Inhibition of proprotein convertases is associated with loss of growth and tumorigenicity of HT-29 human colon carcinoma cells: importance of insulin-like growth factor-1 (IGF-1) receptor processing in IGF-1-mediated functions

IGF1R deficiency in vascular smooth muscle cells impairs myogenic autoregulation and cognition in mice

Introduction

Cerebrovascular pathologies contribute to cognitive decline during aging, leading to vascular cognitive impairment and dementia (VCID). Levels of circulating insulin-like growth factor 1 (IGF-1), a vasoprotective hormone, decrease during aging. Decreased circulating IGF-1 in animal models leads to the development of VCID-like symptoms, but the cellular mechanisms underlying IGF-1-deficiency associated pathologies in the aged cerebrovasculature remain poorly understood. Here, we test the hypothesis that vascular smooth muscle cells (VSMCs) play an integral part in mediating the vasoprotective effects of IGF-1.

Methods

We used a hypertension-based model of cerebrovascular dysfunction in mice with VSMC-specific IGF-1 receptor (Igf1r) deficiency and evaluated the development of cerebrovascular pathologies and cognitive dysfunction.

Results

VSMC-specific Igf1r deficiency led to impaired cerebral myogenic autoregulation, independent of blood pressure changes, which was also associated with impaired spatial learning and memory function as measured by radial arm water maze and impaired motor learning measured by rotarod. In contrast, VSMC-specific IGF-1 receptor knockdown did not lead to cerebral microvascular rarefaction.

Discussion

These studies suggest that VSMCs are key targets for IGF-1 in the context of cerebrovascular health, playing a role in vessel stability alongside other cells in the neurovascular unit, and that VSMC dysfunction in aging likely contributes to VCID.

Mapping respiratory syncytial virus fusion protein interactions with the receptor IGF1R and the impact of alanine-scanning mutagenesis on viral infection

Respiratory syncytial virus (RSV) has two main surface glycoproteins, the attachment glycoprotein (G) and the fusion (F) protein, which together mediate viral entry. Attachment is mediated by the RSV-G protein, while the RSV-F protein makes specific contact with the cellular insulin-like growth factor 1 receptor (IGF1R). This interaction leads to IGF1R activation and initiates a signalling cascade that calls the co-receptor, nucleolin, from the nucleus to the cell surface, where it can trigger viral fusion. We performed molecular docking analysis, which provided a potential set of 35 residues in IGF1R that may be important for interactions with RSV-F. We used alanine-scanning mutagenesis to generate IGF1R mutants and assessed their abundance and maturation, as well as the effect of mutation on RSV infection. We identified several mutations that appear to inhibit IGF1R maturation; but surprisingly, these mutations had no significant effect on RSV infection. This suggests that maturation of IGF1R may not be required for RSV infection. Additionally, we identified one residue, S788, that, when mutated, significantly reduced RSV infection. Further analysis revealed that this mutation disrupted a hydrogen bonding network that may be important for both IGF1R maturation and RSV infection.

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

The regulation of Insulin/IGF-1 signaling by miR-142-3p associated with human longevity

MicroRNAs (miRNAs) have been demonstrated to modulate life span in the invertebrates C. elegans and Drosophila by targeting conserved pathways of aging, such as insulin/IGF-1 signaling (IIS). However, a role for miRNAs in modulating human longevity has not been fully explored. Here we investigated novel roles of miRNAs as a major epigenetic component of exceptional longevity in humans. By profiling the miRNAs in B-cells from Ashkenazi Jewish centenarians and 70-year-old controls without a longevity history, we found that the majority of differentially expressed miRNAs were upregulated in centenarians and predicted to modulate the IIS pathway. Notably, decreased IIS activity was found in B cells from centenarians who harbored these upregulated miRNAs. miR-142-3p, the top upregulated miRNA, was verified to dampen the IIS pathway by targeting multiple genes including GNB2, AKT1S1, RHEB and FURIN . Overexpression of miR-142-3p improved the stress resistance under genotoxicity and induced the impairment of cell cycle progression in IMR90 cells. Furthermore, mice injected with a miR-142-3p mimic showed reduced IIS signaling and improved longevity-associated phenotypes including enhanced stress resistance, improved diet/aging-induced glucose intolerance, and longevity-associated change of metabolic profile. These data suggest that miR-142-3p is involved in human longevity through regulating IIS-mediated pro-longevity effects. This study provides strong support for the use of miR-142-3p as a novel therapeutic to promote longevity or prevent aging/aging-related diseases in human.

Genome-scale functional genomics identify genes preferentially essential for multiple myeloma cells compared to other neoplasias

Clinical progress in multiple myeloma (MM), an incurable plasma cell (PC) neoplasia, has been driven by therapies that have limited applications beyond MM/PC neoplasias and do not target specific oncogenic mutations in MM. Instead, these agents target pathways critical for PC biology yet largely dispensable for malignant or normal cells of most other lineages. Here we systematically characterized the lineage-preferential molecular dependencies of MM through genome-scale clustered regularly interspaced short palindromic repeats (CRISPR) studies in 19 MM versus hundreds of non-MM lines and identified 116 genes whose disruption more significantly affects MM cell fitness compared with other malignancies. These genes, some known, others not previously linked to MM, encode transcription factors, chromatin modifiers, endoplasmic reticulum components, metabolic regulators or signaling molecules. Most of these genes are not among the top amplified, overexpressed or mutated in MM. Functional genomics approaches thus define new therapeutic targets in MM not readily identifiable by standard genomic, transcriptional or epigenetic profiling analyses.

Permethrin as a Potential Furin Inhibitor through a Novel Non-Competitive Allosteric Inhibition

Furin is a potential target protein associated with numerous diseases; especially closely related to tumors and multiple viral infections including SARS-CoV-2. Most of the existing efficient furin inhibitors adopt a substrate analogous structure, and other types of small molecule inhibitors need to be discovered urgently. In this study, a high-throughput screening combining virtual and physical screening of natural product libraries was performed, coupled with experimental validation and preliminary mechanistic assays at the molecular level, cellular level, and molecular simulation. A novel furin inhibitor, permethrin, which is a derivative from pyrethrin I generated by Pyrethrum cinerariifolium Trev. was identified, and this study confirmed that it binds to a novel allosteric pocket of furin through non-competitive inhibition. It exhibits a very favorable protease-selective inhibition and good cellular activity and specificity. In summary, permethrin shows a new parent nucleus with a new mode of inhibition. It could be used as a highly promising lead compound against furin for targeting related tumors and various resistant viral infections, including SARS-CoV-2.

Androgen-Independent Prostate Cancer Is Sensitive to CDC42-PAK7 Kinase Inhibition

Prostate cancer is a common form of cancer in men, and androgen-deprivation therapy (ADT) is often used as a first-line treatment. However, some patients develop resistance to ADT, and their disease is called castration-resistant prostate cancer (CRPC). Identifying potential therapeutic targets for this aggressive subtype of prostate cancer is crucial. In this study, we show that statins can selectively inhibit the growth of these CRPC tumors that have lost their androgen receptor (AR) and have overexpressed the RNA-binding protein QKI. We found that the repression of microRNA-200 by QKI overexpression promotes the rise of AR-low mesenchymal-like CRPC cells. Using in silico drug/gene perturbation combined screening, we discovered that QKI-overexpressing cancer cells are selectively vulnerable to CDC42-PAK7 inhibition by statins. We also confirmed that PAK7 overexpression is present in prostate cancer that coexists with hyperlipidemia. Our results demonstrate a previously unseen mechanism of action for statins in these QKI-expressing AR-lost CRPCs. This may explain the clinical benefits of the drug and support the development of a biology-driven drug-repurposing clinical trial. This is an important finding that could help improve treatment options for patients with this aggressive form of prostate cancer.

