Angiotensin II promotes pulmonary metastasis of melanoma through the activation of adhesion molecules in vascular endothelial cells

Increased risk of metastasis in patients with incidental use of renin-angiotensin system inhibitors: a retrospective analysis for multiple types of cancer based on electronic medical records

Renin-angiotensin system inhibitors have been shown to prevent cancer metastasis in experimental models, but there are limited data in clinical studies. We aimed to explore whether renin-angiotensin system inhibitors administered during the period of cancer resection can influence the subsequent development of metastasis by analyzing multiple individual types of primary cancers. A total of 4927 patients who had undergone resection of primary cancers at Kyushu University Hospital from 2009 to 2014 were enrolled and categorized into 3 groups based on the use of antihypertensive drugs: renin-angiotensin system inhibitors, other drugs, and none. Cumulative incidence functions of metastasis, treating death as a competing risk, were calculated, and the difference was examined among groups by Gray's test. Fine and Gray's model was employed to evaluate multivariate-adjusted hazards of incidental metastasis. In the multivariate-adjusted analysis, patients with skin and renal cancers showed statistically higher risks of metastasis with the use of renin-angiotensin system inhibitors (hazard ratio [95% confidence interval], 5.81 [1.07-31.57] and 4.24 [1.71-10.53], respectively). Regarding pancreatic cancer, patients treated with antihypertensive drugs other than renin-angiotensin system inhibitors had a significantly increased risk of metastasis (hazard ratio [95% confidence interval], 3.31 [1.43-7.69]). Future larger studies are needed to ascertain whether renin-angiotensin system inhibitors can increase the risk of metastasis in skin and renal cancers, focusing on specific tissue types and potential factors associated with renin-angiotensin system inhibitor use.

Insights Into Vascular Anomalies, Cancer, and Fibroproliferative Conditions: The Role of Stem Cells and the Renin-Angiotensin System

Cells exhibiting embryonic stem cell (ESC) characteristics have been demonstrated in vascular anomalies (VAs), cancer, and fibroproliferative conditions, which are commonly managed by plastic surgeons and remain largely unsolved. The efficacy of the mTOR inhibitor sirolimus, and targeted therapies that block the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways in many types of cancer and VAs, further supports the critical role of ESC-like cells in the pathogenesis of these conditions. ESC-like cells in VAs, cancer, and fibroproliferative conditions express components of the renin-angiotensin system (RAS) – a homeostatic endocrine signaling cascade that regulates cells with ESC characteristics. ESC-like cells are influenced by the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways, which directly regulate cellular proliferation and stemness, and interact with the RAS at multiple points. Gain-of-function mutations affecting these pathways have been identified in many types of cancer and VAs, that have been treated with targeted therapies with some success. In cancer, the RAS promotes tumor progression, treatment resistance, recurrence, and metastasis. The RAS modulates cellular invasion, migration, proliferation, and angiogenesis. It also indirectly regulates ESC-like cells via its direct influence on the tissue microenvironment and by its interaction with the immune system. In vitro studies show that RAS inhibition suppresses the hallmarks of cancer in different experimental models. Numerous epidemiological studies show a reduced incidence of cancer and improved survival outcomes in patients taking RAS inhibitors, although some studies have shown no such effect. The discovery of ESC-like cells that express RAS components in infantile hemangioma (IH) underscores the paradigm shift in the understanding of its programmed biologic behavior and accelerated involution induced by β-blockers and angiotensin-converting enzyme inhibitors. The findings of SOX18 inhibition by R-propranolol suggests the possibility of targeting ESC-like cells in IH without β-adrenergic blockade, and its associated side effects. This article provides an overview of the current knowledge of ESC-like cells and the RAS in VAs, cancer, and fibroproliferative conditions. It also highlights new lines of research and potential novel therapeutic approaches for these unsolved problems in plastic surgery, by targeting the ESC-like cells through manipulation of the RAS, its bypass loops and converging signaling pathways using existing low-cost, commonly available, and safe oral medications.

Angiotensin II Receptor Antagonist, Valsartan, Has Beneficial Effect in Lung Metastasis of Colorectal Cancer Treated with Fluorouracil

PURPOSE

Lung metastasis is the main cause of death in patients with colorectal carcinoma (CRC). Angiotensin II has been confirmed to facilitate cancer cell progression and metastasis. In this study, the possible anti-metastatic effects of an angiotensin II receptor type 1 (AT1R) antagonist, valsartan, have been investigated in an experimental CRC lung metastasis model.

