Identification of transcripts encoding a parathyroid hormone-like peptide in messenger RNAs from a variety of human and animal tumors associated with humoral hypercalcemia of malignancy

Parathyroid Hormone-Related Protein, Its Regulation of Cartilage and Bone Development, and Role in Treating Bone Diseases

Although parathyroid hormone-related protein (PTHrP) was discovered as a cancer-derived hormone, it has been revealed as an important paracrine/autocrine regulator in many tissues, where its effects are context dependent. Thus its location and action in the vasculature explained decades-long observations that injection of PTH into animals rapidly lowered blood pressure by producing vasodilatation. Its roles have been specified in development and maturity in cartilage and bone as a crucial regulator of endochondral bone formation and bone remodeling, respectively. Although it shares actions with parathyroid hormone (PTH) through the use of their common receptor, PTHR1, PTHrP has other actions mediated by regions within the molecule beyond the amino-terminal sequence that resembles PTH, including the ability to promote placental transfer of calcium from mother to fetus. A striking feature of the physiology of PTHrP is that it possesses structural features that equip it to be transported in and out of the nucleus, and makes use of a specific nuclear import mechanism to do so. Evidence from mouse genetic experiments shows that PTHrP generated locally in bone is essential for normal bone remodeling. Whereas the main physiological function of PTH is the hormonal regulation of calcium metabolism, locally generated PTHrP is the important physiological mediator of bone remodeling postnatally. Thus the use of intermittent injection of PTH as an anabolic therapy for bone appears to be a pharmacological application of the physiological function of PTHrP. There is much current interest in the possibility of developing PTHrP analogs that might enhance the therapeutic anabolic effects.

New concepts of breast cell communication to bone

Lactation is the most extreme case of normal physiological bone loss during a lifetime, and breast cancers have a strong tendency to metastasize to bone. In both the physiological and pathological circumstances, parathyroid hormone-related peptide (PTHrP) plays a central role. Until recently there were no regulatory mechanisms to explain the induction of endocrine PTHrP secretion from breast cells during lactation. The mammary epithelium possesses a local serotonin signaling system which drives PTHrP expression during lactation and in breast cancer cells. The mammary gland serotonin system is highly induced in response to alveolar dilation due to milk secretion. Discovery of serotonergic control of PTHrP suggests that it may be possible to manipulate the breast-to-bone axis by targeting serotonin signaling.

E-selectin ligand 1 regulates bone remodeling by limiting bioactive TGF-β in the bone microenvironment

TGF-β is abundantly produced in the skeletal system and plays a crucial role in skeletal homeostasis. E-selectin ligand-1 (ESL-1), a Golgi apparatus-localized protein, acts as a negative regulator of TGF-β bioavailability by attenuating maturation of pro-TGF-β during cartilage homeostasis. However, whether regulation of intracellular TGF-β maturation by ESL-1 is also crucial during bone homeostasis has not been well defined. Here, we show that Esl-1(-/-) mice exhibit a severe osteopenia with elevated bone resorption and decreased bone mineralization. In primary culture, Esl-1(-/-) osteoclast progenitors show no difference in osteoclastogenesis. However, Esl-1(-/-) osteoblasts show delayed differentiation and mineralization and stimulate osteoclastogenesis more potently in the osteoblast-osteoclast coculture, suggesting that ESL-1 primarily acts in osteoblasts to regulate bone homeostasis. In addition, Esl-1(-/-) calvaria exhibit an elevated mature TGF-β/pro-TGF-β ratio, with increased expression of TGF-β downstream targets (plasminogen activator inhibitor-1, parathyroid hormone-related peptide, connective tissue growth factor, and matrix metallopeptidase 13, etc.) and a key regulator of osteoclastogenesis (receptor activator of nuclear factor κB ligand). Moreover, in vivo treatment with 1D11, a pan-TGF-β antibody, significantly improved the low bone mass of Esl-1(-/-) mice, suggesting that elevated TGF-β signaling is the major cause of osteopenia in Esl-1(-/-) mice. In summary, our study identifies ESL-1 as an important regulator of bone remodeling and demonstrates that the modulation of TGF-β maturation is pivotal in the maintenance of a homeostatic bone microenvironment and for proper osteoblast-osteoclast coupling.

Parathyroid Hormone-Related Protein (PTHrP): A Key Regulator of Life/Death Decisions by Tumor Cells with Potential Clinical Applications

Parathyroid hormone-related protein (PTHrP), classically regarded as the mediator of the humoral hypercalcemia of malignancy syndrome, is a polyhormone that undergoes proteolytic processing into smaller bioactive forms. These bioactive forms comprise an N-terminal- as well as midregion- and C-terminal peptides, which have been shown to regulate various biological events, such as survival, proliferation and differentiation, in diverse cell model systems, both normal and pathological. A number of experimental data have demonstrated that PTHrP is also able to modulate tumor-relevant phenotypic expressions, thereby playing a role in early and advanced tumorigenesis, and in the response to treatment. In particular, interest has mainly been focused on the effects of PTHrP on cell proliferation/apoptosis, migration and invasion, which are the main roles involved in cancer development in vivo. The objective of this review is to discuss collectively the literature data on the molecular and biochemical basis of the mechanisms underlying the different, and sometimes opposite, effects exerted by PTHrP on various neoplastic cytotypes, with some final comments on both present and potential utilization of PTHrP as a target for anti-cancer therapy.

Development of craniofacial structures in transgenic mice with constitutively active PTH/PTHrP receptor

Parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP) regulate calcium homeostasis, and PTHrP further regulates growth and development. A transgenic mouse carrying the constitutively active PTH/PTHrP receptor (HKrk-H223R) under the control of the mouse bone and odontoblast-specific alpha1(I) collagen promoter (Col1-caPPR) has been developed to demonstrate the complex actions of this mutant receptor in hard tissue formation. We have further characterized Col1-caPPR mice abnormalities in the craniofacial region as a function of development. Col1-caPPR mice exhibited a delay in embryonic bone formation, followed by expansion of a number of craniofacial bones including the maxilla and mandible, delay in tooth eruption and teratosis, and a disrupted temporomandibular joint (TMJ). These findings suggest that the Col1-caPPR mouse is a useful model for characterization of the downstream effects of the constitutively active receptor during development and growth, and as a model for development of treatments of human diseases with similar characteristics.

