ELA/APELA precursor cleaved by furin displays tumor suppressor function in renal cell carcinoma through mTORC1 activation

Apela promotes blood vessel regeneration and remodeling in zebrafish

In contrast to adult mammals, zebrafish display a high capacity to heal injuries and repair damage to various organs. One of the earliest responses to injury in adult zebrafish is revascularization, followed by tissue morphogenesis. Tissue vascularization entails the formation of a blood vessel plexus that remodels into arteries and veins. The mechanisms that coordinate these processes during vessel regeneration are poorly understood. Hence, investigating and identifying the factors that promote revascularization and vessel remodeling have great therapeutic potential. Here, we revealed that fin vessel remodeling critically depends on Apela peptide. We found that Apela selectively accumulated in newly formed zebrafish fin tissue and vessels. The temporal expression of Apela, Apln, and their receptor Aplnr is different during the regenerative process. While morpholino-mediated knockdown of Apela (Mo-Apela) prevented vessel remodeling, exogenous Apela peptide mediated plexus repression and the development of arteries in regenerated fins. In contrast, Apela enhanced subintestinal venous plexus formation (SIVP). The use of sunitinib completely inhibited vascular plexus formation in zebrafish, which was not prevented by exogenous application. Furthermore, Apela regulates the expression of vessel remolding-related genes including VWF, IGFPB3, ESM1, VEGFR2, Apln, and Aplnr, thereby linking Apela to the vascular plexus factor network as generated by the STRING online database. Together, our findings reveal a new role for Apela in vessel regeneration and remodeling in fin zebrafish and provide a framework for further understanding the cellular and molecular mechanisms involved in vessel regeneration.

Targeting the apelin system for the treatment of cardiovascular diseases

Cardiovascular disease is the leading cause of death worldwide. Its prevalence is rising due to ageing populations and the increasing incidence of diseases such as chronic kidney disease, obesity, and diabetes that are associated with elevated cardiovascular risk. Despite currently available treatments, there remains a huge burden of cardiovascular disease-associated morbidity for patients and healthcare systems, and newer treatments are needed. The apelin system, comprising the apelin receptor and its two endogenous ligands apelin and elabela, is a broad regulator of physiology that opposes the actions of the renin-angiotensin and vasopressin systems. Activation of the apelin receptor promotes endothelium-dependent vasodilatation and inotropy, lowers blood pressure, and promotes angiogenesis. The apelin system appears to protect against arrhythmias, inhibits thrombosis, and has broad anti-inflammatory and anti-fibrotic actions. It also promotes aqueous diuresis through direct and indirect (central) effects in the kidney. Thus, the apelin system offers therapeutic promise for a range of cardiovascular, kidney, and metabolic diseases. This review will discuss current cardiovascular disease targets of the apelin system and future clinical utility of apelin receptor agonism.

Inhibition of the membrane repair protein annexin-A2 prevents tumor invasion and metastasis

Cancer cells are exposed to major compressive and shearing forces during invasion and metastasis, leading to extensive plasma membrane damage. To survive this mechanical stress, they need to repair membrane injury efficiently. Targeting the membrane repair machinery is thus potentially a new way to prevent invasion and metastasis. We show here that annexin-A2 (ANXA2) is required for membrane repair in invasive breast and pancreatic cancer cells. Mechanistically, we show by fluorescence and electron microscopy that cells fail to reseal shear-stress damaged membrane when ANXA2 is silenced or the protein is inhibited with neutralizing antibody. Silencing of ANXA2 has no effect on proliferation in vitro, and may even accelerate migration in wound healing assays, but reduces tumor cell dissemination in both mice and zebrafish. We expect that inhibiting membrane repair will be particularly effective in aggressive, poor prognosis tumors because they rely on the membrane repair machinery to survive membrane damage during tumor invasion and metastasis. This could be achieved either with anti-ANXA2 antibodies, which have been shown to inhibit metastasis of breast and pancreatic cancer cells, or with small molecule drugs.