MBTPS1 regulates proliferation of colorectal cancer primarily through its action on sterol regulatory element-binding proteins

Among the main metabolic pathways implicated in cancer cell proliferation are those of cholesterol and fatty acid synthesis, both of which are tightly regulated by sterol regulatory element-binding proteins (SREBPs). SREBPs are activated through specific cleavage by membrane-bound transcription factor protease 1 (MBTPS1), a serine protease that cleaves additional substrates (ATF6, BDNF, CREBs and somatostatin), some of which are also implicated in cell proliferation. The goal of this study was to determine whether MBTPS1 may serve as a master regulator in proliferation of colorectal cancer (CRC). Tumors from CRC patients showed variable levels of MBTPS1 mRNA, which were in positive correlation with the levels of SREBPs and ATF6, and in reverse correlation with BDNF levels. Chemical inhibition of MBTPS1 activity in two CRC-derived cell lines resulted in a marked decrease in the levels of SREBPs, but not of its other substrates and a marked decrease in cell proliferation, which suggested that MBTPS1 activity is critical for proliferation of these cells. In accordance, CRISPR/Cas9 targeted knockout (KO) of the MBTPS1 gene resulted in the survival of only a single clone that presented a phenotype of severely attenuated proliferation and marked downregulation of several energy metabolism pathways. We further showed that survival of the MBTPS1 KO clone was dependent upon significant upregulation of the type-1 interferon pathway, the inhibition of which halted proliferation entirely. Finally, rescue of the MBTPS1 KO cells, resulted in partial restoration of MBTPS1 levels, which was in accordance with partial recovery in proliferation and in SREBP levels. These finding suggest that MBTPS1 plays a critical role in regulating colon cancer proliferation primarily through SREBP-associated lipid metabolism, and as such may serve as a possible therapeutic target in CRC.

Inhibitors of Activin Receptor-like Kinase 5 Interfere with SARS-CoV-2 S-Protein Processing and Spike-Mediated Cell Fusion via Attenuation of Furin Expression

Screening of a protein kinase inhibitor library identified SB431542, targeting activin receptor-like kinase 5 (ALK5), as a compound interfering with SARS-CoV-2 replication. Since ALK5 is implicated in transforming growth factor β (TGF-β) signaling and regulation of the cellular endoprotease furin, we pursued this research to clarify the role of this protein kinase for SARS-CoV-2 infection. We show that TGF-β1 induces the expression of furin in a broad spectrum of cells including Huh-7 and Calu-3 that are permissive for SARS-CoV-2. The inhibition of ALK5 by incubation with SB431542 revealed a dose-dependent downregulation of both basal and TGF-β1 induced furin expression. Furthermore, we demonstrate that the ALK5 inhibitors SB431542 and Vactosertib negatively affect the proteolytic processing of the SARS-CoV-2 Spike protein and significantly reduce spike-mediated cell-cell fusion. This correlated with an inhibitory effect of ALK5 inhibition on the production of infectious SARS-CoV-2. Altogether, our study shows that interference with ALK5 signaling attenuates SARS-CoV-2 infectivity and cell-cell spread via downregulation of furin which is most pronounced upon TGF-β stimulation. Since a TGF-β dominated cytokine storm is a hallmark of severe COVID-19, ALK5 inhibitors undergoing clinical trials might represent a potential therapy option for COVID-19.

Testicular Germ Cell Tumours and Proprotein Convertases

Simple Summary

Despite the high survival rate of the most common neoplasia in young Caucasian men: Testicular Germ Cell Tumors (TGCT), the quality of life of these patients is impaired by the multiple long-term side effects of their treatment. The study of molecules that can serve both as diagnostic biomarkers for tumor development and as therapeutic targets seems necessary. Proprotein convertases (PC) are a group of proteases responsible for the maturation of inactive proproteins with very diverse functions, whose alterations in expression have been associated with various diseases, such as other types of cancer and inflammation. The study of the immune tumor microenvironment and the substrates of PCs could contribute to the development of new and necessary immunotherapies to treat this pathology.

Abstract

Testicular Germ Cell Tumours (TGCT) are widely considered a “curable cancer” due to their exceptionally high survival rate, even if it is reduced by many years after the diagnosis due to metastases and relapses. The most common therapeutic approach to TGCTs has not changed in the last 50 years despite its multiple long-term side effects, and because it is the most common malignancy in young Caucasian men, much research is needed to better the quality of life of the many survivors. Proprotein Convertases (PC) are nine serine proteases responsible for the maturation of inactive proproteins with many diverse functions. Alterations in their expression have been associated with various diseases, including cancer and inflammation. Many of their substrates are adhesion molecules, metalloproteases and proinflammatory molecules, all of which are involved in tumour development. Inhibition of certain convertases has also been shown to slow tumour formation, demonstrating their involvement in this process. Considering the very established link between PCs and inflammation-related malignancies and the recent studies carried out into the immune microenvironment of TGCTs, the study of the involvement of PCs in testicular cancer may open up avenues for being both a biomarker for diagnosis and a therapeutic target.

Identification of Kukoamine A, Zeaxanthin, and Clexane as New Furin Inhibitors

The endogenous protease furin is a key protein in many different diseases, such as cancer and infections. For this reason, a wide range of studies has focused on targeting furin from a therapeutic point of view. Our main objective consisted of identifying new compounds that could enlarge the furin inhibitor arsenal; secondarily, we assayed their adjuvant effect in combination with a known furin inhibitor, CMK, which avoids the SARS-CoV-2 S protein cleavage by means of that inhibition. Virtual screening was carried out to identify potential furin inhibitors. The inhibition of physiological and purified recombinant furin by screening selected compounds, Clexane, and these drugs in combination with CMK was assayed in fluorogenic tests by using a specific furin substrate. The effects of the selected inhibitors from virtual screening on cell viability (293T HEK cell line) were assayed by means of flow cytometry. Through virtual screening, Zeaxanthin and Kukoamine A were selected as the main potential furin inhibitors. In fluorogenic assays, these two compounds and Clexane inhibited both physiological and recombinant furin in a dose-dependent way. In addition, these compounds increased physiological furin inhibition by CMK, showing an adjuvant effect. In conclusion, we identified Kukoamine A, Zeaxanthin, and Clexane as new furin inhibitors. In addition, these drugs were able to increase furin inhibition by CMK, so they could also increase its efficiency when avoiding S protein proteolysis, which is essential for SARS-CoV-2 cell infection.

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.

