Calcium-sensing receptor activation stimulates parathyroid hormone-related protein secretion in prostate cancer cells: role of epidermal growth factor receptor transactivation

TSPAN18 facilitates bone metastasis of prostate cancer by protecting STIM1 from TRIM32-mediated ubiquitination

BACKGROUND

Bone metastasis is a principal cause of mortality in patients with prostate cancer (PCa). Increasing evidence indicates that high expression of stromal interaction molecule 1 (STIM1)-mediated store-operated calcium entry (SOCE) significantly activates the calcium (Ca2+) signaling pathway and is involved in multiple steps of bone metastasis in PCa. However, the regulatory mechanism and target therapy of STIM1 is poorly defined.

METHODS

Liquid chromatography-mass spectrometry analysis was performed to identify tetraspanin 18 (TSPAN18) as a binding protein of STIM1. Co-IP assay was carried out to explore the mechanism by which TSPAN18 inhibits STIM1 degradation. The biological function of TSPAN18 in bone metastasis of PCa was further investigated in vitro and in vivo models.

RESULT

We identified that STIM1 directly interacted with TSPAN18, and TSPAN18 competitively inhibited E3 ligase tripartite motif containing 32 (TRIM32)-mediated STIM1 ubiquitination and degradation, leading to increasing STIM1 protein stability. Furthermore, TSPAN18 significantly stimulated Ca2+ influx in an STIM1-dependent manner, and then markedly accelerated PCa cells migration and invasion in vitro and bone metastasis in vivo. Clinically, overexpression of TSPAN18 was positively associated with STIM1 protein expression, bone metastasis and poor prognosis in PCa.

CONCLUSION

Taken together, this work discovers a novel STIM1 regulative mechanism that TSPAN18 protects STIM1 from TRIM32-mediated ubiquitination, and enhances bone metastasis of PCa by activating the STIM1-Ca2+ signaling axis, suggesting that TSPAN18 may be an attractive therapeutic target for blocking bone metastasis in PCa.

Characterizing the Role of Calcium Sensing Receptor in the Progression of Obesity-Mediated Aggressive Prostate Cancer Phenotype

Obesity increases the risk of advanced prostate cancer (PCa). The calcium sensing receptor (CaSR) has been shown to be responsive to obesity-mediated cytokines and is upregulated in metastatic PCa. This study used a novel in vitro approach, involving the exposure of PCa cells to sera, from obese or normal weight males, and to CaSR inhibitor NPS-2143. Cell viability was determined using MTT assay. MMP-9 activity and invasion were assessed using zymography and invasion chambers, respectively. Microscopy was used to visualize EMT proteins. qRT-PCR and immunoblot analysis were used to quantify changes in genes and proteins important for tumorigenesis. Exposure to obese sera increased the proliferation, and the invasive capacity of PCa cells and de-localized epithelial-mesenchymal transition markers, which were attenuated with CaSR inhibition. Exposure to obese sera upregulated mRNA expression of PTHrP and protein expression of COX-2, IL-6, and CaSR. Inhibition of CaSR downregulated the mRNA expression of PTHrP and RANK, and protein expression of pERK and TNF-α. Obesity was shown to increase invasion and upregulate the expression of genes and proteins involved in PCa tumorigenesis. CaSR inhibition downregulated the expression of several of these factors. Thus, CaSR is a potentially important protein to target in obesity-mediated PCa progression.

Mutations and clinical significance of calcium voltage-gated channel subunit alpha 1E (CACNA1E) in non-small cell lung cancer

CACNA1E is a gene encoding the ion-conducting α1 subunit of R-type voltage-dependent calcium channels, whose roles in tumorigenesis remain to be determined. We previously showed that CACNA1E was significantly mutated in patients with non-small cell lung cancer (NSCLC) who were long-term exposed to household air pollution, with a mutation rate of 19% (15 of 79 cases). Here we showed that CACNA1E was also mutated in 207 (12.8%) of the 1616 patients with NSCLC in The Cancer Genome Atlas (TCGA) datasets. At mRNA and protein levels, CACNA1E was elevated in tumor tissues compared to counterpart non-tumoral lung tissues in NSCLCs of the public datasets and our settings, and its expression level was inversely associated with clinical outcome of the patients. Overexpression of wild type (WT) or A275S or R249G mutant CACNA1E transcripts promoted NSCLC cell proliferation with activation of epidermal growth factor receptor (EGFR) signaling pathway, whereas knockdown of this gene exerted inhibitory effects on NSCLC cells in vitro and in vivo. CACNA1E increased current density and Ca2+ entrance, whereas calcium channel blockers inhibited NSCLC cell proliferation. These data indicate that CACNA1E is required for NSCLC cell proliferation, and blockade of this oncoprotein may have therapeutic potentials for this deadly disease.

Calcium sensing receptor stimulates breast cancer cell migration via the Gβγ-AKT-mTORC2 signaling pathway

Calcium sensing receptor, a pleiotropic G protein coupled receptor, activates secretory pathways in cancer cells and putatively exacerbates their metastatic behavior. Here, we show that various CaSR mutants, identified in breast cancer patients, differ in their ability to stimulate Rac, a small Rho GTPase linked to cytoskeletal reorganization and cell protrusion, but are similarly active on the mitogenic ERK pathway. To investigate how CaSR activates Rac and drives cell migration, we used invasive MDA-MB-231 breast cancer cells. We revealed, by pharmacological and knockdown strategies, that CaSR activates Rac and cell migration via the Gβγ-PI3K-mTORC2 pathway. These findings further support current efforts to validate CaSR as a relevant therapeutic target in metastatic cancer.

Osteosarcoma and Metastasis Associated Bone Degradation-A Tale of Osteoclast and Malignant Cell Cooperativity

Cancer-induced bone degradation is part of the pathological process associated with both primary bone cancers, such as osteosarcoma, and bone metastases originating from, e.g., breast, prostate, and colon carcinomas. Typically, this includes a cancer-dependent hijacking of processes also occurring during physiological bone remodeling, including osteoclast-mediated disruption of the inorganic bone component and collagenolysis. Extensive research has revealed the significance of osteoclast-mediated bone resorption throughout the course of disease for both primary and secondary bone cancer. Nevertheless, cancer cells representing both primary bone cancer and bone metastasis have also been implicated directly in bone degradation. We will present and discuss observations on the contribution of osteoclasts and cancer cells in cancer-associated bone degradation and reciprocal modulatory actions between these cells. The focus of this review is osteosarcoma, but we will also include relevant observations from studies of bone metastasis. Additionally, we propose a model for cancer-associated bone degradation that involves a collaboration between osteoclasts and cancer cells and in which both cell types may directly participate in the degradation process.

