Differential responses to parathyroid hormone‐related protein (PTHrP) deficiency in the various craniofacial cartilages

PTHrP null mutant mice exhibit skeletal abnormalities both in the craniofacial region and limbs. In the growth plate cartilage of the null mutant, a diminished number of proliferating chondrocytes and accelerated chondrocytic differentiation are observed. In order to examine the effect of PTHrP deficiency on the craniofacial morphology and highlight the differential feature of the composing cartilages, we examined the various cartilages in the craniofacial region of neonatal PTHrP deficient mice. The major part of the cartilaginous anterior cranial base appeared to be normal in the homozygous PTHrP deficient mice. However, acceleration of chondrocytic differentiation and endochondral bone formation was observed in the posterior part of the anterior cranial base and in the cranial base synchondroses. Ectopic bone formation was observed in the soft tissue‐running mid‐portion of the Meckel's cartilage, where the cartilage degenerates and converts to ligament in the course of normal development. The zonal structure of the mandibular condylar cartilage was scarcely affected, but the whole condyle was reduced in size. These results suggest the effect of PTHrP deficiency varies widely between the craniofacial cartilages, according to the differential features of each cartilage. Anat Rec 255:452–457, 1999. © 1999 Wiley‐Liss, Inc.     

Expression of parathyroid hormone-related protein (PTHrP) in multiple myeloma

Multiple myeloma is a plasma cell neoplasia often associated with multiple skeletal lesions and hypercalcemia. Several cytokines, including interleukin (IL)-1, IL-6 and tumor necrosis factor-beta (TNF-beta), derived from myeloma cells are thought to accelerate osteoclastic bone resorption and cause hypercalcemia through a paracrine mechanism. We report on a case of a 69-year-old man with multiple myeloma associated with hypercalcemia and advanced osteolytic lesions. After bisphosphonate treatment and MP (melphalan and prednisolone) therapy, the patient's serum calcium level was successfully but transiently recovered to the normal range. Biochemical analysis showed a remarkable increase in serum parathyroid hormone-related protein (PTHrP; 3.7 pmol/L) and IL-6 (22.0 pg/mL). On the other hand, parathyroid hormone and 1alpha,25(OH)2 vitamin D3 were suppressed. By immunohistochemistry and in situ hybridization on aspiration-biopsied bone marrow clot sections, PTHrP mRNA and protein were detected in the cytoplasm of myeloma cells. The rate of PTHrP-positive myeloma cells was estimated to be at least one-third. Since PTHrP can, as an endocrine factor, systemically act on bone and kidney, hypercalcemia in this case might have been caused through both local osteolytic hypercalcemia and humoral hypercalcemia of malignancy mechanisms.     

Parathyroid hormone-related protein (PTHrP) production sites in elasmobranchs

This study describes the distribution of parathyroid hormone-related protein (PTHrP) antigen and its mRNA in seven species of cartilaginous fish from six elasmobranch families. Antigen was detected using antibodies to synthetic human PTHrP and the mRNA with a riboprobe to human PTHrP gene sequence. The distribution pattern of PTHrP in the cartilaginous fish studied, reflected that observed in mammals but PTHrP further occurs in some sites unique to cartilaginous fish. Of particular note was the demonstration of PTHrP in the shark skeleton, which although considered not to contain bone, may form by a process similar to that forming the early stages of mammalian endochondral bone. The distribution of PTHrP in the elasmobranch skeleton resembled the distribution of PTHrP in the developing mammalian skeleton. Differences in the staining pattern between antisera to N-terminal PTHrP and mid-molecule PTHrP in the brain and pituitary suggested that the PTHrP molecule might be post-translationally processed in these tissues. The successful use of antibodies and a probe to human PTHrP in tissues from the early vertebrates examined in this study suggests that the PTHrP molecule is conserved from elasmobranchs to humans.     

Mandibular deformities in parathyroid hormone-related protein (PTHrP) deficient mice: possible involvement of masseter muscle

Previous studies using parathyroid hormone-related protein (PTHrP) null mutant mice have indicated severe abnormalities in the endochondral ossification, suggesting that PTHrP affects chondrocyte differentiation. In this study, we found in newborn PTHrP-deficient mice some deformities in the mandible that is formed via intramembranous ossification. The mandibular ramus was bent downwards and a prominent bone crest to which the deep layer of masseter muscle was tendinously attached was observed in the mandibular body. Transmission electron microscopic studies showed that active bone formation was progressing along the tendon fibers of the masseter muscle. The examination of 3-D reconstruction models indicated that the mandibular ramus was bent at the site of muscle attachment, which was shifted in the direction of the muscle fibers. Muscle fiber type analysis using myosin ATPase staining showed that the masseter muscle in the newborn PTHrP-deficient mice contained numerous type 2B fibers, demonstrating premature maturation of this muscle. Based on these findings, we speculated that premature maturation of the masseter muscle leads, probably due to increased tensile forces, to accelerated bone crest formation and subsequent bending of the mandibular ramus. These results further suggest that PTHrP is involved in the regulation of muscle development in normal animals.     

