the mediator of shared hormone‐dependent regulation, which was invariably associated with nuclear translocation of this mutant AR. Microarray analysis of gene regulation by DHT, E2, or R5020 disclosed that more than half of the genes downstream of the AR (Thr‐Ala877) overlapped in the LNCaP cells. Of particular interest, we realized that the AR (wild‐type [wt]) and AR (Thr‐Ala877) were equally responsible for the E2‐AR interactions. Fluorescence microscopy experiments demonstrated that both EGFP‐AR (wt) and EGFP‐AR (Thr‐Ala877) were exclusively localized within the nucleus after E2 or DHT treatment. Furthermore, reporter assays revealed that some other cancer cells exhibited aberrant E2‐AR (wt) signaling similar to that in the LNCaP cells. We herein postulate the presence of entangled interactions between wt AR and E2 in certain hormone‐sensitive cancer cells. J. Cell. Physiol. 230: 1594–1606, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Negative regulation of parathyroid hormone-related protein expression by steroid hormones

Elevated parathyroid hormone-related protein (PTHrP) is responsible for humoral hypercalcemia of malignancy (HHM), which is of clinical significance in treatment of terminal patients with malignancies. Steroid hormones were known to cause suppression of PTHrP expression. However, detailed studies linking multiple steroid hormones to PTHrP expression are lacking. Here we studied PTHrP expression in response to steroid hormones in four cell lines with excessive PTHrP production. Our study established that steroid hormones negatively regulate PTHrP expression. Vitamin D receptor, estrogen receptor α, glucocorticoid receptor, and progesterone receptor, were required for repression of PTHrP expression by the cognate ligands. A notable exception was the androgen receptor, which was dispensable for suppression of PTHrP expression in androgen-treated cells. We propose a pathway(s) involving nuclear receptors to suppress PTHrP expression.

The parathyroid hormone family of peptides: structure, tissue distribution, regulation, and potential functional roles in calcium and phosphate balance in fish

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are two factors that share amino acid sequence homology and act via a common receptor. In tetrapods, PTH is the main endocrine factor acting in bone and kidney to regulate calcium and phosphate. PTHrP is an essential paracrine developmental factor present in many tissues and is involved in the regulation of ossification, mammary gland development, muscle relaxation, and other functions. Fish apparently lack an equivalent of the parathyroid gland and were long thought to be devoid of PTH. Only in recent years has the existence of PTH-like peptides and their receptors in fish been firmly established. Two forms of PTH, two of PTHrP, and a protein with intermediate characteristics designated PTH-L are encoded by separate genes in teleost fish. Three receptors encoded by separate genes in fish mediate PTH/PTHrP actions, whereas only two receptors have so far been found in terrestrial vertebrates. PTHrP has been more intensively studied than PTH, from lampreys to advanced teleosts. It is expressed in many tissues and is present in high concentration in fish blood. Administration of this peptide alters calcium metabolism and has marked effects on associated gene expression and enzyme activity in vivo and in vitro. This review provides a comprehensive overview of the physiological roles, distribution, and molecular relationships of the piscine PTH-like peptides.

Cortisol and parathyroid hormone-related peptide are reciprocally modulated by negative feedback

In previous in vitro studies, we have shown that the N-terminal region of parathyroid hormone-related protein (PTHrP) can stimulate cortisol production in sea bream, Sparus auratus, interrenal tissue, possibly through a paracrine action. In the current study, the systemic interaction between cortisol and PTHrP was studied in vivo. Sustained elevated blood cortisol levels, induced either by cortisol injection or confinement stress, suppressed circulating PTHrP 6 and 24-fold, respectively, by comparison to control fish. Dexamethasone treatment reduced cortisol levels, prevented the decrease of plasma PTHrP observed in confined fish and raised plasma PTHrP levels in non-confined fish. In contrast, a single injection of (1-34) PTHrP caused a short-term (within 30 min and up to 2.5 h) decrease in plasma cortisol. The antagonistic effects between PTHrP and cortisol were substantiated by an overall (data pooled from all experiments) highly significant negative correlation (r0=-0.745, p<0.001, n=115) between the plasma levels of the two hormones. Although the underlying mechanism of the interaction still has to be determined, the high levels of PTHrP in circulation and the existence of systemic regulation favour the hypothesis that in fish PTHrP may act as an endocrine factor, although the gland that produces it still remains to be identified.

