Calcitonin receptor mRNA expression in the human prostate

Neuroendocrine cells of the prostate: Histology, biological functions, and molecular mechanisms

Prostate cancer (PCa) is a common cause of cancer-related mortality in men worldwide. Although most men are diagnosed with low grade, indolent tumors that are potentially curable, a significant subset develops advanced disease where hormone therapy is required to target the androgen receptor (AR). Despite its initial effect, hormone therapy eventually fails and the tumor progresses to lethal stages even through continued inhibition of AR. This review article focuses on the role of PCa cellular heterogeneity in therapy resistance and disease progression. Although AR-positive luminal-type cells represent the vast majority of PCa cells, there exists a minor component of AR-negative neuroendocrine (NE) cells that are resistant to hormonal therapy and are enriched by the treatment. In addition, it is now well accepted that a significant subset of hormonally treated tumors recur as small cell neuroendocrine carcinoma (SCNC), further highlighting the importance of targeting NE cells in addition to the more abundant luminal-type cancer cells. Although it has been long recognized that NE cells are present in PCa, their underlying function in benign prostate and molecular mechanisms contributing to PCa progression remains poorly understood. In this article, we review the morphology and function of NE cells in benign prostate and PCa as well as underlying molecular mechanisms. In addition, we review the major reported mechanisms for transformation from common adenocarcinoma histology to the highly lethal SCNC, a significant clinical challenge in the management of advanced PCa.

Building the case for the calcitonin receptor as a viable target for the treatment of glioblastoma

Researchers are actively seeking novel targeted therapies for the brain tumour glioblastoma (GBM) as the mean survival is less than 15 months. Here we discuss the proposal that the calcitonin receptor (CT Receptor), expressed in 76-86% of patient biopsies, is expressed by both malignant glioma cells and putative glioma stem cells (GSCs), and therefore represents a potential therapeutic target. Forty-two per cent (42%) of high-grade glioma (HGG; representative of GSCs) cell lines express CT Receptor protein. CT Receptors are widely expressed throughout the life cycle of organisms and in some instances promote apoptosis. Which of the common isoforms of the CT Receptor are predominantly expressed is currently unknown, but a functional response to cell stress of the insert-positive isoform is hypothesised. A model for resistant malignancies is one in which chemotherapy plays a direct role in activating quiescent stem cells for replacement of the tumour tissue hierarchy. The putative role that the CT Receptor plays in maintenance of quiescent cancer stem cells is discussed in view of the activation of the Notch-CT Receptor-collagen V axis in quiescent muscle (satellite) stem cells. The pharmacological CT response profiles of four of the HGG cell lines were reported. Both CT responders and non-responders were sensitive to an immunotoxin based on an anti-CT Receptor antibody. The CALCR mRNA exhibits alternative splicing commonly associated with cancer cells, which could result in the atypical pharmacology exhibited by CT non-responders and an explanation of tumour suppression. Due to the inherent instability of CALCR mRNA, analysis of CT Receptor protein in patient samples will lead to improved data for the expression of CT Receptor in GBM and other cancers, and an understanding of the role and activity of the splice variants. This knowledge will aid the effective targeting of this receptor for treatment of GBM.

Dianthin-30 or gelonin versus monomethyl auristatin E, each configured with an anti-calcitonin receptor antibody, are differentially potent in vitro in high-grade glioma cell lines derived from glioblastoma

