Parathyroid hormone-related protein is expressed by prostatic neuroendocrine cells

AMPK/SIRT1 signaling through p38MAPK mediates Interleukin-6 induced neuroendocrine differentiation of LNCaP prostate cancer cells

Neuroendocrine Prostate Cancer (NEPC) is an aggressive form of androgen independent prostate cancer (AIPC), correlated with therapeutic resistance. Interleukin (IL)-6 promotes proliferation and neuroendocrine differentiation (NED) of androgen dependent LNCaP cells. We treated LNCaP cells with IL-6 and observed for in vitro NED of cells and also expression of NE markers βIII tubulin, neuron-specific enolase (NSE) and chromogranin A (ChA). Here we investigated the proteins and/or pathways involved in NED of LNCaP cells induced by IL-6 and characterized their role in NED of PCa cells. We found that the altered proteins modulated AMPK signaling pathway in NE cells. Remarkably, IL-6 induces NED of LNCaP cells through activation of AMPK and SIRT1 and also both of these are co-regulated while playing a predominant role in NED of LNCaP cells. Of the few requirements of AMPK-SIRT1 activation, increased eNOS is essential for NED by elevating Nitric oxide (NO) levels. Pleiotropic effects of NO ultimately regulate p38MAPK in IL-6 induced NED. Hence, IL-6 induced AMPK-SIRT1 activation eventually transfers its activation signals through p38MAPK for advancing NED of LNCaP cells. Moreover, inactivation of p38MAPK with specific inhibitor (SB203580) attenuated IL-6 induced NED of LNCaP cells. Therefore, IL-6 promotes NED of PCa cells via AMPK/SIRT1/p38MAPK signaling. Finally, targeting AMPK-SIRT1 or p38MAPK in androgen independent PC3 cells with neuroendocrine features reversed their neuroendocrine characteristics. Taken together these novel findings reveal that targeting p38MAPK mitigated NED of PCa cells, and thus it can be a favorable target to overcome progression of NEPC.

Neuroendocrine Differentiation in Prostatic Malignancy

Neuroendocrine differentiation in prostatic malignancy is receiving considerable attention; this occurs commonly as a “focal” histological variant and, most rarely, in the form of small cell carcinoma (“oat cell carcinoma”) and carcinoid tumor. In prostate cancer, neuroendocrine differentiation may be the response to androgen deprivation and neuroendocrine products, either biogenic amines or peptides, have been shown to stimulate proliferation of androgen-ablation refractory cancer cells. Serum chromogranins, neuron-specific enolase and other neuroendocrine products as well as 111-In-chromogranin A “three step” immunoscintigraphy and somatostatin-receptor scintigraphy may be useful for predicting tumor behaviour and patient prognosis.

Several of the neuroendocrine products, particularly somatostatin analogues, are candidates for new therapeutic approaches. The paper aims to outline the advances in this field on the basis of the review of the literature.

Dual Paraneoplastic Endocrine Syndromes Heralding Onset of Extrapulmonary Small Cell Carcinoma: A Case Report and Narrative Review

OBJECTIVE

Extrapulmonary small cell carcinoma (EPSCC) is rare and frequent metastases at presentation can complicate efforts to identify a site of origin. In particular, SCC comprises <1% of prostate cancers and has been implicated in castration resistance.

METHODS

Clinical, laboratory, imaging, and pathology data are presented.

RESULTS

A 56-year-old man with locally advanced prostate adenocarcinoma on androgen deprivation therapy presented with a clogged nephrostomy tube. Laboratory results included calcium 13.8 mg/dL (8.5-10.5 mg/dL), albumin 3.6 g/dL (3.5-5 mg/dL), and potassium 2.8 mmol/L (3.5-5.2 mmol/L). Hypercalcemia investigation revealed intact PTH 19 pg/mL (16-87 pg/mL), 25-OH vitamin D 15.7 ng/mL (>30 ng/mL), and PTH-related peptide (PTHrP) 63.4 pmol/L (<2.3 pmol/L). Workup for hypokalemia yielded aldosterone 5.3 ng/dL (<31 ng/dL), renin 0.6 ng/mL/h (0.5-4 ng/mL/h), and 6:00 a.m. cortisol 82 µg/dL (6.7-22.6 µg/dL) with ACTH 147 pg/mL (no ref. range). High-dose Dexamethasone suppression testing suggested ACTH-dependent ectopic hypercortisolism. Contrast-enhanced CT findings included masses in the liver and right renal pelvis, a heterogeneous enlarged mass in the region of the prostate invading the bladder, bilateral adrenal thickening, and lytic lesions in the pelvis and spine. Liver biopsy identified epithelioid malignancy with Ki proliferation index 98% and immunohistochemical staining positive for synaptophysin and neuron-specific enolase, compatible with high-grade small cell carcinoma. Staining for ACTH was negative; no stain for CRH was available. Two weeks after chemotherapy, 6:00 a.m. cortisol normalized and CT scans showed universal improvement.

CONCLUSION

Extensive literature details paraneoplastic syndromes associated with SCC, but we report the first case of EPSCC diagnosed due to onset of dual paraneoplastic syndromes.

Prospective study on the relationship between clinical efficacy of secondary hormone therapy with flutamide and neuroendocrine differentiation in patients with relapsed prostate cancer after first line hormone therapy

OBJECTIVE

The aim of this study was to prospectively verify the relationship between the clinical efficacies of secondary hormone therapy for castration-resistant prostate cancer (CRPC) following first line hormone therapy and neuroendocrine differentiation (NED).