Role of Calcium Signaling in Prostate Cancer Progression: Effects on Cancer Hallmarks and Bone Metastatic Mechanisms

Advanced prostate cancers that progress to tumor metastases are often considered incurable or difficult to treat. The etiology of prostate cancers is multi-factorial. Among other factors, de-regulation of calcium signals in prostate tumor cells mediates several pathological dysfunctions associated with tumor progression. Calcium plays a relevant role on tumor cell death, proliferation, motility-invasion and tumor metastasis. Calcium controls molecular factors and signaling pathways involved in the development of prostate cancer and its progression. Such factors and pathways include calcium channels and calcium-binding proteins. Nevertheless, the involvement of calcium signaling on prostate cancer predisposition for bone tropism has been relatively unexplored. In this regard, a diversity of mechanisms triggers transient accumulation of intracellular calcium in prostate cancer cells, potentially favoring bone metastases development. New therapies for the treatment of prostate cancer include compounds characterized by potent and specific actions that target calcium channels/transporters or pumps. These novel drugs for prostate cancer treatment encompass calcium-ATPase inhibitors, voltage-gated calcium channel inhibitors, transient receptor potential (TRP) channel regulators or Orai inhibitors. This review details the latest results that have evaluated the relationship between calcium signaling and progression of prostate cancer, as well as potential therapies aiming to modulate calcium signaling in prostate tumor progression.

Serum parathyroid hormone levels in patients with chronic right heart failure

Parathyroid hormone (PTH) is a novel cardiovascular biomarker which is particularly useful for detection and assessment of heart failure (HF). However, previous studies examining PTH in heart failure have primarily focused on left HF; thus, the relationship between PTH and right HF remains unclear. The aim of the present study was to evaluate the serum PTH levels in patients with chronic right HF. A total of 154 patients with chronic right HF were enrolled in the present study. A binary logistic regression analysis model was used to assess the independent predictive value of PTH levels in chronic right HF. Partial correlative analysis was used to demonstrate the relevance of PTH levels on the parameters of assessment of right heart function. A multiple linear regression analysis model was used to evaluate the independent factors of PTH levels in patients with right HF. The results showed that the serum PTH levels in the right HF group were significantly higher compared with the control group. After adjusting for predictors of right HF, serum PTH levels were associated with right HF with an odds ratio of 1.066 (95% confidence interval: 1.030-1.102, P<0.001. Serum PTH levels were independently correlated with plasma N-terminal pro-B-type natriuretic peptide levels, right ventricular end-diastolic diameter and severity of lower extremity edema (all P<0.05). Therefore, based on the results of the present study, PTH may be a useful biomarker for detection and assessment of right HF.

Dietary Carcinogens and DNA Adducts in Prostate Cancer

Prostate cancer (PC) is the most commonly diagnosed non-cutaneous cancer and the second leading cause of cancer-related to death in men. The major risk factors for PC are age, family history, and African American ethnicity. Epidemiological studies have reported large geographical variations in PC incidence and mortality, and thus lifestyle and dietary factors influence PC risk. High fat diet, dairy products, alcohol and red meats, are considered as risk factors for PC. This book chapter provides a comprehensive, literature-based review on dietary factors and their molecular mechanisms of prostate carcinogenesis. A large portion of our knowledge is based on epidemiological studies where dietary factors such as cancer promoting agents, including high-fat, dairy products, alcohol, and cancer-initiating genotoxicants formed in cooked meats have been evaluated for PC risk. However, the precise mechanisms in the etiology of PC development remain uncertain. Additional animal and human cell-based studies are required to further our understandings of risk factors involved in PC etiology. Specific biomarkers of chemical exposures and DNA damage in the prostate can provide evidence of cancer-causing agents in the prostate. Collectively, these studies can improve public health research, nutritional education and chemoprevention strategies.

Fatty Acids and Calcium Regulation in Prostate Cancer

Prostate cancer is a widespread malignancy characterized by a comparative ease of primary diagnosis and difficulty in choosing the individualized course of treatment. Management of prostate cancer would benefit from a clearer understanding of the molecular mechanisms behind the transition to the lethal, late-stage forms of the disease, which could potentially yield new biomarkers for differential prognosis and treatment prioritization in addition to possible new therapeutic targets. Epidemiological research has uncovered a significant correlation of prostate cancer incidence and progression with the intake (and often co-intake) of fatty acids and calcium. Additionally, there is evidence of the impact of these nutrients on intracellular signaling, including the mechanisms mediated by the calcium ion as a second messenger. The present review surveys the recent literature on the molecular mechanisms associated with the critical steps in the prostate cancer progression, with special attention paid to the regulation of these processes by fatty acids and calcium homeostasis. Testable hypotheses are put forward that integrate some of the recent results in a more unified picture of these phenomena at the interface of cell signaling and metabolism.

Recent Advances in Comprehending the Signaling Pathways Involved in the Progression of Breast Cancer

This review describes recent advances in the comprehension of signaling pathways involved in breast cancer progression. Calcium sensing receptor (CaSR), caveolae signaling, signaling referred to hypoxia-inducing factors and disturbances in the apoptotic machinery are related to more general biological mechanisms and are considered first. The others refer to signaling pathways of more specific biological mechanisms, namely the heparin/heparin-sulfate interactome, over-expression of miRNA-378a-5p, restriction of luminal and basal epithelial cells, fatty-acid synthesis, molecular pathways related to epithelial to mesenchimal transition (EMT), HER-2/neu gene amplification and protein expression, and the expression of other members of the epithelial growth factor receptor family. This progress in basic research is fundamental to foster the ongoing efforts that use the new genotyping technologies, and aim at defining new prognostic and predictive biomarkers for a better personalized management of breast cancer disease.

Association of calcium sensing receptor polymorphisms at rs1801725 with circulating calcium in breast cancer patients

BACKGROUND

Breast cancer (BC) patients with late-stage and/or rapidly growing tumors are prone to develop high serum calcium levels which have been shown to be associated with larger and aggressive breast tumors in post and premenopausal women respectively. Given the pivotal role of the calcium sensing receptor (CaSR) in calcium homeostasis, we evaluated whether polymorphisms of the CASR gene at rs1801725 and rs1801726 SNPs in exon 7, are associated with circulating calcium levels in African American and Caucasian control subjects and BC cases.

METHODS

In this retrospective case-control study, we assessed the mean circulating calcium levels, the distribution of two inactivating CaSR SNPs at rs1801725 and rs1801726 in 199 cases and 384 age-matched controls, and used multivariable regression analysis to determine whether these SNPs are associated with circulating calcium in control subjects and BC cases.

RESULTS

We found that the mean circulating calcium levels in African American subjects were higher than those in Caucasian subjects (p < 0.001). As expected, the mean calcium levels were higher in BC cases compared to control subjects (p < 0.001), but the calcium levels in BC patients were independent of race. We also show that in BC cases and control subjects, the major alleles at rs1801725 (G/T, A986S) and at rs1801726 (C/G, Q1011E) were common among Caucasians and African Americans respectively. Compared to the wild type alleles, polymorphisms at the rs1801725 SNP were associated with higher calcium levels (p = 0.006) while those at rs1801726 were not. Using multivariable linear mixed-effects models and adjusting for age and race, we show that circulating calcium levels in BC cases were associated with tumor grade (p = 0.009), clinical stage (p = 0.003) and more importantly, with inactivating mutations of the CASR at the rs1801725 SNP (p = 0.038).

CONCLUSIONS

These data suggest that decreased sensitivity of the CaSR to calcium due to inactivating polymorphisms at rs1801725, may predispose up to 20% of BC cases to high circulating calcium-associated larger and/or aggressive breast tumors.

