Legumain: a biomarker for diagnosis and prognosis of human ovarian cancer

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Tumor-Targeted Fluorescent/Photoacoustic Imaging of Legumain Activity In Vivo

Legumain has been identified as a target for diagnosis and treatment of associated cancers. Therefore, real-time imaging of legumain activity in vivo is helpful in diagnosing and evaluating therapeutic efficacy of associated cancers. Fluorescent/photoacoustic (FL/PA) dual-modal imaging developed rapidly because of its good sensitivity and spatial resolution. As far as we know, a tumor-targeted probe for FL/PA imaging of legumain activity in vivo has not been reported. Hence, we intended to develop a tumor-targeted hemicyanine (HCy) probe (HCy-AAN-Bio) for FL/PA imaging of legumain in vivo. The control probe HCy-AAN does not have tumor-targeting ability. Legumain can specifically cleave HCy-AAN-Bio or HCy-AAN with the generation of FL/PA signal while more HCy-AAN-Bio could be recognized by legumain than HCy-AAN with higher sensitivity in vitro. Due to the tumor-targeting ability, HCy-AAN-Bio could image 4T1 cells with an additional 1.3-fold FL enhancement and 1.9-fold PA enhancement than HCy-AAN. In addition, HCy-AAN-Bio could image legumain activity in vivo with an additional 1.5-fold FL enhancement and 1.9-fold PA enhancement than HCy-AAN. We expected that HCy-AAN-Bio will be a powerful tool for early diagnosis of associated cancer.

Pigmented Microbial Extract (PMB) from Exiguobacterium Species MB2 Strain (PMB1) and Bacillus subtilis Strain MB1 (PMB2) Inhibited Breast Cancer Cells Growth In Vivo and In Vitro

Breast cancer (BC) continues to be one of the major causes of cancer deaths in women. Progress has been made in targeting hormone and growth factor receptor-positive BCs with clinical efficacy and success. However, little progress has been made to develop a clinically viable treatment for the triple-negative BC cases (TNBCs). The current study aims to identify potent agents that can target TNBCs. Extracts from microbial sources have been reported to contain pharmacological agents that can selectively inhibit cancer cell growth. We have screened and identified pigmented microbial extracts (PMBs) that can inhibit BC cell proliferation by targeting legumain (LGMN). LGMN is an oncogenic protein expressed not only in malignant cells but also in tumor microenvironment cells, including tumor-associated macrophages. An LGMN inhibition assay was performed, and microbial extracts were evaluated for in vitro anticancer activity in BC cell lines, angiogenesis assay with chick chorioallantoic membrane (CAM), and tumor xenograft models in Swiss albino mice. We have identified that PMB from the Exiguobacterium (PMB1), inhibits BC growth more potently than PMB2, from the Bacillus subtilis strain. The analysis of PMB1 by GC-MS showed the presence of a variety of fatty acids and fatty-acid derivatives, small molecule phenolics, and aldehydes. PMB1 inhibited the activity of oncogenic legumain in BC cells and induced cell cycle arrest and apoptosis. PMB1 reduced the angiogenesis and inhibited BC cell migration. In mice, intraperitoneal administration of PMB1 retarded the growth of xenografted Ehrlich ascites mammary tumors and mitigated the proliferation of tumor cells in the peritoneal cavity in vivo. In summary, our findings demonstrate the high antitumor potential of PMB1.

Clonorchis sinensis legumain promotes migration and invasion of cholangiocarcinoma cells via regulating tumor-related molecules

BACKGROUND

Clonorchis sinensis infection causes serious pathological changes in the bile duct and is highly correlated with cholangiocarcinoma. The excretory-secretory products (ESP) of C. sinensis play a critical role in the oncogenesis and progression of cholangiocarcinoma, while the components and precise mechanism remain unclear. Here, we evaluated the function of C. sinensis legumain (Cslegumain) in promoting the invasion and migration of cholangiocarcinoma cells and the mechanism involved.

METHODS

The structural and molecular characteristics of Cslegumain were predicted and analyzed using the online program Phyre2. Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemical staining were performed to test the transcriptional level of Cslegumain and its localization in the adult. Native Cslegumain was detected by western blotting assay. The effects of Cslegumain on the proliferation, invasion and migration of cholangiocarcinoma cells were checked using CCK-8 assay, Matrigel transwell assay and scratch wound healing assay. Expression levels of tumor-related molecules regulated by Cslegumain were evaluated by qRT-PCR and western blotting assay.

RESULTS

Cslegumain showed high similarity with human legumain in the secondary and tertiary structures and displayed higher transcriptional levels in the adult worm than in the metacercariae. Native Cslegumain was detected in a catalytic form and was localized mainly in the intestine of the C. sinensis adult and epithelial cells of the intrahepatic bile duct. After transfection into RBE cells, Cslegumain showed high ability in promoting the invasion and migration but not the proliferation of cholangiocarcinoma RBE cells. Furthermore, the expression levels of some molecules including E-cadherin and N-cadherin were downregulated, while the levels of α-actinin 4, β-catenin and inducible nitric oxide synthase (iNOS) were upregulated.

CONCLUSIONS

Our findings indicated that Cslegumain showed very similar structures as those of human legumain and could promote the invasion and migration of cholangiocarcinoma cells by regulating some tumor-related molecules.

Metformin regulates autophagy via LGMN to inhibit choriocarcinoma

Choriocarcinoma has the problem of chemotherapy insensitivity and recurrence. Metformin may be a promising candidate to restrict choriocarcinoma progress because of its indirect and direct beneficial role on inhabitations of cancer cells without severe adverse side effects. In this study, metformin pressed the proliferation and invasion of choriocarcinoma JAR cells in vitro and the growth of the JAR subcutaneous xenografts in vivo. The high throughput sequencing and bioinformatics technology identified the low expression of legumain (LGMN) in lysosomal pathway caused by metformin, which was upregulated in human choriocarcinoma tissues compared with the early pregnancy tissues. As elevating metformin concentration and treatment time, the mRNA and protein expression of LGMN both depressed in two choriocarcinoma cell lines (JAR and JEG-3). LGMN was involved in metformin-mediated inhibition of cell proliferation and invasion. Furthermore, metformin induced autophagy via inhibiting LGMN through AKT/mTOR/LC3II signaling pathway of choriocarcinoma. Autophagy inhibitor could depress metformin-induced autophagy and improve cell proliferation and invasion ability dropped by metformin, while autophagy inducer could partially reverse the change of cell proliferation and invasion modulated by combination of metformin and LGMN overexpression. These results indicated that metformin inhibited cell proliferation and invasion ability by inducing autophagy in a LGMN-dependent manner so as to play a role in the treatment of choriocarcinoma.

