Immunoassay and immunohistology studies of chromogranin A as a neuroendocrine marker in patients with carcinoma of the prostate

OBJECTIVES

Neuroendocrine differentiation in carcinoma of the prostate is characterized by the expression of neuroendocrine cell products such as chromogranin A (CgA). We studied serum levels and tissue staining for CgA in prostate cancer to assess their clinical value.

METHODS

In 82 patients with prostate cancer, serum specimens were obtained at diagnosis and studied by both CgA and prostate-specific antigen (PSA) immunoassays. In 43 additional patients with prostate cancer, paraffin-embedded tissue from core biopsies or transurethral resections and serum samples were studied, respectively, by immunohistology and immunoassay for CgA.

RESULTS

In serum samples from the 82 patients in whom CgA and PSA levels were measured, 26 of 82 (32%) had an elevated CgA (greater than 200 ng/mL), and 36 of 82 (44%) had an elevated PSA (greater than 4.0 ng/mL). Of the patients with Stage D2 cancer, 11 of 18 (61%) had an elevated CgA and 6 of 18 (33%) had an elevated PSA. Four of 5 patients with local recurrence had an elevated CgA, but only 1 patient had an elevated PSA. Of the 43 patients in whom serum and tissue CgA studies were performed, 12 (28%) had elevated serum CgA, and 15 of the 43 (35%) had CgA staining in their prostate tissue. Of the 14 of these patients with D2 disease (distant metastases), 9 (64%) had elevated serum levels of CgA and 6 (43%) had positive staining in their prostate tissue. Of the 9 patients with Stage D2 disease and elevated serum CgA, 6 had a normal serum PSA.

CONCLUSIONS

Our studies complement those of others and indicate that CgA has potential as a clinically useful serum and tumor marker for prostate cancer. Serum CgA measurements can identify some patients with advanced disease who do not have elevated serum PSA. However, further studies in larger groups of patients are needed to define the clinical value of CgA as a marker for prostate cancer.

Parathyroid hormone--related protein (PTHrP) is an epidermal growth factor-regulated secretory product of human prostatic epithelial cells

Parathyroid hormone-related protein (PTHrP) has previously been shown to be expressed in human prostatic tissue and in prostatic cancer cell lines. In the present study, PTHrP immunoreactivity was detected in the glandular epithelium of normal prostate and benign prostatic hyperplasia (BPH), as well as in prostatic adenocarcinoma (CaP). Epithelial cell cultures derived from normal, BPH, and CaP tissues were also stained by antibodies against PTHrP, and northern analysis revealed multiple transcripts of PTHrP in the cellular RNA. PTHrP (1-34) was measurable by radioimmunoassay (RIA) in media conditioned by the prostatic epithelial cell cultures, and PTHrP accumulated in conditioned media during a 72 hr time course. Addition of complete growth medium to starved cells resulted in increased PTHrP mRNA levels by 1 hr, with maximal stimulation at 8-24 hr. Several individual factors contained in the complete growth medium were tested for their ability to regulate PTHrP expression. Epidermal growth factor (EGF) was the major inducer of PTHrP expression, while cholera toxin, bovine pituitary extract, hydrocortisone, and insulin had minimal or no effect on PTHrP transcript levels. Since each of these factors is growth stimulatory, the unique ability of EGF to induce PTHrP is apparently unrelated to mitogenicity. 1,25-Dihydroxyvitamin D3[1,25(OH)2D3], an inhibitor of PTHrP expression in several other cell types, had no effect on steady-state levels of PTHrP mRNA expressed by epithelial cells in complete growth medium, although prostate cells have vitamin D receptors and are responsive to 1,25(OH)2D3 in other ways. Our results indicate that PTHrP expression is not confined to the neuroendocrine cells of the human prostate and that our culture system can be used as a model to investigate the role of PTHrP in the prostate.

