All major lung cancer cell types produce parathyroid hormone-like protein: heterogeneity assessed by high performance liquid chromatography

Parathyroid hormone‐related protein inhibition blocks triple‐negative breast cancer expansion in bone through epithelial to mesenchymal transition reversal

Parathyroid hormone‐related protein (PTHrP) plays a major role in skeletal metastasis but its action mechanism has not been fully defined. We previously demonstrated the crucial importance of PTHrP in promoting mammary tumor initiation, growth, and metastasis in a mouse model with a mammary epithelium‐targeted Pthlh gene ablation. We demonstrate here a novel mechanism for bone invasion involving PTHrP induction of epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs) regulation. Clustered regularly interspaced short palindromic repeats (CRISPR)‐mediated Pthlh gene ablation was used to study EMT markers, phenotype, and invasiveness in two triple‐negative breast cancer (TNBC) cell types (established MDA‐MB‐231 and patient‐derived PT‐TNBC cells). In vitro, Pthlh ablation in TNBC cells reduced EMT markers, mammosphere‐forming ability, and CD44^high/CD24^low cells ratio. In vivo, cells were injected intratibially into athymic nude mice, and therapeutic treatment with our anti‐PTHrP blocking antibody was started 2 weeks after skeletal tumors were established. In vivo, compared to control, lytic bone lesion from Pthlh ‐ablated cells decreased significantly over 2 weeks by 27% for MDA‐MB‐231 and by 75% for PT‐TNBC‐injected mice (p < 0.001). Micro‐CT (μCT) analyses also showed that antibody therapy reduced bone lytic volume loss by 52% and 48% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.05). Antibody therapy reduced skeletal tumor burden by 45% and 87% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.002) and caused a significant decrease of CSC/EMT markers ALDH1, vimentin, and Slug, and an increase in E‐cadherin in bone lesions. We conclude that PTHrP is a targetable EMT molecular driver and suggest that its pharmacological blockade can provide a potential therapeutic approach against established TNBC‐derived skeletal lesions. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Lung carcinoma progression and survival versus amino- and carboxyl-parathyroid hormone-related protein expression

PURPOSE

Expression of the carboxyl PTHrP region of parathyroid hormone-related protein (PTHrP) is a positive prognostic indicator in women with lung cancer, but amino PTHrP is a negative indicator in other lung cancer patients. This project investigated whether PTHrP could be expressed as predominantly amino PTHrP or carboxyl PTHrP in individual lung carcinomas. It also assessed domain-specific effects on cancer progression and patient survival.

METHODS

PTHrP immunoreactivities were analyzed versus survival in a human lung cancer tissue microarray (TMA). Growth was compared in athymic mice for isogenic lung carcinoma xenografts differing in expression of amino and carboxyl PTHrP domains.

RESULTS

In the TMA, 33 of 99 patient tumors expressed only one PTHrP domain, while 54 expressed both. By Cox regression, the hazard ratio for cancer-specific mortality (95% confidence interval) was 2.6 (1.28-5.44) for amino PTHrP (P = 0.008) and 0.6 (0-2.58) for carboxyl PTHrP (P = 0.092). Xenografts of H358 lung adenocarcinoma cells that overexpressed amino PTHrP grew twice as fast as isogenic low PTHrP tumors in athymic mice, but growth of tumors expressing amino plus carboxyl PTHrP was not significantly different than growth of the control tumors. In summary, the presence of amino PTHrP signifies worse prognosis in lung cancer patients. In mouse xenografts, this effect was abrogated if carboxyl PTHrP was also present.

CONCLUSION

Amino PTHrP and carboxyl PTHrP can vary independently in different lung carcinomas. Carboxyl PTHrP may temper the stimulatory effect of amino PTHrP on cancer progression.

Parathyroid hormone-related protein: potential therapeutic target for melanoma invasion and metastasis

The role of PTHrP in the highly metastatic human melanoma disease is not known. This study investigates the mechanisms of action of this secreted factor through homozygous inactivation of the Pthrp gene in A375 human melanoma cells. In vitro, Pthrp-ablated cells (knockout [KO]-A375, -/-) showed decreased motility and anchorage-independent growth, rounder morphology, and a significant reduction in invasion capacity compared with nonablated A375 cells (wild-type [WT]-A375, +/+). PTHrP peptide 1-34 and conditioned medium from WT-A375 cells partially restored the invasive phenotype in KO-A375. Pthrp ablation substantially decreased actin polymerization, matrix metallopeptidase 9 expression and focal adhesion kinase phosphorylation. In vivo, green fluorescent protein-transduced ablated and nonablated A375 cells were injected intracardially or sc into nude mice to study proliferation and multiorgan metastasis. Dissemination of injected Pthrp-ablated cells to lung and liver was reduced by 85% and 50%, respectively, compared with nonablated controls (120 hours after injection). The number of metastatic lesions and the percentage of animals with metastasis were markedly lower in mice injected with Pthrp-ablated A375, and 45% of these animals survived a 7-week period compared with 15% of mice injected with nonablated WT-A375. When mice injected with WT-A375 were treated with our blocking anti-PTHrP monoclonal antibody raised against the first 33 amino acids of human PTHrP, tumor size was decreased by more than 80% over 4 weeks and survival was significantly improved over 8 months. This study provides direct evidence of the major role for PTHrP in melanoma invasion and metastasis and suggests that agents that suppress PTHrP may be beneficial against melanoma progression.