Advances in the study of ELABELA in renal physiological functions and related diseases

ELABELA (ELA), also known as Toddler or Apela, is a novel endogenous ligand of the angiotensin receptor AT1-related receptor protein (APJ). ELA is highly expressed in human embryonic, cardiac, and renal tissues and involves various biological functions, such as embryonic development, blood circulation regulation, and maintaining body fluid homeostasis. ELA is also closely related to the occurrence and development of acute kidney injury, hypertensive kidney damage, diabetic nephropathy, renal tumors, and other diseases. Understanding the physiological role of ELA and its mechanism of action in kidney-related diseases would provide new targets and directions for the clinical treatment of kidney diseases.

An Overview of the Role of Furin in Type 2 Diabetes

Post-translational modifications (PTMs) play important roles in regulating several human diseases, like cancer, neurodegenerative disorders, and metabolic disorders. Investigating PTMs' contribution to protein functions is critical for modern biology and medicine. Proprotein convertases (PCs) are irreversible post-translational modifiers that have been extensively studied and are considered as key targets for novel therapeutics. They cleave proteins at specific sites causing conformational changes affecting their functions. Furin is considered as a PC model in regulating growth factors and is involved in regulating many pro-proteins. The mammalian target of the rapamycin (mTOR) signaling pathway is another key player in regulating cellular processes and its dysregulation is linked to several diseases including type 2 diabetes (T2D). The role of furin in the context of diabetes has been rarely explored and is currently lacking. Moreover, furin variants have altered activity that could have implications on overall health. In this review, we aim to highlight the role of furin in T2D in relation to mTOR signaling. We will also address furin genetic variants and their potential effect on T2D and β-cell functions. Understanding the role of furin in prediabetes and dissecting it from other confounding factors like obesity is crucial for future therapeutic interventions in metabolic disorders.

Proprotein convertases regulate trafficking and maturation of key proteins within the secretory pathway

Proprotein Convertases (PCs) are serine endoproteases that regulate the homeostasis of protein substrates in the cell. The PCs family counts 9 members-PC1/3, PC2, PC4, PACE4, PC5/6, PC7, Furin, SKI-1/S1P, and PCSK9. The first seven PCs are known as Basic Proprotein Convertases due to their propensity to cleave after polybasic clusters. SKI-1/S1P requires the additional presence of hydrophobic residues for processing, whereas PCSK9 is catalytically dead after autoactivation and exerts its functions using mechanisms alternative to direct cleavage. All PCs traffic through the canonical secretory pathway, reaching different compartments where the various substrates reside. Despite PCs members do not share the same subcellular localization, most of the cellular organelles count one or more Proprotein Convertases, including ER, Golgi stack, endosomes, secretory granules, and plasma membranes. The widespread expression of these enzymes at the systemic level speaks for their importance in the homeostasis of a large number of biological functions. Among others, PCs cleave precursors of hormones and growth factors and activate receptors and transcription factors. Notably, dysregulation of the enzymatic activity of Proprotein Convertases is associated to major human pathologies, such as cardiovascular diseases, cancer, diabetes, infections, inflammation, autoimmunity diseases, and Parkinson. In the current COVID-19 pandemic, Furin has further attracted the attention as a key player for conferring high pathogenicity to SARS-CoV-2. Here, we review the Proprotein Convertases family and their most important substrates along the secretory pathway. Knowledge about the complex functions of PCs is important to identify potential drug strategies targeting this class of enzymes.

Elabela blunts doxorubicin-induced oxidative stress and ferroptosis in rat aortic adventitial fibroblasts by activating the KLF15/GPX4 signaling

