Parathyroid hormone-related peptide: expression in fetal and neonatal development

Continuous and intermittent exposure of neonatal rat calvarial cells to PTHrP (1-36) inhibits bone nodule mineralization in vitro by downregulating bone sialoprotein expression via the cAMP signaling pathway

The development and growth of the skeleton in the absence of parathyroid-hormone-related protein (PTHrP) is abnormal.  The shortening of appendicular bones in PTHrP gene null mice is explained by an effect of PTHrP on endochondral bone growth.  Whether or not PTHrP influences intramembranous ossification is less clear.  The purpose of this study was to determine the effect of exogenous PTHrP on intramembranous ossification in vitro.  Neonatal rat calvarial cells maintained in primary cell culture conditions that permit spontaneous formation of woven bone nodules by intramembranous ossification were studied. The expression of PTHrP, parathyroid hormone 1 receptor (PTH1R), and alkaline phosphatase (AP) by osteogenic cells in developing nodules and the effects of PTHrP (1-36) on nodule development was determined over 3-18 days. PTHrP and PTH1R were detected colonies of osteogenic cells on culture day three, and AP was detected on day six. PTHrP and its receptor were localized in pre-osteoblasts, osteoblasts, and osteocytes, and AP activity was detected in pre-osteoblasts and osteoblasts but not osteocytes. Continuous and intermittent exposure to PTHrP (1-36) decreased the number of mineralized bone nodules and bone sialoprotein (BSP) mRNA and protein, but had no effect on the number of AP-positive osteogenic cell colonies, cell proliferation, apoptosis, or osteopontin (OPN) mRNA. These results demonstrate that osteogenic cells that participate in the formation of woven bone nodules in vitro exhibit PTHrP and PTH1R before they demonstrate AP activity. Exogenous PTHrP (1-36) inhibits the mineralization of woven bone deposited during bone nodule formation in vitro, possibly by reducing the expression of BSP.

Changes in serum parathyroid hormone-related protein in breastfed preterm infants

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has the ability to activate parathyroid hormone receptors and cause hypercalcemia. In a previous study we have demonstrated high concentrations of PTHrP in both term and preterm human milk (HM). PTHrP intestinal absorption and its influence upon calcium homeostasis of the preterm infant have not been studied yet. This study assessed the correlation between PTHrP concentrations in preterm HM and PTHrP in maternal and neonatal serum.

STUDY DESIGN

We collected samples of expressed HM obtained from 16 mothers of preterm infants (25-34 weeks of gestation) and drew blood samples from both mothers and infants on postpartum days 2 and 10. PTHrP concentrations were measured by two-site immunoradiometric assay. Blood calcium (Ca), phosphorus (P), and alkaline phosphatase (ALP) concentrations were also measured.

RESULTS

Neither maternal nor neonatal PTHrP serum concentrations varied significantly after 10 days of breastfeeding. There was a correlation between PTHrP concentrations in maternal serum and HM concentrations (R² = 0.24, p = 0.04), but not between HM and neonatal serum concentrations or between PTHrP concentrations in HM and preterm serum concentrations of Ca, P, and ALP.

CONCLUSIONS

Despite high concentrations of PTHrP in preterm HM, serum concentrations of PTHrP of breastfed preterm infants did not increase over time. There was no correlation between PTHrP concentrations in HM and neonatal serum Ca concentration.

Up-regulation of fetal rat lung parathyroid hormone-related protein gene regulatory network down-regulates the Sonic Hedgehog/Wnt/betacatenin gene regulatory network

Lung development depends on endodermal Sonic Hedgehog (Shh) signaling to mesodermal Wingless/int/beta catenin (Wnt/betacatenin), followed by parathyroid hormone-related protein (PTHrP) signaling from endoderm to mesoderm. Fluid distension of fetal rat lung explants up-regulates PTHrP signaling and down-regulates Shh/Wnt/betacatenin signaling, marked by decreases in Patched, Gli, Frizzled, and Dishevelled, inducing fibroblast triglyceride uptake, type II cell saturated phosphatidylcholine, and surfactant protein-B expression. Bumetanide, which inhibits fluid distension, blocked down-regulation of the Shh/Wnt/betacatenin pathway and up-regulation of the PTHrP pathway, whereas PTHrP (1-34, 5 x 10(-7) M) treatment overcame bumetanide inhibition, and the PTHrP receptor antagonist PTHrP (7-34) amide (5 x 10(-6) M) mimicked bumetanide, indicating that PTHrP signaling mediates fluid distension-induced alveolar differentiation. Fetal rat lung explant automaturation was characterized by decreased Wnt/betacatenin signaling and increased PTHrP/PTHrP receptor signaling, up-regulating fibroblast-specific adipocyte differentiation related protein (ADRP) and peroxisome proliferator-activated receptor gamma. Wnt/betacatenin agonists (LiCl or SB415268) maintained Shh/Wnt/betacatenin signaling, blocking spontaneous up-regulation of the PTHrP pathway, whereas PTHrP or cAMP down-regulated Shh/Wnt/betacatenin signaling and stimulated PTHrP signaling for fibroblast and type II cell differentiation. This is the first evidence that alveolar fluid distension is an organizing principle for PTHrP signaling down-regulation of the Shh/Wnt/betacatenin pathway.