PTHrP stimulated by the calcium-sensing receptor requires MAP kinase activation

Increases in extracellular calcium concentration ([Ca(2+)](o)) stimulate from normal and malignant cells secretion of parathroid hormone-related protein (PTHrP), a major mediator of humoral hypercalcemia of malignancy. Because the calcium-sensing receptor (CaR) is a determinant of calcium-regulated hormone secretion, we examined whether HEK cells stably transfected with human CaR secreted PTHrP in response to CaR stimulation. Increases in [Ca(2+)](o) or neomycin and Gd(3+) all substantially increased PTHrP secretion in CaR-HEK cells but had no effect on nontransfected cells. CaR activation likewise increased PTHrP transcripts. PD-098059 and U-0126, inhibitors of the mitogen-activated protein kinase kinase MEK1/2, abolished CaR-stimulated secretion but had no effect on basal secretion. An inhibitor of p38 MAP kinase, SB-203580, also attenuated CaR-stimulated secretion. Western analysis revealed that CaR activation caused a robust increase in MEK1/2 and p38 MAP kinase phosphorylation. A Src family kinase inhibitor, PP2, blocked both basal and CaR-stimulated secretion. We conclude that CaR specifically mediates the effect of increasing [Ca(2+)](o) on PTHrP synthesis and secretion and that activated MEK1/2 and p38 MAP kinases are determinants of the CaR's stimulation of PTHrP secretion.

Cystic fibrosis transmembrane conductance regulator modulates neurosecretory function in pulmonary neuroendocrine cell-related tumor cell line models

The pulmonary neuroendocrine cell (PNEC) system consists of solitary cells and distinctive cell clusters termed neuroepithelial bodies (NEB) localized in the airway epithelium. PNEC/NEB express a variety of bioactive substances, including amine (serotonin, 5HT) and neuropeptides. We have previously shown that NEB cells are O(2) sensors expressing nicotinamide adenine diphosphate oxidase complex and O(2) sensitive K(+) channel. Recently, we demonstrated expression of functional cystic fibrosis transmembrane conductance regulator (CFTR) and Cl(-) conductances in NEB cells of rabbit neonatal lung. Because PNEC/NEB are sparsely distributed and difficult to study in native lung, we investigated small-cell lung carcinoma (SCLC) and carcinoid tumor cell lines (tumor counterparts of normal PNEC/NEB) as models for PNEC/NEB. SCLC (H146, H345) and carcinoid (H727) cell lines express neuroendocrine cell markers, including chromogranin A, neural cell adhesion molecule (N-CAM), 5HT, and tryptophan hydroxylase. We report that H146, H345, and H727 express CFTR messenger RNA (reverse transcription polymerase chain reaction) and protein (immunoblotting) and possess functional CFTR Cl(-) conductance, demonstrated by an iodide efflux assay inhibitable by transfection with antisense CFTR. Using an immunoassay to quantitate 5HT secretion, we also show that downregulation of CFTR abolishes hypoxia-induced 5HT release, and reduces secretory response to high potassium. Our findings suggest that CFTR may modulate neurosecretory activity of PNEC/NEB possessing O(2) sensor function. We propose that these tumor cell lines may be useful models for investigating the role of CFTR in PNEC/NEB functions in health and disease.

Regulation of secretion of PTHrP by Ca(2+)-sensing receptor in human astrocytes, astrocytomas, and meningiomas

Parathyroid hormone-related protein (PTHrP) is the major mediator of the humoral hypercalcemia of malignancy and of malignant osteolysis associated with skeletal metastases of common epithelial cancers. PTHrP secretion is regulated by the extracellular calcium concentration ([Ca(2+)](o)) in several types of normal and malignant cells. Because the [Ca(2+)](o)-sensing receptor (CaR) is a key mediator of [Ca(2+)](o)-regulated hormone secretion [e.g., of parathyroid hormone (PTH) by parathyroid chief cells], we investigated the expression of the CaR and PTHrP in normal and neoplastic glial cells and studied the effects of [Ca(2+)](o) on PTHrP secretion. Our results show that primary embryonic human astrocytes (HPA) express CaR mRNA and protein as detected by RT-PCR and Western analysis, respectively. Furthermore, astrocytomas and meningiomas also express the CaR at similar levels as assessed by RT-PCR and Northern and Western blot analyses. HPA and astrocytomas express transcripts encoding all three known isoforms of PTHrP [PTHrP(139), PTHrP(141), and PTHrP(173), comprising 139, 141, and 173 predicted amino acid residues, respectively] as assessed by RT-PCR, whereas meningiomas express only the first two of these. Finally, elevated levels of [Ca(2+)](o) and other polycationic CaR agonists dose dependently stimulate PTHrP secretion from HPA, astrocytomas, and meningiomas, although both basal and high [Ca(2+)](o)-stimulated rates of PTHrP secretion are approximately 2. 5-fold higher in HPA than in the glial tumors studied here. Therefore, our results show that HPA, astrocytomas, and meningiomas express both the CaR and PTHrP and that CaR agonists stimulate PTHrP secretion.