GABABR-Induced EGFR Transactivation Promotes Migration of Human Prostate Cancer Cells

G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) act in concert to regulate cell growth, proliferation, survival, and migration. Metabotropic GABA_B receptor (GABA_BR) is the GPCR for the main inhibitory neurotransmitter GABA in the central nervous system. Increased expression of GABA_BR has been detected in human cancer tissues and cancer cell lines, but the role of GABA_BR in these cells is controversial and the underlying mechanism remains poorly understood. Here, we investigated whether GABA_BR hijacks RTK signaling to modulate the fates of human prostate cancer cells. RTK array analysis revealed that the GABA_BR-specific agonist baclofen selectively induced the transactivation of EGFR in PC-3 cells. EGFR transactivation resulted in the activation of ERK1/2 by a mechanism that is dependent on G_i/o protein and that requires matrix metalloproteinase-mediated proligand shedding. Positive allosteric modulators (PAMs) of GABA_BR, such as CGP7930, rac-BHFF, and GS39783, can function as PAM agonists to induce EGFR transactivation and subsequent ERK1/2 activation. Moreover, both baclofen and CGP7930 promoted cell migration and invasion through EGFR signaling. In summary, our observations demonstrated that GABA_BR transactivated EGFR in a ligand-dependent mechanism to promote prostate cancer cell migration and invasion, thus providing new insights into developing a novel strategy for prostate cancer treatment by targeting neurotransmitter signaling.

Overexpression of a functional calcium-sensing receptor dramatically increases osteolytic potential of MDA-MB-231 cells in a mouse model of bone metastasis through epiregulin-mediated osteoprotegerin downregulation

Introduction and Aims

Osteolytic bone metastases are observed in advanced cases of breast cancer. In vitro data suggest that the activity of the calcium-sensing receptor (CaSR) expressed by metastatic cells could potentiate their osteolytic potential. This study aimed to demonstrate in vivo the involvement of the CaSR in breast cancer cells osteolytic potential and to identify potential targets linked to CaSR activity.

Methods and Results

MDA-MB-231 stably transfected with plasmids containing either a full-length wild-type CaSR (CaSR-WT), or a functionally inactive dominant negative mutant (CaSR-DN) or an empty vector (EV) were intratibially injected into Balb/c-Nude mice. X-ray analysis performed 19 days after injection showed a dramatic increase of osteolytic lesions in mice injected with CaSR-WT-transfected cells as compared to mice injected with EV- or CaSR-DN-transfected cells. This was associated with decreased BV/TV ratio and increased tumor burden. Epiregulin, an EGF-like ligand, was identified by a DNA microarray as a possible candidate involved in CaSR-mediated osteolysis. Indeed, in vitro, CaSR overexpression increased both epiregulin expression and secretion as compared to EV- or CaSR-DN-transfected cells. Increased epiregulin expression was also detected in osteolytic bone lesions from mice injected with CaSR-WT-transfected MDA-MB-231. In vitro, exposure of osteoblastic cells (HOB and SaOS2) to exogenous epiregulin significantly decreased OPG mRNA expression. Exposure of osteoblastic cells to conditioned media prepared from CaSR-WT-transfected cells also decreased OPG expression. This effect was partially blocked after addition of an anti-epiregulin antibody.

Conclusions

Overexpression of a functional CaSR in metastatic breast cancer cells dramatically amplifies their osteolytic potential through epiregulin-mediated OPG downregulation.

Dmp1 Promoter-Driven Diphtheria Toxin Receptor Transgene Expression Directs Unforeseen Effects in Multiple Tissues

Mice harbouring a dentin matrix protein 1 (Dmp1) promoter-driven human diphtheria toxin (DT) receptor (HDTR) transgene (Tg) have recently been used to attain targeted ablation of osteocytes by diphtheria toxin (DT) treatment in order to define osteocyte function. Use of these Tg mice has asserted mechano- and novel paracrine regulatory osteocyte functions. To explore osteocyte roles fully, we sought to confirm the selectivity of DT effects in these transgenic mice. However, our findings revealed incomplete DT-induced osteocyte ablation, prevalent HDTR misexpression, as well as more prominent histopathological DT-induced changes in multiple organs in Tg than in wild-type (WT) littermate mice. Mechanistic evidence for DT action, via prominent regulation of phosphorylation status of elongation factor-2 (EF-2), was also found in many non-skeletal tissues in Tg mice; indicative of direct "off-target" DT action. Finally, very rapid deterioration in health and welfare status in response to DT treatment was observed in these Tg when compared to WT control mice. Together, these data lead us to conclude that alternative models for osteocyte ablation should be sought and caution be exercised when drawing conclusions from experiments using these Tg mice alone.

Calcium-sensing-receptor (CaSR) controls IL-6 secretion in metastatic breast cancer MDA-MB-231 cells by a dual mechanism revealed by agonist and inverse-agonist modulators

IL-6 is a tightly controlled pleiotropic cytokine with hormone-like properties whose levels are frequently altered in cancer and inflammatory diseases. In highly invasive MDA-MB-231 breast cancer cells, basal activity of endogenously expressed calcium sensing receptor (CaSR) promotes IL-6 secretion. Interestingly, upon agonist stimulation, CaSR reduces IL-6 levels whereas it promotes secretion of various other cytokines and growth factors, raising intriguing questions about how CaSR signaling modulates IL-6 secretion. Here, using NPS-2143, which acted as an inverse agonist, we show that IL-6 secretion promoted by constitutive activity of CaSR is mechanistically linked to Gαs/PKC, MEK1/2 and mTORC1 signaling pathways, integrated by transactivated EGFR. On the other hand, agonist-stimulated CaSR engages in a Rab11a-dependent trafficking pathway critical to inhibit constitutive IL-6 secretion via the PI3K/AKT and PKC signaling pathways. These results support the emerging potential of CaSR as a therapeutic target in metastatic breast cancer whose pharmacological modulation would reduce IL-6.

Calcium-Sensing Receptor in Breast Physiology and Cancer

The calcium-sensing receptor (CaSR) is expressed in normal breast epithelial cells and in breast cancer cells. During lactation, activation of the CaSR in mammary epithelial cells increases calcium transport into milk and inhibits parathyroid hormone-related protein (PTHrP) secretion into milk and into the circulation. The ability to sense changes in extracellular calcium allows the lactating breast to actively participate in the regulation of systemic calcium and bone metabolism, and to coordinate calcium usage with calcium availability during milk production. Interestingly, as compared to normal breast cells, in breast cancer cells, the regulation of PTHrP secretion by the CaSR becomes rewired due to a switch in its G-protein usage such that activation of the CaSR increases instead of decreases PTHrP production. In normal cells the CaSR couples to Gα_i to inhibit cAMP and PTHrP production, whereas in breast cancer cells, it couples to Gα_s to stimulate cAMP and PTHrP production. Activation of the CaSR on breast cancer cells regulates breast cancer cell proliferation, death and migration, in part, by stimulating PTHrP production. In this article, we discuss the biology of the CaSR in the normal breast and in breast cancer, and review recent findings suggesting that the CaSR activates a nuclear pathway of PTHrP action that stimulates cellular proliferation and inhibits cell death, helping cancer cells adapt to elevated extracellular calcium levels. Understanding the diverse actions mediated by the CaSR may help us better understand lactation physiology, breast cancer progression and osteolytic bone metastases.

