A plastid protein crucial for Ca2+-regulated stomatal responses

* Guard cell movements are regulated by environmental cues including, for example, elevations in extracellular Ca(2+) concentration. Here, the subcellular localization and physiological function of the Ca(2+)-sensing receptor (CAS) protein was investigated. * CAS protein localization was ascertained by microscopic analyses of green fluorescent protein (GFP) fusion proteins and biochemical fractionation assays. Comparative guard cell movement investigations were performed in wild-type and cas loss-of-function mutant lines of Arabidopsis thaliana. Cytoplasmic Ca(2+) dynamics were addressed in plants expressing the yellow cameleon reporter protein YC3.6. * This study identified CAS as a chloroplast-localized protein that is crucial for proper stomatal regulation in response to elevations of external Ca(2+). CAS fulfils this role through modulation of the cytoplasmic Ca(2+) concentration. * This work reveals a novel role of the chloroplast in cellular Ca(2+) signal transduction.

Evidence in favor of a calcium-sensing receptor in arterial endothelial cells: studies with calindol and Calhex 231

Small increases in extracellular Ca2+ dilate isolated blood vessels. In the present study, the possibility that a vascular, extracellular Ca2+-sensing receptor (CaSR) could mediate these vasodilator actions was investigated. Novel ligands that interact with the CaSR were used in microelectrode recordings from rat isolated mesenteric and porcine coronary arteries. The major findings were that (1) raising extracellular Ca2+ or adding calindol, a CaSR agonist, produced concentration-dependent hyperpolarizations of vascular myocytes, actions attenuated by Calhex 231, a negative allosteric modulator of CaSR. (2) Calindol-induced hyperpolarizations were inhibited by the intermediate conductance, Ca2+-sensitive K+ (IKCa) channel inhibitors, TRAM-34, and TRAM-39. (3) The effects of calindol were not observed in the absence of endothelium. (4) CaSR mRNA and protein were present in rat mesenteric arteries and in porcine coronary artery endothelial cells. (5) CaSR and IKCa proteins were restricted to caveolin-poor membrane fractions. We conclude that activation of vascular endothelial CaSRs opens endothelial cell IKCa channels with subsequent myocyte hyperpolarization. The endothelial cell CaSR may have a physiological role in the control of arterial blood pressure.

Calcium-sensing receptor in the brain

Following its cloning through an homology-based method from a rat striatal library, the calcium-sensing receptor (CaR) has been localized in the brains of adult and developing rats by immunocytochemistry and in situ hybridization with CaR-specific antibodies and cDNA probes, respectively. The receptor resides in numerous regions of the brain at widely varying levels. The highest levels are present within the subfornical organ (SFO) and the olfactory bulbs. Substantial levels of expression are also evident within the hippocampus, striatum, cingulate cortex, cerebellum, ependymal zones of the cerebral ventricles, and perivascular nerves around cerebral arteries. There are abundant levels of CaR expression within the SFO, an important hypothalamic thirst center, suggesting that it participates in the central control of systemic fluid and electrolyte balance. Therefore, while mineral ion homeostasis is not often considered to have central regulatory elements (i.e. in the brain), there are perhaps more complex relationships than recognized previously among the system governing mineral ion homeostasis and other homeostatic systems known to exhibit prominent neuroendocrine elements (i.e. water homeostasis). Furthermore, the expression of the CaR in all three types of glial cells indicates potential roles in the maintenance of local ionic homeostasis as well as in disease processes such as glioma.

The role of the calcium-sensing receptor in epidermal differentiation

Calcium regulates the proliferation and differentiation of keratinocytes both in vivo and in vitro. Elevated extracellular Ca2+ concentration ([Ca2+]o) raises the intracellular free calcium ([Ca2+]i) and activates differentiation-related genes. Cells lacking the calcium-sensing receptor (CaR) fail to respond to [Ca2+]o and to differentiate, indicating a role for CaR in keratinocyte differentiation. These concepts derived from in vitro experiments have been tested and confirmed in two mouse models.