MATERIAL AND METHODS

Forty-six consecutive patients with CRPC following first line hormone therapy who were treated with flutamide as secondary hormone therapy were prospectively assessed with a median follow-up of 21 months. Serum chromogranin A (CgA), as a marker of NED, was measured using an immunoradiometric assay.

RESULTS

Of the 46 patients, 22 (48%) responded to the secondary hormone therapy as a 50% or more reduction from baseline prostate-specific antigen (PSA) with a median response duration of 9.2 months. The PSA response group was correlated with significantly favorable cancer-specific survival (CSS) (92% vs 59% at 5 years, p = 0.0146) compared with the non-response group. Above-normal CgA levels at study entry were detected in 15 patients (33%), but no association with CSS was identified. Data on CgA kinetics were available in 35 patients. The CgA levels before and at 3 months during the treatment were similar. However, eight patients (23%) with an increase in CgA level of a quarter or more from baseline had a tendency for worse CSS (63% vs 84% at 5 years, p = 0.0507) compared with the remaining patients.

CONCLUSION

Within limitations, in this study secondary hormone therapy with flutamide was effective for CRPC following first line hormone therapy. The above-normal CgA level in the first hormone resistance phase is mostly unrelated to prognosis. However, some patients with a remarkable increase in CgA in a short duration may have an unfavorable prognosis caused by NED as well.

Parathyroid hormone-related protein regulates integrin α6 and β4 levels via transcriptional and post-translational pathways

Parathyroid hormone-related protein (PTHrP) enhances prostate cancer (CaP) growth and metastasis in vivo. PTHrP also increases cell survival and migration, and upregulates pro-invasive integrin α6β4 expression. We used the human CaP cell lines C4-2 and PC-3 as model systems to study the mechanisms via which PTHrP regulates α6β4 levels. We report that PTHrP regulates α6 and β4 levels via a transcriptional pathway; β4 regulation involves the NF-κB pathway. PTHrP also regulates β4 levels at the post-translational level. PTHrP inhibits caspase-3 and -7 activities. Post-translational regulation of β4 by PTHrP is mediated via attenuation of its proteolytic cleavage by these caspases. Since α6 dimerizes with β4, increased β4 levels result in elevated α6 levels. Suppressing β4 using siRNA attenuates the effect of caspase inhibition on apoptosis and cell migration. These results provide evidence of a link between PTHrP, integrin α6β4 levels as a function of caspase activity, and cell survival and migration. Targeting PTHrP in CaP cancer, thereby reversing the effect on caspase activity and α6β4 levels, may thus prove therapeutically beneficial.

1,25-Dihydroxyvitamin D(3) regulates PTHrP expression via transcriptional, post-transcriptional and post-translational pathways

Parathyroid hormone-related protein (PTHrP) increases the growth and osteolytic potential of prostate cancer cells, making it important to control PTHrP expression. PTHrP expression is suppressed by 1,25-dihydroxyvitamin D(3) (1,25D). The aim of this study was to identify the pathways via which 1,25D exerts these effects. Our main findings are that 1,25D regulates PTHrP levels via multiple pathways in PC-3 and C4-2 (human prostate cancer) cell lines, and regulation is dependent on VDR expression. The human PTHrP gene has three promoters (P); PC-3 cells preferentially utilize P2 and P3, while C4-2 cells preferentially utilize P1. 1,25D regulates PTHrP transcriptional activity from both P1 and P3. The 1,25D-mediated decrease in PTHrP mRNA levels also involves a post-transcriptional pathway since 1,25D decreases PTHrP mRNA stability. 1,25D also suppresses PTHrP expression directly at the protein level by increasing its degradation. Regulation of PTHrP levels is dependent on VDR expression, as using siRNAs to deplete VDR expression negates the 1,25D-mediated downregulation of PTHrP expression. These results indicate the importance of maintaining adequate 1,25D levels and VDR status to control PTHrP levels.

Regulation of bombesin-stimulated cyclooxygenase-2 expression in prostate cancer cells

Background

Cyclooxygenase-2 (COX-2) and the bombesin (BBS)-like peptide, gastrin-releasing peptide (GRP), have been implicated in the progression of hormone-refractory prostate cancer; however, a mechanistic link between the bioactive peptide and COX-2 expression in prostate cells has not been made.

Results

We report that BBS stimulates COX-2 mRNA and protein expression, and the release of prostaglandin E₂ from the GRP receptor (GRPR)-positive, androgen-insensitive prostate cancer cell line, PC-3. BBS-stimulated COX-2 expression is mediated, in part, by p38^MAPK and PI3 kinase (PI3K)/Akt pathways, and blocked by a GRPR antagonist. The PI3K/Akt pathway couples GRPR to the transcription factor, activator protein-1 (AP-1), and enhanced COX-2 promoter activity. Although BBS stimulates nuclear factor-kappaB (NF-κB) in PC-3, NF-κB does not regulate GRPR-mediated COX-2 expression. The p38^MAPK pathway increases BBS-stimulated COX-2 expression by slowing the degradation of COX-2 mRNA. Expression of recombinant GRPR in the androgen-sensitive cell line LNCaP is sufficient to confer BBS-stimulated COX-2 expression via the p38^MAPK and PI3K/Akt pathways.

