Calcium-sensing receptor expression and signalling in human parathyroid adenomas and primary hyperplasia

Cinacalcet HCl, an allosteric modulator of the calcium-sensing receptor (CaR), has recently been approved for the treatment of secondary hyperparathyroidism in patients with chronic kidney disease on dialysis, due to its suppressive effect on parathyroid hormone (PTH) secretion. Although cinacalcet’s effects in patients with primary and secondary hyperparathyroidism have been reported, the crucial relationship between the effect of calcimimetics and CaR expression on the parathyroid glands requires better understanding. To investigate its suppressive effect on PTH secretion in primary hyperparathyroidism, in which hypercalcemia may already have stimulated considerable CaR activity, we investigated the effect of cinacalcet HCl on PTH-cyclin D1 transgenic mice (PC2 mice), a model of primary hyperparathyroidism with hypo-expression of CaR on their parathyroid glands. A single administration of 30 mg/kg body weight (BW) of cinacalcet HCl significantly suppressed serum calcium (Ca) levels 2 h after administration in 65- to 85-week-old PC2 mice with chronic biochemical hyperparathyroidism. The percentage reduction in serum PTH was significantly correlated with CaR hypo-expression in the parathyroid glands. In older PC2 mice (93–99 weeks old) with advanced hyperparathyroidism, serum Ca and PTH levels were not suppressed by 30 mg cinacalcet HCl/kg. However, serum Ca and PTH levels were significantly suppressed by 100 mg/kg of cinacalcet HCl, suggesting that higher doses of this compound could overcome severe hyperparathyroidism. To conclude, cinacalcet HCl demonstrated potency in a murine model of primary hyperparathyroidism in spite of any presumed endogenous CaR activation by hypercalcemia and hypo-expression of CaR in the parathyroid glands.

Download Full-text

(Regulation of E-cadherin and β-catenin by Ca2+in Colon Carcinoma Is Dependent on Calcium-sensing Receptor Expression and Function. Int J Cancer 2007;121:1455-1462)

Korean Journal of Gastroenterology ◽

10.4166/kjg.2010.55.2.149 ◽

2010 ◽

Vol 55 (2) ◽

pp. 149

Keyword(s):

Colon Carcinoma ◽

Receptor Expression ◽

Calcium Sensing Receptor ◽

Calcium Sensing ◽

And Function ◽

E Cadherin

Download Full-text

The Calcium Sensing Receptor: From Understanding Parathyroid Calcium Homeostasis to Bone Metastases

Annals of The Royal College of Surgeons of England ◽

10.1308/003588408x286044 ◽

2008 ◽

Vol 90 (4) ◽

pp. 271-277 ◽

Cited By ~ 11

Author(s):

Radu Mihai

Keyword(s):