Mechanical regulation of PTHrP expression in entheses

The PTHrP gene is expressed in the periosteum and in tendon and ligament insertion sites in a PTHrP-lacZ knockin reporter mouse. Here, we present a more detailed histological evaluation of PTHrP expression in these sites and study the effects of mechanical force on PTHrP expression in selected sites. We studied the periosteum and selected entheses by histological, histochemical, and in situ hybridization histochemical techniques, and tendons or ligaments were unloaded by tail suspension or surgical transection. In the periosteum, PTHrP is expressed in the fibrous layer and the type 1 PTH/PTHrP receptor (PTH1R) in the subjacent cambial layer. PTHrP has distinct temporospatial patterns of expression in the periosteum, one hot spot being the metaphyseal periosteum in growing animals. PTHrP is also strongly expressed in a number of fibrous insertion sites. In the tibia these include the insertions of the medial collateral ligament (MCL) and the semimembranosus (SM). In young animals, the MCL and SM sites display a combination of underlying osteoblastic and osteoclastic activities that may be associated with the migration of these entheses during linear growth. Unloading the MCL and SM by tail suspension or surgical transection leads to a marked decrease in PTHrP/lacZ expression and a rapid disappearance of the subjacent osteoblastic population. We have not been able to identify PTHrP-lacZ in any internal bone cell population in the PTHrP-lacZ knockin mouse in either a CD-1 or C57Bl/6 genetic background. In conclusion, we have identified PTHrP expression in surface structures that connect skeletal elements to each other and to surrounding muscle but not in intrinsic internal bone cell populations. In these surface sites, mechanical force seems to be an important regulator of PTHrP expression. In selected sites and/or at specific times, PTHrP may influence the recruitment and/or activities of underlying bone cell populations.

An etiologic model proposing that sporadic adult-onset carcinoma is extramedullary hematopoiesis

This model proposes that primary carcinomatous tumors and almost all metastases are extramedullary hematopoietic tissue formed to compensate for reduced hematopoietic activity in the bone marrow. These marrow lesions are currently considered to be metastatic in origin, but as fibrosis and sclerosis are identifying features they are here equated to myelofibrosis. Myelofibrotic marrow is characterized by an increase in the number and size of vascular sinusoids. The increased blood flow suggested by this morphology, and observed in myelofibrosis patients, causes a rise in marrow pressure which may trigger the fibrosis. Specific carcinoma morphologies are equated to stages in endochondral bone and marrow formation and, as such, cancer cell identity varies with morphology. For example, infiltrating carcinomas of the breast consist of collagen and mucoid secreting cells in single file formation. This morphology is equated to the cartilagenous stage of marrow formation, when mesenchymal stem cells proliferate and differentiate into chondroblasts. In this model "infiltrating" cells arise in situ from stem cells located in the connective tissue. Tubular breast carcinoma, with its single layer of osteoblast-like carcinoma cells encircling small lumens and long branching tubules, is equated to the trabecular stage of marrow formation during which osteoblasts surround small pieces of calcified cartilage and begin secreting osteoid that will form the trabeculae. Lobular carcinoma in situ consists of cancer cell clusters separated by narrow clear spaces that, under high magnification, appear vascular. This morphology is equated to hematopoietic tissue in which primitive hematopoietic cells lie between anastomosing sinusoids. Similar cartilagenous, trabecular and hematopoietic morphologies can be found in carcinomatous tumors of most organs, but the nomenclature is variable. The hematopoietic carcinomas share numerous features with hematopoietic tissue including a structure composed of intermingled normoxic and hypoxic regions and a metabolism characterized by elevated levels of glycolysis. They also contain similar proportions of clonal cells. If this model is correct it necessitates a change in the treatment of carcinoma. If cancer cells are not the enemy, but desperately needed immature blood cells, and the medical problem is not the presence of tumors, but the inefficiency of this extramedullary hematopoietic tissue, then treatment should focus on increasing marrow hematopoiesis. As evidence suggests that the marrow lesion is the result of increased hydrostatic pressure this could be done by reducing blood volume. One way to accomplish this may be through the ingestion of ephedrine, as it is hypothesized to increase vascular tone.

Initial characterization of PTH-related protein gene-driven lacZ expression in the mouse

The PTHrP gene generates low-abundance mRNA and protein products that are not easily localized by in situ hybridization histochemistry or immunohistochemistry. We report here a PTHrP-lacZ knockin mouse in which beta-gal activity seems to provide a simple and sensitive read-out of PTHrP gene expression.

INTRODUCTION

PTH-related protein (PTHrP) is widely expressed in fetal and adult tissues, typically as low-abundance mRNA and protein products that maybe difficult to localize by conventional methods. We created a PTHrP-lacZ knockin mouse as a means of surveying PTHrP gene expression in general and of identifying previously unrecognized sites of PTHrP expression.

MATERIALS AND METHODS

We created a lacZ reporter construct under the control of endogenous PTHrP gene regulatory sequences. The AU-rich instability sequences in the PTHrP 3' untranslated region (UTR) were replaced with SV40 sequences, generating products with lacZ/beta gal kinetics rather than those of PTHrP. A nuclear localization sequence was not present in the construct.

RESULTS

We characterized beta-galactosidase (beta-gal) activity in embryonic whole mounts and in the skeleton in young and adult animals. In embryos, we confirmed widespread PTHrP expression in many known sites and in several novel epidermal appendages (nail beds and footpads). In costal cartilage, beta-gal activity localized to the perichondrium but not the underlying chondrocytes. In the cartilaginous molds of forming long bones, beta-gal activity was first evident at the proximal and distal ends. Shortly after birth, the developing secondary ossification center formed in the center of this PTHrP-rich chondrocyte population. As the secondary ossification center developed, it segregated this population into two distinct PTHrP beta-gal+ subpopulations: a subarticular subpopulation immediately subjacent to articular chondrocytes and a proliferative chondrocyte subpopulation proximal to the chondrocyte columns in the growth plate. These discrete populations remained into adulthood. beta-gal activity was not identified in osteoblasts but was present in many periosteal sites. These included simple periosteum as well as fibrous tendon insertion sites of the so-called bony and periosteal types; the beta-gal-expressing cells in these sites were in the outer fibrous layer of the periosteum or its apparent equivalents at tendon insertion sites. Homozygous PTHrP-lacZ knockin mice had the expected chondrodysplastic phenotype and a much expanded region of proximal beta-gal activity in long bones, which appeared to reflect in large part the effects of feedback signaling by Indian hedgehog on proximal cell proliferation and PTHrP gene expression.

CONCLUSIONS

The PTHrP-lacZ mouse seems to provide a sensitive reporter system that may prove useful as a means of studying PTHrP gene expression.

