Expression profiling of colorectal cancer cells reveals inhibition of DNA replication licensing by extracellular calcium

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.

Chemopreventive effects of vitamin D3 and its analogue, paricalcitol, in combination with 5-fluorouracil against colorectal cancer: The role of calcium signalling molecules

BACKGROUND

Although vitamin D (VD) is chemoprotective and enhances 5-fluorouracil (5-FU) cytotoxicity against colorectal cancer (CRC), little is known about its potential calcium (Ca²⁺)-mediated anti-tumorigenic actions. Therefore, this study compared between VD and its non-calcaemic analogue, Paricalcitol (Pcal), ± 5-FU in relation to chemoprevention and Ca²⁺-mediated apoptosis in vivo and in vitro.

METHODS

Seventy male mice were distributed to: negative controls, positive controls (PC), VD, Pcal, 5-FU, VD + 5-FU and Pcal+5-FU groups. All groups, except negative, received two consecutive azoxymethane (AOM)-injections (10 mg/Kg/week) for CRC induction. VD₃ (1000 IU/kg; three times/week) and Pcal (1.25 μg/kg; three times/week) injections started week-16 post-AOM and for 10 weeks. Three successive 5-FU cycles began at week-21 (50 mg/Kg/week). Similar protocols with VD₃, Pcal and/or 5-FU were applied in the HT29 colon cancer cells.

RESULTS

The PC group had abundant malignant tumours, markedly elevated proliferation markers (survivin/CCND1) and declines in cyclin-dependent kinase-inhibitor-1A, pro-apoptotic molecules (p53/BAX/cytochrome_C/caspase-3), tissue Ca²⁺ concentrations and Ca²⁺-dependent proteins (CaSR/CAM/CAMKIIA). All monotherapies equally reduced tumour numbers and proliferation markers whilst promoting the anti-tumorigenic molecules. VD and/or 5-FU, but not Pcal monotherapy, enhanced Ca²⁺ levels and Ca²⁺-related molecules (CaSR/CAM/CAMKIIA/BAX/cytochrome_C) in vivo and in vitro. However, VD + 5-FU co-therapy showed the lowest tumour numbers, the highest cell numbers in sub-G1 phase of cell cycle, alongside the most effective modulations of oncogenes, tumour suppressors and Ca²⁺-related molecules at the gene and protein levels in vivo and in vitro.

CONCLUSIONS

VD₃ was superior than Paricalcitol in potentiating 5-FU cytotoxicity, possibly by upregulating several Ca²⁺-related molecules involved in tumour suppression.

International Union of Basic and Clinical Pharmacology. CVIII. Calcium-Sensing Receptor Nomenclature, Pharmacology, and Function

The calcium-sensing receptor (CaSR) is a class C G protein-coupled receptor that responds to multiple endogenous agonists and allosteric modulators, including divalent and trivalent cations, L-amino acids, γ-glutamyl peptides, polyamines, polycationic peptides, and protons. The CaSR plays a critical role in extracellular calcium (Ca2+ o) homeostasis, as demonstrated by the many naturally occurring mutations in the CaSR or its signaling partners that cause Ca2+ o homeostasis disorders. However, CaSR tissue expression in mammals is broad and includes tissues unrelated to Ca2+ o homeostasis, in which it, for example, regulates the secretion of digestive hormones, airway constriction, cardiovascular effects, cellular differentiation, and proliferation. Thus, although the CaSR is targeted clinically by the positive allosteric modulators (PAMs) cinacalcet, evocalcet, and etelcalcetide in hyperparathyroidism, it is also a putative therapeutic target in diabetes, asthma, cardiovascular disease, and cancer. The CaSR is somewhat unique in possessing multiple ligand binding sites, including at least five putative sites for the "orthosteric" agonist Ca2+ o, an allosteric site for endogenous L-amino acids, two further allosteric sites for small molecules and the peptide PAM, etelcalcetide, and additional sites for other cations and anions. The CaSR is promiscuous in its G protein-coupling preferences, and signals via Gq/11, Gi/o, potentially G12/13, and even Gs in some cell types. Not surprisingly, the CaSR is subject to biased agonism, in which distinct ligands preferentially stimulate a subset of the CaSR's possible signaling responses, to the exclusion of others. The CaSR thus serves as a model receptor to study natural bias and allostery. SIGNIFICANCE STATEMENT: The calcium-sensing receptor (CaSR) is a complex G protein-coupled receptor that possesses multiple orthosteric and allosteric binding sites, is subject to biased signaling via several different G proteins, and has numerous (patho)physiological roles. Understanding the complexities of CaSR structure, function, and biology will aid future drug discovery efforts seeking to target this receptor for a diversity of diseases. This review summarizes what is known to date regarding key structural, pharmacological, and physiological features of the CaSR.

