Parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor expression and mitogenic responses in human breast cancer cell lines

Baseline renal function and the risk of cancer among apparently healthy middle-aged adults

BACKGROUND

The association between mildly impaired renal function with all-site and site-specific cancer risk is not established. We aim to explore this association among apparently healthy adults.

METHODS

We followed 25,073 men and women, aged 40-79 years, free of cancer or cardiovascular disease at baseline who were screened annually in preventive healthcare settings. The estimated glomerular filtration rate (eGFR) was calculated using the CKD Epidemiology Collaboration equation (CKD-EPI) and classified into four mutually exclusive groups: <60, 60-74, 75-89, ≥90 (mL/min/1.73 m²). The primary outcome was all-site cancer while the secondary outcome was site-specific cancer. Cancer data was available from a national registry.

RESULTS

Mean age at baseline was 50 ± 8 years and 7973 (32 %) were women. During a median follow-up of 9 years (IQR 3-16) and 256,279 person years, 2045 (8.2 %) participants were diagnosed with cancer. Multivariable Cox model showed a 1.2 (95 %CI: 1.0-1.4 p = 0.05), 1.2 (95 %CI: 1.0-1.4 p = 0.02), and 1.4 (95 %CI: 1.1-1.7 p = 0.003) higher risk for cancer with eGFR of 75-89, 60-74, and < 60, respectively. Site-specific analysis demonstrated a 1.8 (95 %CI: 1.2-2.6 p = 0.004), 1.7 (95 %CI: 1.2-2.6 p = 0.004) and 2.2 (95 %CI: 1.3-3.6 p = 0.002) increased risk for prostate cancer with eGFR of 75-89, 60-74, and < 60, respectively. eGFR< 60 was associated with a 2.0 (95 %CI: 1.1-3.7 p = 0.03) and 3.7 (95 %CI: 1.1-13.1 p = 0.04) greater risk for melanoma and gynecological caner respectively.

CONCLUSIONS

CKD stage 2 and worse is independently associated with higher risk for cancer incidence, primarily prostate cancer. Early intervention and screening are warranted among these individuals in order to reduce cancer burden.

Parathyroid Hormone-Related Protein/Parathyroid Hormone Receptor 1 Signaling in Cancer and Metastasis

PTHrP exerts its effects by binding to its receptor, PTH1R, a G protein-coupled receptor (GPCR), activating the downstream cAMP signaling pathway. As an autocrine, paracrine, or intracrine factor, PTHrP has been found to stimulate cancer cell proliferation, inhibit apoptosis, and promote tumor-induced osteolysis of bone. Despite these findings, attempts to develop PTHrP and PTH1R as drug targets have not produced successful results in the clinic. Nevertheless, the efficacy of blocking PTHrP and PTH1R has been shown in various types of cancer, suggesting its potential for therapeutic applications. In light of these conflicting data, we conducted a comprehensive review of the studies of PTHrP/PTH1R in cancer progression and metastasis and highlighted the strengths and limitations of targeting PTHrP or PTH1R in cancer therapy. This review also offers our perspectives for future research in this field.

Chronic Kidney Disease and Cancer: Inter-Relationships and Mechanisms

Chronic kidney disease (CKD) has been recognized as an increasingly serious public health problem globally over the decades. Accumulating evidence has shown that the incidence rate of cancer was relatively higher in CKD patients than that in general population, which, mechanistically, may be related to chronic inflammation, accumulation of carcinogenic compounds, oxidative stress, impairment of DNA repair, excessive parathyroid hormone and changes in intestinal microbiota, etc. And in patients with cancer, regardless of tumor types or anticancer treatment, it has been indicated that the morbidity and incidence rate of concomitant CKD was also increased, suggesting a complex inter-relationship between CKD and cancer and arousing increasing attention from both nephrologists and oncologists. This narrative review focused on the correlation between CKD and cancer, and underlying molecular mechanisms, which might provide an overview of novel interdisciplinary research interests and the potential challenges related to the screening and treatment of CKD and cancer. A better understanding of this field might be of help for both nephrologists and oncologists in the clinical practice.

An Insight into GPCR and G-Proteins as Cancer Drivers

G-protein-coupled receptors (GPCRs) are the largest family of cell surface signaling receptors known to play a crucial role in various physiological functions, including tumor growth and metastasis. Various molecules such as hormones, lipids, peptides, and neurotransmitters activate GPCRs that enable the coupling of these receptors to highly specialized transducer proteins, called G-proteins, and initiate multiple signaling pathways. Integration of these intricate networks of signaling cascades leads to numerous biochemical responses involved in diverse pathophysiological activities, including cancer development. While several studies indicate the role of GPCRs in controlling various aspects of cancer progression such as tumor growth, invasion, migration, survival, and metastasis through its aberrant overexpression, mutations, or increased release of agonists, the explicit mechanisms of the involvement of GPCRs in cancer progression is still puzzling. This review provides an insight into the various responses mediated by GPCRs in the development of cancers, the molecular mechanisms involved and the novel pharmacological approaches currently preferred for the treatment of cancer. Thus, these findings extend the knowledge of GPCRs in cancer cells and help in the identification of therapeutics for cancer patients.

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

The SuprMam1 breast cancer susceptibility locus disrupts the vitamin D/ calcium/ parathyroid hormone pathway and alters bone structure in congenic mice

Breast cancer is a complex disease, and approximately 30% of cases are considered to be hereditary or familial, with a large fraction of this being polygenic. However, it is difficult to demonstrate the functional importance of genes of small effect in population studies, and these genes are not always easily targeted for prevention. The SuprMam (suppressor of mammary tumour) breast cancer susceptibility alleles were previously identified as contributors to spontaneous mammary tumour development in Trp53^+/- mice. In this study, we have generated and characterised congenic mice that contain the BALB/c SuprMam1 (susceptibility) locus on a C57BL/6 (resistant) background and discovered a subtle impairment in the vitamin D/ calcium/ parathyroid hormone (PTH) pathway. This was evident as altered gene expression in the mammary glands of key players in this pathway. Further functional analysis of the mice revealed elevated PTH levels, reduced Cyp27b1 expression in kidneys, and reduced trabecular bone volume/ tissue volume percentage. Plasma 25(OH)D and serum calcium were unchanged. This impairment was a result of genetic differences and occurred only in females, but the elevated PTH levels could be overcome with either calcium or vitamin D dietary supplementation. Either low levels of active vitamin D (1,25(OH)₂D) or chronically elevated PTH levels may contribute to increased breast cancer susceptibility. These indicators are not easily measured in human population studies, but either mechanism may be preventable with dietary calcium or vitamin D supplements. Therefore, SuprMam congenic mice could serve as a valuable model for studying the role of gene-hormone-environment interactions of the vitamin D/ calcium/ PTH pathway in cancer and other diseases and for testing preventive interventions.