HIV-1 Envelope Glycoproteins Proteolytic Cleavage Protects Infected Cells from ADCC Mediated by Plasma from Infected Individuals

The HIV-1 envelope glycoprotein (Env) is synthesized in the endoplasmic reticulum as a trimeric gp160 precursor, which requires proteolytic cleavage by a cellular furin protease to mediate virus-cell fusion. Env is conformationally flexible but controls its transition from the unbound "closed" conformation (State 1) to downstream CD4-bound conformations (States 2/3), which are required for fusion. In particular, HIV-1 has evolved several mechanisms that reduce the premature "opening" of Env which exposes highly conserved epitopes recognized by non-neutralizing antibodies (nnAbs) capable of mediating antibody-dependent cellular cytotoxicity (ADCC). Env cleavage decreases its conformational transitions favoring the adoption of the "closed" conformation. Here we altered the gp160 furin cleavage site to impair Env cleavage and to examine its impact on ADCC responses mediated by plasma from HIV-1-infected individuals. We found that infected primary CD4+ T cells expressing uncleaved, but not wildtype, Env are efficiently recognized by nnAbs and become highly susceptible to ADCC responses mediated by plasma from HIV-1-infected individuals. Thus, HIV-1 limits the exposure of uncleaved Env at the surface of HIV-1-infected cells at least in part to escape ADCC responses.

Integrative oncogene-dependency mapping identifies RIT1 vulnerabilities and synergies in lung cancer

CRISPR-based cancer dependency maps are accelerating advances in cancer precision medicine, but adequate functional maps are limited to the most common oncogenes. To identify opportunities for therapeutic intervention in other rarer subsets of cancer, we investigate the oncogene-specific dependencies conferred by the lung cancer oncogene, RIT1. Here, genome-wide CRISPR screening in KRAS, EGFR, and RIT1-mutant isogenic lung cancer cells identifies shared and unique vulnerabilities of each oncogene. Combining this genetic data with small-molecule sensitivity profiling, we identify a unique vulnerability of RIT1-mutant cells to loss of spindle assembly checkpoint regulators. Oncogenic RIT1M90I weakens the spindle assembly checkpoint and perturbs mitotic timing, resulting in sensitivity to Aurora A inhibition. In addition, we observe synergy between mutant RIT1 and activation of YAP1 in multiple models and frequent nuclear overexpression of YAP1 in human primary RIT1-mutant lung tumors. These results provide a genome-wide atlas of oncogenic RIT1 functional interactions and identify components of the RAS pathway, spindle assembly checkpoint, and Hippo/YAP1 network as candidate therapeutic targets in RIT1-mutant lung 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.

Insulin-like growth factor receptor signaling in tumorigenesis and drug resistance: a challenge for cancer therapy

Insulin-like growth factors (IGFs) play important roles in mammalian growth, development, aging, and diseases. Aberrant IGFs signaling may lead to malignant transformation and tumor progression, thus providing the rationale for targeting IGF axis in cancer. However, clinical trials of the type I IGF receptor (IGF-IR)-targeted agents have been largely disappointing. Accumulating evidence demonstrates that the IGF axis not only promotes tumorigenesis, but also confers resistance to standard treatments. Furthermore, there are diverse pathways leading to the resistance to IGF-IR-targeted therapy. Recent studies characterizing the complex IGFs signaling in cancer have raised hope to refine the strategies for targeting the IGF axis. This review highlights the biological activities of IGF-IR signaling in cancer and the contribution of IGF-IR to cytotoxic, endocrine, and molecular targeted therapies resistance. Moreover, we update the diverse mechanisms underlying resistance to IGF-IR-targeted agents and discuss the strategies for future development of the IGF axis-targeted agents.

CRISPR screens in cancer spheroids identify 3D growth-specific vulnerabilities

Cancer genomics studies have identified thousands of putative cancer driver genes1. Development of high-throughput and accurate models to define the functions of these genes is a major challenge. Here we devised a scalable cancer-spheroid model and performed genome-wide CRISPR screens in 2D monolayers and 3D lung-cancer spheroids. CRISPR phenotypes in 3D more accurately recapitulated those of in vivo tumours, and genes with differential sensitivities between 2D and 3D conditions were highly enriched for genes that are mutated in lung cancers. These analyses also revealed drivers that are essential for cancer growth in 3D and in vivo, but not in 2D. Notably, we found that carboxypeptidase D is responsible for removal of a C-terminal RKRR motif2 from the α-chain of the insulin-like growth factor 1 receptor that is critical for receptor activity. Carboxypeptidase D expression correlates with patient outcomes in patients with lung cancer, and loss of carboxypeptidase D reduced tumour growth. Our results reveal key differences between 2D and 3D cancer models, and establish a generalizable strategy for performing CRISPR screens in spheroids to reveal cancer vulnerabilities.

The proprotein convertase furin is a pro-oncogenic driver in KRAS and BRAF driven colorectal cancer

Mutations in KRAS and/or BRAF that activate the ERK kinase are frequently found in colorectal cancer (CRC) and drive resistance to targeted therapies. Therefore, the identification of therapeutic targets that affect multiple signaling pathways simultaneously is crucial for improving the treatment of patients with KRAS or BRAF mutations. The proprotein convertase furin activates several oncogenic protein precursors involved in the ERK-MAPK pathway by endoproteolytic cleavage. Here we show that genetic inactivation of furin suppresses tumorigenic growth, proliferation, and migration in KRAS or BRAF mutant CRC cell lines but not in wild-type KRAS and BRAF cells. In a mouse xenograft model, these KRAS or BRAF mutant cells lacking furin displayed reduced growth and angiogenesis, and increased apoptosis. Mechanistically, furin inactivation prevents the processing of various protein pecursors including proIGF1R, proIR, proc-MET, proTGF-β1 and NOTCH1 leading to potent and durable ERK-MAPK pathway suppression in KRAS or BRAF mutant cells. Furthermore, we identified genes involved in activating the ERK-MAPK pathway, such as PTGS2, which are downregulated in the KRAS or BRAF mutant cells after furin inactivation but upregulated in wild-type KRAS and BRAF cells. Analysis of human colorectal tumor samples reveals a positive correlation between enhanced furin expression and KRAS or BRAF expression. These results indicate that furin plays an important role in KRAS or BRAF-associated ERK-MAPK pathway activation and tumorigenesis, providing a potential target for personalized treatment.

The motif EXEXXXL in the cytosolic tail of the secretory human proprotein convertase PC7 regulates its trafficking and cleavage activity

Many secretory proteins are activated by cleavage at specific sites. The proprotein convertases (PCs) form a family of nine secretory subtilisin-like serine proteases, seven of which cleave at specific basic residues within the trans-Golgi network, granules, or at the cell surface/endosomes. The seventh member, PC7, is a type-I transmembrane (TM) protein with a 97-residue-long cytosolic tail (CT). PC7 sheds human transferrin receptor 1 (hTfR1) into soluble shTfR1 in endosomes. To better understand the physiological roles of PC7, here we focused on the relationship between the CT-regulated trafficking of PC7 and its ability to shed hTfR1. Deletion of the TMCT resulted in soluble PC7 and loss of its hTfR1 shedding activity. Extensive CT deletions and mutagenesis analyses helped us zoom in on three residues in the CT, namely Glu-719, Glu-721, and Leu-725, that are part of a novel motif, EXEXXXL⁷²⁵, critical for PC7 activity on hTfR1. NMR studies of two 14-mer peptides mimicking this region of the CT and its Ala variants revealed that the three exposed residues are on the same side of the molecule. This led to the identification of adaptor protein 2 (AP-2) as a protein that recognizes the EXEXXXL⁷²⁵ motif, thus representing a potentially new regulator of PC7 trafficking and cleavage activity. Immunocytochemistry of the subcellular localization of PC7 and its Ala variants of Leu-725 and Glu-719 and Glu-721 revealed that Leu-725 enhances PC7 localization to early endosomes and that, together with Glu-719 and Glu-721, it increases the endosomal activity of PC7 on hTfR1.

