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

From Good to Bad: The Opposing Effects of PTHrP on Tumor Growth, Dormancy, and Metastasis Throughout Cancer Progression

Parathyroid hormone related protein (PTHrP) is a multifaceted protein with several biologically active domains that regulate its many roles in normal physiology and human disease. PTHrP causes humoral hypercalcemia of malignancy (HHM) through its endocrine actions and tumor-induced bone destruction through its paracrine actions. PTHrP has more recently been investigated as a regulator of tumor dormancy owing to its roles in regulating tumor cell proliferation, apoptosis, and survival through autocrine/paracrine and intracrine signaling. Tumor expression of PTHrP in late stages of cancer progression has been shown to promote distant metastasis formation, especially in bone by promoting tumor-induced osteolysis and exit from dormancy. In contrast, PTHrP may protect against further tumor progression and improve patient survival in early disease stages. This review highlights current knowledge from preclinical and clinical studies examining the role of PTHrP in promoting tumor progression as well as skeletal and soft tissue metastasis, especially with regards to the protein as a regulator of tumor dormancy. The discussion will also provide perspectives on PTHrP as a prognostic factor and therapeutic target to inhibit tumor progression, prevent tumor recurrence, and improve patient survival.

Extensive calcification in adenocarcinoma of the lung: A case report

Calcification in lung nodules usually indicates a benign lesion. Here, we report the case of a 59‐year‐old male patient with a well defined 30 mm calcified nodule in his right upper lung lobe and calcified mediastinal lymph nodes. The mass was diagnosed as adenocarcinoma by transbronchial biopsy. He received systemic chemotherapy, followed by lobectomy and mediastinal lymph node dissection. During surgery, the lymph nodes were tightly adherent to the superior vena cava with invasion of the vascular wall. Pathological diagnosis confirmed acinar adenocarcinoma and psammoma bodies (PBs). Immunohistochemical analysis revealed tumor cells positive for parathyroid hormone‐related proteins 1 and 2. Calcification of primary lung adenocarcinoma is rare. We report a calcified lesion where the secretion of parathyroid hormone by the tumor may have caused the accumulation of PBs. Calcification of metastatic lymph nodes may increase the risk of adhesion, requiring care during surgery.

Key points

Significant findings of the study

Lung adenocarcinoma with extensive calcification in primary and metastatic lymph node lesions is rare and the mechanism involved is poorly understood. Of significance, calcification in our case was related to parathyroid hormone‐related proteins 1 and 2 secreted by the tumor.

What this study adds

This study suggests the potential role of parathyroid hormone‐related proteins in lung tumor calcification. The implications for clinicians are that calcified metastatic lymph nodes and tumors might be tightly fused to tissues. Therefore, surgery should be conducted with care.

β-Alanine mediated inhibition of PTHR1suppresses the proliferation, invasion and tumorigenesis in metastatic human osteosarcoma U2OS cells

The present study was aimed to investigate the effect of β-alanine mediated inhibition of parathyroid hormone 1 receptor (PTHR1), suppresses the proliferation, invasion, and tumorigenesis in metastatic human osteosarcoma U2OS cells. Cell survival rate was reduced 96.54, 91.23, 84.62, 76.42 and 69.72% following incubation of β-alanine at 50-250 mM respectively. Annexin-V/propidium iodide (PI) staining showed a reduced level of viable cells (71.37%) at 250 mM of β-alanine. U2OS cell proliferation, adhesion, invasion, and migration were decreased following incubation with β-alanine. Matrix metalloproteinases-2/9 (MMP-2/9) mRNA expression was reduced, whereas tissue inhibitors of metalloproteinases-1/2 (TIMP-1/2) mRNA expression was increased remarkably. The mRNA and protein of PTHR1 were reduced in the cells following incubation with β-alanine. Vacuole membrane protein 1 (Vmp1) mRNA and protein were increased in the cells following incubation with β-alanine. In tunel assay, the number of PTHR1 positive cells was 67, 34 and 17 following incubation with β-alanine at 150, 200 and 250 mM respectively. Taking all these data together, it is concluded that β-alanine mediated inhibition of PTHR1 reduced the U2OS cell proliferation, invasion, migration, and tumorigenesis. Furthermore, the results indicated that the β-alanine induced expression of PTHR1 has a positive relationship with invasion and metastasis of osteosarcoma cells.