Role of LGMN in tumor development and its progression and connection with the tumor microenvironment

Legumain (LGMN) has been demonstrated to be overexpressed not just in breast, prostatic, and liver tumor cells, but also in the macrophages that compose the tumor microenvironment. This supports the idea that LGMN is a pivotal protein in regulating tumor development, invasion, and dissemination. Targeting LGMN with siRNA or chemotherapeutic medicines and peptides can suppress cancer cell proliferation in culture and reduce tumor growth in vivo. Furthermore, legumain can be used as a marker for cancer detection and targeting due to its expression being significantly lower in normal cells compared to tumors or tumor-associated macrophages (TAMs). Tumor formation is influenced by aberrant expression of proteins and alterations in cellular architecture, but the tumor microenvironment is a crucial deciding factor. Legumain (LGMN) is an in vivo-active cysteine protease that catalyzes the degradation of numerous proteins. Its precise biological mechanism encompasses a number of routes, including effects on tumor-associated macrophage and neovascular endothelium in the tumor microenvironment. The purpose of this work is to establish a rationale for thoroughly investigating the function of LGMN in the tumor microenvironment and discovering novel tumor early diagnosis markers and therapeutic targets by reviewing the function of LGMN in tumor genesis and progression and its relationship with tumor milieu.

Asparaginyl endopeptidase contributes to cetuximab resistance via MEK/ERK signaling in RAS wide-type metastatic colorectal cancer

BACKGROUND

Cetuximab, a monoclonal antibody targeting epidermal growth factor receptor (EGFR), is effective for RAS wild-type metastatic colorectal cancer (mCRC) patients. However, cetuximab resistance often occur and the mechanism has not been fully elucidated. The purpose of this study was to investigate the role of asparaginyl endopeptidase (AEP) in cetuximab resistance.

METHODS

Differentially expressed genes between cetuximab responders and non-responders were identified by analyzing the gene expression profile GSE5851, retrieved from Gene Expression Omnibus (GEO). The potential genes were further validated in cetuximab-resistant CRC cell lines. The expression of AEP in the peripheral blood and tumor tissues of mCRC patients in our hospital were detected by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry, respectively. The survival analysis was carried out by Kaplan-Meier method. The function and associated pathways of AEP were further investigated by lentivirus transfection, CCK8 assay, colony formation assay, real-time polymerase chain reaction (qPCR) and western blot.

RESULTS

Through bioinformatics analysis, we found that the expression of AEP gene was related to progress free survival (PFS) of mCRC patients treated with cetuximab alone (P = 0.00133). The expression of AEP was significantly higher in the cetuximab-resistant CRC cell lines, as well as in mCRC patients with shorter PFS treated with cetuximab-containing therapy. Furthermore, AEP could decrease the sensitivity of CRC cells to cetuximab in vitro. And the phosphorylation level of MEK and ERK1/2 was increased in AEP overexpression cells. The downregulation of AEP using specific inhibitors could partially restore the sensitivity of CRC cells to cetuximab.

CONCLUSION

The higher expression of AEP could contribute to the shorter PFS of cetuximab treatment in mCRC. The reason might be that AEP could promote the phosphorylation of MEK/ERK protein in the downstream signal pathway of EGFR.

Structural and functional studies of legumain-mycocypin complexes revealed a competitive, exosite-regulated mode of interaction

Under pathophysiologic conditions such as Alzheimer’s disease and cancer, the endolysosomal cysteine protease legumain was found to translocate to the cytosol, the nucleus, and the extracellular space. These noncanonical localizations demand for a tight regulation of legumain activity, which is in part conferred by protein inhibitors. While there is a significant body of knowledge on the interaction of human legumain with endogenous cystatins, only little is known on its regulation by fungal mycocypins. Mycocypins are characterized by (i) versatile, plastic surface loops allowing them to inhibit different classes of enzymes and (ii) a high resistance toward extremes of pH and temperature. These properties make mycocypins attractive starting points for biotechnological and medical applications. In this study, we show that mycocypins utilize an adaptable reactive center loop to target the active site of legumain in a substrate-like manner. The interaction was further stabilized by variable, isoform-specific exosites, converting the substrate recognition into inhibition. Additionally, we found that selected mycocypins were capable of covalent complex formation with legumain by forming a disulfide bond to the active site cysteine. Furthermore, our inhibition studies with other clan CD proteases suggested that mycocypins may serve as broad-spectrum inhibitors of clan CD proteases. Our studies uncovered the potential of mycocypins as a new scaffold for drug development, providing the basis for the design of specific legumain inhibitors.

Protease-targeting peptide-functionalized porous silicon nanoparticles for cancer fluorescence imaging

Background: Porous silicon (pSi) nanoparticles (NPs) functionalized with suitable targeting ligands are now established cancer bioimaging agents and drug-delivery platforms. With growing interest in peptides as tumor-targeting ligands, much work has focused on the use of various peptides in combination with pSi NPs for cancer theranostics. Here, the authors investigated the targeting potential of pSi NPs functionalized with two types of peptide, a linear 10-mer peptide and its branched (Y-shaped) equivalent, that respond to legumain activity in tumor cells. Results: In vitro experiments established that the linear peptide-pSi NP conjugate had better aqueous stability under tumor conditions and higher binding efficiency (p < 0.001) toward legumain-expressing cells such as RAW 264.7 cells compared with that of its branched equivalent. In vivo studies (analyzed using ex vivo fluorescence) with the linear peptide-pSi NP formulation using a syngeneic mouse model of breast cancer showed a higher accumulation (p > 0.05) of linear peptide-conjugated pSi NPs in the tumor site within 4 h compared with nonconjugated pSi NPs. These results suggest that the linear peptide-pSi NP formulation is a nontoxic, stable and efficient fluorescence bioimaging agent and potential drug-delivery platform.

