Calcium-sensing receptor silencing in colorectal cancer is associated with promoter hypermethylation and loss of acetylation on histone 3

Implication of calcium supplementations in health and diseases with special focus on colorectal cancer

Calcium is a fundamental and integrative element and helps to ensure optimal health by regulating various physiological and pathological processes. While there is substantiated evidence confirming the beneficial effects of calcium in the treatment, management, and prevention of various health conditions, including cancer, conflicting studies are imperative to acknowledge the potential negative role of calcium supplementation. The studies on calcium supplementation showed that a specific dose can help in the maintenance of good human health, and in the control of different types of diseases, including cancer. Calcium alone and when combined with vitamin D, emerges as a promising therapeutic option for efficiently managing cancer growth, when used with chemotherapy. Combination therapy is considered a more effective approach for treating advanced types of colorectal cancer. Nevertheless, several challenges drastically influence the treatment of cancer, such as individual discrepancy, drug resistance, and stage of cancer, among others. Henceforth, novel preventive, reliable therapeutic modalities are essential to control and reduce the incidence and mortality of colorectal cancer (CRC). The calcium-sensing receptor (CaSR) plays a pivotal role in calcium homeostasis, metabolism, and regulation of oncogenesis. Numerous studies have underscored the potential of CaSR, a G protein-coupled receptor, as a potential biomarker and target for colorectal cancer prevention and treatment. The multifaceted involvement of CaSR in anti-inflammatory and anti-carcinogenic processes paves the way for its utilization in the diagnosis and management of colorectal cancer. The current review highlights the important role of supplemental calcium in overall health and disease, along with the exploration of intricate mechanisms of CaSR pathways in the management and prevention of colorectal cancer.

Molecular regulation of calcium-sensing receptor (CaSR)-mediated signaling

Calcium-sensing receptor (CaSR), a family C G-protein-coupled receptor, plays a crucial role in regulating calcium homeostasis by sensing small concentration changes of extracellular Ca2+, Mg2+, amino acids (e.g., L-Trp and L-Phe), small peptides, anions (e.g., HCO3 - and PO4 3-), and pH. CaSR-mediated intracellular Ca2+ signaling regulates a diverse set of cellular processes including gene transcription, cell proliferation, differentiation, apoptosis, muscle contraction, and neuronal transmission. Dysfunction of CaSR with mutations results in diseases such as autosomal dominant hypocalcemia, familial hypocalciuric hypercalcemia, and neonatal severe hyperparathyroidism. CaSR also influences calciotropic disorders, such as osteoporosis, and noncalciotropic disorders, such as cancer, Alzheimer's disease, and pulmonary arterial hypertension. This study first reviews recent advances in biochemical and structural determination of the framework of CaSR and its interaction sites with natural ligands, as well as exogenous positive allosteric modulators and negative allosteric modulators. The establishment of the first CaSR protein-protein interactome network revealed 94 novel players involved in protein processing in endoplasmic reticulum, trafficking, cell surface expression, endocytosis, degradation, and signaling pathways. The roles of these proteins in Ca2+-dependent cellular physiological processes and in CaSR-dependent cellular signaling provide new insights into the molecular basis of diseases caused by CaSR mutations and dysregulated CaSR activity caused by its protein interactors and facilitate the design of therapeutic agents that target CaSR and other family C G-protein-coupled receptors.

Comprehensive DNA Methylation Profiling of Medullary Thyroid Carcinoma: Molecular Classification, Potential Therapeutic Target, and Classifier System

PURPOSE

Medullary thyroid carcinoma (MTC) presents a distinct biological context from other thyroid cancers due to its specific cellular origin. This heterogeneous and rare tumor has a high prevalence of advanced diseases, making it crucial to address the limited therapeutic options and enhance complex clinical management. Given the high clinical accessibility of methylation information, we construct the largest MTC methylation cohort to date.

EXPERIMENTAL DESIGN

Seventy-eight fresh-frozen MTC samples constituted our methylation cohort. The comprehensive study process incorporated machine learning, statistical analysis, and in vitro experiments.

RESULTS

Our study pioneered the identification of a three-class clustering system for risk stratification, exhibiting pronounced epigenomic heterogeneity. The elevated overall methylation status in MTC-B, combined with the "mutual exclusivity" of hypomethylated sites displayed by MTC-A and MTC-C, distinctively characterized the MTC-specific methylation pattern. Integrating with the transcriptome, we further depicted the features of these three clusters to scrutinize biological properties. Several MTC-specific aberrant DNA methylation events were emphasized in our study. NNAT expression was found to be notably reduced in poor-prognostic MTC-C, with its promoter region overlapping with an upregulated differentially methylated region. In vitro experiments further affirmed NNAT's therapeutic potential. Moreover, we built an elastic-net logistic regression model with a relatively high AUC encompassing 68 probes, intended for future validation and systematic clinical application.

CONCLUSIONS

Conducting research on diseases with low incidence poses significant challenges, and we provide a robust resource and comprehensive research framework to assist in ongoing MTC case inclusion and facilitate in-depth dissection of its molecular biological features.

