Calcium-Sensing Receptor Promotes Breast Cancer by Stimulating Intracrine Actions of Parathyroid Hormone-Related Protein

Hypercalcemia in Cancer: Causes, Effects, and Treatment Strategies

Calcium plays central roles in numerous biological processes, thereby, its levels in the blood are under strict control to maintain homeostatic balance and enable the proper functioning of living organisms. The regulatory mechanisms ensuring this balance can be affected by pathologies such as cancer, and as a result, hyper- or hypocalcemia can occur. These states, characterized by elevated or decreased calcium blood levels, respectively, have a significant effect on general homeostasis. This article focuses on a particular form of calcium metabolism disorder, which is hypercalcemia in neoplasms. It also constitutes a summary of the current knowledge regarding the diagnosis of hypercalcemia and its management. Hypercalcemia of malignancy is estimated to affect over 40% of cancer patients and can be associated with both solid and blood cancers. Elevated calcium levels can be an indicator of developing cancer. The main mechanism of hypercalcemia development in tumors appears to be excessive production of parathyroid hormone-related peptides. Among the known treatment methods, bisphosphonates, calcitonin, steroids, and denosumab should be mentioned, but ongoing research promotes progress in pharmacotherapy. Given the rising global cancer prevalence, the problem of hypercalcemia is of high importance and requires attention.

Calcium-Sensing Receptor Expression in Breast Cancer

The calcium-sensing receptor (CaSR) plays a crucial role in maintaining the balance of calcium in the body. Altered signaling through the CaSR has been linked to the development of various tumors, such as colorectal and breast tumors. This retrospective study enrolled 79 patients who underwent surgical removal of invasive breast carcinoma of no special type (NST) to explore the expression of the CaSR in breast cancer. The patients were categorized based on age, tumor size, hormone receptor status, HER2 status, Ki-67 proliferation index, tumor grade, and TNM staging. Immunohistochemistry was conducted on core needle biopsy samples to assess CaSR expression. The results revealed a positive correlation between CaSR expression and tumor size, regardless of the tumor surrogate subtype (p = 0.001). The expression of ER exhibited a negative correlation with CaSR expression (p = 0.033). In contrast, a positive correlation was observed between CaSR expression and the presence of HER2 receptors (p = 0.002). Increased CaSR expression was significantly associated with lymph node involvement and the presence of distant metastasis (p = 0.001 and p = 0.038, respectively). CaSR values were significantly higher in the patients with increased Ki-67 (p = 0.042). Collectively, higher CaSR expression in breast cancer could suggest a poor prognosis and treatment outcome regardless of the breast cancer subtype.

Astragalus Polysaccharides Alleviate Lung Adenocarcinoma Bone Metastases by Inhibiting the CaSR/PTHrP Signaling Pathway

Bone metastasis is one of the common complications of lung cancer and can lead to bone-related adverse events, such as pathological fractures, spinal cord defects, and nerve compression syndrome. As an effective medicinal component of Astragalus membranaceus, Astragalus polysaccharide (APS) has antitumor activity and alleviates osteoporosis to a certain extent. In this study, we explored the possible role and mechanism underlying APS inhibition of lung adenocarcinoma bone metastases by constructing a mouse model of lung adenocarcinoma bone metastases. First, we constructed osteoclast (OC) and osteoblast (OB) culture systems in vitro to confirm that APS affected the differentiation and function of OCs and OBs. Then, using the mouse bone metastasis model, microCT, and bone histopathology, we confirmed that APS inhibited osteolytic metastasis and tumor cell proliferation in mice, and the effect was mainly realized by inhibiting the CaSR/PTHrP signal pathway. The results showed that APS had a protective effect on lung adenocarcinoma bone metastases.

A Tumor Accelerator Based on Multicomponent Bone Scaffolds and Cancer Cell Homing

Bone tissue attracts cancer cell homing biologically, mechanically, or chemically. It is difficult and time consuming to identify their complex cross-talk using existed methods. In this study, a multi-component bone matrix was fabricated using gelatin, hydroxyapatite (HAp), and epidermal growth factor (EGF) as raw materials to investigate how “acellular” bone matrix affects cancer cell homing in bone. Then, EGF-responsive cancer cells were cultured with the scaffold in a dynamical bioreactor. For different culture periods, the effects of HAp, gelatin, and EGF on the cell adhesion, proliferation, 3D growth, and migration of cancer were evaluated. The results indicated that a small amount of calcium ion released from the scaffolds accelerated cancer MDA-MB-231 adhesion on the surface of inner pores. Moreover, degradable gelatin key caused cancer cell growth on the scaffold surface to turn into a 3D aggregation. Despite this, the formation of cancer spheroids was slow, and required 14 days of dynamic culture. Thankfully, EGF promoted cancer cell adhesion, proliferation, and migration, and cancer spheroids were observed only after 3-day culture. We concluded that the combination of the multiple components in this scaffold allows cancer cells to meet multiple requirements of cancer dynamic progression.

Vitamin D, Th17 Lymphocytes, and Breast Cancer

Simple Summary

The effect of vitamin D₃ on the development of breast cancer (favorable, ineffective, or even unfavorable) depends on many factors, such as age, menopausal status, or obesity. The immunomodulatory effect of vitamin D may be unfavorable in case of breast cancer progression. The effect of vitamin D on Th17 cells may depend on disease type and patients’ age. Our goal was to summarize the data available and to find indications of vitamin D treatment failure or success. Therefore, in this review, we present data describing the effects of vitamin D₃ on Th17 cells, mainly in breast cancer.

Abstract

Vitamin D₃, which is well known to maintain calcium homeostasis, plays an important role in various cellular processes. It regulates the proliferation and differentiation of several normal cells, including immune and neoplastic cells, influences the cell cycle, and stimulates cell maturation and apoptosis through a mechanism dependent on the vitamin D receptor. The involvement of vitamin D₃ in breast cancer development has been observed in numerous clinical studies. However, not all studies support the protective effect of vitamin D₃ against the development of this condition. Furthermore, animal studies have revealed that calcitriol or its analogs may stimulate tumor growth or metastasis in some breast cancer models. It has been postulated that the effect of vitamin D₃ on T helper (Th) 17 lymphocytes is one of the mechanisms promoting metastasis in these murine models. Herein we present a literature review on the existing data according to the interplay between vitamin D, Th17 cell and breast cancer. We also discuss the effects of this vitamin on Th17 lymphocytes in various disease entities known to date, due to the scarcity of scientific data on Th17 lymphocytes and breast cancer. The presented data indicate that the effect of vitamin D₃ on breast cancer development depends on many factors, such as age, menopausal status, or obesity. According to that, more extensive clinical trials and studies are needed to assess the importance of vitamin D in breast cancer, especially when no correlations seem to be obvious.