Calcium-Sensing Receptor Tumor Expression and Lethal Prostate Cancer Progression

CONTEXT

Prostate cancer metastases preferentially target bone, and the calcium-sensing receptor (CaSR) may play a role in promoting this metastatic progression.

OBJECTIVE

We evaluated the association of prostate tumor CaSR expression with lethal prostate cancer.

DESIGN

A validated CaSR immunohistochemistry assay was performed on tumor tissue microarrays. Vitamin D receptor (VDR) expression and phosphatase and tensin homolog tumor status were previously assessed in a subset of cases by immunohistochemistry. Cox proportional hazards models adjusting for age and body mass index at diagnosis, Gleason grade, and pathological tumor node metastasis stage were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association of CaSR expression with lethal prostate cancer.

SETTING

The investigation was conducted in the Health Professionals Follow-up Study and Physicians' Health Study.

PARTICIPANTS

We studied 1241 incident prostate cancer cases diagnosed between 1983 and 2009.

MAIN OUTCOME

Participants were followed up or cancer-specific mortality or development of metastatic disease.

RESULTS

On average, men were followed up 13.6 years, during which there were 83 lethal events. High CaSR expression was associated with lethal prostate cancer independent of clinical and pathological variables (HR 2.0; 95% CI 1.2-3.3). Additionally, there was evidence of effect modification by VDR expression; CaSR was associated with lethal progression among men with low tumor VDR expression (HR 3.2; 95% CI 1.4-7.3) but not in cases with high tumor VDR expression (HR 0.8; 95% CI 0.2-3.0).

CONCLUSIONS

Tumor CaSR expression is associated with an increased risk of lethal prostate cancer, particularly in tumors with low VDR expression. These results support further investigating the mechanism linking CaSR with metastases.

Calcium intake, polymorphisms of the calcium-sensing receptor, and recurrent/aggressive prostate cancer

PURPOSE

To assess whether calcium intake and common genetic variants of the calcium-sensing receptor (CASR) are associated with either aggressive prostate cancer (PCa) or disease recurrence after prostatectomy.

METHODS

Calcium intake at diagnosis was assessed, and 65 common single-nucleotide polymorphisms (SNPs) in CASR were genotyped in 886 prostatectomy patients. We investigated the association between calcium intake and CASR variants with both PCa recurrence and aggressiveness (defined as Gleason score ≥4 + 3, stage ≥pT3, or nodal-positive disease).

RESULTS

A total of 285 men had aggressive disease and 91 experienced recurrence. A U-shaped relationship between calcium intake and both disease recurrence and aggressiveness was observed. Compared to the middle quintile, the HR for disease recurrence was 3.07 (95% CI 1.41-6.69) for the lowest quintile and 3.21 (95% CI 1.47-7.00) and 2.97 (95% CI 1.37-6.45) for the two upper quintiles, respectively. Compared to the middle quintile, the OR for aggressive disease was 1.80 (95% CI 1.11-2.91) for the lowest quintile and 1.75 (95% CI 1.08-2.85) for the highest quintile of calcium intake. The main effects of CASR variants were not associated with PCa recurrence or aggressiveness. In the subgroup of patients with moderate calcium intake, 31 SNPs in four distinct blocks of high linkage disequilibrium were associated with PCa recurrence.

CONCLUSIONS

We observed a protective effect of moderate calcium intake for PCa aggressiveness and recurrence. While CASR variants were not associated with these outcomes in the entire cohort, they may be associated with disease recurrence in men with moderate calcium intakes.

Calcium and phosphorus intake and prostate cancer risk: a 24-y follow-up study

BACKGROUND

High calcium intake has been associated with an increased risk of advanced-stage and high-grade prostate cancer. Several studies have found a positive association between phosphorus intake and prostate cancer risk.

OBJECTIVE

We investigated the joint association between calcium and phosphorus and risk of prostate cancer in the Health Professionals Follow-Up Study, with a focus on lethal and high-grade disease.

DESIGN

In total, 47,885 men in the cohort reported diet data in 1986 and every 4 y thereafter. From 1986 to 2010, 5861 cases of prostate cancer were identified, including 789 lethal cancers (fatal or metastatic). We used Cox proportional hazards models to assess the association between calcium and phosphorus intake and prostate cancer, with adjustment for potential confounding.

RESULTS

Calcium intakes >2000 mg/d were associated with greater risk of total prostate cancer and lethal and high-grade cancers. These associations were attenuated and no longer statistically significant when phosphorus intake was adjusted for. Phosphorus intake was associated with greater risk of total, lethal, and high-grade cancers, independent of calcium and intakes of red meat, white meat, dairy, and fish. In latency analysis, calcium and phosphorus had independent effects for different time periods between exposure and diagnosis. Calcium intake was associated with an increased risk of advanced-stage and high-grade disease 12-16 y after exposure, whereas high phosphorus was associated with increased risk of advanced-stage and high-grade disease 0-8 y after exposure.

CONCLUSIONS

Phosphorus is independently associated with risk of lethal and high-grade prostate cancer. Calcium may not have a strong independent effect on prostate cancer risk except with long latency periods.

Lipid rafts, KCa/ClCa/Ca2+ channel complexes and EGFR signaling: Novel targets to reduce tumor development by lipids?

Membrane lipid rafts are distinct plasma membrane nanodomains that are enriched with cholesterol, sphingolipids and gangliosides, with occasional presence of saturated fatty acids and phospholipids containing saturated acyl chains. It is well known that they organize receptors (such as Epithelial Growth Factor Receptor), ion channels and their downstream acting molecules to regulate intracellular signaling pathways. Among them are Ca2+ signaling pathways, which are modified in tumor cells and inhibited upon membrane raft disruption. In addition to protein components, lipids from rafts also contribute to the organization and function of Ca2+ signaling microdomains. This article aims to focus on the lipid raft KCa/ClCa/Ca2+ channel complexes that regulate Ca2+ and EGFR signaling in cancer cells, and discusses the potential modification of these complexes by lipids as a novel therapeutic approach in tumor development. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Prostate cancer metastatic to bone has higher expression of the calcium-sensing receptor (CaSR) than primary prostate cancer

The calcium-sensing receptor (CaSR) is the principal regulator of the secretion of parathyroid hormone and plays key roles in extracellular calcium (Ca²⁺_o) homeostasis. It is also thought to participate in the development of cancer, especially bony metastases of breast and prostate cancer. However, the expression of CaSR has not been systematically analyzed in prostate cancer from patients with or without bony metastases. By comparing human prostate cancer tissue sections in microarrays, we found that the CaSR was expressed in both normal prostate and primary prostate cancer as assessed by immunohistochemistry (IHC). We used two methods to analyze the expression level of CaSR. One was the pathological score read by a pathologist, the other was the positivity% obtained from the Aperio positive pixel count algorithm. Both of the methods gave consistent results. Metastatic prostate cancer tissue obtained from bone had higher CaSR expression than primary prostate cancer (P <0.05). The expression of CaSR in primary prostate cancers of patients with metastases to tissues other than bone was not different from that in primary prostate cancer of patients with or without bony metastases (P >0.05). The expression of CaSR in cancer tissue was not associated with the stage or status of differentiation of the cancer. These results suggest that CaSR may have a role in promoting bony metastasis of prostate cancer, hence raising the possibility of reducing the risk of such metastases with CaSR-based therapeutics.