Conclusions

Our study establishes a mechanistic link between GRPR activation and enhanced COX-2 expression in prostate cancer cell lines, and suggests that inhibiting GRPR may, in the future, provide an effective therapeutic alternative to non-steroidal anti-inflammatory drugs for inhibiting COX-2 in patients with recurrent prostate cancer.

Hypercalcemia in Prostate Cancer with Positive Neuron‐Specific Enolase Stain

Hypercalcemia is a common complication of malignant diseases with or without bone metastasis. Hypercalcemia in prostate cancer is rarely seen. The exact mechanism of prostate cancer-related hypercalcemia is still uncertain. Secretion of parathyroid hormone-related peptides (PTH-rP) is thought to be one of the possible mechanisms. We reported a rare case of prostate cancer with hypercalcemia (13 mg/dL). Bone marrow biopsy showed metastatic adenocarcinoma. The cells were also positive for neuron-specific enolase, which is the specific marker for neuroendocrine cell. The finding suggested that the prostate cancer cell derived from the neuroendocrine cell, which might synthesize PTH-rP and be responsible for the observed hypercalcemia.

EB1089 inhibits the parathyroid hormone-related protein-enhanced bone metastasis and xenograft growth of human prostate cancer cells

Parathyroid hormone-related protein (PTHrP) plays a major role in prostate carcinoma progression and bone metastasis. Once prostate cancers become androgen-independent, treatment options become limited. Vitamin D analogues represent a potentially valuable class of agents in this clinical context. Using the prostate cancer cell line C4-2 as a model, we studied the effects of PTHrP and the noncalcemic vitamin D analogue EB1089 on markers of prostate cancer cell progression in vitro and in vivo. C4-2 is a second-generation androgen-independent LNCaP subline that metastasizes to the lymph nodes and bone when injected into nude mice and produces mixed lytic/blastic lesions, mimicking the in vivo situation. We report that PTHrP increases cell migration and invasion, and that a pathway via which EB1089 inhibits these processes is through down-regulation of PTHrP expression. PTHrP also increases anchorage-independent cell growth in vitro and xenograft growth in vivo; EB1089 reverses these effects. The in vivo PTHrP effects are accompanied by increased tumor cell proliferation and survival. Treatment with EB1089 reverses the proliferative but not the antiapoptotic effects of PTHrP. PTHrP also increases intratumor vessel density and vascular endothelial growth factor expression; EB1089 reverses these effects. Intracardially injected C4-2 cells produce predominantly osteoblastic lesions; PTHrP overexpression decreases the latency, increases the severity and alters the bone lesion profile to predominantly osteolytic. EB1089 largely reverses these PTHrP effects. A direct correlation between PTHrP immunoreactivity and increasing tumor grade is observed in human prostate cancer specimens. Thus, decreasing PTHrP production by treatment with vitamin D analogues may prove therapeutically beneficial for prostate cancer.

Parathyroid hormone-related protein regulates cell survival pathways via integrin alpha6beta4-mediated activation of phosphatidylinositol 3-kinase/Akt signaling

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissues and cancer cell lines. PTHrP enhances tumor cell growth and metastasis in vivo and up-regulates proinvasive integrin alpha6beta4 expression in vitro. Hallmarks of malignant tumor cells include resistance to apoptosis and anchorage-independent cell growth. In this study, we used the human prostate cancer cell lines C4-2 and PC-3 as model systems to study the effects of PTHrP on these processes. We report that PTHrP protects these cells from doxorubicin-induced apoptosis and promotes anchorage-independent cell growth via an intracrine pathway. Conversely, autocrine/paracrine PTHrP action increases apoptosis in C4-2 cells and has no effect on apoptosis in PC-3 cells. The intracrine effects of PTHrP on apoptosis are mediated via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. PTHrP also affects the phosphorylation state of Akt substrates implicated in apoptosis suppression, including glycogen synthase kinase-3 and Bad. The prosurvival effects of PTHrP are accompanied by increases in the ratio of antiapoptotic to proapoptotic members of the Bcl-2 family and in levels of c-myc. PTHrP also increases nuclear factor-kappaB activity via a PI3K-dependent pathway. Integrin alpha6beta4 is known to activate PI3K. Here, we also show that knockdown of integrin alpha6beta4 negates the PTHrP-mediated activation of the PI3K/Akt pathway. Taken together, these observations provide evidence of a link between PTHrP and the PI3K/Akt signaling pathway through integrin alpha6beta4, resulting in the activation of survival pathways. Targeting PTHrP production in prostate cancer may thus prove therapeutically beneficial.

Detection of circulating tumor cells in prostate cancer patients: methodological pitfalls and clinical relevance

Disseminated malignancy is the major cause of prostate cancer-related mortality. Circulating tumor cells (CTCs) are essential for the establishment of metastasis. Various contemporary and molecular methods using prostate-specific biomarkers have been applied to detect extraprostatic disease that is undetectable by conventional imaging techniques, assessing the risk for disease recurrence after therapy of curative intent. However, the clinical relevance of CTC detection is still controversial. We review current literature regarding molecular methods used for the detection of CTCs in the peripheral blood and bone marrow biopsies of patients with prostate cancer, and we discuss the methodological pitfalls that influence the clinical significance of molecular staging.