Expression of parathyroid hormone-related peptide and insulin-like growth factor I during rat fracture healing

Parathyroid hormone-related peptide (PTHrP) and insulin-like growth factor I (IGF-I) are both involved in the regulation of bone and cartilage metabolisms and their interaction has been reported in osteoblasts. To investigate the interaction of PTHrP and IGF-I during fracture healing, the expression of mRNA for PTHrP and IGF-I, and receptors for PTH/PTHrP and IGF were examined during rat femoral fracture healing using an in situ hybridization method and an immunohistochemistry method, respectively. During intramembranous ossification, PTHrP mRNA, IGF-I mRNA and IGF receptors were detected in preosteoblasts, differentiated osteoblasts and osteocytes in the newly formed trabecular bone. PTH/PTHrP receptors were markedly detected in osteoblasts and osteocytes, but only barely so in preosteoblasts. During cartilaginous callus formation, PTHrP mRNA was expressed by mesenchymal cells and proliferating chondrocytes. PTH/PTHrP receptors were detected in proliferating chondrocytes and early hypertrophic chondrocytes. IGF-I mRNA and IGF receptor were co-expressed by mesenchymal cells, proliferating chondrocytes, and early hypertrophic chondrocytes. At the endochondral ossification front, osteoblasts were positive for PTHrP and IGF-I mRNA as well as their receptors. These results suggest that IGF-I is involved in cell proliferation or differentiation in mesenchymal cells, periosteal cells, osteoblasts and chondrocytes in an autocrine and/or paracrine fashion. Furthermore, PTHrP may be involved in primary callus formation presumably co-operating with IGF-I in osteoblasts and osteocytes, and by regulating chondrocyte differentiation in endochondral ossification.

Developmental aspects of parathyroid hormone-related protein biology

Parathyroid hormone-related protein (PTHrP) has been discovered as a parathyroid hormone (PTH)-like factor responsible for the humoral hypercalcaemia of malignancies. Further studies revealed that PTHrP is ubiquitously expressed, in mature as well as in developing normal tissues from various species. Although not completely understood, the biological roles of PTHrP concern a variety of domains, including calcium phosphorus metabolism and bone mineralization, smooth muscle relaxation, cell growth and differentiation, and embryonic development. As a poly-hormone, PTHrP is now acknowledged to act via the paracrine, autocrine, and even the intracrine pathways. This review focuses on the main developmental features of the biology of PTHrP. During embryonic development, PTHrP is considered to be involved as a growth factor that promotes cell proliferation and delays cell terminal maturation. PTHrP has been shown to intervene in the development of various tissues and organs such as the skeleton, skin, hair follicles, tooth, pancreas, and the kidney. In addition, through its midregion sequence, which is able to promote an active transplacental calcium transport, PTHrP may intervene indirectly in the mineralization of the foetal skeleton. PTHrP has also been shown to be necessary for the normal development of the mammary gland, while huge amounts of PTHrP are found in the human milk. Finally, observations of physiologic, vasodilating effects of PTHrP in the kidney suggest its involvment in the control of renal hemodynamics, especially in the perinatal period.

