Upregulation of calcium-sensing receptor and mitogen-activated protein kinase signalling in the regulation of growth and differentiation in colon carcinoma

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.

Role of the calcium-sensing receptor (CaSR) in cancer metastasis to bone: Identifying a potential therapeutic target

Cancer is a major cause of morbidity and mortality worldwide due to its ability to evade immune surveillance and metastasize from its origin to a secondary point of contact. Though several treatment techniques have been developed to suppress or manage cancer spread, a strategy for total control over the disease continues to evade researchers. In considering ways to control or prevent cancer from metastasizing to the bone, we analyze the impact of the calcium-sensing receptor (CaSR), whose primary role is to maintain calcium (Ca²⁺) homeostasis in cellular and systemic physiological processes. CaSR is a pleiotropic receptor capable of enhancing the proliferation of some cancers such as breast, lung, prostate and kidney cancers at its primary site(s) and stimulating bone metastasis, while exerting a suppressive effect in others such as colon cancer. The activity of CaSR not only increases cancer cell proliferation, migration and suppression of apoptosis in the organs indicated, but also increases the secretion of parathyroid hormone-related protein (PTHrP) and epiregulin, which induce osteolytic activity and osteoblastic suppression. In addition, released cytokines and Ca²⁺ from bone resorption are critical factors that further promote cancer proliferation. In this review, we seek to highlight previous viewpoints on CaSR, discuss its role in a new context, and consider its potential clinical application in cancer treatment.

Calcium-sensing receptor in colorectal inflammation and cancer: Current insights and future perspectives

The extracellular calcium-sensing receptor (CaSR) is best known for its action in the parathyroid gland and kidneys where it controls body calcium homeostasis. However, the CaSR has different roles in the gastrointestinal tract, where it is ubiquitously expressed. In the colon, the CaSR is involved in controlling multiple mechanisms, including fluid transport, inflammation, cell proliferation and differentiation. Although the expression pattern and functions of the CaSR in the colonic microenvironment are far from being completely understood, evidence has been accumulating that the CaSR might play a protective role against both colonic inflammation and colorectal cancer. For example, CaSR agonists such as dipeptides have been suggested to reduce colonic inflammation, while dietary calcium was shown to reduce the risk of colorectal cancer. CaSR expression is lost in colonic malignancies, indicating that the CaSR is a biomarker for colonic cancer progression. This dual anti-inflammatory and anti-tumourigenic role of the CaSR makes it especially interesting in colitis-associated colorectal cancer. In this review, we describe the clinical and experimental evidence for the role of the CaSR in colonic inflammation and colorectal cancer, the intracellular signalling pathways which are putatively involved in these actions, and the possibilities to exploit these actions of the CaSR for future therapies of colonic inflammation and cancer.

Significance of calcium-sensing receptor expression in gastric cancer

OBJECTIVE

The calcium-sensing receptor (CaSR) is known to have differential expression in various carcinomas and normal tissues. It has been shown to be involved in carcinogenesis or tumor suppression. However, its role in gastric cancer remains unknown. This study was performed to determine the CaSR expression level in gastric cancer and non-tumor gastric tissues and to examine the related clinicopathological factors.

MATERIALS AND METHODS

Thirty-one pairs of gastric cancer tissues and matched non-tumor gastric tissues were obtained from surgical tissues after gastrectomy. Using real-time polymerase chain reaction, we measured CaSR mRNA expression. We evaluated the association between CaSR mRNA expression and clinicopathological variables based on the downregulation or upregulation of CaSR mRNA expression in gastric cancer tissues compared to those of matched non-tumor gastric tissues. By immunohistochemistry, we confirmed CaSR expression levels in gastric cancer tissues.

RESULTS

Downregulation of CaSR mRNA was observed in 77.4% of gastric cancer tissues compared to their matched normal tissues. Downregulated CaSR was associated with a tendency for deeper invasion into the proper muscle (p = 0.028) and more advanced stage (II-IV; p = 0.012).

CONCLUSION

We conclude that downregulation of CaSR may contribute to the prevention or suppression of tumor outgrowth.

The Extracellular Calcium-Sensing Receptor (CASR) Regulates Gonadotropins-Induced Meiotic Maturation of Porcine Oocytes

Gonadotropins and epidermal growth factor (EGF) play crucial roles in promoting oocyte maturation. The regulatory network downstream of these key factors is not well understood. The present study was designed to investigate the role of the calcium-sensing receptor (CASR) in porcine oocyte in vitro maturation. CASR expression was up-regulated in oocytes matured in gonadotropin-containing medium. Cortical distribution of CASR was enhanced with gonadotropins but not EGF. Supplementation of a CASR agonist (NPS R-568) in the gonadotropin (FSH and/or LH)-containing maturation medium significantly enhanced oocyte nuclear maturation. Addition of NPS2390, a CASR antagonist, compromised oocyte nuclear maturation. Furthermore, increased cortical distribution and decreased expression of CASR was observed after the NPS R-568 treatment. Oocytes treated with NPS R-568 had higher concentration of CYCLIN B1, decreased reactive oxygen species, and increased glutathione levels, indicative of advanced cytoplasmic maturation. In contrast, NPS2390 treatment compromised oocyte cytoplasmic maturation. A higher blastocyst formation rate after parthenogenetic activation was observed when oocytes were matured in the presence of the CASR agonist, NPS R-568. MAPK3/1 phosphorylation was increased during in vitro maturation and after NPS R-568 treatment, and decreased following CASR antagonist supplementation. Taken together, our data showed that the CASR is a gonadotropin-regulated factor that promotes porcine oocyte maturation in a MAPK-dependent manner.