PTHrP contributes to the anti-proliferative and integrin alpha6beta4-regulating effects of 1,25-dihydroxyvitamin D(3)

Parathyroid hormone-related protein (PTHrP) increases the growth and metastatic potential of prostate cancer cells, making it important to control PTHrP expression in these cells. 1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] suppresses PTHrP expression and exerts an anti-proliferative effect in prostate carcinoma cells. We used the human prostate cancer cell line C4-2 as a model system to ask whether down-regulation of PTHrP expression by 1,25(OH)(2)D(3) plays a role in the anti-proliferative effects of 1,25(OH)(2)D(3). Since PTHrP increases the expression of the pro-invasive integrin alpha6beta4, we also asked whether 1,25(OH)(2)D(3) decreases integrin alpha6beta4 expression in C4-2 cells, and whether modulation of PTHrP expression by 1,25(OH)(2)D(3) plays a role in the effects of 1,25(OH)(2)D(3) on integrin alpha6beta4 expression. Two strategies were utilized to modulate PTHrP levels: overexpression of PTHrP (-36 to +139) and suppression of endogenous PTHrP expression using siRNAs. We report a direct correlation between PTHrP expression, C4-2 cell proliferation and integrin alpha6beta4 expression at the mRNA and cell surface protein level. Treatment of parental C4-2 cells with 1,25(OH)(2)D(3) decreased cell proliferation and integrin alpha6 and beta4 expression. These 1,25(OH)(2)D(3) effects were significantly attenuated in cells with suppressed PTHrP expression. 1,25(OH)(2)D(3) regulates PTHrP expression via a negative vitamin D response element (nVDRE) within the noncoding region of the PTHrP gene. The effects of 1,25(OH)(2)D(3) on cell proliferation and integrin alpha6beta4 expression were significantly attenuated in cells overexpressing PTHrP (-36 to +139), which lacks the nVDRE. These findings suggest that one of the pathways via which 1,25(OH)(2)D(3) exerts its anti-proliferative effects is through down-regulation of PTHrP expression.

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

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

Clinical implications of neuroendocrine differentiation in prostate cancer

The cellular signaling pathways of the prostate play a central role in the induction, maintenance, and progression of prostate cancer (CaP). Neuroendocrine (NE) cells demonstrate attributes that suggest they are an integral part of these signaling cascades. We summarize what is known regarding NE cells in CaP focusing on NE cellular transdifferentiation. This significant event in CaP progression appears to be accelerated by androgen deprivation (AD) treatment. We examine biochemical pathways that may impact NE differentiation in a chronological manner focusing on AD therapy (ADT) as a central event in inducing androgen-independent CaP. Our analysis is limited to the common adenocarcinoma pattern of CaP and excludes small-cell and carcinoid prostatic variants. In conclusion, we speculate on the future of treatment and research in this area.

Immunohistochemical and ultrastructural features of neuroendocrine differentiated carcinomas of the prostate: an immunoelectron microscopic study

The purpose of this study was to further define the immunohistochemical and ultrastructural characteristics of neuroendocrine (NE) differentiated prostatic carcinomas. Seventy-seven specimens were obtained from prostatic carcinoma tumors during prostatectomy, transurethral resection of prostate or biopsy in 77 prostate cancer patients, and analyzed by immunohistochemical staining for chromogranin A (CgA). Nine of these tumors were also studied by elctron microscopy and 4 were examined by pre-embedding immunoelectron microscopy. CgA-stained cells were detected in 36 tumors (47%). Clinically advanced tumors or tumors with higher histological grades were associated with increased NE differentiation. Three of the tumors studied by electron microscopy contained cells showing unequivocal NE differentiation revealed by the presence of neurosecretory granules, while the poorly NE-differentiated malignant cells contained pleomorphic granules, which were lysosomal-like rather than NE-type granules. Immunoelectron microscopy demonstrated the presence of CgA immunoreactivity on the pleomorphic granules in the poorly differentiated malignant glands. This study suggests that NE-differentiated malignant cells in prostate cancer tissues may induce aggressive behavior in adjacent proliferating neoplastic cells via a paracrine mechanism.

Neuroendocrine differentiation in hormone refractory prostate cancer following androgen deprivation therapy

OBJECTIVE

To evaluate the relationship between neuroendocrine differentiation (NED) status and hormone refractory prostate cancer (HRPC) following hormone therapy based on immunohistochemical study.

METHODS

Seventy-two prostate cancer specimens obtained at radical prostatectomy and 21 prostate cancer autopsy specimens from patients who died from HRPC after androgen deprivation therapy were examined for NED status using an antibody against chromogranin A. These specimens were classified into 3 arms: 38 radical prostatectomy specimens from patients with no neoadjuvant hormone therapy (Group 1); 34 from patients with neoadjuvant hormone therapy for 3 to 6 months (Group 2); and 21 autopsy specimens from patients with HRPC following androgen deprivation therapy for more than 1 year (Group 3). Staining of prostatic carcinoma was scored as: 0 = no staining; 1 = staining cells <10%; 2 = staining cells 10-20%; and 3 = staining cells >20%. Differences in scores among the groups were compared using the Kruskal-Wallis rank test. Multivariate analysis using a logistic regression model was performed to examine whether NED status was associated with pathological stage (pT), grade and group.