Expression of parathyroid hormone-related protein and the parathyroid hormone/parathyroid hormone-related protein receptor in rat thymic epithelial cells

Thymic epithelial cells are an important source of cytokines and other regulatory peptides which guide thymocyte proliferation and maturation. Parathyroid hormone-related protein (PTHrP), a cytokine-like peptide, has been reported to affect the proliferation of lymphocytes in vitro. The studies presented here were undertaken to test the hypotheses that PTHrP is produced locally within the thymus where it could influence thymocyte maturation and, more specifically, that thymic epithelial cells (TEC) could be the intrathymic source of PTHrP expression. To this end, immunohistochemical studies were performed to localise PTHrP and the PTH/PTHrP receptor within the adult rat thymus. Antibodies directed against 2 different PTHrP epitopes, PTHrP(1–34) and PTHrP(34–53), demonstrated prominent specific PTHrP immunoreactivity in both subcapsular and medullary TEC. In addition, faint but specific staining for PTHrP was seen in the cortex, interdigitating between cortical lymphocytes while sparing epithelial-free subcapsular areas, thus suggesting that cortical TEC could also be a source of PTHrP immunoreactivity. In contrast, PTH/PTHrP receptor immunoreactivity was only seen in medullary and occasional septal TEC; no evidence of cortical or lymphocytic PTH/PTHrP receptor immunoreactivity was detected. Immunohistochemical studies of cultured cytokeratin-positive rat TEC confirmed the results of these in situ studies as cultured TEC were immunoreactive both for PTHrP and the PTH/PTHrP receptor. Thus these results demonstrate that PTHrP is produced by the epithelial cells of the mature rat thymus. This suggests that PTHrP, a peptide with known cytokine, growth factor and neuroendocrine actions, could exert important intrathymic effects mediated by direct interactions with TEC, or indirect effects on PTH/PTHrP receptor-negative thymocytes.     

The presence of immunoreactive parathyroid hormone-related protein in parathyroid adenoma cells.

Parathyroid hormone-related protein (PTHrP) was first identified in human malignant tumors associated with humoral hypercalcemia of malignancy. We immunohistochemically examined the distribution of PTHrP both in 7 normal parathyroid glands and in a 20 parathyroid adenomas. Sixty-five percent of parathyroid adenomas (13 cases) were positive for PTHrP, whereas only one normal parathyroid gland was positive for PTHrP in the area of transitional oxyphil cells. Many parathyroid adenomas (12 cases) were composed of both PTHrP-positive cells and--negative cells, and these two different type of cells showed a tendency to form nodules respectively in parathyroid adenoma. Although both chief cells and oxyphil or transitional oxyphil cells were positive for PTHrP in parathyroid adenoma, oxyphil or transitional oxyphil cells were more responsible for PTHrP production than chief cells. Chief cells are thought to produce parathyroid hormone mainly in parathyroid adenoma. On the other hand, little is known concerning the function and role of oxyphil or transitional oxyphil cells. Our results suggest that oxyphil or transitional oxyphil cells in parathyroid adenoma may have some functional roles different from those of chief cells through the production of PTHrP.     

Production and characterisation of monoclonal antibodies to parathyroid hormone-related protein.

The production and characterisation of 17 monoclonal antibodies to human parathyroid hormone-related protein (PTH-rP) 1-34 is described. Five of the antibodies were shown to be of high avidity (Ka 4 X 10(10)-1.9 X 10(11) L/M) and able to detect 15-100 pg PTH-rP 1-34 per tube by RIA. None cross-reacted with PTH 1-34, and inhibition studies with peptide subfragments of PTH-rP 1-34 indicated that all recognise a central region extending from residues 9-18 to between residues 23 and 34. All antibodies tested cross-reacted with native PTH-rP in culture fluids from keratinocytes and squamous cancer cell lines and in human and bovine milk. The concentrations of PTH-rP 1-34 (ng/ml) in these fluids as determined by RIA were: keratinocytes 1-3, squamous cancer 0.2-2.5, human milk, up to 80. Selected antibodies coupled to Sepharose 4B were used to extract PTH-rP from biological fluids with high yields.     