We have reported that calcitonin receptor (CTR) is widely expressed in biopsies from the lethal brain tumour glioblastoma by malignant glioma and brain tumour-initiating cells (glioma stem cells) using anti-human CTR antibodies. A monoclonal antibody against an epitope within the extracellular domain of CTR was raised (mAb2C4) and chemically conjugated to either plant ribosome-inactivating proteins (RIPs) dianthin-30 or gelonin, or the drug monomethyl auristatin E (MMAE), and purified. In the high-grade glioma cell line (HGG, representing glioma stem cells) SB2b, in the presence of the triterpene glycoside SO1861, the EC50 for mAb2C4:dianthin was 10.0 pM and for mAb2C4:MMAE [antibody drug conjugate (ADC)] 2.5 nM, 250-fold less potent. With the cell line U87MG, in the presence of SO1861, the EC50 for mAb2C4:dianthin was 20 pM, mAb2C4:gelonin, 20 pM, compared to the ADC (6.3 nM), which is >300 less potent. Several other HGG cell lines that express CTR were tested and the efficacies of mAb2C4:RIP (dianthin or gelonin) were similar. Co-administration of the enhancer SO1861 purified from plants enhances lysosomal escape. Enhancement with SO1861 increased potency of the immunotoxin (>3 log values) compared to the ADC (1 log). The uptake of antibody was demonstrated with the fluorescent conjugate mAb2C4:Alexa Fluor 568, and the release of dianthin-30:Alexa Fluor488 into the cytosol following addition of SO1861 supports our model. These data demonstrate that the immunotoxins are highly potent and that CTR is an effective target expressed by a large proportion of HGG cell lines representative of glioma stem cells and isolated from individual patients.

A novel ligand of calcitonin receptor reveals a potential new sensor that modulates programmed cell death

We have discovered that the accumulation of an anti-calcitonin receptor (anti-CTR) antibody conjugated to a fluorophore (mAb2C4:AF568) provides a robust signal for cells undergoing apoptotic programmed cell death (PCD). PCD is an absolute requirement for normal development of metazoan organisms. PCD is a hallmark of common diseases such as cardiovascular disease and tissue rejection in graft versus host pathologies, and chemotherapeutics work by increasing PCD. This robust signal or high fluorescent events were verified by confocal microscopy and flow cytometry in several cell lines and a primary culture in which PCD had been induced. In Jurkat cells, GBM-L2 and MG63 cells, the percentage undergoing PCD that were positive for both mAb2C4:AF568 and annexin V ranged between 70 and >90%. In MG63 cells induced for the preapoptotic cell stress response (PACSR), the normal expression of α-tubulin, a key structural component of the cytoskeleton, and accumulation of mAb2C4:AF568 were mutually exclusive. Our data support a model in which CTR is upregulated during PACSR and recycles to the plasma membrane with apoptosis. In cells committed to apoptosis (α-tubulin negative), there is accumulation of the CTR-ligand mAb2C4:AF568 generating a high fluorescent event. The reagent mAb2C4:AF568 effectively identifies a novel event linked to apoptosis.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Cadherin switching and activation of beta-catenin signaling underlie proinvasive actions of calcitonin-calcitonin receptor axis in prostate cancer

Calcitonin, a neuroendocrine peptide, and its receptor are localized in the basal epithelium of benign prostate but in the secretory epithelium of malignant prostates. The abundance of calcitonin and calcitonin receptor mRNA displays positive correlation with the Gleason grade of primary prostate cancers. Moreover, calcitonin increases tumorigenicity and invasiveness of multiple prostate cancer cell lines by cyclic AMP-dependent protein kinase-mediated actions. These actions include increased secretion of matrix metalloproteinases and urokinase-type plasminogen activator and an increase in prostate cancer cell invasion. Activation of calcitonin-calcitonin receptor autocrine loop in prostate cancer cell lines led to the loss of cell-cell adhesion, destabilization of tight and adherens junctions, and internalization of key integral membrane proteins. In addition, the activation of calcitonin-calcitonin receptor axis induced epithelial-mesenchymal transition of prostate cancer cells as characterized by cadherin switch and the expression of the mesenchymal marker, vimentin. The activated calcitonin receptor phosphorylated glycogen synthase kinase-3, a key regulator of cytosolic beta-catenin degradation within the WNT signaling pathway. This resulted in the accumulation of intracellular beta-catenin, its translocation in the nucleus, and transactivation of beta-catenin-responsive genes. These results for the first time identify actions of calcitonin-calcitonin receptor axis on prostate cancer cells that lead to the destabilization of cell-cell junctions, epithelial-to-mesenchymal transition, and activation of WNT/beta-catenin signaling. The results also suggest that cyclic AMP-dependent protein kinase plays a key role in calcitonin receptor-induced destabilization of cell-cell junctions and activation of WNT-beta-catenin signaling.

