AT1 angiotensin II receptor mediates intracellular calcium mobilization in normal and cancerous breast cells in primary culture

How clathrin-coated pits control nanoparticle avidity for cells

The paramount relevance of clathrin-coated pits (CCPs) to receptor-mediated endocytosis of nanoparticles, extracellular vesicles, and viruses has made them the focus of many studies; however, the role of CCP geometry in the ligand-receptor interactions between multivalent nanoparticles and cells has not been investigated. We hypothesized the general dependence of nanoparticle binding energy on local membrane curvature to be expandable to the specific case of ligand-functionalized nanoparticles binding cell membranes, in the sense that membrane structures whose curvature matches that of the particle (e.g., CCPs) signficantly contribute to binding avidity. We investigated this hypothesis with nanoparticles that bind multivalently to angiotensin II receptor type 1, which is subject to clathrin-mediated endocytosis. When we used cholesterol extraction to prevent the action of CCPs, we found a 67 to 100-fold loss in avidity. We created a theoretical model that predicts this decrease based on the loss of ligand-receptor interactions when CCPs, which perfectly match nanoparticle geometry, are absent. Our findings shed new light on how cells "see" nanoparticles. The presence or absence of CPPs is so influential on how cells interact with nanoparticles that the number of particles required to be visible to cells changes by two orders of magnitude depending on CCP presence.

Store-Operated Ca2+ Entry in Breast Cancer Cells: Remodeling and Functional Role

Breast cancer is the most common type of cancer in women. It is a heterogeneous disease that ranges from the less undifferentiated luminal A to the more aggressive basal or triple negative breast cancer molecular subtype. Ca²⁺ influx from the extracellular medium, but more specifically store-operated Ca²⁺ entry (SOCE), has been reported to play an important role in tumorigenesis and the maintenance of a variety of cancer hallmarks, including cell migration, proliferation, invasion or epithelial to mesenchymal transition. Breast cancer cells remodel the expression and functional role of the molecular components of SOCE. This review focuses on the functional role and remodeling of SOCE in breast cancer cells. The current studies suggest the need to deepen our understanding of SOCE in the biology of the different breast cancer subtypes in order to develop new and specific therapeutic strategies.

Matrix stiffness modulates infection of endothelial cells by Listeria monocytogenes via expression of cell surface vimentin

Extracellular matrix stiffness (ECM) is one of the many mechanical forces acting on mammalian adherent cells and an important determinant of cellular function. While the effect of ECM stiffness on many aspects of cellular behavior has been studied previously, how ECM stiffness might mediate susceptibility of host cells to infection by bacterial pathogens is hitherto unexplored. To address this open question, we manufactured hydrogels of varying physiologically relevant stiffness and seeded human microvascular endothelial cells (HMEC-1) on them. We then infected HMEC-1 with the bacterial pathogen Listeria monocytogenes (Lm) and found that adhesion of Lm to host cells increases monotonically with increasing matrix stiffness, an effect that requires the activity of focal adhesion kinase (FAK). We identified cell surface vimentin as a candidate surface receptor mediating stiffness-dependent adhesion of Lm to HMEC-1 and found that bacterial infection of these host cells is decreased when the amount of surface vimentin is reduced. Our results provide the first evidence that ECM stiffness can mediate the susceptibility of mammalian host cells to infection by a bacterial pathogen.

Effect of angiotensin receptor blockade on prevention and reversion of tamoxifen-resistant phenotype in MCF-7 cells

Tamoxifen (TAM) is a standard adjuvant endocrine therapy in postmenopausal breast cancer patients, but innate or acquired TAM resistance has remained to be a therapeutic challenge for clinicians. The aim of this study was to explore the possible participation of renin-angiotensin system (RAS) in the acquisition of TAM resistance and try to prevent and regress the resistance using an angiotensin II receptor type-1 (AGTR1) blocker, losartan. Establishment of TAM-resistant (TAM-R) cells was accomplished by continuous exposure of MCF-7 cells to 1 μmol/L TAM. MTT (3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was performed to determine cell growth. Moreover, messenger RNA (mRNA) expression levels of AGTR1 and angiotensin II receptor type-2 (AGTR2) were measured by quantitative real-time polymerase chain reaction. A significant increase of AGTR1 and AGTR2 transcripts was observed in TAM-R cells compared to MCF-7 cells. Interestingly, losartan-TAM combination effectively resensitized TAM-R cells to tamoxifen treatment by inducing cell death. Therefore, our findings suggest an important role of RAS in acquired TAM resistance and targeting of RAS by losartan may overcome TAM resistance phenomenon and provide a novel avenue for treatment of resistant breast cancers.