Parathyroid hormone-related peptide and bone: pathological and physiological aspects

Parathyroid hormone-related peptide (PTHrP) was initially discovered as a tumor-derived systemic factor which causes humoral hypercalcemia of malignancy. When overproduced and secreted by tumor cells, PTHrP acts on target organs such as bone and kidney to cause hypercalcemia through its 'PTH-like effects'. The hypercalcemic effects of PTHrP are attributed to its N-terminal portion (1-36) which shows a limited homology with PTH and is able to bind to the common PTH/PTHrP receptor. In contrast to such pathological effects as a humoral factor, PTHrP is now recognized as a locally active cytokine produced by a variety of tissues and cell types. Gene knockout experiments have revealed critical roles for PTHrP in a wide spectrum of physiological processes including chondrogenesis. It also significantly contributes to various pathological processes such as tumor metastasis to bone and bone destruction in arthropathies, acting as a bone-resorbing cytokine. Consistent with its divergent roles, regulation of PTHrP expression as well as its mode of action seems to be much more complex than its hormonal counterpart, PTH. In this article, we will briefly review the recent progress in our understanding of both physiological and pathological aspects of PTHrP biology, with a particular focus on its roles as a bone cytokine.

JLP5B9: new monoclonal antibody against polysialylated neural cell adhesion molecule is of value in phenotyping lung cancer

Non-small-cell lung cancer (NSCLC) is currently one of the most prevalent malignant tumors. It displays a wide variety of phenotypes which includes neuroendocrine markers commonly found on small-cell lung cancers (SCLC) such as the neural cell adhesion molecule (NCAM) and in particular its highly polysialylated isoform, embryonic NCAM (eNCAM). NSCLC with neuroendocrine differentiation may represent a subset of tumors whose cells have a more aggressive biological behavior. A tumor marker that distinguishes this latter sub-type could be of clinical relevance. Accordingly, we have raised a monoclonal antibody of the IgM type (JLP5B9) directed against capsular polysaccharides of N. meningitidis B which bears polysialic acid groups. We have demonstrated that JLP5B9 recognizes eNCAM with high affinity and that it is specifically directed against the polysialic acid moieties of NCAM. JLP5B9 was also found to react with human SCLC, NSCLC and neuroblastoma cell lines. We then used JLP5B9 as a specific probe for the detection of tissue eNCAM and found that it was expressed on up to 20% of tumor cells obtained from 5 out of 13 patients with NSCLC. This mAb deserves further investigation to evaluate its potential as a tool for serodiagnosis of lung cancer.

Parathyroid hormone-related protein in tracheal aspirates of newborn infants

PTH-related protein (PTHrP) is found with its receptor in a variety of normal mammalian embryonic tissues where it apparently regulates cellular growth and differentiation. PTHrP stimulates phosphatidylcholine synthesis in rat fetal lung explants, suggesting a role in fetal type II alveolar maturation and surfactant production. We investigated PTHrP levels in tracheal aspirates of newborn infants. We collected tracheal aspirates from 40 intubated newborn infants within the first 24 h of life. PTHrP levels were measured by a RIA using rabbit antisera to PTHrP peptide 38-64. We found significantly lower PTHrP levels in tracheal aspirates from infants born at less than 35 wk of gestation (p = 0.02) and with a birth weight less than 2 kg (p = 0.04). We also found significantly lower PTHrP levels in male preterm (<35 wk of gestation) infants compared with female infants (p = 0.01), and in preterm infants who required multiple doses of surfactant (p = 0.005). Preterm infants exposed to antenatal steroids had significantly higher levels of PTHrP in tracheal aspirates (p = 0.02). PTHrP is associated with various indices of lung maturation and may prove to be a mediator of differentiation and growth.