Calcium-sensing receptor-mediated NLRP3 inflammasome activation in rheumatoid arthritis and autoinflammation

The calcium-sensing receptor (CaSR) is expressed in many cell types - including immune cells and in particular circulating monocytes. Here, the receptor plays an important physiological role as a regulator of constitutive macropinocytosis. This review article provides an overview of the literature on the role of the calcium sensing receptor in the context of inflammatory processes. Special emphasis is laid upon the importance for monocytes in the context of rheumatoid arthritis. We have shown previously, that stimulation of the receptor by increased extracellular Ca²⁺ ([Ca²⁺]_ex) triggers a pro-inflammatory response due to NLRP3 inflammasome assembly and interleukin (IL)-1β release. The underlying mechanism includes macropinocytosis of calciprotein particles (CPPs), which are taken up in a [Ca²⁺]_ex-induced, CaSR dependent manner, and leads to strong IL-1β release. In rheumatoid arthritis (RA), this uptake and the resulting IL-1β release is significantly increased due to increased expression of the receptor. Moreover, increased [Ca²⁺]_ex-induced CPP uptake and IL-1β release is associated with more active disease, while CaSR overexpression has been reported to be associated with cardiovascular complications of RA. Most importantly, however, in animal experiments with arthritic mice, increased local calcium concentrations are present, which in combination with release of fetuin-A from eroded bone could contribute to formation of CPPs. We propose, that increased [Ca²⁺]_ex, CPPs and pro-inflammatory cytokines drive a vicious cycle of inflammation and bone destruction which in turn offers new potential therapeutic approaches.

Aberrant Epigenetic Alteration of PAX1 Expression Contributes to Parathyroid Tumorigenesis

CONTEXT

Primary hyperparathyroidism (PHPT) results from the hypersecretion of parathyroid hormone from parathyroid tumors. A transcription factor, namely Paired box1 (PAX1), is active in parathyroid gland development.

OBJECTIVE

We aimed to study potential epigenetic-mediated mechanism of PAX1 gene in sporadic parathyroid adenomas.

METHODS

In parathyroid adenomas tissues, we analyzed the DNA methylation via bisulfite-specific polymerase chain reaction (BSP) and histone modifications via chromatin immunoprecipitation in regulating the differential expression of PAX1.

RESULTS

The results showed that mRNA and protein expression of PAX1 was significantly reduced in parathyroid adenomas. Bisulfite sequencing demonstrated hypermethylation in the promoter region of PAX1 (35%; 14/40) and lower levels of histone 3 lysine 9 acetylation (H3K9ac) were observed on the promoter region of PAX1 (6-fold; P < .004) in parathyroid adenomas. Furthermore, upon treatment with a pharmacologic inhibitor, namely 5'aza-2 deoxycytidine, in rat parathyroid continuous cells, we found re-expression of PAX1 gene.

CONCLUSION

Our study not only reveals expression of PAX1 is epigenetically deregulated but also paves a way for clinical and therapeutic implications in patients with PHPT.

GCM2 Silencing in Parathyroid Adenoma Is Associated With Promoter Hypermethylation and Gain of Methylation on Histone 3

CONTEXT

Glial cells missing 2 (GCM2), a zinc finger-transcription factor, is essentially required for the development of the parathyroid glands.

OBJECTIVE

We sought to identify whether the epigenetic alterations in GCM2 transcription are involved in the pathogenesis of sporadic parathyroid adenoma. In addition, we examined the association between promoter methylation and histone modifications with disease indices.

METHODS

Messenger RNA (mRNA) and protein expression of GCM2 were analyzed by reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry in 33 adenomatous and 10 control parathyroid tissues. DNA methylation and histone methylation/acetylation of the GCM2 promoter were measured by bisulfite sequencing and chromatin immunoprecipitation-qPCR. Additionally, we investigated the role of epigenetic modifications on GCM2 and DNA methyltransferase 1 (DNMT1) expression in parathyroid (PTH)-C1 cells by treating with 5-aza-2'-deoxycytidine (DAC) and BRD4770 and assessed for GCM2 mRNA and DNMT1 protein levels.

RESULTS

mRNA and protein expression of GCM2 were lower in sporadic adenomatous than in control parathyroid tissues. This reduction correlated with hypermethylation (P < .001) and higher H3K9me3 levels in the GCM2 promoter (P < .04) in adenomas. In PTH-C1 cells, DAC treatment resulted in increased GCM2 transcription and decreased DNMT1 protein expression, while cells treated with the BRD4770 showed reduced H3K9me3 levels but a nonsignificant change in GCM2 transcription.

CONCLUSION

These findings suggest the concurrent association of promoter hypermethylation and higher H3K9me3 with the repression of GCM2 expression in parathyroid adenomas. Treatment with DAC restored GCM2 expression in PTH-C1 cells. Our results showed a possible epigenetic landscape in the tumorigenesis of parathyroid adenoma and also that DAC may be a promising avenue of research for parathyroid adenoma therapeutics.

