Identification of a cDNA encoding a parathyroid hormone-like peptide from a human tumor associated with humoral hypercalcemia of malignancy

Genomic structure and expression of parathyroid hormone-related protein gene (PTHrP) in a teleost, Fugu rubripes

In this study we describe the isolation and characterisation of the parathyroid hormone-related protein (PTHrP) gene from the teleost Fugu rubripes. The gene has a relatively simple structure, compared with tetrapod PTHrP genes, composed of three exons and two introns, encompassing 2.25kb of genomic DNA. The gene encodes a protein of 163 amino acids, with a putative signal peptide of 37 amino acids and a mature peptide of 126 amino acids. The overall homology with known tetrapod PTHrP proteins is low (36%), with a novel sequence inserted between positions 38 and 65, the absence of the conserved pentapeptide (TRSAW) and shortened C-terminal domain. The N-terminus shows greater conservation (62%), suggesting that it may have a hypercalcaemic function similar to that of tetrapod PTHrP. In situ localisation and RT-PCR have demonstrated the presence of PTHrP in a wide range of tissues with varying levels of expression. Sequence scanning of overlapping cosmids has identified three additional genes, TMPO, LDHB and KCNA1, which map to human chromosome 12, with the latter two mapping to 12p12-11.2. PTHrP in human also maps to this chromosome 12 sub-region, thus demonstrating conservation of synteny between human and Fugu.

Secretin, glucagon, gastric inhibitory polypeptide, parathyroid hormone, and related peptides in the regulation of the hypothalamus- pituitary-adrenal axis

Secretin, glucagon, gastric inhibitory polypeptide (GIP), and parathyroid hormone (PTH) belong, together with vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase (AC)-activating polypeptide, to a family of peptides (the VIP-secretin-glucagon family), which also includes growth hormone-releasing hormone and exendins. All the members of this peptide family possess a remarkable amino-acid sequence homology, and bind to G-protein-coupled receptors, whose signaling mechanism primarily involves AC/protein kinase A and phospholipase C/protein kinase C cascades. VIP and pituitary AC-activating polypeptide play a role in the regulation of the hypothalamus-pituitary-adrenal (HPA) axis, and in this review we survey findings that also other members of the VIP-secretin-glucagon family may have the same function. Secretin and secretin receptors are expressed in the hypothalamus and pituitary gland, and secretin inhibits adrenocorticotropic hormone (ACTH) release. No evidence is available for the presence of secretin receptors in adrenal glands, but secretin selectively depresses the glucocorticoid response to ACTH of dispersed zona fasciculata-reticularis (ZF/R) cells. Glucagon and glucagon-like peptide-1 are contained in the hypothalamus, and all the components of the HPA axis are provided with glucagon and glucagons-like-1 receptors. These peptides exert a short-term inhibitory effect on stress-induced pituitary ACTH release and depress the ZF/R cell response to ACTH by inhibiting the AC/protein kinase A cascade; they also stimulate hypothalamic arginine-vasopressin release. GIP receptors are present in the ZF/R of the normal adrenals, and are particularly abundant in some types of adrenocortical adenomas and hyperplasias. GIP, through the activation of the AC/protein kinase A cascade, evokes a sizeable glucocorticoid secretagogue effect, leading to the identification of a food/GIP-dependent Cushing's syndrome. PTH and PTH-related protein are expressed in the hypothalamus and pituitary gland, and PTH and PTH-related protein receptors in all the components of the HPA axis. Both peptides enhance ACTH and arginine-vasopressin release, as well as stimulate aldosterone and glucocorticoid secretion of dispersed zona glomerulosa and ZF/R cells, respectively. The involvement of growth hormone-releasing hormone and exendins in the functional regulation of the HPA axis has not yet been extensively investigated.

Receptors for PTH and PTHrP: their biological importance and functional properties

The type 1 receptor (PTH1R) for parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) is a G protein-coupled receptor that is highly expressed in bone and kidney and mediates in these tissues the PTH-dependent regulation of mineral ion homeostasis. The PTH1R also mediates the paracrine actions of PTHrP, which play a particularly vital role in the process of endochondral bone formation. These important functions, the likely involvement of the PTH1R in certain genetic diseases affecting skeletal development and calcium homeostasis, and the potential utility of PTH in treating osteoporosis have been the driving force behind intense investigations of both the receptor and its peptide ligands. Recent lines of work have led to the identification of constitutively active PTH1Rs in patients with Jansen's metaphyseal chondrodysplasia, the demonstration of inverse agonism by certain ligand analogs, and the discovery of the PTH-2 receptor subtype that responds to PTH but not PTHrP. As reviewed herein, a detailed exploration of the receptor-ligand interaction process is currently being pursued through the use of site-directed mutagenesis and photoaffinity cross-linking methods; ultimately, such work could enable the development of novel PTH receptor ligands that have therapeutic value in treating diseases such as osteoporosis and certain forms of hypercalcemia.

A novel retinal degeneration locus identified by linkage and comparative mapping of canine early retinal degeneration

Early retinal degeneration (erd) is an early onset progressive retinal atrophy, a hereditary canine retinal disease phenotypically similar to human retinitis pigmentosa (RP). In previous efforts to identify the erd locus, canine homologs of genes causally associated with RP in humans, such as opsin (RHO), the beta-subunit gene for cyclic GMP phosphodiesterase (PDE6B), and RDS/peripherin, were excluded. A genome-wide screen was undertaken on canine families segregating the erd disease. Analysis of over 150 canine-specific markers has localized erd to a single linkage group comprising two previously identified canine linkage groups, 20 and 26, corresponding to canine radiation hybrid groups RH.34-a and RH.40-a. Multipoint analysis places erd in the interval between marker FH2289 (distance 23.6 cM) and FH2407 (5.9 cM) with a lod score of 12.23. Although the erd linkage group has not been assigned to an identified canine chromosome, conserved synteny of this linkage group with human 12p13-q13 suggests several candidates for erd and identifies a novel retinal degeneration locus. The rapid progress now occurring in canine genetics will expedite identification of the genes and molecular mechanisms underlying the inherited traits and diseases that make the dog a unique asset for study of mammalian traits.

Paraneoplastic syndromes of leukocytosis, thrombocytosis, and hypercalcemia associated with squamous cell carcinoma

Paraneoplastic syndromes including leukocytosis, thrombocytosis and hypercalcemia are occasionally seen in patients suffering from progressive malignant disorders. Recent studies have revealed the production of several humoral factors by tumor cells and normal splenic cells of tumor-bearing patients to be the major cause of these reactions. Granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte-colony stimulating factor (G-CSF), parathyroid hormone-related peptide, interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF) have been implicated. We describe a 58-year-old Japanese man with squamous cell carcinoma (SCC) on the left sole, which developed in a deep linear scar after a train crash. He developed pulmonary and lymph node metastases, then leukocytosis (57,110/mm3 with 95% neutrophilia), thrombocytosis (86.3 x 10(4)/mm3), and hypercalcemia (7.0 mEq/1), and finally cachexia, followed by death. Serum G-CSF, IL-1 alpha, IL-1 beta, and TNF-beta were determined; revealing G-CSF and IL-1 beta levels were above the upper limits of their normal ranges at 39.2 pg/ml and 4.63 pg/ml, respectively. It is probable that these humoral factors were partially responsible for the paraneoplastic syndromes induced by the cutaneous SCC with metastasis in the present case.