RESULTS

Forty-nine (53%) tumors had CgA stained cells. NED status increased with longer duration of hormone therapy (p<0.0001). The mean staining score (and standard deviation) was 0.4+/-0.7 in Group 1, 0.7+/-0.7 in Group 2, and 1.4+/-1.1 in Group 3, respectively. By multivariate analysis Group 3 had a relative risk of 5.46 (95%CI 1.28-23.29) for NED compared to the other groups. But other variables were not related to NED. HRPC following Long-term hormonal therapy was the only independent predictor of NED.

CONCLUSIONS

The results of this study demonstrated that NED status was significantly increased in patients with HRPC following long-term androgen deprivation therapy, but it could not be discriminate whether the increase of NED is attributable to condition of hormone refractoriness or long-term hormonal therapy.

Presence of neuroendocrine cells during postnatal development in rat prostate: Immunohistochemical, molecular, and quantitative study

BACKGROUND

This work was undertaken to study the prostate neuroendocrine cells (PNEC) during the post-natal development of rats.

METHODS

Forty male Wistar rats (pre-pubertals, pubertals, young, and aged adults) were used for immunohistochemistry of chromogranin A (cgA), serotonin (SER), and protein gene product 9.5 (PGP9.5). They were also evaluated for numerical cell density (NV SER) and PNEC number per prostate (N SER). Five additional young adult rats were used for a RT-PCR study (mRNA cgA detection).

RESULTS

Weak immunoreactivity to cgA was observed in pubertal rats. No PNEC immunostained to PGP 9.5 was observed. Cells expressing SER were detected in all the groups exclusively located in periurethral ducts. The NV SER increased significantly in pubertal animals. In aged animals, it decreased to levels observed in pre-pubertal rats. The N SER increased significantly from pre-pubertal to young adults, decreasing in aged adults. There was weak production of cgA mRNA, with more expression in the dorsal prostate.

CONCLUSIONS

PNEC differ in rats when compared to humans: they are weakly immunopositive to cgA, do not express PGP 9.5, only show immunoreactivity to SER, and do not appear in acini. The changes in the amount of rat PNEC during the post-natal development suggest an androgenic influx. PNEC might regulate the contractility of periurethral ducts.

Parathyroid hormone-related protein upregulates integrin expression via an intracrine pathway in PC-3 prostate cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.

PTH-related protein modulates PC-3 prostate cancer cell adhesion and integrin subunit profile

Parathyroid hormone-related protein (PTHrP), which has been localized in prostate cancer tissue and cell lines, plays a role in the development of bone metastases, a frequent complication in prostate cancer patients. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. The present experiments examined the ability of PTHrP to influence adhesion of the human prostate cancer cell line PC-3 to several ECM proteins found in normal tissues. Clonal PC-3 cells induced to overexpress PTHrP by stable transfection with PTHrP complementary DNA showed significantly higher adhesion to collagen type 1, fibronectin, and laminin than control (empty vector-transfected) cells. PTHrP-overexpressing cells also exhibited higher expression of the alpha1, alpha5, alpha6, and beta4 integrin subunits. These results suggest that PTHrP may play a role in prostate tumor invasion and metastasis by influencing cell adhesion to the ECM via upregulation of specific integrin subunits.

Parathyroid hormone-related protein enhances PC-3 prostate cancer cell growth via both autocrine/paracrine and intracrine pathways

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and positively influences primary prostate tumor growth in vivo. The human prostate cancer cell line PC-3, which expresses functional PTH/PTHrP receptors, was used as a model to study the effects of PTHrP on prostate cancer cell growth. Addition of PTHrP (1-34), (1-86), and (1-139) increased cell number and [3H]thymidine incorporation; these effects were reversed by anti-PTHrP antiserum. This antiserum also decreased endogenous PC-3 cell growth. Clonal PTHrP-overexpressing PC-3 cell lines also showed enhanced cell growth and [3H]thymidine incorporation and were enriched in the G2+M phase of the cell cycle, suggesting an effect of PTHrP on mitosis. Overexpression of PTHrP with the nuclear localization sequence (NLS) deletion partially reversed the growth-stimulatory effects. The growth rate of these cells was midway between that of wild-type PTHrP-overexpressing and control cells, presumably because NLS-mutated PTHrP is still secreted and acts through the cell surface PTH/PTHrP receptor. In contrast to NLS-mutated PTHrP, wild-type protein showed preferential nuclear localization. These results suggest that the proliferative effects of PTHrP in PC-3 cells are mediated via both autocrine/paracrine and intracrine pathways, and that controlling PTHrP production in prostate cancer may be therapeutically beneficial.

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.

Parathyroid hormone related peptide and receptor expression in paired primary prostate cancer and bone metastases

Parathyroid hormone-related peptide is a regulatory protein implicated in the pathogenesis of bone metastases, particularly in breast carcinoma. Parathyroid hormone-related peptide is widely expressed in primary prostate cancers but there are few reports of its expression in prostatic metastases. The aim of this study was to examine the expression of parathyroid hormone-related peptide and its receptor in matched primary and in bone metastatic tissue from patients with untreated adenocarcinoma of the prostate. Eight-millimetre trephine iliac crest bone biopsies containing metastatic prostate cancer were obtained from 14 patients from whom matched primary tumour tissue was also available. Histological grading was performed by an independent pathologist. The cellular location of mRNA for parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor was identified using in situ hybridization with (35)S-labelled probe. Expression of parathyroid hormone-related peptide and its receptor was described as uniform, heterogenous or negative within the tumour cell population. Parathyroid hormone-related peptide expression was positive in 13 out of 14 primary tumours and in all 14 metastases. Receptor expression was evident in all 14 primaries and 12 out of 14 metastases. Co-expression of parathyroid hormone-related peptide and parathyroid hormone-related peptide receptor was common (13 primary tumours, 12 metastases). The co-expression of parathyroid hormone-related peptide and its receptor suggest that autocrine parathyroid hormone-related peptide mediated stimulation may be a mechanism of escape from normal growth regulatory pathways. The high frequency of parathyroid hormone-related peptide expression in metastases is consistent with a role in the pathogenesis of bone metastases.