The calcium sensing receptor (CaSR) promotes Rab27B expression and activity to control secretion in breast cancer cells

Chemotactic and angiogenic factors secreted within the tumor microenvironment eventually facilitate the metastatic dissemination of cancer cells. Calcium-sensing receptor (CaSR) activates secretory pathways in breast cancer cells via a mechanism driven by vesicular trafficking of this receptor. However, it remains to be elucidated how endosomal proteins in secretory vesicles are controlled by CaSR. In the present study, we demonstrate that CaSR promotes expression of Rab27B and activates this secretory small GTPase via PI3K, PKA, mTOR and MADD, a guanine nucleotide exchange factor, also known as DENN/Rab3GEP. Active Rab27B leads secretion of various cytokines and chemokines, including IL-6, IL-1β, IL-8, IP-10 and RANTES. Expression of Rab27B is stimulated by CaSR in MDA-MB-231 and MCF-7 breast epithelial cancer cells, but not in non-cancerous MCF-10A cells. This regulatory mechanism also occurs in HeLa and PC3 cells. Our findings provide insightful information regarding how CaSR activates a Rab27B-dependent mechanism to control secretion of factors known to intervene in paracrine communication circuits within the tumor microenvironment.

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.

Reduced Calcium Sensing Receptor (CaSR) Expression Is Epigenetically Deregulated in Parathyroid Adenomas

AIM

Reduced calcium sensing receptor (CaSR) expression has been implicated in parathyroid tumorigenesis, but the underlying mechanism remains elusive. Accordingly, we aimed to explore the epigenetic changes (DNA methylation and histone modifications) involved in CaSR regulation in sporadic parathyroid adenomas and correlate epigenetic state with disease indices.

EXPERIMENTAL DESIGN

Forty sporadic parathyroid adenomas and 10 control parathyroid tissues were studied. Real-time quantitative PCR (qPCR) for mRNA and immunohistochemistry for protein expression of CaSR were performed. The methylation status of the CaSR promoter 2 was determined by bisulphite sequencing analysis of sodium bisulphite-converted DNA. To determine the role of histone modifications in the CaSR regulation, chromatin immunoprecipitation-qPCR assay was performed.

RESULTS

Real-time qPCR revealed reduced CaSR mRNA expression with a fold reduction of 0.12 (P < 0.0001) in parathyroid adenomas. Immunohistochemistry revealed reduced protein expression of CaSR in 90% (36/40) of adenomas. The promoter 2 region of CaSR displayed significant hypermethylation in 45% (18/40) of the adenomas compared with the controls (6.7%; 1 of 10) (P < 0.002). Bisulphite sequencing analysis revealed maximum methylated CpG at glial cell missing 2 binding site on the CaSR promoter 2 compared to other CpG sites. The methylation status of CaSR correlated directly with plasma intact parathyroid hormone levels in patients with parathyroid adenoma. With chromatin immunoprecipitation-qPCR analysis, H3K9me3 levels showed increased enrichment by 10-fold in adenomas and correlated with CaSR-mRNA expression (r = 0.61; P < 0.003). Treatment with 5-aza-2'deoxycytidine restored the expression of CaSR in a parathyroid cell line.

CONCLUSION

Our data suggest that hypermethylation and increased H3K9me3 of the CaSR promoter 2 are involved in silencing CaSR expression in sporadic parathyroid adenoma.

The CaSR in Pathogenesis of Breast Cancer: A New Target for Early Stage Bone Metastases

The Ca2+-sensing receptor (CaSR) is a class-C G protein-coupled receptor which plays a pivotal role in calciotropic processes, primarily in regulating parathyroid hormone secretion to maintain systemic calcium homeostasis. Among its non-calciotropic roles, where the CaSR sits at the intersection of myriad processes, it has steadily garnered attention as an oncogene or tumor suppressor in different organs. In maternal breast tissues the CaSR promotes lactation but in breast cancer it acts as an oncoprotein and has been shown to drive the pathogenesis of skeletal metastases from breast cancer. Even though research has made great strides in treating primary breast cancer, there is an unmet need when it comes to treatment of metastatic breast cancer. This review focuses on how the CaSR leads to the pathogenesis of breast cancer by contrasting its role in healthy tissues and tumorigenesis, and by drawing brief parallels with the tissues where it has been implicated as an oncogene. A class of compounds called calcilytics, which are CaSR antagonists, have also been surveyed in the instances where they have been used to target the receptor in cancerous tissues and constitute a proof of principle for repurposing them. Current clinical therapies for treating bone metastases from breast cancer are limited to targeting osteoclasts and a deeper understanding of the CaSR signaling nexus in this context can bolster them or lead to novel therapeutic interventions.

DNA methylome profiling of granulosa cells reveals altered methylation in genes regulating vital ovarian functions in polycystic ovary syndrome

Background

Women with polycystic ovary syndrome (PCOS) manifest a host of ovarian defects like impaired folliculogenesis, anovulation, and poor oocyte quality, which grossly affect their reproductive health. Addressing the putative epigenetic anomalies that tightly regulate these events is of foremost importance in this disorder. We therefore aimed to carry out DNA methylome profiling of cumulus granulosa cells and assess the methylation and transcript expression profiles of a few differentially methylated genes contributing to ovarian defects in PCOS. A total of 20 controls and 20 women with PCOS were selected from a larger cohort of women undergoing IVF, after carefully screening their sera and follicular fluids for hormonal and biochemical parameters. DNA extracted from cumulus granulosa cells of three women each, from control and PCOS groups was subjected to high-throughput, next generation bisulfite sequencing, using the Illumina HiSeq 2500® platform. Remaining samples were used for the validation of methylation status of some identified genes by pyrosequencing, and the transcript expression profiles of these genes were assessed by quantitative real-time PCR.