Parathyroid hormone-related protein (PTHrP) gene expression in solid tumours associated with normocalcaemia and hypercalcaemia

Parathyroid hormone-related protein (PTHrP) is an important humoral factor in the syndrome of humoral hypercalcaemia of malignancy (HHM) and its importance is evident by the many studies examining either PTHrP mRNA expression, intracellular peptide, or circulating PTHrP levels in patients with malignancy. However, the relationship between PTHrP mRNA expression, intracellular localization of peptide, and circulating PTHrP levels in the same group of patients with malignancy has not been examined. This study was carried out to explore this relationship in a group of patients with solid tumours associated with either normocalcaemia or hypercalcaemia. PTHrP mRNA and peptide were localized by in situ hybridization and immunohistochemistry respectively in 26 squamous carcinomas and 15 adenocarcinomas from patients who were either hypercalcaemic or normocalcaemic. Plasma PTHrP1–86 and serum PTH1–84 concentrations were measured by two-site immunoradiometric assays. PTHrP mRNA and peptide were localized in 11 (100 per cent) and 10 (91 per cent) of 11 squamous tumours from hypercalcaemic patients, all of whom had detectable circulating PTHrP levels, and in 14 (97 per cent) and 11 (73 per cent) respectively of 15 squamous tumours from normocalcaemic patients. PTHrP mRNA and peptide were localized in only two (28 per cent) and four (57 per cent) respectively of seven adenocarcinomas associated with hypercalcaemia. Since the majority of squamous tumours synthesized PTHrP irrespective of the calcium status of the patient, this suggests that the clinical expression of tumour-derived PTH-like bioactivity may depend on the rate of secretion of PTHrP rather than gene expression, and that the bioactivity of secreted PTHrP may be modulated by post-translational processing.     

Immunohistochemical localization of parathyroid hormone-related protein in parathyroid adenoma and hyperplasia

Parathyroid hormone-related protein (PTHrP) is invoked as the cause of humoral hypercalcaemia of malignancy (HHM); it is contained in the keratinocyte layer of normal skin; and there is evidence that is is produced by fetal parathyroids. Antibodies against synthetic PTHrP peptides have been raised in rabbits and sheep. This immunohistochemical study has found that primary parathyroid adenomata and hyperplastic glands from patients with chronic renal failure stain positively with antisera against PTHrP(1-34) and PTHrP(50-69). Primary hyperplastic glands are negative. No staining with anti-PTHrP(106-141) antiserum could be detected immunohistochemically in any of the parathyroid adenomata or hyperplasia.     

A parathyroid hormone related protein (PTHrP) implicated in hypercalcemia associated with malignancy: research of the PTHrP for novel hormonal tumor marker

A cDNA complementary to the parathyroid hormone related protein (PTHrP), the humoral hypercalcemia factor in malignancy, was recently isolated and sequenced. PTHrP expression in human carcinomas was examined (determined) by Northern blot hybridization, Southern blot hybridization and radioimmunoassay (RIA). Expression of PTHrP mRNA was detected in three out of four lung squamous cell carcinomas, two out of ten breast carcinomas and the one adenosquamous carcinoma of the maxilla. No clinical hypercalcemia was found in these PTHrP mRNA positive carcinomas. No expression of PTHrP was detected in normal human or rat tissues. In Southern blot hybridization, no amplification of PTHrP gene was found in PTHrP positive cases. An insertion in one allele of promotor region of the gene was identified in one PTHrP positive lung squamous cell carcinoma. The serum level of PTHrP was examined using human PTHrP (1-34) RIA in lung carcinomas. We found no correlation between the level of PTHrP and clinical hypercalcemia or the histopathological diagnosis. We discuss some problems of the PTHrP assay as a novel tumor marker for malignancies. A new RIA assay study using recombinant human PTHrP expressed in Escherichia coli is also reported.     