Aquaporin-5 expression, but not other peripheral lung marker genes, is reduced in PTH/PTHrP receptor null mutant fetal mice

Parathyroid hormone-related peptide (PTHrP) and the parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) receptor are important developmental regulators of cell growth and differentiation in some organs. In lung, both the peptide and the receptor are expressed early in development and in alveolar cells in adults. In adult alveolar cells, PTHrP appears to promote the alveolar type II cell phenotype in vitro. Mice carrying null mutations in genes for either receptor or ligand die at birth of respiratory failure. To determine if absence of the PTH/PTHrP receptor alters morphogenesis or cellular differentiation of the distal lung, we analyzed the morphology and gene expression patterns in PTH/PTHrP receptor null mutant mice right before birth and compared them with wild-type and heterozygous null littermates. Using semiquantitative Northern blots, we observed that messenger RNA (mRNA) for aquaporin-5, the type I cell-specific water channel, was markedly decreased. The abundance of other marker mRNAs for type I and type II cell phenotypes, including T1alpha, surfactant proteins, and others, was unaltered. Gross morphology and lung pattern, assessed by in situ hybridization for surfactant protein C, were normal. We conclude therefore that, although signaling through this receptor may influence expression of specific lung genes, it does not play a major role in the general regulation of lung development and growth.

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.

Expression and role of parathyroid hormone-related protein in human renal proximal tubule cells during recovery from ATP depletion

Parathyroid hormone (PTH)-related protein (PTHrP) is widely expressed in normal fetal and adult tissues and regulates growth and differentiation in a number of organ systems. Although various renal cell types produce PTHrP, and PTHrP expression in rat proximal renal tubules is upregulated in response to ischemic injury in vivo, the role of PTHrP in the kidney is unknown. To study the effects of injury on PTHrP expression and its consequences in more detail, the immortalized human proximal tubule cell line HK-2 was used in an in vitro model of ATP depletion to mimic in vivo renal ischemic injury. These cells secrete PTHrP into conditioned medium and express the type I PTH/PTHrP receptor. Treatment of confluent HK-2 cells for 2 h with substrate-free, glucose-free medium containing the mitochondrial inhibitor antimycin A (1 microM) resulted in 75% depletion of cellular ATP. After an additional 2 h in glucose-containing medium, cellular ATP levels recovered to approximately 75% of baseline levels. PTHrP mRNA levels, as measured in RNase protection assays, peaked at 2 h into the recovery period (at four times baseline expression). The increase in PTHrP mRNA expression was correlated with an increase in PTHrP protein content in HK-2 cells at 2 to 6 h into the recovery period. Heat shock protein-70 mRNA expression was not detectable under baseline conditions but likewise peaked at 2 h into the recovery period. Treatment of HK-2 cells during the recovery period after injury with an anti-PTHrP(1-36) antibody (at a dilution of 1:250) resulted in significant reductions in cell number and uptake of [3H]thymidine, compared with nonimmune serum at the same titer. Similar results were observed in uninjured HK-2 cells. It is concluded that this in vitro model of ATP depletion in a human proximal tubule cell line reproduces the pattern of gene expression previously observed in vivo in rat kidney after ischemic injury and that PTHrP plays a mitogenic role in the proliferative response after energy depletion.

Clinicopathological implications of parathyroid hormone-related protein in human colorectal tumours

The purpose of the present study was to clarify the relationship of parathyroid hormone-related protein (PTHrP) to the oncogenesis and progression of colorectal adenocarcinoma. A total of 108 colorectal tumours, including 12 adenomas, six adenocarcinomas in adenomas, and 90 adenocarcinomas, were studied. Immunohistochemistry, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR) techniques were used to evaluate the expression of PTHrP. Positivity of immunostaining for PTHrP was defined as highly positive (++), slightly positive (+), and negative (-). None of the adenomas of background non-neoplastic mucosal epithelia showed immunostaining of PTHrP. In contrast, PTHrP was expressed in 85 (94.4 per cent) of 90 colorectal adenocarcinomas. Immunoreactivity of PTHrP was greater in poorly differentiated adenocarcinomas than in well-differentiated ones. Furthermore, advancing margins of primary tumours stained more intensely than other sites. Highly positive immunoreactivity of PTHrP, classified by histological invasiveness, was 22.6 per cent within the muscularis propria and 69.5 per cent beyond the muscularis propria. PTHrP expression was significantly correlated with differentiation, depth of invasion, lymphatic invasion, lymph node metastasis, hepatic metastases, and Dukes' classification. In carcinoma, PTHrP mRNA expression was evident in tumour cells by in situ hybridization. PTHrP transcripts were also detected in two resected human colorectal adenocarcinomas by RT-PCR. These findings suggest that PTHrP is related to carcinogenesis, differentiation, progression, and prognosis of colorectal adenocarcinomas.

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.