Activated PTHLH coupling feedback phosphoinositide to G-protein receptor signal-induced cell adhesion network in human hepatocellular carcinoma by systems-theoretic analysis

Studies were done on analysis of biological processes in the same high expression (fold change ≥2) activated PTHLH feedback-mediated cell adhesion gene ontology (GO) network of human hepatocellular carcinoma (HCC) compared with the corresponding low expression activated GO network of no-tumor hepatitis/cirrhotic tissues (HBV or HCV infection). Activated PTHLH feedback-mediated cell adhesion network consisted of anaphase-promoting complex-dependent proteasomal ubiquitin-dependent protein catabolism, cell adhesion, cell differentiation, cell-cell signaling, G-protein-coupled receptor protein signaling pathway, intracellular transport, metabolism, phosphoinositide-mediated signaling, positive regulation of transcription, regulation of cyclin-dependent protein kinase activity, regulation of transcription, signal transduction, transcription, and transport in HCC. We proposed activated PTHLH coupling feedback phosphoinositide to G-protein receptor signal-induced cell adhesion network. Our hypothesis was verified by the different activated PTHLH feedback-mediated cell adhesion GO network of HCC compared with the corresponding inhibited GO network of no-tumor hepatitis/cirrhotic tissues, or the same compared with the corresponding inhibited GO network of HCC. Activated PTHLH coupling feedback phosphoinositide to G-protein receptor signal-induced cell adhesion network included BUB1B, GNG10, PTHR2, GNAZ, RFC4, UBE2C, NRXN3, BAP1, PVRL2, TROAP, and VCAN in HCC from GEO dataset using gene regulatory network inference method and our programming.

PTHrP drives breast tumor initiation, progression, and metastasis in mice and is a potential therapy target

Parathyroid hormone-related protein (PTHrP) is a secreted factor expressed in almost all normal fetal and adult tissues. It is involved in a wide range of developmental and physiological processes, including serum calcium regulation. PTHrP is also associated with the progression of skeletal metastases, and its dysregulated expression in advanced cancers causes malignancy-associated hypercalcemia. Although PTHrP is frequently expressed by breast tumors and other solid cancers, its effects on tumor progression are unclear. Here, we demonstrate in mice pleiotropic involvement of PTHrP in key steps of breast cancer - it influences the initiation and progression of primary tumors and metastases. Pthrp ablation in the mammary epithelium of the PyMT-MMTV breast cancer mouse model caused a delay in primary tumor initiation, inhibited tumor progression, and reduced metastasis to distal sites. Mechanistically, it reduced expression of molecular markers of cell proliferation (Ki67) and angiogenesis (factor VIII), antiapoptotic factor Bcl-2, cell-cycle progression regulator cyclin D1, and survival factor AKT1. PTHrP also influenced expression of the adhesion factor CXCR4, and coexpression of PTHrP and CXCR4 was crucial for metastatic spread. Importantly, PTHrP-specific neutralizing antibodies slowed the progression and metastasis of human breast cancer xenografts. Our data identify what we believe to be new functions for PTHrP in several key steps of breast cancer and suggest that PTHrP may constitute a novel target for therapeutic intervention.

PTHrP stimulates prostate cancer cell growth and upregulates aldo-keto reductase 1C3

The aim of the study was to demonstrate the role of parathyroid hormone related protein (PTHrP) in stimulating aldo-keto reductase (AKR) 1C3 expression in prostate cancer (CaP) cells. CaP cell proliferation and resistance to apoptosis was increased by PTHrP transfection. Conversely, reducing AKR1C3 expression by siRNA decreased cell proliferation. Since these effects could be mediated through AKR1C3-catalyzed reductions of the PPARγ ligand, 15-DeoxyΔ(12,14)-PGJ(2), we treated the cells with prostaglandins (PG). (PG) D(2) inhibited cell proliferation, but its metabolite, 9α,11β-PGF(2), did not effect CaP cell growth. The AKR1C family members serve as potential therapeutic targets for CaP therapy.

Parathyroid hormone related protein (PTHrP) in tumor progression

Parathyroid hormone-related protein (PTHrP) is widely expressed in fetal and adult tissues and is a key regulator for cellular calcium transport and smooth muscle cell contractility, as well as a crucial control factor in cell proliferation, development and differentiation. PTHrP stimulates or inhibits apoptosis in an autocrine/paracrine and intracrine fashion, and is particularly important for hair follicle and bone development, mammary epithelial development and tooth eruption. PTHrP's dysregulated expression has traditionally been associated with oncogenic pathologies as the major causative agent of malignancy-associated hypercalcemia, but recent evidence revealed a driving role in skeletal metastasis progression. Here, we demonstrate that PTHrP is also closely involved in breast cancer initiation, growth and metastasis through mechanisms separate from its bone turnover action, and we suggest that PTHrP as a facilitator of oncogenes would be a novel target for therapeutic purposes.

Parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor type 1 expression in human lung adenocarcinoma

BACKGROUND

In many primary tumors, parathyroid hormone-related peptide (PTHrP) and PTHrP type 1 receptor (PTH1R) are coexpressed, supporting the possibility that PTHrP/PTH1R system can mediate important signals for tumor progression through paracrine/autocrine mechanisms. In non-small cell lung carcinoma the clinical relevance of the expression of PTH1R remains to be investigated.

METHODS

Fifty-four lung adenocarcinomas of mixed histologic type from patients with stage I and II cancer were assayed by quantitative immunohistochemistry for the expression of PTHrP and PTH1R.

RESULTS

PTHrP and PTH1R were expressed in a wide range of intensity in the cytoplasm of tumor cells, and their values showed a positive correlation. PTH1R, but not PTHrP, was expressed by plasma cells infiltrating the tumor stroma. PTHrP and PTH1R were not associated with age, tumor diameter, or histopathologic grading, whereas they were directly associated with lymph node involvement at presentation. Cox regression analysis, using PTHrP and PTH1R as continuous covariates, showed that the covariate levels were directly associated with the risk of death and metastasis. Patients whose tumors coexpressed high levels of PTHrP and PTH1R showed the highest risk of metastasis (relative risk, 5.89; 95% CI, 2.1-16.6; P = .0003) and death (relative risk, 6.24; 95% CI, 1.6-23.9; P = .0033). The presence of PTH1R-positive plasma cells in the tumor stroma was associated with a more favorable survival rate independently from the PTHrP status of the tumor.