Agonists and allosteric modulators of the calcium-sensing receptor and their therapeutic applications

The calcium-sensing receptor (CaR) belongs to the G protein-coupled receptor superfamily, with a characteristic structure consisting of seven transmembrane helices, an intracellular C-terminal and an extracellular N terminal domain. The primary physiological function of the CaR is the maintenance of constant blood Ca2+ levels, as a result of its ability to sense very small changes in extracellular Ca2+ (Ca2+(o)). Nevertheless, in addition to being expressed in tissues involved in Ca2+(o) homeostasis, the CaR is also expressed in tissues not involved in mineral homeostasis, suggestive of additional physiological functions. Numerous agonists and modulators of the CaR are now known in addition to Ca2+(o), including various divalent and trivalent cations, aromatic l-amino acids, polyamines, and aminoglycoside antibiotics. The signaling of the CaR is also regulated by extracellular pH and ionic strength. The activated CaR couples mainly to the phospholipase Cbeta and extracellular signal-regulated kinase 1/2 signaling pathways, and it decreases intracellular cAMP levels, leading to various physiological effects. The recent identification of synthetic allosteric modulators of the CaR has opened up a new field of research possibilities. Calcimimetics and calcilytics, which increase and decrease agonist signaling via the CaR, respectively, may facilitate the manipulation of the CaR and thus aid in further investigations of its precise signaling. These allosteric modulators, as well as strontium, have been demonstrated to have therapeutic potential for the treatment of disorders involving the CaR. This review discusses the various agonists and modulators of the CaR, differences in their binding and signaling, and their roles as therapeutics in various diseases.

Expression of the calcium receptor in human breast cancer--a potential new marker predicting the risk of bone metastases

AIMS

This study investigates whether the calcium-sensing receptor (CaR) is commonly expressed in primary breast cancers. The CaR controls secretion of PTHrP in several breast cancer cell lines and PTHrP is known to stimulate osteolysis during metastatic bone resorption. Whether this could explain the propensity of breast cancers to develop bone metastases has not been explored.

METHODS

With Ethical Committee approval, immunohistochemistry was performed using a commercially available antiCaR antibody (AffinityBioReagents, Cambridge, UK) on archived histological sections of primary tumours from patients who died with advanced breast cancer. Intensity of CaR expression was assessed by two independent observers on a 6-point scale.

RESULTS

One hundred and eight patients with breast cancer were found to have positive bone scans, 42 patients had died. Of the patients with negative bone scans, 23 had liver or lung metastases. Most patients with strongly expressed CaR (score 4-5 on immunohistochemistry) had bone metastases (13/15 patients) compared with 2/23 patients with normal bone scans (p < 0.001, chi(2) test). Other clinical/pathological markers (ER, PR, c-erb B-2, LN status) were not significantly different between patients with CaR-positive or CaR-negative tumours.

CONCLUSIONS

CaR expression is common in a selected group of patients with advanced primary breast cancers. A prospective study should investigate if patients with CaR-positive tumours are more likely to develop bone metastases.

Differential expression of the calcium sensing receptor and combined loss of chromosomes 1q and 11q in parathyroid carcinoma

Malignant transformation of parathyroid tumours is rare. Nevertheless, this small subset of malignant tumours often creates diagnostic and therapeutic problems. In this work, the morphological characteristics of 26 primary parathyroid carcinomas and seven metastases have been studied. Furthermore, immunohistochemical expression profiles for the calcium sensing receptor (CASR), cyclin D1 (CCND1), and Ki-67 were determined for parathyroid carcinomas and compared with adenomas and hyperplasias using a tissue microarray. Loss of heterozygosity (LOH) of the chromosome 1q region containing the HRPT2 gene and chromosome 11q (MEN1) was determined in the carcinomas. In contrast to the adenomas and hyperplasias, 31% of carcinomas demonstrated down-regulation of CASR. A significant correlation was found between CASR expression and the Ki-67 proliferation index. Chromosome 1q and chromosome 11q LOH were found in 12 of 22 (55%) and 11 of 22 (50%) carcinomas tested, respectively. Combined 1q and 11q LOH was seen in 8 of 22 (36%) carcinomas, in contrast to the low percentage of LOH reported in both regions in adenomas. In conclusion, this study demonstrates that combined 1q and 11q LOH in parathyroid tumours is suggestive of malignant behaviour. Strong down-regulation of the CASR protein is seen in a proportion of parathyroid carcinomas with a high proliferation index.