Proprotein convertases: Key players in inflammation-related malignancies and metastasis

Many cancers occur from locations of inflammation due to chronic irritation and/or infection. Tumor microenvironment contains various different inflammatory cells and mediators that orchestrate diverse neoplastic processes, including proliferation, survival, adhesion and migration. In parallel, tumor cells have adapted some of the signaling molecules used by inflammatory cells, such as selectins and chemokines as well as their receptors for invasion, extravasation and subsequently metastasis. Expression and/or activation of the majority of these molecules is mediated by the proprotein convertases (PCs); proteases expressed by both tumor cells and inflammatory cells. This review analyzes the potential role of these enzymatic system in inflammation-associated cancer impacting on the malignant and metastatic potential of cancer cells, describing the possible use of PCs as a new anti-inflammatory therapeutic approach to tumor progression and metastasis.

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Proteins maturation by the proprotein convertases plays important role in inflammation-related cancer and metastasis.

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Protein precursors require the proprotein convertases for the induction of inflammation.

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Understanding of the molecular mechanism linking the proprotein convertases to inflammation will allow novel therapies.

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Inhibitors of the proprotein convertases constitute great potential for cancer treatment.

Inactivation of Proprotein Convertases in T Cells Inhibits PD-1 Expression and Creates a Favorable Immune Microenvironment in Colorectal Cancer

Proprotein convertases (PC) activate precursor proteins that play crucial roles in various cancers. In this study, we investigated whether PC enzyme activity is required for expression of the checkpoint protein programmed cell death protein 1 (PD-1) on cytotoxic T lymphocytes (CTL) in colon cancer. Although altered expression of the PC secretory pathway was observed in human colon cancers, only furin showed highly diffuse expression throughout the tumors. Inhibition of PCs in T cells using the general protein-based inhibitor α1-PDX or the pharmacologic inhibitor Decanoyl-Arg-Val-Lys-Arg-chloromethylketone repressed PD-1 and exhausted CTLs via induction of T-cell proliferation and apoptosis inhibition, which improved CTL efficacy against microsatellite instable and microsatellite stable colon cancer cells. In vivo, inhibition of PCs enhanced CTL infiltration in colorectal tumors and increased tumor clearance in syngeneic mice compared with immunodeficient mice. Inhibition of PCs repressed PD-1 expression by blocking proteolytic maturation of the Notch precursor, inhibiting calcium/NFAT and NF-κB signaling, and enhancing ERK activation. These findings define a key role for PCs in regulating PD-1 expression and suggest targeting PCs as an adjunct approach to colorectal tumor immunotherapy. SIGNIFICANCE: Protein convertase enzymatic activity is required for PD-1 expression on T cells, and inhibition of protein convertase improves T-cell targeting of microsatellite instable and stable colorectal cancer. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/79/19/5008/F1.large.jpg.

Anthrax toxin requires ZDHHC5-mediated palmitoylation of its surface-processing host enzymes

Toxins exploit numerous pathways of their host cells to gain cellular entry and promote intoxication. Therefore, studying the action of toxins allows us to better understand basic mechanisms in cell biology. In this study, we found that ZDHHC5, an enzyme that adds a lipid posttranslational modification to cysteines of proteins, is responsible for allowing anthrax toxin to enter cells. This enzyme acts on proprotein convertases that are needed to cleave these toxins to their active forms. ZDHHC5 does not affect the enzymatic activity of these proteases, but allows them to encounter the toxin by favoring their partitioning in microdomains on the cell surface, domains where the toxin has previously been shown to preferentially reside.

The protein acyl transferase ZDHHC5 was recently proposed to regulate trafficking in the endocytic pathway. Therefore, we explored the function of this enzyme in controlling the action of bacterial toxins. We found that ZDHHC5 activity is required for two very different toxins: the anthrax lethal toxin and the pore-forming toxin aerolysin. Both of these toxins have precursor forms, the protoxins, which can use the proprotein convertases Furin and PC7 for activation. We show that ZDHHC5 indeed affects the processing of the protoxins to their active forms. We found that Furin and PC7 can both be S-palmitoylated and are substrates of ZDHHC5. The impact of ZDHHC5 on Furin/PC7-mediated anthrax toxin cleavage is dual, having an indirect and a direct component. First, ZDHHC5 affects the homeostasis and trafficking of a subset of cellular proteins, including Furin and PC7, presumably by affecting the endocytic/recycling pathway. Second, while not inhibiting the protease activity per se, ZDHHC5-mediated Furin/PC7 palmitoylation is required for the cleavage of the anthrax toxin. Finally, we show that palmitoylation of Furin and PC7 promotes their association with plasma membrane microdomains. Both the receptor-bound toxin and the convertases are of very low abundance at the cell surface. Their encounter is unlikely on reasonable time scales. This work indicates that palmitoylation drives their encounter in specific domains, allowing processing and thereby intoxication of the cell.

Furin inhibitor protects against neuronal cell death induced by activated NMDA receptors

The proprotein convertases (PCs) act as serine proteases and are known to convert diverse precursor proteins into their active forms. Among the PCs, furin has been considered to play a crucial role not only in embryogenesis, but also in the initiation and progression of certain pathologic conditions. However, the roles played by furin with respect to neuronal cell injuries remain to be determined. An excessive influx of Ca²⁺ through the N-methyl-d-aspartate (NMDA) receptor has been associated with diverse neurological and neurodegenerative disorders. The aim of this study was to achieve further insight into the pathophysiologic roles of furin in cultured cortical neurons. We demonstrated that furin inhibitors dose-dependently prevented neuronal injury induced by NMDA treatment. Neuronal injury induced by NMDA treatment was attenuated by the calpain inhibitor calpeptin. And the increase observed in the activity of calpain after NMDA treatment was significantly inhibited by these furin inhibitors. Furthermore, calpain-2 activity, which was evaluated by means of the immunoblotting assay, was increased by NMDA treatment. It was noteworthy that this increased activity was almost completely inhibited by a furin inhibitor. Our findings suggested that furin is involved in NMDA-induced neuronal injury by acting upstream of calpain.