Is there a role for platinum chemotherapy in the treatment of patients with hormone-refractory prostate cancer?

Docetaxel chemotherapy is the current standard of care for metastatic hormone-refractory prostate cancer (HRPC). Platinum chemotherapy drugs, such as cisplatin and carboplatin, have moderate single-agent activity in HRPC. Next-generation platinum drugs, including satraplatin and oxaliplatin, may have additional activity in the management of HRPC. Furthermore, neuroendocrine differentiation may play a role in disease progression, providing a rationale for platinum-based chemotherapy in the management of HRPC. The authors reviewed the MEDLINE database for reports related to platinum-based chemotherapy in patients with advanced prostate cancer and evaluated studies that reviewed the role of neuroendocrine differentiation in the progression of HRPC. Older studies from the 1970s and 1980s suggested a lack of activity of cisplatin and carboplatin; however, those studies were flawed at least in part by their methods of response assessment. More recent Phase II studies of carboplatin suggested a moderate level of clinical and palliative activity when it was used as a single agent. However, when carboplatin was combined with a taxane and estramustine, high response rates were observed in several recent clinical trials. In addition, a randomized trial suggested that satraplatin plus prednisone improved progression-free survival compared with prednisone alone. For patients who progressed after docetaxel, no standard options existed in the literature that was reviewed. Several preliminary reports suggested that carboplatin and oxaliplatin may have activity as second-line chemotherapy. Platinum chemotherapy drugs historically have been considered inactive in HRPC, although a review of the data suggested otherwise. Carboplatin, in particular, induced very high response rates when it was combined with estramustine and a taxane, but it also appeared to have activity in patients who progressed after docetaxel. Satraplatin plus prednisone is being investigated in a large Phase III trial as second-line chemotherapy for HRPC. Targeting neuroendocrine cells may provide a new therapeutic approach to HRPC.

Protein tyrosine phosphatase PTP1B is involved in neuroendocrine differentiation of prostate cancer

BACKGROUND

Prostate cancer (PC) contains a minor component of neuroendocrine (NE) cells that may stimulate androgen-independent growth of the tumor. The mechanism of neuroendocrine differentiation remains unknown.

METHODS

The expression of PTP1B, a protein tyrosine phosphatase, was studied in LNCaP cells induced to show neuroendocrine phenotype by androgen withdrawal. Wild-type PTP1B and its dominant-negative mutant were transfected into LNCaP cells to study their effects on neuroendocrine differentiation. In vivo expression of PTP1B in human prostate cancer was studied by immunohistochemistry.

RESULTS

Androgen withdrawal of LNCaP cells led to increased expression of PTP1B with a corresponding increase in its tyrosine phosphatase activity. Overexpression of PTP1B in LNCaP cells led to neuroendocrine differentiation while expression of its dominant-negative mutant inhibited neuroendocrine differentiation. Immunohistochemical study showed that PTP1B was exclusively expressed in neuroendocrine cells of human prostate cancer tissue.

CONCLUSION

Our findings suggest that PTP1B plays an important role in neuroendocrine differentiation, and therefore, may possibly be involved in the progression of prostate cancer.

Calcitonin receptor isoforms expressed in the developing rat kidney

BACKGROUND

Development in the metanephric-kidney transition period involves the precise expression of paracrine and autocrine events in an ordered spatio-temporal manner. Expression of these molecular events is tightly controlled and includes positive and negative growth factors and cognate receptors within close proximity in developing structures in the expanding renal cortex and medulla. The expression of calcitonin receptor (CTR) isoforms C1a and C1b in this context has not previously been described. Our current study also explored the relationship between the expression of CTR isoforms and amylin binding sites.

METHODS

Techniques included immunohistochemistry with novel antibodies that detect CTR isoforms, real time PCR for the quantification of CTR isoforms, Western blot and in vitro autoradiography, on tissues from embryo day 18 to postnatal day 30.

RESULTS

The CTR C1a isoform is expressed in the ureteric ducts of the metanephros and both isoforms are expressed in the developing distal convoluted tubules, ascending limbs of the loop of Henle and collecting ducts in the postnatal rat kidney. There was a 60-fold excess of C1a versus C1b isoforms. An apparent molecular weight of 63 kD was found. In vitro autoradiography demonstrated that while amylin binding sites were predominantly in the cortex, CTR expression was largely localized in the medulla in an earlier event, followed by cortical expression.