Expression of parathyroid hormone-related peptide messenger ribonucleic acid in developing kidney

BACKGROUND

Parathyroid hormone (PTH)-related peptide (PTHrP), originally identified as a causative agent of hypercalcemia of malignancy, has been implicated in the regulation of growth and differentiation of endochondral bone, hair follicle, and breast as an autocrine/paracrine factor. Although some experiments indicate that PTHrP works as a growth factor for primary renal cells in vitro, the role of PTHrP in the kidney in vivo is not yet known.

METHODS

We examined the amounts of PTHrP and PTH/ PTHrP receptor (PTHR) mRNA in the mouse kidney developmental process by reverse transcription-polymerase chain reaction, and investigated which cells produce PTHrP and PTHR in vivo by in situ hybridization.

RESULTS

We observed high levels of PTHrP mRNA during mouse kidney maturation. PTHrP mRNA was expressed in the collecting duct, urothelium of the pelvis, and immature elements in the cortex of the developing kidney, including the S-shaped body, ureteric bud, and glomerulus. However, the expression of PTHR mRNA was lower during maturation than after the completion of the maturation process, and it was not detected in the collecting duct, urothelium of the pelvis, or nephrogenic zone in embryonic day 16 or 0-day-old mouse kidneys.

CONCLUSION

These findings suggest that PTHrP has a role in mouse kidney maturation or glomerular development.

The parathyroid hormone-related protein (PTHrP) gene: use of downstream TATA promotor and PTHrP 1-139 coding pathways in primary breast cancers vary with the occurrence of bone metastasis

We analyzed the use of different promoters and the splicing patterns of the exons encoding 5'- and 3'-untranslated sequence amounts of parathyroid hormone-related protein (PTHrP) gene products in breast cancers. Tumor samples from 74 cases of primary breast cancer that had been followed from 1 to 14 years were selected retrospectively according to the occurrence of metastasis: 18 patients developed no metastasis (NM), 56 developed metastases (M), 22 of whom developed metastases in soft tissues (MB-) and 34 of whom developed bone metastases (MB+). The amount of the 1-139 isoform mRNA was much higher in the tumors of patients who later developed metastases (M: 0.29 +/- 0.03) than in those of patients who developed no metastases (NM, 0.13 +/- 0.03; p < 0.01). This isoform mRNA was also more abundant in breast tumors from patients who developed bone metastases (MB+, 0.39 +/- 0.04) than in those of patients who developed metastases in soft tissues (MB-, 0.15 +/- 0.03; p < 0. 0001). By contrast, the amounts of the 1-141 isoform mRNA in these three groups of tumors were similar, but its concentration was higher in the tumors of premenopausal women than in those of postmenopausal women (p < 0.05). Analysis with 5' untranslated regions-specific primers showed transcription from all three putative transcription start sites of PTHrP (P1, P2, and P3). The P3-initiated transcripts were more abundant in patients who developed metastases (M, 0.31 +/- 0.03) than in the nonmetastatic tumors (NM, 0.13 +/- 0.03; p < 0.01). The amount of P3 element did not differ with the site of metastasis (BM+, 0.32 +/- 0.05; BM-, 0. 28 +/- 0.05; NS). The same trend was observed for the P2 element. However, the use of P2-initiated messages was strongly associated with the absence of estrogen receptors from the breast tumors (p < 0. 01). We thus find a close association between the pattern of PTHrP gene expression and the outcome of breast cancer. The P3-initiated start site and the presence of PTHrP 139 mRNA could help identify patients at risk of developing metastases.

Comparison of recombinant human PTH(1-34) (LY333334) with a C-terminally substituted analog of human PTH-related protein(1-34) (RS-66271): In vitro activity and in vivo pharmacological effects in rats

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are believed to exert their biological actions through binding and activation of a common cell surface receptor. Recently, an analog of PTHrP (RS-66271), was described that demonstrated reduced binding affinity for the PTH/PTHrP receptor compared with bovine PTH(1-34) but retained equal biological activity. The present study investigated the receptor binding affinities of synthetic RS-66271 and recombinant human PTH(1-34) (LY333334) and compared their in vitro and in vivo pharmacological effects. RS-66271 had one hundredth the activity of PTH(1-34) in competing for the binding of [125I] [Nle8,18, Tyr34]human PTH(1-34) to the human PTH/PTHrP receptor stably expressed in a human kidney cell line. Despite this reduced binding affinity, RS-66271 had equivalent activity in increasing both cAMP production in osteoblast-like cells and bone resorption in neonatal mouse calvariae. However, RS-66271 was 7. 6-fold less active in stimulating inositol phosphate production. For in vivo studies, young, male Fisher rats received a daily subcutaneous dose of either 10 or 40 microg/kg of peptide for 1, 2, or 4 weeks. Volumetric bone mineral density and total bone mineral content of the proximal tibia were determined by peripheral quantitative computerized tomography. Trabecular and cortical bone of the distal femur were analyzed for calcium and dry weight. Lumbar vertebrae (L4-L6) were analyzed by histomorphometry. Trabecular and cortical bone mass showed a dose- and time-dependent increase in the treated animals compared with the controls. These increases were evident as early as 1 week after initiation of dosing. There were no consistent significant differences in the comparative effects of PTH(1-34) and RS-66271 on the measured bone parameters. In conclusion, despite the reduced binding affinity of RS-66271 for the PTH/PTHrP receptor compared with human PTH(1-34), both peptides displayed similar in vitro and in vivo pharmacological effects.

Role of polypeptides in the treatment and diagnosis of osteoporosis

Osteoporosis is a common disorder characterized by reduced bone mineral density, deterioration of the microarchitecture of bone tissue and increased risk of fracture. The aim of treatment of osteoporosis is to maintain and, ideally, to restore bone strength safely. In recent years the role of polypeptide growth factors in bone metabolism has begun to appear. It has been proposed that alterations in the expression or production of growth factor can modulate the proliferation and activity of bone forming cells. In this direction, the role of structurally diverse peptides for the management and diagnosis of osteoporosis has attracted the attention of many investigators. This paper reviews numerous findings concerning the use of polypeptides, hormones, and growth factors, for the management of osteoporosis. Many of the compounds mentioned here are experimental prototypes of new therapeutic classes. Though it is unlikely that some of the compounds may ever be used clinically, development of safe and efficacious agents in each class will define the future course of therapy for osteoporosis.