Doxorubicin (DOX) is a chemotherapeutic drug for a variety of malignancies, while its application is restricted by the cardiovascular toxic effects characterized by oxidative stress. Ferroptosis is a novel iron-dependent regulated cell death driven by lipid peroxidation. Our study aimed to investigate the role of Elabela (ELA) in DOX-induced oxidative stress and ferroptosis. In cultured rat aortic adventitial fibroblasts (AFs), stimulation with DOX dramatically induced cytotoxicity with reduced cell viability and migration ability, and enhanced lactate dehydrogenase (LDH) activity. Importantly, ELA and ferrostatin-1 (Fer-1) mitigated DOX-mediated augmentation of reactive oxygen species (ROS) in rat aortic AFs, accompanied by upregulated levels of Nrf2, SLC7A11, GPX4, and GSH. In addition, ELA reversed DOX-induced dysregulation of apoptosis- and inflammation-related factors including Bax, Bcl2, interleukin (IL)-1β, IL6, IL-10, and CXCL1. Intriguingly, knockdown of Krüppel-like factor 15 (KLF15) by siRNA abolished ELA-mediated alleviation of ROS production and inflammatory responses. More importanly, KLF15 siRNA impeded the beneficial roles of ELA in DOX-pretreated rat aortic AFs by suppressing the Nrf2/SLC7A11/GPX4 signaling. In conclusion, ELA prevents DOX-triggered promotion of cytotoxicity, and exerts anti-oxidative and anti-ferroptotic effects in rat aortic AFs via activation of the KLF15/GPX4 signaling, indicating a promising therapeutic value of ELA in antagonizing DOX-mediated cardiovascular abnormality and disorders.

The nuclear factor of activated T cells 5 (NFAT5) contributes to the renal corticomedullary differences in gene expression

The corticomedullary osmotic gradient between renal cortex and medulla induces a specific spatial gene expression pattern. The factors that controls these differences are not fully addressed. Adaptation to hypertonic environment is mediated by the actions of the nuclear factor of activated T-cells 5 (NFAT5). NFAT5 induces the expression of genes that lead to intracellular accumulation of organic osmolytes. However, a systematical analysis of the NFAT5-dependent gene expression in the kidneys was missing. We used primary cultivated inner medullary collecting duct (IMCD) cells from control and NFAT5 deficient mice as well as renal cortex and inner medulla from principal cell specific NFAT5 deficient mice for gene expression profiling. In primary NFAT5 deficient IMCD cells, hyperosmolality induced changes in gene expression were abolished. The majority of the hyperosmolality induced transcripts in primary IMCD culture were determined to have the greatest expression in the inner medulla. Loss of NFAT5 altered the expression of more than 3000 genes in the renal cortex and more than 5000 genes in the inner medulla. Gene enrichment analysis indicated that loss of NFAT5 is associated with renal inflammation and increased expression of kidney injury marker genes, like lipocalin-2 or kidney injury molecule-1. In conclusion we show that NFAT5 is a master regulator of gene expression in the kidney collecting duct and in vivo loss of NFAT function induces a kidney injury like phenotype.

The emerging role of the apelinergic system in kidney physiology and disease

The apelinergic system (AS) is a novel pleiotropic system with an essential role in renal and cardiovascular physiology and disease, including water homeostasis and blood pressure regulation. It consists of two highly conserved peptide ligands, apelin and apela, and a G-protein-coupled apelin receptor. The two ligands have many isoforms and a short half-life and exert both similar and divergent effects. Vasopressin, apelin and their receptors colocalize in hypothalamic regions essential for body fluid homeostasis and interact at the central and renal levels to regulate water homeostasis and diuresis in inverse directions. In addition, the AS and renin-angiotensin system interact both systemically and in the kidney, with implications for the cardiovascular system. A role for the AS in diverse pathological states, including disorders of sodium and water balance, hypertension, heart failure, pre-eclampsia, acute kidney injury, sepsis and diabetic nephropathy, has recently been reported. Furthermore, several metabolically stable apelin analogues have been developed, with potential applications in diverse diseases. We review here what is currently known about the physiological functions of the AS, focusing on renal, cardiovascular and metabolic homeostasis, and the role of the AS in associated diseases. We also describe several hurdles and research opportunities worthy of the attention of the nephrology community.

Elabela Peptide: An Emerging Target in Therapeutics

Elabela, a bioactive micropeptide, is recognized as the second endogenous ligand for the Apelin receptor and is widely distributed in different tissues and organs. Elabela plays an important role in various physiological processes, such as blood pressure control, heart morphogenesis, apoptosis, angiogenesis, cell proliferation, migration, etc. Elabela is also implicated in pathological conditions, like cardiac dysfunctions, heart failure, hypertension, kidney diseases, cancer and CNS disorders. The association of Elabela with these disease conditions makes it a potential target for their therapy. This review summarizes the physiological role of Elabela peptide as well as its implication in various disease conditions.