Elimination of the carboxy-terminal sequences of parathyroid hormone-related protein 1-173 increases production and secretion of the truncated forms

The endoproteolytic processing of polypeptides at basic residues into distinct biologically active peptides is a common theme in prohormone maturation and processing. PTH-related protein (PTHrP) 1-173 contains eight putative endoproteolytic consensus sites that include a mono-arginyl (R37), paired basic (RR154-155), and related basic residue motifs (RLKR-4 to -1, RRR19-21, KKKK88-91, KRK96-98, KKKRR102-106, and KKKK147-150). To analyze the primary structural determinants involved in the posttranslational processing and secretion of PTHrP 1-173, we constructed a series of nonsense mutants that code for carboxy-terminal truncated polypeptides. Since the basic residue motifs are probable sites of endoproteolysis, these sites and the residues downstream were serially eliminated, thereby creating PTHrP 1-152, 1-146, 1-101, 1-95, 1-87, 1-36, and 1-18. The wild type PTHrP 1-173 and nonsense mutant constructs were transiently transfected into two cell lines, COS-1 and SK-N-BE(2). The COS-1 cells have a constitutive secretory pathway, whereas the neuroblastoma-derived BE-2 cells have, in addition, a regulated secretory pathway. PTHrP was measured in the conditioned media and cell extracts of the transfected cells with two peptide-specific RIAs. In COS-1 cells, PTHrP truncation mutants 1-152, 1-146, 1-101, 1-95, and 1-87 were present relative to wild type isoform 1-173, at 4.4-, 3-, 19-, 12-, and 57-fold excess, respectively; a similar pattern was also detected with BE-2 transfected cells, although the relative increases above the quantities of PTHrP 1-173 were not as dramatic. As the carboxy-terminal sequences were eliminated, the amount of total and secreted PTHrP increased, and the percentage found within the cell decreased. In COS-1 cells, 10.5% of the total PTHrP 1-173 was intracellular, whereas only 1% of the total PTHrP 1-87 was intracellular. In BE-2 cells, 54% of the total PTHrP 1-173 and only 9% of the total 1-87 mutant were intracellular. In COS-1 cells, a time course analysis demonstrated that PTHrP 1-87 and 1-95 were detectable in media 3 h after transfection, whereas 1-173 was barely detectable after 24 h. Our studies suggest that the carboxy-terminal sequence of PTHrP 1-173 is responsible for the intracellular degradation of this polypeptide, which may be the endogenous cellular mechanism that regulates the amount of processed and secreted PTHrP.

The humoral hypercalcemia of benignancy. A newly appreciated syndrome

It has become recently appreciated that the hypercalcemia of malignancy is commonly caused by the increased production of parathyroid hormone-related protein (PTHrP) by the cancer. In fact, the demonstration of increased PTHrP production in a patient with hypercalcemia is regarded as pathognomonic of malignancy. The authors describe a patient with a benign ovarian lesion that produced PTHrP and caused hypercalcemia. They identify other reports of hypercalcemia associated with hypercalcemia and benign tumors, and refer to this syndrome as the humoral hypercalcemia of benignancy. Although apparently rare, a benign PTHrP-producing tumor should be considered in the differential diagnosis of hypercalcemia.

Parathyroid hormone-related protein, an autocrine regulatory factor in alveolar epithelial cells

Alveolar epithelial cells in vivo, primary cultures of adult rat type II cells, and human A549 alveolar carcinoma cells express parathyroid hormone-related protein (PTHrP). Here we demonstrated that type II cells and A549 cells also express the PTHrP receptor and that they exhibit differentiation-related responses to the amino-terminal PTHrP fragment, PTHrP-(1-34). PTHrP receptor expression in A549 cells was shown by detection of a 0.3-kb reverse transcriptase polymerase chain reaction product formed by primers specific for PTHrP receptor. In situ hybridization studies localized the site of production of PTHrP and PTHrP receptor mRNA in rat lung cells with morphology and location typical of type II cells. Primary cultures of such type II cells also expressed PTHrP receptor mRNA. Incubation with PTHrP-(1-34) stimulated disaturated phosphatidylcholine (DSPC) synthesis in A549 cells and increased the release of newly synthesized DSPC by cultured type II cells and A549 cells. In addition, PTHrP-(1-34) increased the number of lamellar bodies per type II cell and increased their expression of alkaline phosphatase in a dose-dependent manner. Thus PTHrP-(1-34) promoted a differentiated type II cell phenotype. Since cultured type II cells, alveolar epithelial cells in vivo, and A549 cells express PTHrP and the PTHrP receptor, PTHrP-(1-34) may be an autocrine regulatory factor in type II cells and lung cancer cells.