Effects of parathyroid hormone on calcium ions in rat bone marrow mesenchymal stem cells

The present study was conducted in order to explore the mechanisms whereby parathyroid hormone (PTH) maintains in vitro proliferation of bone marrow mesenchymal stem cells (BMSCs). Bone marrow was isolated from Sprague Dawley (SD) rat femurs, cultured in vitro, and passaged using a cell adherent culture method. The BMSC proliferation was evaluated by the methyl thiazolyl tetrazolium (MTT) assay and the fluorescence intensity of calcium ions in BMSCs was analyzed by laser scanning confocal microscopy (LSCM). Our results show that BMSC proliferation in the experimental group treated with PTH was more significant than controls. The calcium ion fluorescence intensity in BMSCs was significantly higher for the experimental group as compared to the control group. For each group, there was significant difference in the fluorescence intensity of calcium ions in BMSCs between 7 d and 14 d. In conclusion, parathyroid hormone increased the fluorescence intensity of calcium ions in BMSCs, which might represent a key mechanism whereby BMSC proliferation is maintained.

Calcium-sensing receptor (CaSR): pharmacological properties and signaling pathways

In this article we consider the mechanisms by which the calcium-sensing receptor (CaSR) induces its cellular responses via the control (activation or inhibition) of signaling pathways. We consider key features of CaSR-mediated signaling including its control of the heterotrimeric G-proteins Gq/11, Gi/o and G12/13 and the downstream consequences recognizing that very few CaSR-mediated cell phenomena have been fully described. We also consider the manner in which the CaSR contributes to the formation of specific signaling scaffolds via peptide recognition sequences in its intracellular C-terminal along with the origins of its high level of cooperativity, particularly for Ca(2+)o, and its remarkable resistance to desensitization. We also consider the nature of the mechanisms by which the CaSR controls oscillatory and sustained Ca(2+)i mobilizing responses and inhibits or elevates cyclic adenosine monophosphate (cAMP) levels dependent on the cellular and signaling context. Finally, we consider the diversity of the receptor's ligands, ligand binding sites and broader compartment-dependent physiological roles leading to the identification of pronounced ligand-biased signaling for agonists including Sr(2+) and modulators including l-amino acids and the clinically effective calcimimetic cinacalcet. We note the implications of these findings for the development of new designer drugs that might target the CaSR in pathophysiological contexts beyond those established for the treatment of disorders of calcium metabolism.

Role of calcium sensing receptor (CaSR) in tumorigenesis

The extracellular Ca(2+)-sensing receptor (CaSR) is a robust promoter of differentiation in colonic epithelial cells and functions as a tumor suppressor in colon cancer. CaSR mediates its biologic effects through diverse mechanisms. Loss of CaSR expression activates a myriad of stem cell-like molecular features that drive and sustain the malignant and drug-resistant phenotypes of colon cancer. This CaSR-null phenotype, however, is not irreversible and induction of CaSR expression in CaSR-null cells promotes cell death mechanisms and restores drug sensitivity. The CaSR also functions as a tumor suppressor in breast cancer and promotes cellular sensitivity to cytotoxic drugs. BRCA1 and CaSR functions intersect in breast cancer cells, and CaSR activation can rescue breast cancer cells from the deleterious effect of BRCA1 mutations.

The calcium-sensing receptor in the breast

Normal breast epithelial cells and breast cancer cells express the calcium-sensing receptor (CaSR), the master regulator of systemic calcium metabolism. During lactation, activation of the CaSR in mammary epithelial cells downregulates parathyroid hormone-related protein (PTHrP) levels in milk and in the circulation, and increases calcium transport into milk. In contrast, in breast cancer cells the CaSR upregulates PTHrP production. A switch in G-protein usage underlies the opposing effects of the CaSR on PTHrP expression in normal and malignant breast cells. During lactation, the CaSR in normal breast cells coordinates a feedback loop that matches the transport of calcium into milk and maternal calcium metabolism to the supply of calcium. A switch in CaSR G-protein usage during malignant transformation converts this feedback loop into a feed-forward cycle in breast cancer cells that may promote the growth of osteolytic skeletal metastases.

Calcium sensing receptor modulation for cancer therapy

The calcium sensing receptor (CaSR) is a member of the largest family of cell surface receptors, the G protein-coupled receptors involved in calcium homeostasis. The role of the CaSR in neoplasia appears to be homeostatic; loss of normal CaSR-induced response to extracellular calcium is observed in cancers of the colon and ovary, while increased release of PTHrP is observed in cancers of the breast, prostate and Leydig cells. Currently CaSR can be considered as a molecule that can either promote or prevent tumor growth depending on the type of cancer. Therefore, recognition of the multifaceted role of CaSR in gliomas and other malignant tumors in general is fundamental to elucidating the mechanisms of tumor progression and the development of novel therapeutic agents. Emphasis should be placed on development of drug-targeting methods to modulate CaSR activity in cancer cells.

Calcium nutrition and extracellular calcium sensing: relevance for the pathogenesis of osteoporosis, cancer and cardiovascular diseases

Through a systematic search in Pubmed for literature, on links between calcium malnutrition and risk of chronic diseases, we found the highest degree of evidence for osteoporosis, colorectal and breast cancer, as well as for hypertension, as the only major cardiovascular risk factor. Low calcium intake apparently has some impact also on cardiovascular events and disease outcome. Calcium malnutrition can causally be related to low activity of the extracellular calcium-sensing receptor (CaSR). This member of the family of 7-TM G-protein coupled receptors allows extracellular Ca2+ to function as a "first messenger" for various intracellular signaling cascades. Evidence demonstrates that Ca2+/CaSR signaling in functional linkage with vitamin D receptor (VDR)-activated pathways (i) promotes osteoblast differentiation and formation of mineralized bone; (ii) targets downstream effectors of the canonical and non-canonical Wnt pathway to inhibit proliferation and induce differentiation of colorectal cancer cells; (iii) evokes Ca2+ influx into breast cancer cells, thereby activating pro-apoptotic intracellular signaling. Furthermore, Ca2+/CaSR signaling opens Ca2+-sensitive K+ conductance channels in vascular endothelial cells, and also participates in IP(3)-dependent regulation of cytoplasmic Ca2+, the key intermediate of cardiomyocyte functions. Consequently, impairment of Ca2+/CaSR signaling may contribute to inadequate bone formation, tumor progression, hypertension, vascular calcification and, probably, cardiovascular disease.