Parathyroid hormone-related protein (PTHrP) and malignancy

PTHrP (parathyroid hormone related protein) is an important mediator of malignancy-related tumor progression and hypercalcemia that shares considerable homology and functionality with parathyroid hormone. In this chapter, we review what has been elucidated to date regarding PTHrP's role in malignancies. Starting with a review of calcium metabolism and regulation, we then summarize the discovery and structure of PTHrP and development of sensitive immunoassays for specific measurement. Subsequently, we explore its role in tumor progression, with emphasis on the primary tumor as well as skeletal and non-osseus metastases. We then consider the clinical implications of PTHrP in cancer before concluding with a discussion of both established and potential treatments for malignancy associated hypercalcemia and bone metastases.

Origin and Therapies of Osteosarcoma

Simple Summary

Osteosarcoma is the most common malignant bone tumor in children, with a 5-year survival rate ranging from 70% to 20% depending on the aggressiveness of the disease. The current treatments have not evolved over the past four decades due in part to the genetic complexity of the disease and its heterogeneity. This review will summarize the current knowledge of OS origin, diagnosis and therapies.

Abstract

Osteosarcoma (OS) is the most frequent primary bone tumor, mainly affecting children and young adults. Despite therapeutic advances, the 5-year survival rate is 70% but drastically decreases to 20–30% for poor responders to therapies or for patients with metastasis. No real evolution of the survival rates has been observed for four decades, explained by poor knowledge of the origin, difficulties related to diagnosis and the lack of targeted therapies for this pediatric tumor. This review will describe a non-exhaustive overview of osteosarcoma disease from a clinical and biological point of view, describing the origin, diagnosis and therapies.

Nutritional and metabolic signalling through GPCRs

Deregulated metabolism is a well-known feature of several challenging diseases, including diabetes, obesity and cancer. Besides their important role as intracellular bioenergetic molecules, dietary nutrients and metabolic intermediates are released in the extracellular environment. As such, they may achieve unconventional roles as hormone-like molecules by activating cell-surface G-protein-coupled receptors (GPCRs) that regulate several pathophysiological processes. In this review, we provide an insight into the role of lactate, succinate, fatty acids, amino acids, ketogenesis-derived and β-oxidation-derived intermediates as extracellular signalling molecules. Moreover, the mechanisms by which their cognate metabolite-sensing GPCRs integrate nutritional and metabolic signals with specific intracellular pathways will be described. A better comprehension of these aspects is of fundamental importance to identify GPCRs as novel druggable targets.

PTHrP induces STAT5 activation, secretory differentiation and accelerates mammary tumor development

BACKGROUND

Parathyroid hormone-related protein (PTHrP) is required for embryonic breast development and has important functions during lactation, when it is produced by alveolar epithelial cells and secreted into the maternal circulation to mobilize skeletal calcium used for milk production. PTHrP is also produced by breast cancers, and GWAS studies suggest that it influences breast cancer risk. However, the exact functions of PTHrP in breast cancer biology remain unsettled.

METHODS

We developed a tetracycline-regulated, MMTV (mouse mammary tumor virus)-driven model of PTHrP overexpression in mammary epithelial cells (Tet-PTHrP mice) and bred these mice with the MMTV-PyMT (polyoma middle tumor-antigen) breast cancer model to analyze the impact of PTHrP overexpression on normal mammary gland biology and in breast cancer progression.

RESULTS

Overexpression of PTHrP in luminal epithelial cells caused alveolar hyperplasia and secretory differentiation of the mammary epithelium with milk production. This was accompanied by activation of Stat5 and increased expression of E74-like factor-5 (Elf5) as well as a delay in post-lactation involution. In MMTV-PyMT mice, overexpression of PTHrP (Tet-PTHrP;PyMT mice) shortened tumor latency and accelerated tumor growth, ultimately reducing overall survival. Tumors overproducing PTHrP also displayed increased expression of nuclear pSTAT5 and Elf5, increased expression of markers of secretory differentiation and milk constituents, and histologically resembled secretory carcinomas of the breast. Overexpression of PTHrP within cells isolated from tumors, but not PTHrP exogenously added to cell culture media, led to activation of STAT5 and milk protein gene expression. In addition, neither ablating the Type 1 PTH/PTHrP receptor (PTH1R) in epithelial cells nor treating Tet-PTHrP;PyMT mice with an anti-PTH1R antibody prevented secretory differentiation or altered tumor latency. These data suggest that PTHrP acts in a cell-autonomous, intracrine manner. Finally, expression of PTHrP in human breast cancers is associated with expression of genes involved in milk production and STAT5 signaling.

CONCLUSIONS

Our study suggests that PTHrP promotes pathways leading to secretory differentiation and proliferation in both normal mammary epithelial cells and in breast tumor cells.

Calcium sensing receptor stimulates breast cancer cell migration via the Gβγ-AKT-mTORC2 signaling pathway

Calcium sensing receptor, a pleiotropic G protein coupled receptor, activates secretory pathways in cancer cells and putatively exacerbates their metastatic behavior. Here, we show that various CaSR mutants, identified in breast cancer patients, differ in their ability to stimulate Rac, a small Rho GTPase linked to cytoskeletal reorganization and cell protrusion, but are similarly active on the mitogenic ERK pathway. To investigate how CaSR activates Rac and drives cell migration, we used invasive MDA-MB-231 breast cancer cells. We revealed, by pharmacological and knockdown strategies, that CaSR activates Rac and cell migration via the Gβγ-PI3K-mTORC2 pathway. These findings further support current efforts to validate CaSR as a relevant therapeutic target in metastatic cancer.