Alteration of secretion of parathyroid hormone-related peptide and expression of its mRNA in a human hepatoma cell line (HEP G2) treated with agents that affect cell growth

Previously, using human hepatoma cells (HepG2), we found that immunoneutralization of secreted PTHrP increased cell growth. Here we asked whether PTHrP production was affected by agents that alter growth of Hep G2 cells. Immunoreactive PTHrP in medium and PTHrP mRNA expression were examined. Treatment of cells with 10 μM hydrocortisone or 1 ng/mL TGF-β1 for 72 h inhibited cell growth by 28±6 and 36±2% and increased PTHrP in medium by 128±10 and 525 ±27%, respectively. The increase in PTHrP produced by both agents was dose-and time-dependent, and the increased PTHrP was accompanied by dose-and time-dependent enhanced expression of PTHrP mRNA. In contrast, 10% fetal bovine serum (FBS) for 72 h increased cell growth by 38±6% (vs serum-free medium) and decreased PTHrP production by 49±4% whereas culture in high glucose (3-4g/L) increased cell growth by 43±1% (vs 1 g/L glucose) and decreased PTHrP by 55±0.4%. Inhibition of PTHrP by both FBS and glucose was dose-dependent; FBS also inhibited PTHrP mRNA. The results show that increased cell growth was associated with decreased PTHrP production, while decreased growth was accompanied by increased PTHrP production. The findings imply that PTHrP may help mediate growth effects of these agents on Hep G2 cells.

Glucocorticoids decrease the production of parathyroid hormone-related protein in vitro but not in vivo in the Walker carcinosarcoma 256 rat model

In 50-90% of cases, humoral hypercalcemia of malignancy (HHM) is due to tumor secretion of parathyroid hormone-related protein (PTHrP). Glucocorticoids are sometimes used as calcium lowering agents and there are in vitro results showing that glucocorticoids diminish PTHrP production. In this study we tested whether the serum-calcium-lowering effect of glucocorticoids is due to decreased PTHrP production by the tumor. As an animal and cell culture model we used the Walker carcinosarcoma (WCS) 256, a rat mammary carcinoma cell line producing PTHrP. In vitro, dexamethasone caused a dose-dependent inhibition of PTHrP production, whereby already 1-5 nmol/L revealed a significant decrease by WCS 256 cells. In contrast to these in vitro results, in WCS 256 tumor-bearing rats, dexamethasone (4 mg/kg body weight on day 4, and 1 mg/kg body weight from day 5 until day 7 after WCS transplantation; circulating dexamethasone levels > 20 nmol/L) did not decrease PTHrP production, PTHrP secretion, serum calcium, or tumor weight in vivo. We conclude that, in this PTHrP-mediated model of humoral hypercalcemia of malignancy, glucocorticoids do not decrease PTHrP production and secretion in vivo and do not show a calcium-lowering effect.

Transcriptional control and the regulation of endocrine genes

1. Endocrine genes are regulated at a number of levels during their expression. Regulation can occur during transcription, mRNA splicing, mRNA degradation, translation, or post-translational processing of protein precursors. 2. Transcription is controlled by an increasingly well studied and enlarging family of transcription factors that bind to basal control DNA sequences (promoters) and transcriptional activator sequences (enhancers). 3. Steroid receptors act as transcription factors, as do the proteins involved in the gene regulation by cyclic AMP. Parathyroid hormone related protein is typical of many endocrine genes in that it is regulated by multiple agonists including glucocorticoids and hormones activating the cyclic AMP cascade.

The expression of the gene coding for parathyroid hormone-related protein (PTHrP) during tooth development in the rat

By means of in situ hybridisation studies, it is shown that parathyroid hormone-related protein (PTHrP) mRNA is strongly expressed in the developing enamel organs of rat teeth. In particular, the cervical loop hybridises strongly with the PTHrP probe and expression is maintained at this site throughout life in the permanently erupting incisor teeth. In mature molar teeth, expression is downregulated to low levels and confined to the epithelial cell rests of Malassez and/or cementoblasts which may derive from these. The gene is also expressed at low levels in the tissue overlying the erupting molars and, thereafter, in the junctional epithelia and connective tissue cells of the epithelial attachment on all tooth surfaces. The premise that PTHrP may undergo post-translational processing and that the resultant products could act in different ways raises the possibility of its exerting multiple paracrine actions during tooth development. These could include the control of cell division and local vascular dilation during development.