Nuclear targeting of a midregion PTHrP fragment is necessary for stimulating growth in breast cancer cells

Parathyroid-hormone related protein (PTHrP) is the primary factor in humoral hypercalcemia of malignancy and is highly secreted by breast cancers. The pro-hormone undergoes post-translational processing and cleavage to give rise to mature secretory peptides, one of which is midregion PTHrP (38-94/95/101) containing a nuclear localisation sequence (NLS) in amino acids (87-106). The current study investigates whether the NLS in midregion PTHrP is important in breast cancer growth. PTHrP-(67-101), a midregion PTHrP fragment containing NLS-(87-101) significantly increased growth of MCF-7 and MDA-MB231 cells (126.3 and 121.3% of control respectively in serum conditions), independent of PTHR1 whereas PTHrP-(67-86), which lacks the NLS did not. Fluorescent-labelled PTHrP-(67-101) translocated to the nucleus, whereas PTHrP-(67-86) remained cytosolic and a scrambled(+NLS) peptide was not internalised. In comparison, no growth influence or uptake was seen in non-tumour breast cells (Hs578Bst). Increases in intracellular calcium mobilisation were observed in breast cancer cells stimulated with both PTHrP-(67-101) and PTHrP-(67-86) (EC(50) of 3.2 pM and 2.2 pM respectively for MCF-7 cells), whereas inositide turnover was not detected. Both nuclear uptake and calcium signalling were attenuated in the presence of EGTA, but not with U73122 or N-terminal PTHrP peptides. Our studies indicate that the NLS-containing midregion PTHrP peptide is dependent on both internalisation and nuclear translocation to induce growth in breast cancer cells. These findings highlight the importance of midregion PTHrP and its receptor in breast cancer growth and may provide potential targets for future therapeutic intervention.

Altered expression of inflammatory cytokines in primary osteoarthritis by human T lymphotropic virus type I retrovirus infection: a cross-sectional study

Human T cell leukaemia virus type I (HTLV-I) is known to be involved in late-onset chronic polyarthritis as HTLV-I-associated arthropathy. However, it is unclear whether HTLV-I infection could modify the pathophysiology of osteoarthritis (OA). In this study we compared several inflammatory cytokines, such as C-terminal parathyroid hormone-related peptide (C-PTHrP), soluble interleukin-2 receptor (sIL-2R) and interleukin (IL)-6, and an osteo-destruction marker, deoxypyridinoline, in synovial fluid (SF) samples obtained from 22 HTLV-I carriers and 58 control non-carrier patients with OA. These patients were diagnosed clinically and radiographically with primary OA affecting one or both knee joints, and were similar with regard to age, sex and clinical symptoms. We also performed histopathological examination as well as immunohistochemistry of HTLV-I-derived Tax protein in eight synovial tissues taken from carrier patients. C-PTHrP in SF was significantly higher in HTLV-I carriers (287 ± 280 pM) than in non-carriers (69 ± 34 pM), and the concentration in 13 carriers was above the upper range of OA. In HTLV-I carriers, the concentrations of sIL-2R (741 ± 530 IU/ml), IL-6 (55 ± 86 ng/ml) and deoxypyridinoline (3.1 ± 1.8 nM) were higher than in non-carriers (299 ± 303, 2.5 ± 4.0, 0.96 ± 1.0, respectively), and correlated positively with C-PTHrP. C-PTHrP, sIL-2R and IL-6 concentrations in SF positive for IgM antibody against HTLV-I antigen, a marker of persistent viral replication, were higher than of IgM-negative SF. Histologically, five and two synovia showed mild and moderate synovial proliferation with or without some degree of inflammatory reaction, respectively, and could not be distinguished from OA. Tax-positive synoviocytes were observed sparsely in all samples, and often appeared frequently in actively proliferating regions. Our results suggest that although HTLV-I infection does not necessarily worsen the clinical outcome and local synovitis, the virus can potentially modify the pathophysiology of OA by increasing the inflammatory activity in a subset of carrier patients, especially those with IgM antibody. Longitudinal studies are required to assess the association between HTLV-I infection and OA.

Humoral hypercalcemia of malignancy: severe combined immunodeficient/beige mouse model of adult T-cell lymphoma independent of human T-cell lymphotropic virus type-1 tax expression

The majority of patients with adult T-cell leukemia/lymphoma (ATL) resulting from human T-cell lymphotropic virus type-1 (HTLV-1) infection develop humoral hypercalcemia of malignancy (HHM). We used an animal model using severe combined immunodeficient (SCID)/beige mice to study the pathogenesis of HHM. SCID/beige mice were inoculated intraperitoneally with a human ATL line (RV-ATL) and were euthanized 20 to 32 days after inoculation. SCID/beige mice with engrafted RV-ATL cells developed lymphoma in the mesentery, liver, thymus, lungs, and spleen. The lymphomas stained positively for human CD45RO surface receptor and normal mouse lymphocytes stained negatively confirming the human origin of the tumors. The ATL cells were immunohistochemically positive for parathyroid hormone-related protein (PTHrP). In addition, PTHrP mRNA was highly expressed in lymphomas when compared to MT-2 cells (HTLV-1-positive cell line). Mice with lymphoma developed severe hypercalcemia. Plasma PTHrP concentrations were markedly increased in mice with hypercalcemia, and correlated with the increase in plasma calcium concentrations. Bone densitometry and histomorphometry in lymphoma-bearing mice revealed significant bone loss because of a marked increase in osteoclastic bone resorption. RV-ATL cells contained 1.5 HTLV-1 proviral copies of the tax gene as determined by quantitative real-time polymerase chain reaction (PCR). However, tax expression was not detected by Western blot or reverse transcriptase (RT)-PCR in RV-ATL cells, which suggests that factors other than Tax are modulators of PTHrP gene expression. The SCID/beige mouse model mimics HHM as it occurs in ATL patients, and will be useful to investigate the regulation of PTHrP expression by ATL cells in vivo.

Hypercalcaemia associated with chronic lymphocytic leukaemia in a Giant Schnauzer

A 7-year-old male Giant Schnauzer was referred with a history of severe vomiting, lethargy, weight loss, polydipsia and polyuria. Detailed investigations revealed leucocytosis with a marked lymphocytosis, mild non-regenerative anaemia, thrombocytopenia, hypercalcaemia and azotaemia. Circulating lymphocytes were small and well-differentiated, and the same lymphoid population was present in bone marrow. Chronic lymphocyctic leukaemia with associated paraneoplastic hypercalcaemia was diagnosed. Immunohistochemical staining of a bone marrow biopsy revealed a neoplastic B-cell line expressing CD79. The dog responded to therapy with prednisolone and chlorambucil for a period of 8 months.