Results

In all, 6486 CpG sites representing 3840 genes associated with Wnt signaling, G protein receptor, endothelin/integrin signaling, angiogenesis, chemokine/cytokine-mediated inflammation, etc., showed differential methylation in PCOS. Hypomethylation was noted in 2977 CpGs representing 2063 genes while 2509 CpGs within 1777 genes showed hypermethylation. Methylation differences were also noted in noncoding RNAs regulating several ovarian functions that are dysregulated in PCOS. Few differentially methylated genes such as aldo-keto reductase family 1 member C3, calcium-sensing receptor, resistin, mastermind-like domain 1, growth hormone-releasing hormone receptor and tumor necrosis factor, which predominantly contribute to hyperandrogenism, premature luteolysis, and oocyte development defects, were explored as novel epigenetic candidates in mediating ovarian dysfunction. Methylation profiles of these genes matched with our NGS findings, and their transcript expression patterns correlated with the gene hypo- or hypermethylation status.

Conclusion

Our findings suggest that the epigenetic dysregulation of genes involved in important processes associated with follicular development may contribute to ovarian defects observed in women with PCOS.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0657-6) contains supplementary material, which is available to authorized users.

The calcium-sensing receptor in physiology and in calcitropic and noncalcitropic diseases

The Ca2+-sensing receptor (CaSR) is a dimeric family C G protein-coupled receptor that is expressed in calcitropic tissues such as the parathyroid glands and the kidneys and signals via G proteins and β-arrestin. The CaSR has a pivotal role in bone and mineral metabolism, as it regulates parathyroid hormone secretion, urinary Ca2+ excretion, skeletal development and lactation. The importance of the CaSR for these calcitropic processes is highlighted by loss-of-function and gain-of-function CaSR mutations that cause familial hypocalciuric hypercalcaemia and autosomal dominant hypocalcaemia, respectively, and also by the fact that alterations in parathyroid CaSR expression contribute to the pathogenesis of primary and secondary hyperparathyroidism. Moreover, the CaSR is an established therapeutic target for hyperparathyroid disorders. The CaSR is also expressed in organs not involved in Ca2+ homeostasis: it has noncalcitropic roles in lung and neuronal development, vascular tone, gastrointestinal nutrient sensing, wound healing and secretion of insulin and enteroendocrine hormones. Furthermore, the abnormal expression or function of the CaSR is implicated in cardiovascular and neurological diseases, as well as in asthma, and the CaSR is reported to protect against colorectal cancer and neuroblastoma but increase the malignant potential of prostate and breast cancers.

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.

Calcium-sensing receptor in nutrient sensing: an insight into the modulation of intestinal homoeostasis

The animal gut effectively prevents the entry of hazardous substances and microbes while permitting the transfer of nutrients, such as water, electrolytes, vitamins, proteins, lipids, carbohydrates, minerals and microbial metabolites, which are intimately associated with intestinal homoeostasis. The gut maintains biological functions through its nutrient-sensing receptors, including the Ca-sensing receptor (CaSR), which activates a variety of signalling pathways, depending on cellular context. CaSR coordinates food digestion and nutrient absorption, promotes cell proliferation and differentiation, regulates energy metabolism and immune response, stimulates hormone secretion, mitigates secretory diarrhoea and enhances intestinal barrier function. Thus, CaSR is crucial to the maintenance of gut homoeostasis and protection of intestinal health. In this review, we focused on the emerging roles of CaSR in the modulation of intestinal homoeostasis including related underlying mechanisms. By elucidating the relationship between CaSR and animal gut homoeostasis, effective and inexpensive methods for treating intestinal health imbalance through nutritional manipulation can be developed. This article is expected to provide experimental data of the effects of CaSR on animal or human health.

Calcium intake and risk of colorectal cancer according to expression status of calcium-sensing receptor (CASR)

OBJECTIVE

Although evidence suggests an inverse association between calcium intake and the risk of colorectal cancer, the mechanisms remain unclear. The calcium-sensing receptor (CASR) is expressed abundantly in normal colonic epithelium and may influence carcinogenesis. We hypothesized that calcium intake might be associated with lower risk of CASR-positive, but not CASR-negative, colorectal cancer.

DESIGN

We assessed tumour CASR protein expression using immunohistochemistry in 779 incident colon and rectal cancer cases that developed among 136 249 individuals in the Nurses' Health Study and Health Professionals Follow-Up Study. Duplication method Cox proportional hazards regression analysis was used to assess associations of calcium intake with incidence of colorectal adenocarcinoma subtypes by CASR status.

RESULTS

Total calcium intake was inversely associated with the risk of developing colorectal cancer (p_trend=0.01, comparing ≥1200 vs <600 mg/day: multivariable HR=0.75, 95% CI 0.60 to 0.95). For the same comparison, higher total calcium intake was associated with a lower risk of CASR-positive tumours (p_trend=0.003, multivariable HR=0.67, 95% CI 0.51 to 0.86) but not with CASR-negative tumours (p_trend=0.67, multivariable HR=1.15, 95% CI 0.75 to 1.78; p_{heterogeneity}=0.06 between the CASR subtypes). The stronger inverse associations of calcium intake with CASR-positive but not CASR-negative tumours generally appeared consistent regardless of sex, tumour location and source of calcium.