The proprotein convertase furin is required to maintain viability of alveolar rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Success of current therapies is still limited and outcome is particularly poor for metastatic alveolar rhabdomyosarcoma (aRMS). We previously identified the proprotein convertase furin as potential target for specific drug delivery with RMS-homing peptides. Furin is a protease that converts inactive precursor proteins into bioactive proteins and peptides. In this study, we investigate the biological role of furin in aRMS progression in vitro and in vivo. Furin expression was confirmed in over 86% RMS biopsies in a tissue microarray (n=89). Inducible furin silencing in vitro led to significant impairment of cell viability and proliferation in all investigated aRMS cell lines, but not in MRC5 fibroblasts. Furthermore, the aRMS cell lines Rh3 and Rh4 revealed to be very sensitive to furin silencing, undergoing caspase-dependent cell death. Notably, furin silencing in vivo led to complete remission of established Rh4 tumors and to delayed growth in Rh30 tumors. Taken together, these findings identify furin as an important factor for aRMS progression and survival. Thus, we propose furin as a novel therapeutic target for treatment of aRMS.

Impact of selective anti-BMP9 treatment on tumor cells and tumor angiogenesis

The role of bone morphogenic protein 9 (BMP9) signaling in angiogenesis has been controversial, with a number of studies showing that it acts either as a pro-angiogenic or, conversely, as an anti-angiogenic factor in a context-dependent manner. Notably, BMP9 was also reported to function in both pro- or anti-tumorigenic roles during tumor progression. It has therefore remained unclear, whether selective BMP9 inhibition is a useful target for antibody therapy of cancer. To shed light on these questions, we characterized BMP9 expression in plasma of patients with different cancer indications and found elevated levels of pro-domains and precursor BMP9 with a strong response in renal cell carcinoma (RCC). These studies prompted us to evaluate the potential of selective anti-BMP9 cancer therapy in RCC. We generated a novel monoclonal therapeutic antibody candidate, mAb BMP9-0093, that selectively targets all different BMP9 variants but does not bind to the closest homolog BMP10. In vitro, mAb BMP9-0093 treatment inhibited signaling, endothelin-1 (ET-1) production and spreading of endothelial cells and restored BMP9-induced decrease in pericyte migration and attachment. Furthermore, BMP9-mediated epithelial-mesenchymal transition of renal cell carcinoma cells was reversed by mAb BMP9-0093 treatment in vitro. In vivo, mAb BMP9-0093 showed significant anti-tumor activity that was associated with an increase in apoptosis as well as a decrease in tumor cell proliferation and ET-1 release. Furthermore, mAb BMP9-0093 induced mural cell coverage of endothelial cells, which was corroborated by a reduction in vascular permeability, demonstrated by a diminished penetration of omalizumab-Alexa 647 into tumor tissue. Our findings provide new evidence for a better understanding of BMP9 contribution in tumor progression and angiogenesis that may result in the development of effective targeted therapeutic interventions.

Furin inhibitor D6R suppresses epithelial-mesenchymal transition in SW1990 and PaTu8988 cells via the Hippo-YAP signaling pathway

Hexa-D-arginine (D6R), an inhibitor of furin, has potential therapeutic applications in different types of human tumor. However, the function of D6R in targeting pancreatic cancer cells remains to be elucidated. In the present study, the proliferation, invasion and migration abilities of SW1990 and PaTu8988 cells were examined using a Cell Counting Kit-8, and Transwell and wound healing assays. Subsequently, the expression of proteins associated with epithelial-mesenchymal transition (EMT) and the Hippo-yes-associated protein (YAP) pathway were detected using western blot analysis. It was revealed that D6R significantly inhibited the proliferation, migration and invasion abilities of SW1990 and PaTu8988 cells. Additionally, D6R led to the upregulation of E-cadherin (an epithelial marker), and the downregulation of N-cadherin and vimentin (mesenchymal markers) in SW1990 and PaTu8988 cells. Furthermore, the results of the present study revealed that D6R significantly affected the YAP phosphorylation level and the total YAP protein level, indicating that D6R was functionally involved in the Hippo-YAP signaling pathway. It has been suggested that D6R-suppressed EMT in SW1990 and PaTu8988 cells may occur via the Hippo-YAP pathway and that it may be a feasible drug to ameliorate the malignant phenotype of SW1990 and PaTu8988 cells.

The proprotein convertase furin in tumour progression

Proprotein convertases are proteases that have been implicated in the activation of a wide variety of proteins. These proteins are generally synthesised as precursor proteins and require limited proteolysis for conversion into their mature bioactive counterparts. Many of these proteins, including metalloproteases, growth factors and their receptors or adhesion molecules, have been shown to facilitate tumour formation and progression. Hence, this review will focus on the proprotein convertase furin and its role in cancer. The expression of furin has been confirmed in a large spectrum of cancers such as head and neck squamous cell carcinoma, breast cancer and rhabdomyosarcoma. Functional studies modulating furin activity uncovered its importance for the processing of many cancer-related substrates and strongly indicate that high furin activity promotes the malignant phenotype of cancer cells. In this review, we summarise the expression and function of furin in different cancer types, discuss its role in processing cancer-related proproteins and give examples of potential therapeutic approaches that take advantage of the proteolytic activity of furin in cancer cells.

Prolonged circulation and increased tumor accumulation of liposomal vincristine in a mouse model of rhabdomyosarcoma

AIM

Our goal was to improve vincristine (VCR) based rhabdomyosarcoma (RMS) therapy by encapsulating the drug into liposomes. A targeting strategy was attempted to enhance tumor accumulation.

MATERIALS & METHODS

VCR was loaded in control and peptide-decorated liposomes via an active method. The interaction of an RMS-specific peptide with the presumed target furin and the cellular uptake of both liposomal groups were studied in vitro. Pharmacokinetics and biodistribution of VCR-containing liposomes were assessed in an RMS xenograft mouse model.

RESULTS

Liposomes ensured high VCR concentration in plasma and in the tumor. Peptide-decorated liposomes showed modest uptake in RMS cells.

CONCLUSION

The investigated peptide-modified liposomal formulation may not be optimal for furin-mediated RMS targeting. Nevertheless, VCR-loaded liposomes could serve as a delivery platform for experimental RMS.

PACE4 is an important driver of ZR-75-1 estrogen receptor-positive breast cancer proliferation and tumor progression

Breast cancer is the most frequent and deadly malignancy in women worldwide. Despite national screening programs combined with new treatments relapse rate remain high and new therapies are needed. From previous work, we identified PACE4, a member of the proprotein convertase (PCs) family of endoproteases, as a novel therapeutic target in prostate cancer. In the present study we asked the question if PACE4 could also be a potential target in breast cancer. In clinical samples of breast adenocarcinoma, we observed a specific overexpression of PACE4 in the estrogen-receptor (ER) positive subtype. We therefore looked for a breast cancer cell line model which would be representative and thus focused on the ZR-75-1 since it both expresses PACE4 and is estrogen-receptor positive. We compared stable knockdowns of furin, PACE4 and PC7 in the estrogen-receptor-positive cell line ZR-75-1 to evaluate their respective contribution to cell growth and tumor progression. PACE4 was the only PC displaying an impact on cell growth. A PACE4 peptide-based inhibitor (C23) was tested and shown to decrease proliferation of ZR-75-1 cells in cell based assays. C23 also had potent effects of tumor progression in vivo on xenografts of the ZR-75-1 cell line in athymic nude mice. Thus, PACE4-silencing and systemic administration of a PACE4 inhibitor resulted in hindered tumor progression with reduction in proliferative indices and increased cell quiescence assessed with biomarkers. Our results suggest that PACE4 is a promising target for estrogen-receptor-positive breast cancer.