Temporal expression of PTHrP during endochondral bone formation in mouse and intramembranous bone formation in an in vivo rabbit model

Expression of parathyroid hormone-related protein (PTHrP) messenger RNA (mRNA) and protein was investigated throughout the developmental progression of endochondral bone formation in mouse and intramembranous bone formation in an in vivo model in rabbit, using in situ hybridization and immunohistochemistry. Endochondral bone formation was investigated in a developing embryo, newborn, and adult mouse. In fetal long bones through to newborn (day 7), PTHrP mRNA and protein were consistently expressed in chondrocytes within the proliferative, transitional, and hypertrophic zones. In addition, high levels of PTHrP were also detected in osteoblasts on the surface of trabecular bone surfaces. Similarly, at the adult stage (week 7), PTHrP mRNA and protein were consistently expressed in chondrocytes at epiphyseal ends of the subarticular cartilage, within cortical periosteum, as well as in osteoblasts located at the metaphyseal trabecular bone surfaces. Using an in vivo intramembranous bone formation model in rabbits, expression of PTHrP mRNA and protein was demonstrated in preosteoblasts prior to trabecular bone formation (1-week bone harvest). As bone formed (2-, 3-, and 4-week bone tissue harvests), PTHrP mRNA and protein were highly expressed in actively synthesizing osteoblasts and in those osteocytes embedded within the superficial layers of the bone matrix. Lining osteoblasts and osteocytes buried deeply in the bone matrix displayed weak or no signal for PTHrP. The pattern of spatial and temporal expression of PTHrP demonstrated in cartilage cells and osteoblasts in the two systems suggests an important role of PTHrP in both endochondral and intramembranous bone formation.

Cellular hypertrophy and calcification of embryonal carcinoma-derived chondrogenic cell line ATDC5 in vitro

During the process of endochondral bone formation, proliferating chondrocytes give rise to hypertrophic cells, which then deposit a mineralized matrix to form calcified cartilage prior to replacement by bone. Previously, we reported that a clonal cell line, ATDC5, undergoes efficient chondrogenic differentiation through a cellular condensation stage. Here we report that the differentiated ATDC5 cells became hypertrophic at the center of cartilage nodules, when the cells ceased to grow. Formation of hypertrophic chondrocytes took place in association with type X collagen gene expression and a dramatic elevation of alkaline phosphate (ALPase) activity. After 5 weeks of culture, mineralization of the culture could be discerned as Alizarin red-positive spots, which spread throughout the nodules even in the absence of beta-glycerophosphate. Electron microscopy and electron probe microanalysis revealed that calcification was first initiated at matrix vesicles in the territorial matrix and that it advanced progressively along the collagen fibers in a manner similar to that which occurs in vivo. The infrared spectrum of the mineralized nodules indicated two absorption doublets around 1030 cm-1 and 600 cm-1, which are characteristic of apatitic mineral. Calcifying cultures of ATDC5 cells retained responsiveness to parathyroid hormone (PTH): PTH markedly inhibited elevation of ALPase activity and calcification in the culture in a dose-dependent manner. Thus, we demonstrated that ATDC5 cells keep track of the multistep differentiation process encompassing the stages from mesenchymal condensation to calcification in vitro. ATDC5 cells provide an excellent model to study the molecular mechanism underlying regulation of cartilage differentiation during endochondral bone formation.

Immunocytochemical expression of parathyroid hormone related protein (PTHrP) in odontogenic jaw cysts

OBJECTIVE

To investigate the immunocytochemical expression of parathyroid-hormone-related protein (PTHrP) in odontogenic jaw cysts.

DESIGN

Retrospective study of archival tissue.

SETTING

University department, UK.

MATERIAL

Odontogenic keratocysts (n=27), and dentigerous and radicular cysts (n=10 each).

INTERVENTION

Immunocytochemistry by biotin streptavidin technique.

MAIN OUTCOME MEASURE

Intensity of staining of PTHrP determined by TV image analysis.

RESULTS

The epithelial linings of all the odontogenic keratocysts, 9/10 dentigerous, and 8/10 radicular cysts showed reactivity for PTHrP mainly localised to the basal and suprabasal layers. Odontogenic keratocyst linings expressed significantly higher levels of PTHrP than those of dentigerous and radicular cysts (P<0.003 in each case). There were no differences in epithelial expression of PTHrP between solitary, recurrent and naevoid basal cell carcinoma syndrome-associated odontogenic keratocysts. The fibrous tissue walls of all types of cyst reacted strongly for PTHrP with a trend towards decreasing intensity from odontogenic keratocysts, to dentigerous and then radicular cysts.