Calcitonin receptor mRNA expression in the human prostate

OBJECTIVES

A subpopulation of prostate neuroendocrine (NE) cells contain calcitonin (CT). It has been postulated that CT-producing cells in the prostate account for the high CT level in the semen, and may be involved in the regulation of other epithelial cells via a paracrine mechanism. The presence of CT binding sites in the plasma membrane fraction of prostate tissue has been demonstrated by radioligand binding assay. In the present study, we investigated the CT receptor gene expression in the human prostate, a key component of the autocrine/paracrine loop in the CT functional pathway.

METHODS

Reverse transcription polymerase chain reaction (RT-PCR) was carried out to evaluate the CT receptor mRNA expression in normal prostate tissue. Subsequent DNA sequencing was used to verify RT-PCR amplified products and to determine the isoform of the receptor. To define the location of the CT receptor expression, nonradioactive in situ hybridization was performed with a digoxigenin-labeled probe complementary to the coding region of the CT receptor mRNA. A polyclonal antibody against CT was used to reveal the CT-secreting cells in the prostate.

RESULTS

CT receptor MRNA expression was detected in the prostate tissue. Further analysis of the DNA sequence showed that CT receptor expressed in the prostate was the isoform without a 16-amino acid insert in the first intracellular domain. In situ hybridization revealed that CT receptor was present in the prostate NE cells. Immunocytochemical staining of mirror image sections showed that some CT-secreting cells also expressed CT receptor.

CONCLUSIONS

CT receptor expression in the prostate, a key component in the CT functional pathway, is located in subsets of dispersed NE cells (CT secreting and CT nonsecreting), which indicates that prostate CT may play an important role in the autocrine/paracrine regulation of the prostate NE system.

Expression of the nucleoside triphosphate pyrophosphohydrolase PC-1 is induced by basic fibroblast growth factor (bFGF) and modulated by activation of the protein kinase A and C pathways in osteoblast-like osteosarcoma cells

The closely related cytokines bFGF and aFGF regulate the function of bone cells and mineralization. Osteoblasts express PPi-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH)/nucleotide phosphodiesterase I activity. bFGF and aFGF (10 ng/ml) up-regulated NTPPPH in human SaOS-2 and U2OS osteosarcoma cells, which express osteoblast-like features in culture. The induction was selective as alkaline phosphatase activity was down-regulated and specific as insulin-like growth factor-1 (IGF-1) and interleukin-1 beta (IL-1 beta) were not active. Furthermore, IL-1 beta but not IGF-1 inhibited bFGF-induced up-regulation of NTPPPH. The induced NTPPPH remained predominantly associated with cells. bFGF can induce signaling through pathways including protein kinase A (PKA) and protein kinase C (PKC)-mediated transduction. An activator of the PKA pathway (8-bromo cyclic adenosine monophosphate [cAMP]) induced NTPPPH. Furthermore, pretreatment with the PKC activator phorbol myristate acetate (PMA) (80 nM) markedly increased subsequent NTPPPH induction by both bFGF and cAMP. The PMA effect was associated with morphologic changes characterized by long, thin intercellular extensions. PKC desensitization also potentially contributed to this effect because the PKC inhibitors staurosporine and H-7 enhanced bFGF-induced and cAMP-induced NTPPPH expression in the absence of morphologic changes. We observed that bFGF induced expression of PC-1, a member of the NTPPPH gene family. The majority of NTPPPH activity was depleted by immunoadsorption using a monoclonal antibody to native human PC-1. bFGF- and aFGF-induced production of PC-1/NTPPPH in osteoblastoid cells may contribute to the effects of FGFs on bone metabolism.