Predictive and Prognostic Biomarkers for Lung Cancer Bone Metastasis and Their Therapeutic Value

Lung cancer is the leading cause of cancer-related death worldwide. Bone metastasis, which usually accompanies severe skeletal-related events, is the most common site for tumor distant dissemination and detected in more than one-third of patients with advanced lung cancer. Biopsy and imaging play critical roles in the diagnosis of bone metastasis; however, these approaches are characterized by evident limitations. Recently, studies regarding potential biomarkers in the serum, urine, and tumor tissue, were performed to predict the bone metastases and prognosis in patients with lung cancer. In this review, we summarize the findings of recent clinical research studies on biomarkers detected in samples obtained from patients with lung cancer bone metastasis. These markers include the following: (1) bone resorption-associated markers, such as N-terminal telopeptide (NTx)/C-terminal telopeptide (CTx), C-terminal telopeptide of type I collagen (CTx-I), tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), pyridinoline (PYD), and parathyroid hormone related peptide (PTHrP); (2) bone formation-associated markers, including total serum alkaline phosphatase (ALP)/bone specific alkaline phosphatase(BAP), osteopontin (OP), osteocalcin (OS), amino-terminal extension propeptide of type I procollagen/carboxy-terminal extension propeptide of type I procollagen (PICP/PINP); (3) signaling markers, including epidermal growth factor receptor/Kirsten rat sarcoma/anaplastic lymphoma kinase (EGFR/KRAS/ALK), receptor activator of nuclear factor κB ligand/receptor activator of nuclear factor κB/osteoprotegerin (RANKL/RANK/OPG), C-X-C motif chemokine ligand 12/C-X-C motif chemokine receptor 4 (CXCL12/CXCR4), complement component 5a receptor (C5AR); and (4) other potential markers, such as calcium sensing receptor (CASR), bone sialoprotein (BSP), bone morphogenetic protein 2 (BMP2), cytokeratin 19 fragment/carcinoembryonic antigen (CYFRA/CEA), tissue factor, cell-free DNA, long non-coding RNA, and microRNA. The prognostic value of these markers is also investigated. Furthermore, we listed some clinical trials targeting hotspot biomarkers in advanced lung cancer referring for their therapeutic effects.

Mechanisms, Diagnosis and Treatment of Bone Metastases

Bone and bone marrow are among the most frequent metastatic sites of cancer. The occurrence of bone metastasis is frequently associated with a dismal disease outcome. The prevention and therapy of bone metastases is a priority in the treatment of cancer patients. However, current therapeutic options for patients with bone metastatic disease are limited in efficacy and associated with increased morbidity. Therefore, most current therapies are mainly palliative in nature. A better understanding of the underlying molecular pathways of the bone metastatic process is warranted to develop novel, well-tolerated and more successful treatments for a significant improvement of patients' quality of life and disease outcome. In this review, we provide comparative mechanistic insights into the bone metastatic process of various solid tumors, including pediatric cancers. We also highlight current and innovative approaches to biologically targeted therapy and immunotherapy. In particular, we discuss the role of the bone marrow microenvironment in the attraction, homing, dormancy and outgrowth of metastatic tumor cells and the ensuing therapeutic implications. Multiple signaling pathways have been described to contribute to metastatic spread to the bone of specific cancer entities, with most knowledge derived from the study of breast and prostate cancer. However, it is likely that similar mechanisms are involved in different types of cancer, including multiple myeloma, primary bone sarcomas and neuroblastoma. The metastatic rate-limiting interaction of tumor cells with the various cellular and noncellular components of the bone-marrow niche provides attractive therapeutic targets, which are already partially exploited by novel promising immunotherapies.

The bromodomain inhibitor JQ1+ reduces calcium-sensing receptor activity in pituitary cell lines

Corticotrophinomas represent 10% of all surgically removed pituitary adenomas, however, current treatment options are often not effective, and there is a need for improved pharmacological treatments. Recently, JQ1+, a bromodomain inhibitor that promotes gene transcription by binding acetylated histone residues and recruiting transcriptional machinery, has been shown to reduce proliferation in a murine corticotroph cell line, AtT20. RNA-Seq analysis of AtT20 cells following treatment with JQ1+ identified the calcium-sensing receptor (CaSR) gene as significantly downregulated, which was subsequently confirmed using real-time PCR and Western blot analysis. CaSR is a G protein-coupled receptor that plays a central role in calcium homeostasis but can elicit non-calcitropic effects in multiple tissues, including the anterior pituitary where it helps regulate hormone secretion. However, in AtT20 cells, CaSR activates a tumour-specific cAMP pathway that promotes ACTH and PTHrP hypersecretion. We hypothesised that the Casr promoter may harbour binding sites for BET proteins, and using chromatin immunoprecipitation (ChIP)-sequencing demonstrated that the BET protein Brd3 binds to the promoter of the Casr gene. Assessment of CaSR signalling showed that JQ1+ significantly reduced Ca2+e-mediated increases in intracellular calcium (Ca2+i) mobilisation and cAMP signalling. However, the CaSR-negative allosteric modulator, NPS-2143, was unable to reduce AtT20 cell proliferation, indicating that reducing CaSR expression rather than activity is likely required to reduce pituitary cell proliferation. Thus, these studies demonstrate that reducing CaSR expression may be a viable option in the treatment of pituitary tumours. Moreover, current strategies to reduce CaSR activity, rather than protein expression for cancer treatments, may be ineffective.

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

Calcium Metabolism and Breast Cancer: Echoes of Lactation?

Lactation requires a series of adaptations in maternal calcium and bone metabolism to ensure a steady supply of calcium to the lactating mammary gland. The alterations in systemic metabolism are accompanied by alterations in the expression of calcium receptors, channels, binding proteins, pumps and transporters in mammary epithelial cells to increase the uptake of calcium from the extracellular fluid and to transport it into milk. Intracellular calcium regulates signaling pathways that mediate changes in cell proliferation, differentiation and death and many of the molecules involved in supporting and coordinating calcium secretion into milk are re-expressed and redeployed to support malignant behavior in breast cancer cells. In this article, we review adaptations of systemic calcium homeostasis during lactation, as well as the mechanisms of milk calcium transport. We then discuss how reactivation of these pathways contributes to the pathophysiology of breast cancer.

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.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

CaSR Induces Osteoclast Differentiation and Promotes Bone Metastasis in Lung Adenocarcinoma

Objective: Explore the mechanism of CaSR's involvement in bone metastasis in lung adenocarcinoma.