CONCLUSIONS

CTR C1a protein expression has been identified in the ureteric ducts in the metanephros and both isoforms expressed in the distal portions of the developing nephrons and collecting ducts. Since amylin binding sites have been localized on the proximal tubules of the cortex, it is unlikely that amylin receptors can be represented by modification of CTR affinity with receptor activity modifying proteins in the kidney.

Ontogeny of calcitonin receptor mRNA and protein in the developing central nervous system of the rat

In this study, the expression of receptors for calcitonin (CTR), the CTR C1a and C1b isoforms, was investigated during development of the fetal rat central nervous system (CNS) by using in situ hybridization and immunohistochemistry. Coincident expression with both techniques was evident. Immunohistochemical evidence for the expression of the C1a isoform alone was found. Expression was first observed at embryonic day 12/13 (E12/E13) within and adjacent to the ventricular zones known to include primary matrices of proliferation, in regions of the preoptic area, anterior and posterior hypothalamus, anterior and posterior pons, medulla, and spinal cord. At later times, with the decline in the density of immunoreactivity at these loci (E15), expression in primary matrices was found later at distinct loci within the ventricular zones of cerebellum (E17), and at E19, the tectum, lateral ventricle, and cortical subplate. By E19, the density of staining had increased and was widespread throughout the expanding CNS. In the rostral domains, moderate to high density was found in the external plexiform layer; the medial preoptic area and nucleus; the ventromedial, dorsomedial, and arcuate hypothalamic nuclei; and the lateral and posterior hypothalamic areas. In the midbrain, similar levels of expression were noted in the central nucleus of raphe; the deep mesencephalic, dorsal raphe, and laterodorsal tegmental nuclei; and the ventral periaqueductal gray. In the pons, positive loci included the locus coeruleus and the gigantocellular and pontine reticular nuclei. In the medulla, high expression was evident in the gigantocellular, intermediate, magnocellular, and medullary reticular, spinal trigeminal and cuneate nuclei; and the nucleus tractus solitarius. In the spinal cord, moderate to high density of staining was found in the ventral, dorsal, and lateral horns, and in the ventral, dorsal, and cuneate funiculi. On the other hand, transitory expression was found in the diagonal band, bed nucleus of the stria terminalis, amygdala, and the lateral mamillary and anterobasal nuclei of the hypothalamus. These studies indicate a role for CTR in the activation of some premigratory neuroblasts in the CNS as well as a possible role later in an undefined function associated with mature neurons of particular nuclei.

Neuroendocrine differentiation of human prostatic primary epithelial cells in vitro

BACKGROUND

Dispersed prostatic neuroendocrine cells are involved in growth regulation of the prostate and are considered to play a role in the pathogenesis of prostate carcinoma and benign prostatic hyperplasia (BPH). They are meant either to be derived from the neural crest during embryogenesis or by direct differentiation of the cells from locally present precursor cells.

METHODS

An in vitro model was developed for human prostatic epithelial and neuroendocrine cell differentiation. Minced explants from radical prostatectomies were seeded on collagen I-coated plates.

RESULTS

The majority of outgrowing cells were basal cells, positive for cytokeratin markers K 5/14 and CD 44, as determined by confocal laser scanning microscopy. A small fraction of interdispersed single cells expressing c-kit, which is found on pluripotent precursors, was identified by immunofluorescence. From these basal cells, in vitro differentiation of cells with neuroendocrine morphology could be achieved within 3 days. These were at rest, i.e., non-bromodeoxyuridine incorporating cells and characteristically coexpressed K 5/14, K 18, and the neuroendocrine marker chromogranin A. Luminal cells staining for K 8 or 18 were not observed.

CONCLUSION

Neuroendocrine differentiation of adult prostatic cells was achieved in vitro, favoring the hypothesis that neuroendocrine cells are derived from peripheral precursor cells. The acceleration of this differentiation pathway may be the reason for the increased presence of neuroendocrine cells in areas of epithelial hyperplasia in BPH.