Identification and characterization of a neuroendocrine-specific 5'-regulatory region of the human chromogranin A gene

Chromogranin A (CgA) expression is specific to cells of endocrine and neuroendocrine (NE) tissues. Our transfection studies with CgA have identified two DNA regions 5' of the transcription start site that regulate CgA gene transcription: a distal regulatory region (DRR) located between -726 and -455, and a proximal regulatory region (PRR) between -60 and -26. In studies of the DRR using four human NE and six human non-NE cell lines, we demonstrated enhanced transcription of DRR-containing CgA-GH plasmids by the NE cells as a group compared to the non-NE cells. DNase I footprinting identified a protected area in the DRR from -570 to -555 base pairs (bp) composed of the sequence TAATGATGACTAAACA. Centered in this sequence is the simian virus 40 version of the activator protein-1-binding site, TGACTAA. Electrophoretic mobility shift assays (EMSAs) with an oligonucleotide containing the 27 bp of the DRR between -576 and -550, which we refer to as the distal regulatory element (DRE), produced a specific complex with the NE BEN and non-NE COS-1 cell nuclear extracts. The addition of c-Jun and c-Fos antibodies produced strong supershifts of the complex generated by COS-1 extract, but very weak supershifts of the complex formed by BEN extract. These EMSA studies suggest that NE cells such as BEN contain unique nuclear factors distinguishable from activator protein-1 that interact with the DRE. The enhancer effect of the 271-bp DRR could be replaced by the 27-bp DRE in both CgA and calcitonin promoter constructs in BEN cells. Replacement of the DRR with the DRE resulted in a further increase in expression from these plasmids, suggesting the presence of suppressor sequences in the DRR. In transfection studies of the PRR, deletion of its cAMP response element (CRE) dramatically lowered transcription. In addition to demonstrating that its CRE can bind CRE-binding protein, EMSAs with the PRR demonstrated that an intervening sequence between the CRE and the TATA box formed a complex with BEN cell nuclear extract. Our studies demonstrate that both the PRR and DRR are important for high level transcription of the CgA gene in NE cells. The presence of both distal and proximal 5'-regulatory regions in the human CgA gene indicates a complex mechanism of transcriptional regulation. Although the PRR is important for the formation of a functional transcription complex at the TATA region, the DRR is important for the enhancement of CgA gene expression in NE cells.

Parathyroid hormone-related protein expression in human gastric adenocarcinomas not associated with hypercalcemia

OBJECTIVE

Our evaluation of a patient with a parathyroid hormone-related protein (PTHrP)-producing gastric adenocarcinoma and hypercalcemia prompted us to study the expression of PTHrP in 13 additional patients with gastric cancer and in 10 control cases. Our objective was to investigate by immunohistology the expression of PTHrP in gastric cancer.

METHODS

Immunohistology studies were conducted with two murine monoclonal antibodies to synthetic peptides of human PTHrP, 9H7, and 8B12. The 9H7 antibody was raised to the carboxy-terminal amino acid fragment (109-141) of PTHrP, and the 8B12 antibody was raised to the amino-terminal amino acid fragment (1-34) of PTHrP.

RESULTS

Paraffin-embedded tumor specimens from 13 of 14 cases of gastric adenocarcinoma stained positively with the antibody to the carboxy terminus of the PTHrP peptide, but none stained positively with the antibody directed against the amino terminus. None of 10 control cases stained positively with either antibody. The staining was predominately evident in the cytoplasm of the tumor cells. Except for the sentinel case, none of the other patients with gastric adenocarcinoma had hypercalcemia. Thus, gastric adenocarcinoma seems to rarely result in systemic hypercalcemia.

CONCLUSIONS

Our studies demonstrated that abnormal PTHrP production can occur in malignant cells without producing hypercalcemia. PTHrP may play a role in the pathogenesis of gastric adenocarcinoma that is independent of its hypercalcemic effects. PTHrP measurements may be clinically valuable in patients with cancer who are not hypercalcemic.

Expression of parathyroid hormone-related peptide and its receptor messenger ribonucleic acid in human amnion and chorion-decidua: implications for secretion and function

OBJECTIVE

Our purpose was to define the location and packaging of parathyroid hormone-related peptide in amnion-chorion and the potential target tissues for its action in fetal membranes.