Methods: Immunohistochemistry (IHC) was used to detect the expression of calcium-sensing receptor (CaSR) in 120 cases of lung adenocarcinoma with bone metastasis. Stably transfected cell lines with CaSR overexpression and knockdown based on A549 cells were constructed. The expression of CaSR was verified by western blot and qPCR. The proliferation and migration abilities of A549 cells were tested using cholecystokinin-8 (CCK-8) and Transwell assays, respectively. Western blotting was used to detect the expression of matrix metalloproteinases MMP2, MMP9, CaSR, and NF-κB. The supernatant from each cell culture group was collected as a conditional co-culture solution to study the induction of osteoclast precursor cells and osteoblasts. Western blot and qPCR were used to validate the expression of bone matrix degradation-related enzymes cathepsin K and hormone calcitonin receptor (CTR) and osteoblast-induced osteoclast maturation and differentiation enzyme receptor activator of nuclear factor-κB ligand (RANKL), macrophage colony-stimulating factor (M-CSF), osteoprotegerin (OPG), and PTHrP. Immunofluorescent staining was used to detect F-actin ring formation and osteocalcin expression. Western blot results for NF-κB expression identified a regulatory relationship between NF-κB and CaSR.

Results: CaSR expression in lung cancer tissues was significantly higher than that in adjacent and normal lung tissues. The expression of CaSR in lung cancer tissues with bone metastasis was higher than that in non-metastatic lung cancer tissues. The proliferation and migration ability of A549 cells increased significantly with overexpressed CaSR. The co-culture solution directly induced osteoclast precursor cells and the expression of bone matrix degradation-related enzymes significantly increased. Osteoblasts were significantly inhibited and osteoblast-induced osteoclast maturation and differentiation enzymes were significantly downregulated. It was found that the expression of NF-κB and PTHrP increased when CaSR was overexpressed. Osteoclast differentiation factor expression was also significantly increased, which directly induces osteoclast differentiation and maturation. These results were reversed when CaSR was knocked down.

Conclusions: CaSR can positively regulate NF-κB and PTHrP expression in A549 cells with a high metastatic potential, thereby promoting osteoclast differentiation and maturation, and facilitating the occurrence and development of bone metastasis in lung adenocarcinoma.

Signal Transduction Pathways in Breast Cancer: The Important Role of PI3K/Akt/mTOR

Breast cancer is the cancer with the highest prevalence in women and is the number-one cause of cancer mortality worldwide. Cell transduction is a fundamental process in the development and progression of cancer. Modifications in various cell signalling pathways promote tumour cell proliferation, progression, and survival. The PI3K/Akt/mTOR pathway is an example of that, and it is involved in growth, proliferation, survival, motility, metabolism, and immune response regulation. Activation of this pathway is one of the main causes of cancer cell resistance to antitumour therapies. This makes PI3K/Akt/mTOR signalling a crucial object of study for understanding the development and progression of this disease. Thus, this pathway may have a role as a potential therapeutic target, as well as prognostic and diagnostic value, in patients with breast cancer. Despite the existence of selective PI3K/Akt/mTOR pathway inhibitors and current clinical trials, the cellular mechanisms are not yet known. The present review aims to understand the current state of this important disease and the paths that must be forged.

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.

Calcium-sensing receptor promotes tumor proliferation and migration in human intrahepatic cholangiocarcinoma by targeting ERK signaling pathway

The Calcium-sensing receptor (CaSR) is functionally expressed in the biliary epithelial cells and it has been verified to possess various regulatory functions in several different forms of human cancers. But its pathological role in human intrahepatic cholangiocarcinoma (ICC) development remains obscure. Here, we confirmed that CaSR expression was up-regulated in ICC tumor specimens and cell lines, which was positively correlated with number of tumors, lymph node metastasis and poor prognosis of ICC patients. CaSR activation induced by CaCl₂ or Calindol (a selective CaSR agonist) markedly facilitated cell proliferation and migration in ICC cells, while knockdown of CaSR or NPS2143 treatment (a CaSR antagonist) dramatically suppressed the above effects. We also demonstrated that alteration of CaSR activity mediated tumorigenesis and growth of ICC in vivo. Mechanistically, CaSR activation could promote cell cycle progression and induce an upregulation of MMP-2 and MMP-9 expression partly via the simulation of ERK1/2 signaling pathway. And further inhibition of ERK pathway significantly suppressed ICC cell viability and migration capacity. Together, our findings shed novel light on the role of CaSR as an oncogene in ICC progression and indicated that modulation of CaSR might serve as a preventive or therapeutic strategy for ICC.

Sensing Extracellular Calcium - An Insight into the Structure and Function of the Calcium-Sensing Receptor (CaSR)

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor that plays a key role in calcium homeostasis, by sensing free calcium levels in blood and regulating parathyroid hormone secretion in response. The CaSR is highly expressed in parathyroid gland and kidney where its role is well characterised, but also in other tissues where its function remains to be determined. The CaSR can be activated by a variety of endogenous ligands, as well as by synthetic modulators such as Cinacalcet, used in the clinic to treat secondary hyperparathyroidism in patients with chronic kidney disease. The CaSR couples to multiple G proteins, in a tissue-specific manner, activating several signalling pathways and thus regulating diverse intracellular events. The multifaceted nature of this receptor makes it a valuable therapeutic target for calciotropic and non-calciotropic diseases. It is therefore essential to understand the complexity behind the pharmacology, trafficking, and signalling characteristics of this receptor. This review provides an overview of the latest knowledge about the CaSR and discusses future hot topics in this field.

The Roles of Bone Marrow-Resident Cells as a Microenvironment for Bone Metastasis

It has been appreciated that the cross talk between bone metastatic cancer cells and bone marrow microenvironment influence one another to worsen bone metastatic disease progression. Bone marrow contains various cell types, including (1) cells of mesenchymal origin (e.g., osteoblasts, osteocytes, and adipocytes), (2) cells of hematopoietic origin (e.g., osteoclast and immune cells), and (3) others (e.g., endothelial cells and nerves). The recent studies have enabled us to discover many important cancer-derived factors responsible for the development of bone metastasis. However, many critical questions regarding the roles of bone microenvironment in bone metastatic progression remain elusive. To answer these questions, a deeper understanding of the cross talk between bone metastatic cancer and bone marrow microenvironment is clearly warranted.