Molecular mechanisms associated with PTHrP-induced proliferation of colon cancer cells

Parathyroid Hormone-related Protein (PTHrP) is normally produced in many tissues and is recognized for its endocrine, paracrine, autocrine and intracrine modes of action. PTHrP is also implicated in different types of cancer and its expression correlates with the severity of colon carcinoma. Using the human colon cell line Caco-2 we recently obtained evidence that PTHrP, through a paracrine pathway, exerts a protective effect under apoptotic conditions. However, if exogenous PTHrP is able or not to induce the proliferation of these intestinal tumor cells is not known. We found that PTHrP treatment increases the number of live Caco-2 cells. The hormone induces the phosphorylation and nuclear translocation of ERK 1/2, α p38 MAPK, and Akt, without affecting JNK phosphorylation. In addition, PTHrP-dependent ERK phosphorylation is reverted when PI3K activity was inhibited. Following MAPKs nuclear translocation, the transcription factors ATF-1 and CREB were activated in a biphasic manner. In addition PTHrP induces the translocation into the nucleus of β-catenin, protein that plays key role in maintaining the growth and proliferation of colorectal cancer, and increases the amount of both positive cell cycle regulators c-Myc and Cyclin D. Studies with ERK1/2, α p38 MAPK, and PI3K specific inhibitors showed that PTHrP regulates Caco-2 cell proliferation via these signaling pathways. In conclusion, the results obtained in this work expand our knowledge on the role of exogenous PTHrP in intestinal tumor cells and identify the signaling pathways that are involved in the mitogenic effect of the hormone on Caco-2 cells.

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.

Prognostic implications of parathyroid hormone-related protein in males and females with non--small-cell lung cancer

BACKGROUND

Non-small-cell lung carcinoma immunoreactivity for parathyroid hormone-related protein has been associated with increased survival in female patients but not in male patients. The current investigation attempted to substantiate this finding in 2 new patient groups.

METHODS

Patients were divided into groups with and without immunoreactivity for a carboxyl-terminal parathyroid hormone-related protein epitope assessed in deparaffinized sections by a blinded observer. One group included 85 female patients with stage I lung cancer, and the second group had 48 female and 66 male patients with stage I-IV lung cancer. Survival times were compared by the log-rank test between groups separated by tumor parathyroid hormone-related protein status.

RESULTS

Parathyroid hormone-related protein was present in 70%-80% of the patients, independent of sex, stage, and smoking history. In the females with stage I lung cancer, parathyroid hormone-related protein increased median survival from 25 to 60 months (P < .05). In the second group, parathyroid hormone-related protein expression increased 48-month disease-free survival of female lung cancer patients from 44% to 63% (P < .05), but had no effect in male patients. Parathyroid hormone-related protein remained a significant, independent predictor when evaluated together with other covariates by Cox multivariate regression.

CONCLUSION

This study verifies that parathyroid hormone-related protein is a sex-dependent survival factor for non-small-cell lung carcinoma, that it correlates with disease-free survival, and that the association with survival holds for women with early-stage disease as well as more advanced cancer. Thus, the protein could find use as a prognostic indicator and could be a target for therapy.

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

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

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.

Cell cycle actions of parathyroid hormone-related protein in non-small cell lung carcinoma

Parathyroid hormone-related protein (PTHrP), a paraneoplastic protein expressed by two-thirds of human non-small cell lung cancers, has been reported to slow progression of lung carcinomas in mouse models and to lengthen survival of patients with lung cancer. This study investigated the effects of ectopic expression of PTHrP on proliferation and cell cycle progression of two human lung adenocarcinoma cell lines that are normally PTHrP negative. Stable transfection with PTHrP decreased H1944 cell DNA synthesis, measured by thymidine incorporation, bromodeoxyuridine uptake, and MTT proliferation assay. A substantial fraction of PTHrP-positive cells was arrested in or slowly progressing through G1. Cyclin D2 and cyclin A2 protein levels were 60-70% lower in PTHrP-expressing cells compared with control cells (P < 0.05, N = 3 independent clones per group), while expression of p27(Kip1), a cyclin-dependent kinase inhibitor, was increased by 35 +/- 9% (mean +/- SE, P < 0.05) in the presence of PTHrP. Expression of other cyclins, including cyclins D1 and D3, and cyclin-dependent kinases was unaffected by PTHrP. PTHrP did not alter the phosphorylation state of Rb, but decreased cyclin-dependent kinase (CDK) 2-cyclin A2 complex formation. Ectopic expression of PTHrP stimulated ERK phosphorylation. In MV522 cells, PTHrP had similar effects on DNA synthesis, cyclin A2 expression, pRb levels, CDK2-cyclin A2 association, and ERK activation. In summary, PTHrP appears to slow progression of lung cancer cells into S phase, possibly by decreasing activation of CDK2. Slower cancer cell proliferation could contribute to slower tumor progression and increased survival of patients with PTHrP-positive lung cancer.