CONCLUSION

The paracrine/autocrine signaling through PTHrP/PTH1R could be important in early-stage lung adenocarcinoma progression.

Parathyroid hormone-related protein and ezrin are up-regulated in human lung cancer bone metastases

Lung cancer often metastasizes to bone in patients with advanced disease. Identification of the factors involved in the interactions between lung cancer cells and bone will improve the prevention and treatment of bone metastases. We identified changes in metastasis-related gene expression of human HARA lung squamous carcinoma cells co-cultured with neonatal mouse calvariae using a pathway-specific microarray analysis. Nine genes were up-regulated and two genes down-regulated in HARA cells co-cultured with mouse calvariae. Five of the nine up-regulated genes, including caveolin 1, CD44, EphB2, ezrin, and Parathyroid hormone-related protein (PTHrP), and one down-regulated gene, SLPI, were further confirmed by Reverse transcription-polymerase chain reaction (RT-PCR). A mouse model was subsequently used to study the role of PTHrP and ezrin in bone metastasis in vivo. PTHrP (all three isoforms) and ezrin were up-regulated in HARA cells at sites of bone metastasis as detected by RT-PCR and immunohistochemistry. The PTHrP 141 mRNA isoform was increased by the greatest extent (13.9-fold) in bone metastases compared to PTHrP 139 and PTHrP 173 mRNA. We then generated a HARA cell line in which PTHrP expression was inducibly silenced by RNA interference. Silencing of PTHrP expression caused significant reduction of submembranous F-actin and decreased HARA cell invasion. Ezrin up-regulation was confirmed by Western blots on HARA cells co-cultured with adult mouse long bones. Further, Transforming growth factor beta (TGF-beta) was identified as one of the factors in the bone microenvironment that was responsible for the up-regulation of ezrin. The identification of PTHrP and ezrin as important regulators of lung cancer bone metastasis offers new mechanistic insights into the metastasis of lung cancer and provides potential targets for the prevention and treatment of lung cancer metastasis.

Skeletal metastasis: Established and emerging roles of parathyroid hormone related protein (PTHrP)

Parathyroid hormone related protein (PTHrP) is a well characterized tumor derived product that also has integral functions in normal development and homeostasis. PTHrP is produced by virtually all tumor types that metastasize to bone and numerous studies have demonstrated a correlation between PTHrP expression and skeletal localization of tumors. PTHrP has prominent effects in bone via its interaction with the PTH-1 receptor on osteoblastic cells. Through indirect means, PTHrP supports osteoclastogenesis by upregulating the receptor activator of NFkappaB ligand (RANKL) in osteoblasts. PTHrP also regulates osteoblast proliferation and differentiation in manners that are temporal and dose dependent. Bone turnover has been implicated in the localization of tumors to bone and PTHrP increases bone turnover. Bone turnover results in the release of growth factors such as TGFbeta and minerals such as calcium, both of which impact tumor cell growth and contribute to continued PTHrP production. PTHrP also has anabolic properties and could be in part responsible for osteoblastic type reactions in prostate cancer. Finally, emerging roles of PTH and PTHrP in the support of hematopoietic stem cell development in the bone marrow microenvironment suggest that an interaction between hematopoietic cells and tumor cells warrants further investigation.

Sex-Specific Survival Advantage with Parathyroid Hormone–Related Protein in Non–Small Cell Lung Carcinoma Patients

PURPOSE

Parathyroid hormone-related protein (PTHrP) is commonly expressed in non-small cell lung carcinomas (NSCLC). Expression of the protein could have implications for progression of the disease because it regulates cancer cell growth, apoptosis, and angiogenesis. However, its relationship with survival has not been evaluated in a large-scale investigation.

EXPERIMENTAL DESIGN

PTHrP expression was assessed in paraffin-embedded tumor samples from 407 patients with NSCLC by immunohistochemistry. A pathologist unaware of the clinical history classified specimens as PTHrP positive or PTHrP negative. The log-rank test was used to compare survivals of PTHrP-positive and PTHrP-negative groups, and Cox regression was used to adjust for additional covariates.

RESULTS

Median survival was 55 versus 22 months (P < 0.001) in female patients with and without tumor PTHrP, respectively. Male survival was 38 months independent of PTHrP status. Stage, histology, age, and smoking history were also associated with increased longevity. PTHrP remained a significant predictor of survival for female patients after controlling for stage, histology, and age.

CONCLUSIONS

In this study, PTHrP expression was associated with a survival advantage in female patients. Additional investigations must be done to ascertain whether the result is reproducible and independent of potential confounding covariates. Sex-dependent effects of PTHrP in lung cancer would open new avenues of research into the role of sex in cancer progression.

Parathyroid hormone-related protein regulates apoptosis in lung cancer cells through protein kinase A

Parathyroid hormone-related protein (PTHrP)-(1–34) and PTHrP-(140–173) protect lung cancer cells from apoptosis after ultraviolet (UV) irradiation. This study evaluated upstream signaling in PTHrP-mediated alteration of lung cancer cell sensitivity to apoptosis. The two peptides increased cAMP levels in BEN lung cancer cells by 15–35% in a dose-dependent fashion, suggesting signaling through protein kinase A (PKA). In line with this view, the PKA inhibitor H89 abrogated the protective effects of PTHrP-(1–34) and PTHrP-(140–173) against caspase activation and DNA loss. PKA activation by forskolin, 3-isobutyl-1-methylxanthine (IBMX), or 8-(4-chlorophenylthio)adenosine 3′,5′-cyclic monophosphate attenuated and H89 augmented apoptosis after UV exposure as indicated by caspase-3 activation, cell DNA loss, and morphological criteria. Studies with IBMX and varying doses of forskolin indicated that small increases in cAMP, on the order of those generated by IBMX alone and the PTHrP peptides, were sufficient to protect lung cancer cells from apoptosis. In summary, PTHrP-(1–34) and PTHrP-(140–173) stimulate PKA in lung carcinoma cells and protect cells against UV-induced caspase-3 activation and DNA fragmentation. PKA activation by other means also induces resistance to apoptosis, and the protective effect of the PTHrP peptide is blocked by PKA inhibition. Thus PKA appears to have a role in the regulatory effects of PTHrP on lung cancer cell survival.