Lymph node metastasis in lung squamous cell carcinoma and identification of metastasis-related genes based on the Cancer Genome Atlas

Squamous cell carcinoma (SCC) is a unique clinical and histological category that accounts for about 30% of total lung cancer. To identify risk factors for lymph node metastasis and analyze the molecular features of these metastases in lung SCC, a retrospective study was performed for 170 lung SCC patients who underwent surgical treatment. The overall survival of these patients with or without lymph node metastasis (LM/NLM) was analyzed using the Kaplan‐Meier method. We also used the TCGA database to compare the differentially expressed genes (DEGs) in patients with stage T1‐2 and T3‐4 lung SCC. Data from both our retrospective study and the TCGA database demonstrated a correlation between age and stage T1‐T2 LM (P = .002). There were significant differences between the LM and NLM groups in both mean survival time and median survival time for different T‐stages (P = .031). There were 176 upregulated and 177 downregulated DEGs between the LM and NLM groups in the stage T1‐2 group and 93 upregulated and 34 downregulated DEGs in the stage T3‐T4 group. These differentially expressed genes were predicted to participate in five cellular components, five molecular functions, and five biological processes. There were 20 genes, including GCG, CASR, NPY, CGA, TAC1, ALB, APOA1, CRH, CHRH, TRH, and GHSR, located at the core of the protein‐protein interaction network in the stage T1‐2 group and 11 genes, including F2, CASR, GRM1, GNRHR, GRPR, NTSR1, PROKR2, UTS2D, PTH, ALB, and FGA, in the stage T3‐4 group. Overall, LM plays a key role in the treatment response and prognosis of SCC patients. Several risk factors, including age and stage, were identified for LM. There was a previously undiscovered enrichment of significant novel genes in lung SCC between the LM and NLM groups, which may have the potential for predicting prognosis and targeting.

The Mode-of-Action of Targeted Alpha Therapy Radium-223 as an Enabler for Novel Combinations to Treat Patients with Bone Metastasis

Bone metastasis is a common clinical complication in several cancer types, and it causes a severe reduction in quality of life as well as lowering survival time. Bone metastases proceed through a vicious self-reinforcing cycle that can be osteolytic or osteoblastic in nature. The vicious cycle is characterized by cancer cells residing in bone releasing signal molecules that promote the differentiation of osteoclasts and osteoblasts either directly or indirectly. The increased activity of osteoclasts and osteoblasts then increases bone turnover, which releases growth factors that benefit metastatic cancer cells. In order to improve the prognosis of patients with bone metastases this cycle must be broken. Radium-223 dichloride (radium-223), the first targeted alpha therapy (TAT) approved, is an osteomimetic radionuclide that is incorporated into bone metastases where its high-linear energy transfer alpha radiation disrupts both the activity of bone cells and cancer cells. Therefore, radium-223 treatment has been shown preclinically to directly affect cancer cells in both osteolytic breast cancer and osteoblastic prostate cancer bone metastases as well as to inhibit the differentiation of osteoblasts and osteoclasts. Clinical studies have demonstrated an increase in survival in patients with metastatic castration-resistant prostate cancer. Due to the effectiveness and low toxicity of radium-223, several novel combination treatment strategies are currently eliciting considerable research interest.

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.

Gestational Gigantomastia Complicated by PTHrP-Mediated Hypercalcemia

CONTEXT

Gestational gigantomastia is an uncommon condition characterized by abnormal and excessive growth of breast tissue during an otherwise uncomplicated pregnancy. Gestational gigantomastia may be accompanied by hypercalcemia, which in some cases has been associated with elevated serum levels of PTHrP. The source of the PTHrP in these cases has been suggested to be the enlarged breasts.

OBJECTIVE

To describe the rapid resolution of hypercalcemia and normalization of serum PTHrP after elective termination of pregnancy, indicating that the placenta was the source of the PTHrP.

DESIGN

A retrospective analysis of clinical and biochemical data over a 2-year interval and review of literature.

SETTING

An academic medical center.

PATIENT

A 33-year-old G8P4 female who presented at week 8 of pregnancy with gestational gigantomastia and subsequently developed marked hypercalcemia at week 13. Serum levels of PTH were suppressed but circulating PTHrP was elevated. There was no history of hypercalcemia or significant breast growth during previous pregnancies.

INTERVENTION

Hypercalcemia was poorly responsive to IV saline, prednisone, calcitonin, and cinacalcet. She requested termination of pregnancy at week 20.

RESULTS

Serum levels of calcium, PTH, and PTHrP normalized within 48 hours of termination of pregnancy.

CONCLUSION

The rapid resolution of hypercalcemia after termination of pregnancy, despite persistent gigantomastia, provides evidence for a pathologic role of the placenta in the excess production of PTHrP, possibly through an as yet uncharacterized placenta-breast hormonal axis.

Interaction between Tumor-Associated Dendritic Cells and Colon Cancer Cells Contributes to Tumor Progression via CXCL1

Crosstalk of a tumor with its microenvironment is a critical factor contributing to cancer development. This study investigates the soluble factors released by tumor-associated dendritic cells (TADCs) responsible for increasing cancer stem cell (CSC) properties, cell mobility, and epithelial-to-mesenchymal transition (EMT). Dendritic cells (DCs) of colon cancer patients were collected for phenotype and CXCL1 expression by flow cytometry and Luminex assays. The transcriptome of CXCL1-treated cancer cells was established by next generation sequencing. Inflammatory chemokine CXCL1, present in large amounts in DCs isolated from colon cancer patients, and SW620-conditioned TADCs, enhance CSC characteristics in cancer, supported by enhanced anchorage-independent growth, CD133 expression and aldehyde dehydrogenase activity. Additionally, CXCL1 increases the metastatic ability of a cancer by enhancing cell migration, matrix metalloproteinase-7 expression and EMT. The enhanced CXCL1 expression in DCs is also noted in mice transplanted with colon cancer cells. Transcriptome analysis of CXCL1-treated SW620 cells indicates that CXCL1 increases potential oncogene expression in colon cancer, including PTHLH, TYRP1, FOXO1, TCF4 and ZNF880. Concurrently, CXCL1 displays a specific microRNA (miR) upregulated by the prototypical colon cancer onco-miR miR-105. Analysis of publicly available data reveals CXCL1-driven oncogenes and miR-105 have a negative prognostic impact on the outcome of colon cancer. This study indicates a new mechanism by which the colon cancer milieu exploits DC plasticity to support cancer progression.