The Apelin/APLNR system modulates tumor immune response by reshaping the tumor microenvironment

Apelin is an endogenous ligand of the Apelin receptor (APLNR), a seven-transmembrane G protein-coupled receptor, which is widely distributed in human tissue. The Apelin/APLNR system is involved in regulating several physiological and pathological processes. The Apelin expression is increased in a variety of cancer and the Apelin/APLNR system could regulate the development of tumors through mediating autophagy, apoptosis, pyroptosis, and other biological processes to regulate tumor cell proliferation, migration, and invasion. The Apelin/APLNR system also participates in immune response and immune regulation through PI3K-Akt, ERK-MAPK, and other signal pathways. The latest research points out that there is a negative regulatory relationship between APLNR and immune checkpoint PD-L1. In this review, we outline the significance of the Apelin/APLNR signaling pathway in tumorigenesis and its immune regulation. These endeavors provide new insights into the translational application of Apelin/APLNR in cancer and may contribute to the promotion of more effective treatments for cancers.

On Methods for the Measurement of the Apelin Receptor Ligand Apelin

Apelin exists in many isoforms, both in the circulation and in specific tissues. Apelin peptides have a short half-life but preservation before measurement is scarcely studied. Reproducible mass spectrometry methods to specifically measure a broad range of apelinergic peptide isoforms are currently lacking. A sample protocol to conserve apelinergic peptides in the preanalytical phase and a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method to measure apelinergic isoforms was developed. Apelin was measured in plasma. For validation, human embryonic kidney (HEK) cells transfected with cDNA for preproapelin were used. Results were compared with a validated radioimmunoassay (RIA) method. Acidifying plasma to pH 2.5 improves post-sampling stability of apelin. HPLC-MS/MS was unable to detect apelin isoforms in plasma of healthy volunteers (n = 16) and chronic kidney disease patients (n = 4). RIA could detect apelin in concentrations between 71 and 263 fmol/l in 10 healthy volunteers. An optimized preanalytical protocol was developed. A sensitive and specific HPLC-MS/MS method failed to detect apelin in human plasma. Apelin-36 was detected in HEK cells transfected with cDNA for preproapelin. Currently, RIA with relatively selective antibodies is the best alternative for the measurement of apelin but novel sensitive and specific methods are needed.

Role of Furin in Colon Cancer Stem Cells Malignant Phenotype and Expression of LGR5 and NANOG in KRAS and BRAF-Mutated Colon Tumors

Proprotein convertases or PCs are known to regulate the malignant phenotype of colon cancer cells by different mechanisms, but their effects on cancer stem cells (CSCs) have been less widely investigated. Here, we report that PCs expression is altered in colon CSCs, and the inhibition of their activity reduced colon CSCs growth, survival, and invasion in three-dimensional spheroid cultures. In vivo, repression of PCs activity by the general PC inhibitors α1-PDX, Spn4A, or decanoyl-RVKR-chloromethylketone (CMK) significantly reduced tumor expression levels of the stem cell markers LGR5 and NANOG that are associated with reduced tumor xenografts. Further analysis revealed that reduced tumor growth mediated by specific silencing of the convertase Furin in KRAS or BRAF mutated-induced colon tumors was associated with reduced expression of LGR5 and NANOG compared to wild-type KRAS and BRAF tumors. Analysis of various calcium regulator molecules revealed that while the calcium-transporting ATPase 4 (ATP2B4) is downregulated in all the Furin-silenced colon cancer cells, the Ca2+-mobilizing P2Y receptors, was specifically repressed in BRAF mutated cells and ORAI1 and CACNA1H in KRAS mutated cells. Taken together, our findings indicate that PCs play an important role in the malignant phenotype of colon CSCs and stem cell markers’ expression and highlight PCs repression, particularly of Furin, to target colon tumors with KRAS or BRAF mutation.