Calcium-sensing receptors and parathyroid hormone-related protein in the caudal neurosecretory system of the flounder (Platichthys flesus)

The caudal neurosecretory system of the flounder (Platichthys flesus) has been examined by immunocytochemistry and in situ hybridization for the expression of parathyroid hormone-related protein (PTHrP) and calcium-sensing receptors (CaSR). The N-terminus nucleotide and deduced amino acid sequences of flounder PTHrP were determined and used to prepare oligonucleotide probes and homologous antiserum. The Dahlgren cells of the posterior spinal cord and their axons contained PTHrP protein which was also detected around the capillaries of the urophysis. PTHrP gene expression was abundant in the Dahlgren perikarya and axons in the spinal cord, but it was absent from nerve endings in the urophysis. Calcium-sensing receptor protein was present in the Dahlgren perikarya and axons, also with abundant gene expression, but there was neither protein nor mRNA in the urophysis. There were no apparent differences between freshwater- and seawater-adapted fish in either CaSR or PTHrP expression in the caudal neurosecretory system. These observations suggest that Dahlgren cells produce PTHrP which may be released from axons abutting capillaries in the urophysis. However, the sensing of ionic calcium appears to be confined to the perikarya of the Dahlgren cells in the spinal cord neuropil, suggesting that they are responsive to calcium in the central nervous system rather than the general circulation.     

Role of parathyroid hormone (PTH) and PTH-related protein (PTHrP) in regulating mineral homeostasis during fetal development

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) play complementary and overlapping roles in regulating fetal mineral homeostasis. PTHrP is expressed within the growth plate, directs endochondral bone formation, and determines the fate of chondrocytes before bone formation can be initiated. It is expressed in placenta and is present at high levels in the fetal circulation. It stimulates placental calcium (and possibly magnesium) transfer and raises blood mineral levels above ambient maternal values in order to effect mineralization of the skeleton. It does not upregulate in response to absence of PTH or hypocalcemia, and thus, its secretion may be regulated autonomously or in response to placental signals. PTH is expressed in fetal parathyroids and placenta. Despite circulating at low levels, it has a more dominant effect than PTHrP in regulating the blood calcium and ensuring adequate mineralization of the skeleton. It may also have effects on bone formation in the steps that occur after apoptosis of hypertrophic chondrocytes. Unlike PTHrP, it increases with fetal hypocalcemia, but its secretion is constrained by the calcium-sensing receptor to maintain the adult calcium level, well below what the fetus normally achieves. PTH also stimulates placental calcium transfer, and its absence disrupts placental expression of calciotropic and cation transporter genes.     

Proapoptotic effects of parathyroid hormone-related protein in type II pneumocytes

Parathyroid hormone-related protein (PTHrP) promotes or suppresses apoptosis in various settings depending on cell type and context. PTHrP 1-34 and PTHrP 67-86 are type II cell growth factors with effects on pneumocyte growth and surfactant secretion. This study investigated the effects of 24 h pretreatment with these two peptides on rat type II cell apoptosis after 0.3 J/cm2 ultraviolet-B irradiation. Adherent cells decreased in number by 15 +/- 5% and nonadherent cells increased > 5-fold 24 h after ultraviolet irradiation. Cell loss was due predominantly to apoptosis, based on ethidium bromide exclusion, nuclear condensation, and caspase 3 activity. Nuclear condensation increased from 15.6 +/- 2.2% of irradiated cells with no treatment to 25.6 +/- 4.9 and 22.9 +/- 1.8% of cells in ultraviolet/PTHrP 1-34 and ultraviolet/PTHrP 67-86 groups, respectively (P < 0.01), along with a 60% increase in caspase 3 activity. Effects on apoptosis were unaffected by the presence or absence of serum, but were ameliorated by growth to confluence or adherence to fibronectin. PTHrP 1-34 and PTHrP 67-86 augmented inositol phosphate levels, but had minimal effects on cAMP. Thus, PTHrP 1-34 and PTHrP 67-86 sensitize type II cells to apoptosis, possibly by a phospholipase C-dependent mechanism. The effects appear to be regulated by cell-matrix and cell-cell interactions.     

Growth in craniofacial cartilages studied by 3H-thymidine incorporation.

Various cartilaginous zones in the craniofacial region were studied using radioactive thymidine incorporation. An increase in the cpm/DNA ratios was found in all zones investigated between the 10th and the 14th day with the exception of the spheno-occipital synchondrosis, corresponding to a period of great weight increase of the animals. Autoradiography of the mandibular condyle revealed no thymidine marking centrally, tending to show that this structure grows purely by surface apposition.     