Serum levels of vitamin D, parathyroid hormone and calcium in relation to survival following breast cancer

Purpose

Vitamin D, parathyroid hormone (PTH) and calcium in blood are correlated with each other. Previous studies have suggested vitamin D to have anti-proliferative effects on tumor cells, whereas PTH may have carcinogenic effects. A cancer disease may influence calcium levels in blood, but less is known about calcium and its potential effect on cancer risk and survival. The aim of this study was to examine pre-diagnostic levels of vitamin D (25OHD), PTH and calcium in relation to survival after breast cancer.

Methods

The Malmö Diet and Cancer Study enrolled 17,035 women between 1991 and 1996. 672 patients developed incident invasive breast cancer up until 31 December 2006. Serum samples collected at baseline were analyzed for 25OHD, PTH and calcium. All patients were followed until 31 December 2010 using the Swedish Cause of Death Registry. The analytes were divided into tertiles and the risk of death from breast cancer was analyzed using an adjusted Cox proportional hazards analysis, yielding hazard ratios with 95 % confidence intervals.

Results

Levels of 25OHD and breast cancer mortality were associated in a u-shaped manner with the highest mortality among patients in the first (2.46: 1.38–4.37) and third tertiles (1.99: 1.14–3.49), as compared to the second. An inverse relation was found between calcium levels and breast cancer mortality, with the lowest mortality in the third tertile, (0.53: 0.30–0.92) as compared to the first. There was no clear association between PTH and breast cancer mortality.

Conclusions

This study shows that pre-diagnostic 25OHD and calcium may affect survival following breast cancer.

Prognostic role of serum parathyroid hormone levels in advanced prostate cancer patients undergoing zoledronic acid administration

BACKGROUND

Secondary hyperparathyroidism is frequent in prostate cancer patients with bone metastases, and this condition is worsened by the administration of potent bisphosphonates. Serum parathyroid hormone (PTH) elevation can impair the efficacy of these drugs in terms of survival.

METHODS

The prognostic role of elevated serum PTH levels at baseline and after 3 months of zoledronic acid administration was assessed prospectively in 643 bone metastatic prostate cancer patients enrolled in a prospective randomized, placebo-controlled study.

RESULTS

On multivariate analysis, after adjusting for major prognostic factors and bone turnover markers, elevated baseline serum PTH level was negatively associated with overall survival (hazard ratio [HR], 1.448; 95% confidence interval [CI], 1.045-2.006; p < .03) in zoledronic acid-treated patients but not in placebo-treated patients. In patients with normal baseline PTH levels, there was a trend but insignificant association between zoledronic acid administration and a better survival outcome than with placebo (HR, 0.81; 95% CI, 0.65-1.01; p = .065), whereas a trend in the opposite direction was observed in patients with elevated PTH levels (HR, 1.45; 95% CI, 0.87-2.39; p = .151); interaction test, p = .040. Elevated serum PTH level after 3 months of zoledronic acid treatment was not significantly associated with survival outcome.

CONCLUSIONS

Secondary hyperparathyroidism has a negative prognostic impact in metastatic prostate cancer patients undergoing zoledronic acid administration. Counteracting elevated PTH levels by adequate doses of vitamin D may improve the efficacy of this drug.

The vitamin D pathway and mammographic breast density among postmenopausal women

Laboratory studies have demonstrated that vitamin D has a number of chemopreventive properties, and that these properties may be mediated or modified by other molecules in the vitamin D pathway, such as parathyroid hormone (PTH) or calcium. However, there is little epidemiologic data exploring the effects of vitamin D on breast cancer risk in the context of these other molecules. We examined a panel of molecules in the vitamin D pathway in relation to mammographic breast density, a marker of breast cancer risk, in the Wisconsin Breast Density Study. A total of 238 postmenopausal women (ages 55-70, with no history of postmenopausal hormone use) were enrolled from mammography clinics in Madison, Wisconsin. Subjects provided blood samples that were analyzed for levels of 25-hydroxy vitamin D [25(OH)D], PTH, insulin-like growth factor-1 (IGF-1), IGF-binding protein 3 (IGFBP-3), retinol, and calcium. Percent breast density was measured using Cumulus software. In age-adjusted analyses there was a positive association between 25(OH)D and percent breast density (P = 0.05; mean percent density = 11.3% vs. 15.6% for 1st vs. 4th quartile of 25(OH)D). Breast density was inversely associated with PTH (P = 0.05; 16.0% vs. 11.4% for Q1 vs. Q4) and positively associated with the IGF-1:IGFBP-3 molar ratio (P = 0.02; 11.9% vs. 15.6% for Q1 vs. Q4). However, these associations were all null after further adjustment for body mass index (BMI; P > 0.25). The independent relation between 25(OH)D and breast density remained null among subgroups defined by BMI and serum levels of retinol, calcium, and estradiol. These results suggest no strong independent associations between the circulating molecules of the vitamin D pathway and mammographic breast density in postmenopausal women. While it remains possible that vitamin D could influence breast cancer risk, our results suggest that such an effect would be mediated through pathways other than breast density.

Serum levels of vitamin D, PTH and calcium and breast cancer risk-a prospective nested case-control study

Previous studies indicate that calcium and its regulating hormones, i.e., parathyroid hormone (PTH) and vitamin D, might affect breast cancer risk. Evidence also suggests that this relationship could be influenced by menopausal status and BMI. We examined breast cancer risk related to prediagnostic serum levels of vitamin D (25OHD(2) and 25OHD(3)), PTH and calcium using a nested case-control design within the Malmö Diet and Cancer Study. There were 764 incident breast cancer cases, and 764 controls were selected by incidence density matching, using age as the underlying time scale, matching on calendar time at inclusion, menopausal status and age at inclusion. Using logistic regression analysis, odds ratios (OR) with 95% confidence intervals were calculated for breast cancer risk in different quartiles of the analyzed factors. All analyses were adjusted for risk factors for breast cancer, and for levels of albumin, creatinine and phosphate. Analyses were repeated stratified for BMI and menopausal status, and for low vs. high levels of 25OHD(3), PTH and calcium. There was a weak, nonsignificant inverse association between breast cancer risk and 25OHD(3), and the OR for the 2nd, 3rd and 4th quartiles, as compared to the first, were 0.84 (0.60-1.15), 0.84 (0.60-1.17) and 0.93 (0.66-1.33). Serum calcium was positively associated with breast cancer in premenopausal women (OR for the 4th quartile = 3.10:1.33-7.22 and p for quartile trend = 0.04), and in women with BMI > 25 (OR for the 4th quartile = 1.94:1.12-3.37 and p for trend < 0.01). There was no association between baseline serum PTH and breast cancer risk.

Immunohistochemical identification of the PTHR1 parathyroid hormone receptor in normal and neoplastic human tissues

BACKGROUND

Parathyroid hormone (PTH) is a crucial regulator of calcium homoeostasis in humans. Although it is well known that PTH acts primarily on kidney and bone, the precise cellular and subcellular sites of PTH action have not been visualised in human tissues.