Transforming growth factor-beta stimulates mouse blastocyst outgrowth through a mechanism involving parathyroid hormone-related protein

The goals of this study were 1) to compare the effects of transforming growth factor-beta (TGF-beta) and parathyroid hormone-related protein (PTHrP) on mouse blastocyst attachment and outgrowth in vitro, 2) to determine whether TGF-beta acts through a mechanism involving PTHrP, 3) to examine effects of PTHrP on preimplantation mouse embryo development, and 4) to determine the pattern of expression of PTHrP protein in the uterus of the mouse during early gestation. In the first set of experiments, hatched blastocysts were placed in fibronectin-coated wells. Cultures were treated with PTHrP or TGF-beta1 and assessed at 24, 48, and 72 h for attachment and surface area of blastocyst outgrowth. Results showed that both PTHrP and TGF-beta1 increased blastocyst outgrowth significantly. A PTHrP-neutralizing antibody blocked the stimulatory effect of both PTHrP and TGF-beta1, suggesting that TGF-beta1 acts to increase endogenous production of PTHrP by the blastocyst. Immunoassay of conditioned medium from blastocysts treated with either TGF-beta1 or PTHrP 1-34 confirmed a 3- to 4-fold increase in levels of PTHrP 1-141. In the second series of experiments, pronuclear zygotes were cultured in various concentrations of PTHrP for 96 h. Blastocysts then were subjected to differential fluorescent staining of inner cell mass and trophectoderm cells. Treatment of mouse embryos with the various concentrations of PTHrP altered neither the number developing to the blastocyst stage nor the number of inner cell mass or trophectoderm cells in the resulting blastocysts. In the third experiment, pregnant mice were killed at Days 3, 4, 5, 6, and 7 of gestation, and uterine horns were processed for immunohistochemistry. Uterine sections were stained with antibodies to PTHrP, desmin, and laminin. On Days 3, 4, and 5, uterine luminal and glandular epithelial cells stained intensely for PTHrP, while stromal cells were negative. By Days 6 and 7, decidualized stromal cells stained positively for PTHrP, desmin, and laminin. These results support the hypothesis that TGF-beta and PTHrP play an important role in the process of implantation.

Proliferation of parathyroid cells negatively correlates with expression of parathyroid hormone-related protein in secondary parathyroid hyperplasia

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is now suspected to act as an autocrine or paracrine regulator of cell growth or differentiation, although it was originally reported as a hypercalcemic substance in malignancies. This study was performed to assess the relationship between PTHrP expression and cell proliferation in human parathyroid glands.

METHODS

The localization of PTH and PTHrP was studied in 42 samples of hyperplastic parathyroid from 14 long-term hemodialysis cases with immunohistochemistry and in situ hybridization. Results were compared with proliferative activity (proliferating cell nuclear antigen index: counts of proliferating cell nuclear antigen-positive cells/100 cells). The localization of the PTH/PTHrP receptor was also examined. Ten normal glands were studied as controls.

RESULTS

In hyperplasia, cells positive for PTH, PTHrP, or both were observed immunohistochemically. The areas expressing PTHrP mRNA completely coincided with those positive for PTHrP immunohistochemically. Oxyphilic or transitional oxyphilic cells were consistently positive for PTHrP. PTH/PTHrP receptors were located in the cytoplasmic membrane in most parathyroid cells. Proliferating cell nuclear antigen-positive cells were rare in normal glands with an index of 0. 22 +/- 0.09 (mean +/- sem). They were significantly increased in hyperplastic cases but less for PTHrP-positive than for -negative cells (1.25 +/- 0.16 as compared with 7.80 +/- 0.52; P < 0.0001).

CONCLUSION

The observed low level of proliferation of PTHrP-positive cells suggests a functional role for PTHrP as a possible growth suppressor in the human parathyroid.

Parathyroid hormone-related protein: a developmental regulatory molecule necessary for mammary gland development

Parathyroid hormone-related protein (PTHrP) was originally identified as the tumor factor responsible for a clinical syndrome known as humoral hypercalcemia of malignancy. It is now appreciated that PTHrP3 is a developmental regulatory molecule expressed during the formation of a wide variety of organs. Recently, our laboratory has demonstrated that PTHrP is necessary for mammary gland development. Our studies have suggested that this molecule participates in the regulation of epithelial-mesenchymal interactions during embryonic mammary development and perhaps also during adolescent ductal morphogenesis. In addition, it has been suggested that PTHrP plays a critical role in the establishment of bone metastases in breast cancer. In this article, we will discuss the current knowledge of the mechanisms underlying PTHrPs actions during normal mammary development and in breast cancer.

Parathyroid hormone-related protein expression in vascular smooth muscle of spontaneously hypertensive rats: evidence for lack of response to angiotensin II

OBJECTIVE

We studied the expression of parathyroid hormone (PTH)-related protein in vascular smooth muscle cells of spontaneously hypertensive rats (SHR) using Wistar-Kyoto (WKY) and Sprague-Dawley rats as normotensive controls.

METHODS

Aortae from 4- and 18-week-old SHR versus age-matched WKY and Sprague-Dawley rats were excised to obtain total RNA or smooth muscle cells. The cells were subcultured in Dulbecco's Modified Eagle's Medium containing 10% fetal calf serum, then serum-deprived for 72 h and stimulated with 0.1 micromol/I angiotensin II. PTH-related protein, c-myc and angiotensin II type qa receptor (AT1aR) messenger (m)RNA levels were measured by Northern blot, using total RNA extracted by phenol/chloroform. The effects of PTH-related protein(1-34)NH2 intravenous injections on arterial blood pressure and the heart rate were studied in anesthetized SHR and WKY rats.

RESULTS

The Northern blots showed a significantly higher abundance of PTH-related protein mRNA in aortae of SHR versus WKY rats in the prehypertensive state but no significant difference in adult animals. In cultured aortic smooth muscle cells, angiotensin II induced a four- to sixfold increase in PTH-related protein mRNA levels in smooth muscle cells from normotensive animals, but failed to elicit a significant response in smooth muscle cells derived from SHR in either the prehypertensive or the hypertensive state. This lack of response to angiotensin II in SHR smooth muscle cells was not due to decreased expression or responsiveness of the AT1aR, since SHR smooth muscle cells had more AT1aR mRNA than Sprague-Dawley smooth muscle cells, and angiotensin II-induced activation of c-myc was faster and greater in smooth muscle cells derived from 4- or 18-week-old SHR than in Sprague-Dawley smooth muscle cells. In contrast, PTH-related protein(1-34)NH2 induced a long-lasting dose-dependent hypotensive and tachycardic response in both SHR and WKY rats, indicating that SHR retained responsiveness to the vasodilator.

CONCLUSIONS

PTH-related protein gene expression in response to angiotensin II is impaired in SHR arteries. A deficiency in this potent local vasodilator may contribute to the development and/or maintenance of arterial hypertension in this model.