Expression of calcium sensing receptor and E-cadherin correlated with survival of lung adenocarcinoma

Background

It has been reported that the calcium sensing receptor (CaSR), a widely expressed G protein-coupled receptor, can stimulate cell differentiation and proliferation. However, in malignant tumors, loss of CaSR expression has been associated with tumorigenesis, metastasis, and progression. Recent studies have indicated that the CaSR could promote the expression of E-cadherin, which was considered a tumor suppressor. However, in human lung adenocarcinoma, the importance of the CaSR and E-cadherin has not been sufficiently investigated.

Methods

Expression levels of CaSR and E-cadherin in paraffin sections from 117 resected lung adenocarcinoma patients were evaluated by immunohistochemistry. We analyzed the correlation between our target proteins and clinical variables. Clinical significance was analyzed by multivariate Cox regression analysis, Kaplan–Meier curve, and log-rank test.

Results

Expression of the CaSR in lung adenocarcinoma tissue was significantly lower than in the normal sample (P = 0.003). Kendall tau-b analysis showed that, in a lung adenocarcinoma sample, the expression of CaSR positively correlated with a high level of E-cadherin (P < 0.001). Lung adenocarcinoma patients with a strong expression of CaSR (P = 0.034) or E-cadherin (P = 0.001) had longer overall survival. Multivariate Cox proportional hazards model analysis showed that the combined marker was an independent prognostic indicator of overall survival (hazard ratio = 0.440, confidence interval = 0.249–0.779, P = 0.005).

Conclusions

We identified the CaSR as a new prognostic biomarker in lung adenocarcinoma. These results also suggested that the CaSR may become a new therapeutic target of lung adenocarcinoma.

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.

Engendering biased signalling from the calcium-sensing receptor for the pharmacotherapy of diverse disorders

The human calcium-sensing receptor (CaSR) is widely expressed in the body, where its activity is regulated by multiple orthosteric and endogenous allosteric ligands. Each ligand stabilizes a unique subset of conformational states, which enables the CaSR to couple to distinct intracellular signalling pathways depending on the extracellular milieu in which it is bathed. Differential signalling arising from distinct receptor conformations favoured by each ligand is referred to as biased signalling. The outcome of CaSR activation also depends on the cell type in which it is expressed. Thus, the same ligand may activate diverse pathways in distinct cell types. Given that the CaSR is implicated in numerous physiological and pathophysiological processes, it is an ideal target for biased ligands that could be rationally designed to selectively regulate desired signalling pathways in preferred cell types.

Induction of calcium sensing receptor in human colon cancer cells by calcium, vitamin D and aquamin: Promotion of a more differentiated, less malignant and indolent phenotype

The calcium sensing receptor (CaSR) is a robust promoter of differentiation in colonic epithelial cells and functions as a tumor suppressor. Cancer cells that do not express CaSR (termed CaSR null) are highly malignant while acquisition of CaSR expression in these cells circumvents the malignant phenotype. We hypothesize that chemopreventive agents mediate their action through the induction of CaSR. Here, we compare the effectiveness of Ca(2+), vitamin D, and Aquamin (a marine algae product containing Ca(2+), magnesium and detectable levels of 72 additional minerals) on the induction of CaSR in the CBS and HCT116 human colon carcinoma cell lines and the corresponding CaSR null cells isolated from these lines. All three agonists induced CaSR mRNA and protein expression and inhibited cellular proliferation in the parental and CaSR null cells. Aquamin was found to be most potent in this regard. Induction of CaSR expression by these agonists resulted in demethylation of the CaSR gene promoter with a concurrent increase in CaSR promoter reporter activity. However, demethylation per se did not induce CaSR transcription. Induction of CaSR expression resulted in a down-regulated expression of tumor inducers and up-regulated expression of tumor suppressors. Again, Aquamin was found to be most potent in these biologic effects. This study provides a rationale for the use of a multi-mineral approach in the chemoprevention of colon cancer and suggests that induction of CaSR may be a measure of the effectiveness of chemopreventive agents.

Induction of CaSR expression circumvents the molecular features of malignant CaSR null colon cancer cells

We recently reported on the isolation and characterization of calcium sensing receptor (CaSR) null human colon cancer cells (Singh et al., Int J Cancer 2013; 132: 1996-2005). CaSR null cells possess a myriad of molecular features that are linked to a highly malignant and drug resistant phenotype of colon cancer. The CaSR null phenotype can be maintained in defined human embryonic stem cell culture medium. We now show that the CaSR null cells can be induced to differentiate in conventional culture medium, regained the expression of CaSR with a concurrent reversal of the cellular and molecular features associated with the null phenotype. These features include cellular morphology, expression of colon cancer stem cell markers, expression of survivin and thymidylate synthase and sensitivity to fluorouracil. Other features include the expression of epithelial mesenchymal transition linked molecules and transcription factors, oncogenic miRNAs and tumor suppressive molecule and miRNA. With the exception of cancer stem cell markers, the reversal of molecular features, upon the induction of CaSR expression, is directly linked to the expression and function of CaSR because blocking CaSR induction by shRNA circumvented such reversal. We further report that methylation and demethylation of the CaSR gene promoter underlie CaSR expression. Due to the malignant nature of the CaSR null cells, inclusion of the CaSR null phenotype in disease management may improve on the mortality of this disease. Because CaSR is a robust promoter of differentiation and mediates its action through diverse mechanisms and pathways, inactivation of CaSR may serve as a new paradigm in colon carcinogenesis.

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.