METHOD

We developed and characterised a novel anti-peptide antibody to the carboxy-terminal region of the human PTH receptor type 1 (PTHR1). Specificity of the antiserum was demonstrated by i) detection of a broad band migrating at M(r) 85,000-95,000 in western blots of membranes from human kidney and PTHR1-transfected cells; ii) cell surface staining of PTHR1-transfected cells; iii) translocation of PTHR1 receptor immunostaining after agonist exposure; and iv) abolition of tissue immunostaining by preadsorption of the antibody with its immunising peptide. The distribution of PTHR1 receptors was investigated in 320 human tumours and their tissues of origin.

RESULTS

In the kidney, PTHR1 receptors were predominantly detected at the basolateral plasma membrane of epithelial cells in the proximal and distal tubules but not in the thin limbs of Henle, collecting ducts or glomeruli. In bone, PTHR1 receptors were detected as discrete plasma membrane staining of osteocytes and osteoblasts, whereas osteoclasts remained unstained. In addition, PTHR1 was found in the gut and in a number of neoplastic tissues including colorectal carcinoma, prostate cancer, renal cell carcinoma and osteosarcoma.

CONCLUSION

This is the first localisation of PTHR1 receptors in human tissues at the cellular level. The overexpression of PTHR1 receptors may provide a molecular basis for efficient targeting of human tumours with radiolabelled PTH analogues.

Serum calcium and tumour aggressiveness in breast cancer: a prospective study of 7847 women

Experimental, epidemiological and clinical studies suggest that calcium and/or its regulating hormones affect breast cancer risk. There has been no prospective cohort study investigating serum calcium levels and breast cancer aggressiveness, as determined by tumour histology and stage. Dichotomized prediagnostic serum calcium levels were investigated in relation to breast cancer aggressiveness as determined by grade (mitotic frequency, tubule formation, nuclear atypia) and stage (tumour size and axillary lymph node status). Cox's proportional hazards analysis and heterogeneity analysis were used to investigate the associations between low/high calcium and grade/stage in a prospective cohort study of 7847 women, out of whom 462 women were diagnosed with incident breast cancer during a mean follow-up of 17.2 years. All analyses were stratified for body mass index and menopausal status. Prediagnostic serum calcium levels in premenopausal women were positively associated with increased tumour aggressiveness as determined by a higher risk of nodal metastasis; relative risk (RR) for calcium above median as compared with calcium below median was 1.88 with a 95% confidence interval (CI) of 1.04-3.38. In overweight women, prediagnostic serum calcium levels were also associated with tumour aggressiveness, as determined by both a higher risk of nodal metastasis [RR (95% CI) 1.69 (0.95-3.02)] and severe nuclear atypia [RR (95% CI) 2.06 (1.10-3.86)]. Results also indicate that, in overweight women, calcium is positively associated with worse grade as determined by tubule formation and mitotic frequency. In conclusion, prediagnostic serum calcium levels are positively associated with increased tumour aggressiveness in premenopausal and/or overweight women.

Serum calcium and breast cancer risk: results from a prospective cohort study of 7,847 women

Experimental and epidemiological studies suggest that calcium-regulating hormones--parathyroid hormone (PTH) and vitamin D--may be associated with breast cancer risk. No prospective cohort study has investigated the association between pre-diagnostic calcium levels and subsequent risk of breast cancer. We have examined this in a cohort of 7,847 women where serum calcium levels and established risk factors for breast cancer had been assessed at baseline. During a mean follow-up of 17.8 years, 437 incident breast cancer cases were diagnosed. Incidence of breast cancer was calculated in different quartiles of serum calcium levels and a Cox's proportional hazards analysis was used to obtain corresponding relative risks (RR), with a 95% confidence interval (CI), adjusted for potential confounders. In premenopausal women, serum calcium levels were inversely associated with breast cancer risk in a dose-response manner. The adjusted RR (95% CI) of breast cancer was in the 2nd calcium quartile 0.91 (0.65-1.30), in the 3rd quartile 0.89 (0.60-1.31), and in the 4th quartile 0.56 (0.32-0.98), as compared to the 1st calcium quartile. In postmenopausal overweight women (BMI > 25), breast cancer risk was higher in calcium quartiles 2-4 as compared to the 1st quartile. Our findings may have implications for primary prevention of breast cancer and for the management of asymptomatic primary hyperparathyroidism.

Characterisation of ligand binding to the parathyroid hormone/parathyroid hormone-related peptide receptor in MCF7 breast cancer cells and SaOS-2 osteosarcoma cells

Parathyroid hormone-related peptide (PTHrP) and parathyroid hormone (PTH)/PTHrP-receptor, PTH/PTHrP-R, are frequently expressed in mammary carcinomas as well as in bone cells. In this study we compared the ligand binding characteristics of the PTH/PTHrP-R in SaOS-2 human osteosarcoma cells with those in MCF7 breast cancer cells. We used both Scatchard analysis of saturation kinetics for iodinated ligand and the level of expressed receptor protein by visualising the single radio-labelled receptor-ligand complex from isolated membrane preparations from the two cell lines. In MCF7 cells, ligand binding, (receptor number) was increased by prior exposure of the cultured cells to epidermal growth factor (EGF), estradiol (E2), or dexamethasone (DEX), and decreased following calcitriol (1,25 DHCC). In contrast in the SaOS-2 cells, PTH/PTHrP-R number was increased by exposure to E2 and 1,25DHCC and decreased by DEX while EGF had no effect. These data were confirmed when the PTH/PTHrP-R was cross linked with (125)I-PTHrP-1-34(Tyr), and extended by visualising the intensity of the isolated radiolabelled receptor complex by autoradiography following SDS-PAGE at several time points during the treatment.

PTH-related protein upregulates integrin alpha6beta4 expression and activates Akt in breast cancer cells

Breast cancer is the most common carcinoma that metastasizes to bone. Tumor-produced parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption, is a major mediator of the osteolytic process in breast cancer. We have previously shown that PTHrP increases breast cancer cell proliferation, survival, migration, and pro-invasive integrin alpha6beta4 expression. To determine the role of integrin alpha6beta4 in these PTHrP-mediated effects, we utilized two strategies to modulate expression of the alpha6 and beta4 subunits in parental and PTHrP-overexpressing MDA-MB-231 and MCF-7 cells: overexpression of alpha6beta4 by transfection with constructs encoding the alpha6 and beta4 subunits, and suppression of endogenous alpha6beta4 expression by transfection with siRNAs targeting these subunits. We now show that the effects of PTHrP are mediated via upregulation of integrin alpha6beta4 expression. We also show that integrin alpha6beta4 expression is modulated at the mRNA level, indicating a transcriptional and/or post-transcriptional mechanism of action for PTHrP. PTHrP expression also increased the levels of phosphorylated Akt, with a consequent increase in the levels of phosphorylated (inactive) glycogen synthase kinase-3 (GSK-3). The role of PTHrP in breast cancer growth and metastasis may thus be mediated via upregulation of integrin alpha6beta4 expression and Akt activation, with consequent inactivation of GSK-3.