Elevated inferior petrosal sinus levels of PTHrP in a patient with Cushing's disease

PTHrP has been found in various tissues, including prolactinomas and growth hormone producing adenomas. The function and clinical importance of PTHrP are poorly understood. We report the case of a 25-year-old female patient with hirsutism. Autonomous ACTH-dependent hypercortisolism was documented by endocrine testing. Magnetic resonance imaging (MRI) revealed a 3-mm intrasellar hypointense lesion in the left side of the pituitary gland. The inferior petrosal sinus sampling disclosed a gradient of ACTH left central/peripheral of 30.5 and right central/peripheral of 2.0 and suggested the diagnosis of a left-sided pituitary ACTH secreting microadenoma. Interestingly, we found elevated PTHrP levels in the left inferior petrosal sinus with a gradient of 4.7 compared to peripheral venous blood and of 3.6 compared to the right sinus. Our results fit very well to the concept of a para-/autocrine secretion of PTHrP which has been proposed recently and suggest a role in the regulation of cell growth of pituitary adenomas.

Ameloblastic carcinoma ex ameloblastoma of the mandible with malignancy-associated hypercalcemia

Ameloblastoma is a rare, locally destructive, benign neoplasm of the jawbones, which arises from epithelium derived from the epithelial components of the developing tooth. Ameloblastic carcinoma is the term used to designate any ameloblastoma in which there is histologic evidence of malignancy in the primary tumor, regardless of whether it has metastasized. Most ameloblastic carcinomas are presumed to have arisen de novo, with few cases of malignant transformation of ameloblastoma being apparent. Hypercalcemia is the most common metabolic complication of malignancy. Although malignancy-associated hypercalcemia is often reported in association with other malignancies, it is exceedingly unusual in association with ameloblastoma, malignant ameloblastoma, or ameloblastic carcinoma. We describe a patient with multiple recurrences of ameloblastoma, with subsequent malignant transformation presenting with malignancy-associated hypercalcemia.

Dissection of differentially regulated (G+C)-rich promoters of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene

The PTH/PTH-related peptide (PTHrP) receptor (PTHR) is required for normal skeletal development, and a wide array of physiological responses mediated by PTH and PTHrP. We have previously identified three promoters, P1-P3, which control human PTHR gene transcription. P2 and P3 are (G+C)-rich, function in a number of tissues, lie within the same CpG island, and display many hallmarks of housekeeping promoters. However, they are differentially regulated during development as P2, but not P3, functions in fetal tissues. Here, we have used both stably and transiently transfected human osteoblast-like cells to delineate regions of P2 and P3 required for promoter activity. Deletion analyses performed in stably transfected cells indicated that sequences extending from -91 to -12 relative to the transcription start site were required for function of the P2 promoter. No negative regulatory elements were detected in P2. In contrast, deletion of an A-rich region of P3 extending from -147 to -115 was required for optimal basal activity, suggesting that this sequence acts as a repressor of P3. Strikingly, however, whereas the A-rich region also functioned as a negative element when inserted upstream of the (G+C)-rich P2 promoter, it enhanced expression from the thymidine kinase promoter, suggesting that its function depends on other transcription factors bound to promoter sequences. Fine deletion of P3 sequences proximal to -115 implicated Spl motifs and downstream initiation sites in P3 function. These studies indicate that function of P2 and P3 is controlled by ubiquitously expressed transcription factors and raise the possibility that P3 activity is repressed during fetal development.

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

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

Developmental upregulation of human parathyroid hormone (PTH)/PTH-related peptide receptor gene expression from conserved and human-specific promoters

The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR) functions in skeletal development and mediates an array of other physiological responses modulated by PTH and PTHrP. PTHR gene transcription in mouse is controlled by two promoters: P1, which is highly and selectively active in kidney; and P2, which functions in a variety of tissues. P1 and P2 are conserved in human tissue; however, P1 activity in kidney is weak. We have now identified a third human promoter, P3, which is widely expressed and accounts for approximately 80% of renal PTHR transcripts in the adult. No P3 activity was detected in mouse kidney, indicating that renal PTHR gene expression is controlled by different signals in human and mouse. During development, only P2 is active at midgestation in many human tissues, including calvaria and long bone. This strongly suggests that factors regulating well conserved P2 control PTHR gene expression during skeletal development. Our results indicate that human PTHR gene transcription is upregulated late in development with the induction of both P1 and P3 promoter activities. In addition, P2-specific transcripts are differentially spliced in a number of human cell lines and adult tissues, but not in fetal tissues, giving rise to a shorter and less structured 5' UTR. Thus, our studies show that both human PTHR gene transcription and mRNA splicing are developmentally regulated. Moreover, our data indicate that renal and nonrenal PTHR gene expression are tightly coordinated in humans.

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.

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.

The role of interleukin-6 in the induction of hypercalcemia in renal cell carcinoma transplanted into nude mice

Hypercalcemia is a well known complication of renal cell carcinoma (RCC). As RCCs can produce IL-6, and IL-6 may stimulate bone resorption and cause mild hypercalcemia, we examined whether IL-6 is involved in renal cancer-associated hypercalcemia in vivo. Three human renal cell carcinoma tumor lines (RC-8, RC-9, and NC-65) growing in nude mice were studied. Tumors were implanted s.c., and parameters of bone metabolism and serum human IL-6 levels were determined in relation to tumor volume (TV). All three tumor lines secreted human IL-6, although in different quantities. The maximum level of IL-6 in RC-8 was 434 pg/ml (TV, 200 mm3), that in RC-9 was 81 pg/ml (TV, 1800 mm3), and that in NC-65 was 2368 pg/ml (TV, 1800 mm3). Hypercalcemia developed in RC-8 and RC-9 tumor-bearing animals, but not in NC-65-bearing animals. The hypercalcemia in both RC-8 and RC-9 tumor lines was associated with elevated levels of PTH-related peptide (PTHrP) and loss of trabecular bone volume. Serum calcium and phosphate concentrations showed an almost linear relationship with plasma PTHrP independently of the tumor line and serum IL-6 levels. No hypercalcemia occurred in the NC-65 animals, which had the highest levels of IL-6, but no detectable plasma PTHrP and PTHrP messenger RNA expression in the tumor. Administration of neutralizing antibodies to IL-6 to RC-8 animals normalized serum calcium concentrations and PTHrP values and induced a significant inhibition of tumor growth. No such effect on tumor growth of anti-IL-6 was seen in the other two tumor lines. The normalization of serum calcium in RC-8 mice is most likely attributed to the growth-inhibiting effect of anti-IL-6 on RC-8 tumor. We conclude that IL-6 secreted by RCC does not contribute directly to hypercalcemia, but may enhance hypercalcemia by stimulating the tumor growth of a subpopulation of PTHrP-secreting carcinomas.