Loss of Nuclear Localized Parathyroid Hormone-Related Protein in Primary Breast Cancer Predicts Poor Clinical Outcome and Correlates with Suppressed Stat5 Signaling

PURPOSE

Parathyroid hormone-related protein (PTHrP) is required for normal mammary gland development and biology. A PTHLH gene polymorphism is associated with breast cancer risk, and PTHrP promotes growth of osteolytic breast cancer bone metastases. Accordingly, current dogma holds that PTHrP is upregulated in malignant primary breast tumors, but solid evidence for this assumption is missing.

EXPERIMENTAL DESIGN

We used quantitative IHC to measure PTHrP in normal and malignant breast epithelia, and correlated PTHrP levels in primary breast cancer with clinical outcome.

RESULTS

PTHrP levels were markedly downregulated in malignant compared with normal breast epithelia. Moreover, low levels of nuclear localized PTHrP in cancer cells correlated with unfavorable clinical outcome in a test and a validation cohort of breast cancer treated at different institutions totaling nearly 800 cases. PTHrP mRNA levels in tumors of a third cohort of 737 patients corroborated this association, also after multivariable adjustment for standard clinicopathologic parameters. Breast cancer PTHrP levels correlated strongly with transcription factors Stat5a/b, which are established markers of favorable prognosis and key mediators of prolactin signaling. Prolactin stimulated PTHrP transcript and protein in breast cancer cell lines in vitro and in vivo, effects mediated by Stat5 through the P2 gene promoter, producing transcript AT6 encoding the PTHrP 1-173 isoform. Low levels of AT6, but not two alternative transcripts, correlated with poor clinical outcome.

CONCLUSIONS

This study overturns the prevailing view that PTHrP is upregulated in primary breast cancers and identifies a direct prolactin-Stat5-PTHrP axis that is progressively lost in more aggressive tumors.

The Osteoclast in Bone Metastasis: Player and Target

Bone metastases are frequently the final fate of breast and prostate cancer patients. According to the definition of metastasis as an incurable disease, to date there are no effective treatments for tumor-associated bone metastases and this represents a real challenge for the researchers in the field. The bone is a heterogeneous environment that represents a fertile soil for tumor cells, supporting their growth. Among the different cell types present in the bone, in this review we will focus our attention on the osteoclasts, which are crucial players in the so called “vicious cycle”, a phenomenon triggered by tumor cells eventually leading to both tumor proliferation as well as bone deregulation, thus fueling the development of bone metastasis. The complex network, linking tumor cells to the bone by activating osteoclasts, represents a fruitful target for the treatment of bone metastases. In this review we will describe how tumor cells perturb the bone microenvironment by actively influencing osteoclast formation and activity. Moreover, we will describe the current antiresorptive drugs employed in the treatment of bone metastases as well as new, targeted therapies able to affect both cancer cells and osteoclasts.

Enhanced ZnR/GPR39 Activity in Breast Cancer, an Alternative Trigger of Signaling Leading to Cell Growth

Acquired resistance to the estrogen receptor (ER) antagonist tamoxifen, is a major obstacle in treatment of breast cancer. Changes in Zn2+ accumulation and distribution are associated with tamoxifen-resistance and breast cancer progression. The Zn2+-sensing G-protein coupled receptor, ZnR/GPR39, triggers signaling leading to cell growth, but a role for this receptor in breast cancer in unknown. Using fluorescence imaging, we found Zn2+-dependent Ca2+ release, mediated by ZnR/GPR39 activity, in TAMR tamoxifen-resistant cells derived from MCF-7 cells, but not in ER-expressing MCF-7 or T47D cells. Furthermore, ZnR/GPR39 signaling was monitored in ER negative BT20, MDA-MB-453 and JIMT-1 cells. Expression of ZnR/GPR39 was increased in grade 3 human breast cancer biopsies compared to grade 2. Consistently, analysis of two breast cancer patient cohorts, GDS4057 and TCGA, indicated that in ER-negative tumors higher ZnR/GPR39 mRNA levels are associated with more aggressive tumors. Activation of ZnR/GPR39 in TAMR cells triggered MAPK, mTOR and PI3K signaling. Importantly, enhanced cell growth and invasiveness was observed in the ER negative breast cancer cells, TAMR, MDA-MB-453 and BT20 cells but not in the ER expressing MCF-7 cells. Thus, we suggest ZnR/GPR39 as a potential therapeutic target for combination treatment in breast cancer, particularly relevant in ER negative tumors.

Cancer Stem Cells, Bone and Tumor Microenvironment: Key Players in Bone Metastases

Tumor mass is constituted by a heterogeneous group of cells, among which a key role is played by the cancer stem cells (CSCs), possessing high regenerative properties. CSCs directly metastasize to bone, since bone microenvironment represents a fertile environment that protects CSCs against the immune system, and maintains their properties and plasticity. CSCs can migrate from the primary tumor to the bone marrow (BM), due to their capacity to perform the epithelial-to-mesenchymal transition. Once in BM, they can also perform the mesenchymal-to-epithelial transition, allowing them to proliferate and initiate bone lesions. Another factor explaining the osteotropism of CSCs is their ability to recognize chemokine gradients toward BM, through the CXCL12–CXCR4 axis, also known to be involved in tumor metastasis to other organs. Moreover, the expression of CXCR4 is associated with the maintenance of CSCs’ stemness, and CXCL12 expression by osteoblasts attracts CSCs to the BM niches. CSCs localize in the pre-metastatic niches, which are anatomically distinct regions within the tumor microenvironment and govern the metastatic progression. According to the stimuli received in the niches, CSCs can remain dormant for long time or outgrow from dormancy and create bone lesions. This review resumes different aspects of the CSCs’ bone metastastic process and discusses available treatments to target CSCs.