Role of PTHrp and PTHrp-engaged pathways in MCF-7 cells migration/invasion

In this paper the effect of N-terminal parathyroid hormone-related protein (PTHrp) and PTHrp-engaged pathways on MCF-7 breast cancer cell migration/invasivity and matrix metalloproteinases (MMPs) production were investigated. We found that: a) migration is not affected by PTHrp and Forskolin (FK)-activated PKA, while Phorbol Myristate Acetate (PMA)-activated PKC strongly stimulates MCF-7 cells motility. b) MMPs production was unaffected by PTHrp, but FK reduced membrane-type (MT)-1 MMP expression. Conversely, PMA induced a marked increase of MT1-MMP and MMP-9. c) Chemical activation of PKC is not sufficient, by itself, to confer invasive ability to MCF-7 cells, unless they were provided with additional factors, supplied by fibroblasts. d) Matrix invasion likely occurs through an activation cascade, involving at least three components: pro-MMP-9 and MT-1 MMP (supplied by PMA-stimulated MCF-7 cells) and pro MMP-2 (supplied by fibroblasts). e) The selective chemical inhibition of the adenylylciclase (AC)/PKA and phospholipase C (PLC)/PKC pathways confirmed that MCF-7 cells invasivity is not affected by exogenous PTHrp, which can only modulate their growth. However, the PTHrp responsibility in breast cancer invasion cannot be completely excluded. Indeed, fibroblasts are known to respond to PTHrp (which is a normal product of MCF-7 as well as other breast cancer cells) with enhanced release of MMP-2. On the basis of the documented requirement of fibroblast-derived MMP-2 for MCF-7 cell invasivity, a novel humoral fibroblast-breast cancer cell interaction, mediated by PTHrp, can be recognised.

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.

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.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

PTH-related protein enhances MCF-7 breast cancer cell adhesion, migration, and invasion via an intracrine pathway

Breast cancer is the most common carcinoma that metastasizes to the bone. Parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption, is a major mediator of the osteolytic process in breast cancer. PTHrP overexpression increases mitogenesis and decreases apoptosis in the human breast cancer cell line MCF-7. In this study, MCF-7 cells were used as a model system to study the effects of PTHrP on breast cancer cell adhesion, migration, and invasion. Clones of MCF-7 cells were established that overexpress wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Wild-type PTHrP-overexpressing cells showed significantly higher laminin adhesion and migration, and Matrigel invasion than empty vector-transfectants or cells overexpressing NLS-mutated PTHrP. Wild-type PTHrP also increased the cell surface expression of the pro-invasive integrins alpha6 and beta4; deletion of the NLS negated these effects. Exogenous PTHrP (1-34), (67-86), (107-139), and (140-173) had no effect on integrin expression, or on cell adhesion, migration, and invasion. These results indicate that PTHrP exerts its effects on cell adhesion, migration, invasion, and integrin expression via an intracrine pathway. PTHrP may play a role in breast cancer metastasis by upregulating proinvasive integrin expression, and controlling PTHrP production in breast cancer may provide therapeutic benefit.

Ets2 and protein kinase C epsilon are important regulators of parathyroid hormone-related protein expression in MCF-7 breast cancer cells

Parathyroid hormone-related protein (PTHrP) promotes the metastatic potential and proliferation of breast cancer cells, and acts anti-apoptotically. In invasive MDA-MB-231 breast cancer cells, transforming growth factor beta-regulated PTHrP synthesis is mediated by an Ets1/Smad3-dependent activation of the PTHrP P3 promoter. In the present study, we studied the regulation of PTHrP expression in non-invasive, Ets1-deficient and transforming growth factor beta-resistant MCF-7 cells. We found PMA to be a strong stimulator of P3-dependent PTHrP expression in MCF-7 cells. Mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase 1 (MEK-1)/ERK1/2 inhibitor PD98059 interfered with this activity. Promoter studies revealed that the PMA effect depended on the Ets and stimulating protein-1 (Sp1)-binding sites. Of several Ets factors tested, Ets2, but not Ese-1, Elf-1 or Ets1, supported the PMA-dependent increase in promoter activity. PD98059 and a threonine to alanine mutation of the ERK1/2-responsive Ets2 phosphorylation site at position 72 inhibited the Ets2/PMA effect. Activated protein kinase C (PKC) epsilon could mimic PMA by stimulating the P3 promoter alone or in co-operation with Ets2 in an MEK-1/ERK1/2-dependent manner. Activated PKC alpha, although capable of co-operating with Ets2, failed to induce transcription from the P3 promoter on its own. The Ets2/PKalpha synergistic effect was neither sensitive to PD98059 nor to Thr(72)/Ala(72) mutation. PMA neither increased the expression of Sp1 nor modulated the transcriptional activity of Sp1. However, it induced the displacement of a yet unknown factor from the Sp1-binding site, which may result in Sp1 recruitment to the promoter. Our results suggest an ERK1/2-dependent Ets2/PKC epsilon synergism to be involved in PTHrP expression in MCF-7 breast cancer cells.

Differential expression and/or activation of P38MAPK, erk1/2, and jnk during the initiation and progression of prostate cancer

BACKGROUND

Members of the mitogen-activated protein kinase (MAPK) family are capable of transducing signals from a wide variety of stimuli, including growth factors, G-protein coupled receptors, and cytokines that are likely to play a role in the initiation and/or progression of prostate cancer.

METHODS

The expression and activation of three members of the MAPK family, namely, erk, jnk, and p38MAPK was examined using Western blotting and immunohistochemistry during tumor progression in a transgenic mouse model for prostate cancer.

RESULTS

Activation of p38MAPK was significantly elevated (2.3-fold) in well-differentiated prostatic tumors compared to normal controls. Furthermore, prostatic intraepithelial neoplastic (PIN) lesions expressing activated p38MAPK were observed to be proliferative rather than apoptotic. Expression of activated erk1/2 also preferentially co-located to a sub-population of epithelial cells within PIN lesions that correlated with Ki67 expression. In dramatic contrast, activated forms of erk1/2, jnk, and p38MAPK were reduced or absent in late stage adenocarcinomas and metastatic deposits.

CONCLUSIONS

Erk1/2, jnk, and p38MAPKs are differentially expressed and/or activated during prostate cancer progression. Activation of both erk1/2 and p38MAPK occurs concomitant with prostatic epithelial cell proliferation and the initiation of prostate cancer while inactivation is contemporaneous with the emergence of the poorly differentiated metastatic and androgen-independent phenotype.