Cloning and characterization of the promoter regions of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene: analysis of deoxyribonucleic acid from normal subjects and patients with pseudohypoparathyroidism type 1b

Expression of the PTH/PTH-related peptide (PTHrP) receptor (PTHR) in the mouse is controlled by at least two promoters. The downstream promoter (P2) is ubiquitously expressed, whereas expression of the upstream promoter (P1) is largely restricted to kidney. These observations may provide a genetic basis for a human PTH resistance syndrome, pseudohypoparathyroidism type 1b (PHP1b), in which renal, but not osseous, signaling by PTH is defective. We, therefore, cloned and characterized the 5'-end of the human PTHR gene and found that its organization is very similar to that of the mouse. Transcription initiation sites of human P1 and P2 promoters are in similar, but not identical, positions to those of the mouse gene. The identification of a human P2 promoter is significant because no P2-specific human PTHR complementary DNAs have been isolated to date. Southern analysis of genomic DNA from seven PHP1b patients did not reveal any rearrangements in proximal promoter regions or exons encoding 5'-untranslated region sequences. No significant sequence differences were found in clones of normal and patient DNAs encompassing proximal promoter sequences, and untranslated region and signal sequence exons. Thus, in the seven PHP1b patients analyzed, no defects were identified that would influence initiation site selection, stability, or splicing of renal PTHR transcripts. These data indicate that the genetic defect(s) in PHP1b in these patients lies in distal enhancer elements of the gene, in an essential transcriptional regulator, or in some as yet unidentified cofactor required for renal PTH signaling.

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.

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.

Lymphoid leukosis viruses, their recognition as 'persistent' viruses and comparisons with certain other retroviruses of veterinary importance

Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of 'persistent virus infections'. Disease produced by LLV infection and its underlying mechanisms is compared with 'persistent' infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances. Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of 'biological clocks', such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.

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.

Parathyroid hormone related protein and interleukin-6 mRNA expression in larynx and renal cell carcinomas from normocalcaemic and hypercalcaemic patients

AIMS

To determine the expression of parathyroid hormone related protein (PTHrP) and interleukin-6 (IL-6) mRNAs and their possible relation in malignant tumours, derived from patients with and without hypercalcaemia, commonly associated with humoral hypercalcaemia of malignancy.

METHODS

PTHrP and IL-6 mRNA expression was studied by northern blot analysis in tumour specimens from 13 consecutive patients. Six patients (two with hypercalcaemia) had squamous cell carcinomas of the larynx and seven (one with hypercalcaemia) had renal cell carcinomas.

RESULTS

There was no relation between the histological features of the tumours and the expression of either PTHrP or IL-6 mRNAs. PTHrP mRNA was detected in all squamous cell carcinomas, expression being highest in the two patients with hypercalcaemia. In the renal cell carcinomas PTHrP mRNA was expressed only in the patient with hypercalcaemia. IL-6 mRNA was detected in nearly all tumours studied but there was no apparent relation between its expression and that of PTHrP mRNA or serum calcium concentrations.

CONCLUSIONS

PTHrP mRNA expression is increased in patients with hypercalcaemia but is not related to IL-6 mRNA expression. The results suggest a quantitative relation between PTHrP gene expression and hypercalcaemia, and imply that different mechanisms account for this expression in squamous and renal cell carcinomas.

Parathyroid hormone/parathyroid hormone related peptide receptor gene transcripts are expressed from tissue-specific and ubiquitous promoters

Parathyroid hormone (PTH) and PTH related peptide (PTHrP) stimulate diverse physiological responses in a number of tissues by binding to the same receptor. We have previously cloned the gene encoding the mouse PTH/PTHrP receptor (PTHR), and have identified a promoter region. The first exon transcribed from this promoter contains untranslated sequence and is followed by an exon encoding signal sequence and the first amino acids of the mature polypeptide. We have now identified and characterized a second promoter region, located > 3 kb upstream of the original. Four partial cDNA clones, amplified from mouse kidney RNA by reverse transcription followed by the polymerase chain reaction, contain sequence corresponding to two previously unidentified exons composed of untranslated sequence. The second (3') of the two exons is spliced to the previously identified signal sequence exon. These cDNAs are highly homologous to the 5' end of a cDNA isolated from human kidney, strongly suggesting that the promoter region is conserved between mouse and humans. RNase protection and primer extension experiments have identified several transcriptional start sites extending over a region of approximately 100 bp. Unlike the previously identified promoter, this promoter is not (G+C)-rich. It lacks a consensus TATA element, but does contain a consensus CCAAT box. We have determined the expression patterns of both promoters by RNase protection with total and poly A+ RNA from several mouse tissues. The newly identified promoter is highly tissue specific, being strongly active in kidney and weakly active in liver, but not expressed in the other tissues studied. The previously identified (G+C)-rich promoter is expressed in all tissues studied. This indicates that the PTHR gene expression is controlled by regulatory signals specific to kidney and liver, as well as signals functioning in a wide variety of cell types. These results may provide insight into certain defects in PTH signalling found in humans.

Plasma levels of parathyroid hormone-related peptide are elevated in hyperprolactinemia and correlated to bone density status

Osteopenia is an important clinical manifestation of hyperprolactinemia. Bone loss in these patients has mainly been attributed to concomitant deficiency of gonadal hormones rather than to hyperprolactinemia per se. Parathyroid hormone-related peptide (PTHrP) is expressed in human mammary tissue, and elevated circulating PTHrP levels as well as concomitant hypercalcemia have been described during lactation. We sought to determine circulating PTHrP levels in patients with long-standing hyperprolactinemia and whether PTHrP may exert possible systemic effects on bone and mineral metabolism. We studied 45 patients (30 women and 15 men) with persisting hyperprolactinemia 6 +/- 4 years (mean +/- SD) after trans-sphenoidal surgery for prolactin-producing pituitary adenomas. PTHrP levels in 117 healthy controls were 10.6 +/- 7.3 pmol-eq/l (mean +/- SD). In hyperprolactinemic patients, plasma PTHrP was elevated to 30.3 +/- 13.4 pmol-eq/l (p < 0.001, n = 45), and in patients with humoral hypercalcemia of malignancy PTHrP levels were 52.9 +/- 29.6 (p < 0.001 to controls and hyperprolactinemic patients). Fifty-three percent of hyperprolactinemic patients (n = 24) had clearly elevated PTHrP levels (> 2 SD). Retrospective immunocytochemical studies of the removed pituitary adenomas from 19 patients generally showed a higher degree of immunoreactivity for PTHrP (1-34) in all but one case when compared with normal pituitary tissue. Patients with elevated circulating PTHrP levels showed in most instances strong immunoreactivity to PTHrP in 70-100% of tumor cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Humoral Hypercalcemia of Hepatocellular Carcinoma Associated with Elevated Levels of Parathyroid-Hormone-Related-Peptide