STUDY DESIGN

We studied fetal membranes by use of light microscopic immunocytochemistry with three monoclonal antibodies against distinct regions of the parathyroid hormone-related peptide molecule. For electron microscopy immunogold analysis with a monoclonal antibody specific to the 109-141 fragment was used to observe parathyroid hormone-related peptide intracellularly in amnion membrane and in the chorion layers. Multiplex reverse transcriptase-polymerase chain reaction with Southern blotting was used to identify parathyroid hormone/parathyroid hormone-related peptide receptor and control messenger ribonucleic acids in amnion and chorion-decidua.

RESULTS

All monoclonal antibodies revealed immunoreactive parathyroid hormone-related peptide in the amniotic epithelial cells and in some fibroblast-like cells embedded in the extracellular matrix of the amnion. Parathyroid hormone-related peptide was also found in the chorion in fibroblast and trophoblast layers and in decidua. Ultrastructurally immunogold particles were evenly distributed throughout the amniotic epithelial cells and were present in apical microvilli and near the basal membranes. Electron microscopy studies of the chorion cytotrophoblast also showed freely dispersed immunogold particles of parathyroid hormone-related peptide with no packaging in secretory granules. Low to undetectable levels of parathyroid hormone/parathyroid hormone-related peptide receptor messenger ribonucleic acid were found in amnion tissue, whereas abundant receptor messenger ribonucleic acid was found in chorion-decidua.

CONCLUSIONS

These results suggest the presence of a parathyroid hormone-related peptide paracrine system within the human fetal membranes.

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

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

Neoplastic hormone-producing cells of the placenta produce and secrete parathyroid hormone-related protein. Studies by immunohistology, immunoassay, and polymerase chain reaction

BACKGROUND

Parathyroid hormone-related protein (PTHrP) was originally discovered as a product of tumors associated with hypercalcemia. Subsequent studies have demonstrated the widespread production of PTHrP in both fetal and adult tissues, among them the placenta, where it has been identified in amniotic epithelial cells and trophoblasts. However, studies of PTHrP production by the neoplastic placenta have not been reported.

EXPERIMENTAL DESIGN

We have studied placental cells and tissues for PTHrP by immunohistology, immunoassay, and the polymerase chain reaction. We studied normal placenta, placenta neoplasia, and placental cell lines grown in culture.

RESULTS

Our studies in abnormal placenta demonstrate that PTHrP is produced by chorioangioma, choriocarcinomas, and hydatidiform moles, indicating that PTHrP may be a marker for neoplasia of the placenta. Our studies in normal placenta demonstrate that PTHrP is produced by several placental cell types, including, syncytiotrophoblast, intermediate trophoblasts, cytotrophoblasts, and amniotic epithelium, suggesting an important role for this protein in several aspects of placental function. Cell lines derived from trophoblasts and amniotic epithelium also produced PTHrP and secreted it into culture medium. Polymerase chain reaction with PTHrP coding sequence primers demonstrated the appropriate polymerase chain reaction product in these placental cells.

CONCLUSIONS

The production of PTHrP by several normal and abnormal placental cell types is evidence for an important function for PTHrP in normal and neoplastic placenta.

Alveolar epithelial cells express and secrete parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) was discovered as a hypercalcemia-inducing product of malignant cells and has since been demonstrated to be a product of many tissues. Although it is robustly expressed in fetal lung, PTHrP expression has not been assigned to alveolar epithelial cells in adult lung. We have shown that PTHrP is expressed in the adult rat lung and by cultured rat alveolar type II epithelial cells with sensitive and specific immunoassays and immunohistochemical techniques. Immunoassay of cell extracts demonstrated that freshly isolated type II cells contained PTHrP (136 pg/10(7) cells), whereas freshly isolated alveolar macrophages and cultured macrophages did not express PTHrP. Cultured type II cells secreted PTHrP into medium, 202 +/- 11 fg PTHrP/micrograms cell protein in 24 h. Basal secretion remained stable up to 7 days in culture. Treatment with phorbol myristate acetate or 1-oleoyl-2-acetyl-sn-glycerol produced a dose-related, 2- to 4-fold increase in PTHrP secretion. However, forskolin, ionomycin, ATP, phenylephrine, capsaicin, and bradykinin had no effect. Thus, PTHrP secretion appeared to be regulated by a protein kinase C-dependent pathway. PTHrP could also be demonstrated in pulmonary lavage fluid. Although the function of PTHrP in the adult lung is unknown, it could involve control of cell growth and differentiation or control of surfactant lipid secretion. Further studies are necessary to elucidate the function of PTHrP in the lung.