METHODS

An animal CRC lung metastasis model was used, involving intravenous injection of CRC cells. The experimental groups included (1) control group; (2) 5-FU (5-fluorouracil) group (5 mg/kg/every other day; ip); (3) valsartan group (40 mg/kg/day; po); and (4) valsartan + 5-FU group (combination group; valsartan 40 mg/kg/day, oral gavage, and 5-FU 5 mg/kg/every other day; ip). After 11 days, macroscopic and histological evaluations of lung tissues have been done for evaluation of lung metastatic nodules. In addition, inflammatory and angiogenic markers and oxidative stress index were measured in lung tissue.

RESULTS

Our results showed that administration of valsartan especially in combination with 5-FU significantly reduced lung metastatic nodule and metastatic area (p < 0.05) in macroscopic and histological evaluations stained by hematoxylin-eosin. Measurement of inflammatory, angiogenic, and oxidative/antioxidative markers in lung tissue indicated that the level of IL-6, angiogenic markers (VEGF and VEGFR-1), and antioxidative markers significantly reduced in combination group (p < 0.05) while the MDA as a marker of oxidative stress increased (p < 0.05).

CONCLUSION

These results suggest that valsartan in combination with standard chemotherapeutic agents can have a synergistic effect in treatment of lung metastasis of CRC.

Comprehensive landscape of the renin-angiotensin system in Pan-cancer: a potential downstream mediated mechanism of SARS-CoV-2

Background: SARS-CoV-2, the cause of the worldwide COVID-19 pandemic, utilizes the mechanism of binding to ACE2 (a crucial component of the renin-angiotensin system [RAS]), subsequently mediating a secondary imbalance of the RAS family and leading to severe injury to the host. However, very few studies have been conducted to reveal the mechanism behind the effect of SARS-CoV-2 on tumors.

Methods: Demographic data extracted from 33 cancer types and over 10,000 samples were employed to determine the comprehensive landscape of the RAS. Expression distribution, pretranscriptional and posttranscriptional regulation and posttranslational modifications (PTMs) as well as genomic alterations, DNA methylation and m6A modification were analyzed in both tissue and cell lines. The clinical phenotype, prognostic value and significance of the RAS during immune infiltration were identified.

Results: Low expression of AGTR1 was common in tumors compared to normal tissues, while very low expression of AGTR2 and MAS1 was detected in both tissues and cell lines. Differential expression patterns of ACE in ovarian serous cystadenocarcinoma (OV) and kidney renal clear cell carcinoma (KIRC) were correlated with ubiquitin modification involving E3 ligases. Genomic alterations of the RAS family were infrequent across TCGA pan-cancer program, and ACE had the highest alteration frequency compared with other members. Low expression of AGTR1 may result from hypermethylation in the promoter. Downregulation of RAS family was linked to higher clinical stage and worse survival (as measured by disease-specific survival [DSS], overall survival [OS] or progression-free interval [PFI]), especially for ACE2 and AGTR1 in KIRC. ACE-AGTR1, a classical axis of the RAS family related to immune infiltration, was positively correlated with M2-type macrophages, cancer-associated fibroblasts (CAFs) and immune checkpoint genes in most cancers.

Conclusion: ACE, ACE2, AGT and AGTR1 were differentially expressed in 33 types of cancers. PTM of RAS family was found to rely on ubiquitination. ACE2 and AGTR1 might serve as independent prognostic factors for LGG and KIRC. SARS-CoV-2 might modify the tumor microenvironment by regulating the RAS family, thus affecting the biological processes of cancer.

Melanoma and hypertension, is there an association? A U.S. population based study

BACKGROUND

Melanoma is one of the three major types of skin cancer. In this study we aimed to investigate the association between melanoma and hypertension comorbidity.

METHODS

We performed a population based study using NHANES database during the period 1999-2004. Data were analyzed using SPSS version 24.

RESULTS

Data for 12446 individuals of which 146 had a diagnosis for melanoma were extracted. Melanoma group were older than the no melanoma group as 51% of the melanoma group were 60 years or elder; however 53.6% of the no melanoma group falls below 30 years old. Melanoma group had higher frequency of hypertension (37%) compared to the no melanoma group (22.5%). Logistic regression revealed that melanoma patients had higher odds of hypertension prevalence using the unadjusted model (odds ratio (OR): 2.03, 95% confidence interval (CI): 1.45-2.84, p <0.001). However, after controlling of all potential confounding factors the significance was lost (OR: 0.89, 95% CI: 0.61-1.3, p = 0.54).