Paracrine mediators of mechanotransduction in lung development

The process of normal fetal lung development is dependent on "mild" tissue distension (approximately 3 mm Hg) by fluid, resulting in the production of pulmonary surfactant which is necessary for survival at the time of birth. The mechanical "stretching" of lung tissue triggers a cellular differentiation cycle, in part by stimulating the expression and production of cell phenotype-specific soluble cytokines. Pulmonary cytokines regulate differentiation and metabolic function of neighboring cells. For example, tonic stretching of type II alveolar epithelial cells in monolayer culture stimulates the expression and production of the differentiation factor parathyroid hormone-related peptide (PTHrP), which is released by type II cells and specifically binds to its receptor on contiguous fibroblasts, stimulating the "second messenger" cyclic AMP. Tonic distension of cultured type II cells increases PTHrP production, and distension of fibroblasts in monolayer culture increases their PTHrP responsiveness, suggesting that stretching couples and coordinates the production and receptor-mediated action of PTHrP. These data provide a mechanistic basis for the previously observed hand-in-glove spatial pattern of PTHrP and the PTHrP receptor (PTHrPR) in developing terminal airways. PTHrP stimulates specific differentiated functions of fetal lung fibroblasts by: 1) augmenting glucocorticoid binding; 2) increasing metabolic activities directly related to surfactant synthesis, such as lipoprotein lipase elaboration and triglyceride uptake rate; 3) stimulating cytokines, such as interleukins 6 and 11, that can act in a retrograde fashion on epithelial cells; 4) thereby increasing the synthesis of surfactant phospholipids and surfactant-associated proteins, closing this stretch-mediated cell-cell interactive loop. Experimental interruption of this mechanism at any of these steps blocks the spontaneous maturation of the lung in vitro, as evidenced by the inhibition of surfactant production.

Calcitropic peptides: neural perspectives

In mammals and higher vertebrates, calcitropic peptides are produced by peripheral endocrine glands: the parathyroid gland (PTH), thyroid or ultimobranchial gland (calcitonin) and the anterior pituitary gland (growth hormone and prolactin). These hormones are, however, also found in the neural tissues of lower vertebrates and invertebrates that lack these endocrine organs, suggesting that neural tissue may be an ancestral site of calcitropic peptide synthesis. Indeed, the demonstration of CNS receptors for these calcitropic peptides and their induction of neurological actions suggest that these hormones arose as neuropeptides. Neural and neuroendocrine roles of some of these calcitropic hormones (calcitonin and parathyroid hormone) and related peptides (calcitonin gene related peptide, stanniocalcin and parathyroid hormone related peptide) are thus the focus of this review.

Role of interleukin-6 in uncoupling of bone in vivo in a human squamous carcinoma coproducing parathyroid hormone-related peptide and interleukin-6

OCC tumor has been established from a human squamous carcinoma associated with humoral hypercalcemia of malignancy (HHM) and shown to overproduce parathyroid hormone-related peptide (PTHrP) and cause aggressive hypercalcemia when implanted into nude rats. In the present study, we have demonstrated by reverse transcription-polymerase chain reaction and Northern blot analysis that OCC tumor also overexpressed interleukin 6 (IL-6) mRNA and that tumor-bearing animals exhibited a marked increase in plasma IL-6 as well as PTHrP concentrations. When a monoclonal antibody against human IL-6 was injected to block the activities of tumor-derived IL-6, bone loss in tumor-bearing animals was significantly prevented. Quantitative bone histomorphometric analysis revealed that treatment with anti-IL-6 antibody caused a substantial decrease in both osteoclast number and eroded surface (as parameters of bone resorption) and also a significant increase in the mineral apposition rate, but little effect on the osteoblastic surface. These results provide in vivo evidence suggesting that in tumors coproducing IL-6 and PTHrP, IL-6 is involved not only in the acceleration of osteoclastic bone resorption but also, at least in part, in the suppression of osteoblastic functions in HHM syndrome.

Establishment of two human small cell lung cancer cell lines: the evidence of accelerated production of parathyroid hormone-related protein with tumor progression

Two small cell lung cancer (SCLC) cell lines have been established from malignant effusions obtained from an SCLC patient with hypercalcemia during a 3-month follow-up period. The two cell lines established were shown to transcribe the parathyroid hormone-related protein (PTHrP) gene and to constantly secrete fairly large amounts of PTHrP into the culture medium. The efficiency of PTHrP gene transcription and secretion was greater in the cell line established in the late stage (KOT-2) as compared with that obtained in the early stage (KOT-1). Immunohistochemical studies showed that these cells also coexpress neuroendocrine (NE) products such as chromogranin A and neuron-specific enolase (NSE).

Simian T cell leukemia virus type I-induced malignant adult T cell leukemia-like disease in a naturally infected African green monkey: implication of CD8+ T cell leukemia

Spontaneous T cell leukemia was found in an African green monkey (Cercopithecus aethiops, AGM) naturally infected with simian T cell leukemia virus type I (STLV-I). The hematological features and the evidence for monoclonal integration of provirus DNA in the leukemic cells revealed that the leukemia was an ATL-like disease. The expression of surface markers on the leukemic cells indicated that they were defined as an activated CD8+ T cell subset. Together with the finding that seven in vitro spontaneously STLV-I-transformed cell lines were CD4-CD8+, it is likely that CD8+ T cells are transformed by STLV-I in AGMs, in contrast with human ATL. Finally, we assessed characteristics of the CD8 chains on these transformed cells. The result indicated that the leukemic cells expressed only the alpha chains but not the beta chains. However, in the case of in vitro-transformed cell lines the expression pattern of the CD8 chains varied in individual monkeys. Thus, STLV-I may preferentially transform CD8+ (both alphaalpha+ and alphabeta+) T cells in AGMs.

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.

Centrally administered parathyroid hormone (PTH)-related protein(1-34) but not PTH(1-34) stimulates arginine-vasopressin secretion and its messenger ribonucleic acid expression in supraoptic nucleus of the conscious rats

It has been suggested that PTH-related protein (PTHrP) is an endogenous modulator of cardiovascular systems. We have reported that PTHrP(1-34), but not PTH(1-34), causes the release of arginine-vasopressin (AVP) from the supraoptic nucleus (SON) of the hypothalamus in vitro through a novel receptor distinct from the PTH/PTHrP receptors (type I or type II) described previously. In this study, we have investigated the in vivo effects of PTHrP(1-34) on AVP secretion and its, messenger RNA (mRNA) expression in the SON in conscious rats. Intracerebroventricular (i.c.v.) administration of PTHrP(1-34) resulted in an increase in plasma AVP concentration in a dose-dependent manner (0-400 pmol/rat). The maximal effect was obtained at 15 min after i.c.v. administration of PTHrP(1-34). Neither PTHrP(7-34) nor PTH(1-34) had any effect on plasma AVP levels. PTHrP(1-34)-induced AVP secretion was antagonized by pretreatment with PTHrP(7-34) but not by that with PTH(1-34). In addition, in situ hybridization study revealed that AVP mRNA expression in the SON and paraventricular nucleus was significantly increased 30 min after i.c.v. administration of PTHrP(1-34) and reached a maximum at 180 min. Furthermore, in Northern blot analyses, AVP mRNA expression in the SON was increased to approximately a 2-fold of basal level by PTHrP(1-34). On the other hand, neither PTHrP(7-34) or PTH(1-34) had any effect on the mRNA expression. The PTHrP(1-34)-stimulated AVP mRNA expression was eliminated by pretreatment with PTHrP(7-34) but not with PTH(1-34). These results suggest that, in the central nervous system, PTHrP(1-34) is involved in AVP secretion through a novel receptor distinct from the PTH/PTHrP receptors reported previously, playing a role in the body water and electrolyte homeostasis.