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

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

Histochemical analysis of heme degradation enzymes

Histochemical analysis can be used to study the cellular localization, expression, and regulation of enzymes responsible for catabolism of the heme molecule. This unit describes protocols for assessing the expression and regulation of specific HO-1 and HO-2 mRNAs by in situ hybridization using digoxigenin-tagged probes. Immunohistochemistry is used to visualize specific cellular sites of HO-1 and HO-2 protein expression.

Correlation between neovascularisation and neuroendocrine differentiation in prostatic carcinoma

Neuroendocrine (NE) differentiated tumor cells are found in almost all prostatic carcinomas. Prostatic carcinomas with a high NE differentiation have a poor prognosis and increased metastatic potential. A relationship between the neovascularisation density in the tumor and the metastatic potential in prostatic carcinoma is well known. NE cells and microvessels were demonstrated immunohistochemically on 102 radical prostatectomy specimens using antibodies against Chromogranin A and CD34. Standard areas (7.9 mm2) of maximal Chromogranin A expression and highest vascularisation were determined and topographically related by light microscopy. Area density of microvessels was evaluated morphometrically. NE tumor cells were present in all prostatic carcinomas studied. High grade prostatic carcinomas expressed significantly more NE tumor cells and exhibited a higher neovascularisation than low grade carcinomas. There was significantly higher neovascularisation in high grade tumors with many, as compared to high grade tumors with few, NE tumor cells. Poorer pathological staging correlated with increased neovascularisation and stronger NE differentiation. A topographical relationship between the area of maximal NE tumor cells and the area of highest neovascularisation was found in 80.4% of all cases. An analysis of variance revealed a large number of NE tumor cells as the only predictor of an increased neovascularisation (p = 0.0006). These observations support the concept that increased neovascularisation is influenced not only by poor pathological grading but also by a high NE differentiation.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Osteomimetic properties of prostate cancer cells: a hypothesis supporting the predilection of prostate cancer metastasis and growth in the bone environment

BACKGROUND

Unlike most other malignancies, prostate cancer metastasizes preferentially to the skeleton and elicits osteoblastic reactions.

METHODS

We present a hypothesis, based upon results obtained from our laboratory and others, on the nature of progression of prostate cancer cells and their predilection to growth and metastasis in the bone microenvironment. We propose the hypothesis that osseous metastatic prostate cancer cells must be osteomimetic in order to metastasize, grow, and survive in the skeleton. The reciprocal interaction between prostate cancer and bone stromal growth factors, including basic fibroblast growth factor (bFGF), hepatocyte growth factor/scatter factor (HGF/SF), and especially the insulin growth factor (IGF) axis initiates bone tropism, and is enhanced by prostate secreted endothelin-1 (ET-1) and urokinase-type plasminogen activator (uPA). Growth factors and peptides that have differentiating activity, such as transforming growth factor beta (TGF-beta), parathyroid hormone-related protein (PTH-rp), and the bone morphogenetic proteins (BMPs), can shift local homeostasis to produce the characteristic blastic phenotype, via interaction with prostate-secreted human kalikrein 2 (hK2), and prostate-specific antigen (PSA). This proposal asserts that altering the expression of certain critical transcription factors, such as Cbfa and MSX in prostate cancer cells, which presumably are under the inductive influences of prostate or bone stromal cells, can confer profiles of gene expression, such as osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP), that mimic that of osteoblasts.

RESULTS AND CONCLUSIONS

Elucidation of common proteins, presumably driven by the same promoters, expressed by both prostate cancer and bone stromal cells, could result in the development of novel preventive and therapeutic strategies for the treatment of prostate cancer skeletal metastasis. Agents developed using these strategies could have the potential advantage of interfering with growth and enhancing apoptosis in both prostate cancer and bone stromal compartments. The selective application of gene therapy strategy, driven by tissue-specific and tumor-restricted promoters for the safe delivery and expression of therapeutic genes in experimental models of prostate cancer metastasis, is discussed.

Neuroendocrine differentiation in prostatic carcinoma

BACKGROUND

Information is presented on prostatic neuroendocrine cells and neuroendocrine differentiation in prostatic carcinoma. The prognostic and therapeutic implications of neuroendocrine differentiation in prostatic carcinoma are reviewed.

METHODS

Data are presented that support the intriguing link between neuroendocrine differentiation, tumor progression, and androgen-independent prostate cancer. The hormones, and the receptors, expressed by prostatic neuroendocrine cells are investigated in order to elucidate their significance for prognosis and therapy.