High extracellular calcium attenuates adipogenesis in 3T3-L1 preadipocytes

We studied the effect of extracellular Ca(2+) concentration ([Ca(2+)](e)) on adipocyte differentiation. Preadipocytes exposed to continuous [Ca(2+)](e) higher than 2.5 mmol/l accumulated little or no cytoplasmic lipid compared to controls in 1.8 mmol/l [Ca(2+)](e). Differentiation was monitored by Oil Red O staining of cytoplasmic lipid and triglyceride assay of accumulated lipid, by RT-PCR analysis of adipogenic markers, and by the activity of glycerol-3-phosphate dehydrogenase (GPDH). Elevated [Ca(2+)](e) inhibited expression of peroxisome proliferator-activated receptor gamma, CCAAT/enhancer binding protein alpha, and steroid regulatory binding element protein. High [Ca(2+)](e) significantly inhibited differentiation marker expression including adipocyte fatty acid binding protein, and GPDH. The decrease in Pref-1 expression that accompanied differentiation also was prevented by high [Ca(2+)](e). Treatment of 3T3-L1 cells with high [Ca(2+)](e) did not significantly affect cell number or viability and did not trigger apoptosis. Levels of intracellular Ca(+2) remained unchanged in various [Ca(2+)](e). Treatment of 3T3-L1 with pertussis toxin (PTX) partially restored lipid accumulation and increased differentiation markers in cells treated with 5 mmol/l [Ca(2+)](e). 'Classical' parathyroid cell Ca(2+) sensing receptors (CaSR) were not detected either by RT-PCR or by Western blotting. These results suggest that continuous exposure to high [Ca(2+)](e) inhibits preadipocyte differentiation and that this may involve a G-protein-coupled mechanism mediated by a novel Ca(2+) sensor or receptor.

Calcium-Sensing Receptor Endocytosis Links Extracellular Calcium Signaling to Parathyroid Hormone-Related Peptide Secretion via a Rab11a-Dependent and AMSH-Sensitive Mechanism

The calcium-sensing receptor (CaR) helps to maintain the homeostasis of extracellular calcium by controlling the secretion of hormones associated with this process. The mechanism of agonist-induced endocytosis and down-regulation of CaR and the influence of this event on the secretion of CaR-regulated hormones is not fully understood. In this study, we show that CaR is constitutively endocytosed and recycled to the plasma membrane by a Rab11a-dependent mechanism; during this process, the level of total cellular CaR is maintained. This trafficking of CaR promotes the secretion of PTH-related peptide (PTHrP), as evidenced by a decrease on PTHrP secretion in the presence of a dominant-negative mutant of Rab11a. Interestingly, this Rab11a dominant-negative mutant does not interfere with CaR-dependent activation of ERK 1/2, suggesting that ERK signaling is not sufficient to promote PTHrP secretion downstream of CaR. In addition, AMSH (associated molecule with the SH3 domain of STAM), a CaR carboxyl-terminal binding protein, redirects CaR from slow recycling to down-regulation, reducing CaR expression and decreasing PTHrP secretion. Our results indicate that endocytosis and trafficking of CaR modulate PTHrP secretion.

Direct in vitro evidence of the suppressive effect of cinacalcet HCl on parathyroid hormone secretion in human parathyroid cells with pathologically reduced calcium-sensing receptor levels

Clinical studies have been performed to determine the effect of cinacalcet HCl (cinacalcet), an allosteric modulator of the calcium-sensing receptor (CaR), on primary hyperparathyroidism (PHPT) and secondary hyperparathyroidism of uremia (SHPT). However, no in vitro studies on human parathyroid cells have been reported to date. In this study, the inhibitory effect of cinacalcet on PTH secretion was analyzed in primary cultured parathyroid cells obtained from patients. The investigation involved three PHPT and three SHPT patients subjected to therapeutic parathyroidectomy. Notably, all SHPT patients were resistant to intravenous vitamin D analogue therapy. Removed parathyroid tumors were used for immunohistochemistry and parathyroid cell primary culture. Immunohistochemical analyses revealed diminished expression of CaR and vitamin D receptor (VDR) in all parathyroid tumors. PTH secretion from cultured parathyroid cells of PHPT and SHPT patients was suppressed by extracellular Ca2+ and cinacalcet in a dose-dependent manner. Rates of suppression of PTH secretion in PHPT and SHPT by cinacalcet (1000 nmol/l) were 61% +/- 21% and 61% +/- 19%, respectively. Cinacalcet demonstrates significant potency in the suppression of PTH secretion in primary cultured human parathyroid cells in vitro, despite reduced levels of the target protein, CaR. Data from this in vitro analysis support the clinical application of cinacalcet in PHPT and SHPT therapy.

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.

Simultaneous expression analysis of vitamin D receptor, calcium-sensing receptor, cyclin D1, and PTH in symptomatic primary hyperparathyroidism in Asian Indians

BACKGROUND

To explore underlying molecular mechanisms in the pathogenesis of symptomatic sporadic primary hyperparathyroidism (PHPT).