Cellular responses to TGFβ and TGFβ receptor expression in human colonic epithelial cells require CaSR expression and function

CaSR and TGFβ are robust promoters of differentiation in the colonic epithelium. Loss of cellular responses to TGFβ or loss of CaSR expression is tightly linked to malignant progression. Human colonic epithelial CBS cells, originally developed from a differentiated human colon tumor, retain CaSR expression and function, TGFβ responsiveness and TGFβ receptor expression. Thus, these cells offer a unique opportunity in determining the functional linkage (if any) between CaSR and TGFβ. Knocking down CaSR expression abrogated TGFβ-mediated cellular responses and attenuated the expression of TGFβ receptors. Ca²⁺ or vitamin D treatment induced CaSR expression with a concurrent up-regulation of TGFβ receptor expression. Ca²⁺ or vitamin D, however, did not induce CaSR in CaSR knocked down cells and without CaSR; there was no up-regulation of TGFβ receptor. It is concluded that TGFβ receptor expression and TGFβ mediated responses requires CaSR expression and function.

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.

Grape seed extract triggers apoptosis in Caco-2 human colon cancer cells through reactive oxygen species and calcium increase: extracellular signal-regulated kinase involvement

Grape seed extract (GSE) from Italia, Palieri and Red Globe cultivars inhibits cell growth and induces apoptosis in Caco-2 human colon cancer cells in a dose-dependent manner. In order to investigate the mechanism(s) supporting the apoptotic process, we analysed reactive oxygen species (ROS) production, intracellular Ca2+ handling and extracellular signal-regulated kinase (ERK) activation. Upon exposure to GSE, ROS and intracellular Ca2+ levels increased in Caco-2 cells, concomitantly with ERK inactivation. As ERK activity is thought to be essential for promoting survival pathways, inhibition of this kinase is likely to play a relevant role in GSE-mediated anticancer effects. Indeed, pretreatment with N-acetyl cysteine, a ROS scavenger, reversed GSE-induced apoptosis, and promoted ERK phosphorylation. This effect was strengthened by ethylene glycol tetraacetic acid-mediated inhibition of extracellular Ca2+ influx. ROS and Ca2+ influx inhibition, in turn, increased ERK phosphorylation, and hence almost entirely suppressed GSE-mediated apoptosis. These data suggested that GSE triggers a previously unrecognised ERK-based mechanism, involving both ROS production and intracellular Ca2+ increase, eventually leading to apoptosis 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.

Isolation and characterization of calcium sensing receptor null cells: a highly malignant and drug resistant phenotype of colon cancer

The expression of calcium sensing receptor (CaSR) in the human colonic crypt epithelium is linked to cellular differentiation while its lack of expression is associated with undifferentiated and invasive colon carcinoma. Human colon carcinoma cell lines contain small subpopulations (10-20%) that do not express CaSR (termed CaSR null cells). Here, we report on the isolation, propagation, maintenance and characterization of CaSR null cells from the CBS and HCT116 human colon carcinoma cell lines. CaSR null cells grew as three-dimensional non-adherent spherical clusters with increased propensity for anchorage independent growth, cellular proliferation and invasion of matrigels. CaSR null cells were highly resistant to fluorouracil and expressed abundant amount of thymidylate synthase and survivin. Molecular profiling by real time reverse transcription-polymerase chain reaction (RT-PCR) and Western blots showed a high level of expression of the previously reported cancer stem cell markers CD133, CD44 and Nanog in CaSR null cells. A significant increase in the expression of epithelial-mesenchymal transitional molecules and transcription factors was also observed. These include N-cadherin, β-catenin, vimentin, fibronectin, Snail1, Snail2, Twist and FOXC2. The expression of the tumor suppressive E-cadherin and miR145, on the other hand, was greatly reduced while expression of the oncogenic microRNAs: miR21, miR135a and miR135b was significantly up-regulated. CaSR null cells possess a myriad of cellular and molecular features that drive and sustain the malignant phenotype. We conclude that CaSR null constitutes a highly malignant and drug resistant phenotype of colon cancer.

The role of the calcium-sensing receptor in human disease

Following the discovery of the calcium-sensing receptor (CaSR) in 1993, its pivotal role in disorders of calcium homeostasis such as Familial Hypocalciuric Hypercalcemia (FHH) was quickly demonstrated. Since then, it has become clear that the CaSR has immense functional versatility largely through its ability to activate many different signaling pathways in a ligand- and tissue-specific manner. This allows the receptor to play diverse and crucial roles in human physiology and pathophysiology, both in calcium homeostasis and in tissues and biological processes unrelated to calcium balance. This review covers current knowledge of the role of the CaSR in disorders of calcium homeostasis (FHH, neonatal severe hyperparathyroidism, autosomal dominant hypocalcemia, primary and secondary hyperparathyroidism, hypercalcemia of malignancy) as well as unrelated diseases such as breast and colorectal cancer (where the receptor appears to play a tumor suppressor role), Alzheimer's disease, pancreatitis, diabetes mellitus, hypertension and bone and gastrointestinal disorders. In addition, it examines the use or potential use of CaSR agonists or antagonists (calcimimetics and calcilytics) and other drugs mediated through the CaSR, in the management of disorders as diverse as hyperparathyroidism, osteoporosis and gastrointestinal disease.

Calcium, calcium-sensing receptor and growth control in the colonic mucosa

A role for calcium in epithelial growth control is well-established in the colon and other tissues. In the colon, Ca²+ "drives" the differentiation process. This results in sequestration of β-catenin in the cell surface / cytoskeletal complex, leaving β-catenin unavailable to serve as a growth-promoting transcription enhancer in the nucleus. The signaling events that lead from Ca²+ stimulation to differentiation are not fully understood. A critical role for the extracellular calcium-sensing receptor (CaSR) is assumed, based on CaSR localization to the differentiating epithelial cells in the normal colonic mucosa (upper half of the crypt and crypt surface), decreased CaSR expression in colon carcinoma, and the results from in vitro studies with colonic epithelial cell lines. While Ca²+ is well-accepted as a growth-regulating agent in the colon, suppression of cell proliferation is not complete. At least part of the reason for this is the inherent variability in Ca²+ responsiveness among individual epithelial cells. Of interest, colon epithelial cells that are resistant to the growth-regulating activity of Ca²+ alone are still responsive to Ca²+ in conjunction with other transition metals. Whether a multi-mineral approach will, ultimately, prove to be more effective than Ca²+ alone as a colon cancer chemopreventive agent remains to be seen, but certainly worth investigating.