Parathyroid hormone-related protein varies with sex and androgen status in nonsmall cell lung cancer

BACKGROUND

In nonsmall cell lung cancer, tumor parathyroid hormone-related protein (PTHrP) expression predicts longer survival in women but not in men. To explain the sex-dependent survival effect, the authors proposed that hormonal influences decrease PTHrP in men versus women, that PTHrP inhibits tumor growth, and that the effect is greater in women than in men. The objectives of this study were to compare lung carcinoma PTHrP expression and carcinoma growth in male and female mice and to determine whether gonadal steroids regulate PTHrP in lung cancer cells.

METHODS

Tumor PTHrP content was measured by immunoassay, and tumor burden was assessed with multiple measures in BEN squamous cell orthotopic lung carcinomas in athymic mice. In addition, lung adenocarcinoma PTHrP messenger RNA (mRNA) values determined by microarray analyses were compared between men and women. Cultured lung cancer cells were assayed for PTHrP after treatment with estradiol or R1881, a synthetic androgen.

RESULTS

Lung carcinomas contained approximately 3 times more PTHrP in female mice than in male mice. Similarly, levels of PTHrP mRNA were significantly greater in adenocarcinomas from patients who were women than from patients who were men. Male mice had greater tumor burden than female mice. Androgen treatment reduced PTHrP in 3 lung cancer lines. Estradiol had no effect. Testosterone treatment also reduced lung carcinoma PTHrP in female mice.

CONCLUSIONS

Lung carcinomas in females expressed more PTHrP than in males possibly because of negative regulation by androgens in males. Female mice with higher tumor PTHrP content had significantly less tumor burden than male mice, supporting the hypothesis that PTHrP inhibits tumor growth.

Human parathyroid hormone-related protein and human parathyroid hormone receptor type 1 are expressed in human medulloblastomas and regulate cell proliferation and apoptosis in medulloblastoma-derived cell lines

Human parathyroid hormone-related protein (hPTHrP), identified in patients with paraneoplastic hypercalcemia and expressed by different cell types during development and adult life, plays important roles in many human neoplasms. Immunohistochemical and RT-PCR analyses of hPTHrP and human parathyroid hormone receptor type 1 (PTHR-1) in primary medulloblastoma confirmed their expression in both classic and desmoplastic variants at RNA and protein levels. To evaluate the functional role of hPTHrP, DAOY and D283 medulloblastoma and U87MG glioma cells, expressing high levels of hPTHrP and PTHR-1, were treated with anti-sense oligonucleotides for hPTHrP. Anti-sense treatment produced in all cell lines a decrease of cell proliferation and clonogenic activity and an increase of apoptosis, while addition of exogenous hPTHrP (1-37) prevented these effects. Anti-sense induced the increase of Caspase-3, Fas (CD95) mRNAs and Bax/Bcl-2 mRNA ratio after 12 h of cell treatment. Exogenous hPTHrP (1-37) increased intracellular Ca(2+) concentration in DAOY cells as revealed by FURA. Anti-sense treated cells showed a significant decrease of steady-state levels of intracellular Ca(2+), which was reverted by addition of exogenous hPTHrP (1-37). This study indicates that hPTHrP and PTHR-1 are expressed in medulloblastoma and could promote tumor growth, protecting cells from apoptosis.