MATERIALS AND METHODS

Forty-one parathyroid adenomas from patients with symptomatic PHPT and ten normal parathyroid glands either from patients with PHPT (n=3) or from euthyroid patients without PHPT during thyroid surgery (n=7) were analyzed for vitamin D receptor (VDR), calcium-sensing receptor (CASR), cyclin D1 (CD1), and parathyroid hormone (PTH) expressions. The protein expressions were assessed semiquantitatively by immunohistochemistry, based on percentage of positive cells and staining intensity, and confirmed by quantitative real-time PCR.

RESULTS

Immunohistochemistry revealed significant reductions in VDR (both nuclear and cytoplasmic) and CASR expressions and significant increases in CD1 and PTH expressions in adenomatous compared with normal parathyroid tissue. Consistent with immunohistochemistry findings, both VDR and CASR mRNAs were reduced by 0.36- and 0.45-fold change (P<0.001) and CD1 and PTH mRNAs were increased by 9.4- and 17.4-fold change respectively (P<0.001) in adenomatous parathyroid tissue. PTH mRNA correlated with plasma PTH (r=0.864; P<0.001), but not with adenoma weight, while CD1 mRNA correlated with adenoma weight (r=0.715; P<0.001). There were no correlations between VDR and CASR mRNA levels and serum Ca, plasma intact PTH, or 25-hydroxyvitamin D levels. In addition, there was no relationship between the decreases in VDR and CASR mRNA expressions and the increases in PTH and CD1 mRNA expressions.

CONCLUSIONS

The expression of both VDR and CASR are reduced in symptomatic PHPT in Asian Indians. In addition, CD1 expression was greatly increased and correlated with adenoma weight, implying a potential role for CD1 in adenoma growth and differential clinical expression of PHPT.

Chondrocyte calcium-sensing receptor expression is up-regulated in early guinea pig knee osteoarthritis and modulates PTHrP, MMP-13, and TIMP-3 expression

OBJECTIVE

Growth plate chondrocytes up-regulate calcium-sensing receptor (CaR) expression as they mature to hypertrophy. In cells other than chondrocytes, extracellular calcium-sensing via the CaR functions partly to promote expression of parathyroid hormone-related protein (PTHrP), a critical regulator of endochondral development. Moreover, PTHrP is up-regulated in human osteoarthritis (OA) and surgically induced rabbit OA cartilages and may promote both chondrocyte proliferation and osteophyte formation therein. Hence, we examined chondrocyte CaR-mediated calcium-sensing in OA pathogenesis.

METHODS

We studied spontaneous knee OA in male Hartley guinea pigs. We also evaluated cultured bovine knee chondrocytes and immortalized human articular chondrocytes (CH-8 cells), employing the CaR calcimimetic agonist NPS R-467 or altering physiologic extracellular calcium (1.8 mM).

RESULTS

Immunohistochemistry revealed that CaR expression became up-regulated in the superficial zone at 4 months of age in the guinea pig medial tibial plateau cartilage as early OA developed. CaR expression later became up-regulated in the middle zone. PTHrP content, measured by immunoassay, was significantly increased in the medial tibial plateau cartilage as OA developed and progressed. In cultured chondrocytic cells, CaR-mediated extracellular calcium-sensing, stimulated by the calcimimetic NPS R-467, induced PTHrP and matrix metalloproteinase (MMP)-13 expression and suppressed expression of tissue inhibitor of metalloproteinase (TIMP)-3 dose-dependently, effects shared by elevated extracellular calcium (3 mM). Extracellular calcium-sensing appeared essential for PTHrP and interleukin (IL)-1 to induce MMP-13 and for PTHrP 1-34 to suppress TIMP-3 expression.

CONCLUSIONS

Chondrocyte CaR expression becomes up-regulated early in the course of spontaneous guinea pig knee OA. Chondrocyte CaR-mediated extracellular calcium-sensing promotes PTHrP expression, modulates the effects of PTHrP and IL-1, and promotes MMP-13 expression and TIMP-3 depletion. Our results implicate up-regulated extracellular calcium-sensing via the CaR as a novel mediator of OA progression.

Pharmacoperones and the calcium sensing receptor: exogenous and endogenous regulators

Calcium sensing receptor (CaSR) mutations or altered expression cause disorders of calcium handling. Recent studies suggest that reduced targeting to the plasma membrane is a feature common to many CaSR loss-of-function mutations. Allosteric agonists (calcimimetics) can rescue signaling of a subset of CaSR mutants. This review evaluates our current understanding of the subcellular site(s) for allosteric modulator rescue of CaSR mutants. Studies to date make a strong case for calcimimetic potentiation of signaling not only at plasma membrane-localized CaSR, but at the endoplasmic reticulum, acting as pharmacoperones to assist in navigation of multiple quality control checkpoints. The possible role of endogenous pharmacoperones, calcium and glutathione, in folding and stabilization of the CaSR extracellular and transmembrane domains are considered. Finally, the possibility that dihydropyridines act as unintended pharmacoperones of CaSR is proposed. While our understanding of pharmacoperone rescue of CaSR requires refinement, promising results to date argue that this may be a fruitful avenue for drug discovery.