Islet amyloid polypeptide (amylin) increases the renal excretion of calcium in the conscious dog

Islet amyloid polypeptide (IAPP) is a member of the calcitonin/CGRP family and has been isolated from the beta-cell of pancreatic islets. Recent evidence suggests that this peptide may be involved in calcium metabolism in that its administration resulted in lowering of serum calcium levels. To determine the mechanism of IAPP-induced hypocalcemia, the peptide was infused at 50 pmol/min/kg for 90 minutes in conscious male mongrel dogs. Infusion of the peptide resulted in a modest decline in the total serum calcium concentration (10.4 +/- 0.2 to 9.4 +/- 0.2 mg/dl; P < 0.05) and a concomitant increase in urinary calcium excretion (3.6 +/- 0.6 to 6.9 +/- 2.0 mg/dl; P < 0.01). Based on an extracellular volume of 7 liter in a 28 kg dog, the total decrement in calcium due to IAPP was 41.3 +/- 2.4 mg, whereas the total increase in urinary calcium was 3.2 +/- 0.7 mg. There were no detectable changes in calcitonin. We conclude that IAPP lowers serum calcium and increases the renal excretion of calcium independently of calcitonin. However, the calciuria can only account for a small component of the hypocalcemic effect and therefore, an additional calcium lowering effect of IAPP exits.

Immunoreactive parathyroid hormone-related protein is present in human seminal plasma and is of prostate origin

Parathyroid hormone-related protein (PTHrP) is a regulatory peptide that has been associated with normal fetal growth and differentiation as well as the regulation of fetal calcium. We recently demonstrated the expression of PTHrP in neuroendocrine cells of human prostatic glands. The present study was undertaken to determine if semen contained PTHrP and to determine if there were any differences in seminal PTHrP between normal and vasectomized men. Radioimmunoassay was used to examine whether immunoreactive PTHrP in seminal fluid is secreted by the prostate. Significant quantities of immunoreactive PTHrP were detected in all seminal samples from normal men of ages 24-34 years (mean +/- SD, 12.94 +/- 8.2 ng/ml). Vasectomy did not decrease the semen levels of PTHrP (25.53 +/- 12.14 ng/ml). In addition, immunohistochemical evaluation with a monoclonal antibody used in our previous study did not show PTHrP immunostaining in the seminal vesicles. These findings indicate that seminal PTHrP is predominantly of prostatic origin. Moreover, the significant correlations between PTHrP and calcium levels in human seminal plasma from both normal (P < 0.001) and vasectomized (P < 0.02) patients suggest that PTHrP may serve as a regulatory factor of calcium secretion in the prostate.

The short-term effects of conjugated estrogen on bone turnover in older women

Estrogen replacement therapy (ERT) prevents bone loss and fracture in early postmenopausal women, but its benefit for women over 70 yr of age has not been determined. We have examined the effect of a short course of ERT on biochemical markers of bone turnover in older women. Eleven women (mean age, 77 yr) were given conjugated estrogen (Premarin; 0.625 mg/day) for 6 weeks. Biochemical markers were measured on serum and urine collected at baseline (two samples), after 5 and 6 weeks of ERT, and 5 and 6 weeks post-ERT. Markers of bone formation were osteocalcin, bone alkaline phosphatase, and type I procollagen peptide. Markers of bone resorption were total urinary hydroxyproline, total and free pyridinoline and deoxypyridinoline cross-links, type I collagen cross-linked N-telopeptides, and serum C-terminal cross-linked telopeptide. Data were analyzed by repeated measures multivariate analysis of variance to estimate the overall effect of ERT on the biochemical markers. Markers of bone resorption decreased during ERT and returned to baseline after ERT (P < 0.05). Markers of bone formation declined less during ERT and continued to decline after ERT (P < 0.05). We conclude that ERT reduces bone turnover in older women and that markers of bone turnover may be useful in assessing the response to treatment in this age group.