The Proteolytic Landscape of Ovarian Cancer: Applications in Nanomedicine

Ovarian cancer (OvCa) is one of the leading causes of mortality globally with an overall 5-year survival of 47%. The predominant subtype of OvCa is epithelial carcinoma, which can be highly aggressive. This review launches with a summary of the clinical features of OvCa, including staging and current techniques for diagnosis and therapy. Further, the important role of proteases in OvCa progression and dissemination is described. Proteases contribute to tumor angiogenesis, remodeling of extracellular matrix, migration and invasion, major processes in OvCa pathology. Multiple proteases, such as metalloproteinases, trypsin, cathepsin and others, are overexpressed in the tumor tissue. Presence of these catabolic enzymes in OvCa tissue can be exploited for improving early diagnosis and therapeutic options in advanced cases. Nanomedicine, being on the interface of molecular and cellular scales, can be designed to be activated by proteases in the OvCa microenvironment. Various types of protease-enabled nanomedicines are described and the studies that focus on their diagnostic, therapeutic and theranostic potential are reviewed.

Autocrine pro-legumain promotes breast cancer metastasis via binding to integrin αvβ3

Tumor metastasis is the leading cause of cancer-associated mortality. Unfortunately, the underlying mechanism of metastasis is poorly understood. Expression of legumain (LGMN), an endo-lysosomal cysteine protease, positively correlates with breast cancer metastatic progression and poor prognosis. Here, we report that LGMN is secreted in the zymogen form by motile breast cancer cells. Through binding to cell surface integrin αvβ3 via an RGD motif, the autocrine pro-LGMN activates FAK-Src-RhoA signaling in cancer cells and promotes cancer cell migration and invasion independent of LGMN protease activity. Either silencing LGMN expression or mutationally abolishing pro-LGMN‒αvβ3 interaction significantly inhibits cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Finally, we developed a monoclonal antibody against LGMN RGD motif, which blocks pro-LGMN‒αvβ3 binding, and effectively suppresses cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Thus, disruption of pro-LGMN‒integrin αvβ3 interaction may be a potentially promising strategy for treating breast cancer metastasis.

Combined legumain- and integrin-targeted nanobubbles for molecular ultrasound imaging of breast cancer

Molecular ultrasound imaging is a promising strategy for non-invasive and precise cancer diagnosis. Previously reported ultrasound contrast agents (UCAs) are mostly microbubbles or nanobubbles (NBs) larger than 200 nm, leading to less efficient tumor delivery. Here we synthesized NBs with a small size (~49 nm) and modified the NB surface with alanine-alanine-asparagine (NB-A) or arginine-glycine-aspartic acid peptide (NB-R) for concurrent active targeting towards legumain in tumor cells and integrin in tumor neovasculature. In vitro, the NB-A and NB-R presented echogenicity comparable with SonoVue MBs and showed specific binding with tumors cells and endothelial cells, respectively. In vivo, the combined NB-A/NB-R accumulated in tumor tissues selectively and provided ultrasound signals with prolonged duration and that were significantly stronger than non-targeted NBs, single-targeted NBs and SonoVue MBs. Overall, the dual targeted NBs served as efficient UCAs for specific imaging of breast cancer, and hold great potential for general cancer diagnosis/monitoring in the future.

The High Expression of Legumain in Canine Neoplasms: A Retrospective Analysis of 100 Cases

Simple Summary

Cancer is the leading cause of death in humans and is one of the most common canine diseases. The similarities in pathological features and tumor behaviors between spontaneous canine tumors and their human counterparts make dogs ideal models for comparative cancer research. Legumain is a novel asparaginyl endopeptidase that is overexpressed in numerous types of human tumors. Furthermore, legumain-targeted cancer therapy has been proposed, and the treatment efficacy is well-tolerated. Previous studies have shown that legumain regulates extracellular matrix degradation and triggers the invasion and the metastasis of tumors. However, in dogs, the role of legumain in the progression of tumors remains largely unknown, and few investigations have described the expression levels of this protein in canine tumors. The present study was carried out to evaluate whether legumain is expressed in ten different types of canine neoplasms. We found that heightened signals of legumain were expressed in all canine tumor samples in the study, and, notably, the non-mesenchymal types of tumors harbored relatively high expression levels. This study is the first to describe the legumain distribution pattern in a series of canine tumors. Though further investigation is needed, the current study has provided large-scale pan-screening data on legumain as a potential biomarker, or a therapeutic target, in veterinary oncology.

Abstract

Legumain, a novel asparaginyl endopeptidase, has been observed to be overexpressed in several types of human solid tumors. Elevated levels of legumain are found in human cancers, and this oncoprotein may facilitate tumor invasion and metastasis when overexpressed. These findings suggest that legumain plays a malignant role in cancer biology. However, currently, no publications have identified the role of legumain in the development of canine cancers. The present study first compared the expression patterns of legumain in paraffin-embedded canine tumor tissues, with those of normal tissues, by immunohistochemistry. A total of 100 canine tumor samples, including mast cell tumors, soft tissue sarcoma, hemangiosarcoma, lymphoma, mammary gland carcinoma, hepatoid gland tumor, squamous cell carcinoma, trichoblastoma, and melanoma were evaluated. Compared with the normal tissues, all tumor samples displayed high intensities of legumain expression. Mesenchymal-type tumors displayed immunoreactivity for legumain, with an average expression of 40.07% ± 1.70%, which was significantly lower than those of epithelial tumors and other types of tumors, which had median expressions of 49.12% ± 1.75% and 47.35% ± 2.71%, respectively (p < 0.05). These findings indicate that legumain has a high potential to be a candidate for distinguishing tumors from normal tissues. Although further studies on a larger number of cases are necessary to clarify the clinical application of legumain, the overexpression patterns of legumain in canine tumor tissues are reported, for the first time, in this study.