The parathyroid hormone-related protein receptor is expressed in breast cancer bone metastases and promotes autocrine proliferation in breast carcinoma cells

Overproduction of parathyroid hormone-related protein (PTHRP) occurs in a high proportion of primary breast cancers (PBC) and is strongly implicated in their metastatic spread to bone. Although the PTHRP-receptor (PTHRP-R) is often coexpressed with PTHRP in PBC, its role in regulating breast cancer cell proliferation and metastases to bone remains unclear. The aims of this study were to determine the expression of the PTHRP-R in breast cancer bone metastases (BM) and to investigate the effects of PTHRP-R overexpression on breast cancer cell proliferation. PTHRP-R expression occurred in 85% (11 out of 13) of BM compared with 58% (39 out of 67) of PBC. Median expression was higher (P<0.05) in BM compared with PBC. PTHRP increased cAMP accumulation and DNA synthesis in MCF-7 cells stably overexpressing the PTHRP-R (MCF-7(WTR)) but not in MCF-7(VEC) control cells. The increase in DNA synthesis was mimicked by the cAMP pathway activator forskolin. The receptor antagonist PTHRP(7-34) reduced DNA synthesis in MCF-7(WTR) cells, but not MCF-7(VEC) cells, indicating that receptor overexpression promotes autocrine PTHRP activity. MCF-7(WTR) cells showed increased mitogenic responsiveness to fetal calf serum and reduced doubling times. PTHRP induced weak activation of ERK1 and ERK2 and potentiated their activation by serum growth factors. Collectively these results show that the PTHRP-R is frequently expressed in breast cancer BM and indicate that receptor overexpression drives proliferation via autocrine signals that are mediated via cAMP and ERK pathways.

Parathyroid hormone-related protein measured at the time of first visit is an indicator of bone metastases and survival in lung carcinoma patients with hypercalcemia

BACKGROUND

Parathyroid hormone-related protein (PTH-rP) is a major cause of tumor-induced hypercalcemia (TIH) and frequently is found to be elevated in serum of patients with TIH. In the current study, the authors examined the usefulness of PTH-rP measurement at the time of first presentation in the follow-up of lung carcinoma patients with TIH.

METHODS

The authors retrospectively studied 23 of 1149 lung carcinoma patients who were found to have TIH at the time of first presentation for the correlation between serum PTH-rP and the development of bone metastases and survival compared with lung carcinoma patients without TIH who were matched by gender, age, Eastern Cooperative Oncology Group performance status, histological type of tumor, and stage of the disease.

RESULTS

Twenty-three lung carcinoma patients with TIH demonstrated significantly increased serum levels of PTH-rP (mean +/- standard error [SE], 84.1 +/- 16.5 pmol/L) compared with control patients without TIH (mean +/- SE, 36.2 +/- 2.0 pmol/L) at the time of first presentation, (P < 0.001). In these hypercalcemic patients, patients whose serum PTH-rP was > 150 pmol/L (n = 16) were found to have a significantly increased rate of bone metastases (71.4% vs. 12.5%; P = 0.01) and decreased survival (median survival of 1.4 months vs. 5.4 months; P < 0.015) compared with patients whose serum PTH-rP was < 150 pmol/L (n = 7).

CONCLUSIONS

The data from the current study suggest that serum PTH-rP as determined at the time of first presentation is a useful indicator of not only hypercalcemia but also bone metastasis and eventual survival in patients with lung carcinoma.

Hypercalcemia associated with parathyroid hormone-related protein at the terminal stage of uncomplicated squamous cell carcinoma in the head and neck region

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is mainly responsible for hypercalcemia in squamous cell carcinomas (SCCs).

METHODS

We retrospectively checked the appearance of hypercalcemia among 33 patients who died with head and neck SCC. Serum concentrations of C-terminal region of PTHrP (C-PTHrP) were measured in 15 of them. The intracellular PTHrP expression was immunohistochemically stained in 42 SCC sections obtained from the 33 before the appearance of hypercalcemia.

RESULTS

Hypercalcemia appeared in 24 of the 33, and increased serum C-PTHrP levels were confirmed in 11 of 12 hypercalcemic patients. PTHrP was identified in all SCC sections, and a stronger intensity than in normal squamous epithelia was observed in 50% of those obtained within 1 year before the onset of hypercalcemia.

CONCLUSION

A high incidence of PTHrP-induced hypercalcemia was shown among patients dying with head and neck SCCs. The intracellular increase in PTHrP might be observed preceding hypercalcemia.

Transforming growth factor beta regulates parathyroid hormone-related protein expression in MDA-MB-231 breast cancer cells through a novel Smad/Ets synergism

The majority of breast cancers metastasizing to bone secrete parathyroid hormone-related protein (PTHrP). PTHrP induces local osteolysis that leads to activation of bone matrix-borne transforming growth factor beta (TGF beta). In turn, TGF beta stimulates PTHrP expression and, thereby, accelerates bone destruction. We studied the mechanism by which TGF beta activates PTHrP in invasive MDA-MB-231 breast cancer cells. We demonstrate that TGF beta 1 up-regulates specifically the level of PTHrP P3 promoter-derived RNA in an actinomycin D-sensitive fashion. Transient transfection studies revealed that TGF beta 1 and its effector Smad3 are able to activate the P3 promoter. This effect depended upon an AGAC box and a previously described Ets binding site. Addition of Ets1 greatly enhanced the Smad3/TGF beta-mediated activation. Ets2 had also some effect, whereas other Ets proteins, Elf-1, Ese-1, and Erf-1, failed to cooperate with Smad3. In comparison, Ets1 did not increase Smad3/TGF beta-induced stimulation of the TGF beta-responsive plasminogen activator inhibitor 1 (PAI-1) promoter. Smad3 and Smad4 were able to specifically interact with the PTHrP P3-AGAC box and to bind to the P3 promoter together with Ets1. Inhibition of endogenous Ets1 expression by calphostin C abrogated TGF beta-induced up-regulation of the P3 transcript, whereas it did not affect the TGF beta effect on PAI expression. In TGF beta receptor II- and Ets1-deficient, noninvasive MCF-7 breast cancer cells, TGF beta 1 neither influenced endogenous PTHrP expression nor stimulated the PTHrP P3 promoter. These data suggest that TGF beta activates PTHrP expression by specifically up-regulating transcription from the PTHrP P3 promoter through a novel Smad3/Ets1 synergism.