Parathyroid hormone-related protein and lung biology

Parathyroid hormone-related protein (PTHrP) is expressed in normal and malignant lung and has roles in development, homeostasis, and pathophysiology of injury and cancer. Its effects in developing lung include regulation of branching morphogenesis and type II cell maturation. In adult lung, PTHrP stimulates disaturated phosphatidylcholine secretion, inhibits type II cell growth, and sensitizes them to apoptosis. In lung cancer, PTHrP may play a role in carcinoma progression, or metastasis. The protein could be a useful marker for assessing lung maturity or type II cell function, predicting risk of injury, and detecting lung cancer. PTHrP-based therapies could also prove useful in lung injury and lung cancer.

The extracellular matrix differentially regulates the expression of PTHrP and the PTH/PTHrP receptor in FG pancreatic cancer cells

OBJECTIVES

Previous studies by our laboratory have demonstrated that parathyroid hormone-related protein (PTHrP) and its receptor (PTH/PTHrP receptor) are commonly expressed in pancreatic cancer and suggest their participation in the progression of this devastating disease. It has also been demonstrated that one of the major hallmarks of pancreatic adenocarcinoma is an increased production of the extracellular matrix (ECM), a critical regulator of diverse cellular processes such as differentiation, proliferation, and angiogenesis. The present study focused on the relationship between the PTHrP and ECM axes in the pathobiology of pancreatic cancer.

METHOD AND RESULTS

Using the FG pancreatic adenocarcinoma cell line, we demonstrate a significant inverse correlation between FG cell proliferation and PTHrP expression that depended on the ECM protein on which the cells were cultured (P < 0.05). Generally, ECM proteins that promoted the strongest proliferation, including type I collagen, type IV collagen, and laminin, resulted in decreased expression of PTHrP. Conversely, ECM proteins that promoted the weakest proliferation, including fibronectin, vitronectin, and BSA, resulted in increased expression of PTHrP. A similar trend was found between FG cell proliferation and the PTH/PTHrP receptor expression, with Pearson correlation coefficients of 0.480 (mRNA) and -0.591 (protein).

CONCLUSION

These observations demonstrate a unique functional relationship between the ECM and PTHrP axes and have important implications for our understanding of the complex mechanisms responsible for the progression of pancreatic cancer and its metastases.

Arrested pulmonary alveolar cytodifferentiation and defective surfactant synthesis in mice missing the gene for parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) and PTH/PTHrP receptor expression are developmentally regulated in lung epithelium and adepithelial mesenchyme, respectively. To test the hypothesis that PTHrP is a developmental regulator of terminal airway development, we investigated in vivo and in vitro models of alveolar cytodifferentiation using mice in which the gene encoding PTHrP was ablated by homologous recombination. We have determined that fetal and newborn PTHrP(-/-) lungs showed delayed mesenchymal-epithelial interactions, arrested type II cell differentiation, and reduced surfactant lamellar body formation and pulmonary surfactant production. Embryonic PTHrP(-/-) lung buds cultured in the absence of skeletal constriction or systemic compensating factors also exhibited delayed alveolar epithelial (type II cell) and mesenchymal cytodifferentiation, as well as a > 40% inhibition of surfactant phospholipid production (n = 3-5). Addition of exogenous PTHrP to embryonic PTHrP(-/-) lung cultures normalized interstitial cell morphology and surfactant phospholipid production. The importance of PTHrP as an endogenous regulatory molecule in mammalian lung development is supported by the findings that ablation of PTHrP expression in isolated developing lung is sufficient to disrupt normal development of the alveolar ducts and the centriacinar regions.

Parathyroid hormone-related protein ameliorates death receptor-mediated apoptosis in lung cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed in more advanced, aggressive tumors and may play an active role in cancer progression. This study investigated the effects of PTHrP on apoptosis after UV irradiation, Fas ligation, or staurosporine treatment in BEN human squamous lung carcinoma cells. Cells at 70% confluency were treated for 24 h with 100 nM PTHrP-(1-34), PTHrP-(38-64), PTHrP-(67-86), PTHrP-(107-139), or PTHrP-(140-173) in media with serum, exposed for 30 min to UV-B radiation (0.9 mJ/cm2), and maintained for another 24 h. Caspase-3, caspase-8, and caspase-9 activities increased fivefold. Pretreatment with PTHrP-(1-34) and PTHrP-(140-173) ameliorated apoptosis after UV irradiation, as indicated by reduced caspase activities, increased cell protein, decreased nuclear condensation, and increased clonal survival. Other peptides had no effect on measures of apoptosis. PTHrP-(140-173) also reduced caspase activities after Fas ligation by activating antibody, but neither peptide had effects on caspase-3 or caspase-9 activity after 1 microM staurosporine. These data indicate that PTHrP-(1-34) and PTHrP-(140-173) protect against death receptor-induced apoptosis in BEN lung cancer cells but are ineffective against mitochondrial pathways. PTHrP contributes to lung cancer cell survival in culture and could promote cancer progression in vivo. The mechanism for the protective effect against apoptosis remains to be determined.