Expression of extracellular matrix proteins nidogen-1 and legumain in endometrial carcinomas

PURPOSE

Our purpose was to comparatively investigate the expressions of nidogen-1 (NID1) and legumain (LGMN) in patients with endometrial cancer, endometrial intraepithelial neoplasia, and proliferative endometrium.

METHODS

A cross-sectional, single-center study was performed by the obstetrics and gynecology and pathology departments of our institution. The relationships between descriptive data, clinicopathologic information, and immunohistochemical expressions of NID1 and LGMN were investigated.

RESULTS

The histological grades of endometrial cancers (n = 124) as classified by FIGO included 1 (41, 21.1%), 2 (48, 24.7%), and 3 (35, 18.0%). The medians and ranges of deep and superficial NID1 expressions were 50.00 (0-285) and 5.00 (0-100), respectively. The intensity of legumain expression was noted as negative (30, 24.2%), mild (16, 12.9%), moderate (27, 21.8%), or strong (51, 41.1%). Median disease-free survival and overall survival were 75.00 (range: 1 to 170) months and 77.00 (range: 1 to 170) months, respectively. Patients with more intense expression of NID1 and LGMN displayed a higher histological grade. These patients were more likely to have a positive peritoneal cytology, larger tumor size, higher tendency for myometrial or lymphovascular invasion, involvement of ovaries, cervix, omentum, as well as lymph node metastasis, and recurrence.

CONCLUSION

Our data indicated that the expressions of NID1 and LGMN may have important diagnostic implications in endometrial pathologies. Further studies should be performed to understand the significance of NID1 and LGMN in the pathogenesis of endometrial tumors.

A Novel Legumain-Like Protease in Macrobrachium nipponense: Identification, Characterization, and Function Analysis in Ovary Maturation

Legumain, also called aspartic endopeptidase (AEP), is a member of the cysteine protease family and is involved in various physiological processes. In this study, we analyzed the characteristics of a novel legumain-like (named Mn-Lel) in the female oriental river prawn, Macrobrachium nipponense, which is involved in ovary maturation. The Mn-Lel is 1,454 bp in length, including a 1,290-bp open reading frame that encodes 430 amino acids. qPCR analysis indicated that Mn-Lel is specifically highly expressed in the hepatopancreas and ovaries of female prawns. It is rarely expressed in embryogenesis, weakly expressed in early larval development stages, and then significantly increased after metamorphosis, which indicated that Mn-Lel is not a maternal gene and mainly plays a role in adults. During the different ovarian stages, Mn-Lel expression in the hepatopancreas had no obvious rules, while its expression in the ovaries had a significant peak in stage III. In situ hybridization studies revealed that Mn-Lel is localized in the oocyte of the ovary. Changes in the gonadosomatic index confirmed the inhibitory effects of Mn-Lel dsRNA on ovary maturation. These results suggest that Mn-Lel has a key role in promoting ovary maturation.

The Peptide Ligase Activity of Human Legumain Depends on Fold Stabilization and Balanced Substrate Affinities

Protein modification by enzymatic breaking and forming of peptide bonds significantly expands the repertoire of genetically encoded protein sequences. The dual protease-ligase legumain exerts the two opposing activities within a single protein scaffold. Primarily localized to the endolysosomal system, legumain represents a key enzyme in the generation of antigenic peptides for subsequent presentation on the MHCII complex. Here we show that human legumain catalyzes the ligation and cyclization of linear peptides at near-neutral pH conditions, where legumain is intrinsically unstable. Conformational stabilization significantly enhanced legumain's ligase activity, which further benefited from engineering the prime substrate recognition sites for improved affinity. Additionally, we provide evidence that specific legumain activation states allow for differential regulation of its activities. Together these results set the basis for engineering legumain proteases and ligases with applications in biotechnology and drug development.

Protease-triggered bioresponsive drug delivery for the targeted theranostics of malignancy

Proteases have a fundamental role in maintaining physiological homeostasis, but their dysregulation results in severe activity imbalance and pathological conditions, including cancer onset, progression, invasion, and metastasis. This striking importance plus superior biological recognition and catalytic performance of proteases, combining with the excellent physicochemical characteristics of nanomaterials, results in enzyme-activated nano-drug delivery systems (nanoDDS) that perform theranostic functions in highly specific response to the tumor phenotype stimulus. In the tutorial review, the key advances of protease-responsive nanoDDS in the specific diagnosis and targeted treatment for malignancies are emphatically classified according to the effector biomolecule types, on the premise of summarizing the structure and function of each protease. Subsequently, the incomplete matching and recognition between enzyme and substrate, structural design complexity, volume production, and toxicological issues related to the nanocomposites are highlighted to clarify the direction of efforts in nanotheranostics. This will facilitate the promotion of nanotechnology in the management of malignant tumors.

The Tumor Proteolytic Landscape: A Challenging Frontier in Cancer Diagnosis and Therapy

In recent decades, dysregulation of proteases and atypical proteolysis have become increasingly recognized as important hallmarks of cancer, driving community-wide efforts to explore the proteolytic landscape of oncologic disease. With more than 100 proteases currently associated with different aspects of cancer development and progression, there is a clear impetus to harness their potential in the context of oncology. Advances in the protease field have yielded technologies enabling sensitive protease detection in various settings, paving the way towards diagnostic profiling of disease-related protease activity patterns. Methods including activity-based probes and substrates, antibodies, and various nanosystems that generate reporter signals, i.e., for PET or MRI, after interaction with the target protease have shown potential for clinical translation. Nevertheless, these technologies are costly, not easily multiplexed, and require advanced imaging technologies. While the current clinical applications of protease-responsive technologies in oncologic settings are still limited, emerging technologies and protease sensors are poised to enable comprehensive exploration of the tumor proteolytic landscape as a diagnostic and therapeutic frontier. This review aims to give an overview of the most relevant classes of proteases as indicators for tumor diagnosis, current approaches to detect and monitor their activity in vivo, and associated therapeutic applications.