Decrease in calcium-sensing receptor in the progress of diabetic cardiomyopathy

To observe the dynamic expression of calcium-sensing receptor (CaSR) in myocardium of diabetic rats and explore its role in diabetic cardiomyopathy (DCM), 40 male Wistar rats were randomly divided into 4 groups including control, diabetic-4 weeks, diabetic-8 weeks and spermine treatment groups (240 μM of spermine in drinking water). The type 2 Diabetes mellitus (DM) models were established by intraperitoneal injection of streptozotocin (STZ, 30 mg/kg) after high-fat and high-sugar diet for one month. The echocardiographic parameters were measured, cardiac morphology was observed by electron microscope and HE staining. The intracellular calcium concentration ([Ca(2+)](i)) was detected by laser-scanning confocal microscope. Western blot analyzed the expression of CaSR, protein kinase C α(PKC-α) and calcium handling regulators, such as phospholamban (PLN), Ca(2+)-ATPase (SERCA), and ryanodine receptor (RyR). Compared with control group, [Ca(2+)](i) and the expression of CaSR, RyR and SERCA/PLN were decreased, while PKC-α and PLN were significantly increased in a time-dependent manner in diabetic groups. Meanwhile diabetic rats displayed abnormal cardiac structure and systolic and diastolic dysfunction, and spermine (CaSR agonist) could prevent or slow its progression. These results indicate that the CaSR expression of myocardium is reduced in the progress of DCM, and its potential mechanism is related to the impaired intracellular calcium homeostasis.

Novel mutations in the calcium-sensing receptor gene associated with biochemical and functional differences in familial hypocalciuric hypercalcaemia

OBJECTIVE

Heterozygous inactivating mutations of the calcium-sensing receptor (CaR) gene cause familial hypocalciuric hypercalcaemia (FHH), a generally benign disorder characterized by mild to moderate PTH-dependent hypercalcaemia. We aimed to identify the causative CaR mutations in three families with FHH and examine the correlation between type of mutation and biochemical and/or functional phenotypes. PATIENTS, DESIGN AND MEASUREMENTS: The CaR gene from FHH family members was assessed for mutations by direct DNA sequencing and mutations were confirmed by restriction enzyme analysis. Functional studies on two missense mutations were conducted by introducing them by site-directed mutagenesis into the CaR cloned into a mammalian expression vector, and assessing calcium responsiveness using an inositol phosphate (IP) assay in HEK293 cells. Biochemical data from patients heterozygous for each type of mutant were correlated with functionality.

RESULTS

Two novel nonsense mutations (R25stop and K323stop) and one novel missense mutation (G778D) were identified. The G778D mutant receptor and another mutation identified in an earlier study (L174R) demonstrated a complete lack of Ca2+ responsiveness using the IP assay. When cotransfected with wild-type receptor, the mutant receptors demonstrated a dominant-negative effect on wild-type receptor response, with L174R having a more pronounced effect than G778D. Significantly more severe hypercalcaemia and a trend towards higher PTH levels were observed in patients heterozygous for CaR mutants with a stronger dominant-negative effect.

CONCLUSIONS

Naturally occurring CaR mutations with differences in dominant-negative effect on wild-type receptor demonstrate differences in biochemical severity in FHH.

A cell-based microarrayed compound screening format for identifying agonists of G-protein-coupled receptors