Breast Cancer ◽

Bone Metastases ◽

Intracellular Calcium ◽

Calcium Homeostasis ◽

Membrane Trafficking ◽

Calcium Concentration ◽

Fluorescent Microscopy ◽

Calcium Sensing Receptor ◽

Calcium Sensing ◽

Parathyroid Adenomas

The cloning of the calcium sensing receptor (CaR) confirmed that parathyroid cells monitor extracellular calcium concentration ([Ca2+]ext) via a receptor-type mechanism. This lead to the hypothesis that abnormalities in the expression and/or function of the CaR could explain the biochemical abnormalities in primary hyperparathyroidism (PHPT). Cultured cells from parathyroid adenomas of patients operated for PHPT were used to monitor real-time changes in intracellular calcium concentration ([Ca2+]i) as measured by fluorescent microscopy using the Fura-2/AM dye. We found that CaR agonists trigger release of intracellular calcium pools and such responses are amplified by increasing the affinity of IP3 receptors. Using confocal microscopy to monitor membrane trafficking in living parathyroid cells labelled with the fluorescent dye FM1-43, we found that a decrease in [Ca2+]i rather than an absolute change in [Ca2+]ext is the main stimulus for exocytosis from human parathyroid cells. These data suggest that, in PHPT, a defective signalling mechanism from the CaR allows cells from parathyroid adenomas to maintain low [Ca2+]i with uninhibited PTH secretion in the face of hypercalcaemia. Over longer periods of time, CaR controls parathyroid proliferation via changes in tyrosine phosphorylation. We found that multiple proteins of molecular weight 20–65 kDa are phosphorylated within 10–60 min in response to CaR agonists. Further work demonstrated that high [Ca2+]i stimulates the expression of bcl-2 oncoprotein in cultured human parathyroid cells and that, in parathyroid adenomas, predominant expression of bcl-2 rather than bax oncoprotein might prevent apoptosis and explain the slow growth rate of these tumours. More recently, it became apparent that CaR stimulates cell proliferation in several cell types not involved in calcium homeostasis. Using archived histological material from 65 patients who died with metastatic breast cancer, we identified CaR expression predominantly in tumours from patients who developed bone rather than visceral metastases (35 of 49 versus 7 of 16; P < 0.01, chi-squared test). These data suggest that CaR expression has the potential to become a new biological marker predicting the risk of bone metastases in patients with breast cancer. A prospective study should investigate if patients with CaR-positive tumours are more likely to develop bone metastases and whether they could benefit more from prophylactic treatment with bisphosphonates or the newly developed CaR antagonists.

Download Full-text

Calcitriol Prevents In Vitro Vascular Smooth Muscle Cell Mineralization by Regulating Calcium-Sensing Receptor Expression

Endocrinology ◽

10.1210/en.2014-1744 ◽

2015 ◽

Vol 156 (6) ◽

pp. 1965-1974 ◽

Cited By ~ 24

Author(s):

Aurélien Mary ◽

Lucie Hénaut ◽

Cédric Boudot ◽

Isabelle Six ◽

Michel Brazier ◽

...

Keyword(s):

Vitamin D ◽

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Small Interfering Rna ◽

Receptor Expression ◽

Calcium Sensing Receptor ◽

Down Regulation ◽

Calcium Sensing ◽

Cardiovascular Morbidity And Mortality ◽

Interfering Rna

Abstract Vascular calcification (VC) is a degenerative disease that contributes to cardiovascular morbidity and mortality. A negative relationship has been demonstrated between VC and calcium sensing receptor (CaSR) expression in the vasculature. Of interest, vitamin D response elements, which allow responsiveness to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], are present in the promoters of the CaSR gene. We hypothesized that 1,25(OH)2D3, by modulating CaSR expression in vascular smooth muscle cells (VSMCs), might protect against VC. Human VSMCs were exposed to increasing concentrations of 1,25(OH)2D3 (0.01–10 nmol/L) in noncalcifying (1.8 mmol/L) or procalcifying Ca2+0 condition (5.0 mmol/L). Using quantitative RT-PCR and Western blotting we observed a significant increase in both CaSR mRNA and protein levels after exposure to 1.0 nmol/L 1,25(OH)2D3. This effect was associated with a maximal increase in CaSR expression at the cell surface after 48 hours of 1,25(OH)2D3 treatment, as assessed by flow cytometry. Down-regulation of the vitamin D receptor by small interfering RNA abolished these effects. In the procalcifying condition, 1.0 nmol/L 1,25(OH)2D3 blocked the Ca2+0-induced decrease in total and surface CaSR expression and protected against mineralization. Down-regulation of CaSR expression by CaSR small interfering RNA abolished this protective effect. 1,25(OH)2D3 concentrations of 0.5 and 5.0 nmol/L were also effective, but other (0.01, 0.1, and 10 nmol/L) concentrations did not modify CaSR expression and human VSMC mineralization. In conclusion, these findings suggest that nanomolar concentrations of 1,25(OH)2D3 induce a CaSR-dependent protection against VC. Both lower and higher concentrations are either ineffective or may even promote VC. Whether this also holds true in the clinical setting requires further study.

Download Full-text