Human colon tissue in organ culture: preservation of normal and neoplastic characteristics

Normal and neoplastic human colon tissue obtained at surgery was used to establish conditions for organ culture. Optimal conditions included an atmosphere of 5% CO2 and 95% O2; tissue partially submerged with mucosa at the gas interface; and serum-free medium with 1.5 mM Ca2+ and a number of growth supplements. Histological, histochemical, and immunohistochemical features that distinguish normal and neoplastic tissue were preserved over a 2-d period. With normal tissue, this included the presence of elongated crypts with small, densely packed cells at the crypt base and mucin-containing goblet cells in the upper portion. Ki67 staining, for proliferating cells, was confined to the lower third of the crypt, while expression of extracellular calcium-sensing receptor was seen in the upper third and surface epithelium. E-cadherin and β-catenin were expressed throughout the epithelium and confined to the cell surface. In tumor tissue, the same disorganized, abnormal glandular structures seen at time zero were present after 2 d. The majority of cells in these structures were mucin-poor, but occasional goblet cells were seen and mucin staining was present. Ki67 staining was seen throughout the abnormal epithelium and calcium-sensing receptor expression was weak and variable. E-cadherin was seen at the cell surface (similar to normal tissue), but in some places, there was diffuse cytoplasmic staining. Finally, intense cytoplasmic and nuclear β-catenin staining was observed in cultured neoplastic tissue.

Review article: loss of the calcium-sensing receptor in colonic epithelium is a key event in the pathogenesis of colon cancer

The calcium-sensing receptor (CaSR) is expressed abundantly in normal colonic epithelium and lost in colon cancer, but its exact role on a molecular level and within the carcinogenesis pathway is yet to be described. Epidemiologic studies show that inadequate dietary calcium predisposes to colon cancer; this may be due to the ability of calcium to bind and upregulate the CaSR. Loss of CaSR expression does not seem to be an early event in carcinogenesis; indeed it is associated with late stage, poorly differentiated, chemo-resistant tumors. Induction of CaSR expression in neoplastic colonocytes arrests tumor progression and deems tumors more sensitive to chemotherapy; hence CaSR may be an important target in colon cancer treatment. The CaSR has a complex role in colon cancer; however, more investigation is required on a molecular level to clarify its exact function in carcinogenesis. This review describes the mechanisms by which the CaSR is currently implicated in colon cancer and identifies areas where further study is needed.

Epigenetic inactivation of calcium-sensing receptor in colorectal carcinogenesis

Ca2+ is a chemopreventive agent for colon cancer. Ion transport systems are often altered in human cancer. The aim of this study was to clarify the alterations of calcium-sensing receptor (CASR), a member of the G protein-coupled receptor family, in colorectal carcinogenesis. We analyzed the expression of CASR in colorectal cancer cell lines and in cancer and adenoma tissues by RT-PCR and immunostaining. In addition, we analyzed methylation of the CASR promoter by using bisulfite sequence analysis and methylation-specific PCR. CASR mRNA and protein expression was significantly downregulated in most of the cancer cell lines. CpG islands were densely methylated in cancer cell lines with reduced CASR mRNA expression. Treatment with a demethylating agent, 5-aza-2'-deoxycytidine, and/or a histone deacetylase inhibitor, trichostatin A, restored CASR expression in the cancer cell lines. Disruption of CASR expression in CASR-unmethylated HCT-8 cells blocked the enhancing effect of Ca2+ on the cytotoxic response to 5-fluorouracil. CASR expression was observed in normal colonic epithelial cells and was retained in most adenoma tissues. CASR mRNA and protein expression was significantly downregulated in cancer tissues. There was an inverse relationship between CASR expression and degree of differentiation. Immunohistochemical CASR staining was reduced more predominantly in less-differentiated cancer tissues and/or in cancer cells at the invasive front, where nuclear/cytoplasmic β-catenin was often localized. CASR methylation was detected in 69% of colorectal cancer tissues and 90% of lymph node metastatic tissues and was significantly correlated with reduced CASR expression. CASR methylation was also detected in 32% of advanced adenoma tissues but was detected in only 9% of adenoma tissues and was not detected in hyperplastic polyp tissues. CASR methylation seems to occur at an early stage and progress in colorectal carcinogenesis. The results suggest that epigenetic inactivation of CASR has an important role in colorectal carcinogenesis.

Functional expression of the extracellular calcium sensing receptor (CaSR) in equine umbilical cord matrix size-sieved stem cells

BACKGROUND

The present study investigates the effects of high external calcium concentration ([Ca(2+)](o)) and the calcimimetic NPS R-467, a known calcium-sensing receptor (CaSR) agonist, on growth/proliferation of two equine size-sieved umbilical cord matrix mesenchymal stem cell (eUCM-MSC) lines. The involvement of CaSR on observed cell response was analyzed at both the mRNA and protein level.