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 in human renal cell carcinoma

Parathyroid hormone-related protein (PTHrP), a polyprotein discovered in 1987, plays crucial roles not only in development and in various physiological events associated with normal life, but also in a number of pathological conditions such as cancer. PTHrP appears as the major causative agent in humoral hypercalcemia of malignancy (HHM) associated to a broad range of tumors. However, this is only one aspect of the multiple facets of PTHrP in cancer biology. Indeed, the complex growth factor-like properties of PTHrP has shed new light onto potential roles of this peptide in the regulation of tumor growth and invasion. Initial studies in breast, prostate and lung cancer and recent results in renal cell carcinoma (RCC) suggest such roles and highlight the therapeutic potential of PTHrP-targeting strategies in human cancer including RCC. In this review, the role of PTHrP in RCC tumorigenesis and its potential as a therapeutic target will be discussed.

Antitumor effect of parathyroid hormone-related protein neutralizing antibody in human renal cell carcinoma in vitro and in vivo

Functional inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene occurs in 40-80% of human conventional renal cell carcinomas (RCCs). We showed recently that VHL-deficient RCCs expressed large amounts of parathyroid hormone-related protein (PTHrP), and that PTHrP, acting through the PTH1 receptor (PTH1R), plays an essential role in tumor growth. We also showed that PTHrP expression is negatively regulated by the VHL gene products (pVHL). Our goal was to determine whether blocking the PTHrP/PTH1R system might be of therapeutic value against RCC, independent of VHL status and PTHrP expression levels. The antitumor activity of PTHrP neutralizing antibody and of PTH1R antagonist were evaluated in vitro and in vivo in a panel of human RCC lines expressing or not pVHL. PTHrP is upregulated compared with normal tubular cells. In vitro, tumor cell growth and viability was decreased by up to 80% by the antibody in all cell lines. These effects resulted from apoptosis. Exogenously added PTHrP had no effect on cell growth and viability, but reversed the inhibitory effects of the antibody. The growth inhibition was reproduced by a specific PTH1R antagonist in all cell lines. In vivo, the treatment of nude mice bearing the Caki-1 RCC tumor with the PTHrP antibody inhibited tumor growth by 80%, by inducing apoptosis. Proliferation and neovascularization were not affected by the antiserum. Anti-PTHrP treatment induced no side effects as assessed by animal weight and blood chemistries. Current therapeutic strategies are only marginally effective against metastatic RCC, and adverse effects are common. This study provides a rationale for evaluating the blockade of PTHrP signaling as therapy for human RCC in a clinical setting.

Advantages of multi-color fluorescent proteins for whole-body and in vivo cellular imaging

The revolution of in vivo cancer biology enabled by fluorescent proteins is described. The high extinction coefficients, quantum yields, and unique spectral properties of fluorescent proteins have been taken advantage of in order to visualize, in real time, the important aspects of cancer in living animals, including tumor cell trafficking, invasion, metastasis, and angiogenesis. Fluorescent proteins enable whole-body imaging of tumors on internal organs. These multicolored proteins have allowed the color-coding of cancer cells growing in vivo with distinction of different cell types, including host from tumor, with single-cell resolution.

GSK3 and PKB/Akt are associated with integrin-mediated regulation of PTHrP, IL-6 and IL-8 expression in FG pancreatic cancer cells

We have demonstrated recently that PTHrP is upregulated in pancreatic adenocarcinoma and that the ECM exerts regulatory control, at least in part, over PTHrP expression. In our present study, we examined the potential signaling interactions between these 2 pathways. Our results demonstrate that, under serum-free conditions, adhesion of FG pancreatic adenocarcinoma cells on Fn is mediated by the alpha5beta1 integrin, whereas adhesion to Type I collagen is mediated by the alpha2beta1 integrin. alpha5beta1 integrin-mediated adhesion to Fn results in a phenotype that includes a reduction in cell proliferation, increased E-cadherin localization in cell-cell contacts, increased beta-catenin localization throughout the cell, inhibition of haptokinetic cell migration, and increased expression of PTHrP, IL-6 and IL-8 relative to alpha2beta1 integrin-mediated adhesion on Type I collagen. A phosphoprotein immunoblotting screen of FG pancreatic cancer cells grown on either Fn or Type I collagen indicates that GSK3 and PKB/Akt are differentially phosphorylated on these 2 substrates. These results implicate GSK3 and PKB/Akt in the integrin-mediated regulation of PTHrP, IL-6 and IL-8 in pancreatic cancer.

Establishment of green fluorescent protein-expressing hepatocellular carcinoma cell lines with different metastatic potential: relevant models for in vivo monitoring of metastasis and angiogenesis

PURPOSE

To establish stable green fluorescent protein (GFP)-expressing metastatic human hepatocellular carcinoma (HCC) cell lines with different metastatic potential for long-term in vivo studies of metastasis and angiogenesis.