The proprotein convertase furin in cancer: more than an oncogene

Furin is the first discovered proprotein convertase member and is present in almost all mammalian cells. Therefore, by regulating the maturation of a wide range of proproteins, Furin expression and/or activity is involved in various physiological and pathophysiological processes ranging from embryonic development to carcinogenesis. Since many of these protein precursors are involved in initiating and maintaining the hallmarks of cancer, Furin has been proposed as a potential target for treating several human cancers. In contrast, other studies have revealed that some types of cancer do not benefit from Furin inhibition. Therefore, understanding the heterogeneous functions of Furin in cancer will provide important insights into the design of effective strategies targeting Furin in cancer treatment. Here, we present recent advances in understanding how Furin expression and activity are regulated in cancer cells and their influences on the activity of Furin substrates in carcinogenesis. Furthermore, we discuss how Furin represses tumorigenic properties of several cancer cells and why Furin inhibition leads to aggressive phenotypes in other tumors. Finally, we summarize the clinical applications of Furin inhibition in treating human cancers.

The therapeutic potential of apelin in kidney disease

Chronic kidney disease (CKD) is a leading cause of global morbidity and mortality and is independently associated with cardiovascular disease. The mainstay of treatment for CKD is blockade of the renin-angiotensin-aldosterone system (RAAS), which reduces blood pressure and proteinuria and slows kidney function decline. Despite this treatment, many patients progress to kidney failure, which requires dialysis or kidney transplantation, and/or die as a result of cardiovascular disease. The apelin system is an endogenous physiological regulator that is emerging as a potential therapeutic target for many diseases. This system comprises the apelin receptor and its two families of endogenous ligands, apelin and elabela/toddler. Preclinical and clinical studies show that apelin receptor ligands are endothelium-dependent vasodilators and potent inotropes, and the apelin system has a reciprocal relationship with the RAAS. In preclinical studies, apelin regulates glomerular haemodynamics and acts on the tubule to promote aquaresis. In addition, apelin is protective in several kidney injury models. Although the apelin system has not yet been studied in patients with CKD, the available data suggest that apelin is a promising potential therapeutic target for kidney disease.

In vitro metabolism of synthetic Elabela/Toddler (ELA-32) peptide in human plasma and kidney homogenates analyzed with mass spectrometry and validation of endogenous peptide quantification in tissues by ELISA

BACKGROUND

Elabela/Toddler (ELA) is a novel endogenous ligand of the apelin receptor, whose signalling has emerged as a therapeutic target, for example, in cardiovascular disease and cancer. Shorter forms of ELA-32 have been predicted, including ELA-21 and ELA-11, but metabolism and stability of ELA-32 in humans is poorly understood. We, therefore, developed an LC-MS/MS assay to identify ELA-32 metabolites in human plasma and tissues.

METHOD

Human kidney homogenates or plasma were incubated at 37 °C with ELA-32 and aliquots withdrawn over 2-4 h into guanidine hydrochloride. Proteins were precipitated and supernatant solid-phase extracted. Peptides were extracted from coronary artery, brain and kidney by immunoprecipitation or solid-phase extraction following acidification. All samples were reduced and alkylated before analysis on an Orbitrap mass spectrometer in high and nano flow mode.

RESULTS

The half-life of ELA-32 in plasma and kidney were 47.2 ± 5.7 min and 44.2 ± 3 s, respectively. Using PEAKS Studio and manual data analysis, the most important fragments of ELA-32 with potential biological activity identified were ELA-11, ELA-16, ELA-19 and ELA-20. The corresponding fragments resulting from the loss of C-terminal amino acids were also identified. Endogenous levels of these peptides could not be measured, as ELA peptides are prone to oxidation and poor chromatographic peaks.

CONCLUSIONS

The relatively long ELA plasma half-life observed and identification of a potentially more stable fragment, ELA-16, may suggest that ELA could be a better tool compound and novel template for the development of new drugs acting at the apelin receptor.