METHODOLOGY/PRINCIPAL FINDINGS

A large (>8 µm in diameter) and a small (<8 µm) cell line were cultured in medium containing: 1) low [Ca(2+)](o) (0.37 mM); 2) high [Ca(2+)](o) (2.87 mM); 3) NPS R-467 (3 µM) in presence of high [Ca(2+)](o) and 4) the CaSR antagonist NPS 2390 (10 µM for 30 min.) followed by incubation in presence of NPS R-467 in medium with high [Ca(2+)](o). Growth/proliferation rates were compared between groups. In large cells, the addition of NPS R-467 significantly increased cell growth whereas increasing [Ca(2+)](o) was not effective in this cell line. In small cells, both higher [Ca(2+)](o) and NPS R-467 increased cell growth. In both cell lines, preincubation with the CaSR antagonist NPS 2390 significantly inhibited the agonistic effect of NPS R-467. In both cell lines, increased [Ca(2+)](o) and/or NPS R-467 reduced doubling time values.Treatment with NPS R-467 down-regulated CaSR mRNA expression in both cell lines. In large cells, NPS R-467 reduced CaSR labeling in the cytosol and increased it at cortical level.

CONCLUSIONS/SIGNIFICANCE

In conclusion, calcium and the calcimimetic NPS R-467 reduce CaSR mRNA expression and stimulate cell growth/proliferation in eUCM-MSC. Their use as components of media for eUCM-MSC culture could be beneficial to obtain enough cells for down-stream purposes.

A short primer on the calcium sensing receptor: an important cog in the colon cancer wheel?

The gastrointestinal (GI) tract handles a complex task of nutrient absorption and excretion of excess fluid, electrolytes, and toxic substances. GI epithelium is under constant proliferation and renewal. Differentiation of colonocytes occurs as they migrate from the basal layer to the apex of the crypt. Cells of the basal layer are highly proliferative but less differentiated, whereas apical cells are highly differentiated but non-proliferative. Alterations of this intricate process lead to abnormal proliferation and differentiation of colorectal mucosa leading to development of polyps and neoplasia. The effects of calcium (Ca) on colorectal mucosal growth have been extensively studied after the discovery of the calcium sensing receptor (CaSR). Fluctuation in extracellular Ca can induce hyperproliferation or quiescence. Disruption in the function of CaSR and/or changes in the level of CaSR expression can cause loss of growth suppressing effects of extracellular Ca. This review addresses the role of Ca and CaSR in the physiology and pathophysiology of colonocyte proliferation.

Human colon tissue in organ culture: calcium and multi-mineral-induced mucosal differentiation

We have recently shown that a multi-mineral extract from the marine red algae, Lithothamnion calcareum, suppresses colon polyp formation and inflammation in mice. In the present study, we used intact human colon tissue in organ culture to compare responses initiated by Ca(2+) supplementation versus the multi-mineral extract. Normal human colon tissue was treated for 2 d in culture with various concentrations of calcium or the mineral-rich extract. The tissue was then prepared for histology/immunohistochemistry, and the culture supernatants were assayed for levels of type I procollagen and type I collagen. At higher Ca(2+) concentrations or with the mineral-rich extract, proliferation of epithelial cells at the base and walls of the mucosal crypts was suppressed, as visualized by reduced Ki67 staining. E-cadherin, a marker of differentiation, was more strongly expressed at the upper third of the crypt and at the luminal surface. Treatment with Ca(2+) or with the multi-mineral extract influenced collagen turnover, with decreased procollagen and increased type I collagen. These data suggest that calcium or mineral-rich extract has the capacity to (1) promote differentiation in human colon tissue in organ culture and (2) modulate stromal function as assessed by increased levels of type I collagen. Taken together, these data suggest that human colon tissue in organ culture (supporting in vivo finding in mice) will provide a valuable model for the preclinical assessment of agents that regulate growth and differentiation in the colonic mucosa.

A randomized clinical trial of the effects of supplemental calcium and vitamin D3 on markers of their metabolism in normal mucosa of colorectal adenoma patients

In cancer cell lines and rodent models, calcium and vitamin D favorably modulate cell proliferation, differentiation, and apoptosis in colonic epithelia. These effects may be modulated by local expression of the calcium receptor (CaR), the vitamin D receptor (VDR), and the P450 cytochromes, CYP27B1 and CYP24A1; however, they have yet to be investigated in humans. To address this gap, we conducted a randomized, double-blinded, placebo-controlled 2×2 factorial clinical trial. Patients with at least one pathology-confirmed colorectal adenoma were treated with 2 g/d elemental calcium and/or 800 IU/d vitamin D3 versus placebo over 6 months (n=92; 23 per group). CaR, VDR, CYP27B1, and CYP24A1 expression and distribution in biopsies of normal appearing rectal mucosa were detected by standardized, automated immunohistochemistry and quantified by image analysis. In the calcium-supplemented group, CaR expression increased 27% (P=0.03) and CYP24A1 expression decreased 21% (P=0.79). In the vitamin D3-supplemented group, CaR expression increased 39% (P=0.01) and CYP27B1 expression increased 159% (P=0.06). In patients supplemented with both calcium and vitamin D3, VDR expression increased 19% (P=0.13) and CaR expression increased 24% (P=0.05). These results provide mechanistic support for further investigation of calcium and vitamin D3 as chemopreventive agents against colorectal neoplasms, and CaR, VDR, CYP27B1, and CYP24A1 as modifiable, preneoplastic risk biomarkers for colorectal neoplasms.