Calcium sensing receptor signalling in physiology and cancer

The calcium sensing receptor (CaSR) is a class C G-protein-coupled receptor that is crucial for the feedback regulation of extracellular free ionised calcium homeostasis. While extracellular calcium (Ca(2+)o) is considered the primary physiological ligand, the CaSR is activated physiologically by a plethora of molecules including polyamines and l-amino acids. Activation of the CaSR by different ligands has the ability to stabilise unique conformations of the receptor, which may lead to preferential coupling of different G proteins; a phenomenon termed 'ligand-biased signalling'. While mutations of the CaSR are currently not linked with any malignancies, altered CaSR expression and function are associated with cancer progression. Interestingly, the CaSR appears to act both as a tumour suppressor and an oncogene, depending on the pathophysiology involved. Reduced expression of the CaSR occurs in both parathyroid and colon cancers, leading to loss of the growth suppressing effect of high Ca(2+)o. On the other hand, activation of the CaSR might facilitate metastasis to bone in breast and prostate cancer. A deeper understanding of the mechanisms driving CaSR signalling in different tissues, aided by a systems biology approach, will be instrumental in developing novel drugs that target the CaSR or its ligands in cancer. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Common genetic variation of the calcium-sensing receptor and lethal prostate cancer risk

BACKGROUND

Bony metastases cause substantial morbidity and mortality from prostate cancer (PCa). The calcium-sensing receptor (CaSR) is expressed on prostate tumors and may participate in bone metastases development. We assessed whether (i) common genetic variation in CaSR was associated with PCa risk and (ii) these associations varied by calcium intake or plasma 25-hydroxyvitamin D [25(OH)D] levels.

METHODS

We included 1,193 PCa cases and 1,244 controls nested in the prospective Health Professionals Follow-up Study (1993-2004). We genotyped 18 CaSR single-nucleotide polymorphism (SNPs) to capture common variation. The main outcome was risk of lethal PCa (n = 113); secondary outcomes were overall (n = 1,193) and high-grade PCa (n = 225). We used the kernel machine approach to conduct a gene-level multimarker analysis and unconditional logistic regression to compute per-allele ORs and 95% confidence intervals (CI) for individual SNPs.

RESULTS

The joint association of SNPs in CaSR was significant for lethal PCa (P = 0.04); this association was stronger in those with low 25(OH)D (P = 0.009). No individual SNPs were associated after considering multiple testing; three SNPs were nominally associated (P < 0.05) with lethal PCa with ORs (95% CI) of 0.65(0.42-0.99): rs6438705; 0.65(0.47-0.89): rs13083990; and 1.55(1.09-2.20): rs2270916. The three nonsynonymous SNPs (rs1801725, rs1042636, and rs1801726) were not significantly associated; however, the association for rs1801725 was stronger in men with low 25(OH)D [OR(95%CI): 0.54(0.31-0.95)]. There were no significant associations with overall or high-grade PCa.

CONCLUSIONS

Our findings indicate that CaSR may be involved in PCa progression.

IMPACT

Further studies investigating potential mechanisms for CaSR and PCa, including bone remodeling and metastases are warranted.

A prospective study of total and ionized serum calcium and time to fatal prostate cancer

BACKGROUND

Higher levels of total and ionized serum calcium have been shown to predict fatal prostate cancer in prospective studies. Because the follow-up time in these studies was relatively short, these associations could reflect the effect of clinically significant but occult prostate tumors on serum calcium levels. If this were true, prostate cancer mortality rates among men with higher levels of serum calcium should be higher during the early follow-up period and should decline thereafter.

METHODS

We tested this hypothesis by estimating the relative risk of death from prostate cancer in the National Health and Nutrition Examination Survey III for incremental increases in total and ionized serum calcium using Cox proportional hazards regression with time-dependent effects.

RESULTS

Forty-nine (49) fatal prostate cancers occurred over 204 months of follow-up and 1,069,327 person-months of observation. Men with higher total serum calcium and higher serum ionized calcium had increased risks of fatal prostate cancer during the first 96 months of follow-up [Relative Hazard (RH) = 1.50 per 0.1 mmol/L total serum calcium, 95% confidence interval (CI) = 1.04-2.17; RH = 1.72 per 0.05 mmol/L ionized calcium, 95% CI = 1.11-2.66]. Evidence of an association between total and ionized serum calcium and prostate cancer deaths was not significant after 96 months.

CONCLUSIONS

Our analyses support the hypothesis that the elevated risk for fatal prostate cancer observed in men with high serum calcium is because of the presence of extant, but occult prostate cancer.

IMPACT

These findings have implications for the potential use of serum calcium in the detection of clinically significant prostate cancer.

Minireview: the intimate link between calcium sensing receptor trafficking and signaling: implications for disorders of calcium homeostasis

The calcium-sensing receptor (CaSR) regulates organismal Ca(2+) homeostasis. Dysregulation of CaSR expression or mutations in the CASR gene cause disorders of Ca(2+) homeostasis and contribute to the progression or severity of cancers and cardiovascular disease. This brief review highlights recent findings that define the CaSR life cycle, which controls the cellular abundance of CaSR and CaSR signaling. A novel mechanism, termed agonist-driven insertional signaling (ADIS), contributes to the unique hallmarks of CaSR signaling, including the high degree of cooperativity and the lack of functional desensitization. Agonist-mediated activation of plasma membrane-localized CaSR increases the rate of insertion of CaSR at the plasma membrane without altering the constitutive endocytosis rate, thereby acutely increasing the maximum signaling response. Prolonged CaSR signaling requires a large intracellular ADIS-mobilizable pool of CaSR, which is maintained by signaling-mediated increases in biosynthesis. This model provides a rational framework for characterizing the defects caused by CaSR mutations and the altered functional expression of wild-type CaSR in disease states. Mechanistic dissection of ADIS of CaSR should lead to optimized pharmacological approaches to normalize CaSR signaling in disorders of Ca(2+) homeostasis.

Biased agonism of the calcium-sensing receptor

After the discovery of molecules modulating G protein-coupled receptors (GPCRs) that are able to selectively affect one signaling pathway over others for a specific GPCR, thereby "biasing" the signaling, it has become obvious that the original model of GPCRs existing in either an "on" or "off" conformation is too simple. The current explanation for this biased agonism is that GPCRs can adopt multiple active conformations stabilized by different molecules, and that each conformation affects intracellular signaling in a different way. In the present study we sought to investigate biased agonism of the calcium-sensing receptor (CaSR), by looking at 12 well-known orthosteric CaSR agonists in 3 different CaSR signaling pathways: G(q/11) protein, G(i/o) protein, and extracellular signal-regulated kinases 1 and 2 (ERK1/2). Here we show that apart from G(q/11) and G(i/o) signaling, ERK1/2 is activated through recruitment of β-arrestins. Next, by measuring activity of all three signaling pathways we found that barium, spermine, neomycin, and tobramycin act as biased agonist in terms of efficacy and/or potency. Finally, polyamines and aminoglycosides in general were biased in their potencies toward ERK1/2 signaling. In conclusion, the results of this study indicate that several active conformations of CaSR, stabilized by different molecules, exist, which affect intracellular signaling distinctly.