A prostate-derived cDNA that is mapped to human chromosome 19 encodes a novel protein

The epithelial cells of prostate gland secrete various secretory products that play an important role in the growth and differentiation of prostate gland. These secretory products have also been implicated in neuroendocrine differentiation of benign prostatic hyperplasia and prostate malignancy. We have cloned a prostate-derived cDNA encoding a novel protein with a predicted molecular weight of 78 kDa (P(78)), and precisely mapped the cDNA sequence to chromosome 19. The P(78) gene has a complex genomic structure with 18 exons and 17 introns. The P(78) contains two conserved structural domains with limited similarity to domain D of synapsin I. The P(78) mRNA was expressed in various human cell lines. Western blot analysis using antibody specific for the P(78) revealed the presence of the P(78) protein in the prostate cancer cell lines with much lower level in metastatic prostate cancer cell lines compared to that in a primary prostate cancer cell line.

Neuroendocrine pathogenesis in adenocarcinoma of the prostate

BACKGROUND

In the prostate, the importance of sex hormones for its normal development and function is well known. However, it has been proposed that various neuroendocrine (NE) hormones and growth factors may be involved in the pathogenesis of prostatic carcinoma (CaP). Neuroendocrine differentiation appears to be associated with tumour progression and the androgen-independent state, for which there is currently no successful therapy. Therefore, we need to improve our understanding of NE cells, their regulatory products and influence on the prostate gland. Finally, new therapeutic protocols need to be developed.

METHODS

Information is presented on prostatic NE cells and neuroendocrine differentiation (NED) in prostatic carcinoma. Neuroendocrine secretory products and interactions with epithelial prostate cells are investigated in order to understand their significance for the pathogenesis of the prostate gland, prognosis and therapy.

RESULTS

Recent research suggests that NE-secreted products. such as serotonin, somatostatin and bombesin, may influence growth, invasiveness, metastatic processes and angiogenesis in CaP. During recent years. new experimental models for NED have been developed to provide evidence that NE products may promote proliferation and confer antiapoptotic capabilities on non-neuroendocrine cells in close proximity to NE cells. Cancerous epithelial cells may become more responsive to NE factors by upregulation of receptors for neuropeptides, or may induce NE cells to upregulate the secretion and synthesis of NE factors. In the androgen independent state, neuropeptides and their intracellular signals may activate the androgen receptor. Furthermore, androgen ablation may lead to downregulation of neural endopeptidase 24.11 (a zinc-dependent metalloproteinase) and PSA, which would lead to increased levels of NE products becoming available. These studies confirm that NE cells and NED may have a significant impact on prostate cancer, especially in the androgen independent state.

CONCLUSIONS

Recent developments in molecular biology and pathophysiology of prostate cancer have increased our understanding of the NE regulatory mechanisms. Hopefully, this will lead to the development of entirely new therapeutic modalities. For example, somatostatin agonists may suppress angiogenesis and proliferation, and simultaneously promote apoptosis in prostate cancer cells. Somatostatin may thus have an important role in tumour biology, and in the future there may be a potential role for somatostatin analogues in the treatment of prostate cancer, but also for serotonin and bombesin receptor antagonists. However, a review of the accumulated knowledge in this field suggests that we still need to improve our understanding of NE cells and their regulatory products and influence on the prostate gland. and that clinical trials are needed, to test drugs based on neuroendocrine hormones and their agonists/antagonists.