A mineral-rich red algae extract inhibits polyp formation and inflammation in the gastrointestinal tract of mice on a high-fat diet

The purpose of this study was to determine whether a mineral-rich extract derived from the red marine algae Lithothamnion calcareum could be used as a dietary supplement for chemoprevention against colon polyp formation. A total of 60 C57bl/6 mice were divided into 3 groups based on diet. One group received a low-fat, rodent chow diet (AIN76A). The second group received a high-fat "Western-style" diet (HFWD). The third group was fed the same HFWD with the mineral-rich extract included as a dietary supplement. Mice were maintained on the respective diets for 15 months. Autopsies were performed at the time of death or at the completion of the study. To summarize, the cumulative mortality rate was higher in mice on the HFWD during the 15-month period (55%) than in mice from the low-fat diet or the extract-supplemented high-fat diet groups (20% and 30%, respectively; P < .05 with respect to both). Autopsies revealed colon polyps in 20% of the animals on the HFWD and none in animals of the other 2 groups (P < .05). In addition to the grossly visible polyps, areas of hyperplasia in the colonic mucosa and inflammatory foci throughout the gastrointestinal tract were observed histologically in animals on the high-fat diet. Both were significantly reduced in animals on the low-fat diet and animals on the extract-supplemented HFWD.These data suggest that the mineral-rich algae extract may provide a novel approach to chemoprevention in the colon.

Vitamin D mediates its action in human colon carcinoma cells in a calcium-sensing receptor-dependent manner: downregulates malignant cell behavior and the expression of thymidylate synthase and survivin and promotes cellular sensitivity to 5-FU

Vitamin D (VD) protects against colon carcinogenesis by mechanisms not fully understood. We had earlier reported on the similarity in the biologic action of VD and that of the calcium-sensing receptor (CaSR) in human colon carcinoma cells. At the molecular level, the CaSR gene contains 2 VD response elements and VD stimulates the expression of CaSR. In this study, we investigated on the relationship between VD action and CaSR function. We determined and compared the action of VD in human colon carcinoma cells (CBS, Moser, Caco-2 and HCT116) and their CaSR knocked-down counterparts. VD inhibited cellular proliferation, cellular invasion, and anchorage-independent growth and stimulated the expression of p21/Waf1 but not in CaSR knocked-down cells. These results demonstrate, for the first time, that the known tumor-suppressive function of VD requires functional CaSR and knocking down CaSR expression abrogated this function of VD. We recently reported that activation of CaSR in human colon carcinoma cells downregulated the expression of thymidylate synthase (TS) and survivin and promoted a significant increase in sensitivity to cytotoxic drugs. We now demonstrate, for the first time, that VD suppressed the expression of TS and survivin, TS and survivin gene transcriptional activities and promoted a cytotoxic response to 5-FU in a CaSR-dependent manner. Ectopic expression of wild-type CaSR in colon carcinoma cells also inhibited the expression of TS and survivin and enhanced cellular sensitivity to 5-FU. VD, however, could no longer enhance cellular sensitivity to 5-FU in cells overexpressing CaSR.

Growth-inhibitory effects of a mineralized extract from the red marine algae, Lithothamnion calcareum, on Ca(2+)-sensitive and Ca(2+)-resistant human colon carcinoma cells

Proliferation and differentiation were assessed in a series of human colon carcinoma cell lines in response to a mineral-rich extract derived from the red marine algae, Lithothamnion calcareum. The extract contains 12% Ca2+, 1% Mg2+, and detectable amounts of 72 trace elements, but essentially no organic material. The red algae extract was as effective as inorganic Ca2+ alone in suppressing growth and inducing differentiation of colon carcinoma cells that are responsive to a physiological level of extracellular Ca2+ (1.4mM). However, with cells that are resistant to Ca2+ alone, the extract was still able to reduce proliferation and stimulate differentiation.

The role of the calcium-sensing receptor in the development and progression of cancer

The calcium-sensing receptor (CaR) is responsive to changes in the extracellular Ca(2+) (Ca(2+)(o)) concentration. It is a member of the largest family of cell surface receptors, the G protein-coupled receptors, and it has been shown to be involved in Ca(2+)(o) homeostasis. Apart from its primary role in Ca(2+)(o) homeostasis, the CaR may be involved in phenomena that allow for the development of many types of benign or malignant tumors, from parathyroid adenomas to breast, prostate, and colon cancers. For example, whereas the CaR is expressed in both normal and malignant breast tissue, increased CaR levels have been reported in highly metastatic primary breast cancer cells and breast cancer cell lines, possibly contributing to their malignancy and associated alterations in their biological properties. In these settings the CaR exhibits oncogenic properties. Enhanced CaR expression and altered proliferation of prostate cancer cells in response to increased Ca(2+)(o) have also been described. In contrast, colon and parathyroid cancers often present with reduced or absent CaR expression, and activation of this receptor decreases cell proliferation, suggesting a role for the CaR as a tumor suppressor gene. Thus, the CaR may play an important role in the development of many types of neoplasia. Herein, we review the role of the CaR in various benign and malignant tumors in further detail, describing its contribution to parathyroid tumors, breast, prostate, and colon cancers, and we evaluate how pharmacological manipulations of this receptor may be of interest for the treatment of certain cancers in the future.

Calcium and calcium sensing receptor modulates the expression of thymidylate synthase, NAD(P)H:quinone oxidoreductase 1 and survivin in human colon carcinoma cells: promotion of cytotoxic response to mitomycin C and fluorouracil

Ca(2+) and the cell-surface calcium sensing receptor (CaSR) constitute a novel and robust ligand/receptor system in regulating the proliferation and differentiation of colonic epithelial cells. Here we show that activation of CaSR by extracellular Ca(2+) (or CaSR agonists) enhanced the sensitivity of human colon carcinoma cells to mitomycin C (MMC) and fluorouracil (5-FU). Activation of CaSR up-regulated the expression of MMC activating enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO-1) and down-regulated the expression of 5-FU target, thymidylate synthase (TS) and the anti-apoptotic protein survivin. Cells that were resistant to drugs expressed little or no CaSR but abundant amount of survivin. Disruption of CaSR expression by shRNA targeting the CaSR abrogated these modulating effects of CaSR activation on the expression of NQO1, TS, survivin and cytotoxic response to drugs. It is concluded that activation of CaSR can enhance colon cancer cell sensitivity to MMC and 5-FU and can modulate the expression of molecules involved in the cellular responses to these cytotoxic drugs.