Expression and secretion of parathyroid hormone-related protein by human bone-derived cells in vitro: effects of glucocorticoids

We investigated the production of parathyroid hormone-related protein (PTHrP) by cells derived from explants of human bone. Using an immunoradiometric assay (IRMA), PTHrP was detected in conditioned medium from cultures of bone-derived cells from 6 of 7 patients investigated in this study. PTHrP mRNA was identified in human bone cells using reverse transcriptase-linked polymerase chain reaction (RT-PCR) and by Northern analysis. Transcripts for PTHrP were detected in a purified population of alkaline phosphatase positive cells isolated from human bone marrow cultures by flow cytometry, confirming the expression of PTHrP mRNA by cells of the osteoblastic lineage. Production of PTHrP was inhibited by 10(-6) M of the glucocorticoids, prednisolone and desacetylated deflazacort, in a dose-dependent manner. In addition, RT-PCR followed by Southern blot analysis detected a decrease in steady-state PTHrP mRNA in cultures of human bone-derived cells treated with 10(-6) M prednisolone.

Parathyroid hormone-related protein

We review the current state of knowledge of the molecular properties and actions of parathyroid hormone-related protein (PTHrP) both in cancer patients and in normal physiology. PTHrP is a common product of squamous cancers and is the major mediator of the syndrome of humoral hypercalcemia of malignancy (HHM) by its actions through parathyroid hormone receptors in bone and kidney. Recently developed radioimmunoassays and tissue localization techniques indicate that PTHrP is produced by many more cancers than was originally indicated by clinical studies and that it contributes significantly to malignancy-related hypercalcemia associated with other etiologies, for example, cancers metastatic to bone and hematological malignancies. The gene encoding PTHrP is complex, with multiple exons coding for up to 12 alternate transcripts and three different length proteins, potentially in a tissue-specific manner, by the use of three promoters. Its expression is regulated by hormones and growth factors, and the untranslated exons display features in common with many cytokine genes. Although potential endocrine actions of PTHrP are evident in fetal development, further evidence suggesting that the normal physiological role of PTHrP is predominantly as a locally produced regulator/cytokine comes from localization studies and investigations of its actions in a variety of tissues. Such studies indicate that in addition to its parathyroid hormone-like actions, PTHrP has multiple activities, including those in fetal development, placental calcium transfer, lactation, smooth muscle relaxation, and on epithelial cell growth. Although PTHrP was discovered because of its production by cancers, evidence for its actions as a local regulator highlights the importance of understanding its roles not only in the etiology of HHM in cancer patients but also in normal tissues.

Thymus carcinoid producing parathyroid hormone (PTH)-related protein: report of a case

We report herein the rare case of a thymus carcinoid producing parathyroid hormone (PTH)-related protein (PTHrP) found in a 43-year-old Japanese man who presented with a 19-month history of dyspnea. The diagnosis of a carcinoid was established by light microscopic, electron microscopic, and immunohistochemical examinations. The tumor was considered to be thymic in origin because of its anatomic location, the presence of feeders to the tumor (derived from the internal thoracic arteries), and the fact that no other tumors from which it could have originated were found. After an excisional biopsy, which revealed PTH-related immunoreactivity in the tumor cells, 60 Gy of irradiation was delivered, resulting in a 48% reduction in the size of the tumor. Flow cytometry showed a diploid DNA pattern, with 94% of the cells in the G1 phase, 4% in the S phase, 2% in the G2 + M phase, and a G2 + M/G1 ratio of 1.95. The primary cell culture showed some cells adopted in a cord-like pattern. To our knowledge, this is the first report of a carcinoid tumor in which positive staining for PTHrP by immunohistochemical methods was demonstrated.

Dexamethasone regulation of parathyroid hormone-related protein (PTHrP) expression in a squamous cancer cell line

Dexamethasone regulation of PTHrP expression has been studied in an epidermal squamous cancer cell line COLO 16, which secretes immunoreactive PTHrP into conditioned medium. Dexamethasone was found to suppress PTHrP expression in a time- and dose-dependent manner, which was reversible upon removal of dexamethasone. The half-maximal effective concentration of dexamethasone was 1 nM and an effect of dexamethasone on PTHrP mRNA was first observed after 2 h of treatment, with maximal inhibition by 6 h. Dexamethasone action on PTHrP expression was steroid specific since progestin, 5alpha-dihydroxytestosterone and oestrogen did not regulate PTHrP expression in COLO 16 cells. The gluocorticoid/progesterone receptor antagonist RU486 inhibited the dexamethasone effect, indicating glucocorticoid receptor-mediated regulation of PTHrP expression. The half-life of PTHrP mRNA in COLO 16 cells was approximately 120 min and was not altered by treatment of cells with dexamethasone. Nuclear run-on assays revealed that dexamethasone reduced PTHrP gene transcription in COLO 16 cells. Transient transfection assays with a series of reporter gene constructs encompassing 3.5 kb of the 5' end of the PTHrP gene failed to identify a region of the gene responsible for glucocorticoid down-regulation. PCR of reverse-transcribed RNA from COLO 16 cells revealed that dexamethasone down-regulated transcripts driven from all three promoters (i.e., the TATA promoters 5' to exons I and IV and the GC-rich promoter 5' to exon III) of the human PTHrP gene.