Different apoptotic effects of [Pt(O,O'-acac)(γ-acac)(DMS)] and cisplatin on normal and cancerous human epithelial breast cells in primary culture

BACKGROUND AND PURPOSE

The aim of this study was to determine whether [platinum (Pt)(O,O'-acetylacetonate (acac))(γ-acac)(dimethylsulphide (DMS))] is differentially cytotoxic in normal and cancer cells, and to measure comparative levels of cytotoxicity compared with cisplatin in the same cells.

EXPERIMENTAL APPROACH

We performed experiments on cancerous and normal epithelial breast cells in primary culture obtained from the same patients. The apoptotic effects [Pt(O,O'-acac)(γ-acac)(DMS)] and cisplatin in cancerous and normal breast cells were compared.

KEY RESULTS

Cancer cells were more sensitive to [Pt(O,O'-acac)(γ-acac)(DMS)] (IC50 = 5.22 ± 1.2 μmol·L(-1)) than normal cells (IC50 = 116.9 ± 8.8 μmol·L(-1)). However, the difference was less strong when cisplatin was used (IC50 = 96.0 ± 6.9 and 61.9 ± 6.1 μmol·L(-1) for cancer and normal cells respectively). Both compounds caused reactive oxygen species (ROS) production with different mechanisms: [Pt(O,O'-acac)(γ-acac)(DMS)] quickly activated NAD(P)H oxidase while cisplatin caused a slower formation of mitochondrial ROS. Cisplatin and [Pt(O,O'-acac)(γ-acac)(DMS)] caused activation of caspases, proteolysis of PARP and modulation of Bcl-2, Bax and Bid. [Pt(O,O'-acac)(γ-acac)(DMS)] also caused leakage of cytochrome c from the mitochondria. Overall, these processes proceeded more quickly in cells treated with [Pt(O,O'-acac)(γ-acac)(DMS)] compared with cisplatin. [Pt(O,O'-acac)(γ-acac)(DMS)] effects were faster and quantitatively greater in cancer than in normal cells. [Pt(O,O'-acac)(γ-acac)(DMS)] caused a fast decrease of mitochondrial membrane potential, especially in cancer cells.

CONCLUSIONS AND IMPLICATIONS

[Pt(O,O'-acac)(γ-acac)(DMS)] was specific to breast cancer cells in primary culture, and this observation makes this compound potentially more interesting than cisplatin.

Angiotensin II induces the generation of procoagulant microparticles by human mononuclear cells via an angiotensin type 2 receptor-mediated pathway

INTRODUCTION

Microparticles are small vesicles shed by cells upon activation and during apoptosis which participate in physiologically relevant phenomena, including blood coagulation. Intracellular calcium mobilization is one of the mechanisms of microparticle generation during cell activation. Because the renin-angiotensin system has been proposed as a link between hypertension and increased thrombotic risk, we investigated whether angiotensin II upregulates the generation of procoagulant microparticles by human mononuclear cells.

MATERIALS AND METHODS

Human mononuclear cells were exposed to angiotensin II for 15min. Intracellular calcium concentration was assessed by a Fluo 4 based kit. The supernatants were analyzed for both microparticle content, with a commercially available kit based on phosphatidylserine analysis, and microparticle-associated tissue factor, with a one-stage clotting assay.

RESULTS

Intracellular calcium concentration is increased upon exposure of mononuclear cells to angiotensin II. Incubation with angiotensin II stimulates microparticles release; microparticle-associated tissue factor is also upregulated. The effect is inhibited by an angiotensin receptor type 2 antagonist (PD123319) and not by two angiotensin type 1 antagonists (Losartan and Olmesartan).

CONCLUSIONS

Angiotensin receptor 2-mediated upregulation of tissue factor-bearing, procoagulant microparticle generation represents a novel mechanism linking the renin-angiotensin system to thrombosis.