Parathyroid-hormone-related-peptide (PTHrP) has been shown to be important in the pathogenesis of hypercalcemia of malignancy. The malignancies most commonly associated with hypersecretion of PTHrP include squamous cell carcinoma and breast cancer. The pathogenesis of hypercalcemia associated with hepatocellular carcinoma was evaluated in this study. Two male patients with hepatocellular carcinoma were found to have severe hypercalcemia at initial presentation. PTHrP was measured with radioimmunoassay in these two patients before treatment as well as in nine other patients with hepatocellular carcinoma but without hypercalcemia. The levels were markedly elevated in the two patients with hypercalcemia (29.3 and 32.1 pM), but were less than 5 pM in the nine patients without hypercalcemia. These results suggest that PTHrP was important in the pathogenesis of hypercalcemia associated with hepatocellular carcinoma in these men.

[Parathyroid hormone related peptide (PTHrP) and bone metabolism]

The discovery of PTHrP was the result of research on the mechanisms by which some cancers cause hypercalcemia (humoral hypercalcemia of malignancy) without necessarily metastasizing to bone. PTHrP is also present in various normal adult and fetal tissues. Its concentration is normally very low (picomolar) in blood, but it is more abundant in milk (nanomolar concentration). PTHrP seems able to exert autocrine/paracrine as well as endocrine effects on bone metabolism. A major role for PTHrP in regulation of fetal bone metabolism has been demonstrated in mice. Homologous recombination has been used in these rodents to remove the major coding exon from one copy of the mouse PTHrP gene in embryonic stem cells. Subsequently generated chimeric mice transmit the mutant PTHrP allele through the germline. Homozygous mutants died immediately after birth and had a multitude of skeletal abnormalities. So PTHrP seems necessary to embryonic development of the skeleton. PTHrP (1-34), like PTH (1-34) fragments, might be responsible for both bone resorption and formation. Although the effects of the carboxyl-terminal fragments are still controversial, PTHrP (107-111) fragment seems able to inhibit osteoclast activity. PTHrP (1-34), whose 8 of the first 13 amino-acids are identical with those in PTH (1-34), acts through the same receptor as PTH on osteoblasts and renal cells membrane. The PTHrP/PTH receptor sequence is now well established. PTHrP-receptor coupling is mediated by cyclic AMP and/or inositols-phosphate. The consequent activation of protein kinase A and intracellular calcium or protein kinase C, respectively, locally induces growth factors or cytokines secretion, responsible for the observed effects. The role of PTHrP appears important during pregnancy and lactation, when it stimulates fetal bone growth by increasing calcium transport from the dam to its fetus and maternal bone resorption allowing calcium supply for milk production, respectively. Such a role would be particularly important in domestic ruminants, which are often simultaneously pregnant and lactating. The role of PTHrP during aging (especially in post-menopausal women in which bone loss may induce osteoporosis) remains unknown and might be of peculiar interest since PTHrP (1-34) and (107-111) are able to restore bone loss induced by ovariectomy in rats.

In vivo evidence for progressive activation of parathyroid hormone-related peptide gene transcription with tumor growth and stimulation of osteoblastic bone formation at an early stage of humoral hypercalcemia of cancer

The present study was undertaken to clarify in vivo the temporal profile of parathyroid hormone-related peptide (PTHRP) gene expression as well as bone histomorphometric features as a function of tumor growth, using an athymic rat model associated with humoral hypercalcemia of malignancy (HHM). Tumor-bearing animals exhibited hypercalcemia, hypophosphatemia, and increased circulating levels of PTHRP, and died within 3 weeks. Steady-state PTHRP mRNA levels and the transcription rate of PTHRP gene in the tumors were markedly increased with tumor growth. RNAse mapping analysis revealed that both upstream and downstream promoters of the human PTHRP gene were utilized in the tumors and became progressively activated with time. Bone histomorphometric analysis showed that osteoclastic bone resorption was progressively increased throughout the course, whereas osteoblastic bone formation was stimulated more than 2-fold at a very early stage (day 6 after tumor implantation) and then markedly suppressed thereafter on day 12 and day 18 compared with age-matched control animals. These results provide in vivo evidence that PTHRP gene transcription is progressively activated with tumor growth and that activation of osteoblasts does occur at a very early phase of HHM syndrome in contrast to the marked suppression of bone formation at later stages.

Parathyroid hormone-related protein

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

Fatal parathyroid hormone-related protein-induced humoral hypercalcemia of malignancy in a 3-month-old infant

Parathyroid hormone-related protein (PTHrP) is the factor responsible for the syndrome of humoral hypercalcemia of malignancy (HHM). The syndrome is well documented in adult cancer patients, but has not previously been described in young children. We report the case of a 3-month-old infant who developed refractory hypercalcemia (peak total calcium 13.8 mg/dl; normal 8.5-10.5, ionized calcium 3.3 meq/l; normal 2.0-2.5) associated with a high-grade, poorly differentiated malignant hepatic sarcoma. Parathyroid hormone (intact) levels were suppressed (7.5 pg/ml; normal 10-65). Fractional excretion of phosphate was markedly elevated (73.5%; normal 8%-20%) as were urinary cAMP levels (12.48 nmol/dl glomerular filtrate; normal 1.83-4.47) suggesting a PTH-like effect. Increased levels of PTHrP were present both in the serum (4.9 pmol/l; normal for adults < 1.5) and ascitic fluid (6.1 pmol/l). Since previous studies have demonstrated a potential role for PTHrP in the regulation of embryonal tissue differentiation and transmembrane calcium flux, our observation of elevated PTHrP levels associated with the development of a poorly differentiated hepatic sarcoma in a young infant may provide insight into the molecular mechanisms underlying HHM. We suggest that serum or plasma PTHrP levels be determined in all children with hypercalcemia of malignancy in whom the hypercalcemia cannot otherwise be explained.