CONCLUSION

It is possible that PTHrP modulates growth and bone resorption in odontogenic cysts. PTHrP may act synergistically with interleukin-1 to increase bone resorption or stimulate osteoblasts and inhibit osteoclasts (resulting in reduced resorption) via its transforming growth factor beta-like activity.

Conflicting data on intervillous circulation in early pregnancy

According to classic embryological textbooks intervillous circulation is established early in the first trimester. This process starts with trophoblastic invasion of the decidua in which proteolytic enzymes facilitate the penetration and erosion of the adjacent maternal capillaries with formation of the lacunae. After the lacunar or previllous stage trophoblast invades deeper portions of endometrium with belonging spiral arteries. This gradual process finishes with direct opening of the spiral arteries in the intervillous space under the fully developed placenta. This classic concept of establishment of the intervillous circulation was challenged in 1987 and 1988 by the experiments of HUSTIN and SHAAPS. The authors believed that blood flow in the intervillous space is absent in incompletely development before 12 weeks of gestation. After the introduction of the new generation of far more sensitive color Doppler devices in the last few years, our group and several others reported a positive finding of intervillous circulation during the first trimester of pregnancy.

Parathyroid hormone-related peptide: immunolocalisation in normal salivary glands and in pleomorphic adenomas

Parathyroid hormone-related peptide (PTHrP) has been shown to be produced as an early step in the differentiation sequence and is considered to be a marker of some progenitor cells. We investigated the presence and distribution of PTHrP in 7 normal parotid glands and in 18 salivary pleomorphic adenomas (PA). Localisation of PTHrP was studied by immunohistochemistry with a three-step unlabelled peroxidase-antiperoxidase method. In the normal glands PTHrP is found mainly in the basal and dark cells, and to a lesser extent in the light cells of the ducts. In PA the inner layer of tubulo-ductal structures and all cells of the cyst-like structures show strong positivity for PTHrP. Scattered cells in the dense clusters also stain strongly. Virtually all tumour cells in myxoid and chondroid areas are devoid of staining. In clusters of squamous metaplasia, most cells are slightly positive and scattered cells are stained strongly. PTHrP contributes to cellular differentiation and is also related to keratinisation. We suggest that the PTHrP-positive inner layer cells in pleomorphic adenomas represent a step in the squamous differentiation and in the further elaboration of the tubulo-ductal structures.

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

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

Identification of Metallothionein- and parathyroid hormone-related peptide (PTHrP)-positive cells in salivary gland tumours

Ductal basal cells and myoepithelial cells (MEC) of normal salivary gland share metallothionein (MT)-positivity, while PTHrP positivity is restricted to ductal basal cells. We studied 21 benign and 4 malignant tumours in which MEC are thought to play a role using immuno-histochemical methods for detecting the presence of MT and PTHrP positive cells. In benign tumours, a shared positivity for MT and PTHrP is found in the inner layer of tubulo-ductal and trabecular structures, in part of the cells in the myxoid and chondroid matrices of pleomorphic adenoma, and in the basal epithelial lining of Warthin's tumours. In myoepithelioma almost all tumour cells demonstrate MT reactivity and a restricted positivity for PTHrP. MT-positive cells in oncocytoma were demonstrated in the periphery of some oncocytic islets, while PTHrP positivity was restricted to a few oncocytic cells. In malignant tumours, positivity for MT is found in the periphery of epithelial clusters of mucoepidermoid carcinomas, while PTHrP-positive cells are seen in cyst-like structures and scattered cells in solid arrangements of squamous cells. Although the biologic significance of the presence of MT in neoplastic cells is not yet clearly understood, MT may be necessary for the growth and differentiation in actively growing cells. The variability of MT expression in salivary gland tumours could be a reflection of the morphological heterogeneity and correlate with the degree of differentiation and maturation of the tumour cells. The observations suggest that MT may be considered an oncodevelopmental product.