The parathyroid hormone-related protein gene and its expression

Parathyroid hormone-related protein (PTHrP) was originally identified as a tumor product, but it is now established that PTHrP is expressed in many tissues where it exerts paracrine functions. Three potential isoforms of PTHrP, 139, 141 and 173 amino acids in length, have been described and these isoforms result from alternative splicing of the PTHrP gene. The gene is composed of nine exons of which only two are invariant in PTHrP transcripts. The other seven exons may be represented in the PTHrP mRNA complement as a result of alternative splicing, which allows for the production of up to 15 transcripts. Three spatially-distinct promoters, two TATA and one GC-rich region, are responsible for transcription of the gene and these appear to be differentially regulated. The PTHrP gene contains nucleotide sequence motifs in common with members of the immediate-early response gene family, as well as other hallmark features which include induction by growth factors, serum or cycloheximide and relatively short-lived mRNA.

Parathyroid hormone-like protein is a secretory product of atrial myocytes

Parathyroid hormone-like protein (PLP) was originally identified from tumors associated with hypercalcemia. Recently, it has been found to be expressed in a stretch-responsive manner in several types of smooth muscle. We studied adult rat heart muscle for the presence of the PLP. Using immunohistology and the PCR, we demonstrated the presence of PLP and its mRNA in all heart chambers. Immunoelectron microscopy demonstrated PLP in secretory vesicles of atrial mycocytes. Using immunoassay, we demonstrated that atria contained a higher concentration of PLP than ventricles. Furthermore, primary cultures of both chambers released PLP into conditioned medium, with atria secreting more than ventricles. Considered with studies of the role of PLP in other tissues, our observations suggest that the production and secretion of PLP by cardiac myocytes represents a calcium-related regulatory function for this stretch-responsive polypeptide in the cardiovascular system. PLP in the heart may be the calcium counterpart for the atrial natriuretic-sodium regulatory axis of the cardiovascular system.

Enhancing effect of interleukin-2 on production of parathyroid hormone-related protein by adult T-cell leukemia cells

Leukemic cells from patients with adult T-cell leukemia (ATL) can produce a calcium-regulating protein, parathyroid hormone-related protein (PTHrP). Moreover, it has been reported that ATL cells produce some cytokines besides PTHrP and that these cells respond to the T-cell growth factors, interleukin-2 (IL-2) and interleukin-4 (IL-4). To elucidate whether PTHrP produced by ATL cells is regulated by IL-2 or IL-4, we investigated the in vitro effects of IL-2 and IL-4 on the release of PTHrP. IL-2 increased the release of PTHrP into the conditioned medium from leukemic cells in some, but not all, ATL patients; however, IL-4 did not affect the PTHrP release. PTHrP messenger RNA (mRNA) levels were increased in ATL cells cultured in the presence of IL-2. These data suggest that IL-2 plays a role in the regulation of hypercalcemia by enhancing the production of PTHrP in ATL patients.

Transforming growth factor beta stimulation of parathyroid hormone-related protein (PTHrP): a paracrine regulator?

The regulation of PTHrP expression and production by transforming growth factor-beta (TGF beta) has been investigated in an epidermal squamous cancer cell line COLO 16. TGF beta 1 treatment increased steady-state levels of PTHrP mRNA and concentrations of PTHrP immunoreactivity in conditioned medium in a time- and dose-dependent manner with a half-maximal effect at 40 pM. An effect of TGF beta 1 on PTHrP mRNA was observed first after 4 h treatment and continued to increase up to 48 h with a concomitant increase in PTHrP immunoreactivity in the culture medium. TGF beta 1 was found to stabilize PTHrP mRNA as assessed by actinomycin C1 experiments. In addition, a direct effect of TGF beta to increase PTHrP transcription was indicated by nuclear run-on and transient transfection experiments using a CAT promoter/expression construct encompassing the region -1100 bp to -20 bp from the initiating AUG of the human PTHrP gene. The conditioned medium from COLO 16 cells was also shown to contain both latent and active TGF beta at concentrations of 160 pM and 16 pM, respectively, in 72 h conditioned medium. A neutralizing antibody to TGF beta 1 (and TGF beta 2) decreased the level of immunoassayable PTHrP in the medium.