CONCLUSIONS

There may be a possible association of melanoma with hypertension comorbidity. With the limitations we faced, we encourage further research to confirm the association of melanoma and hypertension comorbidity.

Angiotensin II promotes primary tumor growth and metastasis formation of murine TNBC 4T1 cells through the fibroblasts around cancer cells

Angiotensin II (Ang II) reportedly facilitates primary tumor growth and distal hematogenous metastasis formation in various murine intravenous metastasis models. However, it is unclear whether Ang II accelerates the initial processes of metastasis formation that begins in primary tumors surrounded by tumor microenvironment. We examined the effects of Ang II on primary tumors and lung metastasis lesions using a murine spontaneous metastasis model, in which triple negative breast cancer 4T1 cells constitutively expressing luciferase (4T1-Luc cells) were injected into the mammary fat pad of BALB/c mice. Subcutaneous injection of Ang II significantly accelerated primary tumor growth and lung metastasis formation. Ang II increased the protein expression levels of c-Myc, cyclin D1, fibronectin, vimentin, αSMA and Snail, and the treatment with the Ang II type 1 receptor blocker valsartan significantly suppressed the Ang II-induced increases of fibronectin and vimentin. Valsartan also significantly reduced lung metastatic lesions. However, Ang II did not have significant effects on 4T1-Luc cells including the proliferation, migration, invasion, or the expressions of proteins related to cell proliferation and epithelial-to-mesenchymal transition. In contrast, when 4T1-Luc cells were co-cultured with dermal fibroblasts, Ang II significantly accelerated cell migration and increased the expressions of fibronectin, vimentin, αSMA and Snail in 4T1-Luc cells. And moreover, Ang II significantly increased the mRNA expression of IL-6 in fibroblasts co-cultured with 4T1-Luc cells. These results suggested that Ang II accelerates surrounding fibroblasts by soluble factors such as IL-6 to promote epithelial-to-mesenchymal transition, which result in the initiation of cancer metastasis.

Agomelatine prevents angiotensin II-induced endothelial and mononuclear cell adhesion

Agomelatine is a non-selective melatonin receptor agonist and an atypical antidepressant with anti-inflammatory, neuroprotective, and cardioprotective effects. The renin-angiotensin system modulates blood pressure and vascular homeostasis. Angiotensin II (Ang II) and its receptor Ang II type I receptor (AT₁R) are recognized as contributors to the pathogenesis of cardiovascular and cardiometabolic diseases, including diabetes, obesity, and atherosclerosis. The recruitment and attachment of monocytes to the vascular endothelium is a major event in the early stages of atherosclerosis and other cardiovascular diseases. In the present study, we demonstrate that agomelatine reduced Ang II-induced expression of AT₁R while significantly inhibiting the attachment of monocytes to endothelial cells induced by Ang II and mediated by ICAM-1 and VCAM-1. Additionally, Ang II inhibited the expression of the chemokines CXCL1, MCP-1, and CCL5, which are critical in the process of immune cell recruitment and invasion. Agomelatine also suppressed the expression of TNF-α, IL-8, and IL-12, which are proinflammatory cytokines that promote endothelial dysfunction and atherogenesis. Importantly, we demonstrate that the inhibitory effect of agomelatine against the expression of adhesion molecules is mediated through the downregulation of Egr-1 signaling. Together, our findings provide evidence of a novel mechanism of agomelatine that may be practicable in the treatment and prevention of cardiovascular diseases.

ESDN inhibits melanoma progression by blocking E-selectin expression in endothelial cells via STAT3

An interactive crosstalk between tumor and stroma cells is essential for metastatic melanoma progression. We evidenced that ESDN/DCBLD2/CLCP1 plays a crucial role in endothelial cells during the spread of melanoma. Precisely, increased extravasation and metastasis formation were revealed in ESDN-null mice injected with melanoma cells, even if the primary tumor growth, vessel permeability, and angiogenesis were not enhanced. Interestingly, improved adhesion of melanoma cells to ESDN-depleted endothelial cells was observed, due to the presence of higher levels of E-selectin transcripts/proteins in ESDN-defective cells. In accordance with these results, anticorrelation was observed between ESDN and E-selectin in human endothelial cells. Most importantly, our data revealed that cimetidine, an E-selectin inhibitor, was able to block cell adhesion, extravasation, and metastasis formation in ESDN-null mice, underlying a major role of ESDN in E-selectin transcription upregulation, which according to our data, may presumably be linked to STAT3. Based on our results, we propose a protective role for ESDN during the spread of melanoma and reveal its therapeutic potential.