Osteomimicry: How the Seed Grows in the Soil

Metastasis is defined as a very inefficient process, since less than 0.01% of cancer cells injected into the circulation will engraft in a distant organ, where they must acquire the ability to survive and proliferate inside a "foreign" environment. In bone metastases, the interaction with the host organ is much more favoured if tumour cells gain "osteomimicry", that is the ability to resemble a resident bone cell (i.e. the osteoblast), thus intruding in the physiology of the bone. This is accomplished by the expression of osteoblast markers (e.g. alkaline phosphatase) and the production of bone matrix proteins and paracrine factors which deregulate the physiology of bone, fuelling the so-called "vicious cycle". The main challenge of researchers is therefore to identify the genetic profile determining the osteotropism of tumour cells, which would eventually lead to bone colonisation. This could likely provide the answer to a quite intriguing question, that is why some cancers, such as prostate and breast, have a specific predilection to metastasise to the bone. Therefore, it is important to completely address the molecular mechanisms underlying this aspect of bone oncology, identifying relevant pathways, the targeting of which could make any type of bone metastasis curable or avoidable.

Autocrine and Paracrine Regulation of the Murine Skeleton by Osteocyte-Derived Parathyroid Hormone-Related Protein

Parathyroid hormone-related protein (PTHrP) and parathyroid hormone (PTH) have N-terminal domains that bind a common receptor, PTHR1. N-terminal PTH (teriparatide) and now a modified N-terminal PTHrP (abaloparatide) are US Food and Drug Administration (FDA)-approved therapies for osteoporosis. In physiology, PTHrP does not normally circulate at significant levels, but acts locally, and osteocytes, cells residing within the bone matrix, express both PTHrP and the PTHR1. Because PTHR1 in osteocytes is required for normal bone resorption, we determined how osteocyte-derived PTHrP influences the skeleton. We observed that adult mice with low PTHrP in osteocytes (targeted with the Dmp1(10kb)-Cre) have low trabecular bone volume and osteoblast numbers, but osteoclast numbers were unaffected. In addition, bone size was normal, but cortical bone strength was impaired. Osteocyte-derived PTHrP therefore stimulates bone formation and bone matrix strength, but is not required for normal osteoclastogenesis. PTHrP knockdown and overexpression studies in cultured osteocytes indicate that osteocyte-secreted PTHrP regulates their expression of genes involved in matrix mineralization. We determined that osteocytes secrete full-length PTHrP with no evidence for secretion of lower molecular weight forms containing the N-terminus. We conclude that osteocyte-derived full-length PTHrP acts through both PTHR1 receptor-mediated and receptor-independent actions in a paracrine/autocrine manner to stimulate bone formation and to modify adult cortical bone strength. © 2017 American Society for Bone and Mineral Research.

Parathyroid Hormone-Related Protein Negatively Regulates Tumor Cell Dormancy Genes in a PTHR1/Cyclic AMP-Independent Manner

Parathyroid hormone-related protein (PTHrP) expression in breast cancer is enriched in bone metastases compared to primary tumors. Human MCF7 breast cancer cells "home" to the bones of immune deficient mice following intracardiac inoculation, but do not grow well and stain negatively for Ki67, thus serving as a model of breast cancer dormancy in vivo. We have previously shown that PTHrP overexpression in MCF7 cells overcomes this dormant phenotype, causing them to grow as osteolytic deposits, and that PTHrP-overexpressing MCF7 cells showed significantly lower expression of genes associated with dormancy compared to vector controls. Since early work showed a lack of cyclic AMP (cAMP) response to parathyroid hormone (PTH) in MCF7 cells, and cAMP is activated by PTH/PTHrP receptor (PTHR1) signaling, we hypothesized that the effects of PTHrP on dormancy in MCF7 cells occur through non-canonical (i.e., PTHR1/cAMP-independent) signaling. The data presented here demonstrate the lack of cAMP response in MCF7 cells to full length PTHrP(1-141) and PTH(1-34) in a wide range of doses, while maintaining a response to three known activators of adenylyl cyclase: calcitonin, prostaglandin E₂ (PGE₂), and forskolin. PTHR1 mRNA was detectable in MCF7 cells and was found in eight other human breast and murine mammary carcinoma cell lines. Although PTHrP overexpression in MCF7 cells changed expression levels of many genes, RNAseq analysis revealed that PTHR1 was unaltered, and only 2/32 previous PTHR1/cAMP responsive genes were significantly upregulated. Instead, PTHrP overexpression in MCF7 cells resulted in significant enrichment of the calcium signaling pathway. We conclude that PTHR1 in MCF7 breast cancer cells is not functionally linked to activation of the cAMP pathway. Gene expression responses to PTHrP overexpression must, therefore, result from autocrine or intracrine actions of PTHrP independent of PTHR1, through signals emanating from other domains within the PTHrP molecule.

PTH1R-CaSR Cross Talk: New Treatment Options for Breast Cancer Osteolytic Bone Metastases

Metastatic breast cancer (BrCa) is currently incurable despite great improvements in treatment of primary BrCa. The incidence of skeletal metastases in advanced BrCa occurs up to 70%. Recent findings have established that the distribution of BrCa metastases to the skeleton is not a random process but due to the favorable microenvironment for tumor invasion and growth. The complex interplay among BrCa cells, stromal/osteoblastic cells, and osteoclasts in the osseous microenvironment creates a bone-tumor vicious cycle (a feed-forward loop) that results in excessive bone destruction and progressive tumor growth. Both the type 1 PTH receptor (PTH1R) and extracellular calcium-sensing receptor (CaSR) participate in the vicious cycle and influence the skeletal metastatic niche. Thus, this review focuses on how the PTH1R and CaSR signaling pathways interact and contribute to the pathogenesis of BrCa bone metastases. The effects of intermittent PTH and allosteric modulators of CaSR for the use of bone-anabolic agents and prevention of BrCa bone metastases constitute a proof of principle for therapeutic consideration. Understanding the interplay between PTH1R and CaSR signaling in the development of BrCa bone metastases could lead to a novel therapeutic approach to control both osteolysis and tumor burden in the bone.

Autocrine parathyroid hormone-like hormone promotes intrahepatic cholangiocarcinoma cell proliferation via increased ERK/JNK-ATF2-cyclinD1 signaling

BACKGROUND AND AIMS

Intrahepatic cholangiocarcinoma (ICC) is an aggressive tumor with a high fatality rate. It was recently found that parathyroid hormone-like hormone (PTHLH) was frequently overexpressed in ICC compared with non-tumor tissue. This study aimed to elucidate the underlying mechanisms of PTHLH in ICC development.