The identification of agonist and antagonist leads for G-protein-coupled receptors (GPCRs) is of critical importance to the pharmaceutical and biotechnology industries. We report on the utilization of a novel, high-density, well-less screening platform known as microarrayed compound screening microARCS) that tests 8640 compounds in the footprint of a standard microtiter plate for the identification of novel agonists for a specific G-protein-coupled receptor. Although receptors coupled to the G alpha(q) protein can readily be assessed by fluorescence-based Ca(2+) release measurements, many GPCRs that are coupled to G alpha(s) or G alpha(i/o) proteins are not amenable to functional evaluation in such a high-throughput manner. In this study, the human dopamine D(4.4) receptor, which normally couples through the G alpha(i/o) protein to inhibit adenylate cyclase and to reduce levels of intracellular cAMP, was coupled to intracellular Ca(2+) release by stably coexpressing this receptor with a chimeric G(alpha qo5) protein in HEK-293 cells. In microARCS format, the cells expressing D(4.4) receptor and G alpha(qo5) protein were preloaded with fluo-4, cast into a 1% agarose gel, placed above the compound sheets, and imaged successively using a ViewLux charge-coupled device imaging system. Dopamine and other agonists evoked an increase in fluorescence response that appeared as bright spots in a time- and concentration-dependent manner. Utilizing this technology, a library of 260,000 compounds was rapidly screened and led to the identification of several novel agonists. These agonists were further characterized using a fluorometric imaging plate reader assay. Excellent confirmation rates coupled with enhanced efficiency and throughput enable microARCS to serve as an alternative platform for the screening and identification of novel GPCR agonists.

Parathyroid growth and regression in experimental uremia

Early 1,25-dihydroxyvitamin D(3) (VD(3)) therapy during the course of renal failure prevents the downregulation of VD(3) receptor (VDR), calcium-sensing receptor (CaSR) or p21, and the parathyroid (PT) growth. We hypothesized that VD(3) could restore the decreased expressions of VDR and CaSR, and cause regression in enlarged PT glands. 5/6 nephrectomized rats fed high-phosphorus diet were killed at 1, 3, 5, or 7 days and at 2, 3, 4, 8, or 12 weeks. VD(3)-treated rats were given VD(3) intraperitoneally for 1, 2, 3, or 4 weeks, starting 8 weeks after 5/6 nephrectomy. PT glands were weighed and subjected to immunohistochemical analyses for VDR, CaSR, p21, Ki67, and Tdt-mediated dUTP nick end-labeling (TUNEL) assay. The area per cell was measured as the parameter of cell size. The expression of VDR and p21 began to decrease at day 1, and Ki67 increased at day 3, but decreased thereafter. There was a significant increase in PT gland weight to week 12 with the increase of cell size. VD(3) treatment significantly increased both VDR and CaSR expressions 2 weeks after the start of injection, and reduced the PT gland weight at week 3 with significant increase of TUNEL-positive cells and decrease of cell size. Our results suggest that PT growth in uremic rats involves both PT cell proliferation and hypertrophy, in association with the reduction of VDR, CaSR, and p21 expressions. In addition, VD(3) treatment could reverse PT hyperplasia and hypertrophy via restoration of these proteins.

Cinacalcet HCl: a novel therapeutic for hyperparathyroidism

Hyperparathyroidism (HPT) is a significant clinical concern for patients with a variety of diseases, notably the secondary HPT associated with chronic kidney disease requiring dialysis. Secondary HPT is associated with elevated para-thyroid hormone (PTH) levels, decreased levels of 1,25 dihydroxyvitamin D, and disordered mineral levels (usually high calcium and phosphorus). If not controlled, secondary HPT can result in bone disease, vascular calcification, and ultimately, patient mortality. Established, conventional therapies, such as 1,25dihydroxyvitamin D analogues (vitamin D analogues) and phosphate binders, have proven to be inadequate in enabling patients to meet the National Kidney Foundation's-Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI) treatment goals for PTH, calcium and phosphorus levels. A novel therapeutic, cinacalcet HCl (formerly AMG 073; Sensipar in the US and Mimpara in Europe; Amgen, Inc.), binds directly to the calcium-sensing receptor (CaR) on the cells of the parathyroid gland, increasing the receptor's sensitivity to calcium and reducing PTH, serum calcium and phosphorus levels. Treatment with cinacalcet in clinical trials has safely and effectively improved achievement of the NKF-K/DOQI goals. Cinacalcet has also reduced serum calcium levels in patients with primary HPT, including parathyroid carcinoma, in the clinical trial setting. Evidence suggesting the utility of cinacalcet in these diseases and the potential for additional therapeutic applications will be discussed.