Calcitonin is a prostate epithelium-derived growth stimulatory peptide

Locally secreted growth factors and neuropeptides may play an important role in sustaining the growth of hormone-independent prostate cancer. Our previous studies have shown that calcitonin-like immunoreactive peptide (CTI) is secreted by primary prostate cells in culture, and its secretion from malignant prostate cells is significantly higher than benign cells. Exogenously added calcitonin (CT) induces DNA synthesis in serum-starved prostate cancer LNCaP and PC-3M cells. Present studies extended these findings by cloning cDNAs for CT and CT receptor (CT-R) from prostate cancer cells and studying the expression of CT and CT-R mRNA in prostate cancer cell lines and primary prostate tumor specimens. The results have shown that PC-3 cells expressed CT, and not CT-R, mRNA, whereas CT-R, but not CT, mRNA was expressed by LNCaP cells. Conditioned media from PC-3 cells induced DNA synthesis of LNCaP cells, and this mitogenic response was abolished by anti-CT serum. Highly aggressive PC-3M cells co-expressed CT and CT-R mRNAs. CT also induced a twofold increase in DNA synthesis of primary prostate cells and anti-CT serum caused a 56% decline. In-situ hybridization histochemistry of archival prostate specimens has selectively localized CT and CT-R mRNA in basal epithelium of benign and low grade PC specimens, and these mRNAs were not detected in either luminal epithelium or stroma. In contrast, CT and CT-R mRNA were detected throughout the luminal epithelium of moderate and high-grade PC specimens. Most epithelial cells of low and moderately differentiated tumors expressed either CT or CT-R mRNA, suggesting that CT may serve as a paracrine factor. In contrast, CT and CT-R mRNAs were co-expressed by most tumor cells in advanced PC specimens. The cells expressing CT-R mRNA in primary tumors also co-expressed PCNA. These results, when combined with mitogenic actions of CT on primary prostate cells as well as PC cell lines, strongly support the role for CT in sustaining the growth of cancer cells.

Constitutive activation of stimulatory guanine nucleotide binding protein (G(S)alphaQL)-mediated signaling increases invasiveness and tumorigenicity of PC-3M prostate cancer cells

An abnormal stimulation of cAMP signaling cascade has been implicated in various human carcinomas. Since the agents activating G(S)alpha-mediated signaling pathways have been shown to increase in vitro proliferation of prostate cancer cells, present studies examined the G(S)alpha-mediated signaling in tumorigenicity and invasiveness of PC-3M prostate cancer cells. PC-3M cells were stably transfected with plasmids containing either wild type (G(S)alpha-WT) or constitutively active (gsp mutant of G(S)alpha or G(S)alpha-QL) cDNAs. The stable transfectants were then tested for: (1) colony formation in soft agar; (2) cell migration and penetration of basement matrix in an in vitro invasion assay; and (3) the ability to form tumors and metastases in nude mice. PC-3M cells expressing G(S)alpha-QL protein displayed 15-fold increase in their ability to migrate and penetrate the basement membrane as compared to parental PC-3M cells or those expressing G(S)alpha-WT. G(S)alpha-QL transfectants also displayed a dramatically greater rate of growth in soft agar, and greater tumorigenicity and metastasis forming ability when orthotopically implanted in nude mice. All mice receiving PC-3M cells produced primary tumors within 5 weeks after implantation. However, the cells expressing G(S)alpha-QL displayed a significantly faster tumor growth as assessed by prostate weight (greater than 20-fold as compared to PC-3M cells), and produced metastases in kidneys, lymph nodes, blood vessels, bowel mesentery and intestine. Interestingly, expression of G(S)alpha-WT reduced the ability of PC-3M cells to form tumors in nude mice. These results suggest that persistent activation of G(S)alpha-mediated signaling cascade can dramatically accelerate tumorigenesis and metastasizing ability of prostate cancer cells.

Granin-A, parathyroid hormone-related protein, and calcitonin gene products in neuroendocrine prostate cancer

BACKGROUND

The importance of the expression of granin A (GRN-A, chromogranin-A), calcitonin (CT) gene products (CGPs), and parathyroid hormone-related protein (PTHrP) has become appreciated in the neuroendocrine (NE) differentiation of prostate cancer. We have studied the prostate expression of these three NE cell products with in vivo and in vitro methods.

METHODS

GRN-A secretion was measured by immunoassay in serum samples from patients with prostate cancer. Immunohistology procedures were used to assess GRN-A, CGPs, and PTHrP expression in paraffin-embedded prostate tissue samples. Serum and tumor findings were evaluated according to the patient's clinical status. All three substances were also studied in prostate cancer cell cultures.