Abundant expression of parathyroid hormone-related protein in primary rat aortic smooth muscle cells accompanies serum-induced proliferation

Parathyroid hormone-related protein (PTHrP), which is responsible for producing hypercalcemia in patients with humoral hypercalcemia of malignancy, has recently been identified in several normal tissues. Because PTHrP, like parathyroid hormone (PTH), is known to exhibit vasodilatory properties, we investigated the expression and regulation of PTHrP mRNA in cultured rat aortic smooth muscle cells (SMC). We report here that PTHrP mRNA is expressed in SMC and is markedly induced by serum in a time- and concentration-dependent fashion. Addition of 10% fetal calf serum to serum-deprived, confluent cells, resulted in a marked induction of PTHrP mRNA by 2 h with a peak at 4-6 h. PTHrP was detected in SMC by immunocytochemistry and radioimmunoassay of conditioned medium, and was shown to be up-regulated within 24 h after the addition of serum. The serum induction of PTHrP mRNA was blocked by actinomycin D and by cycloheximide indicating the need for protein synthesis to evoke the serum effect on PTHrP gene transcription. In addition, treatment with dexamethasone, which has been previously shown to reduce the constitutive expression of PTHrP in human cancer cells, also blunted the serum induction of PTHrP mRNA in SMC. Treatment of quiescent cells with the serum mitogens platelet-derived growth factor or insulin-like growth factor-I had no effect on PTHrP, whereas the vasoactive peptides endothelin, norepinephrine and thrombin stimulated PTHrP expression. Exogenous addition of recombinant PTHrP-(1-141) had no significant effect on SMC DNA synthesis as measured by [3H]thymidine incorporation. In summary, the abundance of PTHrP mRNA and the characteristics of its regulation in SMC suggest a major role for PTHrP as a local modulator in vascular smooth muscle.

Effects of glucocorticoids and calcitonin on parathyroid hormone-related protein (PTHrP) gene expression and PTHrP release in human cancer cells causing humoral hypercalcemia

Glucocorticoids are widely used for the treatment of malignancy-associated hypercalcemia to delay the occurrence of an escape phenomenon inherent in calcitonin therapy. Using parathyroid hormone-related protein (PTHrP)-producing squamous carcinoma cells (T3M-1 and EC-GI) established in our laboratory, we investigated the in vitro effects of glucocorticoids and calcitonin on PTHrP mRNA expression in the cells and release of PTHrP into the culture medium. The PTHrP gene was constitutively expressed in the logarithmic growth phase in both squamous carcinoma cell lines. When these cells became superconfluent, PTHrP mRNA expression was greatly diminished in T3M-1 cells but was not distinctly diminished in EC-GI cells. Hydrocortisone inhibited the PTHrP mRNA expression in T3M-1 cells and EC-GI cells in a dose-dependent manner. In accordance with the decreased expression of PTHrP mRNA, the release of immunoreactive as well as bioactive PTHrP also decreased in the conditioned medium of glucocorticoid-treated cells. The minimal effective concentration of prednisolone was about 10(-7) M, which is readily attainable in the serum of patients treated with the agent. Calcitonin and indomethacin did not affect the PTHrP mRNA expression or PTHrP release into the medium. Calcitonin did not modulate the hydrocortisone-induced inhibition of PTHrP production. These in vitro findings suggest that the combined use of glucocorticoids and calcitonin plays a beneficial role in the treatment of malignancy-associated hypercalcemia, since the steroid hormone can suppress PTHrP mRNA expression and release of bioactive PTHrP in certain PTHrP-producing tumors.