Development of an aequorin luminescence calcium assay for high-throughput screening using a plate reader, the LumiLux

A luminescence assay using a new plate reader, the LumiLux (PerkinElmer, Waltham, MA), has been validated for high-throughput screening (HTS). In this study, we compared the aequorin luminescence-based calcium mobilization assay to the fluorescence-based calcium assay. A cell line stably co-expressing apo-aequorin, a chimeric G-protein, and a G-protein-coupled dopamine receptor was used to screen a collection of 8,106 compounds using the Hamamatsu Photonics (Bridgewater, NJ) FDSS6000 and LumiLux as the plate readers. The assay parameters evaluated included hit rate correlation, signal-to-noise ratio, and overall assay performance calculated by Z and standard deviation. The average Z values and hit rates were comparable between assay platforms;however, the standard deviation for the agonist aequorin assay was significantly smaller. There was also a significant decrease in the number of false-positives with the aequorin assay. These results suggest that the aequorin assay in combination with the new plate reader, LumiLux, provides a simple, cost-effective, robust, and sensitive assay for HTS

Clinical Impact of p27Kip1 and CaSR Expression on Primary Hyperparathyroidism

We aimed to investigate the expressions of p27 kinase inhibitory protein 1 (p27^Kip1) and calcium sensing receptor (CaSR) in adenomas and normal parathyroid tissue and to evaluate the relationship of these molecules with clinical and biochemical parameters in primary hyperparathyroidism (PHPT). Fifty-one patients with histopathologically confirmed parathyroid adenomas and 20 patients with normal parathyroid glands (which were removed incidentally during thyroid resection) were included. Immunohistochemical stainings of CaSR and p27^Kip1 were performed in surgical specimens. Clinical features, biochemical parameters, and BMD measurements of patients with PHPT were evaluated retrospectively. Expressions of p27^Kip1 and CaSR were decreased in parathyroid adenomas, compared to normal glands (p < 0.05). High intensity of CaSR staining (3+) was more frequent in normal parathyroid tissue (75%) than adenomas (12%) (p < 0.01). Hypertension was not observed in patients with high staining intensity of CaSR (p = 0.032). There was a negative association between CaSR expression and body mass index (BMI) (p = 0.027, r = - 0.313). There was no significant relationship between p27^Kip1 and CaSR expressions, serum calcium, plasma parathormone, 25-hydroxy vitamin D levels, and bone density (p > 0.05). The expressions of p27^Kip1 and CaSR were decreased in PHPT patients. This reduction may play an important role in the pathogenesis of PHPT. However, neither p27^Kip1 nor CaSR expression was found to be useful in predicting prognosis or severity of disease.

Localization and quantitative expression of the calcium-sensing receptor protein in human oocytes

OBJECTIVE

To investigate the expression of the calcium-sensing receptor (CaSR) protein in human oocytes at the germinal vesicle (GV) and metaphase I (MI) and II (MII) stages.

DESIGN

Prospective study.

SETTING

Academic basic research laboratory and hospital-based fertility center.

PATIENT(S)

Immature and supernumerary mature oocytes (n = 118) excluded from intracytoplasmic sperm injection treatment.

INTERVENTION(S)

Immunofluorescence and Western blot with a primary antibody against human CaSR. Confocal laser scanning microscopy (CLSM) together with quantitative image analysis used to measure the fluorescence intensity variations in oocytes at GV, MI, and MII stages.

MAIN OUTCOME MEASURE(S)

The CaSR expression pattern as evaluated by immunostaining in denuded oocytes and cumulus cells, CLSM, and three-dimensional image reconstructions; quantitative analysis at the equatorial plane of the oocyte.

RESULT(S)

We identified CaSR in human oocytes and cumulus cells. The fluorescence intensity within the oocyte varied with the developmental stage, with the greatest increase at the MI stage.

CONCLUSION(S)

The present study demonstrates for the first time the expression and localization of CaSR protein in human oocytes. Increased CaSR protein expression in the MI stage suggests that it may be involved in the regulation of human oocyte development and maturation.

Extracellular Ca2+-sensing receptor expression and hormonal regulation in rat uterus during the peri-implantation period

The extracellular Ca2+-sensing receptor (CaR) is a member of the superfamily of G protein-coupled receptors (GPCRs). It is an important mediator of a wide range of Ca2+-dependent physiological responses in various tissues. In reproductive tissues it has been reported to play a significant role in promoting or maintaining placentation. Meanwhile, another Ca2+ regulated gene stanniocalcin-1 (STC-1) has been documented to be involved in decidualization and uterine remodelling. The phenomenon that CaR mediates STC-1's transcription responding to extracellular calcium in fish urges us to suppose that CaR, like STC-1, may also play a role in implantation and decidualization. To resolve this conjecture, we have examined the expression and hormonal regulation of the CaR gene in rat uterus during peri-implantation period. CaR mRNA was expressed at a moderate level in the luminal epithelium of the early stage of pregnancy (from day 1 to day 3). From day 2-3 it began to be expressed more strongly in the stromal cells immediately underneath the luminal epithelium, but decreased to a basal level on day 4. From day 6 to day 9 continuously, both CaR mRNA and protein were highly expressed in the primary decidua. Expression of CaR mRNA and protein in these cells was also observed when a delayed implantation was terminated by estrogen treatment to allow the embryo implantation. In contrast, only basal level expression of the molecules was detected in the cells of animals subjected to a normal-delayed implantation or the pseudopregnant condition. Embryo transplantation experiment confirmed that CaR expression at the implantation site was induced by the implanting blastocyst. Consistent with the normal pregnant process, CaR mRNA and protein in the cells were also induced by an artificial decidualization procedure. Further experiments demonstrated that treatment of the ovariectomized rat with estrogen or/and progesterone stimulated a high level expression of CaR mRNA in the uterine epithelial and glandular epithelium. In conclusion, CaR was specifically induced during the processes of implantation and subsequent decidualization and may play a role in these processes.