RESULTS

GRN-A, PTHrP, and CGPs were all secreted products of prostate cancer. Our studies demonstrated that GRN-A can serve as a prostate cancer serum and tumor marker with clinical value for both diagnosis and prognosis. Elevated serum GRN-A levels identified patients with prostate cancer, including some who did not have elevated serum prostate-specific antigen (PSA) levels. Serum GRN-A concentrations also had prognostic value for prostate cancer. PTHrP and CGPs were expressed in prostate cancer in addition to GRN-A, and all three were secreted by prostate cells in culture. Each had effects on prostate cell growth.

CONCLUSIONS

GRN-A, PTHrP, and CGPs are produced and secreted by prostate cells. These three NE cell products can serve as tumor and markers for prostate cancer that have diagnostic and prognostic value. In addition, their derived peptides regulate prostate cell growth. However, studies more conclusive than the preliminary observations of our group and of other investigators are needed to define the roles of PTHrP, GRN-A, and CGPs in prostate cancer.

Stromal and epithelial cells of the canine prostate express parathyroid hormone-related protein, but not the PTH/PTHrP receptor

BACKGROUND

Parathyroid hormone-related protein (PTHrP), a principal factor in the pathogenesis of humoral hypercalcemia of malignancy, is also widely expressed in many normal tissues, including human prostatic epithelial cells. The role of PTHrP in the prostate is not known, but may include regulation of cell growth and differentiation or calcium secretion into prostatic fluid. The dog is a valuable animal model for human prostatic diseases. The objective was to investigate the expression of PTHrP and the PTH/PTHrP (type 1) receptor in primary cultures of canine stromal and epithelial prostatic cells.

METHODS

Expression and secretion of PTHrP and the PTH/PTHrP receptor was measured in homogeneous primary cultures of canine prostatic stromal and epithelial cells using immunohistochemistry, Northern blots, radioimmunoassay, RT-PCR, and receptor stimulation assays.

RESULTS

Epithelial and stromal cells expressed and secreted abundant PTHrP, but PTH/PTHrP receptor expression was not detected in either cell type.

CONCLUSIONS

PTHrP expression by stromal and epithelial prostatic cells and the absence of the PTH/PTHrP (type I) receptor suggest that some functions previously proposed for PTHrP in the prostate are unlikely. The separation procedure presented is a valuable tool for studying the role and regulation of PTHrP in the prostate.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Neuroendocrine cells of the prostate and neuroendocrine differentiation in prostatic carcinoma: a review of morphologic aspects

Neuroendocrine cells of the prostate are intraepithelial regulatory cells that secrete serotonin and a variety of peptide hormones. It is hypothesized that these cells regulate both growth and differentiation, as well as exocrine secretory activity through endocrine, paracrine, neurocrine, and lumenocrine mechanisms. Neuroendocrine differentiation in prostatic carcinoma occurs as pure neuroendocrine malignancies, such as small-cell carcinoma and carcinoid/carcinoid-like tumors, as well as focal neuroendocrine differentiation in a more conventional prostatic adenocarcinoma. Neuroendocrine differentiation in prostatic carcinoma may have diagnostic and prognostic significance.

Calcitonin receptor mRNA expression in TT cells: effect of dexamethasone

Among the four isoforms of the calcitonin receptor (CTR) described in humans, two differ by the presence of h-CTR1 or absence of h-CTR2 of 16 amino acids in the first intracellular loop. Both receptors are biologically active. The TT cell line derived from a human medullary carcinoma of the thyroid is characterized by the secretion of large amounts of calcitonin. We have recently shown that this cell line expresses h-CTR2. In the present work we have studied the expression of CTR during TT cell proliferation and used dexamethasone to modify calcitonin expression in order to establish if an autocrine regulation involving calcitonin and its receptor was functional in the TT cells. The expression of this receptor and of calcitonin during TT cell proliferation was studied by reverse transcriptase-polymerase chain reaction (RT-PCR). Dexamethasone, a potent inhibitor of TT cell proliferation, levels (day 6 of culture) specifically increased receptor levels from day 8 onwards. CT peptide and CT mRNA levels decreased or were similar during experimental time. CTR regulation by glucocorticoids is suggested in TT cells. Autocrine regulation of CTR is also suggested by relation between CT mRNA levels and CTR mRNA.