Regulation of parathyroid hormone-like peptide in cultured normal human keratinocytes. Effect of growth factors and 1,25 dihydroxyvitamin D3 on gene expression and secretion

We have examined the expression and secretion of endogenous parathyroid hormone-like peptide (PLP) in primary cultures of normal human keratinocytes. In response to growth factors and fetal bovine serum, PLP mRNA expression and immunoreactive PLP release into conditioned medium was rapidly increased (within hours) whereas these effects were inhibited by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. These early responses were not influenced by raising the medium calcium concentration from 0.15 to 1.0 mM. In contrast, increasing the medium calcium concentration to 1.0 mM, addition of 1,25(OH)2D3, or a combination of both, resulted in a delayed augmentation (after several days) in PLP production which was associated with an increase in cellular differentiation as assessed by production of high molecular weight keratin. To investigate whether these factors were acting at the level of transcription of the PLP gene, a series of vectors were prepared by fusing segments of the 5' flanking region of the rat PLP gene to a growth hormone reporter gene. Transient transfection of these constructs into cultured keratinocytes and measurement of immunoreactive growth hormone in the medium showed that a region stimulated by growth factors is located in a 1.9-kb fragment of the 5' flanking region and that a PLP gene promoter region less than 1.2 kb and greater than 0.3 kb upstream of the cap site contains cis-acting elements which respond positively to serum, and negatively to 1,25(OH)2D3. These combined studies demonstrate that, in normal human keratinocytes, growth factors may acutely stimulate PLP mRNA levels and PLP release, whereas 1,25(OH)2D3 inhibits these responses. At least part of these effects are at the level of gene transcription. Additionally, PLP synthesis and release are enhanced under conditions in which keratinocyte differentiation is induced.

Parathyroid hormone-related protein: biochemistry and molecular biology

This article critically reviews the current state of knowledge regarding the recently identified and cloned novel hormone parathyroid hormone-related protein (PTHrP). PTHrP is produced by tumors associated with the syndrome of humoral hypercalcemia of malignancy giving rise to the parathyroid hormone (PTH)-like symptoms characteristic of the syndrome. Areas that will be reviewed include identification, purification and cloning, localization, actions, and significance of PTHrP in cancers and normal physiology. The structure and regulation of the PTHrP gene that may be ancestrally related to the PTH gene will also be discussed. Studies in vivo and in vitro with synthetic and recombinant PTHrP sequences and antibodies developed against them have established that the PTH-like actions of PTHrP are mediated via the N-terminal sequences, which show some limited sequence homology with PTH. Evidence for PTH and non-PTH-like actions of PTHrP in normal physiology, which implicate a role for PTHrP in fetal and neonatal development, is also presented.

Parathyroid hormone-related protein and hypercalcemia in pancreatic neuro-endocrine tumors

We investigated the possible involvement of parathyroid hormone-related protein (PTHrP) in 2 cases of metastatic pancreatic neuro-endocrine tumors associated with severe hypercalcemia. Both patients displayed biochemical alterations in renal tubular reabsorption of calcium and phosphate, as well as in urinary cAMP excretion, similar to those encountered in primary hyperparathyroidism, although plasma levels of parathyroid hormone were within the normal range. Tumor protein extracts stimulated cAMP production, which was inhibited by the PTH-antagonist (8,18 Nle, 34 Tyr)bPTH-(3-34)amide, in the PTH-responsive osteoblastic cell line UMR-106. Northern blot analysis of tumor extracts revealed the presence of PTHrP mRNA transcripts, while PTH mRNA was undetectable. In contrast, neither PTHrP mRNA(s) nor cAMP-stimulating activity was detectable in other neuroendocrine tumors not accompanied by hypercalcemia. These results demonstrate that certain pancreatic neuroendocrine tumors associated with hypercalcemia can synthesize and release PTHrP.

Intrauterine occupancy controls expression of the parathyroid hormone-related peptide gene in preterm rat myometrium

The parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHRP) genes are members of a gene family. Whereas PTH is a classical peptide hormone, mounting evidence suggests that the PTHRP may have predominately local actions. We report here that the PTHRP gene is expressed in rat myometrium, with a major peak in PTHRP mRNA expression occurring in the 48 hr immediately preceding parturition. A similar peak in peptide content was found in tissue extracts by biological and immunological assays, but the PTHRP could not be detected in the peripheral circulation or in uterine vein plasma during late gestation. By in situ hybridization histochemistry, PTHRP mRNA was demonstrated in both the longitudinal and circular layers of smooth muscle but was absent in the endometrium. The rise in myometrial PTHRP mRNA in late gestation was dependent upon intrauterine occupancy; it was greatly reduced or absent in nongravid uterine horns. These findings indicate that the expression of the PTHRP gene in preterm myometrium is under the control of a local stimulus and suggest that the PTHRP may play a paracrine or autocrine role in the uterus during the antepartum period, possibly involving myometrial contractility.