Mass spectrometric immunoassay for parathyroid hormone-related protein

This paper describes a novel two-site peptide immunoassay using the isotope 14C as the label and accelerator mass spectrometry as the detection system. A mouse monoclonal antibody (1A5) against the amino terminal region of human parathyroid hormone-related protein (PTHrP) was labeled with 14C by growing the hybridoma cells in a miniPERM bioreactor in the presence of [U-14C]L-leucine and [U-14C]D-glucose. The antibody was purified from the culture media using protein G affinity chromatography. The purified 14C-labeled antibody (14C-1A5) fractions showed excellent correlation between the levels of radioactivity and binding activity for PTHrP. Using 14C-1A5 as the detection antibody in a two-site immunoassay format for PTHrP1-141, a 16-kDa polypeptide, an analytic sensitivity of 10 pmol/L was achieved with a linear measurement range up to 1.3 nmol/L. Only approximately 17 pCi/ well (or 1.6 nCi/96-well microtiter plate) 14C-1A5 was used, which is far below the limit (50 nCi/g) for disposal as nonradioactive waste. This study may serve as a model for the development of sensitive and "nonradioactive" immunoassays for peptides, including polypeptide tumor markers.

Parathyroid hormone-related protein as a novel tumor marker in pancreatic adenocarcinoma

INTRODUCTION

Parathyroid hormone-related protein (PTHrP) can act as an oncoprotein to regulate the growth and proliferation of many common malignancies, including pancreatic cancer. Previous studies have shown that PTHrP is produced by human pancreatic cancer cell lines, can be shown in the cytoplasm and nucleus of paraffin-embedded pancreatic adenocarcinoma tumor specimens, and is secreted into the media of cultured pancreatic adenocarcinoma cells. We hypothesized that PTHrP could serve as a tumor-marker for growth of pancreatic cancer in vivo.

AIM AND METHODOLOGY

To test this hypothesis, we used an orthotopic model developed in our laboratory of the PTHrP-producing human pancreatic cancer line, BxPC-3. This tumor was stably transduced with green fluorescence protein (GFP) to facilitate visualization of tumor growth and metastases. At early (5 weeks) and late (13 weeks) time points after surgical orthotopic implantation, serum PTHrP was measured and primary and metastatic tumor burden was determined for each mouse by assessing GFP expression.

RESULTS

By 5 weeks after surgical orthotopic implantation (early group), the mean serum PTHrP level was 33.3 pg/mL. In contrast, by 13 weeks after surgical orthotopic implantation (late group), the mean serum PTHrP level increased to 158.5 pg/mL. These differences were highly significant (p < 0.001, Student t test). Numerous metastatic lesions were readily visualized by GFP in the late group. Serum PTHrP levels measured by immunoassay correlated with primary pancreatic tumor weights and serum calcium levels (p <0.01). PTHrP levels were not detectable (<21 pg/mL) in any of the 10 control mice with no tumor. Western blotting of BxPC-3-GFP tumor lysates confirmed the presence of PTHrP. BxPC-3-GFP tumor tissue stained with antibody to PTHrP.

CONCLUSION

These results indicate that PTHrP can serve as a tumor marker in animal models of pancreatic cancer and may be a useful tumor marker for clinical pancreatic adenocarcinoma.

Parathyroid hormone-related protein regulates the growth of orthotopic human lung tumors in athymic mice

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has growth regulatory effects for many malignant cells and may influence the progression of carcinomas of the breast, prostate, and lung. In the current study, the authors investigated the in vivo and in vitro effects of PTHrP neutralizing antibody and PTHrP treatment on the growth of BEN cells, a human lung squamous cell carcinoma line that expresses PTHrP and its receptor.

METHODS

Orthotopic lung tumors were produced in 20 athymic mice with BEN-GFP cells (a clonal line that stably expresses green fluorescent protein [GFP]) by instilling suspensions of 3 x 10(6) cells per mouse into the lungs of anesthetized animals. The mice were divided into 2 groups receiving either subcutaneous mouse antihuman PTHrP antibodies or irrelevant mouse immunoglobulin (Ig) G (150 microg) twice weekly.

RESULTS

After 30 days, 6 of 10 mice receiving anti-PTHrP antibodies had lung tumors visible on macroscopic inspection, but only 1 of the 10 mice treated with irrelevant IgG had a lung tumor that was of that size (P < 0.01). GFP fluorescence was significantly greater in lung homogenates of the PTHrP antibody-treated mice than in the mice treated with IgG (6006 +/- 411 vs. 2907 +/- 282 relative fluorescent units, respectively; P < 0.001). Although neutralizing antibodies stimulated BEN cell lung tumor growth, exogenous PTHrP 1-34 treatment (0.01-1 nM) inhibited the growth of cultured BEN cells by approximately 40%.

CONCLUSIONS

Although PTHrP expression has been reported to be associated with more aggressive malignancies, the data from the current study suggest that PTHrP 1-34 was a paracrine growth inhibitor in BEN human lung carcinoma cells. The growth-related effects of PTHrP are complex, and can be both stimulatory and inhibitory.