A Complex Role for Calcium Signaling in Colorectal Cancer Development and Progression

Clinical data suggest that many malignant cancers are associated with hypercalcemia. Hypercalcemia can facilitate the proliferation and metastasis of gastric and colon tumors, and has been considered a hallmark of end-stage disease. However, it has also been reported that dietary calcium or vitamin D supplementation could reduce the risk of many types of cancers. In particular, the intestines can absorb considerable amounts of calcium via Ca²⁺-permeable ion channels, and hypercalcemia is common in patients with colorectal cancer. Thus, this review considers the role of calcium signaling in the context of colorectal cancer and summarizes the functions of specific regulators of cellular calcium levels in the proliferation, invasion, metastasis, cell death, and drug resistance of colorectal cancer cells. The data reveal that even a slight upregulation of intracellular Ca²⁺ signaling can facilitate the onset and progression of colorectal cancer, while continuous Ca²⁺ influx and Ca²⁺ overload may cause tumor cell death. This dual function of Ca²⁺ signaling adds nuance to the debate over the hallmarks of colorectal cancer, and may even provide new directions and strategies for clinical interventions.

Identification of the Altered Proteins Related to Colon Carcinogenesis by iTRAQ-based Quantitative Proteomic Analysis

Background:

The molecular mechanisms or valuable biomarkers for early diagnosis of colorectal cancer (CRC) are not fully elucidated yet.

Objective:

To understand the proteomic changes at the global level in the carcinogenesis of CRC, differentially expressed proteins between normal intestinal epithelial cells CCD841 and colorectal cancer cells HCT116 were identified.

Method:

The isobaric tags for relative and absolute quantitation (iTRAQ) coupled with 2D LC-MS/MS proteomic approach were performed for screening the altered proteins between cells CCD841 and HCT116.

Results:

A total of 1947 proteins were identified after filtering and using a 1% false discovery rate. Based on a final cutoff (> 3.16 and < 0.32), 229 proteins were found to be significantly altered, among which 95 (41%) were up-regulated while 134 (59%) were down-regulated. Gene Ontology analysis revealed that the differentially expressed proteins were mainly cell part proteins involved in cellular process and binding in terms of subcellular distribution, biological process, and molecular function. KEGG analysis indicated that the differentially expressed proteins were significantly involved in the process of focal adhesion, pathogenic Escherichia coli infection, leukocyte transendothelial migration, bacterial invasion of epithelial cells, regulation of actin cytoskeleton, DNA replication and so on.

Conclusion:

Collectively, our data identified differentially expressed proteins in colon cancer carcinogenesis, which could provide the clues on unraveling the molecular mechanism of CRC.

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, a pivotal player in photodynamic therapy?

Photodynamic therapy combines three non-toxic components: light, oxygen and a photosensitizer to generate singlet oxygen and/or other ROS molecules in order to target destruction of cancer cells. The damage induced in the targeted cells can furthermore propagate to non-exposed bystander cells thereby exacerbating the damage. Ca²⁺ signaling is strongly intertwined with ROS signaling and both play crucial roles in cell death. In this review we aimed to review current knowledge on the role of Ca²⁺ and ROS signaling, their effect on cell-cell propagation via connexin-linked mechanisms and the outcome in terms of cell death. In general, photodynamic therapy results in an increased cytosolic Ca²⁺ concentration originating from Ca²⁺ entry or Ca²⁺ release from internal stores. While photodynamic therapy can certainly induce cell death, the outcome depends on the cell type and the photosensitizer used. Connexin channels propagating the Ca²⁺ signal, and presumably regenerating ROS at distance, may play a role in spreading the effect to neighboring non-exposed bystander cells. Given the various cell types and photosensitizers used, there is currently no unified signaling scheme to explain the role of Ca²⁺ and connexins in the responses following photodynamic therapy. This article is part of a Special Issue entitled: Calcium signaling in health, disease and therapy edited by Geert Bultynck and Jan Parys.