Increased parathyroid hormone-related peptide in patients with hypercalcemia associated with islet cell carcinoma

OBJECTIVE

To report the high prevalence of increased parathyroid hormone-related peptide (PTHrP) in patients with islet cell carcinoma and associated hypercalcemia.

DESIGN

We conducted a retrospective study of PTHrP levels in patients with hypercalcemia and eucalcemia associated with islet cell carcinoma and compared these findings with those in healthy subjects.

MATERIAL AND METHODS

Using a sensitive PTHrP immunochemiluminometric assay, we measured PTHrP levels in 17 patients with islet cell carcinoma and 110 healthy subjects. The differences between PTHrP levels in patients with normal and those with high serum calcium concentrations were analyzed statistically.

RESULTS

PTHrP levels were significantly higher (P < 0.01) in 10 patients with hypercalcemia and islet cell carcinoma (median, 14.0 pmol/L; range, undetectable to 40.1) than in 7 patients with eucalcemia and islet cell carcinoma (median, undetectable; range, undetectable to 1.3 pmol/L) or in the 110 healthy subjects (median, undetectable; range, undetectable to 4.2 pmol/L). The range of increased PTHrP levels in hypercalcemic islet cell carcinoma was 2 to 20 times the upper normal limit (2.0 pmol/L). Decreased PTHrP and serum calcium and increased parathyroid hormone levels were demonstrated in two patients after effective therapy. For all seven eucalcemic patients with islet cell carcinoma, PTHrP levels did not differ significantly from those in healthy subjects.

CONCLUSION

PTHrP levels are increased in a substantial proportion of patients with hypercalcemia and islet cell carcinoma and seem to decrease after treatment of the underlying tumor. Measurement of PTHrP levels may be useful for confirming the diagnosis of hypercalcemia associated with malignant disease and for monitoring of therapy.

PTH-related peptide-like immunoreactivity in the median emminence, paraventricular and supraoptic nuclei in colchicine-treated rats

The existence of PTH-related peptide (PTHrP) in the hypothalamus was examined by immunohistochemistry in colchicine-treated rats. Two days after intracerebroventricular administration of colchicine dense PTHrP-like immunoreactivity (LI) was observed in the external zone of the median emminence (ME). PTHrP-LI cells were found in the paraventricular nucleus, the supraoptic nucleus and the periventricular region of the third ventricule. The effects of PTHrP on intracellular Ca2+ concentrations ([Ca2+]i) were examined by a Ca2+ imaging method using fura-2 in perifused preparations of isolated rat anterior pituitary cells. The rise in [Ca2+]i induced by PTHrP was found in approximately 17% of the cells examined. These results suggest that PTHrP-LI cells in the hypothalamus may project to the ME and contribute to the anterior pituitary function.

Increased expression of parathyroid hormone-related peptide gene in blood vessels of spontaneously hypertensive rats

We have shown recently that mechanical stretch of cultured rat aortic smooth muscle cells induces a marked increase in gene expression of the vasorelaxant parathyroid hormone-related peptide. In the present study, we investigated whether mechanical force affected the in vivo parathyroid hormone-related peptide gene expression in blood vessels. Northern blot analysis revealed that stretch of isolated rat aortic strips increased the expression level of parathyroid hormone-related peptide mRNA. The parathyroid hormone-related peptide transcript level in aorta and mesenteric vessels from 18-week-old spontaneously hypertensive rats (SHR) was 2.5- and 2.2-fold higher, respectively, compared with age-matched Wistar-Kyoto (WKY) controls, whereas the parathyroid hormone-related peptide mRNA level in aorta from normotensive 4-week-old SHR was similar to that of age-matched WKY controls. The aortic parathyroid hormone-related peptide content was higher in 18-week-old SHR than in age-matched WKY controls. Moreover, treatment of mature SHR with an angiotensin II type 1 receptor antagonist or hydralazine caused a concomitant decrease in the parathyroid hormone-related peptide transcript level in aorta with lowering of blood pressure. These results suggest that the in vivo parathyroid hormone-related peptide gene expression in blood vessels is under the control of mechanical force, pointing to a role of parathyroid hormone-related peptide in the regulation of vascular tone.

Hypercalcemia in patients with metastatic renal cell carcinoma: effect of nephrectomy and metabolic evaluation

PURPOSE

The role of nephrectomy in the management of hypercalcemia in metastatic renal carcinoma is not known. Hypercalcemia in patients with renal cell carcinoma frequently mimics primary hyperparathyroidism and has been attributed to tumor secretion of parathyroid hormone related protein. We determined the role of cytoreductive surgery in patients with metastatic renal cell carcinoma and hypercalcemia, identified factors that predict patient benefit from surgery, and evaluated the mechanisms of hypercalcemia in these patients.

MATERIALS AND METHODS

A total of 15 patients with metastatic renal cell carcinoma and hypercalcemia underwent metabolic and laboratory evaluation followed by nephrectomy. Post-operatively they were followed for changes in serum calcium levels. We selected 18 normocalcemic patients with metastatic renal cell carcinoma and 4 normocalcemic patients without renal cancer to serve as control groups for survival and parathyroid hormone related protein expression.

RESULTS

A decrease in serum calcium corrected for albumin occurred in 9 of 11 patients at 1 to 4 weeks after nephrectomy and in 7 of 12 patients at 5 to 16 weeks after nephrectomy. Clinical evaluation supported a parathyroid hormone related protein mechanism of hypercalcemia in 5 of 8 patients. Two patients had evidence of local osteolytic hypercalcemia and 1 had prostaglandin mediated hypercalcemia.

CONCLUSIONS

Nephrectomy temporarily ameliorated hypercalcemia in a subgroup of patients with metastatic renal cancer and hypercalcemia. Parathyroid hormone related protein expression was commonly found to be associated with hypercalcemia. Nonparathyroid hormone related protein mechanisms of hypercalcemia in renal carcinoma may be more common than previously thought.