CCL5 production by fibroblasts through a local renin-angiotensin system in malignant melanoma affects tumor immune responses

PURPOSE

To enhance the antitumor effects of anti-programmed death-1 (PD-1) antibodies, it is important to reverse cancer-induced immunosuppression. We previously reported that a localized renin-angiotensin system in the tumor microenvironment inhibited tumor immunity via macrophages. In this study, we analyzed the underlying mechanism through which fibroblasts express tumor immunity influenced by the angiotensin receptor.

METHODS

We used an angiotensin receptor inhibitor (ARB) to inhibit renin-angiotensin system. Furthermore, angiotensin receptors were knocked out from mice fibroblasts, which were then collected. The fibroblasts and a malignant melanoma were then transfused into a mouse model and tumor immunity response was analyzed.

RESULTS

Fibroblasts produced CC motif chemokine ligand 5 (CCL5) on renin-angiotensin system stimulation, and this production decreased after ARB administration. In mice with transplanted malignant melanoma, ARB administration resulted in decreased CCL5 concentration in the blood, increase in tumor-infiltrating T cells, decrease in regulatory T cells, as well as an increase in tumor antigen-specific T-cell responses. The mice in which the angiotensin receptor knockout fibroblasts and malignant melanoma were transplanted showed a similar decrease in CCL5 concentration and increased tumor antigen-specific T-cell responses. Furthermore, ARB and anti-PD-1 antibody were administered in combination, which resulted in significantly better tumor growth inhibition over monotherapy.

CONCLUSION

Inhibiting renin-angiotensin system restored the therapeutic efficacy of inhibited anti-PD-1 antibodies. Thus, this could be considered a valid approach to enhance the therapeutic efficacy of anti-PD-1 antibodies.

Irbesartan inhibits metastasis by interrupting the adherence of tumor cell to endothelial cell induced by angiotensin II in hepatocellular carcinoma

Background

The use of angiotensin II inhibitors is associated with a low risk of recurrence and metastasis in hepatocellular carcinoma (HCC) patients. Vascular cell adhesion molecule-1 (VCAM-1) is a key factor in tumor metastasis.

Methods

The effects of angiotensin II and irbesartan (an angiotensin II inhibitor) on HCC were explored with a xenograft model, microarray analysis and cell adhesion experiments. The relationship between the expression of VCAM-1 in HCC tissues and prognosis was analyzed with public and our institutional clinical databases. The effects of angiotensin II, irbesartan and VCAM-1 on adhesion and metastasis in HCC were explored with a xenograft model and cell adhesion experiments. The regulatory mechanisms were analyzed by Western blot analysis.

Results

Angiotensin II type 1 receptor and VCAM-1 were expressed in HCC tissues. Irbesartan inhibited HCC growth and metastasis in vivo and weakened the adhesion of HCC cells to endothelial cells, an effect that was enhanced by angiotensin II. VCAM-1 was found to be an independent risk factor for recurrence and survival in HCC patients with microvascular invasion. Angiotensin II upregulated VCAM-1 expression, and this upregulation was inhibited by irbesartan. Angiotensin II enhanced adhesion mainly by promoting the expression of VCAM-1 in HCC cells. Irbesartan inhibited the expression of VCAM-1 by reducing p38/MAPK phosphorylation activated by angiotensin II in HCC cells.

Conclusions

Irbesartan attenuates metastasis by inhibiting angiotensin II-activated VCAM-1 via the p38/MAPK pathway in HCC.

The Effect of Local Renin Angiotensin System in the Common Types of Cancer

The Renin Angiotensin System (RAS) is a hormonal system that is responsible for blood pressure hemostasis and electrolyte balance. It is implicated in cancer hallmarks because it is expressed locally in almost all of the body's tissues. In this review, current knowledge on the effect of local RAS in the common types of cancer such as breast, lung, liver, prostate and skin cancer is summarised. The mechanisms by which RAS components could increase or decrease cancer activity are also discussed. In addition to the former, this review explores how the administration of AT1R blockers and ACE inhibitors drugs intervene with cancer therapy and contribute to the outcomes of cancer.