Regulation of stability and trafficking of calcium-sensing receptors by pharmacologic chaperones

Gain- or loss-of-function mutations and polymorphisms of the calcium-sensing receptor (CaSR) cause Ca(2+) handling diseases. Altered expression and/or signaling of wild-type CaSR can also contribute to pathology. Recent studies have demonstrated that a significant proportion of mutations cause altered targeting and/or trafficking of CaSR to the plasma membrane. Pharmacological approaches to rescue of CaSR function include treatment with allosteric modulators, which potentiate the effects of the orthosteric agonist Ca(2+). Dissection of the mechanism(s) contributing to allosteric agonist-mediated rescue of loss-of-function CaSR mutants has demonstrated pharmacologic chaperone actions coincident with CaSR biosynthesis. The distinctive responses to the allosteric agonist (NPS R-568), which promotes CaSR stability, and the allosteric antagonist (NPS 2143), which promotes CaSR degradation, have led to a model for a conformational checkpoint during CaSR biosynthesis. The conformational checkpoint would "tune" CaSR biosynthesis to cellular signaling state. Navigation of a distinct checkpoint for endoplasmic release can also be augmented by pharmacologic chaperones. The diverse, post-endoplasmic reticulum quality control site(s) for pharmacologic chaperone modulation of CaSR stability and trafficking redefines the role(s) of allosteric modulators in regulation of overall GPCR function.

New concepts in calcium-sensing receptor pharmacology and signalling

The calcium-sensing receptor (CaR) is the key controller of extracellular calcium (Ca(2+)(o)) homeostasis via its regulation of parathyroid hormone (PTH) secretion and renal Ca(2+) reabsorption. The CaR-selective calcimimetic drug Cinacalcet stimulates the CaR to suppress PTH secretion in chronic kidney disease and represents the world's first clinically available receptor positive allosteric modulator (PAM). Negative CaR allosteric modulators (NAMs), known as calcilytics, can increase PTH secretion and are being investigated as possible bone anabolic treatments against age-related osteoporosis. Here we address the current state of development and clinical use of a series of positive and negative CaR modulators. In addition, clinical CaR mutations and transgenic mice carrying tissue-specific CaR deletions have provided a novel understanding of the relative functional importance of CaR in both calciotropic tissues and those elsewhere in the body. The development of CaR-selective modulators and signalling reagents have provided us with a more detailed appreciation of how the CaR signals in vivo. Thus, both of these areas of CaR research will be reviewed.

Signaling through the extracellular calcium-sensing receptor (CaSR)

The extracellular calcium ([Formula: see text])-sensing receptor (CaSR) was the first GPCR identified whose principal physiological ligand is an ion, namely extracellular Ca(2+). It maintains the near constancy of [Formula: see text] that complex organisms require to ensure normal cellular function. A wealth of information has accumulated over the past two decades about the CaSR's structure and function, its role in diseases and CaSR-based therapeutics. This review briefly describes the CaSR and key features of its structure and function, then discusses the extracellular signals modulating its activity, provides an overview of the intracellular signaling pathways that it controls, and, finally, briefly describes CaSR signaling both in tissues participating in [Formula: see text] homeostasis as well as those that do not. Factors controlling CaSR signaling include various factors affecting the expression of the CaSR gene as well as modulation of its trafficking to and from the cell surface. The dimeric cell surface CaSR, in turn, links to various heterotrimeric and small molecular weight G proteins to regulate intracellular second messengers, lipid kinases, various protein kinases, and transcription factors that are part of the machinery enabling the receptor to modulate the functions of the wide variety of cells in which it is expressed. CaSR signaling is impacted by its interactions with several binding partners in addition to signaling elements per se (i.e., G proteins), including filamin-A and caveolin-1. These latter two proteins act as scaffolds that bind signaling components and other key cellular elements (e.g., the cytoskeleton). Thus CaSR signaling likely does not take place randomly throughout the cell, but is compartmentalized and organized so as to facilitate the interaction of the receptor with its various signaling pathways.

The calcium-sensing receptor is necessary for the rapid development of hypercalcemia in human lung squamous cell carcinoma

The calcium-sensing receptor (CaR) is responsible for the regulation of extracellular calcium (Ca(2+) (o)) homeostasis. CaR activation has been shown to increase proliferation in several cancer cell lines; however, its presence or function has never been documented in lung cancer. We report that Ca(2+) (o)-activated CaR results in MAPK-mediated stimulation of parathyroid hormone-related protein (PTHrP) production in human lung squamous cell carcinoma (SCC) lines and humoral hypercalcemia of malignancy (HHM) in vivo. Furthermore, a single nucleotide polymorphism in CaR identified from a hypercalcemia-inducing lung SCC reduced the receptor's activation threshold leading to increased PTHrP expression and secretion. Increasing the expression of either wild-type CaR or a CaR variant with a single nucleotide polymorphism in the cytoplasmic domain was both necessary and sufficient for lung SCC to induce HHM. Because lung cancer patients who frequently develop HHM and PTHrP expression in lung cancer has been only partially explained, the significance of our findings indicates that CaR variants may provide a positive feedback between PTHrP and calcium and result in the syndrome of HHM.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Involvement of calcitonin and its receptor in the control of calcium-regulating genes and calcium homeostasis in zebrafish (Danio rerio)

Calcitonin (CT) is one of the hormones involved in vertebrate calcium regulation. It has been proposed to act as a hypocalcemic factor, but the regulatory pathways remain to be clarified. We investigated the CT/calcitonin gene-related peptide (CGRP) family in zebrafish and its potential involvement in calcium homeostasis. We identified the presence of four receptors: CTR, CRLR1, CRLR2, and CRLR3. From the phylogenetic analysis, together with the effect observed after CT and CGRP overexpression, we concluded that CTR appears to be a CT receptor and CRLR1 a CGRP receptor. The distribution of these two receptors shows a major presence in the central nervous system and in tissues involved in ionoregulation. Zebrafish embryos kept in high-Ca(2+)-concentration medium showed upregulation of CT and CTR expression and downregulation of the epithelial calcium channel (ECaC). Embryos injected with CT morpholino (CALC MO) incubated in high-Ca(2+) medium, showed downregulation of CTR together with upregulation on ECaC mRNA expression. In contrast, overexpression of CT cRNA induced the downregulation of ECaC mRNA synthesis, concomitant with the downregulation in the calcium content after 30 hours postfertilization. At 4 days postfertilization, CT cRNA injection induced upregulation of hypercalcemic factors, with subsequent increase in the calcium content. These results suggest that CT acts as a hypocalcemic factor in calcium regulation, probably through inhibition of ECaC synthesis.

The calcium-sensing receptor: a molecular perspective

Compelling evidence of a cell surface receptor sensitive to extracellular calcium was observed as early as the 1980s and was finally realized in 1993 when the calcium-sensing receptor (CaR) was cloned from bovine parathyroid tissue. Initial studies relating to the CaR focused on its key role in extracellular calcium homeostasis, but as the amount of information about the receptor grew it became evident that it was involved in many biological processes unrelated to calcium homeostasis. The CaR responds to a diverse array of stimuli extending well beyond that merely of calcium, and these stimuli can lead to the initiation of a wide variety of intracellular signaling pathways that in turn are able to regulate a diverse range of biological processes. It has been through the examination of the molecular characteristics of the CaR that we now have an understanding of how this single receptor is able to convert extracellular messages into specific cellular responses. Recent CaR-related reviews have focused on specific aspects of the receptor, generally in the context of the CaR's role in physiology and pathophysiology. This review will provide a comprehensive exploration of the different aspects of the receptor, including its structure, stimuli, signalling, interacting protein partners, and tissue expression patterns, and will relate their impact on the functionality of the CaR from a molecular perspective.