Proteolysis of ProPTHrP(1-141) by "prohormone thiol protease" at multibasic residues generates PTHrP-related peptides: implications for PTHrP peptide production in lung cancer cells

The parathyroid hormone-related protein (PTHrP) precursor requires proteolytic processing to generate PTHrP-related peptide products that possess regulatory functions in the control of PTH-like (parathyroid-like) actions and cell growth, calcium transport, and osteoclast activity. Biologically active peptide domains within the PTHrP precursor are typically flanked at their NH2- and COOH-termini by basic residue cleavage sites consisting of multibasic, dibasic, and monobasic residues. These basic residues are predicted to serve as proteolytic cleavage sites for converting the PTHrP precursor into active peptide products. The coexpression of the prohormone processing enzyme PTP ("prohormone thiol protease") in PTHrP-containing lung cancer cells, and the lack of PTP in cell lines that contain little PTHrP, implicate PTP as a candidate processing enzyme for proPTHrP. Therefore, in this study, PTP cleavage of recombinant proPTHrP(1-141) precursor was evaluated by MALDI mass spectrometry to identify peptide products and cleavage sites. PTP cleaved the PTHrP precursor at the predicted basic residue cleavage sites to generate biologically active PTHrP-related peptides that correspond to the NH2-terminal domain (residues 1-37) that possesses PTH-like and growth regulatory activities, the mid-region domain (residues 38-93) that regulates calcium transport, and the COOH-terminal domain (residues 102-141) that modulates osteoclast activity. Lack of cleavage at other types of amino acids demonstrated the specificity of PTP processing at basic residue cleavage sites. Overall, these results demonstrate the ability of PTP to cleave the PTHrP precursor at multibasic, dibasic, and monobasic residue cleavage sites to generate active PTHrP-related peptides. The presence of PTP immunoreactivity in PTHrP-containing lung cancer cells suggests PTP as a candidate processing enzyme for the PTHrP precursor.

Parathyroid hormone-related protein is an independent prognostic factor for renal cell carcinoma

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has been shown to be the principal cause of humoral hypercalcemia associated with renal cell carcinoma (RCC). Recent studies have demonstrated that the amino-terminal region of PTHrP has growth factor-like activities, suggesting it may play a role in the development of RCC. In this study, expression of the carboxy-terminal region of PTHrP was assessed immunohistochemically and its significance in predicting the prognosis of RCC was studied.

METHODS

Forty radical nephrectomy specimens were immunostained with a murine monoclonal antibody (9H7) against the carboxy-terminal region (amino acids 109-141) of PTHrP using the streptavidin-peroxidase enzyme conjugate method. Staining intensity was evaluated semiquantitatively and compared with clinicopathologic features of the corresponding RCC.

RESULTS

Immunoreactivity to 9H7 was observed to be localized to the cytosol of tumor cells at various staining intensities. There were 30 cases (75.0%) with strong staining and 10 cases (25.0%) in which staining was weak or nonexistent. Staining intensity showed no significant correlation with gender, tumor greatest dimension, stage, or grade. Tumors of the clear cell type expressed PTHrP to a significantly greater extent than tumors of the granular cell type. Tumor recurrence was significantly greater in the weakly stained or unstained group compared with the strongly stained group (P = 0.035). Multivariate analysis indicated that PTHrP expression and tumor stage were equally significant prognostic indicators in RCCs measuring <10 cm in greatest dimension.

CONCLUSIONS

Evident PTHrP(109-141) expression is present in the majority of RCCs. The results of the current study indicate PTHrP(109-141) may be a possible marker of cellular differentiation and may be useful for predicting recurrence free survival in RCC patients after radical nephrectomy.

Parathyroid hormone-related proteins is abundant in osteoarthritic cartilage, and the parathyroid hormone-related protein 1-173 isoform is selectively induced by transforming growth factor beta in articular chondrocytes and suppresses generation of extracellular inorganic pyrophosphate

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) is a major, locally expressed regulator of growth cartilage chondrocyte proliferation, differentiation, synthetic function, and mineralization. Because mechanisms that limit cartilage chondrocytes from maturing and mineralizing are diminished in osteoarthritis (OA), we studied PTHrP expression by articular chondrocytes.

METHODS

PTHrP was studied in normal knee cartilage samples and cultured articular chondrocytes, and in cartilage specimens from knees with advanced OA, obtained at the time of joint replacement.

RESULTS

PTHrP was more abundant in OA than in normal human knee articular cartilage. Both demonstrated PTH/PTHrP receptor expression. PTHrP 1-173, one of three alternatively spliced PTHrP isoforms, was exclusively expressed and induced by transforming growth factor beta in cultured chondrocytes. Chondrocytes mainly used the GC-rich P2 alternative promoter to express PTHrP messenger RNA. Inhibition by PTHrP 1-173, but not by PTHrP 1-146 or PTHrP 1-87, of inorganic pyrophosphate (PPi) elaboration suggested selective functional properties of the 1-173 isoform. Exposure to a neutralizing antibody to PTHrP increased PPi elaboration by articular chondrocytes.

CONCLUSION

Increased expression of PTHrP, including the 1-173 isoform, has the potential to contribute to the pathologic differentiated functions of chondrocytes, including mineralization, in OA.

Characterization of the cell-specific expression of parathyroid hormone-related protein in normal and neoplastic prostate tissue

OBJECTIVES

Parathyroid hormone-related protein (PTHrP) is a primary factor in the pathogenesis of malignancy-associated hypercalcemia. By alternative splicing, the human PTHrP gene can generate three different species of mRNA that encode three initial translational isoforms of 139, 173, and 141 amino acids. We recently reported that PTHrP was present in normal prostatic neuroendocrine cells and was overexpressed in prostate cancer tissue as demonstrated by immunostaining. This study was undertaken to further clarify the complex expression of PTHrP gene in normal prostate tissue and prostate cancer.

METHODS

PTHrP mRNA in samples prepared from normal prostate tissue, prostate cancer, and three prostate cancer cell lines, PC3, LNCaP, and DU145 was assessed using Northern hybridization. Expressed PTHrP isoforms were deduced from differential reverse transcription-polymerase chain reaction (RT-PCR) assays with exon-specific primers. Further localization of different species of PTHrP mRNA was performed using nonradioactive in situ hybridization with exon-specific probes on consecutive sections of normal and neoplastic prostate tissue.