Esomeprazole inhibits the lysosomal cysteine protease legumain to prevent cancer metastasis

Legumain is a newly discovered lysosomal cysteine protease that can cleave asparagine bonds and plays crucial roles in regulating immunity and cancer metastasis. Legumain has been shown to be highly expressed in various solid tumors, within the tumor microenvironment and its levels are directly related to tumor metastasis and poor prognosis. Therefore, legumain presents as a potential cancer therapeutic drug target. In this study, we have identified esomeprazole and omeprazole as novel legumain small molecule inhibitors by screening an FDA approved-drug library. These compounds inhibited enzyme activity of both recombinant and endogenous legumain proteins with esomeprazole displaying the highest inhibitory effect. Further molecular docking analysis also indicated that esomeprazole, the S- form of omeprazole had the most stable binding to legumain protein compared to R-omeprazole. Transwell assay data showed that esomeprazole and omeprazole reduced MDA-MB-231 breast cancer cell invasion without effecting cell viability. Moreover, an in vivo orthotopic transplantation nude mouse model study showed that esomeprazole reduced lung metastasis of MDA-MB-231 breast cancer cells. These results indicated that esomeprazole has the exciting potential to be used in anti-cancer therapy by preventing cancer metastasis via the inhibition of legumain enzyme activity. Graphical abstract.

Asparaginyl endopeptidase may promote liver sinusoidal endothelial cell angiogenesis via PI3K/Akt pathway

BACKGROUND AND AIMS

pathological angiogenesis plays an important role in the progression of chronic liver diseases. Asparaginyl endopeptidase (AEP) participates in tumor angiogenesis and was recently shown to be associated with liver fibrosis. This study aimed to explore the effect of AEP on liver sinusoidal endothelial cell (LSECs) angiogenesis and determine the underlying mechanism.

METHODS

cultured LSECs were infected with lentiviruses in order to suppress AEP expression (AEP-KD1, AEP-KD2). The effect of AEP on LSECs proliferation, apoptosis and migration were subsequently determined by a CCK8 assay, flow cytometry and wound-healing and Transwell assays, respectively, in AEP knocked-down and control LSECs. The expression of the endothelial cell surface markers CD31, CD34 and von Willebrand factor (vWF) were detected by immunofluorescence assay and western blot. The angiogenic factors, vascular endothelial growth factor receptor 2 (VEGFR2) and interleukin 8 (IL 8) were detected by real-time PCR and western blot. The effect of AEP on vessel tube formation by LSECs was examined by Matrigel™ tube-formation assay. Phosphoinositide 3-kinase (PI3K)/Akt expression and phosphorylation were detected by western blot.

RESULTS

AEP was effectively knocked down by lentivirus infection in LSECs. Down-regulation of AEP expression significantly decreased proliferation and migration and increased apoptosis of LSECs. Moreover, expression levels of the endothelial cell surface markers CD31, CD34 and vWF, as well as angiogenic factors VEGFR2 and IL 8, were also reduced after AEP was knocked-down. The vessel tube formation abilities of AEP-KD1 and AEP-KD2 LSECs were significantly inhibited compared with LSECs without AEP knocked-down. Down-regulation of AEP also inhibited the phosphorylation of PI3K and Akt.

CONCLUSION

AEP promotes LSECs angiogenesis in vitro, possibly via the PI3K/Akt pathway. AEP may therefore be a potential therapeutic target for preventing the progression of liver fibrosis.

The exosomal integrin α5β1/AEP complex derived from epithelial ovarian cancer cells promotes peritoneal metastasis through regulating mesothelial cell proliferation and migration

PURPOSE

Epithelial ovarian cancer (EOC) is one of the most malignant cancers in the gynecologic system. Many patients are diagnosed at an advanced stage with disseminated intra-peritoneal metastases. EOC spreads via both direct extension and trans-coelomic spread. However, the interplay between human peritoneal mesothelial cells (HPMCs) and EOC cells is still ambiguous. We hypothesize that integrins (ITG) in HPMCs may play important roles in EOC metastasis.

METHODS

The expression of different integrin subtypes from HPMCs was assessed using Western blotting. The expression of integrin α5β1 (ITGA5B1) and its co-localization with asparaginyl endopeptidase (AEP) in HPMCs derived from EOC patients (EOC-HPMCs) were assessed using immunofluorescence. The role and mechanism of the exosomal ITGA5B1/AEP complex in HPMCs was assessed using both in vitro and in vivo assays. A retrospective study involving 234 cases was carried out to assess ITGA5B1 and AEP levels in circulating sera and ascites of EOC patients, as well as associations between ITGA5B1/AEP expression and overall survival.

RESULTS

We found that ITGA5B1was highly expressed and co-localized with AEP in EOC cells, and that the exosomal ITGA5B1/AEP complex secreted by EOC cells played an important role in the proliferation and migration of HPMCs. High levels of exosomal ITGA5B1/AEP were also found in circulating sera and ascites of EOC patients, and the expression of ITGA5B1/AEP in EOC tissues was found to be negatively associated with overall survival.

CONCLUSIONS

Our data indicate that EOCs may regulate the function of HPMCs through exosomal ITGA5B1/AEP, which may be crucial for peritoneal metastasis.

Design of a New Peptide Substrate Probe of the Putative Biomarker Legumain with Potential Application in Prostate Cancer Diagnosis Ex Vivo

The lysosomal endoprotease legumain (asparaginyl endoprotease) has been proposed as a putative biomarker in prostate tumours, in which the enzyme is markedly overexpressed. Overexpression, coupled with highly selective specificity for cleavage of substrates at the C-terminus of asparagine (Asn) residues, make legumain an attractive biochemical target for potential diagnosis, prognosis and treatment. We report the design, synthesis, characterisation and preliminary evaluation of a new rhodamine-B (Rho-B)-labelled legumain peptide substrate probe5[Rho-Pro-Ala-Asn-PEG-AQ(4-OH)] and its selective targeting to lysosomes in PC3 prostate cancer cells. Probe5was efficiently activated by recombinant human legumain to afford the high quantum yield reporter fluorophore tripeptide4b(Rho-Pro-Ala-Asn-OH) with concomitant release of intense fluorescence. Furthermore, probe5was activated upon incubation with homogenates derived from fresh-frozen tissue material of prostatectomy specimens. Probe5represents a new viable biochemical tool for probing the activity of legumain with the potential to be used in ex vivo diagnostics in the cancer pathology laboratory.