Midregion parathyroid hormone-related protein inhibits growth and invasion in vitro and tumorigenesis in vivo of human breast cancer cells

Parathyroid hormone-related protein (PTHrP) is critical for normal mammary development and is overexpressed by breast cancers. PTHrP is a peptide hormone that undergoes extensive post-translational processing, and PTHrP(38-94)-amide is one of the mature secretory forms of the peptide. In this study, we explored the effect of PTHrP(38-94)-amide in a panel of six breast cancer cell lines "in vitro" and in MDA-MB231 cells "in vivo" specifically examining cell viability, proliferation, invasiveness, and growth in nude mice. PTHrP(38-94)-amide markedly inhibited proliferation and also caused striking toxicity and accelerated cell death in breast cancer cells. In addition, direct injection of PTHrP(38-94)-amide into MDA-MB231 breast cancer cells passaged in immunodeficient mice produced a marked reduction in tumor growth. These studies (i) indicate breast cancer cells are one of the few tissues in which specific effects of midregion PTHrP have been established to date, (ii) support a role for midregion secretory forms of PTHrP in modulating not only normal but also pathological mammary growth and differentiation, (iii) add further evidence for the existence of a specific midregion PTHrP receptor, and (iv) provide a novel molecule for modeling of small molecule analogues that may have anti-breast cancer effects.

Significance of the parathyroid hormone-related protein expression in breast carcinoma

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is produced by various neoplasms and is known to be a causative factor of hypercalcemia of malignancy. It has also been suggested to act as a cytokine for tumor progression. The purpose of this study was to clarify the significance of PTHrP expression in breast carcinoma.

METHODS

PTHrP expression was examined in 177 surgically resected breast carcinoma specimens by immunohistochemistry using a monoclonal antibody against the for PTHrP, The relationship of PTHrP expression with clinicopathological factors was analyzed and the clinical courses of the patients are reported.

RESULTS

Positive PTHrP staining was detected in 113 ( 64%) of the breast tumors. Among the positive cases, 36 (32%) of the tumors clearly showed strong expression. When the PTHrP expression was divided into three categories, a significant positive relationship was found between PTHrP expression and histological grade of tumor. PTHrP expression was also significantly related to bone metastasis but the staining degree of PTHrP was not. The patients with positive PTHrP tended to have poor outcome in proportion to the staining degree. Univariate analysis demonstrated a significantly shorter overall survival for patients expressing PTHrP, and in multivariate analysis showed that PTHrP status and nodal status were associated with a significantly shorter overall survival.

CONCLUSION

Our results suggest that PTHrP expression is not only correlated with bone metastasis but is also related to the progression of breast carcinoma, and that overexpression of PTHrP may be a potential prognostic factor for human breast carcinoma.

Parathyroid hormone-related peptide stimulates proliferation of highly tumorigenic human SV40-immortalized breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is the main mediator of humoral hypercalcemia of malignancy (HHM) and it is produced by many tumors, including breast cancers. Breast epithelial cells as well as breast cancer tumors and cell lines have been reported as expressing PTHrP and the PTH/PTHrP receptor, suggesting that PTHrP may act as an autocrine factor influencing proliferation or differentiation of these cell types. We investigated PTHrP gene expression, PTH/PTHrP receptor signaling, and PTHrP-induced mitogenesis in three immortalized human mammary epithelial cell lines that exhibit differential tumorigenicity. The most tumorigenic cells expressed the highest levels of PTHrP messenger RNA (mRNA) and protein. We used reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting to detect the PTH/PTHrP receptor transcripts and proteins in all of the three cell lines. Treatment with human PTHrP(1-34) [hPTHrP(1-34)] and hPTH(1-34) increased intracellular cyclic adenosine monophosphate (cAMP) but not free Ca2+ in the nontumorigenic line. These agonists increased both cAMP and free Ca2+ levels in the moderately tumorigenic line, but only increased free Ca2+ in the highly tumorigenic line. Application of the PTH/PTHrP receptor antagonist [Asn10,Leu11,D Trp12]PTHrP(7-34) or PTHrP antibodies reduced [3H]thymidine incorporation in a dose-dependent fashion in the highly tumorigenic cell line but did not affect the other lines. Thus, treatment with a PTH/PTHrP receptor antagonist reduced cell proliferation, suggesting that PTHrP signaling mediated by the phospholipase C (PLC) pathway stimulates proliferation of a highly tumorigenic immortalized breast epithelial cell line.

Parathyroid hormone may be a cancer promoter - an explanation for the decrease in cancer risk associated with ultraviolet light, calcium, and vitamin D

Epidemiological studies reporting an inverse association between sunlight exposure and risk for cancers of the breast, colon, and prostate, have not yet been explained. Since ultraviolet (UV) light promotes dermal vitamin D generation, studies suggesting that dietary calcium and vitamin D may likewise have cancer-preventive activity are potentially of relevance. UV light, calcium, and vitamin D have the common property of suppressing parathyroid hormone (PTH) production; these considerations raise the possibility that PTH may have promotional activity for certain cancers. PTH might function indirectly in this regard, by increasing hepatic production of the progression growth factor IGF-I, a likely cancer promoter. A more direct role is suggested by recent evidence that many cancers express receptors for PTH/PTH-related protein; these receptors mediate co-mitogenic and/or pro-invasive signals in some cancers. High risk for previous or concurrent neoplasms has been reported in patients with parathyroid adenomas. In light of the increase in cancer risk associated with hypertension, it is notable that PTH levels are typically increased in salt-sensitive hypertensives. Prospective case-control studies examining serum PTH in relation to subsequent cancer risk appear warranted.

Tumour progression and angiogenesis in bone metastasis from breast cancer: new approaches to an old problem

Breast cancer metastasizes frequently to the skeleton and causes considerable morbidity and deterioration of the quality of life. The clinical consequences of skeletal metastases are bone pain, pathological fractures, hypercalcaemia and nerve compression syndromes. From the moment breast cancer cells are located in the bone microenvironment, they may release factors which stimulate bone resorption and angiogenesis leading to growth of skeletal metastases and a subsequent selective increase in the attraction of new cancer cells to bone. In this review, emerging new concepts of breast cancer-bone interactions, in particular the involvement of angiogenesis, proteolysis and the role of cancer-induced bone resorption in skeletal metastasis are discussed. Better understanding of the processes involved in the metastasis of cancer cells to bone, local tumour growth and subsequent destruction of skeletal architecture can lead to optimal methods for the prevention and treatment of metastatic bone disease.

Calcitonin-suppressed expression of parathyroid hormone-related protein in breast cancer cells

Parathyroid hormone-related protein (PTHrP) is a key factor behind humoral hypercalcemia of malignancy (HHM). It is produced in most breast tumors and may be an important local mediator of skeletal metastases due to breast cancer. PTHrP may mediate local bone destruction in the absence of increased circulating PTHrP. Calcitonin (CT) is used for treatment of HHM, but there are data showing that CT can increase PTHrP expression and secretion in vitro. We have therefore studied the effect of CT on PTHrP gene expression and secretion in MCF-7 breast cancer cells. PTHrP mRNA decreased significantly after 4, 8, and 16 h incubation with 10 nM salmon calcitonin (sCT) when compared with the respective controls. PTHrP mRNA also decreased significantly and dose-dependently after incubation with sCT at 0.1 to 10 nM for 16 h. The PTHrP levels in the conditioned medium also decreased in a similar dose-dependent manner. The adenylate cyclase agonist forskolin lowered the PTHrP mRNA dose-dependently. In cells exposed to varying concentrations of sCT for 15 min, the cAMP levels increased dose-dependently. In conclusion, sCT can suppress PTHrP gene expression in MCF-7 breast cancer cells. The suppressive effect is probably exerted mainly via the cAMP-protein kinase A pathways.