PACE4 regulates apoptosis in human pancreatic cancer Panc‑1 cells via the mitochondrial signaling pathway

Previous studies have demonstrated the overexpression of paired basic amino acid cleaving enzyme 4 (PACE4) mRNA in prostate cancer tissues. This overexpression is correlated with higher circulating protein levels in certain patients, however, the role of PACE4 in apoptosis and the potential molecular mechanisms of pancreatic cancer remain to be elucidated. The aim of the present study was to investigate the effect and potential molecular mechanisms of PACE4 on apoptosis in the Panc‑1 pancreatic cancer cell line. Cell proliferation was assessed using a Cell Counting Kit‑8 assay. Apoptotic nuclear shrinkage was monitored using Hoechst 33258 staining. Caspase‑3/7 activities were measured using a colorimetric caspase‑glo 3/7 assay. Alterations in protein expression were monitored using Western blot analysis. The results indicated that PACE4 small interfering (si)RNA inhibited cell proliferation and activated caspase‑3/7 activities. In addition, PACE4 siRNA significantly increased apoptosis via the activation of caspase‑3 and the downregulation of anti‑apoptotic proteins, X‑linked inhibitor of apoptosis protein and phosphorylated‑Akt. In addition, the results showed deregulation of the B cell lymphoma‑2 (Bcl‑2)-associated X protein/Bcl‑2 ratio which led to the release of cytochrome c following PACE4 siRNA transfection. In conclusion, PACE4 siRNA may exert antitumor activity through the mitochondrial pathway and is expected to be a promising therapeutic strategy for the treatment of pancreatic cancer.

Targeting proprotein convertases in furin-rich lung cancer cells results in decreased in vitro and in vivo growth

Proprotein convertases (PCs) are serine proteases with an active role in the post-translational processing of numerous inactive proteins to active proteins including many substrates of paramount importance in cancer development and progression. Furin (PCSKC3), a well-studied member of this family, is overexpressed in numerous human and experimental malignancies. In the present communication, we treated two furin-overexpressing non-small cell carcinoma (NSCLC) cell lines (Calu-6 and HOP-62) with the PC inhibitor CMK (Decanoyl-Arg-Val-Lys-Arg-chloromethylketone). This resulted in a diminished IGF-1R processing and a simultaneous decrease in cell proliferation of two NSCLC lines. Similarly, growth of subcutaneous xenografts of both cell lines, were partially inhibited by an in vivo treatment with the same drug. These observations point to a potential role of PC inhibitors in cancer therapy. © 2016 Wiley Periodicals, Inc.

The Proprotein Convertase Furin Contributes to Rhabdomyosarcoma Malignancy by Promoting Vascularization, Migration and Invasion

The proprotein convertase (PC) furin cleaves precursor proteins, an important step in the activation of many cancer-associated proteins. Substrates of furin and furin-like PCs play a role in proliferation, metastasis and invasion. Some of them are involved in the progression of the pediatric soft tissue sarcoma rhabdomyosarcoma (RMS). In this study, we show that PCs, and in particular furin, are expressed in RMS cell lines. To investigate the functional role of furin, we generated RMS cell lines with modulated furin activity. Silencing or stable inhibition of furin delayed tumor growth in Rh30 and RD xenografts in vivo, and was correlated with lower microvessel density. Reduced furin activity also decreased migration and invasion abilities in vitro, and inhibition of furin in RMS cells diminished processing of IGF1R, VEGF-C, PDGF-B and MT1-MMP, leading to lower levels of mature proteins. Furthermore, we found that furin activity is required for proper IGF signaling in RMS cells, as furin silencing resulted in reduced phosphorylation of Akt upon IGF1 stimulation. Taken together, our results suggest that furin plays an important role in the malignant phenotype of RMS cells by activating proteins involved in tumor growth and vascularization, metastasis and invasion.

Inhibition of furin results in increased growth, invasiveness and cytokine production of synoviocytes from patients with rheumatoid arthritis

OBJECTIVES

Fibroblast-like synoviocytes derived from patients with rheumatoid arthritis play a key role by local production of cytokines and proteolytic enzymes that degrade the extracellular matrix and cartilage. These synoviocytes acquire phenotypic characteristics commonly observed in transformed cells, like anchorage-independent growth, increased proliferation and invasiveness, and insensitivity to apoptosis. Furin is a ubiquitous proprotein convertase that is capable of cleaving precursors of a wide variety of proteins. In patients with rheumatoid arthritis, furin is reported to be highly expressed in the synovial pannus compared with healthy persons. However, the mechanisms are poorly understood. This study is to explore the effect of furin overexpression in rheumatoid synoviocytes.

METHODS

In this study, RNA interference was used to knock down furin expression and to assess the resultant effects on biological behaviors of synoviocytes, such as cell proliferation, invasion, migration, cell cycle and cell apoptosis. In addition, the production of inflammatory cytokines was evaluated.

RESULTS

The results showed that the inhibition of furin enhanced proliferation, invasion, and migration of synoviocytes in vitro. Cell cycle was accelerated and cell death was affected by furin knockdown. Also, the inhibition of furin increased interleukin-1β and tumor necrosis factor-α secretion of synoviocytes.

CONCLUSIONS

Inhibition of furin enhances invasive phenotype of synoviocytes from patients with rheumatoid arthritis, implying a protective role of furin. Agents targeting upregulation of furin may have therapeutic potential for rheumatoid arthritis.

PACE4 inhibitors and their peptidomimetic analogs block prostate cancer tumor progression through quiescence induction, increased apoptosis and impaired neovascularisation

Prostate cancer is the leading cancer in North American men. Current pharmacological treatments are limited to anti-androgen strategies and the development of new therapeutic approaches remains a challenge. As a fundamentally new approach, we propose the inhibition of PACE4, a member of the proprotein convertases family of enzymes, as a therapeutic target in prostate cancer. We developed an inhibitor named the Multi-Leu peptide, with potent in vitro anti-proliferative effects. However, the Multi-Leu peptide has not been tested under in vivo conditions and its potency under such conditions is most likely limited, due to the labile characteristics of peptides in general. Using a peptidomimetic approach, we modified the initial scaffold, generating the analog Ac-[DLeu]LLLRVK-Amba, which demonstrates increased inhibitory potency and stability. The systemic administration of this peptidomimetic significantly inhibits tumor progression in the LNCaP xenograft model of prostate cancer by inducing tumor cell quiescence, increased apoptosis and neovascularization impairment. Pharmacokinetic and biodistribution profiles of this inhibitor confirm adequate tumor delivery properties of the compound. We conclude that PACE4 peptidomimetic inhibitors could result in stable and potent drugs for a novel therapeutic strategy for prostate cancer.