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Parathyroid hormone-related peptide is expressed and rapidly inducible in human liver cell cultures that have a bile duct phenotype

Parathyroid hormone-related peptide is the major factor responsible for hypercalcemia of malignancy. There is increasing evidence that parathyroid hormone-related peptide also plays an important role in the growth and differentiation of both neoplastic and non-neoplastic cells. Recently we found that reactive human bile ductules and cholangiocarcinomas, but not normal bile ducts, human hepatocytes nor hepatocellular carcinomas, express parathyroid hormone-related peptide and we speculated that parathyroid hormone-related peptide may function as a growth and differentiation factor for bile ductular epithelial cells. Using a specific polyclonal antibody for immunostaining and a digoxigenin-random prime-labeled probe for in situ hybridization assay, we found that only cell lines with a bile duct phenotype expressed parathyroid hormone-related peptide and its mRNA. HepG2 cells with hepatocellular phenotype (CK19-, CK7-, CK8+, CK18+, albumin+) do not express parathyroid hormone-related peptide. However, A16 (HepG2 derived cell line) expressing bile duct marker CK19, also expressed parathyroid hormone-related peptide, while hepatocyte markers CK8, CK18, CALLA and albumin were negative. In addition, the H1 cell line (adult human hepatocytes immortalized in our laboratory by SV40 DNA transfection, passaged at least 40 times and cultured for 13 months) expressed bile duct marker CK7 and parathyroid hormone-related peptide, while hepatocyte markers CK8, CK18, CALLA and albumin were negative. Previous studies demonstrated that parathyroid hormone-related peptide gene expression in keratinocytes can be modulated by serum, growth factors and cycloheximide although there is a species and cellular specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of parathyroid hormone-related protein in prostatic intraepithelial neoplasia

Parathyroid hormone-related protein (PTHrP) is a regulatory protein hormone that has been associated with normal fetal growth and differentiation as well as fetal calcium regulation. Parathyroid hormone-related protein has been implicated in a variety of carcinomas as a major factor in the development of humoral hypercalcemia of malignancy and may also play a role as an autocrine growth factor. In a previous immunohistochemical study we found that all prostatic adenocarcinomas (CAP) express PTHrP. In the current study, we evaluated PTHrP in prostate intraepithelial neoplasia (PIN) in radical prostatectomy specimens. A validated mouse monoclonal antibody, 9H7, raised against fragment 109-141 of the carboxy-terminus of PTHrP was used for immunostaining. The results generally showed negative to weak staining of normal and hyperplastic tissue and strong staining in PIN. The staining intensity was further evaluated by computer based image analysis. The relative optical density in PIN (9.24 +/- 9.05) was significantly (P = .008) higher than that in normal gland (.00 +/- 3.6). These findings suggest that PTHrP may be involved in the pathogenesis of prostatic dysplasia, and its immunohistochemical evaluation may have diagnostic use in the evaluation of PIN.

Demonstration of parathyroid hormone-related protein in meninges and its receptor in astrocytes: evidence for a paracrine meningo-astrocytic loop

In contrast to the nervous and glial tissue of the adult rat brain the meninges are immunoreactive for parathyroid hormone-related protein (PTHrP), a hormone that binds with high affinity to the recently cloned PTH/PTHrP receptor. Accordingly immunoreactivity is found in cultured meningeal cells but not in astrocytes. In contrast, astrocytes but not meningeal cells synthesize the mRNA for the PTHrP receptor shown by reverse transcription of total RNA preparations and subsequent polymerase chain reaction with primers specific for the PTHrP receptor. The expression of the PTH/PTHrP receptor was confirmed by the dose-dependent activation of the adenylate cyclase in astrocytes and the rapid development of cellular processes following on incubation with PTHrP. We conclude that PTHrP secreted by meninges forms a paracrine meningo-astrocytic loop and may cause astrocytic differentiation, possibly involved in the formation of the glial limiting membrane.

Expression of parathyroid hormone-related peptide in human thyroid tumours

The purpose of this study was to evaluate the distribution of parathyroid hormone-related peptide (PTHrP) in human thyroid tissues. The presence of PTHrP was studied immunohistochemically in 107 consecutive patients with human thyroid tumours. PTHrP expression was revealed in 97.6 per cent of carcinomas, but not in paranodal normal thyroid epithelial cells. Although there were no differences in the incidence of PTHrP positivity among papillary, follicular, and anaplastic carcinoma cases, PTHrP expression levels were correlated with the growth pattern of thyroid cancer. Strong immunopositivity was detected in 67.3 per cent of papillary growth tissues in papillary carcinomas. A tissue growth pattern consisting of colloid-absent follicles had a high incidence of strong immunopositivity irrespective of the histological type of tumour. Anaplastic carcinoma without colloid production also showed strong immunoreactivity in all cases. In contrast, a growth pattern of colloid-rich follicles did not show strong immunopositivity in either papillary or follicular carcinomas. Follicular adenomas showed positive immunostaining in only one case, and no adenomatous goitres showed PTHrP antigens. In situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR) revealed strong PTHrP mRNA in thyroid cancer tissues, but not in normal thyroid tissues. PTHrP expression was not associated with metastasis, calcification, or hypercalcaemia in thyroid cancers. These results suggest that the expression of PTHrP in human thyroids is closely related to the malignant alteration of normal thyroid epithelial cells, especially in the growth pattern of thyroid carcinoma tissues.