Semysinthetic biflavonoid Morelloflavone-7,4',7″,3‴,4‴-penta-O-butanoyl is a more potent inhibitor of Proprotein Convertases Subtilisin/Kexin PC1/3 than Kex2 and Furin

BACKGROUND

Garcinia brasiliensis is a species native to the Amazon forest. The white mucilaginous pulp is used in folk medicine as a wound healing agent and for peptic ulcer, urinary, and tumor disease treatments. The activity of the proprotein convertases (PCs) Subtilisin/Kex is associated with the development of viral, bacterial and fungal infections, osteoporosis, hyperglycemia, atherosclerosis, cardiovascular, neurodegenerative and neoplastic diseases.

METHODS

Morelloflavone (BF1) and semisynthetic biflavonoid (BF2, 3 and 4) from Garcinia brasiliensis were tested as inhibitor of PCs Kex2, PC1/3 and Furin, and determined IC₅₀, K_i, human proinflammatory cytokines secretion in Caco-2 cells, mechanism of inhibition, and performed molecular docking studies.

RESULTS

Biflavonoids were more effective in the inhibition of neuroendocrine PC1/3 than mammalian Furin and fungal Kex2. BF1 presented a mixed inhibition mechanism for Kex2 and PC1, and competitive inhibition for Furin. BF4 has no good interaction with Kex2 and Furin since carboxypropyl groups results in steric hindrance to ligand-protein interactions. Carboxypropyl groups of BF4 promote steric hindrance with Kex2 and Furin, but effective in the affinity of PC1/3. BF4 was more efficient at inhibiting PCl/3 (IC₅₀ = 1.13 μM and K_i = 0,59 μM, simple linear competitive mechanism of inhibition) than Kex2, Furin. Also, our results strongly suggested that BF4 also inhibits the endogenous cellular PC1/3 activity in Caco-2 cells, since PC1/3 inhibition by BF4 causes a large increase in IL-8 and IL-1β secretion in Caco-2 cells.

CONCLUSIONS

BF4 is a potent and selective inhibitor of PC1/3.

GENERAL SIGNIFICANCE

BF4 is the best candidate for further clinical studies on inhibition of PC1/3.

The network map of Elabela signaling pathway in physiological and pathological conditions

Elabela (ELA; also called Apela and Toddler) is one of the recently discovered ligand among the two endogenous peptide ligands (Apelin and Elabela) of the apelin receptor (APLNR, also known as APJ). Elabela-induced signaling plays a crucial role in diverse biological processes, including formation of the embryonic cardiovascular system and early placental development by reducing the chances of occurrence of preeclampsia during pregnancy. It also plays the major role in the renoprotection by reducing kidney injury and the inflammatory response and regulation of gene expression associated with heart failure and fibrosis. Elabela may be processed into different active peptides, each of which binds to APLNR and predominantly activates the signals through PI3K/AKT pathway. Owing to its biomedical importance, we developed a consolidated signaling map of Elabela, in accordance with the NetPath criteria. The presented Elabela signaling map comprises 12 activation/inhibition events, 15 catalysis events, 1 molecular association, 34 gene regulation events and 32 protein expression events. The Elabela signaling pathway map is freely made available through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5100 ).

Elabela/toddler: New peptide with a promising future in cancer diagnostic and therapy

Elabela/toddler is the second endogenous ligand recently identified after Apelin, that binds to the G protein-coupled receptor APJ. Elabela is a 54-amino acid peptide initially identified in fish and human genomes and classified as noncoding. This precursor can be cleaved to shorter sequences (32, 21, and 11 amino acids), which bind and activate APJ, and can be blocked by APJ antagonists. Contrary to Apelin and APJ, widely distributed in organs and tissues, Elabela expression is more restricted, and different studies have revealed the potential role of Elabela in cancers. This review summarizes the current studies focusing on the role of Elabela in different cancers.

Study Progression of Apelin/APJ Signaling and Apela in Different Types of Cancer

Apelin is an endogenous ligand that binds to the G protein-coupled receptor angiotensin-like-receptor 1 (APJ). Apelin and APJ are widely distributed in organs and tissues and are involved in multiple physiological and pathological processes including cardiovascular regulation, neuroendocrine stress response, energy metabolism, etc. Additionally, apelin/APJ axis was found to play an important role in cancer development and progression. Apela is a newly identified endogenous ligand for APJ. Several studies have revealed the potential role of Apela in cancers. In this article, we review the current studies focusing on the role of apelin/APJ signaling and Apela in different cancers. Potential mechanisms by which apelin/APJ and Apela mediate the regulation of cancer development and progression were also mentioned. The Apelin/APJ signaling and Apela may serve as potential therapeutic candidates for treatment of cancer.