Healthful aging mediated by inhibition of oxidative stress

The progressive increase in lifespan over the past century carries with it some adversity related to the accompanying burden of debilitating diseases prevalent in the older population. This review focuses on oxidative stress as a major mechanism limiting longevity in general, and healthful aging, in particular. Accordingly, the first goal of this review is to discuss the role of oxidative stress in limiting longevity, and compare healthful aging and its mechanisms in different longevity models. Secondly, we discuss common signaling pathways involved in protection against oxidative stress in aging and in the associated diseases of aging, e.g., neurological, cardiovascular and metabolic diseases, and cancer. Much of the literature has focused on murine models of longevity, which will be discussed first, followed by a comparison with human models of longevity and their relationship to oxidative stress protection. Finally, we discuss the extent to which the different longevity models exhibit the healthful aging features through physiological protective mechanisms related to exercise tolerance and increased β-adrenergic signaling and also protection against diabetes and other metabolic diseases, obesity, cancer, neurological diseases, aging-induced cardiomyopathy, cardiac stress and osteoporosis.

Antihypertensives and melanoma: An updated review

Antihypertensive medications are commonly prescribed and well-studied. Given the widespread use and potential side effects, various theories have been made about the relationship between antihypertensives and malignancy, including melanoma. This review describes the current understanding of the most commonly prescribed antihypertensives and their associations with melanoma. The literature demonstrates that diuretics, specifically hydrochlorothiazide and indapamide, may increase the risk of melanoma. While there is no evidence that antihypertensives have a role in melanoma prevention, non-selective β-blocker therapy has been associated with a decreased risk of disease progression and recurrence and may also improve outcomes in patients undergoing immunotherapy. In addition, experimental studies reveal that angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and calcium channel blockers have anti-tumor effects, meriting further study.

Maternal, Fetal, and Placental Selectins in Women With Pre-eclampsia; Association With the Renin-Angiotensin-System

Selectins [endothelial (E), platelet (P), and leucocytes (L)] are a class of cell adhesion molecules, stimulated in response to inflammation. Pre-eclampsia is characterized by inflammation, and angiotensin II is pro-inflammatory. We hypothesized that circulating maternal and fetal concentrations and placental expression of selectins would be increased in women with pre-eclampsia and would be associated with the angiotensin receptors (AT1R and AT2R). Maternal and fetal blood and placental tissue was collected at delivery from White European normotensive controls (n = 17) and women with pre-eclampsia (n = 17). Soluble (s) E-, P- and L-selectin protein concentrations were measured by ELISA and placental protein expression was examined by immunohistochemistry. Maternal sE-selectin concentrations were increased in pre-eclampsia (P < 0.001); conversely fetal sE- and sP-selectin levels were lower in pre-eclampsia (P < 0.05 for both). Staining was mainly localized to the syncytiotrophoblast for all selectins. E-selectin expression was increased, while P-selectin was decreased in placental from pre-eclampsia (P < 0.05 for both); no differences were observed for L-selectin expression. Both E- and L-selectin were positively correlated (P < 0.008; P < 0.02) with AT2R placental expression, whilst P-selectin was negatively associated with AT1R (P < 0.005), all only in the pre-eclampsia group. This novel study reports maternal, fetal and placental expression of selectins in pre-eclampsia. The increased E-selectins reflect the endothelial dysfunction, characteristic of pre-eclampsia. In contrast, the reduced P-selectins and the positive association of placental AT2Rs with both E-and L-selectin in pre-eclampsia could be a protective mechanism to limit the endothelial dysfunction.

[The mechanism of anticancer drug-induced DNA damage response and repair in cardiomyocytes]

Genomic DNA, which contains all of the genetic information, is damaged by a variety of endogenous and environmental factors such as genotoxic chemicals, ionizing radiation and UV light. Consequently, the DNA repair process is constantly active as it responds to damage in the DNA structure. Not only cardiotoxicity of anticancer drug treatment but also ischemic heart disease and heart failure associated with overloaded pressure interfere with DNA damage response and DNA repair regulation in cardiomyocytes. DNA methylation, catalyzed by the DNMTs, plays an important role in maintaining genome stability, but the molecular mechanism is not clear. In this study, we examine and outline the links between DNA methylation and the DNA damage repair systems and discuss the possible mechanisms of how they are orchestrated, with a focus on cardiotoxicity of anticancer drugs.

Renin-angiotensin inhibitors were associated with improving outcomes of hepatocellular carcinoma with primary hypertension after hepatectomy

Background

The activation of the renin-angiotensin system (RAS) promotes tumor progression. In this study, we aimed to assess whether RAS inhibitors (RASIs) could improve the outcome of hepatocellular carcinoma (HCC) patients with primary hypertension after curative liver resection.