Effects of the lactase 13910 C/T and calcium-sensor receptor A986S G/T gene polymorphisms on the incidence and recurrence of colorectal cancer in Hungarian population

Background

Epidemiological studies suggested the chemopreventive role of higher calcium intake in colorectal carcinogenesis. We examined genetic polymorphisms that might influence calcium metabolism: lactase (LCT) gene 13910 C/T polymorphism causing lactose intolerance and calcium-sensing receptor (CaSR) gene A986S polymorphism as a responsible factor for the altered cellular calcium sensation.

Methods

538 Hungarian subjects were studied: 278 patients with colorectal cancer and 260 healthy controls. Median follow-up was 17 months. After genotyping, the relationship between LCT 13910 C/T and CaSR A986S polymorphisms as well as tumor incidence/progression was investigated.

Results

in patient with colorectal cancer, a significantly higher LCT CC frequency was associated with increased distant disease recurrence (OR = 4.04; 95% CI = 1.71–9.58; p = 0.006). The disease free survival calculated from distant recurrence was reduced for those with LCT CC genotype (log rank test p = 0.008). In case of CaSR A986S polymorphism, the homozygous SS genotype was more frequent in patients than in controls (OR = 4.01; 95% CI = 1.33–12.07; p = 0.014). The number of LCT C and CaSR S risk alleles were correlated with tumor incidence (p = 0.035). The CCSS genotype combination was found only in patients with CRC (p = 0.033).

Conclusion

LCT 13910 C/T and CaSR A986S polymorphisms may have an impact on the progression and/or incidence of CRC.

Calcium, calcium-sensing receptor and colon cancer

There is much evidence that dietary Ca(2+) loading reduces colon cell proliferation and carcinogenesis in humans and rodents, but during carcinogenesis it becomes ineffective or even tumor-promoting. We are beginning to see how Ca(2+) balances the continuous massive cell production in colon crypts by driving the terminal differentiation and eventually the apoptosis of the cells mainly on the mucosal surface, and how this Ca(2+) control is lost during colon carcinogenesis. The rapid proliferation of the transit-amplifying (TA) progeny of the colon stem cells is driven by the so-called "Wnt" signaling mechanism, which involves the stimulation of proliferogenic genes such as those for c-Myc and cyclin D1 and the silencing of the gene for the cell cycle-stopping p21(Cip1/WAF1) protein by nuclear beta-catenin*Tcf-4 complexes. TA cells avoid mitotic damage and premature apoptosis by expressing the protein survivin. It appears that TA cell cycling stops and terminal differentiation starts when the cells reach a higher level in the crypt where there is enough lumenal Ca(2+) to stimulate the expression and activation of CaSRs (Ca(2+)-sensing receptors), the signals from which stimulate the expression of E-cadherin. Along with this, the APC (adenomatous polyposis coli) protein appears and some of it enters the nucleus. There it makes the TA cells susceptible to the eventual apoptotic balancing by stopping survivin expression and the beta-catenin*Tcf-4 complex from driving further cell cycling by releasing beta-catenin from the nucleus, and delivering it to cytoplasmic APC*axin*GSK-3beta complexes for ultimate proteasomal destruction. Cytoplasmic beta-catenin is then prevented from returning to the nucleus by either being intercepted and destroyed by APC*axin*GSK-3beta complexes or locked by the emerging E-cadherin into membrane adherens junctions which tie the cell into the sheet of proliferatively shut-down cells with APC-dependent cytoskeletons moving to the mouth of the crypt and onto the flat mucosal surface. A common first step in sporadic colon carcinogenesis is the loss of functional APC which disorients upwardly directed migration and causes the retention of nuclear beta-catenin and proliferogenic beta-catenin*Tcf-4 complexes as well as genomic instability. Eventually the balance between cell proliferation and terminal differentiation and death is radically tipped in favour of proliferation by the appearance of apoptosis-resistant, survivin-expressing clones of Ca(2+)-insensitive cells which are locked into the proliferative, mutation-prone mode because of CaSR-disabling gene mutations which prevent the stimulation of E-cadherin expression and terminal differentiation.

Guanosine promotes B16F10 melanoma cell differentiation through PKC-ERK 1/2 pathway

Malignant melanoma is one of the most lethal cancers. Nowadays, several anti-melanoma therapies have been employed. However, the poor prognosis and/or the increased toxicity of those treatments clearly demonstrate the requirement of searching for new drugs or novel combined chemotherapeutic protocols, contemplating both effectiveness and low toxicity. Guanosine (Guo) has been used in combination with acriflavina to potentiate the latter's antitumor activity, through still unknown mechanisms. Here, we show that Guo induces B16F10 melanoma cell differentiation, attested by growth arrest, dendrite-like outgrowth and increased melanogenesis, and also reduced motility. A sustained ERK 1/2 phosphorylation was observed after Guo treatment and ERK inhibition led to blockage of dendritogenesis. Intracellular cyclic AMP was not involved in ERK activation, since its levels remained unchanged. Protein kinase C (PKC), in contrast to phospholipase C (PLC), inhibition completely prevented ERK activation. While the classical melanoma differentiation agent forskolin activates cAMP-PKA-Raf-MEK-ERK pathway in B16F10 cells, here we suggest that a cAMP-independent, PKC-ERK axis is involved in Guo-induced B16F10 differentiation. Altogether, our results show that Guo acts as a differentiating agent, with cytostatic rather than cytotoxic properties, leading to a decreased melanoma malignancy. Thus, we propose that Guo may be envisaged in combination with lower doses of conventional anti-melanoma drugs, in an attempt to prevent or diminish their adverse effects.