RESULTS

Northern hybridization showed that the PTHrP expression level was higher in prostate cancer than in normal prostate tissue. All three PTHrP isoforms could be detected in normal prostate tissues and prostate cancer with differential RT-PCR. Further analysis using in situ hybridization with exon-specific probes revealed that all three PTHrP isoforms were present in prostatic neuroendocrine cells and only PTHrP-1-139 isoform could be clearly detected in prostate cancer tissue. Two androgen-insensitive cell lines, PC3 and DU145, derived from a bone metastasis and a brain metastasis, respectively, expressed all three mRNA species encoding for the three isoforms, but DU145 cells expressed less than PC3 cells. Androgen-sensitive LNCaP cells exhibited a low level of expression of mRNA species encoding for PTHrP-1-139 and PTHrP-1-173, and no expression of PTHrP1-141 isoform.

CONCLUSIONS

All three initial translational isoforms of PTHrP are produced by prostatic neuroendocrine cells. The mature products of PTHrP might exert their effects on other prostatic epithelial cells in a paracrine fashion and also participate in the homeostatic regulation of the ejaculate. In prostate cancer, differential expression of these three isoforms is evident and PTHrP-1-139 isoform is more abundant than the other two forms. These findings are valuable for designing future research studies to further elucidate the biological functions of PTHrP in normal prostatic glands and prostate cancer.

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

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

Hypercalcemia: mechanisms, differential diagnosis, and remedies

The urgency for treatment of hypercalcemia is assessed by determining the severity of symptoms and complications and the degree of elevation of serum calcium. Increased bone resorption is the most common pathophysiologic mechanism for hypercalcemia, and several agents are used to inhibit this resorption, including calcitonin and bisphosphonates. However, inhibition of bone resorption controls hypercalcemia for only a limited time, and prompt definitive treatment of the underlying cause, such as primary hyperparathyroidism or malignancy, is essential.

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

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

Cell type-specific secretion of parathyroid hormone-related protein via the regulated versus the constitutive secretory pathway

Parathyroid hormone-related protein (PTHrP) is endoproteolytically processed to yield a family of mature secretory forms. These include an amino-terminal, a mid-region, and a carboxyl-terminal form. Prior studies suggested that the mid-region form is secreted via the regulated secretory pathway, whereas the amino- and carboxyl-terminal forms are secreted via the constitutive pathway. Further, PTHrP is unusual in that it is produced under normal circumstances by neuroendocrine cell types as well as by prototypical constitutively secreting cell types. The potential for cell-specific secretory pathway use by PTHrP has not been explored. Using immunohistochemical and perifusion techniques, we demonstrate that all three PTHrP daughter peptides are secreted via the regulated pathway in neuroendocrine cells. In contrast, all three daughter peptides are secreted in a constitutive fashion by non-neuroendocrine cells. Thus, the secretion of PTHrP is unique in that it appears to be cell-specific. When it is expressed in neuroendocrine cells that contain the regulated pathway, it is secreted in a regulated fashion; when it is expressed in non-neuroendocrine cells, it defaults to the constitutive pathway. This phenomenon has not previously been described for a polypeptide hormone in naturally occurring cells.

Evidence for the synthesis of parathyroid hormone-related protein (PTHrP) by nontransformed clonal rat osteoblastic cells in vitro

Parathyroid hormone-related protein (PTHrP) is synthesized by a variety of tumors and is thought to be the main cause of the clinical syndrome of humoral hypercalcemia of malignancy (HHM). In addition to its parathyroid hormone (PTH)-like actions, novel actions of PTHrP on placental calcium transport and inhibition of in vitro osteoclast activity have been demonstrated. The fact that osteoblasts act as mediators of osteoclastic bone resorption prompted us to investigate whether nontranformed, osteoblastlike cells produce PTHrP. PTHrP has been detected in developing human fetal bones and in rat long bones in culture. For this study, osteogenic cells, CRP 5/4 and CRP 10/30, were employed. Both cell types represent clonal bone cell populations established from 1-day-old rats. While CRP 10/30 cells express the osteoblastic phenotype, CRP 5/4 cells resemble cells with preosteoblastic properties. With a radioimmunoassay (RIA), utilizing antiserum directed against the amino-terminal PTHrP(1-40), it was found that both cell types synthesize PTHrP constitutively. CRP 10/30 cells produce about twice as much as CRP 5/4 cells. Transforming growth factor-beta (TGF-beta 1) was shown to increase the synthesis of PTHrP in CRP 5/4 cells by about 2.5-fold, while in CRP 10/30 cells it caused an approximate 50% reduction of PTHrP. Employing the reverse transcriptase polymerase chain reaction (RT-PCR) technique it was found that both bone cell types express mRNA for PTHrP and that the modulation of the PTHrP mRNA levels by TGF-beta 1 in CRP 5/4, and to a lesser degree in CRP 10/30 cells, was reflected in a change in the level of PTHrP protein in the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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 expression in gynecic squamous carcinoma cells

BACKGROUND

The regulation of parathyroid hormone-related protein (PTH-rP) mRNA levels and immunoreactive (ir)PTH-rP formation by peptide growth factors, particularly transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF), in squamous cell carcinomas of gynecologic origin is largely unknown.

METHODS

PTH-rP mRNA levels were evaluated by Northern analysis in A431 cells (derived from a human vulvar epidermoid carcinoma) and ME-180 cells (derived from a human papillomavirus-infected squamous cell carcinoma of the cervix). PTH-rP protein levels in cell culture media were evaluated using both radioimmunoassay and immunoradiometric assay techniques. These results were compared with those from a lung carcinoid cell line known to produce PTH-rP, namely, NCI-H727 cells.

