Significance of calcium-sensing receptor expression in gastric cancer

Calcium Intake Contributed by Whole Foods and Gastric Cancer in Viet Nam: A Case‑Control Study

BACKGROUND

Recent studies revealed the potential tumor-suppressive effects of calcium. We aimed to investigate the association between dietary calcium intake contributed by whole foods and gastric cancer.

METHODS

466 gastric cancer cases and 1531 controls were extracted from the completed case-control studies in hospitals in Hanoi from 2017 to 2019. A validated semi-quantitative food frequency questionnaire was used to obtain data via face-to-face interviews with the trained interviewer. Calcium intake was calculated based on the food frequency intake per year. Adjusted odds ratios (OR) and 95% confidence intervals (95% CI) were calculated.

RESULTS

The study participants consumed less than 50% of 700 mg/day compared to the recommended calcium intake. With increasing calcium intake, we found a reduction in gastric cancer in both genders, men and women (adjusted OR and 95%CI, 5^th vs. 1^st quintile: 0.50 (0.36, 0.70), p_trend 0.000; 0.62 (0.42, 0.92), p_trend 0.019; and 0.30 (0.16, 0.57), p_trend 0.000, respectively). The inverse association remained in the subgroups of never-smokers and those with positive H. pylori infection.

CONCLUSION

We observed substantial benefits of calcium intake from whole foods against gastric cancer in the Vietnamese population with a low nutritious status.

Molecular mechanisms and clinical management of cancer bone metastasis

As one of the most common metastatic sites of malignancies, bone has a unique microenvironment that allows metastatic tumor cells to grow and flourish. The fenestrated capillaries in the bone, bone matrix, and bone cells, including osteoblasts and osteoclasts, together maintain the homeostasis of the bone microenvironment. In contrast, tumor-derived factors act on bone components, leading to subsequent bone resorption or excessive bone formation. The various pathways involved also provide multiple targets for therapeutic strategies against bone metastases. In this review, we summarize the current understanding of the mechanism of bone metastases. Based on the general process of bone metastases, we specifically highlight the complex crosstalk between tumor cells and the bone microenvironment and the current management of cancer bone metastases.

Calcium-sensing receptor antagonist NPS-2143 suppresses proliferation and invasion of gastric cancer cells

NPS-2143 is a calcium-sensing receptor (CaSR) antagonist that has been demonstrated to possess anticancer activity. To date, the effects of NPS-2143 on gastric cancer (GC) cell growth, motility, and apoptosis have not been investigated. In the present study, we firstly investigated the expression of CaSR in GC tissues using immunohistochemistry and western blotting. Then Cell Counting Kit-8 and colony formation assays were conducted to explore the effect of the NPS-2143 on the proliferation of GC cell line AGS. Transwell invasion and migration assays were performed to test the effect of NPS-2143 on AGS cell motility. We determined the percentage of apoptotic cells by flow cytometry and explored the changes of apoptosis-related protein by western blotting. Furthermore, we constructed a CaSR knockdown AGS cell line to determine whether NPS-2143 acted via inhibition of CaSR. We found that the protein expression level of CaSR was higher in GC tissues compared with the paired adjacent normal tissues. In addition, NPS-2143 treatment caused an inhibitory effect on the proliferation, invasion, and migration of AGS cells and a promoting effect on AGS apoptosis. The expression of Bcl-2 was decreased while the levels of Bax and active caspase 3 were enhanced in AGS cells after NPS-2143 treatment. Mechanistically, NPS-2143 lead to a significant decrease in the expression of phosphorylated (p)-AKT, phosphorylated mechanistic target of rapamycin (p-mTOR), p70, and cyclin D1. Knockdown of CaSR also suppressed cell proliferation, invasion, and migration and promoted cell apoptosis. No significant difference was observed between CaSR-silenced AGS cells with and without NPS-2143 treatment. These results confirmed that NPS-2143 has an inhibitory influence on AGS cell growth via inhibiting CaSR, which then suppresses the PI3K/Akt signaling pathway.

Expression and Role of the Calcium-Sensing Receptor in Rat Peripheral Blood Polymorphonuclear Neutrophils

The calcium-sensing receptors (CaSRs) play an important role in many tissues and organs that are involved in inflammatory reactions. Peripheral blood polymorphonuclear neutrophils (PMNs) are important inflammatory cells. However, the expression and functions of CaSR in peripheral blood PMNs are still not reported. In this study, we collected rat peripheral blood PMNs to observe the relationship between CaSR and PMNs. From the results, we found first that the CaSR protein was expressed in PMNs, and it increased after PMNs were activated with fMLP. In addition, CaSR activator cincalcet promoted the expression of CaSR and P-p65 (NF-κB signaling pathway protein) and Bcl-xl (antiapoptosis protein), and it increased the secretion of interleukin-6 (IL-6) and myeloperoxidase (MPO); meanwhile, it decreased proapoptosis protein Bax expression and the production of IL-10 and reactive oxygen species (ROS). At the same time, cincalcet also decreased the PMN apoptosis rate analyzed by flow cytometry. However, CaSR inhibitor NPS-2143 and NF-κB signaling pathway inhibitor PDTC reverse the results cited earlier. All of these results indicated that CaSR can regulate PMN functions and status to play a role in inflammation, which is probably through the NF-κB signaling pathway.

An Excess of CYP24A1, Lack of CaSR, and a Novel lncRNA Near the PTH Gene Characterize an Ectopic PTH-Producing Tumor

Thus far, only 23 cases of the ectopic production of parathyroid hormone (PTH) have been reported. We have characterized the genome-wide transcription profile of an ectopic PTH-producing tumor originating from a retroperitoneal histiocytoma. We found that the calcium-sensing receptor (CaSR) was barely expressed in the tumor. Lack of CaSR, a crucial braking apparatus in the presence of both intraparathyroid and, probably, serendipitous PTH expression, might contribute strongly to the establishment and maintenance of the ectopic transcriptional activation of the PTH gene in nonparathyroid cells. Along with candidate drivers with a crucial frameshift mutation or copy number variation at specific chromosomal areas obtained from whole exome sequencing, we identified robust tumor-specific cytochrome P450 family 24 subfamily A member 1 (CYP24A1) overproduction, which was not observed in other non–PTH-expressing retroperitoneal histiocytoma and parathyroid adenoma samples. We then found a 2.5-kb noncoding RNA in the PTH 3′-downstream region that was exclusively present in the parathyroid adenoma and our tumor. Such a co-occurrence might act as another driver of ectopic PTH-producing tumorigenesis; both might release the control of PTH gene expression by shutting down the other branches of the safety system (e.g., CaSR and the vitamin D3–vitamin D receptor axis).

The role of extracellular calcium in bone metastasis

This review summarizes the role of extracellular calcium, as found present in the bone tissue, in the process of bone metastasis.

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.