RESULTS

The prognostic significance of neuroendocrine differentiation in prostatic malignancy has been controversial, but recent studies employing markers such as chromogranin A and neuron-specific enolase suggest that neuroendocrine differentiation, as reflected by increased tissue expression and/or blood levels of these neuroendocrine secretory products, correlates with poor prognosis, tumor progression, and androgen-independence. Since all malignant neuroendocrine cells are devoid of androgen receptors and since neuroendocrine phenotypic expression is not suppressed by androgen ablation, clonal propagation of androgen receptor-negative neuroendocrine cells may play an important role in the pathway towards the androgen-independent state of prostatic carcinoma. This would have significant implications for the treatment of prostate cancer, as several of the hormones known to be expressed by neuroendocrine-differentiated, malignant prostatic cells are potential candidates for drug therapy. A limited number of hormones have been tested in this context, in particular somatostatin, bombesin, and serotonin.

CONCLUSIONS

Neuroendocrine differentiation in carcinoma of the prostate appears to be associated with poor prognosis, tumor progression, and the androgen-independent state, for which there is currently no successful therapy. Therefore, new therapeutic protocols and trials need to be developed to test drugs based on neuroendocrine hormones and/or their antagonists. An evaluation of this new therapeutic approach against prostatic carcinoma with neuroendocrine differentiation, including hormone-refractory cancer, is easily justified, since these tumors are unresponsive to current modes of therapy.

Kinetics of neuroendocrine differentiation in an androgen-dependent human prostate xenograft model

It was previously shown in the PC-295 xenograft that the number of chromogranin A (CgA)-positive neuroendocrine (NE) cells increased after androgen withdrawal. NE cells did not proliferate and differentiated from G0-phase-arrested cells. Here we further characterized NE differentiation, androgen receptor status, and apoptosis-associated Bcl-2 expression in the PC-295 model after androgen withdrawal to assess the origin of NE cells. PC-295 tumor volumes decreased by 50% in 4 days. Intraperitoneal bromodeoxyuridine (BrdU) incorporation and MIB-1 labeling decreased to 0%, and the apoptosis was maximal at day 4. Androgen receptor expression and prostate-specific antigen (PSA) serum levels decreased rapidly within 2 days. The number of NE cells increased 6-fold at day 4 and 30-fold at day 7. Five and ten percent of the CgA-positive cells were BrdU positive after continuous BrdU labeling for 2 and 4 days, respectively. However, no MIB-1 expression was observed in CgA-positive cells. NE cells expressed the regulated secretory pathway marker secretogranin III but were negative for androgen receptor and Bcl-2. Bcl-2 expression did increase in the non-NE tumor cells. In conclusion, androgen withdrawal leads to a rapid PC-295 tumor regression and a proliferation-independent induction of NE differentiation. The strictly androgen-independent NE cells that were still present after 21 days differentiated mainly from G0-phase-arrested 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.

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

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

Parathyroid hormone-related protein is not an autocrine growth factor for normal prostatic epithelial cells

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is the primary factor responsible for humoral hypercalcemia of malignancy. The hypercalcemic actions of PTHrP occur via stimulation of renal distal tubular calcium reabsorption and increased osteoclastic bone resorption. These effects of PTHrP are thought to be mediated through a common parathyroid hormone (PTH)/PTHrP receptor. In addition to the well-established role of PTHrP in bone remodeling, PTHrP is believed to be an important mediator of cellular growth and differentiation in a number of nonbony tissues. We recently demonstrated abundant expression of PTHrP in normal and malignant human prostatic tissues, and in cultured prostatic epithelial cells.

METHODS

In vitro assays were used to test growth-regulatory activity of synthetic and endogenous PTHrP peptides on normal prostatic epithelial cells.

RESULTS

No growth-regulatory activity could be demonstrated.

CONCLUSIONS

PTHrP is not an autocrine growth factor for normal prostatic epithelial cells.

Enhanced expression of parathyroid hormone-related protein in prostate cancer as compared with benign prostatic hyperplasia

Parathyroid hormone-related protein (PTHrP) has been shown to be the primary factor responsible for humoral hypercalcemia of malignancy. Recently PTHrP has been shown to be an early-response gene that may be involved in cellular proliferation or differentiation. In addition, PTHrP has been implicated in the pathogenesis of bone metastases. Bone metastases are a significant complication in patients with prostate cancer. We compared the expression of PTHrP by immunohistochemical staining using a monoclonal antibody directed against epitope between amino acids [53-64] in benign prostatic hyperplasia (BPH) with that in various stages of prostate cancer. Tissue sections were obtained on formalin-fixed paraffin-embedded blocks from BPH, well-differentiated prostate cancer, poorly differentiated prostate cancer, lymph node metastases (n = 15 each), and normal prostate (n = 2). In the normal prostate tissue there was no staining observed. In BPH, 13 of 15 tissue samples were positive for PTHrP immunoreactivity. An average of 33% of the cells stained positive with 1+ intensity. All samples from prostate cancer stained positive for PTHrP. In the samples from well-differentiated prostate cancer, an average of 87% of cells stained positive for PTHrP, whereas 100% of cells were positive in poorly differentiated and metastatic tumors. The intensity of staining was 3+ in well-differentiated tumors and 4+ in poorly differentiated tumors. Therefore, the expression of PTHrP is enhanced in prostate cancer as compared with BPH and is greater in poorly differentiated carcinoma as compared with the well-differentiated tumors. The role of PTHrP in the pathogenesis of prostate cancer deserves further study.