CONCLUSIONS

Our molecular pathological epidemiology data suggest a causal relationship between higher calcium intake and lower colorectal cancer risk, and a potential role of CASR in mediating antineoplastic effect of calcium.

Mediterranean Diet: Prevention of Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer diagnosis and the second and third leading cause of cancer mortality in men and women, respectively. However, the majority of CRC cases are the result of sporadic tumorigenesis via the adenoma–carcinoma sequence. This process can take up to 20 years, suggesting an important window of opportunity exists for prevention such as switching toward healthier dietary patterns. The Mediterranean diet (MD) is a dietary pattern associated with various health benefits including protection against cardiovascular disease, diabetes, obesity, and various cancers. In this article, we review publications available in the PubMed database within the last 10 years that report on the impact of a MD eating pattern on prevention of CRC. To assist the reader with interpretation of the results and discussion, we first introduce indexes and scoring systems commonly used to experimentally determine adherence to a MD, followed by a brief introduction of the influence of the MD pattern on inflammatory bowel disease, which predisposes to CRC. Finally, we discuss key biological mechanisms through which specific bioactive food components commonly present in the MD are proposed to prevent or delay the development of CRC. We close with a discussion of future research frontiers in CRC prevention with particular reference to the role of epigenetic mechanisms and microbiome related to the MD eating pattern.

Tumor expression of calcium sensing receptor and colorectal cancer survival: Results from the nurses' health study and health professionals follow-up study

Although experimental evidence suggests calcium-sensing receptor (CASR) as a tumor-suppressor, the prognostic role of tumor CASR expression in colorectal carcinoma remains unclear. We hypothesized that higher tumor CASR expression might be associated with improved survival among colorectal cancer patients. We evaluated tumor expression levels of CASR by immunohistochemistry in 809 incident colorectal cancer patients within the Nurses' Health Study and the Health Professionals Follow-up Study. We used Cox proportional hazards regression models to estimate multivariable hazard ratio (HR) for the association of tumor CASR expression with colorectal cancer-specific and all-cause mortality. We adjusted for potential confounders including tumor biomarkers such as microsatellite instability, CpG island methylator phenotype, LINE-1 methylation level, expressions of PTGS2, VDR and CTNNB1 and mutations of KRAS, BRAF and PIK3CA. There were 240 colorectal cancer-specific deaths and 427 all-cause deaths. The median follow-up of censored patients was 10.8 years (interquartile range: 7.2, 15.1). Compared with patients with no or weak expression of CASR, the multivariable HRs for colorectal cancer-specific mortality were 0.80 [95% confidence interval (CI): 0.55-1.16] in patients with moderate CASR expression and 0.50 (95% CI: 0.32-0.79) in patients with intense CASR expression (p-trend = 0.003). The corresponding HRs for overall mortality were 0.85 (0.64-1.13) and 0.81 (0.58-1.12), respectively. Higher tumor CASR expression was associated with a lower risk of colorectal cancer-specific mortality. This finding needs further confirmation and if confirmed, may lead to better understanding of the role of CASR in colorectal cancer progression.

Novel FOXG1 mutations in Chinese patients with Rett syndrome or Rett-like mental retardation

Background

We aimed to delineate clinical phenotypes associated with FOXG1 mutations in Chinese patients with Rett syndrome (RTT) or RTT-like mental retardation (MR).

Methods

Four hundred and fifty-one patients were recruited, including 418 with RTT and 33 with RTT-like MR. Gene mutations were identified by a target capture method and verified by Sanger sequencing.

Results

Four FOXG1 mutations were detected in four patients (three with RTT and one with RTT-like MR), including one previously described mutation and three novel mutations. These mutations included one missense and three micro-insertion mutations. Overall, 0.7% (3/418) of patients who had RTT in our cohort had FOXG1 mutations. All patients had early global developmental delays followed later by severe mental retardation. None of the patients acquired speech or purposeful hand movements, and all of them presented with severe hypotonia, epilepsy, and hypoplasia of the corpus callosum.

Conclusions

Our findings extend the spectrum of FOXG1 mutations and the clinical features of RTT in Chinese patients. We recommend that patients with congenital RTT and Rett-like MR, especially those with brain malformations, such as hypoplasia of the corpus callosum, should be tested for FOXG1 mutations.

Cross Talk between the Calcium-Sensing Receptor and the Vitamin D System in Prevention of Cancer

There is epidemiological evidence for the cancer preventive effect of dietary calcium (Ca²⁺) and vitamin D. This effect is strongest in colorectal cancer (CRC). The active vitamin D metabolite, 1,25-dihydroxyvitamin D₃ (1,25D₃), bound to its receptor, the vitamin D receptor (VDR) regulates the expression of hundreds of different genes in a cell- and tissue-specific manner. While Ca²⁺ acts through multiple mechanisms and pathways, some of its effects are mediated by the calcium-sensing receptor (CaSR). The joint action of Ca²⁺ and 1,25D₃ is due to the fact that both regulate some of the main processes involved in the development of various cancers, such as proliferation, differentiation, apoptosis, migration, and inflammation. Moreover, 1,25D₃, bound to VDR can induce translation of the CaSR, while the amount and activity of the CaSR affects 1,25D₃ signaling. However, the complexity of the cross-talk between the CaSR and the vitamin D system goes beyond regulating similar pathways and affecting each other's expression. Our aim was to review some of the mechanisms that drive the cross-talk between the vitamin D system and the CaSR with a special focus on the interaction in CRC cells. We evaluated the molecular evidence that supports the epidemiological observation that both vitamin D and calcium are needed for protection against malignant transformation of the colon and that their effect is modulated by the presence of a functional CaSR.