Synthesis and evaluation of radioactive/fluorescent peptide probes for imaging of legumain activity

Legumain or asparaginyl endopeptidase is an enzyme overexpressed in some cancers and involved in cancer migration, invasion, and metastasis. We have developed radioiodine- ([¹²⁵I]I-LCP) or fluorescein-labeled peptides (FL-LCP) with a cell-permeable d-Arg nonamer fused to an anionic d-Glu nonamer via a legumain-cleavable linker, to function as peptide probes that measure and monitor legumain activity. Non-cleavable probes of FL-NCP and [¹²⁵I]I-NCP were similarly prepared and evaluated as negative control probes by altering their non-cleavable sequence. Model peptides with the legumain-cleavable or non-cleavable sequence (LCP and NCP, respectively) reacted with recombinant human legumain, and only LCP was digested by this enzyme. [¹²⁵I]I-LCP uptake in legumain-positive HCT116 cells was significantly higher than that of [¹²⁵I]I-NCP (11.2 ± 0.44% vs 1.75 ± 0.06% dose/mg). The accumulation of FL-LCP in the HCT116 cells was rather low (4.75 ± 0.29% dose/mg protein), but not significantly different from the levels of FL-NCP. It is possible that low concentrations of [¹²⁵I]I-LCP (40 pM) can be effectively internalized after legumain cleavage. On the other hand, the cellular uptake of much higher concentrations of the FL-LCP derivative (1 mM) may be restricted by high concentrations of polyanions. The in vivo biodistribution studies in tumor-bearing mice demonstrated that the tumor uptake of [¹²⁵I]I-LCP was 1.34% injected dose per gram (% ID/g) at 30 min. The tumor/blood and tumor/muscle ratios at 30 min were 0.63 and 1.77, respectively, indicating that the [¹²⁵I]I-LCP accumulation in tumors was inadequate for in vivo imaging. Although further structural modifications are necessary to improve pharmacokinetic properties, [¹²⁵I]I-LCP has been demonstrated to be an effective scaffold for the development of nuclear medicine imaging probes to monitor legumain activity in living subjects.

PPA1 promotes NSCLC progression via a JNK- and TP53-dependent manner

Inorganic pyrophosphatase (PPA1) promotes tumor progression in several tumor types. However, the underlying mechanism remains elusive. Here, we disclosed that PPA1 expression is markedly upregulated in lung carcinoma tissue versus normal lung tissue. We also found that the non-small cell lung cancer (NSCLC) cell lines show increased PPA1 expression levels versus normal lung cell line control. Moreover, the knockdown of PPA1 promotes cell apoptosis and inhibits cell proliferation. Whereas, the ectopic expression of PPA1 reduces cell apoptosis and enhances cell proliferation. Most interestingly, the expression of mutant PPA1 (D117A) significantly abolishes PPA1-mediated effect on cell apoptosis and proliferation. The underlying mechanism demonstrated that TP53 expression deficiency or JNK inhibitor treatment could abolish PPA1-mediated NSCLC progression. In summary, the aforementioned findings in this study suggest a new pathway the PPA1 mediates NSCLC progression either via TP53 or JNK. Most important, the pyrophosphatase activity is indispensible for PPA1-mediated NSCLC progression. This may provide a promising target for NSCLC therapy.

Mechanism of Tau Hyperphosphorylation Involving Lysosomal Enzyme Asparagine Endopeptidase in a Mouse Model of Brain Ischemia

Dementias including Alzheimer's disease (AD) are multifactorial disorders that involve several different etiopathogenic mechanisms. Cerebral ischemia has been suspected in the altered regulation of protein kinases and phosphatases that leads to hyperphosphorylation of tau and further neurofibrillary pathology, a key hallmark of AD and related neurodegenerative diseases. However, the deregulation of these enzymes and their relationship with ischemia and AD remain unclear. Previously, we reported a mechanism by which the lysosomal enzyme asparagine endopeptidase (AEP) is associated with brain acidosis and AD. In this study, we subjected mice to middle cerebral artery occlusion and found that compared with wild type mice, the ischemia-induced brain injury and motor deficit in AEP-knockout mice are reduced, probably because ischemia activates AEP. AEP cleaves inhibitor 2 of protein phosphatase 2A (I2PP2A), which translocates from the neuronal nucleus to the cytoplasm and produces hyperphosphorylation of tau through inhibition of PP2A. These findings suggest a possible mechanism of tau pathology associated with ischemia.

A protease-responsive fluorescent probe for sensitive imaging of legumain activity in living tumor cells

Legumain, a lysosomal cysteine protease, is critical for pathological progression and has been found to play an important role in the occurrence and development of several cancers. However, its biological functions remain few recognized. To further understand the role of legumain activity in tumor progression, a legumain protease-responsive fluorescent probe was developed in the present study. The probe 1 was synthesized by conjugating an aminoluciferin fluorophore with an alanine-alanine-asparagine (AAN) peptide sequence. The successful synthesis of probe 1 was validated by NMR and MS spectra as well as HPLC analysis. The probe 1 was non-toxic and exhibited great stability in the physiological solutions. More importantly, compared with the aminoluciferin fluorophore, the peptide conjugation may dramatically increase the targeting specificity. Probe 1 was able to effectively detect the legumain activity in living HCT116 cells through fluorescence imaging. All these results implied that probe 1 could act as a promising fluorescent probe specialized for the monitoring of legumain activity in living cells.