Loss of the proteostasis factor AIRAPL causes myeloid transformation by deregulating IGF-1 signaling

AIRAPL (arsenite-inducible RNA-associated protein-like) is an evolutionarily conserved regulator of cellular proteostasis linked to longevity in nematodes, but its biological function in mammals is unknown. We show herein that AIRAPL-deficient mice develop a fully-penetrant myeloproliferative neoplastic process. Proteomic analysis of AIRAPL-deficient mice revealed that this protein exerts its antineoplastic function through the regulation of the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway. We demonstrate that AIRAPL interacts with newly synthesized insulin-related growth factor-1 receptor (IGF1R) polypeptides, promoting their ubiquitination and proteasome-mediated degradation. Accordingly, genetic and pharmacological IGF1R inhibitory strategies prevent the hematological disease found in AIRAPL-deficient mice as well as that in mice carrying the Jak2(V617F) mutation, thereby demonstrating the causal involvement of this pathway in the pathogenesis of myeloproliferative neoplasms. Consistent with its proposed role as a tumor suppressor of myeloid transformation, AIRAPL expression is widely abrogated in human myeloproliferative disorders. Collectively, these findings support the oncogenic relevance of proteostasis deregulation in hematopoietic cells, and they unveil novel therapeutic targets for these frequent hematological neoplasias.

Furin as proprotein convertase and its role in normal and pathological biological processes

Furin belongs to serine intracellular Ca2+-dependent endopeptidases of the subtilisin family, also known as proprotein convertase (PC). Human furin is synthesized as zymogen with a molecular weight of 104 kDa, which is then activated by autocatalytic in two stages. This process can occur when zymogen migrates from the endoplasmic reticulum to the Golgi apparatus, where a large part of furin is accumulated. The molecular weigh t of the active furin is 98 kDa. Furin relates to enzymes with a narrow substrate specificity: it hydrolyzes peptide bonds at the site of paired basic amino acids and furin activity exhibits in a wide pH range 5-8. Its main biological function is activation of the functionally important protein precursors. It is accompanied by the launch of a cascade of reactions, which lead to appearance of biologically active molecules involved in realization of specific biological functions both in normal and in some patologicheskih processes. Furin substrates are biologically important proteins such as enzymes, hormones, growth factors and differentiation, receptors, adhesion proteins, proteins of blood plasma. Furin plays an important role in the development of processes such as proliferation, invasion, cell migration, survival, maintenance of homeostasis, embryogenesis, as well as the development of a number of pathologies, including cardiovascular, oncologic and neurodegenerative diseases. Furin and furin-like proprotein convertases participate as key factors in the realization of the regulatory functions of proteolytic enzymes, the value of which is currently being evaluated as most important in comparison with the degradative function of proteases.

Notch1 Autoactivation via Transcriptional Regulation of Furin, Which Sustains Notch1 Signaling by Processing Notch1-Activating Proteases ADAM10 and Membrane Type 1 Matrix Metalloproteinase

Notch1 is an evolutionarily conserved transmembrane receptor involved in melanoma growth. Notch1 is first cleaved by furin in the Golgi apparatus to produce the biologically active heterodimer. Following ligand binding, Notch1 is cleaved at the cell membrane by proteases such as ADAM10 and -17 and membrane type 1 matrix metalloproteinase (MT1-MMP), the latter of which we recently identified as a novel protease involved in Notch1 processing. The final cleavage is γ-secretase dependent and releases the active Notch intracellular domain (NIC). We now demonstrate that Notch1 directly regulates furin expression. Aside from activating Notch1, furin cleaves and activates several proteases, including MT1-MMP, ADAM10, and ADAM17. By chromatin immunoprecipitation and a reporter assay, we demonstrate that Notch1 binds at position -1236 of the furin promoter and drives furin expression. The Notch1-dependent enhancement of furin expression increases the activities of MT1-MMP and ADAM10 but not that of ADAM17, as demonstrated by short hairpin RNA (shRNA) knockdown of furin, and promotes the cleavage of Notch1 itself. These data highlight a novel positive-feedback loop whereby Notch1-dependent furin expression can induce Notch1 signaling by increasing Notch1 processing and by potentiating the activity of the proteases responsible for Notch1 activation. This leads to Notch1 signal amplification, which can promote melanoma tumor growth and progression, as demonstrated by the inhibition of cell migration and invasion upon furin inhibition downstream of Notch1. Disruption of such feedback signaling might represent an avenue for the treatment of melanoma.

Cationic Cell-Penetrating Peptides Are Potent Furin Inhibitors

Cationic cell-penetrating peptides have been widely used to enhance the intracellular delivery of various types of cargoes, such as drugs and proteins. These reagents are chemically similar to the multi-basic peptides that are known to be potent proprotein convertase inhibitors. Here, we report that both HIV-1 TAT_47-57 peptide and the Chariot reagent are micromolar inhibitors of furin activity in vitro. In agreement, HIV-1 TAT_47-57 reduced HT1080 cell migration, thought to be mediated by proprotein convertases, by 25%. In addition, cyclic polyarginine peptides containing hydrophobic moieties which have been previously used as transfection reagents also exhibited potent furin inhibition in vitro and also inhibited intracellular convertases. Our finding that cationic cell-penetrating peptides exert potent effects on cellular convertase activity should be taken into account when biological effects are assessed.

Expression of paired basic amino acid-cleaving enzyme 4 (PACE4) correlated with prognosis in non-small cell lung cancer (NSCLC) patients

BACKGROUND

Paired basic amino acid-cleaving enzyme 4 (PACE4) was shown to enhance tumor cells proliferation and invasive. This study provides the first investigation of PACE4 expression in non-small cell lung cancer (NSCLC) and the correlation with clinicopathologic features, prognostic indicators of 172 cases.

METHODS

Quantitative real-time PCR (RT-PCR) and immunofluorescence (IF) were applied to detect PACE4 expression in NSCLC and 16HBE cell lines, then 172 consecutive NSCLC and 15 normal lung tissues were studied through immunohistochemistry (IHC). The association between PACE4 expression and clinicopathological parameters was evaluated. Kaplan-Meier survival analysis and Cox proportional hazards models were used to estimate the effect of PACE4 expression on survival.

RESULTS

PACE4 expression in NSCLC were significantly higher than normal lung cell and tissues (P<0.05). PACE4 had cytoplasmic expression and was observed in 111 of the 172 (64.5%) NSCLC patients. Clinicopathologically, PACE4 expression was significantly associated with lymph node metastasis (N stage) (P=0.007), and clinical stage (P=0.024). Multivariable analysis confirmed that PACE4 expression increased the hazard of death after adjusting for other clinicopathological factors [hazards ratio (HR): 1.584; 95% confidence interval (CI): 1.167-2.151; P<0.001]. Overall survival (OS) was significantly prolonged in PACE4 negative group when compared with PACE4 positive group (5-year survival rates, 23.1% vs. 54.5%, log-rank test, χ(2)=17.717, P<0.001), as was disease-free survival (DFS) (5-year survival rates, 23.4% vs. 55.4%, log-rank test, χ(2)=20.486, P<0.001).

CONCLUSIONS

Our results suggest that positive expression of PACE4 is an independent factor for NSCLC patients and it might serve as a potential prognostic biomarker for patients with NSCLC.