Paraneoplastic syndromes in patients with head and neck cancer

Paraneoplastic syndromes are distinct physiological disorders of malignancy that occur remote from a tumor site. A review of a number of paraneoplastic syndromes occurring in patients with head and neck cancer has been discussed. These syndromes can produce life-threatening sequelae in the patient with cancer. Understanding these syndromes may provide important clinical information to assist in the early detection of occult malignancy and in reducing the occurrence of tumor-associated morbidity.

Molecular cloning of the gene encoding the mouse parathyroid hormone/parathyroid hormone-related peptide receptor

The parathyroid hormone/parathyroid hormone-related peptide receptor (PTHR) is a G-protein-coupled receptor containing seven predicted transmembrane domains. We have isolated and characterized recombinant bacteriophage lambda EMBL3 genomic clones containing the mouse PTHR gene, including 10 kilobases of the promoter region. The gene spans > 32 kilobases and is divided into 15 exons, 8 of which contain the transmembrane domains. The PTHR exons containing the predicted membrane-spanning domains are heterogeneous in length and three of the exon-intron boundaries fall within putative transmembrane sequences, suggesting that the exons did not arise from duplication events. This arrangement is closely related to that of the growth hormone releasing factor receptor gene, particularly in the transmembrane region, providing strong evidence that the two genes evolved from a common precursor. Transcription is initiated principally at a series of sites over a 15-base-pair region. The proximal promoter region is highly (G+C)-rich and lacks an apparent TATA box or initiator element homologies but does contain CCGCCC motifs. The presumptive amino acid sequence of the encoded receptor is 99%, 91%, and 76% identical to those of the rat, human, and opossum receptors, respectively. There is no consensus polyadenylation signal in the 3' untranslated region. The poly(A) tail of the PTHR transcript begins 32 bases downstream of a 35-base-long A-rich sequence, suggesting that this region directs polyadenylylation.

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.

Parathyroid hormone-related protein in normal and neoplastic canine tissues: immunohistochemical localization and biochemical extraction

Two polyclonal antibodies, directed against N-terminal amino acids (1-36) or the midregion (amino acids 34-53) of parathyroid hormone-related protein (PTHrP), were used to localize PTHrP in a variety of normal and neoplastic canine tissues. Parathyroid hormone (PTH) immunoreactivity was demonstrated using anti-bovine PTH (amino acids 14-34). The following tissues (among others) stained strongly positive for PTHrP: all layers of epidermal keratinocytes, with the most intense staining of the basal layer; hair follicle keratinocytes; myoepithelial cells of dermal apocrine glands, mammary glands, and apocrine glands of the anal sac; anal sac epithelium; mammary duct epithelium; and thyroid C cells. Adenocarcinomas of the anal sac stained moderately positive (5/22 dogs), weakly positive (11/22 dogs), or did not stain (6/22 dogs). Most parathyroid gland adenomas stained moderately (2/6 dogs) or weakly positive (3/6 dogs) for PTHrP. Squamous cell carcinomas (6/6 dogs) stained strongly positive. Lymphomas stained weakly positive (2/10 dogs) or did not stain (8/10 dogs). There was no consistent relationship between the staining intensity of the tumors and serum calcium concentrations of the dogs. The anti-PTH antibodies stained only parathyroid chief cells strongly positive. Concentrations of PTHrP were measured by radioimmunoassay in protein extracts from an adenocarcinoma derived from the apocrine glands of the anal sac, pancreas, kidney, liver, heart, thyroid, adrenal, and parathyroid glands. PTHrP concentrations varied from undetectable up to 150 pg/mg in normal tissues as compared with 2,000 pg/mg in apocrine adenocarcinoma of the anal sac.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

Hypercalcemia of malignancy: the central role of parathyroid hormone-related protein

Hypercalcemia is the most common metabolic complication of cancer. Malignancy-associated hypercalcemia (MAHC) can be divided into two syndromes, humoral hypercalcemia of malignancy (HHM) and local osteolytic hypercalcemia (LOH), based on whether a circulating hormone or local paracrine factors mediate accelerated bone resorption. Over the past decade, studies have shown that parathyroid hormone-related protein is the cause of the HHM syndrome, and recent data suggest that this protein may also play a paracrine role in some patients with local osteolytic hypercalcemia. Study of the regulation of parathyroid hormone-related protein gene expression is beginning to shed some light on the molecular mechanisms responsible for this common clinical problem.

Transforming growth factor-beta 1, beta 2, and beta 3, urokinase and parathyroid hormone-related peptide expression in 8701-BC breast cancer cells and clones

8701-BC is a recently characterized cell line isolated from a primary ductal infiltrating carcinoma of the breast (d.i.c.), showing some pleomorphism in cell microanatomy at an ultrastructural level. We have obtained different sublines of 8701-BC cells by cloning in soft agar at different concentrations (0.3% and 0.6%), and we have characterized the cloned lines by some morphological and growth parameters. 8701-BC cells and clones have been submitted to analysis by reverse transcriptase-linked polymerase chain reaction to detect mRNAs of various cytokines (transforming growth factor-beta s, tumour necrosis factors, interleukin 1s, interleukin 6, parathyroid hormone-related peptide, gamma interferon) and of urokinase, which are bioactive molecules commonly involved in cell-cell and cell-stroma interactions at primary and/or secondary sites of invasion. The aims of the present investigation were to determine: (a) if the corresponding genes are active in 8701-BC cell line and (b) if the sublines tested exhibit transcriptional heterogeneity. The results obtained show that 8701-BC cells express transcripts of transforming growth factor-beta s, urokinase and parathyroid hormone-related peptide (PTHrP), the latter product being responsible for the cancer-associated humoral hypercalcemic syndrome. Moreover, while the first two mRNAs are detectable in all the sublines tested, PTHrP is expressed almost uniquely by the clones isolated in 0.6% agar which exhibit a peculiar morphological appearance, a higher growth rate and a more active invasive behaviour in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

In situ localization of parathyroid hormone-like protein and mRNA in intraepithelial neoplasia and invasive carcinoma of the uterine cervix