RESULTS

TGF-beta 1 or EGF treatment caused an increase in the levels of PTH-rP mRNA in A431 cells; these increases in PTH-rP mRNA were detectable after 60 minutes of treatment, were maximal at approximately 4-8 hours, and were approximately additive. Immunoreactive PTH-rP was not detectable (using two different PTH-rP immunoassays) in the culture medium or cell sonicates of A431 cells before or after treatment with TGF-beta 1, EGF, or TGF-beta 1 plus EGF. ME-180 cells responded to EGF (but not to TGF-beta 1) with an increase in the level of PTH-rP mRNA as early as 2 hours; irPTH-rP was present (by use of either immunoassay) in the medium of these cells at 8 and 24 hours. In NCI-H727 (human lung carcinoid) cells, TGF-beta 1 and EGF acted alone and synergistically to effect increases in PTH-rP mRNA and the accumulation of irPTH-rP.

CONCLUSIONS

TGF-beta 1 and EGF regulation of PTH-rP gene expression in squamous cell carcinomas of gynecologic origin is unique for each cell line studied and different from that in human lung carcinoid cells.

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.

Passive immunization with anti-parathyroid hormone-related protein monoclonal antibody markedly prolongs survival time of hypercalcemic nude mice bearing transplanted human PTHrP-producing tumors

Malignancy-associated hypercalcemia is mainly caused by excessive production of parathyroid hormone-related protein (PTHrP) by the tumor. Using anti-PTHrP-(1-34) monoclonal murine antibody (anti-PTHrP MoAb), we studied whether repeated injection of the homologous antibody would continuously decrease the serum calcium concentration in hypercalcemic nude mice bearing transplanted human PTHrP-producing tumors, leading to prolongation of their survival time. Daily SC injections of anti-PTHrP MoAb decreased the serum calcium concentration almost to within the normal range in nude mice bearing transplanted human PTHrP-producing tumors (T3M-1, EC-GI, PC-3, and FA-6) but not in a nude mouse bearing a transplanted parathyroid carcinoma. The antibody did not affect FA-6 tumor growth either in vitro or in vivo. Pancreatic carcinoma cells (FA-6), which caused the most severe hypercalcemia, were inoculated into 6-week-old nude mice. When severe hypercalcemia (approximately 19 mg/dl) had developed, daily SC injection of anti-PTHrP MoAb was started. Within 18 days of this time point, all untreated tumor-bearing mice (n = 10) died of hypercalcemia and cachexia, whereas all the treated mice (n = 10) showed an increase in body weight and survived for at least 25 days. Histologic examination of the treated mice revealed a marked decrease in osteoclastic bone resorption, without toxicologic findings in the kidney and liver. These results suggest that passive immunization against PTHrP can continuously ameliorate the hypercalcemia and markedly prolong the survival time of severely hypercalcemic, tumor-bearing mice. If a human monoclonal antibody against PTHrP-(1-34) could be developed, then passive immunization would be potentially one of the most effective therapies for patients with malignancy-associated hypercalcemia due to excessive production of PTHrP.

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.

Molecular forms of parathyroid hormone-related protein in tumours and biological fluids

OBJECTIVE

We investigated the content and compared the molecular forms of parathyroid hormone-related protein in tumour tissue, plasma and pleural fluid.

DESIGN

Measurement of parathyroid hormone-related protein in tumour extracts and biological fluids and comparison of the elution profiles of parathyroid hormone-related protein (PTHRP) immunoreactivity following gel filtration chromatography on Bio-gel P100.

PATIENTS

Tumours and plasma from patients with humoral hypercalcaemia of malignancy were studied, together with tumours and pleural fluids from patients who were normocalcaemic.

MEASUREMENTS

Immunoreactivity in column fractions, plasma and tumour extracts was measured by a highly sensitive immunoradiometric assay for PTHRP 1-86 with specificity directed at the 17-61 region of PTHRP.

RESULTS

Similar levels of PTHRP immunoreactivity were measured in tumours from normocalcaemic and hyper-calcaemic patients. PTHRP 1-86 (28-4630 fmol/g) was detected in eight of the nine tumours studied. Immunoreactivity in tumour extracts eluted as major peaks in the range 22-33 kDa with an additional peak of 15 kDa in three out of six tumours studied. In contrast, immunoreactivity in plasma and pleural fluid eluted within the range 7-14 kDa.

CONCLUSIONS

The major species of parathyroid hormone-related protein in plasma and pleural fluids was consistently smaller than that in tumour tissue (22-33 kDa) suggesting that tumour-derived parathyroid hormone-related protein is processed at the COOH-terminus to form a species of approximately 10 kDa which circulates in patients with humoral hypercalcaemia of malignancy.

Immunochemical characterisation of parathyroid hormone-related protein from tumour and non-tumour cells

The molecular forms of parathyroid hormone-related protein (PTHRP) in conditioned media from the BEN human lung cancer cell line, rat parathyroid cells (PT-r) and human keratinocytes were studied by gel-filtration chromatography with assay of PTHRP by immunoassays and bioassay. Immunoreactivity (1-86 and 1-34) and bioactivity (1-34) in conditioned media eluted as a coincident major peak (approx. molecular mass 19-22 kDa) and there was evidence of amino-terminal species in the molecular mass range 10-16 kDa in BEN and keratinocyte media. Western blotting of PTHRP affinity purified by monoclonal antibodies directed at regions 1-34 or 37-67, identified a major species in all cell cytosols and media with an apparent molecular mass of 24-25 kDa, consistently slightly larger than recombinant PTHRP(1-141) (mobility of 21 kDa) which may represent an intact or native form of PTHRP. Additional amino-terminal species were identified in medium from keratinocytes (16 and 7 kDa), BEN cells (18 and 14 kDa) and PT-R cells (17 kDa), suggesting that processing occurs at the C-terminus and within the mid-region to form a range of amino-terminal fragments.