Calcium-Sensing Receptor Gene: Regulation of Expression

The human calcium-sensing receptor gene (CASR) has 8 exons, and localizes to chromosome 3q. Exons 1A and 1B encode alternative 5′-untranslated regions (UTRs) that splice to exon 2 encoding the AUG initiation codon. Exons 2–7 encode the CaSR protein of 1078 amino acids. Promoter P1 has TATA and CCAAT boxes upstream of exon 1A, and promoter P2 has Sp1/3 motifs at the start site of exon 1B. Exon 1A transcripts from the P1 promoter are reduced in parathyroid tumors and colon carcinomas. Studies of colon carcinomas and neuroblastomas have emphasized the importance of epigenetic changes—promoter methylation of the GC-rich P2 promoter, histone acetylation—as well as involvement of microRNAs in bringing about CASR gene silencing and reduced CaSR expression. Functional cis-elements in the CASR promoters responsive to 1,25-dihydroxyvitamin D [1,25(OH)₂D], proinflammatory cytokines, and the transcription factor glial cells missing-2 (GCM2) have been characterized. Reduced levels of CaSR and reduced responsiveness to active vitamin D in parathyroid neoplasia and colon carcinoma may blunt the “tumor suppressor” activity of the CaSR. The hypocalcemia of critically ill patients with burn injury or sepsis is associated with CASR gene upregulation by TNF-alpha and IL-1beta via kappaB elements, and by IL-6 via Stat1/3 and Sp1/3 elements in the CASR gene promoters, respectively. The CASR is transactivated by GCM2—the expression of which is essential for parathyroid gland development. Hyperactive forms of GCM2 may contribute to later parathyroid hyperactivity or tumorigenesis. The expression of the CaSR—the calciostat—is regulated physiologically and pathophysiologically at the gene level.

The Calcium-Sensing Receptor in Health and Disease

The extracellular calcium-sensing receptor (CaSR) is a unique G protein-coupled receptor (GPCR) activated by extracellular Ca²⁺ and by other physiological cations including Mg²⁺, amino acids, and polyamines. CaSR is the most important master controller of the extracellular Ca²⁺ homeostatic system being expressed at high levels in the parathyroid gland, kidney, gut and bone, where it regulates parathyroid hormone (PTH) secretion, vitamin D synthesis, and Ca²⁺ absorption and resorption, respectively. Gain and loss of function mutations in the CaSR are responsible for severe disturbances in extracellular Ca²⁺ metabolism. CaSR agonists (calcimimetics) and antagonists (calcilytics) are in use or under intense research for treatment of hyperparathyroidism secondary to kidney failure and hypocalcemia with hypercalciuria, respectively. Expression of the CaSR extends to other tissues and systems beyond the extracellular Ca²⁺ homeostatic system including the cardiovascular system, the airways, and the nervous system where it may play physiological functions yet to be fully understood. As a consequence, CaSR has been recently involved in different pathologies including uncontrolled blood pressure, vascular calcification, asthma, and Alzheimer's disease. Finally, the CaSR has been shown to play a critical role in cancer either contributing to bone metastasis and/or acting as a tumor suppressor in some forms of cancer (parathyroid cancer, colon cancer, and neuroblastoma) and as oncogene in others (breast and prostate cancers). Here we review the role of CaSR in health and disease in calciotropic tissues and others beyond the extracellular calcium homeostatic system.

Effect of 1,25-dihydroxyvitamin D3 on the Wnt pathway in non-malignant colonic cells

Epidemiological studies suggest a correlation between vitamin D deficiency and colorectal cancer (CRC) incidence. The majority of sporadic tumors develop from premalignant lesions with aberrant activation of the Wnt/β-catenin signaling pathway. The adenoma cell line LT97 harbors an adenomatous polyposis coli (APC) mutation leading to constitutively active Wnt signaling. In these cells, expression of Wnt target genes leads to increased survival capacity. We hypothesized that 1,25-dihydroyvitamin D3 (1,25-D3), the active form of vitamin D3, promotes differentiation by modulating β-catenin/T-cell factor (TCF) 4-mediated gene transcription. The effect of dietary vitamin D on colonic Wnt signaling was investigated in mice fed either with 100 IU or 2500 IU vitamin D/kg diet. We examined the effect of 1,25-D3 on differentiation by measuring alkaline phosphatase activity. We analyzed mRNA expression of Wnt target genes by real time qRT-PCR. The impact of 1,25-D3 on β-catenin and TCF4 protein expression was assessed by western blot and immunohistochemistry. In LT97 cells, 1,25-D3 increased cellular differentiation and reduced nuclear β-catenin levels. Further, 1,25-D3 decreased mRNA expression of the Wnt target genes BCL-2, Cyclin D1, Snail1, CD44 and LGR5. In healthy colon of mice fed with high vitamin D diet, the mRNA levels of Wnt5a and ROR2, that promote degradation of β-catenin, were upregulated whereas β-catenin and TCF4 protein expression were decreased. In conclusion, 1,25-D3 inhibits Wnt signaling even in nonmalignant cells underlining its importance in protection against colorectal tumorigenesis and early tumor progression. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Active vitamin D potentiates the anti-neoplastic effects of calcium in the colon: A cross talk through the calcium-sensing receptor