CpG island methylation and promoter usage in the parathyroid hormone-related protein gene of cultured lung cells

Excessive production of a parathyroid hormone-related protein (PTHrP) by tumours commonly results in the syndrome of humoral hypercalcaemia of malignancy. We have investigated whether epigenetic changes play a role in over-expression of the PTHrP gene, using cultures lung cells as a model system. Study of the methylation status of CpG dinucleotides in the 5' region of the gene showed that in normal cells the CpG island was completely unmethylated. In the lung squamous cell carcinoma cell line, BEN, two-thirds of the CpG island was substantially methylated. RT-PCR analysis showed that this heavy methylation did not prevent expression of any of the three PTHrP gene promoters. This is a surprising finding, since methylation is usually associated with inhibition of gene activity. Methylation of the 5' non-coding region of the PTHrP gene may not play a role in the regulation of adjacent promoters. Alternatively, maintenance of a demethylated state in the 170 bp at the 3' end of the CpG island may be fundamental for the use of PTHrP promoters.

Parathyroid hormone-related peptide-(1-34) [PTHrP-(1-34)] induces vasopressin release from the rat supraoptic nucleus in vitro through a novel receptor distinct from a type I or type II PTH/PTHrP receptor

PTH and PTH-related peptide (PTHrP) bind to a type I PTH/PTHrP receptor expressed in bone and kidney or a type II receptor in nonclassical target tissue with equal affinity and similar bioactivities. PTHrP is abundant in the central nervous system, but its physiological role remains unknown. Herein, we examined the role of PTHrP-(1-34) on arginine vasopressin (AVP) release from the rat supraoptic nucleus (SON). Application of PTHrP-(1-34) to SON slices caused an increase in AVP release in a concentration-dependent manner. Neither PTHrP-(7-34) nor PTH-(1-34) had any effect on AVP release from the SON. PTHrP-(1-34)-induced AVP release was antagonized by a large excess of PTHrP-(7-34) and by H89, an inhibitor of cAMP-dependent protein kinase (A kinase), but not by PTH-(1-34) or PTH-(13-34). PTHrP-(1-34), but not PTH-(1-34), also dose-dependently increased the levels of cAMP in the SON. 125I-Labeled PTHrP-(1-34) bound specifically to crude membranes isolated from the SON. Scatchard analysis showed a single class of binding sites for PTHrP-(1-34) with a Kd of 36.4 nM and a maximum binding capacity of 3.94 pmol/mg protein. No specific binding for 125I-labeled PTH-(1-34) was noted. The binding of 125I-labeled PTHrP-(1-34) was displaced by unlabeled PTHrP-(1-34) and unlabeled PTHrP-(7-34), but not by unlabeled PTH-(1-34). These findings suggest that PTHrP-(1-34), but not PTH-(1-34), causes the release of AVP from the SON through a novel receptor distinct from type I or II PTH/PTHrP receptors.

Co-secretion of parathyroid hormone and parathyroid-hormone-related protein via a regulated pathway in human parathyroid adenoma cells

Parathyroid-hormone-related protein (PTHrP) is widely expressed not only in malignant tumors but also in both epithelial and nonepithelial cells of normal tissues. Secreted PTHrP is suspected to act as a paracrine or autocrine regulator. However, little is known about its secretory pathway. To cast light on this question, we studied the intracytoplasmic distribution of parathyroid hormone (PTH) and PTHrP immunohistochemically and immunoelectron microscopically in 10 surgically resected parathyroid adenomas. Double immunostaining was performed using anti-PTH antibody and a newly established anti-PTHrP antibody to reveal the relationship between their two distributions. Additional examination by cell immunoblot assay was performed to determine whether both PTH and PTHrP are secreted simultaneously. Both PTH and PTHrP were actually secreted from individual parathyroid cells simultaneously on cell immunoblot assay. Immunohistochemically, there were two different types of adenoma cells, i.e., one positive only for PTH and the other positive for both PTH and PTHrP. PTH was distributed linearly or fine granularly along the cytoplasmic membrane, whereas PTHrP was distributed diffusely or coarse granularly in the cytoplasm. The intracytoplasmic distributions of PTH and PTHrP often overlapped. Immunoelectron microscopical examination demonstrated that PTHrP co-localized with PTH in the same secretory granules. The results clearly demonstrated that PTHrP can be co-secreted with PTH via a regulated pathway using secretory granules.

Expression of parathyroid hormone-related peptide in human osteoarthritis

To evaluate the involvement of the expression of parathyroid hormone-related peptide gene in human articular cartilage pathology, we performed immunohistochemical staining and in situ hybridization on specimens of femoral head cartilage obtained from 15 patients with osteoarthritis, 11 with rheumatoid arthritis, and 12 control subjects. Parathyroid hormone-related peptide-positive chondrocytes were observed predominantly in degenerated lesions of osteoarthritic tissue and were less evident in rheumatoid arthritic samples, while the normal cartilage expressed little parathyroid hormone-related peptide. In addition, the level of parathyroid hormone-related peptide expression was clearly dependent on the degree of cartilage degeneration; cartilage tissues with moderate degenerative changes contained more positive chondrocytes compared with mildly or severely degenerated cartilage. In situ hybridization confirmed the localization of parathyroid hormone-related peptide protein and demonstrated intense expression of mRNA of the peptide in osteoarthritic samples. This is the first demonstration of parathyroid hormone-related peptide expression in chondrocytes from pathologic articular cartilage of humans. Our results suggest that parathyroid hormone-related peptide may be involved in the pathophysiology of osteoarthritis.

Antiproliferative effect of the C-terminal fragments of parathyroid hormone-related protein, PTHrP-(107-111) and (107-139), on osteoblastic osteosarcoma cells

The C-terminal region of parathyroid hormone-related protein (PTHrP) containing the sequence (107-111) appears to be a potent inhibitor of osteoclastic bone resorption. In the present study, we have investigated the effect of human (h)PTHrP (107-139) and hPTHrP (107-111)NH2 on the proliferation of osteoblastic rat osteosarcoma UMR 106 cells. We found that both C-terminal PTHrP peptides, like hPTHrP (1-141), were antimitogenic for these cells, between 1 pM and 10 nM. [Tyr34]hPTHrP (1-34)NH2 was as potent as these peptides but less effective as growth inhibitor in these cells. UMR 106 cells were found to produce and secrete immunoreactive PTHrP. Addition of anti-PTHrP neutralizing antibodies to C- and N-terminal epitopes of PTHrP increased the growth of these cells. Our data suggest that the antiproliferative effect of these C-terminal PTHrP analogs may be independent of cyclic adenosine 3':5'-monophosphate (cAMP) and mediated by protein kinase C. These findings support an autocrine role of PTHrP in bone metabolism.