XAF1 mediates apoptosis through an extracellular signal-regulated kinase pathway in colon cancer

BACKGROUND

XIAP-associated factor 1 (XAF1) negatively regulates the function of the X-linked inhibitor of apoptosis protein (XIAP), a member of the IAP family that exerts antiapoptotic effects. The extracellular signal-regulated kinase (ERK) pathway is thought to increase cell proliferation and to protect cells from apoptosis. The aim of the study was to investigate the correlation between the ERK1/2 signaling pathway and XAF1 in colon cancer.

METHODS

Four human colon cancer cell lines, HCT1116 and Lovo (wildtype p53), DLD1 and SW1116 (mutant p53), were used. Lovo stable transfectants with XAF1 sense and antisense were established. The effects of dominant-negative MEK1 (DN-MEK1) and MEK-specific inhibitor U0126 on the ERK signaling pathway and expression of XAF1 and XIAP proteins were determined. The transcription activity of core XAF1 promoter was assessed by dual luciferase reporter assay. Cell proliferation was measured by MTT assay. Apoptosis was determined by Hoechst 33258 staining.

RESULTS

U0126 increased the expression of XAF1 in a time- and dose-dependent manner. A similar result was obtained in cells transfected with DN-MEK1 treatment. Conversely, the expression of XIAP was down-regulated. Activity of the putative promoter of the XAF1 gene was significantly increased by U0126 treatment and DN-MEK1 transient transfection. rhEGF-stimulated phosphorylation of ERK appeared to have little or no effect on XAF1 expression. Overexpression of XAF1 was more sensitive to U0126-induced apoptosis, whereas down-regulation of XAF1 by antisense reversed U0126-induced inhibition of cell proliferation.

CONCLUSIONS

XAF1 expression was up-regulated by inhibition of the ERK1/2 pathway through transcriptional regulation, which required de novo protein synthesis. The results suggest that XAF1 mediates apoptosis induced by the ERK1/2 pathway in colon cancer.

Plasma membrane Ca2+-ATPase expression during colon cancer cell line differentiation

The differentiation of colon cancer cell lines is associated with changes in calcium homeostasis. Concomitantly there are changes in the expression of some calcium transporters and G-protein-coupled receptors, which are capable of altering cytosolic-free calcium levels. Recent studies associate alterations in calcium transporter expression with tumourigenesis, such as changes in specific isoforms of the plasma membrane calcium ATPase (PMCA) in breast cancer cell lines. In this study, we examined the expression of PMCA isoforms in the HT-29 colon cancer cell line using two methods of differentiation (sodium butyrate-mediated and spontaneous post-confluency induced differentiation). Our studies show that differentiation of HT-29 colon cancer cells is associated with the up-regulation of the PMCA isoform PMCA4 but no significant alteration in PMCA1. These results suggest that PMCA4 may be important and have a specific role in colon cells as well as being significant in colon cancer tumourigenesis.

Regulation of E-cadherin and β-catenin by Ca2+ in colon carcinoma is dependent on calcium-sensing receptor expression and function

An siRNA directed against the extracellular calcium-sensing receptor (CaSR) was used to down-regulate this protein in CBS colon carcinoma cells. In additional studies, we utilized a variant of the parental CBS line that demonstrates CaSR expression but does not upregulate this protein in response to extracellular Ca(2+). In neither the siRNA-transfected cells nor the Ca(2+)-nonresponsive variant cells did inclusion of Ca(2+) in the culture medium inhibit proliferation or induce morphological alterations. Extracellular Ca(2+) also failed to induce E-cadherin production or a shift in beta-catenin from the cytoplasm to the cell membrane. In mock-transfected cells and in a Ca(2+)-responsive variant line derived from the same parental CBS cells, Ca(2+) treatment resulted in growth-reduction. This was accompanied by increased E-cadherin production and a shift in beta-catenin distribution from the cytoplasm to the cell membrane. Additionally, down-regulation of c-myc and cyclin D1 expression was observed in mock-transfected cells and in the Ca(2+)-responsive variant line (along with reduced T cell factor transcriptional activation). Neither c-myc nor cyclin D1 was significantly down-regulated in the siRNA-transfected cells or in the Ca(2+)-nonresponsive variant cells upon Ca(2+) stimulation. In histological sections of human colon carcinoma CaSR was significantly reduced as compared to the level in normal colonic crypt epithelial cells. Where CaSR expression was high, strong surface staining for E-cadherin and beta-catenin was observed. Where CaSR expression was reduced, beta-catenin surface expression was likewise reduced.

Promoter hypermethylation and silencing of CHFR mitotic stress checkpoint gene in human gastric cancers

CHFR is a recently identified mitotic stress check-point gene. CHFR is ubiquitously expressed in normal human tissues, whereas loss of CHFR expression has been observed in human tumors. Silencing of CHFR has been associated with aberrant promoter methylation and histone deacetylation in several cancer types. In this study, we investigated epigenetic CHFR inactivation in human gastric cancers by examining CHFR expression and methylation status in gastric cancer cell lines with RT-PCR analysis, bisulfite PCR and sequencing. A series of primary gastric tumors were also analyzed for CHFR methylation. Eight of 12 (66.7%) gastric cancer cell lines and 19/43 (44.2%) primary gastric tumors showed CHFR methylation. In addition, CpG methylation status correlated well with CHFR expression in the human gastric cancer cell lines, in which treatment with 5-aza-dC resulted in de novo or enhanced expression of CHFR. Combination treatment of 5-aza-dC with trichostatin A showed a synergistic effect on CHFR expression in some cases. Our results indicate that aberrant promoter methylation of the CHFR gene was observed in a significant proportion of human gastric cancers and was responsible for the inactivation of the CHFR gene in gastric cancers.