Identification of potent and compartment-selective small molecule furin inhibitors using cell-based assays

The proprotein convertase furin is implicated in a variety of pathogenic processes such as bacterial toxin activation, viral propagation, and cancer. Several groups have identified non-peptide compounds with high inhibitory potency against furin in vitro, although their efficacy in various cell-based assays is largely unknown. In this study we show that certain guanidinylated 2,5-dideoxystreptamine derivatives exhibit interesting ex vivo properties. Compound 1b (1,1'-(4-((2,4-diguanidino-5-(4-guanidinophenoxy)cyclohexyl)oxy)-1,3-phenylene)diguanidine) is a potent and cell-permeable inhibitor of cellular furin, since it was able to retard tumor cell migration, block release of a Golgi reporter, and protect cells against Bacillus anthracis (anthrax) and Pseudomonas aeruginosa intoxication, with no evident cell toxicity. Other compounds based on the 2,5-dideoxystreptamine scaffold, such as compound 1g (1,1'-(4,6-bis(4-guanidinophenoxy)cyclohexane-1,3-diyl)diguanidine) also efficiently protected cells against anthrax, but displayed only moderate protection against Pseudomonas exotoxin A and did not inhibit cell migration, suggesting poor cell permeability. Certain bis-guanidinophenyl ether derivatives such as 2f (1,3-bis(2,4-diguanidinophenoxy) benzene) exhibited micromolar potency against furin in vitro, low cell toxicity, and highly efficient protection against anthrax toxin; this compound only slightly inhibited intracellular furin. Thus, compounds 1g and 2f both represent potent furin inhibitors at the cell surface with low intracellular inhibitory action, and these particular compounds might therefore be of preferred therapeutic interest in the treatment of certain bacterial and viral infections.

Proprotein convertase FURIN regulates T cell receptor-induced transactivation

Antigen emergence rapidly stimulates T cells, which leads to changes in cytokine production, cell proliferation, and differentiation. Some of the key molecules involved in these events, such as TGF-β1 and NOTCH1, are synthesized initially as inactive precursors and are proteolytically activated during T cell activation. PCSKs regulate proprotein maturation by catalyzing the proteolytic cleavage of their substrates. The prototype PCSK FURIN is induced upon TCR activation, and its expression in T cells is critical for the maintenance of peripheral immune tolerance. In this study, we tested the hypothesis that FURIN regulates T cell activation. Our data demonstrate that IL-2 is increased initially in FURIN-deficient mouse CD4(+) T cells, but the TCR-induced IL-2 mRNA expression is not sustained in the absence of FURIN. Accordingly, the inhibition of FURIN in human Jurkat T cell lines also results in a decrease in IL-2 production, whereas the overexpression of WT FURIN is associated with elevated IL-2 levels. In Jurkat cells, FURIN is dispensable for immediate TCR signaling steps, such as ERK, ZAP70, or LAT phosphorylation. However, with the use of gene reporter assays, we demonstrate that FURIN regulates the AP-1, NFAT, and NF-κB transcription factors. Finally, by performing a transcription factor-binding site enrichment analysis on FURIN-dependent transcriptomes, we identify the FURIN-regulated transcription factors in mouse CD4(+) T cell subsets. Collectively, our work confirms the hypothesis that the TCR-regulated protease FURIN plays an important role in T cell activation and that it can specifically modulate TCR-activated transactivation.

Repression of liver colorectal metastasis by the serpin Spn4A a naturally occurring inhibitor of the constitutive secretory proprotein convertases

Liver is the most common site of metastasis from colorectal cancers, and liver of patients with liver colorectal metastasis have abnormal levels of the proprotein convertases (PCs). These proteases are involved in the activation and/or expression of various colon cancer-related mediators, making them promising targets in colorectal liver metastasis therapy. Here, we revealed that the serpin Spn4 from Drosophila melanogaster inhibits the activity of all the PCs found in the constitutive secretory pathway and represses the metastatic potential of the colon cancer cells HT-29 and CT-26. In these cells, Spn4A inhibited the processing of the PCs substrates IGF-1R and PDGF-A that associated their reduced anchorage-independent growth, invasiveness and survival in response to apoptotic agents. In vivo, Spn4A-expressing tumor cells showed repressed subcutaneous tumor development and liver metastases formation in response to their intrasplenic inoculation. In these cells Spn4A induced the expression of molecules with anti-metastatic functions and inhibited expression of pro-tumorigenic molecules. Taken together, our findings identify Spn4A as the only endogenous inhibitor of all the constitutive secretory pathway PCs, which is able to repress the metastatic potential of colon cancer cells. These results suggest the potential use of Spn4A and/or derivates as a useful adduct colorectal liver metastasis prevention.

Serum concentration of alpha-1 antitrypsin is significantly higher in colorectal cancer patients than in healthy controls

Background

The association between alpha-1 antitrypsin (AAT) deficiency and colorectal cancer (CRC) is currently controversial. The present study compares AAT serum concentrations and gene frequencies between a group of CRC patients and a control group of healthy unrelated people (HUP).

Methods

267 CRC subjects (63% males, 72 ± 10 years old) were enlisted from a Hospital Clinic setting in Asturias, Spain. The HUP group comprised 327 subjects (67% males, mean age 70 ± 7.5 years old) from the same geographical region. Outcome measures were AAT serum concentrations measured by nephelometry, and AAT phenotyping characterization by isoelectric focusing.

Results

Significantly higher serum concentrations were found among CRC (208 ± 60) than in HUP individuals (144 ± 20.5) (p = 0.0001). No differences were found in the phenotypic distribution of the Pi*S and Pi*Z allelic frequencies (p = 0.639), although the frequency of Pi*Z was higher in CRC (21%) than in HUP subjects (15%).

Conclusions

The only statistically significant finding in this study was the markedly higher AAT serum concentrations found in CRC subjects compared with HUP controls, irrespective of whether their Pi* phenotype was normal (Pi*MM) or deficient (Pi*MS, Pi*MZ and Pi*SZ). Although there was a trend towards the more deficient Pi* phenotype the more advanced the tumor, the results were inconclusive due to the small sample size. Consequently, more powerful studies are needed to reach firmer conclusions on this matter.

Enhanced aggressiveness of benzopyrene-induced squamous carcinomas in transgenic mice overexpressing the proprotein convertase PACE4 (PCSK6)

PACE4 (PCSK6) is a proprotein convertase (PC) capable of processing numerous substrates involved in tumor growth, invasion, and metastasis. Because of the human relevancy of the tobacco-associated carcinogen benzo[a]pyrene (B(a)P) we investigated whether transgenic mice in which this PC is targeted to the epidermis (K5-PACE4) may be more susceptible to B(a)P complete carcinogenesis than wild type (WT) mice. In an in vitro experiment, using cell lines derived from skin tumors obtained after B(a)P treatment, we observed that PACE4 overexpression and activity accounts for an increased proliferation rate, exaggerated sensitivity to the PC inhibitor CMK, and interference with IGF-1R autophosphorylation. Squamous cell carcinomas, obtained from K5-PACE4 mice subjected to complete chemical carcinogenesis, were characterized by a 50% increase in cell proliferation, when compared with similar tumors from WT mice. In addition, tumors from K5-PACE4 mice showed deeper invasion into the underlying dermis. Thus, mice overexpressing PACE4 exhibited tumors of increased growth rate and invasive potential when exposed to the human carcinogen B(a)P, further supporting the significance of PCs in tumor growth and progression.