Asparaginyl endopeptidase induces endothelial permeability and tumor metastasis via downregulating zonula occludens protein ZO-1

Zona occludens-1 (ZO-1) is a key component of tight junctions that govern the function of the endothelial barrier against tumor metastasis. Factors secreted by tumor cells contribute to the maintenance of tumor vascular networks. How tumor cell-derived protein signals regulate ZO-1 expression is unclear. Here, we explored the effect of tumor cell-secreted asparaginyl endopeptidase (AEP) on the permeability of endothelial cells in the tumor microenvironment. First, we confirmed the existence of AEP in conditioned medium (CM) from AEP-overexpressing MDA-MB-231 and 4T1 cells. Treatment with CM from AEP-overexpressing tumor cells increased the permeability and tumor cell transversal of an endothelial monolayer. Furthermore, CM from AEP-overexpressing tumor cells suppressed endothelial ZO-1 expression, as well as ZO-1-associated nucleic acid binding protein ZONAB. In addition, the level of phosphorylated STAT3 was increased by treatment with AEP-containing CM. A mutation of RGD or blocking integrin αvβ3 with antibody recovered the ZO-1 downregulation induced by AEP. In vivo, a lung metastatic mouse model showed increased endothelial permeability in the AEP-overexpressing group compared with the control group. An orthotopic tumor transplantation model was established using AEP-overexpression and compared with mice receiving control 4T1 cells. Compared with controls, overexpression of AEP increased lung metastatic foci and area, as well as vascular instability in primary tumors or lung metastatic sites. Moreover, endothelial ZO-1 was decreased in the AEP-overexpressing group. Taken together, our data show that tumor cell-derived AEP increases the permeability of endothelial barriers. Interactions between RGD and endothelial integrin αvβ3 mediate this effect by downregulating ZO-1.

Legumain is an independent predictor for invasive recurrence in breast ductal carcinoma in situ

Legumain is a proteolytic enzyme that plays a role in the regulation of cell proliferation in invasive breast cancer. Studies evaluating its role in ductal carcinoma in situ (DCIS) are lacking. Here, we aimed to characterize legumain protein expression in DCIS and evaluate its prognostic significance. Legumain was assessed immunohistochemically in a tissue microarray of a well-characterized cohort of DCIS (n = 776 pure DCIS and n = 239 DCIS associated with invasive breast cancer (DCIS-mixed)). Legumain immunoreactivity was scored in tumor cells and surrounding stroma and related to clinicopathological parameters and patient outcome. High legumain expression was observed in 23% of pure DCIS and was associated with features of high-risk DCIS including higher nuclear grade, comedo necrosis, hormone receptor negativity, HER2 positivity, and higher proliferation index. Legumain expression was higher in DCIS associated with invasive breast cancer than in pure DCIS (p < 0.0001). In the DCIS-mixed cohort, the invasive component showed higher legumain expression than the DCIS component (p < 0.0001). Legumain was an independent predictor of shorter local recurrencefree interval for all recurrences (p = 0.0003) and for invasive recurrences (p = 0.002). When incorporated with other risk factors, legumain provided better patient risk stratification. High legumain expression is associated with poor prognosis in DCIS and could be a potential marker to predict DCIS progression to invasive disease.

Application of nanotechnology to target and exploit tumour associated proteases

Proteases are hydrolytic enzymes fundamental for a variety of physiological processes, but the loss of their regulation leads to aberrant functions that promote onset and progression of many diseases including cancer. Proteases have been implicated in almost every hallmark of cancer and whilst widely investigated for tumour therapy, clinical adoption of protease inhibitors as drugs remains a challenge due to issues such as off-target toxicity and inability to achieve therapeutic doses at the disease site. Now, nanotechnology-based solutions and strategies are emerging to circumvent these issues. In this review, preclinical advances in approaches to enhance the delivery of protease drugs and the exploitation of tumour-derived protease activities to promote targeting of nanomedicine formulations is examined. Whilst this field is still in its infancy, innovations to date suggest that nanomedicine approaches to protease targeting or inhibition may hold much therapeutic and diagnostic potential.

USP17 Suppresses Tumorigenesis and Tumor Growth through Deubiquitinating AEP

Ubiquitin-specific protease 17 (USP17), a novel member of deubiquitinase, is reported to play essential roles in several solid tumors. However, the expression and function of USP17 in breast cancer tumorigenesis remains ambiguity. Here we found that the mRNA level of USP17 was lower in breast cancer tissues than normal tissues. Meanwhile, higher USP17 level was detected in normal epithelial cell MCF-10A and a less-malignant cell MCF-7 than malignant cell line MDA-MB-231. Inhibition of USP17 in MCF7 cells enhanced tumorigenesis and tumor growth while overexpression of USP17 in malignant MDA-MB-231 cells reduced its tumorigenesis and growth ability in vitro and in vivo. Further study revealed that USP17 interacted with and deubiquitinated Asparaginyl endopeptidase (AEP), resulting in decreased protein levels of AEP. Moreover, knockdown of AEP inhibited breast cancer tumorigenesis and growth in vitro and in vivo through the inactivation of ERK signaling. Taken together, our works indicate that USP17 deubiquitinates AEP, down-regulates its protein level, and inhibits breast cancer tumorigenesis through disturbing ERK signaling. Thus, our data suggests that USP17 is a potential tumor suppressor in breast cancer and AEP is a promising target in breast cancer therapy.