Furin Prodomain ppFurin Enhances Ca2+ Entry Through Orai and TRPC6 Channels' Activation in Breast Cancer Cells

Simple Summary

Furin, a proprotein convertase that belongs to a family of Ca²⁺-dependent serine peptidases, is involved in the maturation of a variety of proproteins, including growth factors, receptors and differentiation factors, adhesion molecules and proteases. Furin have been associated with tumorigenesis and tumor progression and metastasis; therefore, it has been hypothesized that Furin may constitute a new potential target for cancer therapy. In triple negative breast cancer cells, inhibition of Furin by the prodomain ppFurin results in enhancement of Ca²⁺ influx, which involves both the increase of store-operated calcium entry (SOCE) and the activation of constitutive Ca²⁺ entry. The latter involves the activation of Orai and TRPC6 channels, while the increase of SOCE observed in ppFurin-expressing cells is entirely dependent on Orai channels. As a result, ppFurin expression reduces triple negative breast cancer cell viability and ability to migrate and enhances their sensitization to hydrogen peroxide-induced apoptosis.

Abstract

The intracellular calcium concentration ([Ca²⁺]_i) modulation plays a key role in the regulation of cellular growth and survival in normal cells and failure of [Ca²⁺]_i homeostasis is involved in tumor initiation and progression. Here we showed that inhibition of Furin by its naturally occurring inhibitor the prodomain ppFurin in the MDA-MB-231 breast cancer cells resulted in enhanced store-operated calcium entry (SOCE) and reduced the cell malignant phenotype. Expression of ppFurin in a stable manner in MDA-MB-231 and the melanoma MDA-MB-435 cell lines inhibits Furin activity as assessed by in vitro digestion assays. Accordingly, cell transfection experiments revealed that the ppFurin-expressing cells are unable to adequately process the proprotein convertase (PC) substrates vascular endothelial growth factor C (proVEGF-C) and insulin-like growth factor-1 receptor (proIGF-1R). Compared to MDA-MB-435 cells, expression of ppFurin in MDA-MB-231 and BT20 cells significantly enhanced SOCE and induced constitutive Ca²⁺ entry. The enhanced SOCE is impaired by inhibition of Orai channels while the constitutive Ca²⁺ entry is attenuated by silencing or inhibition of TRPC6 or inhibition of Orai channels. Analysis of TRPC6 activation revealed its upregulated tyrosine phosphorylation in ppFurin-expressing MDA-MB-231 cells. In addition, while ppFurin had no effect on MDA-MB-435 cell viability, in MDA-MB-231 cells ppFurin expression reduced their viability and ability to migrate and enhanced their sensitization to the apoptosis inducer hydrogen peroxide and similar results were observed in BT20 cells. These findings suggest that Furin inhibition by ppFurin may be a useful strategy to interfere with Ca²⁺ mobilization, leading to breast cancer cells’ malignant phenotype repression and reduction of their resistance to treatments.

Apelin and Vasopressin: The Yin and Yang of Water Balance

Apelin, a (neuro)vasoactive peptide, plays a prominent role in controlling body fluid homeostasis and cardiovascular functions. Experimental data performed in rodents have shown that apelin has an aquaretic effect via its central and renal actions. In the brain, apelin inhibits the phasic electrical activity of vasopressinergic neurons and the release of vasopressin from the posterior pituitary into the bloodstream and in the kidney, apelin regulates renal microcirculation and counteracts in the collecting duct, the antidiuretic effect of vasopressin occurring via the vasopressin receptor type 2. In humans and rodents, if plasma osmolality is increased by hypertonic saline infusion/water deprivation or decreased by water loading, plasma vasopressin and apelin are conversely regulated to maintain body fluid homeostasis. In patients with the syndrome of inappropriate antidiuresis, in which vasopressin hypersecretion leads to hyponatremia, the balance between apelin and vasopressin is significantly altered. In order to re-establish the correct balance, a metabolically stable apelin-17 analog, LIT01-196, was developed, to overcome the problem of the very short half-life (in the minute range) of apelin in vivo. In a rat experimental model of vasopressin-induced hyponatremia, subcutaneously (s.c.) administered LIT01-196 blocks the antidiuretic effect of vasopressin and the vasopressin-induced increase in urinary osmolality, and induces a progressive improvement in hyponatremia, suggesting that apelin receptor activation constitutes an original approach for hyponatremia treatment.