Expression of members of the thrombospondin family by human skeletal tissues and cultured cells

We have previously shown that the multifunctional platelet glycoprotein thrombospondin-1 (TSP-1) promotes resorption in an in vitro resorption assay. However, TSP-1 is one of a family of multifunctional TSP molecules, and the current study was undertaken to investigate whether it is TSP-1 or another TSP family member which may be involved in regulation of resorption in vivo. RT-PCR was performed on cultured human bone cells, cultured human chondrocytes, and three separate samples of human osteoclastoma tissue using primers specific for each TSP family member. mRNA for TSP-2 was detected in almost all samples, and significantly in all osteoclastomas in the above tissues, while TSP-1 was detected less frequently and was only seen in one of three osteoclastomas. TSP-3, -4, and COMP were detected only in a minority of cases. These results indicate that TSP-2 is the most common TSP family member found in skeletal tissues and that TSP-2, rather than TSP-1, may be the molecule responsible for promoting resorption in vivo.

Expression of PTHrP and the PTH/PTHrP receptor in purified alveolar epithelial cells, myoepithelial cells, and stromal fibroblasts derived from the lactating rat mammary gland

Parathyroid hormone-related protein (PTHrP) is produced by the lactating mammary gland and secreted into the milk; however, the function of PTHrP during lactation is unknown. Since messenger RNA for both PTHrP and the PTH/PTHrP receptor have been demonstrated within mammary tissue, a paracrine or autocrine function for PTHrP has been proposed. To investigate this hypothesis in lactating tissue, the expression of PTHrP and the PTH/PTHrP receptor was examined in purified subpopulations of cells derived from lactating rat mammary glands. Subpopulations of stromal, myoepithelial, and alveolar epithelial cells were isolated from mammary tissue using enzymatic digestion and immunomagnetic purification. Isolated cells were phenotypically characterized by immunohistochemistry and ultrastructural morphology. The purity of the separated alveolar and myoepithelial cells was assessed ultrastructurally and ranged from 91 to 96%. Messenger RNA and protein expression of PTHrP and the PTH/PTHrP receptor were examined using reverse transcription polymerase chain reaction, immunohistochemistry, and Western blot analysis, respectively. PTHrP mRNA and protein were expressed in alveolar epithelial cells and stromal fibroblasts, whereas PTH/PTHrP receptor mRNA and protein were expressed in all three cell types. The expression patterns for PTHrP and the PTH/PTHrP receptor support an autocrine or paracrine function for PTHrP in alveolar epithelial cells and stromal fibroblasts and a paracrine function for PTHrP in myoepithelial cells in the rat mammary gland during lactation.

Stromal cells are critical targets in the regulation of mammary ductal morphogenesis by parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) was originally identified as the tumor product responsible for humoral hypercalcemia of malignancy. It is now known that PTHrP is produced by many normal tissues in which it appears to play a role as a developmental regulatory molecule. PTHrP is a normal product of mammary epithelial cells, and recent experiments in our laboratory have demonstrated that overexpression or underexpression of PTHrP in the murine mammary gland leads to severe disruptions in its development. The nature of these phenotypes suggests that PTHrP acts to modulate branching growth during mammary development by regulating mammary stromal cell function. We now demonstrate that throughout mammary development, during periods of active ductal-branching morphogenesis, PTHrP is produced by epithelial cells, whereas the PTH/PTHrP receptor is expressed on stromal cells. In addition, we show that mammary stromal cells in culture contain specific binding sites for amino terminal PTHrP and respond with an increase in intracellular cAMP. Finally, we demonstrate that the mammary mesenchyme must express the PTH/PTHrP receptor in order to support mammary epithelial cell morphogenesis. These results demonstrate that PTHrP and the PTH/PTHrP receptor represent an epithelial/mesenchymal signaling circuit that is necessary for mammary morphogenesis and that stromal cells are a critical target for PTHrP's action in the mammary gland.

Reverse transcriptase/polymerase chain reaction analysis of parathyroid hormone-related protein for the detection of tumor cell dissemination in the peripheral blood and bone marrow of patients with breast cancer

Tumor cell dissemination in the bone marrow is an independent prognostic marker for relapse and survival for patients with primary breast cancer. Parathyroid-hormone-related protein (PTHrP) is expressed in most primary tumors and bone metastases of patients with breast cancer. PTHrP acts as an autocrine growth factor for breast cancer cells in vitro and there is evidence that it is especially important for osseous metastasis. For a sensitive detection of PTHrP-positive disseminated tumor cells a reverse transcriptase/polymerase chain reaction (RT/PCR) assay for PTHrP transcripts in the peripheral blood (PB) and in the bone marrow (BM) has been established. In mixing studies, the sensitivity of the reverse transcriptase/polymerase chain reaction (RT/PCR) for PTHrP was one tumor cell in 1 x 10(6) mononuclear cells. At this level of sensitivity, transcripts of PTHrP were detected in none of 30 PB samples and in 3 of 25 BM samples of healthy volunteers; there were also no transcripts of PTHrP in the PB and BM of 6 patients with benign breast lesions. The PB samples of 31 patients and the BM samples of 34 patients with predominantly early-stage breast cancer were tested for PTHrP expression along with immunocytology against cytokeratin 18 (CK18) as a standard immunological detection technique. PTHrP expression was shown in 9 of 31 patients in the PB and in 9 of 34 patients in the BM. In 30 patients, PB and BM samples were available simultaneously. There were cases of combined positive findings in the PB and the BM (4/30) and of isolated positivity in the PB (5/30) or in the BM (4/30). Compared to immunocytology, RT/PCR assay of PTHrP assay was significantly more sensitive in the peripheral blood (8/30 by RT/PCR compared to 1/30 by immunocytology). In the bone marrow there were cases of positivity for both markers (2/34), cases of isolated positivity by immunocytology for CK18 (3/34) and cases of isolated positivity for PTHrP transcripts (7/34). In conclusion the RT/PCR assay for PTHrP transcripts is a feasible and very sensitive technique for the detection of tumor cell dissemination in the PB, even in patients with early-stage breast cancer. The specificity of detection of PTHrP transcripts in the bone marrow is limited, possibly because of autochthonous expression of PTHrP in osteoblastic cells. The clinical follow-up of the subgroups of patients at risk, as defined by this assay, will show its prognostic significance for patients with breast cancer.