Epidemiological studies suggest an inverse correlation between dietary calcium (Ca(2+)) and vitamin D intake and the risk of colorectal cancer (CRC). It has been shown in vitro that the active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25-D3) can upregulate expression of the calcium-sensing receptor (CaSR). In the colon, CaSR has been suggested to regulate proliferation of colonocytes. However, during tumorigenesis colonic CaSR expression is downregulated and we hypothesized that the loss of CaSR could influence the anti-tumorigenic effects of Ca(2+) and vitamin D. Our aim was to assess the impact of CaSR expression and function on the anti-neoplastic effects of 1,25-D3 in colon cancer cell lines. We demonstrated that in the healthy colon of mice, high vitamin D diet (2500 IU/kg diet) increased expression of differentiation and apoptosis markers, decreased expression of proliferation markers and significantly upregulated CaSR mRNA expression, compared with low vitamin D diet (100 IU/kg diet). To determine the role of CaSR in this process, we transfected Caco2-15 and HT29 CRC cells with wild type CaSR (CaSR-WT) or a dominant negative CaSR mutant (CaSR-DN) and treated them with 1,25-D3 alone, or in combination with CaSR activators (Ca(2+) and NPS R-568). 1,25-D3 enhanced the anti-proliferative effects of Ca(2+) and induced differentiation and apoptosis only in cells with a functional CaSR, which were further enhanced in the presence of NPS R-568, a positive allosteric modulator of CaSR. The mutant CaSR inhibited the anti-tumorigenic effects of 1,25-D3 suggesting that the anti-neoplastic effects of 1,25-D3 are, at least in part, mediated by the CaSR. Taken together, our data provides molecular evidence to support the epidemiological observation that both, vitamin D and calcium are needed for protection against malignant transformation of the colon and that their effect is modulated by the presence of a functional CaSR. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

miR-135b- and miR-146b-dependent silencing of calcium-sensing receptor expression in colorectal tumors

Studies have shown that the calcium-sensing receptor (CaSR) mediates the antitumorigenic effects of calcium against colorectal cancer (CRC). Expression of the CaSR in colorectal tumors is often reduced. We have reported previously that silencing of CaSR in CRC is caused in part by methylation of CaSR promoter 2 and loss of histone acetylation. We investigated the impact of aberrant microRNA expression on loss of CaSR expression. A microarray study in two Caco-2 subclones (Caco2/AQ and Caco2/15) that have similar genetic background, but different CaSR expression levels (Caco2/AQ expressing more CaSR than Caco2/15), identified 22 differentially expressed microRNAs that potentially target the CaSR. We validated these results by performing gain- and loss-of-function studies with the top candidates: miR-9, miR-27a, miR-135b, and miR-146b. Modulation of miR-135b or miR-146b expression by mimicking or inhibiting their expression regulated CaSR protein levels in two different colon cancer cell lines: Caco2/AQ (moderate endogenous CaSR expression) and HT29 (low endogenous CaSR levels). Inhibition of miR-135b and miR-146b expression led to high CaSR levels and significantly reduced proliferation. In samples of colorectal tumors we observed overexpression of miR-135b and miR-146b, and this correlated inversely with CaSR expression (miR-135b: r = -0.684, p < 0.001 and miR-146b: r = -0.448, p < 0.001), supporting our in vitro findings. We demonstrate that miR-135b and miR-146b target the CaSR and reduce its expression in colorectal tumors, reducing the antiproliferative and prodifferentiating actions of calcium. This provides a new approach for finding means to prevent CaSR loss, developing better treatment strategies for CRC.

The calcium-sensing receptor: A promising target for prevention of colorectal cancer

The inverse correlation between dietary calcium intake and the risk of colorectal cancer (CRC) is well known, but poorly understood. Expression of the calcium-sensing receptor (CaSR), a calcium-binding G protein-coupled receptor is downregulated in CRC leading us to hypothesize that the CaSR has tumor suppressive roles in the colon. The aim of this study was to understand whether restoration of CaSR expression could reduce the malignant phenotype in CRC. In human colorectal tumors, expression of the CaSR negatively correlated with proliferation markers whereas loss of CaSR correlated with poor tumor differentiation and reduced apoptotic potential. In vivo, dearth of CaSR significantly increased expression of proliferation markers and decreased levels of differentiation and apoptotic markers in the colons of CaSR/PTH double knock-out mice confirming the tumor suppressive functions of CaSR. In vitro CRC cells stably overexpressing wild-type CaSR showed significant reduction in proliferation, as well as increased differentiation and apoptotic potential. The positive allosteric modulator of CaSR, NPS R-568 further enhanced these effects, whereas treatment with the negative allosteric modulator, NPS 2143 inhibited these functions. Interestingly, the dominant-negative mutant (R185Q) was able to abrogate these effects. Our results demonstrate a critical tumor suppressive role of CaSR in the colon. Restoration of CaSR expression and function is linked to regulation of the balance between proliferation, differentiation, and apoptosis and provides a rationale for novel strategies in CRC therapy.