Angiotensin II type 1 receptor (AT-1R) expression correlates with VEGF-A and VEGF-D expression in invasive ductal breast cancer

Recent studies point to the involvement of angiotensin II (Ang II) receptor type 1 (AT-1R) on processes of metastasing, stimulation of invasiveness and angiogenesis in tumours. In this study, the correlation between intensity of AT-1R expression and expression of lymph- and angiogenesis markers in invasive ductal breast cancers (IDC) was examined. Immunohistochemical studies (IHC) were performed on archival material of 102 IDC cases. Only 28 (27.5%) cases manifested low AT-1R expression while 74 (72.5%) cases demonstrated a moderate or pronounced AT-1R expression. Expression intensity of AT-1R was found to correlate with expressions of VEGF-A (r = 0.26; p = 0.008) and VEGF-D (r = 0.24; p = 0.015). Out of the examined markers of angiogenesis and lymphangiogenesis only the pronounced expression of VEGF-C was found to correlate with patient poor clinical outcome (p = 0.009). The positive correlation between AT-1R and VEGF-A and VEGF-D could point to stimulatory action of Ang II on their expression what might result in augmented lymph- and angiogenesis in IDC.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

Aspirin suppresses cardiac fibroblast proliferation and collagen formation through downregulation of angiotensin type 1 receptor transcription

Aspirin (acetyl salicylic acid, ASA) is a common drug used for its analgesic and antipyretic effects. Recent studies show that ASA not only blocks cyclooxygenase, but also inhibits NADPH oxidase and resultant reactive oxygen species (ROS) generation, a pathway that underlies pathogenesis of several ailments, including hypertension and tissue remodeling after injury. In these disease states, angiotensin II (Ang II) activates NADPH oxidase via its type 1 receptor (AT1R) and leads to fibroblast growth and collagen synthesis. In this study, we examined if ASA would inhibit NADPH oxidase activation, upregulation of AT1R transcription, and subsequent collagen generation in mouse cardiac fibroblasts challenged with Ang II. Mouse heart fibroblasts were isolated and treated with Ang II with or without ASA. As expected, Ang II induced AT1R expression, and stimulated cardiac fibroblast growth and collagen synthesis. The AT1R blocker losartan attenuated these effects of Ang II. Similarly to losartan, ASA, and its SA moiety suppressed Ang II-mediated AT1R transcription and fibroblast proliferation as well as expression of collagens and MMPs. ASA also suppressed the expression of NADPH oxidase subunits (p22(phox), p47(phox), p67(phox), NOX2 and NOX4) and ROS generation. ASA did not affect total NF-κB p65, but inhibited its phosphorylation and activation. These observations suggest that ASA inhibits Ang II-induced NADPH oxidase expression, NF-κB activation and AT1R transcription in cardiac fibroblasts, and fibroblast proliferation and collagen expression. The critical role of NADPH oxidase activity in stimulation of AT1R transcription became apparent in experiments where ASA also inhibited AT1R transcription in cardiac fibroblasts challenged with H2O2. Since SA had similar effect as ASA on AT1R expression, we suggest that ASA's effect is mediated by its SA moiety.

Identification of genes differentially expressed in benign versus malignant thyroid tumors

PURPOSE

Although fine-needle aspiration biopsy is the most useful diagnostic tool in evaluating a thyroid nodule, preoperative diagnosis of thyroid nodules is frequently imprecise, with up to 30% of fine-needle aspiration biopsy cytology samples reported as "suspicious" or "indeterminate." Therefore, other adjuncts, such as molecular-based diagnostic approaches are needed in the preoperative distinction of these lesions.

EXPERIMENTAL DESIGN

In an attempt to identify diagnostic markers for the preoperative distinction of these lesions, we chose to study by microarray analysis the eight different thyroid tumor subtypes that can present a diagnostic challenge to the clinician.