METHODS

The pIRES2-EGFP vector, which contains an enhanced GFP gene, was transfected into MHCC97-H and MHCC97-L, HCC cell lines with different metastatic potential. The stability of GFP expression, basic biological characteristics, invasion abilities in vitro, and spontaneous metastasis in vivo of the new cell lines (MHCC97-HG and MHCC97-LG) were studied. Microvessel density (MVD) of orthotopic implanted tumors was compared by anti-CD31 immunohistochemical staining, and real-time angiogenesis and metastasis of GFP-transfected tumors were detected by intravital fluorescent microscope.

RESULTS

The GFP-transfected cell lines stably expressed green fluorescence in the absence of G418 over a 36-day period. Compared with the parental cell lines, they exhibited no distinct differences in biological characteristics. MHCC97-HG showed more aggressive invasion and spontaneous metastatic behavior than MHCC97-LG, and even its parental cell line, MHCC97-H (P<0.01). MVD levels induced by MHCC97-HG orthotopic implanted tumors were significantly higher than MHCC97-LG (P<0.01). Real-time angiogenesis and sequential steps of metastasis could be detected clearly under intravital fluorescent microscope.

CONCLUSIONS

These two stable GFP-expressing HCC cell lines with the same genetic background and different metastatic potential were established, which could be useful models for monitoring metastasis and angiogenesis of HCC.

In vivo cell biology of cancer cells visualized with fluorescent proteins

This chapter describes a new cell biology where the behavior of individual cells can be visualized in the living animal. Previously it has been demonstrated that fluorescent proteins can be used for whole-body imaging of metastatic tumor growth, bacterial infection, and gene expression. An example of the new cell biology is dual-color fluorescence imaging using red fluorescent protein (RFP)-expressing tumors transplanted in green fluorescent protein (GFP)-expressing transgenic mice. These models show with great clarity the details of tumor-stroma interactions and especially tumor-induced angiogenesis, tumor-infiltrating lymphocytes, stromal fibroblasts, and macrophages. Another example is the color coding of cells with RFP or GFP such that both cell types can be simultaneously visualized in vivo. Stem cells can also be visualized and tracked in vivo. Mice in which the regulatory elements of the stem cell marker nestin drive GFP expression enable nascent vasculature to be visualized interacting with transplanted RFP-expressing cancer cells. Nestin-driven GFP expression can also be used to visualize hair follicle stem cells. Dual-color cells expressing GFP in the nucleus and RFP in the cytoplasm enable real-time visualization of nuclear-cytoplasm dynamics including cell cycle events and apoptosis. Highly elongated cancer cells in capillaries in living mice were observed within skin flaps. The migration velocities of the cancer cells in the capillaries were measured by capturing images of the dual-color fluorescent cells over time. The cells in the capillaries elongated to fit the width of these vessels. The use of the dual-color cancer cells differentially labeled in the cytoplasm and nucleus and associated fluorescent imaging provide a powerful tool to understand the mechanism of cancer cell migration and deformation in small vessels.

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.

Parathyroid hormone-related protein is an essential growth factor for human clear cell renal carcinoma and a target for the von Hippel-Lindau tumor suppressor gene

Clear cell renal carcinoma (CCRC) is responsible for 2% of cancer-related deaths worldwide and is resistant to virtually all therapies, indicating the importance of a search for new therapeutic targets. Parathyroid hormone-related protein (PTHrP) is a polyprotein derived from normal and malignant cells that regulates cell growth. In the current study, we show that blocking PTHrP with antibodies or antagonizing the common parathyroid hormone (PTH)/PTHrP receptor, the PTH1 receptor, dramatically blunts the expansion of human CCRC in vitro by promoting cell death. Importantly, in nude mice, anti-PTHrP antibodies induced complete regression of 70% of the implanted tumors by inducing cell death. In addition, we demonstrate that the von Hippel-Lindau tumor suppressor protein, which functions as a gatekeeper for CCRC, negatively regulates PTHrP expression at the post-transcriptional level. These studies indicate that PTHrP is an essential growth factor for CCRC and is a novel target for the von Hippel-Lindau tumor suppressor protein. Taken together, these results strongly suggest that targeting the PTHrP/PTH1 receptor system may provide a new avenue for the treatment of this aggressive cancer in humans.