Bcl-2 lies downstream of parathyroid hormone-related peptide in a signaling pathway that regulates chondrocyte maturation during skeletal development

Parathyroid hormone-related peptide (PTHrP) appears to play a major role in skeletal development. Targeted disruption of the PTHrP gene in mice causes skeletal dysplasia with accelerated chondrocyte maturation (Amizuka, N., H. Warshawsky, J.E. Henderson, D. Goltzman, and A.C. Karaplis. 1994. J. Cell Biol. 126:1611-1623; Karaplis, A.C., A. Luz, J. Glowacki, R.T. Bronson, V.L.J. Tybulewicz, H.M. Kronenberg, and R.C. Mulligan. 1994. Genes Dev. 8: 277-289). A constitutively active mutant PTH/PTHrP receptor has been found in Jansen-type human metaphyseal chondrodysplasia, a disease characterized by delayed skeletal maturation (Schipani, E., K. Kruse, and H. Jüppner. 1995. Science (Wash. DC). 268:98-100). The molecular mechanisms by which PTHrP affects this developmental program remain, however, poorly understood. We report here that PTHrP increases the expression of Bcl-2, a protein that controls programmed cell death in several cell types, in growth plate chondrocytes both in vitro and in vivo, leading to delays in their maturation towards hypertrophy and apoptotic cell death. Consequently, overexpression of PTHrP under the control of the collagen II promoter in transgenic mice resulted in marked delays in skeletal development. As anticipated from these results, deletion of the gene encoding Bcl-2 leads to accelerated maturation of chondrocytes and shortening of long bones. Thus, Bcl-2 lies downstream of PTHrP in a pathway that controls chondrocyte maturation and skeletal development.

Parathyroid hormone-related protein: from hypercalcemia of malignancy to developmental regulatory molecule

Parathyroid hormone-related protein (PTHrP) was originally discovered because of its role in humoral hypercalcemia of malignancy (HHM), a common metabolic complication of many types of cancer. In HHM, PTHrP is released into the circulation by malignant cells and cross reacts with parathyroid hormone (PTH) receptors in bone and kidney, which results in hypercalcemia. In recent years, it has become clear that PTHrP is a normal product of many adult and fetal tissues where it appears to act in an autocrine and/or paracrine fashion to regulate organogenesis. This article explores the molecular evolution of PTHrP and how this understanding has begun to shed some light on the molecular mechanisms responsible for the biochemical manifestations of HHM. In addition, the normal biological function of PTHrP is discussed, with an emphasis on its role as a developmental regulatory molecule.

Tumor-induced hypercalcemia and parathyroid hormone-related protein in lung carcinoma

BACKGROUND

Although lung carcinoma is the most common cause of tumor-induced hypercalcemia (TIH), the precise incidence of TIH remains obscure. Furthermore, the role of parathyroid hormone-related protein (PTHrP) has not been clearly elucidated.

METHODS

This study included 690 consecutive patients who were newly diagnosed as having lung carcinoma between 1989 and 1994 (379 adenocarcinomas, 207 squamous cell carcinomas, 75 small cell carcinomas, and 29 large cell carcinomas). All patients were treated for lung carcinoma and were also periodically monitored for their serum level of calcium (Ca). Hypercalcemia was defined as a serum Ca concentration higher than 11 mg/dL. The serum levels of PTHrP (109-141) were measured by a C-terminal-region-specific radioimmunoassay.

RESULTS

TIH was observed in 17 of 690 patients (2.5%). All 17 patients demonstrated an advanced stage of lung carcinoma (Stage III or IV), 10 squamous cell carcinomas, 5 adenocarcinomas, 1 small cell carcinoma, and 1 large cell carcinoma. In 15 patients, the serum level of C-PTHrP (109-141) was substantially high, ranging from 99 pmol/L to 890 pmol/L (normal range, 21-50.7 pmol/L). There was no significant difference in the serum PTHrP level between patients with or without bone metastasis. The reduction of tumor burden decreased both the serum level of PTHrP and that of Ca in parallel. The median survival time after diagnosis of TIH was only 27 days.

CONCLUSIONS

TIH in lung carcinoma was most likely attributable to PTHrP, and its occurrence appears to be an ominous prognostic sign.

Expression and action of parathyroid hormone-related peptide in human cervical epithelial cells

Parathyroid hormone-related peptide (PTHRP) expression and activity were analyzed in normal human ectocervical keratinocytes (HCX) and keratinocytes immortalized by transfection with human papillomavirus (HPV) types 16 and 18 DNAs. In normal cells, trans-retinoic acid (RA) and 2.0 mM Ca2+ significantly stimulated PTHRP mRNA expression and secretion and led to a significant reduction in the rate of proliferation. In contrast, the basal level of PTHRP production decreased sharply in confluent HCX, and induction by Ca2+ or exogenous growth factors was reduced or lost. After stable transfection with HPV16 and HPV18 DNAs, we observed a sharp decrease of PTHRP production in high-passage poorly differentiated HCX. Finally, addition of exogenous PTHRP-(1-141) inhibited proliferation of both normal cells and low-passage well-differentiated HPV16 immortalized cells. High-passage poorly differentiated cells were refractory to PTHRP. These results demonstrate that PTHRP production varies greatly with the degree of cell proliferation and differentiation and suggest that this peptide acts as an autocrine negative growth regulator for cervical keratinocytes.

A new human breast cancer cell line, KPL-3C, secretes parathyroid hormone-related protein and produces tumours associated with microcalcifications in nude mice

Parathyroid hormone-related protein (PTHrP) is the main cause of humoral hypercalcaemia of malignancy (HHM). We recently established a new human breast cancer cell line, designated KPL-3C, from the malignant effusion of a breast cancer patient with HHM. Morphological, cytogenetic and immunohistochemical analyses indicated that the cell line is derived from human breast cancer. The KPL-3C cells stably secrete immunoreactive PTHrP measured by a two-site immunoradiometric assay, possess both oestrogen and progesterone receptors and are tumorigenic in female nude mice. The addition of phorbol-12-myristate-13-acetate to the medium significantly increased PTHrP secretion from the cells. In contrast, hydrocortisone, medroxyprogesterone acetate and 22-oxacalcitriol decreased PTHrP secretion in a dose-dependent manner. Unexpectedly, a number of microcalcifications were observed in the transplanted tumours. Radiographical examination indicated that the microcalcifications in the tumours are very similar to those commonly observed in human breast cancer. These findings suggest that this KPL-3C cell line may be useful for studying the regulatory mechanisms of PTHrP secretion and the mechanisms that lead to the deposition of microcalcifications in breast cancer.