Parathyroid hormone-related protein in the cardiovascular system

PTH-related protein (PTHrP) is expressed in a stretch-responsive manner in several types of smooth muscle. We previously demonstrated the production of PTHrP in adult rat heart muscle. In this study, we demonstrate the production of PTHrP in the cardiovascular systems of several mammalian species, including human. We demonstrate PTHrP by immunohistology, using a panel of murine monoclonal antibodies to PTHrP epitopes that span the entire length of the human PTHrP amino acid sequence, quantitate the concentration of PTHrP in the rat cardiovascular system by region-specific RIAs, and measure the relative levels of PTHrP messenger RNA (mRNA) by competitive polymerase chain reaction. Immunohistology studies demonstrated the presence of PTHrP in the cardiovascular systems of humans, rats, pigs, and rabbits. The most robust expression was found in atria, followed by the large vessels, then ventricles. No difference was seen between the left and right sides of the heart. Double staining procedures revealed that PTHrP and atrial naturietic peptide were coexpressed in some cells. Using RIAs and polymerase chain reaction, we demonstrated that atria contained a higher concentration of PTHrP than ventricles and that the relative PTHrP concentrations correlated to its mRNA concentrations in these two tissues. The concentrations of PTHrP in the smooth muscle surrounding the aorta and vena cava were comparable to those in atria. However, in these large vessels, the higher PTHrP levels did not correspond to its mRNA levels. Whereas the immunoreactive concentrations of PTHrP were similar in the atria, aorta, and vena cava, the mRNA levels in the aorta and vena cava were 3-fold lower than those in the atria. Certain PTHrP epitopes appeared to be differentially expressed in specific cardiovascular tissues. A comparison of region-specific assays showed that immunoreactivity measured by immunoassays to PTHrP-(38-64) and PTHrP-(109-141) were 3- to 5-fold greater than that determined by an immunoassay to PTHrP-(1-34). Our observations demonstrate that the atria, aorta, and vena cava contain the greatest amounts of PTHrP in the cardiovascular system. The discrepancy between the concentrations of PTHrP and its mRNA present in the aorta and vena cava suggest that the two may be regulated differently in these tissues. The widespread distribution of PTHrP suggests an important function for the protein in the cardiovascular system, possibly functioning as the calcium counterpart for the atrial natriuretic-sodium regulatory axis.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Parathyroid hormone-related protein is expressed by prostatic neuroendocrine cells

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) is a regulatory peptide that has been associated with normal fetal growth and differentiation as well as the regulation of fetal calcium. In a variety of cancers, PTHrP has been implicated in the humoral hypercalcemia of malignancy. Recently, we demonstrated that all prostatic adenocarcinomas express PTHrP. In the present study, the localization of PTHrP and its mRNA in nonmalignant prostate tissue was assessed.

METHODS

Formalin-fixed, paraffin-embedded prostatic tissues from 23 patients were evaluated. Immunocytochemistry (ICC) was performed by the streptavidin-peroxidase enzyme conjugate method using a monoclonal antibody, 8B12, generated against fragment 1-34 of the amino-terminal end of PTHrP. Nonradioactive in situ hybridization was carried out using a digoxigenin labeled single-stranded cDNA probe complementary to the sequence coding for PTHrP(15-120).

RESULTS

PTHrP immunoreactivity was observed in the cytosol of a few epithelial cells. Double labeling and serial section ICC with 8B12 and a monoclonal antibody to chromogranin A (a generic neuroendocrine [NE] marker) revealed that PTHrP was present in a subpopulation of prostatic NE cells. In situ hybridization of mirror image sections demonstrated positive signals in prostatic NE cells in complete accordance with the ICC findings.

CONCLUSIONS

The localization and production of PTHrP in prostatic NE cells suggest that this polypeptide may act in an endocrine-paracrine fashion involved in the prostatic growth and differentiation as well as the regulation of calcium in semen and seminal fluid.