Localization of parathyroid hormone-related peptide (PTHrP) and PTH/PTHrP receptor mRNAs in rat brain

Parathyroid hormone (PTH)-related peptide (PTHrP) has been identified in human tumors associated with the syndrome of humoral hypercalcemia of malignancy. PTHrP mRNA is also expressed in a variety of non-malignant tissues, suggesting that PTHrP is an endogenous peptide with as-yet unidentified autocrine or paracrine functions in normal tissues, including brain (Weir et al., Proc. Natl. Acad. Sci., 87 (1990) 108-112). In the present study, we used in situ hybridization to examine the expression of PTHrP and the common receptor for PTH and PTHrP in adult rat brain. Widespread yet anatomically discrete patterns of hybridization were observed using 35S-labeled antisense cRNA probes. PTHrP gene expression was highest in the supramamillary nucleus of the hypothalamus, medial superior olivary nucleus, and in subpopulations of cells in the neostriatum, hippocampus, and cerebral cortex. Other major sites of PTHrP gene expression included the amygdala, midline thalamic nuclei, pontine nuclei, choroid plexus, and the anterior pituitary gland. Highest levels of PTH/PTHrP receptor mRNA were in the mesencephalic portion of the trigeminal nucleus and the trigeminal ganglion, the lateral reticular, pontine and reticulotegmental nuclei, the hypoglossal nucleus and area postrema. Other major sites of PTH/PTHrP receptor expression included the anterodorsal nucleus of the thalamus, basolateral amygdala, entorhinal cortex, parasubiculum, cells in the Purkinje cell layer of the cerebellum, vestibular nuclei, ventral cochlear nucleus, the motor nucleus of the trigeminal, and the facial and external cuneate nuclei. The expression of genes encoding PTHrP and its receptor in discrete areas of the brain suggests that PTHrP may function as a neurotransmitter in the central nervous system.

Parathyroid hormone-related protein: a potential autocrine growth regulator in human prostate cancer cell lines

OBJECTIVE

We recently demonstrated that parathyroid hormone-related protein (PTHrP) is widely expressed by human prostate cancer tissue, suggesting that PTHrP might be involved in the growth and development of prostate cancer. To study this further, the production of PTHrP and its biologic effect were investigated using human prostate cancer cell lines.

METHODS

The cell lines used were one androgen-dependent cell line, LNCaP, and two androgen-independent cell lines, PC-3 and DU-145. PTHrP secreted by cancer cells was measured by radioimmunoassay. The effect of PTHrP on DNA synthesis in these cells was determined by thymidine incorporation assay.

RESULTS

All cell lines secreted immunodetectable levels of PTHrP in the culture-conditioned media. PC-3 cells secreted significantly higher amounts than the other two cell lines. A synthetic peptide, PTHrP(1-34), stimulated thymidine uptake in PC-3 and DU-145 cells more than threefold the control under serum-free and steroid-free conditions, whereas LNCaP was not affected. However, in the presence of dihydrotestosterone, DNA synthesis of LNCaP cells was stimulated by PTHrP in a dose-dependent manner. Additionally, this PTHrP-induced DNA synthesis was completely neutralized by a validated mouse monoclonal antibody (8B12) raised against PTHrP(1-34).

CONCLUSIONS

Our data suggest that PTHrP may play a significant role in the growth of prostate cancer by acting locally in an autocrine fashion.

Expression of parathyroid hormone-related protein in the rat glomerulus and tubule during recovery from renal ischemia