Bone marrow microenvironment in myelomagenesis: its potential role in early diagnosis

Multiple myeloma (MM) is the second most common hematological malignancy, with an overall survival of 4-6 years. It is always preceded by a premalignant stage called monoclonal gammopathy of unknown significance (MGUS). Importantly, at this time we lack reliable predictors to determine who will progress from MGUS to MM, and who will remain stable. The bone marrow microenvironment plays a key role in myelomagenesis (growth, survival and migration of malignant plasma cells). In the present review, we summarize and discuss our current understanding of the bone marrow microenvironment and its compartments in relation to myelomagenesis. Although it remains to be proven, we believe that an improved characterization of the cellular constituents, the extracellular matrix components and the soluble factors of the bone marrow could open up novel avenues to better understand underlying mechanisms of the transformation from MGUS to MM. Ultimately, this will lead to the development of early treatment of high-risk precursor disease aimed to delay/prevent MM.

Parathyroid hormone-related protein promotes epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is an important process that contributes to renal fibrogenesis. TGF-beta1 and EGF stimulate EMT. Recent studies suggested that parathyroid hormone-related protein (PTHrP) promotes fibrogenesis in the damaged kidney, apparently dependent on its interaction with vascular endothelial growth factor (VEGF), but whether it also interacts with TGF-beta and EGF to modulate EMT is unknown. Here, PTHrP(1-36) increased TGF-beta1 in cultured tubuloepithelial cells and TGF-beta blockade inhibited PTHrP-induced EMT-related changes, including upregulation of alpha-smooth muscle actin and integrin-linked kinase, nuclear translocation of Snail, and downregulation of E-cadherin and zonula occludens-1. PTHrP(1-36) also induced EGF receptor (EGFR) activation; inhibition of protein kinase C and metalloproteases abrogated this activation. Inhibition of EGFR activation abolished these EMT-related changes, the activation of ERK1/2, and upregulation of TGF-beta1 and VEGF by PTHrP(1-36). Moreover, inhibition of ERK1/2 blocked EMT induced by either PTHrP(1-36), TGF-beta1, EGF, or VEGF. In vivo, obstruction of mouse kidneys led to changes consistent with EMT and upregulation of TGF-beta1 mRNA, p-EGFR protein, and PTHrP. Taken together, these data suggest that PTHrP, TGF-beta, EGF, and VEGF might cooperate through activation of ERK1/2 to induce EMT in renal tubuloepithelial cells.

Reconstitution of amphiregulin-epidermal growth factor receptor signaling in lung squamous cell carcinomas activates PTHrP gene expression and contributes to cancer-mediated diseases of the bone

Parathyroid hormone-related protein (PTHrP) is the causative factor of the paraneoplastic syndrome humoral hypercalcemia of malignancy (HHM) and it also contributes to osteolytic metastases, both of which are common complications of squamous carcinomas of the lung. Inhibition of autocrine epidermal growth factor receptor (EGFR) signaling has been shown to reduce plasma calcium and PTHrP concentrations in two lung squamous cell carcinoma xenograft models of HHM. The purpose of this study was to investigate the mechanism by which EGFR is activated and stimulates PTHrP gene expression in lung squamous carcinoma cell lines. Amphiregulin (AREG) was the only EGFR ligand that could be consistently detected in conditioned media from the SCC lines, and reduction of its expression either by siRNA or by precipitating antibody reduced PTHrP mRNA expression as effectively as EGFR-targeted inhibition. Using siRNA knockdown or inhibitors to upstream regulators of AREG shedding including TACE, Src/Lck, and G(i/o), also reduced PTHrP mRNA expression. We determined that blockade of autocrine AREG-EGFR signaling does not affect PTHrP mRNA stability. Of the three PTHrP promoters (P1, P2, and P3), P1 mRNA could be reduced by nearly 100% with an EGFR inhibitor, and both epidermal growth factor and AREG stimulated P1 mRNA by approximately 5-fold. Finally, ectopic expression of EGFR in a receptor-low but AREG-expressing cell line increased PTHrP mRNA levels in vitro, and induced the capability to cause HHM and rapid osteolytic growth in vivo. Taken together, we provide evidence that AREG stimulation of EGFR results in high levels of PTHrP gene expression, contributing to cancer-associated bone pathology.

Vitamin D and calcium insufficiency-related chronic diseases: molecular and cellular pathophysiology

A compromised vitamin D status, characterized by low 25-hydroxyvitamin D (25-(OH)D) serum levels, and a nutritional calcium deficit are widely encountered in European and North American countries, independent of age or gender. Both conditions are linked to the pathogenesis of many degenerative, malignant, inflammatory and metabolic diseases. Studies on tissue-specific expression and activity of vitamin D metabolizing enzymes, 25-(OH)D-1 alpha-hydroxylase and 25-(OH)D-24-hydroxylase, and of the extracellular calcium-sensing receptor (CaR) have led to the understanding of how, in non-renal tissues and cellular systems, locally produced 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) and extracellular Ca(2+) act jointly as key regulators of cellular proliferation, differentiation and function. Impairment of cooperative signalling from the 1,25-(OH)(2)D(3)-activated vitamin D receptor (VDR) and from the CaR in vitamin D and calcium insufficiency causes cellular dysfunction in many organs and biological systems, and, therefore, increases the risk of diseases, particularly of osteoporosis, colorectal and breast cancer, inflammatory bowel disease, insulin-dependent diabetes mellitus type I, metabolic syndrome, diabetes mellitus type II, hypertension and cardiovascular disease. Understanding the underlying molecular and cellular processes provides a rationale for advocating adequate intake of vitamin D and calcium in all populations, thereby preventing many chronic diseases worldwide.

The calcimimetic R-568 induces apoptotic cell death in prostate cancer cells

Background

Increased serum level of parathyroid hormone (PTH) was found in metastatic prostate cancers. Calcimimetic R-568 was reported to reduce PTH expression, to suppress cell proliferation and to induce apoptosis in parathyroid cells. In this study, we investigated the effect of R-568 on cellular survival of prostate cancer cells.

Methods

Prostate cancer cell lines LNCaP and PC-3 were used in this study. Cellular survival was determined with MTT, trypan blue exclusion and fluorescent Live/Death assays. Western blot assay was utilized to assess apoptotic events induced by R-568 treatment. JC-1 staining was used to evaluate mitochondrial membrane potential.

Results

In cultured prostate cancer LNCaP and PC-3 cells, R-568 treatment significantly reduced cellular survival in a dose- and time-dependent manner. R-568-induced cell death was an apoptotic event, as evidenced by caspase-3 processing and PARP cleavage, as well as JC-1 color change in mitochondria. Knocking down calcium sensing receptor (CaSR) significantly reduced R-568-induced cytotoxicity. Enforced expression of Bcl-xL gene abolished R-568-induced cell death, while loss of Bcl-xL expression led to increased cell death in R-568-treated LNCaP cells,.

Conclusion

Taken together, our data demonstrated that calcimimetic R-568 triggers an intrinsic mitochondria-related apoptotic pathway, which is dependent on the CaSR and is modulated by Bcl-xL anti-apoptotic pathway.