Establishment of a clonal cell line producing granulocyte colony-stimulating factor and parathyroid hormone-related protein from a lung cancer patient with leukocytosis and hypercalcemia

Squamous cell lung carcinoma cells obtained from a patient who presented with leukocytosis and hypercalcemia were transplanted into nude mice and a serially transplantable cell line, OKa-N-1, was established. The nude mice transplanted with OKa-N-1 cells displayed leukocytosis and hypercalcemia. Serum levels of granulocyte colony-stimulating factor (G-CSF) and parathyroid hormone-related protein (PTHrP) were both elevated in these mice. In vitro cultivation of this tumor cell line gave rise to a clonal cell line, OKa-C-1. Nude mice transplanted with the OKa-C-1 cell line also showed leukocytosis and hypercalcemia with high serum G-CSF and PTHrP levels. The culture supernatant of OKa-C-1 contained high levels of G-CSF and PTHrP. Immunohistochemical studies showed the expression of PTHrP in OKa-C-1 cells. Reverse transcription polymerase chain reaction revealed the presence of G-CSF and PTHrP mRNA in this cell line. Dexamethasone treatment inhibited the transcription of G-CSF and PTHrP genes. This new human squamous carcinoma cell line, OKa-C-1, would be useful for studying the mechanism of simultaneous production of G-CSF and PTHrP and their control in cancer patients with leukocytosis and hypercalcemia.

Lung tumours immunoreactive for parathyroid hormone related peptide: analysis of serum calcium levels and tumour type

Secretion by tumours of parathyroid hormone-related peptide (PTHrP) in quantities sufficient to raise circulating levels results in the syndrome of humoral hypercalcaemia of malignancy (HHM). Since HHM is commonly associated with squamous carcinoma of lung and rarely with adenocarcinoma or lung neuroendocrine tumours, immunopositivity was related to tumour type, to assess whether this difference was due to a low general incidence of PTHrP expression in the latter two groups. Seventy-six of 82 tumours were immunopositive: 22 of 22 squamous carcinomas, 21 of 25 small cell lung carcinomas, 14 of 15 carcinoids, and 19 of 20 adenocarcinomas. These data confirm and extend previous observations on squamous and neuroendocrine tumours but are in contrast with previous findings in adenocarcinoma, which have suggested that only a small proportion of cases express the peptide. They suggest that the differences in incidence of HHM in the various tumour types are due to patterns of secretion, rather than differences in expression of PTHrP. The second aim of this study was therefore to assess whether tumours immunopositive for PTHrP, but not associated with HHM, might secrete PTHrP at levels which might result in more subtle changes in calcium metabolism. Preoperative calcium levels were analysed in a series of 56 patients with immunopositive lung tumours of all types. One small cell carcinoma was associated with hypercalcaemia, but there was no evidence of any other alteration in serum calcium. These data indicate that the majority of tumours expressing PTHrP do not secrete it in amounts sufficient to alter calcium metabolism.

Signaling by N- and C-terminal sequences of parathyroid hormone-related protein in hippocampal neurons

Parathyroid hormone-related protein (PTHrP) is synthesized in the brain, and a single type of cloned receptor for the N-terminal portion of PTHrP and PTH is present in the central nervous system. Nothing is known about the physiological actions or signaling pathways used by PTHrP in the brain. Using cultured rat hippocampal neurons, we demonstrate that N-terminal PTHrP[1-34] and PTH[1-34] signal via cAMP and cytosolic calcium transients. The cAMP response showed strong acute (< or = 6 h) homologous and heterologous desensitization after preincubation with PTHrP or PTH. In contrast, the acute calcium response did not desensitize after preincubation with PTHrP; in fact, preincubation dramatically recruited additional responsive neurons. Unexpectedly, C-terminal PTHrP[107-139], which does not bind or activate the cloned PTH/PTHrP receptor, signaled in neurons via cytosolic calcium but not cAMP. Although some neurons responded to both PTHrP[1-34] and PTHrP[107-139], others responded only to PTHrP[1-34]. We conclude that certain hippocampal neurons exhibit dual signaling in response to PTHrP[1-34] and that some neurons have a receptor for C-terminal PTHrP that signals only via cytosolic calcium.

Evaluation of serum concentration of parathyroid hormone-related protein and its implication in hypercalcemia in squamous cell carcinoma of the head and neck

Hypercalcemia is a common and serious complication associated with squamous cell carcinoma (SCC) and is considered to be caused by a tumor-derived factor, parathyroid hormone-related protein (PTHrP). However, the correlation between serum levels of calcium and PTHrP and the kinetics of PTHrP in SCC of the head and neck is unknown, because the behavior of the circulating form of PTHrP in patients has not been determined. In the present study, the PTHrP concentrations in serum samples from 54 patients (37 with SCC and 17 with benign tumors) were measured by a recently developed radioimmunoassay directed toward the C-terminal region of PTHrP, and the laboratory data including those calcium levels in corresponding samples were reviewed retrospectively. Results showed hypercalcemia in four patients with advanced cancer and in whom elevation of the serum PTHrP concentration was observed simultaneously. The regression analysis also revealed the linear relationship of the calcium level to the PTHrP concentration, but not to the concentration of phosphorus or creatinine, suggesting that monitoring of serum PTHrP level is useful for prediction of hypercalcemia associated with head and neck cancer.

New trends in bone research

Recent advances in bone research have employed novel cell and molecular biology techniques to determine some of the fundamental mechanisms regulating bone function. Endocrine control of bone cell development and matrix turnover have been defined at a molecular level by studying the interaction of steroid/thyroid hormones with gene promoters. New steroid/thyroid hormone receptors have been cloned, suggesting that our current view of hormonal regulation of bone metabolism is far from complete. The function of one particular steroid hormone receptor, the vitamin D receptor, has come under close scrutiny following the observation that polymorphic variations in this receptor are linked to differences in bone mineral density. Detailed studies of bone cell differentiation have shown that cytokines may be particularly important targets for hormonal control in bone. The role of cell adhesion molecules in regulating bone resorption has also been explored; modulation of their activity may be of benefit in the treatment of diseases such as osteoporosis. Pharmacological intervention via the newly cloned calcium-sensing receptor offers another site for regulation of bone turnover.

Alternative promoter usage and mRNA splicing pathways for parathyroid hormone-related protein in normal tissues and tumours

The parathyroid hormone-related protein (PTHrP) gene consists of nine exons and allows the production of multiple PTHrP mRNA species via the use of three promoters and 5' and 3' alternative splicing; as a result of 3' alternative splicing one of three protein isoforms may be produced. This organisation has potential for tissue-specific splicing patterns. We examined PTHrP mRNA expression and splicing patterns in a series of tumours and normal tissues, using the sensitive reverse transcription-polymerase chain reaction (RT-PCR) technique. Use of promoter 3 and mRNA specifying the 141 amino acid PTHrP isoform were detected in all samples. Transcripts encoding the 139 amino acid isoform were detected in all but two samples. Use of promoters 1 and 2 was less widespread as was detection of mRNA encoding the 173 amino acid isoform. While different PTHrP splicing patterns were observed between tumours, no tissue- or tumour-specific transcripts were detected. In comparing normal and tumour tissue from the same patient, an increase in the number of promoters utilised was observed in the tumour tissue. Furthermore, mRNA for the PTH/PTHrP receptor was detected in all samples, thus the PTHrP produced by these tumours may potentially act in an autocrine or paracrine fashion.