RESULTS

Our microarray-based analysis of 94 thyroid tumors identified 75 genes that are differentially expressed between benign and malignant tumor subtypes. Of these, 33 were overexpressed and 42 were underexpressed in malignant compared with benign thyroid tumors. Statistical analysis of these genes, using nearest-neighbor classification, showed a 73% sensitivity and 82% specificity in predicting malignancy. Real-time reverse transcription-PCR validation for 12 of these genes was confirmatory. Western blot and immunohistochemical analyses of one of the genes, high mobility group AT-hook 2, further validated the microarray and real-time reverse transcription-PCR data.

CONCLUSIONS

Our results suggest that these 12 genes could be useful in the development of a panel of markers to differentiate benign from malignant tumors and thus serve as an important first step in solving the clinical problem associated with suspicious thyroid lesions.

Differential roles of Angiotensinogen and Angiotensin Receptor type 1 polymorphisms in breast cancer risk

While angiotensinogen (AGT) seems to have anti proliferative properties, angiotensin II (ATII) is a potent growth factor and it mediates its actions through the angiotensin type 1 receptor (AGTR1). In the AGT gene, the M235T polymorphism has been associated with the variation in angiotensinogen levels and in the AGTR1 gene; the C573T variant is associated with different pathologies. We aimed to evaluate the relationship of these two variants and the risk of breast cancer. These polymorphisms were genotyped in 3787 women participating the Rotterdam Study. We performed a logistic regression and a disease free survival analysis by genotype. The logistic regression yielded an odds ratio of 1.4 (95% CI: 1.1-1.9) for the MM genotype carriers versus the T allele carriers. The breast cancer free survival by AGT genotype was significantly reduced in MM genotype carriers compared to non-carriers (hazard ratio (HR) = 1.5; 95% CI: 1.1-2.2). We did not find any association of the AGTR1 polymorphism and breast cancer risk or disease free survival. Our results suggest that AGT plays a role in breast cancer risk in postmenopausal women, whereas the role of AGTR1 needs further studying.

Localisation of renin-angiotensin system (RAS) components in breast

Angiotensin II has mitogenic and angiogenic effects and its receptors are widespread, particularly in epithelial tissue. Tissue renin angiotensin systems (tRASs) may be a local source of angiotensin II that has specific paracrine functions. To investigate the presence of a tRAS in normal human breast and tumours. Immunocytochemistry, and quantitative RT–PCR was used to establish: (i) the presence and localisation of RAS components, (ii) the possibility of their involvement in cancer. (1) mRNA coding for angiotensinogen, prorenin, angiotensin converting enzyme (ACE), and both AT1 and AT2 receptors was demonstrated in normal and diseased breast tissues. (2) (pro)renin was identified in epithelial cells in both normal and diseased tissue, but in invasive carcinoma, its distribution was mostly confined to fibroblasts or could not be detected at all. (3) Angiotensin converting enzyme was shown in epithelial cells in both normal and malignant tissue. The results are consistent with the hypothesis that a tRAS is present in the breast, and is disrupted in invasive cancer.

AT1 receptor and ACE mRNA are increased in chemically induced carcinoma of rat mammary gland

Angiotesin II has except of strong vasoconstrict effect also ability to potentiate protein synthesis and cellular growth. The aim of this study was to investigate the gene expression of components of the renin-angiotensin system, angiotensinogen, renin, angiotensin-converting enzyme and AT(1) receptor, in rat mammary gland and in chemically induced carcinoma of this gland. Retinoids are known to inhibit cell proliferation and induce cell differentiation so they are considered as a promising chemopreventive agents. We studied the effect of 13-cis-retinoic acid on the gene expression of mentioned elements of the renin-angiotensin system in tumour tissue. The expressions in control and carcinoma tissue were investigated using RT-PCR and activity of angiotensin-converting enzyme was measured. The amount of angiotensin-converting enzyme and AT(1) receptor mRNA and angiotensin-converting enzyme activity always showed a significant increase in the carcinoma tissue in comparison with the control. Administration of 13-cis-retinoic acid to rats with induced mammary gland carcinoma was without significant effect on either tumour numbers or tumour burden and volume. Similarly, 13-cis-retinoic acid did not change the angiotensin-converting enzyme expression and activity. The AT(1) receptor gene expression displayed a clear tendency to decrease in tumour tissue after retinoic acid treatment. Our results demonstrate the presence of angiotensin-converting enzyme and AT(1) receptor in control and carcinoma tissue of mammary gland. We assume that both proteins might play a role in development of tumour cells and vasculature.