Parathyroid hormone-related protein (PTHrP) is widely expressed in normal adult and fetal tissues, where it acts in an autocrine/paracrine fashion, stimulates growth and differentiation, and shares early response gene characteristics. Since recovery from renal injury is associated with release of local growth factors, we examined the expression and localization of PTHrP in normal and ischemic adult rat kidney. Male Sprague-Dawley rats underwent complete bilateral renal artery occlusion for 45 min, followed by reperfusion for 15 min, and 2, 6, 24, 48, and 72 h. Renal PTHrP mRNA levels, when compared with sham-operated animals, increased twofold after ischemia, and peaked within 6 h after reperfusion. PTH receptor, beta-actin, and cyclophilin mRNA levels all decreased after ischemia. PTHrP immunohistochemical staining intensity increased in proximal tubular cells after ischemia, changing its location from diffusely cytoplasmic to subapical by 24 h after reperfusion. In addition, PTHrP localized to glomerular epithelial cells (visceral and parietal), but not to mesangial cells. PTHrP and PTH stimulated proliferation two- to threefold in cultured mesangial cells. We conclude that PTHrP mRNA and protein production are upregulated after acute renal ischemic injury, that PTHrP is present in glomerulus and in both proximal and distal tubular cells, and that PTHrP stimulates DNA synthesis in mesangial cells. The precise functions of PTHrP in normal and injured kidney remain to be defined.

Parathyroid hormone-related peptide expression in primary and metastatic liver tumours

Parathyroid hormone-related peptide (PTHrP) is a major factor in the pathophysiology of hypercalcaemia of malignancy. Recent evidence suggests that PTHrP may play an important role in the growth and differentiation of neoplastic as well as non-neoplastic cells. PTHrP was originally detected in normal fetal, but not adult, liver. We have used immunocytochemistry to show that reactive human bile ductules expressing a neuroendocrine phenotype contain immunoreactive PTHrP. These observations raised the possibility that PTHrP immunoreactivity may be useful in the differential diagnosis of primary liver tumours and metastases of adenocarcinoma. A total of 24 primary liver tumours and 22 metastases of adenocarcinoma were studied. All cholangiocarcinomas showed immunopositivity for PTHrP and chromogranin A, while all hepatocellular carcinomas were negative for PTHrP and showed only focal and weak positivity for chromogranin A. Mixed types of primary liver tumour contained PTHrP immunoreactivity only in the areas of cholangiocellular differentiation. Moreover, all metastatic adenocarcinomas were negative for PTHrP and chromogranin A except for two out of five metastatic breast adenocarcinomas. These two patients had bone metastases and hypercalcaemia and thus did not yield differential diagnostic problems with cholangiocarcinoma. None of the patients with cholangiocarcinoma and hepatocellular carcinoma had hypercalcaemia. We conclude that PTHrP is a useful marker for primary cholangiocarcinoma, especially in the differential diagnosis of hepatocellular carcinoma and metastatic adenocarcinoma.

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.

Parathyroid hormone-related protein a peptide of diverse physiologic functions

Parathyroid hormone-related protein (PTHrP) is the factor responsible for the syndrome of humoral hypercalcemia of malignancy. PTHrP is produced by a multitude o f normal as well as malignant cells, and exerts both classic parathyroid hormone (PTH)-like and PTH-unlike effects. The molecular cloning of the PTHrP gene, and the subsequent recognition of its widespread expression in normal tissues under normal physiologic conditions, has prompted intense inquiry into its biologic function. PTHrP appears to act in an autocrine or paracrine fashion in (a) normal embryogenesis and neonatal development, (b) cellular growth and differentiation, (c) reproduction and lactation, (d) epithelial calcium transport, and (e) smooth muscle relaxation. These five key emerging physiologic roles of PTHrP are the focus of this review.

Reactive human bile ductules express parathyroid hormone-related peptide

Various cholestatic liver diseases as well as regeneration after submassive necrosis are accompanied by a striking increase in the number of bile ductules. These reactive bile ductules are thought to arise either from proliferation of pre-existing bile ductules or bile ductule-related facultative stem cells, or from ductular metaplasia of hepatocytes. Recently, we found that reactive bile ductules display neuro-endocrine features, and speculated that the substance(s), produced in the neuro-endocrine granules, might play a role in their growth and/or differentiation through an autocrine or paracrine pathway. Parathyroid hormone-related peptide has been shown to be encoded by a growth factor-regulated gene that may play a role in cell growth and differentiation. We studied the immunohistochemical expression of this peptide in human liver, including three normal biopsies, 11 cases of cholestatic liver disease, six cases of focal nodular hyperplasia and three cases of regenerating liver. In regenerating liver, primary biliary cirrhosis, primary sclerosing cholangitis and partial or intermittent obstruction, the majority of reactive ductular cells expressing neuro-endocrine markers also expressed parathyroid hormone-related peptide. In focal nodular hyperplasia, a smaller number of bile ductular cells expressed the peptide. These findings suggest that parathyroid hormone-related peptide is localized in bile ductular cells and may indicate a role for this hormone in the growth and/or differentiation of human reactive bile ductules.