Filamin A and parafibromin expression in parathyroid carcinoma

OBJECTIVE

Parathyroid carcinoma (PC), atypical parathyroid tumours (APT) and parathyroid adenoma (PA), all present with hypercalcemia. Diminished calcium-sensing receptor (CaSR) expression is reported in PC but is rare in benign tumours. Filamin A (FLNA) binds to the CaSR and activates the mitogen-activated protein kinase (MAPK) signalling pathway. FLNA is related to tumour aggressiveness in several cancers, but its role in parathyroid neoplasia is unknown.

DESIGN

We examined FLNA, CaSR and parafibromin expression in PCs (n = 32), APTs (n = 44) and PAs (n = 77) and investigated their potential as diagnostic and/or prognostic markers.

METHODS

Tissue microarray slides were immunohistochemically stained with antibodies for FLNA, CaSR and parafibromin. Staining results were correlated with detailed clinical data.

RESULTS

All tumours stained positively for CaSR, with two tumours (one PC and one APT) showing diminished expression. Carcinomas were characterized by increased cytoplasmic FLNA expression compared to APTs and PAs (P = 0.004). FLNA expression was not correlated with Ki-67 proliferation index or loss of parafibromin expression. Cytoplasmic FLNA expression was also associated with higher serum calcium, PTH concentrations and male sex (P = 0.014, P = 0.017 and P = 0.049 respectively). Using a combined marker score, we found that parathyroid tumours with low FLNA expression and positive parafibromin staining were extremely likely to be benign (P < 0.001).

CONCLUSION

Cytoplasmic and membranous FLNA expression is increased in parathyroid carcinomas compared to benign tumours. A combined FLNA and parafibromin expression score shows potential as a prognostic predictor of indolent behaviour in parathyroid neoplasms.

CaSR expression in normal parathyroid and PHPT: new insights into pathogenesis from an autopsy-based study

PURPOSE

Calcium sensing receptor (CaSR), on the surface of normal parathyroid cells, is essential for maintaining serum calcium levels. The normal pattern of CaSR immunostaining remains undefined and is presumptively circumferential. Given the physiological variation in serum calcium, we postulated that CaSR expression could not be uniformly circumferential. Also, cytoplasmic expression has not been evaluated either in normal or pathological tissues. We studied normal parathyroid tissues derived from forensic autopsies and those rimming parathyroid adenomas for membranous and cytoplasmic CaSR immunoexpression. Results were compared with primary hyperparathyroidism (PHPT) to look for any pathogenetic implications.

MATERIALS AND METHODS

We evaluated 34 normal parathyroid tissues from 11 autopsies, 30 normal rims, 45 parathyroid adenoma, 10 hyperplasia, and 7 carcinoma cases. Membranous expression was categorized complete/incomplete and weak/moderate/strong; scored using Her2/Neu and Histo-scores; predominant pattern noted. Cytoplasmic expression was categorized negative/weak/moderate/strong; predominant intensity noted.

RESULTS

Normal autopsy-derived parathyroid tissues were Her2/Neu 3 + , but incomplete membranous staining predominated in 85%. Their immune-scores were significantly more than the cases (p <  < 0.05). The mean histo-score of normal rims was intermediate between the two (p <  < 0.05). Cytoplasmic expression was strong in all autopsy-derived tissues, weak/negative in hyperplasia (100%), moderate in 16% adenomas, and 43% carcinomas.

CONCLUSIONS

Normal autopsy-derived parathyroid tissues showed strong but predominantly incomplete membranous expression. Surface CaSR expression decreased in PHPT and is probably an early event in parathyroid adenoma, seen even in normal rims. Whether there is a defect in CaSR trafficking from the cytoplasm to the cell surface in adenoma and carcinoma needs further evaluation.