Proprotein convertases blockage up-regulates specifically metallothioneins coding genes in human colon cancer stem cells

Despite continuous exertion made, colon cancer still represents a major health problem and its incidence continues being high worldwide. There is growing evidence in support of the cancer stem cells (CSCs) being central in the initiation of this cancer, and CSCs have been the focus of various studies for the identification of new ways of treatment. Lately, the proprotein convertases (PCs) were reported to regulate the maturation and expression of various molecules involved in the malignant phenotype of colon cancer cells, however, the identity of the molecules regulated by these serine proteases in CSCs is unknown. In this study, we used the general PCs inhibitor, the Decanoyl-RVKR-chloromethylketone (Decanoyl-RVKR-CMK) that inhibits all the PCs found in the secretory pathway, and analyzed its effect on CSCs using RNA-seq analysis. Remarkably, from the only 9 up-regulated genes in the human SW620-derived sphere-forming cells, we identified 7 of the 11 human metallothioneins, all of them localized on chromosome 16, and zinc related proteins as downstream effectors of the PCs. The importance of these molecules in the regulation of cell proliferation, differentiation and chemoresistance, and their reported potential tumor suppressor role and loss in colon cancer patients associated with worse prognosis, suggests that targeting PCs in the control of the malignant phenotype of CSCs is a new potential therapeutic strategy in colon cancer.

Loss of Proprotein Convertase Furin in Mammary Gland Impairs proIGF1R and proIR Processing and Suppresses Tumorigenesis in Triple Negative Breast Cancer

Simple Summary

Triple-negative breast cancer (TNBC) is known to have a poor prognosis and limited treatment options. The aim of the current study is to evaluate the role of Furin, a proprotein convertase involved in the activation of wide range of protein precursors in TNBC progression. The generation of a TNBC mouse model lacking Furin specifically in the mammary gland confirmed that Furin is implicated in TNBC tumor progression and the derived lung metastasis. Further analysis revealed that the proteolytic activation of proIGF1R and proIR receptors, two substrates of Furin involved in TNBC were inhibited in these mice and was associated with reduced AKT and ERK1/2 expression and phosphorylation. In addition, Furin is frequently overexpressed in TNBC tumors and correlates with poor patient prognosis, suggesting the use of Furin inhibition as a potential adjunct therapy in TNBC.

Abstract

In triple negative breast cancer (TNBC) cell lines, the proprotein convertase Furin cleaves and then activates several protein precursors involved in oncogenesis. However, the in vivo role of Furin in the mammary gland and how mammary gland-specific Furin knockout specifically influences tumor initiation and progression of TNBC is unknown. Here, we report that Furin is frequently overexpressed in TNBC tumors and this correlates with poor prognosis in patients with TNBC tumors. In a whey acidic protein (WAP)-induced mammary epithelial cell-specific Furin knockout mouse model, mice show normal mammary development. However, loss of Furin in mammary glands inhibits primary tumor growth and lung metastasis in an oncogene-induced TNBC mouse model. Further analysis of TNBC mice lacking Furin revealed repressed maturation of the Furin substrates proIGF1R and proIR that are associated with reduced expression and activation of their downstream effectors PI3K/AKT and MAPK/ERK1/2. In addition, these tissues showed enhanced apoptotic signaling. In conclusion, our findings reveal that upregulated Furin expression reflects the poor prognosis of TNBC patients and highlights the therapeutic potential of inhibiting Furin in TNBC tumors.