Persistence of furan-induced epigenetic aberrations in the livers of F344 rats

Furan is a heterocyclic organic compound produced in the chemical manufacturing industry and also found in a broad range of food products, including infant formulas and baby foods. Previous reports have indicated that the adverse biological effects of furan, including its liver tumorigenicity, may be associated with epigenetic abnormalities. In the present study, we investigated the persistence of epigenetic alterations in rat liver. Male F344 rats were treated by gavage 5 days per week with 8 mg furan/kg body weight (bw)/day for 90 days. After the last treatment, rats were divided randomly into 4 groups; 1 group of rats was sacrificed 24 h after the last treatment, whereas other groups were maintained without further furan treatment for an additional 90, 180, or 360 days. Treatment with furan for 90 days resulted in alterations in histone lysine methylation and acetylation, induction of base-excision DNA repair genes, suggesting oxidative damage to DNA, and changes in the gene expression in the livers. A majority of these furan-induced molecular changes was transient and disappeared after the cessation of furan treatment. In contrast, histone H3 lysine 9 and H3 lysine 56 showed a sustained and time-depended decrease in acetylation, which was associated with formation of heterochromatin and altered gene expression. These results indicate that furan-induced adverse effects may be mechanistically related to sustained changes in histone lysine acetylation that compromise the ability of cells to maintain and control properly the expression of genetic information.

Upregulation of microRNA-492 induced by epigenetic drug treatment inhibits the malignant phenotype of clear cell renal cell carcinoma in vitro

Clear cell renal cell carcinoma (ccRCC) is the most common type of cancer of the renal parenchyma. MicroRNAs (miRNAs) are non-coding RNAs of ~22 nucleotides in length, which function as post‑transcriptional regulators. Recently, the downregulation of miRNA (miR)-492 was observed to be associated with ccRCC; however, the molecular mechanism by which miR492 inhibited ccRCC remained to be elucidated. In the present study, it was demonstrated that miR-492 was markedly downregulated in ccRCC tissues when compared with adjacent normal tissues, as determined by reverse transcription-quantitative poymerase chain reaction (PCR). This downregulation was predominantly due to the hypermethylation of the CpG island of the miR-492 promoter, which was detected by methylation specific PCR and bisulfite genomic sequencing PCR, and was shown to inhibit miR-492 transcription. Through the use of a DNA demethylation agent, 5-aza-2'-deoxycytidine or the histone deacetylase inhibitor 4-phenylbutyric acid, the expression level of miR-492 was significantly upregulated in ccRCC cells, which further inhibited cell proliferation and invasion, while promoting cell apoptosis and adhesion. In conclusion, the present study provided novel insights into the potential mechanisms involved in ccRCC and it is hypothesized that miR-492 may become a promising therapeutic agent in the treatment of ccRCC.

The calcium-sensing receptor suppresses epithelial-to-mesenchymal transition and stem cell- like phenotype in the colon

BACKGROUND

The calcium sensing receptor (CaSR), a calcium-binding G protein-coupled receptor is expressed also in tissues not directly involved in calcium homeostasis like the colon. We have previously reported that CaSR expression is down-regulated in colorectal cancer (CRC) and that loss of CaSR provides growth advantage to transformed cells. However, detailed mechanisms underlying these processes are largely unknown.

METHODS AND RESULTS

In a cohort of 111 CRC patients, we found significant inverse correlation between CaSR expression and markers of epithelial-to-mesenchymal transition (EMT), a process involved in tumor development in CRC. The colon of CaSR/PTH double-knockout, as well as the intestine-specific CaSR knockout mice showed significantly increased expression of markers involved in the EMT process. In vitro, stable expression of the CaSR (HT29(CaSR)) gave a more epithelial-like morphology to HT29 colon cancer cells with increased levels of E-Cadherin compared with control cells (HT29(EMP)). The HT29(CaSR) cells had reduced invasive potential, which was attributed to the inhibition of the Wnt/β-catenin pathway as measured by a decrease in nuclear translocation of β-catenin and transcriptional regulation of genes like GSK-3β and Cyclin D1. Expression of a spectrum of different mesenchymal markers was significantly down-regulated in HT29(CaSR) cells. The CaSR was able to block upregulation of mesenchymal markers even in an EMT-inducing environment. Moreover, overexpression of the CaSR led to down-regulation of stem cell-like phenotype.

CONCLUSIONS

The results from this study demonstrate that the CaSR inhibits epithelial-to-mesenchymal transition and the acquisition of a stem cell-like phenotype in the colon of mice lacking the CaSR as well as colorectal cancer cells, identifying the CaSR as a key molecule in preventing tumor progression. Our results support the rationale to develop new strategies either preventing CaSR loss or reversing its silencing.