Mitogenic signalling by B2 bradykinin receptor in epithelial breast cells

The kinin peptides are released during inflammation and are amongst the most potent known mediators of vasodilatation, pain, and oedema. A role in the modulation or induction of healthy breast tissue growth has been postulated for tissue kallikrein present in human milk. Moreover, tissue kallikrein was found in malignant human breast tissue and bradykinin (BK) stimulates the proliferation of immortalised breast cancer cells. Aim of the present article was to investigate whether BK also exerts mitogenic activity in normal breast epithelial cells and partially characterise the signalling machinery involved. Results show that BK increased up to 2-fold the 24 h proliferation of breast epithelial cells in primary culture, and that the BK B2 receptor (not B1) inhibitor alone fully blocked the BK response. Intracellular effects of B2 stimulation were the following: (a) the increase of free intracellular Ca(2+) concentration by a mechanism dependent upon the phospholipase C (PLC) activity; (b) the cytosol-to-membrane translocation of conventional (PKC)-alpha and -beta isozymes, novel PKC-delta, -epsilon, and -eta isozymes; (c) the phosphorylation of the extracellular-regulated kinase 1 and 2 (ERK1/2); and (d) the stimulation of the expression of c-Fos protein. EGF, a well known stimulator of cell proliferation, regulated the proliferative response in human epithelial breast cells to the same extent of BK. The effects of BK on proliferation, ERK1/2 phosphorylation, and c-Fos expression were abolished by GF109203X, which inhibits PKC-delta isozyme. Conversely, Gö6976, an inhibitor of PKC-alpha and -beta isozymes, and the 18-h treatment of cells with PMA, that led to the complete down-regulation of PKC-alpha, -beta, -epsilon, and -eta, but not of PKC-delta, did not have any effect, thereby indicating that the PKC-delta mediates the mitogenic signalling of BK. Phosphoinositide 3-kinase (PI3K), tyrosine kinase of the epidermal growth factor receptor (EGFR), and mitogen activated protein kinase kinases (MEK) inhibitors were also tested. The results suggest that EGFR, PI3K, and ERK are required for the proliferative effects of BK. In addition, the BK induced cytosol-to-membrane translocation of PKC-delta was blocked by PI3K inhibition, suggesting that PI3K is upstream to PKC-delta. In conclusion, BK has mitogenic actions in cultured human epithelial breast cells; the activation of PKC-delta through B2 receptor acts in concert with ERK and PI3K pathways to induce cell proliferation.

Angiotensin II activates extracellular signal regulated kinases via protein kinase C and epidermal growth factor receptor in breast cancer cells

Angiotensin II (Ang II) induces, through AT1, intracellular Ca(2+) increase in both normal and cancerous breast cells in primary culture (Greco et al., 2002 Cell Calcium 2:1-10). We here show that Ang II stimulated, in a dose-dependent manner, the 24 h-proliferation of breast cancer cells in primary culture, induced translocation of protein kinase C (PKC)-alpha, -beta1/2, and delta (but not -epsilon, -eta, -theta, -zeta, and -iota), and phosphorylated extracellular-regulated kinases 1 and 2 (ERK1/2). The proliferative effects of Ang II were blocked by the AT1 antagonist, losartan. Also epidermal growth factor (EGF) had mitogenic effects on serum-starved breast cancer cells since induced cell proliferation after 24 h and phosphorylation of ERK1/2. The Ang II-induced proliferation of breast cancer cells was reduced by (a) Gö6976, an inhibitor of conventional PKC-alpha and -beta1, (b) AG1478, an inhibitor of the tyrosine kinase of the EGF receptor (EGFR), and (c) downregulation of 1,2-diacylglycerol-sensitive PKCs achieved by phorbol 12-myristate 13-acetate (PMA). A complete inhibition of the Ang II-induced cell proliferation was achieved using the inhibitor of the mitogen activated protein kinase kinase (MAPKK or MEK), PD098059, or using Gö6976 together with AG1478. These results indicate that in human primary cultured breast cancer cells AT1 regulates mitogenic signaling pathways by two simultaneous mechanisms, one involving conventional PKCs and the other EGFR transactivation.