Amino-terminal and midmolecule parathyroid hormone-related protein, phosphatidylcholine, and type II cell proliferation in silica-injured lung

Acute silica lung injury is marked by alveolar phospholipidosis and type II cell proliferation. Parathyroid hormone-related protein (PTHrP) 1-34 could have a regulatory role in this process because it stimulates phosphatidylcholine secretion and inhibits type II cell growth. Other regions of the PTHrP molecule may have biological activity and can also exert pulmonary effects. This study examined the temporal pattern for expression of several regions of PTHrP after silica lung injury and evaluated the effects of changes in expression on cell proliferation and lung phospholipids. Expression of all PTHrP regions fell at 4 days after injury. Reversing the decline in PTHrP 1-34 or PTHrP 67-86 with one intratracheal dose and four daily subcutaneous doses of PTHrP 1-34 or PTHrP 67-86 stimulated bronchoalveolar lavage disaturated phosphatidylcholine (DSPC) levels. Cell culture studies indicate that the peptides exerted direct effects on DSPC secretion by type II cells. Neither peptide affected type II cell proliferation with this dosing regimen, but addition of an additional intratracheal dose resulted in significant inhibition of growth, consistent with previous effects of PTHrP 1-34 in hyperoxic lung injury. These studies establish a regulatory role for PTHrP 1-34 and PTHrP 67-86 in DSPC metabolism and type II cell proliferation in silica injury. Growth inhibitory effects of PTHrP could interact with phospholipid stimulation by affecting type II cell numbers. Further studies are needed to explore the complex interactions of PTHrP-derived peptides and the type II cell response at various stages of silica lung injury.

The parathyroid hormone-related protein system: more data but more unsolved questions

PURPOSE OF REVIEW

The present review focuses on recent studies that might be considered as the most relevant advances in the parathyroid hormone-related protein field, with special emphasis on proven functions in renovascular and cardiovascular systems, in physiological as well as pathological conditions. Thus, the questions as to whether and how parathyroid hormone-related protein intervenes in vascular development and homeostasis and in vascular diseases such as hypertension, atherosclerosis, restenosis and heart failure have begun to be unraveled.

RECENT FINDINGS

Since its discovery from hypercalcemia-associated tumors in 1987, it has become clear that parathyroid hormone-related protein is a ubiquitously expressed poly-hormone and plays crucial roles in normal life. The early lethality to parathyroid hormone-related protein knockout mice emphasizes the crucial roles of the protein in development but has limited the use of these models. However, data accumulated from transgenic animals overexpressing the protein in particular cells have provided considerable support to its physiological and pathological relevance. The recent demonstration that nascent parathyroid hormone-related protein not only follows the secretory pathways, but also directly translocates to the nucleus, is beginning to uncover new actions for the protein in a number of physiological systems such as bone, mammary gland and vascular smooth muscle, as well as in pathological situations, such as cancer, osteoporosis, sepsis, atherosclerosis and hypertension.

SUMMARY

The development of mice with conditionally deleted parathyroid hormone-related protein or parathyroid hormone-1 receptor alleles will allow the creation of cell- or tissue-specific parathyroid hormone-related protein knockout mice which will greatly facilitate the determination of the biological relevance of this protein in a specific cell or tissue type, particularly in the cardiovascular system.

Green fluorescent protein imaging of tumour growth, metastasis, and angiogenesis in mouse models

We have developed a way of imaging metastases in mice by use of tumour cells expressing green fluorescent protein (GFP) that can be used to examine fresh tissue, both in situ and externally. These mice present many new possibilities for research including real-time studies of tumour progression, metastasis, and drug-response evaluations. We have now also introduced the GFP gene, cloned from bioluminescent organisms, into a series of human and rodent cancer-cell lines in vitro, which stably express GFP after transplantation to rodents with metastatic cancer. Techniques were also developed for transduction of tumours by GFP in vivo. With this fluorescent tool, single cells from tumours and metastases can be imaged. GFP-expressing tumours of the colon, prostate, breast, brain, liver, lymph nodes, lung, pancreas, bone, and other organs have also been visualised externally by use of quantitative transcutaneous whole-body fluorescence imaging. GFP technology has also been used for real-time imaging and quantification of angiogenesis.