Methods

Data on 387 consecutive patients with primary hypertension who underwent curative liver resection for HCC were reviewed. The study population was divided into two groups based on the type of anti-hypertensive medications: the RASI group (patients using RASIs) and the non-RASI group (patients using other anti-hypertensive drugs but not RASIs). Kaplan-Meier curves, log-rank tests and cox proportional hazards regression models were used to analyze time to recurrence (TTR) and overall survival (OS).

Results

There were 144 (37.2%) patients in RASI group and 243 (62.8%) in non-RASI group. The preoperative clinicopathological features were comparable between the two groups. Kaplan-Meier curves demonstrated HCC patients with RASIs had a longer TTR and OS than the patients with non-RASIs (both P<0.001). On multivariate analysis, RASIs administration was identified as an independent prognostic factor for TTR [hazard ratio (HR) =0.52, 95% confidence interval (CI), 0.38-0.70, P<0.001] and OS (HR =0.50, 95% CI, 0.34-0.74, P<0.001). Patients in the RASI group had lower rates of extrahepatic metastases than patients in the non-RASI group (2.8% vs. 7.8%, P<0.042).

Conclusions

Targeting the RAS was associated with a reduced risk of recurrence, decreased rate of extrahepatic metastases and prolonged survival of HCC patients with primary hypertension after curative liver resection.

The more critical murderer of atherosclerosis than lipid metabolism: chronic stress

BACKGROUND

The mortality of atherosclerotic cerebrovascular disease is on the rise, and changes in intimal and media thickness are a leading cause of cerebral ischemia-related death. Levels of low density lipoprotein cholesterol (LDLC), total cholesterol (TC), and chronic stress (CS) are all recognized risk factors for atherosclerosis (AS). However, the leading independent risk factor is indistinct. This study explored the effects of chronic stress, LDLC, and TC on AS and intimal and media thickness, preliminarily explored the main risk factor of AS, and analyzed the related histocyte mechanisms for macrophages and endothelial cells.

METHODS

Conditions include normal, high-fat diet (HF), and HF plus CS. The correlations between intimal and media thickness and general risk factors were analyzed using χ2, Spearman's rho test, and multiple linear regression. Univariate Cox regression was used to identify potential factors that affect the non-depression time (NDT). We performed a ROC curve to determine the ability of this condition to predict the thickness. Immunohistochemistry was implemented to detect macrophagocytes and endotheliocytes.

RESULTS

Based on χ2 and Spearman's rho test, LDLC, TC, and CS are all related with intimal and media thickness (P < 0.05). However, in multiple linear regression, CS is still a risk factor of thickness (P < 0.05) but LDLC and TC are not. High levels of LDLC, TC, and CS were correlated with poor NDT (P < 0.05). This condition can predict the thickness sensitively. The endarterium is richest in macrophagocytes, and the arrangement of endotheliocytes is disordered and cracked under CS.

CONCLUSION

CS is the main independent risk factor for AS and intimal (and media) thickness, rather than LDLC or TC.

No answer to the lack of specificity: mouse monoclonal antibody targeting the angiotensin II type 1 receptor AT1 fails to recognize its target

Numerous antibodies targeting G protein-coupled receptors (GPCRs) have been described as non-specific among the polyclonal antibodies against angiotensin II type 1 receptor (AT₁). We have tested the newly developed AT₁ receptor mouse monoclonal antibody for its specificity. Human embryonic kidney (HEK293) cells, which do not endogenously express AT₁ receptor, were transfected in order to overexpress a fluorescently labeled enhanced green fluorescent protein (EGFP)-tagged human AT₁ receptor. Western blot and immunofluorescence assays were performed to test the specificity of the Santa Cruz monoclonal antibody sc-57036. These results were compared to the ones obtained with the polyclonal sc-1173 anti-AT₁ receptor antibodies that have already been described as non-specific. While the positive controls using GFP antibodies detected the EGFP-tagged AT₁ receptor, both polyclonal and monoclonal anti-AT₁ receptor antibodies failed to specifically recognize the corresponding band by Western blot, as similar bands were revealed in either transfected or non-transfected cells. It also failed to detect AT₁ receptor in immunofluorescence experiments. The lack of target recognition of the monoclonal AT₁ receptor antibody in our experimental conditions suggests that this antibody could give misleading results such as misidentification of the protein. To our knowledge, no specific antibodies targeting AT₁ receptors have been developed so far and the field is thus in need of new technical developments.