Parathyroid-like protein (PLP), or parathyroid hormone-related peptide, is a well-recognized mediator of paraneoplastic hypercalcemia (humoral hypercalcemia of malignancy syndrome). In this study we examined the expression of PLP by 40 invasive squamous cell carcinomas (SCCs) of the cervix and selected carcinomas of nonsquamous histology. Using a polyclonal antibody to human PLP, 93% of SCCs, including two tumors from patients with humoral hypercalcemia of malignancy syndrome, showed moderate to strong cytoplasmic immunoperoxidase staining for PLP. The strongest staining often was observed in areas of invasion associated with stromal desmoplasia. The small number of weak or negatively stained SCCs were all poorly differentiated tumors. Although native uninvolved squamous epithelium showed weak to moderate staining of the superficial layers, there was variable or full-thickness immunostaining in areas of dysplasia. Normal endocervical glands and stroma as well as cervical adenocarcinomas and neuroendocrine carcinomas were negative. In situ hybridization studies showed abundant PLP mRNA within SCC in patients with hypercalcemia. However, PLP mRNA was of relatively low abundance in tumors of normocalcemic patients. Ultrastructural studies showed cytoplasmic, membrane-bound, granular inclusions in tumor cells from the hypercalcemic patients. Our data suggest that increased PLP gene transcription contributes to the increased production of PLP and the pathogenesis of humoral hypercalcemia of malignancy syndrome.

Accumulation of carboxy-terminal fragments of parathyroid hormone-related protein in renal failure

We have recently demonstrated elevations of separate amino- and carboxy-terminal parathyroid hormone-related protein (PTHrP) fragments in patients with humoral hypercalcemia of malignancy (HHM) using both a two-site immunoradiometric assay (IRMA) with amino-terminal specificity for PTHrP, and with a carboxy-terminal radioimmunoassay (RIA) for PTHrP(109-138). PTHrP(109-138) immunoactivity from plasma of patients with HHM could not be extracted using an amino-terminal PTHrP immunoaffinity column, indicating that the carboxy-terminal region circulates as a discrete peptide. Carboxy-terminal immunoreactive (i) PTHrP levels were also elevated in normocalcemic patients with chronic renal failure (without cancer), whereas amino-terminal iPTHrP levels were normal in patients with renal failure. In order to further define the renal handling of carboxy-terminal PTHrP peptides, we have evaluated circulating iPTHrP(109-138) concentrations in patients with a wide range of renal function. We studied 25 patients with abnormal renal function of diverse etiologies whose creatinine clearances ranged from 66 ml/min to less than 5 ml/min. All patients had undetectable or low (< or = 2 pmol/liter) concentrations of iPTHrP(1-74). iPTHrP(109-138) concentrations were undetectable in patients with creatinine clearances > or = 20 ml/min, but became elevated in patients with creatinine clearances < 20 ml/min. The log of iPTHrP(109-138) correlated negatively with the log of creatinine clearance (r = 0.88, P = 0.0001). Mean iPTHrP(109-138) levels were slightly higher for patients on hemodialysis (32.7 +/- 3.1 pM) than for those on chronic ambulatory peritoneal dialysis (22.1 +/- 3.4 pM; P < 0.05), suggesting that some carboxy-terminal PTHrP fragments may be cleared to a greater extent by the peritoneal membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthesis and processing of endogenous parathyroid hormone related peptide (PTHRP) by rat Leydig cell tumor H-500

We have examined in vitro the biosynthesis and processing of endogenous PTHRP in cultured rat H-500 Leydig tumor cells. Cells were grown to confluence and pulse labeled with [3H]Ile, 50 microCi/mL, in Ile free culture medium for 2 min to 6 h. In some experiments incubations were carried out in culture medium alone in the presence of 0.3 mM cycloheximide or 20 micrograms/mL unlabeled Ile. Cell extracts and culture media were analyzed by affinity chromatography employing an antibody directed against the bioactive NH2-terminal region, PTHRP(1-34), followed by gel-permeation or reversed-phase high-performance liquid chromatography. Incorporation of [3H]Ile into PTHRP in cell extracts increased over 20 min during pulse labeling and then remained constant throughout the incubation period up to 6 h. In contrast, the release of [3H]PTHRP into culture medium increased progressively over 6 h. Addition of cycloheximide or unlabeled Ile almost completely blocked incorporation of [3H]Ile into newly synthesised PTHRP. Three molecular forms of PTHRP were seen which comigrated with PTHRP(1-36), PTHRP(1-86), and PTHRP(1-141) standards in both chromatographic systems employed. After 20 min these species comprised approximately 63%, 30%, and 7% of newly synthesized PTHRP, respectively. These three molecular forms of PTHRP were observed both intra- and extracellularly, and no further metabolism of these species was seen after release into conditioned medium. Pulse-chase studies demonstrated a rapid decrease of newly synthesized PTHRP forms within cells after 20 min; there was, however, a progressive increase in [3H]PTHRP in conditioned culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

A case of squamous cell lung carcinoma with high concentration of parathyroid hormone-related peptide in serum and pleural effusion presenting hypercalcemia

A 57-year-old man with lung squamous cell carcinoma revealed hypercalcemia, hypophosphoremia, elevation of nephrogenous cAMP and metabolic alkalosis. Serum parathyroid hormone (PTH) and 1,25(OH)2D3 concentrations were not elevated. These findings were consistent with those in humoral hypercalcemia of malignancy (HHM). PTH-related peptide (PTHrP) concentrations were determined using N- and C-terminal specific radioimmunoassays (PTHrP-N, PTHrP-C), and elevation of both PTHrP-N and PTHrP-C concentrations in the serum was noted (PTHrP-N, 27 pmol/liter (normal < 5); PTHrP-C, 1408 pmol/liter (normal < 50)). High concentration of PTHrP (946 pmol/liter for PTHrP-N and 5983 pmol/liter for PTHrP-C) was also found in the pleural fluid obtained at autopsy. Immunohistochemical study, using paraffin-embedded sections of the tumor tissue obtained at autopsy, revealed numerous PTHrP-positive cells and expression of PTHrP gene was confirmed by Northern blot analysis. These findings indicate that PTHrP, produced in the tumor tissue, was secreted into the blood stream, which caused HHM in the patient. Gel permeation chromatography of the serum and pleural fluid revealed several peaks of both PTHrP-N and PTHrP-C. Molecular forms of PTHrP-N were larger than those of PTHrP-C in the serum as well as pleural fluid. These findings indicate that multiple forms of PTHrP molecules are present in the serum and pleural fluid. Granulocytosis was also noted in the patient. However, granulocyte- and granulocyte macrophage-colony stimulating factor were not detected in the serum, and the mechanism of the granulocytosis in the patient was unclear.