Expression of the receptor for parathyroid hormone-related protein in normal and malignant breast tissue

Parathyroid hormone-related protein (PTHrP) is the cause of humoral hypercalcaemia of malignancy and interacts with parathyroid hormone (PTH) receptors. Breast cancer cells produce PTHrP in vitro and in vivo. The breast cancer cell line MCF-7, which products PTHrP and expresses PTHrP receptors, proliferates in response to PTHrP. The aim of these studies was to determine the tissue location of PTHrP/PTH receptors (PTHrPR) in primary breast carcinomas and to establish whether they had the potential to respond to PTHrP. The cellular location of mRNA for the PTHrP/PTH receptor was identified using in situ hybridization in primary breast carcinomas and normal breast tissue. Immunohistochemistry for PTHrP was carried out on the same specimens. Tumours were assessed and scored by two observers using the product of intensity of signal and number of positive tumour cells (possible range 0-9). Tumours were also assessed for Ki-67 expression by counting positive nuclei. Non-malignant ductular epithelium expressed mRNA for the PTHrP receptor (mean score 2.6, range 1-4). Breast carcinomas (mean score 4.4, range 0-9) showed variable expression of PTHrP receptor mRNA: eight tumours were negative, 50 had scores similar to normal breast tissue, and 49 had higher scores for the receptor. Levels of expression of the receptor within the primary breast carcinomas were unrelated to immunohistochemical detection of PTHrP or to any standard prognostic factor. There was a significant (P = 0.05) relationship between Ki-67 and PTHrPR expression in individual tumours. The presence of PTHrP and its receptor in normal breast epithelium and breast carcinomas demonstrates that most breast tumours are able to respond to PTHrP. The Ki-67 data suggest that PTHrP is a potential autocrine growth factor in primary breast carcinoma.

Activity-dependent expression of parathyroid hormone-related protein (PTHrP) in rat cerebellar granule neurons. Requirement of PTHrP for the activity-dependent survival of granule neurons

To identify genes whose expression is neuronal activity-dependent, we used an mRNA differential display technique and discovered that parathyroid hormone-related protein (PTHrP) is expressed in an activity-dependent manner in primary cultures of rat cerebellar granule neurons. PTHrP mRNA was expressed as early as 1 h by the addition of KCl to a final concentration of 25 mM to the culture medium. This expression was induced by Ca2+ influx through voltage-dependent L-type Ca2+ channels and regulated at the transcriptional step. PTHrP mRNA was persistently expressed before and after the time of commitment of granule neurons to apoptosis when they are cultured in the presence of 25 mM KCl or both 150 microM N-methyl-D-aspartic acid and 15 mM KCl, both of which promote the survival of these neurons. PTHrP was rapidly secreted into the culture medium in a depolarization-dependent manner. Parathyroid hormone/PTHrP receptor mRNA was also expressed in the primary cultures, and its expression was up-regulated by KCl and/or N-methyl-D-aspartic acid. The addition of anti-PTHrP antiserum to the culture medium resulted in a reduction of the activity-dependent survival of the granule neurons. These results suggest that PTHrP is involved in an autocrine loop and required for the survival of granule neurons.

PTHrP and the PTH/PTHrP receptor are co-expressed in human breast and colon tumours

Using RNA extracted from human tumour samples removed during surgery, we have analysed expression of mRNA for parathyroid hormone-related protein (PTHrP) and for the PTH/PTHrP receptor by RT-PCR in a panel of human breast and colon tumours. All but 1 of 18 breast tumour samples expressed PTHrP, whereas receptor expression was detected in 11 of these. Expression of the PTH/PTHrP receptor was found in three out of four metastatic lesions, including one sample in which no receptor was detected in the primary tumour. PTHrP expression was also detected in five colon tumours, and receptor expression detected in two of these. These results demonstrate that PTHrP and the PTHrP receptor are also co-expressed in breast tumours in vivo and provide further evidence that PTHrP may be an important autocrine/paracrine growth factor in breast cancer.

Parathyroid hormone-related protein secretion is inhibited by oestradiol and stimulated by antioestrogens in KPL-3C human breast cancer cells

We recently established a human breast cancer cell line, KPL-3C, from a breast cancer patient with humoral hypercalcaemia. This cell line possesses oestrogen receptor (ER) and secretes parathyroid hormone-related protein (PTHrP) into medium. To investigate the effects of oestrogen and antioestrogens on PTHrP secretion, KPL-3C cells were cultured for 48 h in an oestrogen-eliminated medium with 17beta-oestradiol (E2), tamoxifen (TAM) and/or a pure antioestrogen, ICI182,780 (ICI), and PTHrP secretion was measured using an immunoradiometric assay. The effects of these agents on cell cycle progression were also studied using flow cytometry. E2 (1-100 nM) significantly inhibited PTHrP secretion, whereas both TAM (0.1-10 microM) and ICI (1-100 nM) significantly stimulated it. These effects were completely blocked by the simultaneous addition of 1 nM E2 to the medium. At the same time, E2 significantly increased the percentage of cells during the S and G2/M phases, whereas both antioestrogens significantly increased the percentage of cells during the G0/G1 phase. Again, these cytostatic effects were completely reversed by the addition of E2. These findings indicate that antioestrogens inhibit the growth of ER-positive breast cancer cells but may stimulate PTHrP secretion and that these effects may be mediated by ER.

Extracellular nucleotides stimulate proliferation in MCF-7 breast cancer cells via P2-purinoceptors

Nucleotides such as ATP can act as extracellular effector molecules by interaction with specific cellular receptors known as P2-purinoceptors. Recently, we cloned the human P2U purinoceptor from osteoclastoma and demonstrated its expression in skeletal tissues. In the current study we have investigated the expression of P2U purinoceptors in human breast tumour cell lines and examined functional effects of extracellular nucleotides on these cells. By reverse transcription-linked polymerase chain reaction (RT-PCR) the expression of mRNA for P2U purinoceptors was demonstrated in four human breast cancer cell lines, Hs578T, MCF-7, SK-Br3 and T47-D. In MCF-7 cells, extracellular ATP (1-100 microM) elevated intracellular free calcium concentration [Ca2+]i, indicating that these cells express functional P2-purinoceptors. UTP elevated [Ca2+]i in an identical manner to ATP, whereas 2-methylthioATP was completely ineffective, and ADP only partially effective. This pharmacological profile suggests that the P2U subtype may be the only P2-purinoceptor expressed by these cells. The functional significance of P2U purinoceptor expression by MCF-7 cells was investigated by analysing the effects of extracellular ATP on cell proliferation. The slowly hydrolysed analogue of ATP, ATPgammaS (which was also shown to elevate [Ca2+]i), induced proliferation of MCF-7 cells when added daily to serum-free cultures over a period of 3 days. ATPgammaS-induced proliferation was demonstrated by three separate methods, detection by scintillation counting of [3H]thymidine incorporation, immunocytochemical detection of 5-bromo-2-deoxyuridine incorporation and direct counting of cell numbers. These data suggest that ATP, possibly released at sites of tissue injury or inflammation, may be capable of growth factor action in promotion of tumour proliferation or progression.

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

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