Prostate specific antigen cleaves parathyroid hormone-related protein in the PTH-like domain: inactivation of PTHrP-stimulated cAMP accumulation in mouse osteoblasts

PURPOSE

To determine whether parathyroid hormone-related protein (PTHrP) is a substrate of prostate-specific antigen (PSA) and how the biological activity of PTHrP may be altered by cleavage with PSA.

MATERIALS AND METHODS

Prostate-specific antigen cleavage of recombinant human PTHrP 1-141 was conducted in vitro at 37C and analyzed by SDS-PAGE. Five rounds of automated amino-terminal amino acid sequence analysis were performed on blotted PSA-cleaved PTHrP peptide fragments to determine the PSA cleavage sites. The mouse osteoblast cell line MC3T3-E1 was used to test whether PSA cleavage of PTHrP 1-141 altered its ability to stimulate cAMP production.

RESULTS

Prostate-specific antigen was found to specifically cleave PTHrP 1-141 in a time- and dose-dependent manner. Cleavage of PTHrP 1-141 by PSA generated fragments on Coomassie-stained acrylamide gels that migrated with mobilities that corresponded to 19.5, 17, 15 and < 7 kd. The preferred PSA cleavage site of PTHrP 1-141 was determined to be at the carboxyl-terminus of phenylalanine 23, consistent with chymotryptic-like enzymatic activity of PSA. Cleavage of PTHrP by PSA completely abolished the ability of PTHrP to stimulate cAMP production.

CONCLUSIONS

Cleavage of PTHrP 1-141 by PSA carboxyl-terminal to phenylalanine 23 represents a unique pattern of PTHrP processing that may be specific to the prostate. Prostate-specific antigen inactivation of the cAMP-inducing activity of PTHrP 1-141 demonstrates that PSA cleavage regulates the biological activity of PTHrP. These results have implications for the role of PTHrP in prostate cancer metastasis to bone and its subsequent regulation of bone remodeling. Study of the biological activities of the PSA-generated PTHrP peptides identified in this study merits further investigation.

Alteration of the hormonal bioactivity of parathyroid hormone-related protein (PTHrP) as a result of limited proteolysis by prostate-specific antigen

OBJECTIVES

To discover whether the proteolytic activity of prostate-specific antigen (PSA) affects the structure and function of parathyroid hormone-related protein (PTHrP), as both are abundant components of human seminal plasma.

METHODS

The ability of PTHrP to act as a substrate was studied by incubating a synthetic polypeptide, consisting of 34 amino acid residues of the amino-terminal domain of PTHrP, with purified PSA. The incubate was then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, high-pressure liquid chromatography separation, amino-terminal peptide sequencing, and mass spectrometry. The physiologic effect of the proteolytic activity of PSA on PTHrP was studied by measuring any alteration in PTHrP (1-34)-induced elevation of cyclic adenosine monophosphate (cAMP) production by UMR-106 rat osteosarcoma cells in culture. All cell culture experiments were performed with PSA and PTHrP (1-34) at physiologic concentrations. RESULTS. Our data show that PSA proteolytically cleaves PTHrP (1-34) after either residue 22 or 23, generating three peptide fragments. Both cleavages occur carboxy terminally of a phenylalanine residue. The cAMP production in rat osteosarcoma cells, induced by the amino-terminal portion of PTHrP (1-34), as a result of its structural similarity with parathyroid hormone (PTH), was abated by PSA in a dose- and time-dependent fashion. In contrast, heat-inactivated PSA had no effect on cAMP production.

CONCLUSIONS

Our study demonstrates that PTHrP is a substrate for PSA. The cleavage of the amino-terminal portion of PTHrP completely disrupts its ability to interact with the PTH/PTHrP receptor and thus inhibits its PTH-like activity. The proteolytic processing of PTHrP by PSA may play an important role in the post-translational/post-secretional regulation of prostatic PTHrP activities, which are believed to include regulation of prostate growth and differentiation.

Neuroendocrine differentiation in prostatic malignancy

BACKGROUND

The prostatic neuroendocrine cell is a regulatory cell that produces serotonin and peptide hormones. This cell is part of a more widely dispersed diffuse neuroendocrine regulatory system known as the APUD system. Focal neuroendocrine differentiation is seen in virtually all prostate carcinomas to one degree or another. Specific malignancies that are purely neuroendocrine include small cell carcinoma and carcinoid/carcinoid-like tumors. A variety of studies suggest a possible prognostic significance of neuroendocrine differentiation in prostate carcinoma.

METHODS

The literature on the prostatic neuroendocrine cell and neuroendocrine differentiation in prostate carcinoma is reviewed.

RESULTS

Based on analogy with other better studied elements of the diffuse neuroendocrine regulatory system or APUD system, as well as the morphology and specific products produced by neuroendocrine cells, it is likely that they play an important regulatory role in the prostate. Neuroendocrine differentiation may be of prognostic significance in prostate carcinoma. Mechanisms are not well characterized at this point, but the known growth factor activity of the neuroendocrine cell products, an increase in proliferation in cells surrounding neuroendocrine cells, and a lack of androgen receptor expression in neuroendocrine cells, suggest mechanisms by which they may be of prognostic significance.

CONCLUSIONS

Neuroendocrine differentiation in prostate carcinoma may be of prognostic significance, but better methods to define neuroendocrine, differentiation are necessary. The therapeutic implications of neuroendocrine differentiation in prostate carcinoma may be of significance and need to be explored further.

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.