METHODS

The CCK-8 assay, colony formation assays, flow cytometry and a xenograft model were used to examine the role of PTHLH in ICC cells proliferation. Immunohistochemistry (IHC) and western blot assays were used to detect target proteins. Luciferase reporter, chromatin immunoprecipitation (ChIP) and DNA pull-down assays were used to verify the transcription regulation of activating transcription factor-2 (ATF2).

RESULTS

PTHLH was significantly upregulated in ICC compared with adjacent and normal tissues. Upregulation of PTHLH indicated a poor pathological differentiation and intrahepatic metastasis. Functional study demonstrated that PTHLH silencing markedly suppressed ICC cells growth, while specific overexpression of PTHLH has the opposite effect. Mechanistically, secreted PTHLH could promote ICC cell growth by activating extracellular signal-related kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways, and subsequently upregulated ATF2 and cyclinD1 expression. Further study found that the promoter activity of PTHLH were negatively regulated by ATF2, indicating that a negative feedback loop exists.

CONCLUSIONS

Our findings demonstrated that the ICC-secreted PTHLH plays a characteristic growth-promoting role through activating the canonical ERK/JNK-ATF2-cyclinD1 signaling pathways in ICC development. We identified a negative feedback loop formed by ATF2 and PTHLH. In this study, we explored the therapeutic implication for ICC patients.

Recent Advances in Comprehending the Signaling Pathways Involved in the Progression of Breast Cancer

This review describes recent advances in the comprehension of signaling pathways involved in breast cancer progression. Calcium sensing receptor (CaSR), caveolae signaling, signaling referred to hypoxia-inducing factors and disturbances in the apoptotic machinery are related to more general biological mechanisms and are considered first. The others refer to signaling pathways of more specific biological mechanisms, namely the heparin/heparin-sulfate interactome, over-expression of miRNA-378a-5p, restriction of luminal and basal epithelial cells, fatty-acid synthesis, molecular pathways related to epithelial to mesenchimal transition (EMT), HER-2/neu gene amplification and protein expression, and the expression of other members of the epithelial growth factor receptor family. This progress in basic research is fundamental to foster the ongoing efforts that use the new genotyping technologies, and aim at defining new prognostic and predictive biomarkers for a better personalized management of breast cancer disease.

The calcium-cancer signalling nexus

The calcium signal is a powerful and multifaceted tool by which cells can achieve specific outcomes. Cellular machinery important in tumour progression is often driven or influenced by changes in calcium ions; in some cases this regulation occurs within spatially defined regions. Over the past decade there has been a deeper understanding of how calcium signalling is remodelled in some cancers and the consequences of calcium signalling on key events such as proliferation, invasion and sensitivity to cell death. Specific calcium signalling pathways have also now been identified as playing important roles in the establishment and maintenance of multidrug resistance and the tumour microenvironment.

Mechanisms governing metastatic dormancy in breast cancer

Breast cancer is a systemic disease characterized by early dissemination of tumor cells to distant organs. In this foreign environment, tumor cells may stay in a dormant state as single cells or as micrometastases for many years before growing out into a macrometastatic lesion. As metastasis is the primary cause for breast cancer-related death, it is important to understand the mechanisms underlying the maintenance of dormancy and dormancy escape to find druggable targets to eradicate metastatic tumor cells. Metastatic dormancy is regulated by complex interactions between tumor cells and the local microenvironment. In addition, cancer-directed immunity and systemic instigation play a crucial role.

Cancer Cell Colonisation in the Bone Microenvironment

Bone metastases are a common complication of epithelial cancers, of which breast, prostate and lung carcinomas are the most common. The establishment of cancer cells to distant sites such as the bone microenvironment requires multiple steps. Tumour cells can acquire properties to allow epithelial-to-mesenchymal transition, extravasation and migration. Within the bone metastatic niche, disseminated tumour cells may enter a dormancy stage or proliferate to adapt and survive, interacting with bone cells such as hematopoietic stem cells, osteoblasts and osteoclasts. Cross-talk with the bone may alter tumour cell properties and, conversely, tumour cells may also acquire characteristics of the surrounding microenvironment, in a process known as osteomimicry. Alternatively, these cells may also express osteomimetic genes that allow cell survival or favour seeding to the bone marrow. The seeding of tumour cells in the bone disrupts bone-forming and bone-resorbing activities, which can lead to macrometastasis in bone. At present, bone macrometastases are incurable with only palliative treatment available. A better understanding of how these processes influence the early onset of bone metastasis may give insight into potential therapies. This review will focus on the early steps of bone colonisation, once disseminated tumour cells enter the bone marrow.

Calcium-Sensing Receptor in Breast Physiology and Cancer

The calcium-sensing receptor (CaSR) is expressed in normal breast epithelial cells and in breast cancer cells. During lactation, activation of the CaSR in mammary epithelial cells increases calcium transport into milk and inhibits parathyroid hormone-related protein (PTHrP) secretion into milk and into the circulation. The ability to sense changes in extracellular calcium allows the lactating breast to actively participate in the regulation of systemic calcium and bone metabolism, and to coordinate calcium usage with calcium availability during milk production. Interestingly, as compared to normal breast cells, in breast cancer cells, the regulation of PTHrP secretion by the CaSR becomes rewired due to a switch in its G-protein usage such that activation of the CaSR increases instead of decreases PTHrP production. In normal cells the CaSR couples to Gα_i to inhibit cAMP and PTHrP production, whereas in breast cancer cells, it couples to Gα_s to stimulate cAMP and PTHrP production. Activation of the CaSR on breast cancer cells regulates breast cancer cell proliferation, death and migration, in part, by stimulating PTHrP production. In this article, we discuss the biology of the CaSR in the normal breast and in breast cancer, and review recent findings suggesting that the CaSR activates a nuclear pathway of PTHrP action that stimulates cellular proliferation and inhibits cell death, helping cancer cells adapt to elevated extracellular calcium levels. Understanding the diverse actions mediated by the CaSR may help us better understand lactation physiology, breast cancer progression and osteolytic bone metastases.