Tumors of the parathyroid gland and circulating parathyroid hormone-related protein associated with persistent hypercalcemia

Neoplasms of the parathyroid glands are uncommon in all species of laboratory and domestic animals, but occur in low incidence in rats, Syrian hamsters, and dogs and rarely in mice. Proliferative lesions of the parathyroid gland include hyperplasia (diffuse and focal), adenomas, and carcinomas. The tumors may be functional or nonfunctional. Trophic atrophy of remaining parathyroid tissue is present around functional tumors. Humoral hypercalcemia of malignancy (HHM) is a syndrome that occurs in human and animal patients with certain malignant neoplasms and is characterized by hypercalcemia, hypophosphatemia, and increased osteoclastic bone resorption. The syndrome is thought to be due to the release of parathyroid hormone (PTH)-like factors by the tumor cells which bind to PTH receptors in bone and kidney and result in the clinical manifestations of HHM. Parathyroid hormone-related protein (PTHrP) is a newly purified and sequenced protein which originated from human tumors associated with HHM. PTHrP has been shown to stimulate in vitro and in vivo effects similar to PTH-like proteins isolated from tumors associated with HHM. Well characterized animal models of HHM include a rat Leydig cell tumor line (Rice-500), the rat Walker mammary carcinosarcoma, and the canine apocrine adenocarcinoma. All 3 models have been found to contain 3 biologic activities which are thought to be important in the pathogenesis of HHM, viz., in vitro bone resorbing activity, adenylate cyclase-stimulating activity of bone and kidney cells, and transforming growth factor activity. The first 2 activities are due to PTH-like proteins which are able to compete for binding to the PTH receptor. The complete spectrum of functional disturbances in patients with HHM may be the result of the combined effects of a PTH-like protein (i.e., PTHrP) and transforming growth factors.     

Biological action of parathyroid hormone (PTH)-related peptide (PTHrP) mediated either by the PTH/PTHrP receptor or the nucleolar translocation in chondrocytes

Parathyroid hormone (PTH)-related peptide (PTHrP) has been believed to act by binding the common receptor to PTH (PTH/PTHrP receptor). However, PTHrP is localized not only in the secretory pathway, but also in nucleoli by virtue of its nucleolar targeting signal (NTS). This review demonstrates the bipartite action of PTHrP on chondrocytes, the receptor-mediated and -independent signaling pathway. Mice with deletion of the PTHrP gene were characterized by a chondrodysplasia due to markedly reduced proliferation of epiphyseal chondrocytes. The PTH/PTHrP receptor was localized mainly in proliferative chondrocytes in the epiphyseal cartilage, indicating that PTHrP modulates normal proliferation via the receptor. In contrast to the receptor-mediated action, the mid-region of the amino acid sequence of PTHrP contains an NTS. The PTHrP-translation was found to initiate from both methionine-coding AUG and downstream leucine-coding CUGs in its signal sequence. When translated from CUGs, PTHrP accumulated in the nucleoli, and the translation from AUG localized PTHrP in both the Golgi apparatus and nucleoli. Therefore, nucleolar PTHrP appears to be derived from the translation initiating from both AUG and CUGs. A chondrocytic cell line expressing a full-length PTHrP, but not PTHrP lacking NTS, were resistant to apoptosis caused by serum depletion, suggesting that the nucleolar PTHrP in chondrocytes serves as a survival factor against apoptosis. Thus, PTHrP regulates chondrocyte proliferation, differentiation and apoptosis by mediating its receptor or acting directly on the nucleolus.     

Production and characterisation of monoclonal antibodies to the mid-region 37-67 sequence of parathyroid hormone-related protein.

The production and characterisation of monoclonal antibodies (MAb) to the mid-region sequence 37-67 of human parathyroid hormone-related protein (PTHRP) is described. In spite of the poor immunogenicity of this sub-fragment of PTHRP, a high percentage of specific hybrids were produced by boosting with conjugate and free peptide prior to cell fusion. Seven of the MAbs produced cross-reacted with PTHRP37-67, PTHRP1-86 and native forms of PTHRP. Inhibition studies with peptide sub-fragments of PTHRP37-67 indicated that the majority recognised the 45-59 region. In a RIA for PTHRP1-86, detection limits ranged from 0.17 to 0.9 ng PTHRP1-86/tube, and no cross-reaction was found with PTH1-84. Two MAbs 1D11 and 4B10 were shown to be of potential use in measuring PTHRP1-86 in a two-site immunoradiometric assay in combination with either a solid phase consisting of a MAb to PTHRP1-34, or iodinated affinity purified rabbit antibodies to PTHRP1-34. MAb 1D11 coupled to Sepharose was suitable for immunoextraction of PTHRP, and successfully localised PTHRP on immunoblots. Two additional MAbs were produced which recognised an epitope unique to PTHRP37-67 located in the 37-46 region of the peptide.