Chromogranin A peptide-specific antisera and high-performance size exclusion chromatography demonstrate amino-terminal and carboxy-terminal fragments of the native molecule in human cell lines

We have studied the pattern of amino-terminal and carboxy-terminal protein processing of chromogranin A (CgA) in five human cell lines, four derived from lung cancers: NCI-H478, NCI-H1011, NCI-H727, and BEN; and one derived from human medullary thyroid carcinoma: TT. This was accomplished by fractionation of cell extracts by high-performance size exclusion chromatography (HPSEC) and measurement of CgA in the fractions by radioimmunoassay (RIA). Three RIA's were used, one specific for the amino-terminus of CgA, one specific for the carboxy-terminal region, and a monoclonal antibody-based assay that recognizes only the native CgA molecule. We demonstrated the presence of different amino- and carboxy-terminal immunoreactive species of CgA in the different cell lines. The amino-terminal assay demonstrated distinct low-molecular-size species in the NCI-H478 and NCI-H1011 cell lines, and a similar peak in the TT cells. The amino-terminal assay did not recognize any distinct species in BEN and NCI-H727 cell lines. The carboxy-regional assay demonstrated distinct low-molecular-size species in the NCI-H478 and NCI-H101 cell lines and high-molecular-size species in the NCI-H727 and BEN cells. Our studies demonstrate with region-specific RIA's the presence of both amino- and carboxy- forms of CgA in human cells that secrete this protein. These results provide direct evidence that CgA-producing cells produce, probably through endoproteolytic processing of the native molecule, amino- and carboxy-terminal forms of the protein.

Parathyroid hormone-like protein: alternative messenger RNA splicing pathways in human cancer cell lines

Parathyroid hormone-like protein (PLP) is expressed in a wide variety of cancers and exerts diverse biological effects in addition to hypercalcemia. We studied the expression of the gene for PLP in cancer cell lines derived from different tissues that produce PLP. We used the polymerase chain reaction to evaluate the PLP mRNA species produced in these various cell lines by differential transcription initiation and alternative splicing pathways. A series of exon-specific oligonucleotide primers that hybridize to DNA sequences adjacent to exon-intron splice junctions throughout the PLP gene were designed. These primers were used to evaluate steady state levels of PLP mRNA species. Our analysis with promoter-specific primers demonstrated expression from all three putative transcription start sites of PLP, designated P1, P2, and P3. P2-initiated transcripts were present in all of the cell lines, whereas the presence of P1- and P3-initiated messages were cell line specific. Our analysis with carboxy-terminal coding-specific primers demonstrated the utilization of the alternative splicing pathways that produce all three mature PLP polypeptides, PLP-139, -1-173, and -1-141. The 1-139 mRNA species was found in all of the cell lines, whereas the 1-141 and 1-173 mRNA species were cell line specific. These studies demonstrate the prevalence of the P2-initiated mRNA and the PLP1-139 alternative splicing pathway in the tumor cell lines studied and suggest that other pathways of PLP gene expression may be regulated in a cell line-dependent manner. The particular form of PLP expressed by a given cell can influence its biological effects.

Effect of daily oral vitamin D and calcium therapy, hypophosphatemia, and endogenous 1-25 dihydroxycholecalciferol on parathyroid hormone and phosphate wasting in renal transplant recipients

Ten stable, normocalcemic renal transplant patients with good allograft function, hyperparathyroidism, and variable hypophosphatemia were treated for 2 to 9 months with oral calcium carbonate and replacement doses of vitamin D analogues. Parathyroid hormone levels (PTH) and renal phosphate wasting were not autonomous or fixed but decreased with therapy. Although serum 1-25(OH)2D3 levels could be shown to rise appropriately during oral vitamin D therapy and fall afterwards, a separate study in a larger group of patients showed no effect of elevated parathyroid hormone or hypophosphatemia to increase endogenous 1-25(OH)2D3 levels. Some 42% of patients with elevated carboxy-terminal PTH, had elevated N-terminal PTH, which was closely associated with more severe phosphate wasting. Aggressive oral calcium and vitamin D supplementation in certain normocalcemic renal transplant patients may decrease endogenous PTH levels, improve hypophosphatemia, and provide a physiologic increase in levels of 1-25(OH)2D3.