Mass spectrometry-based proteomics techniques and their application in ovarian cancer research

Ovarian cancer has emerged as one of the leading cause of gynecological malignancies. So far, the measurement of CA125 and HE4 concentrations in blood and transvaginal ultrasound examination are essential ovarian cancer diagnostic methods. However, their sensitivity and specificity are still not sufficient to detect disease at the early stage. Moreover, applied treatment may appear to be ineffective due to drug-resistance. Because of a high mortality rate of ovarian cancer, there is a pressing need to develop innovative strategies leading to a full understanding of complicated molecular pathways related to cancerogenesis. Recent studies have shown the great potential of clinical proteomics in the characterization of many diseases, including ovarian cancer. Therefore, in this review, we summarized achievements of proteomics in ovarian cancer management. Since the development of mass spectrometry has caused a breakthrough in systems biology, we decided to focus on studies based on this technique. According to PubMed engine, in the years 2008-2010 the number of studies concerning OC proteomics was increasing, and since 2010 it has reached a plateau. Proteomics as a rapidly evolving branch of science may be essential in novel biomarkers discovery, therapy decisions, progression predication, monitoring of drug response or resistance. Despite the fact that proteomics has many to offer, we also discussed some limitations occur in ovarian cancer studies. Main difficulties concern both complexity and heterogeneity of ovarian cancer and drawbacks of the mass spectrometry strategies. This review summarizes challenges, capabilities, and promises of the mass spectrometry-based proteomics techniques in ovarian cancer management.

Understanding Ovarian Cancer: iTRAQ-Based Proteomics for Biomarker Discovery

Despite many years of studies, ovarian cancer remains one of the top ten cancers worldwide. Its high mortality rate is mainly due to lack of sufficient diagnostic methods. For this reason, our research focused on the identification of blood markers whose appearance would precede the clinical manifestation of the disease. ITRAQ-tagging (isobaric Tags for Relative and Absolute Quantification) coupled with mass spectrometry technology was applied. Three groups of samples derived from patients with: ovarian cancer, benign ovarian tumor, and healthy controls, were examined. Mass spectrometry analysis allowed for highlighting the dysregulation of several proteins associated with ovarian cancer. Further validation of the obtained results indicated that five proteins (Serotransferrin, Amyloid A1, Hemopexin, C-reactive protein, Albumin) were differentially expressed in ovarian cancer group. Interestingly, the addition of Albumin, Serotransferrin, and Amyloid A1 to CA125 (cancer antigen 125) and HE4 (human epididymis protein4) improved the diagnostic performance of the model discriminating between benign and malignant tumors. Identified proteins shed light on the molecular signaling pathways that are associated with ovarian cancer development and should be further investigated in future studies. Our findings indicate five proteins with a strong potential to use in a multimarker test for screening and detection of ovarian cancer.

Fbxw11 promotes the proliferation of lymphocytic leukemia cells through the concomitant activation of NF-κB and β-catenin/TCF signaling pathways

The ubiquitin–proteasome system (UPS) participates in both physiological and pathological processes through the posttranslational regulation of intracellular signal transduction pathways. F-box and WD-40 domain protein 11 (Fbxw11) is a component of the SCF (Skp1–Cul1–F-box) E3 ubiquitin ligase complex. Fbxw11 regulates various signal transduction pathways, and it may have pathological roles in tumorigenesis. However, the role of Fbxw11 in the development of leukemia and the underlying mechanisms remain largely unknown. In this study, Fbxw11 expression was aberrantly upregulated in patients with lymphocytic leukemia. Its expression was dramatically decreased in patients who achieved complete remission (CR) after chemotherapy. The high level of Fbxw11 expression in L1210 lymphocytic leukemia cells stimulated cell proliferation in vitro and tumor formation in vivo. The effects were mediated by the stimulation of cell cycle progression rather than the induction of apoptosis. Furthermore, a bioinformatics analysis suggested concomitant activation of the NF-κB and β-catenin/TCF signaling pathways, which were confirmed by reporter gene assays. Moreover, blocking experiments suggested the involvement of both pathways in the growth-promoting effects of Fbxw11. Our results reveal the role of Fbxw11 in lymphocytic leukemia cells and imply that Fbxw11 may serve as a potential molecular target for the treatment of lymphocytic leukemia.

Asparaginyl endopeptidase enhances pancreatic ductal adenocarcinoma cell invasion in an exosome-dependent manner and correlates with poor prognosis

Pancreatic cancer is one of the most lethal types of cancer; owing to low early detection rates and high metastasis rates, it is associated with an extremely poor prognosis. Therefore, a better understanding of the molecular mechanisms that underlie its metastasis and the identification of potential prognostic biomarkers are urgently required. Although high expression levels of asparaginyl endopeptidase (AEP) have been detected in various types of solid tumor, the expression and functions of AEP in pancreatic carcinomas have yet to be determined. The present study aimed to examine the putative functions of AEP in pancreatic carcinoma. Immunohistochemical analysis revealed that AEP was highly expressed in pancreatic cancer tissues compared with adjacent normal tissues. Patients with high AEP expression exhibited a significantly shorter overall survival time. Results from multivariate Cox regression analysis revealed that AEP was an independent prognostic factor for overall survival. Gain- and loss-of-function experiments demonstrated that knockdown of AEP expression significantly reduced the invasive ability of pancreatic cancer cells, whereas overexpression of AEP increased the invasive ability. In addition, AEP was detected in exosomes that were derived from cultured pancreatic ductal adenocarcinoma cells (PDACs) and in the serum from patients with PDAC. The Matrigel-Transwell invasion assay revealed that exosomes enriched with AEP were able to enhance the invasive ability of PDAC cells, whereas exosomes lacking AEP decreased the invasive ability. Furthermore, results from the present study suggested that AEP may be crucial for activation of the phosphoinositide 3-kinase/RAC‑α serine/threonine-protein kinase signaling pathway in PDAC cells. The present study data indicated that high AEP expression may be important for pancreatic carcinoma progression in an exosome-dependent manner, and that AEP may be an independent indicator of poor prognosis in patients with PDAC and may be a novel prognostic biomarker or therapeutic target in pancreatic carcinoma.

MiRNA-3978 regulates peritoneal gastric cancer metastasis by targeting legumain

Gastric cancer incidence and mortality are among the highest in China, with majority of the mortality related to peritoneal metastasis of gastric cancer. Treatment is limited to radical resection, which is impeded by incidence of metastasis at time of initial diagnosis, thus making it imperative to identify diagnostic and prognostic biomarkers. Legumain, a lysosomal cysteine endopeptidase of the asparaginyl endopeptidase family, has been shown to be overexpressed in patients with metastatic gastric cancer disease and its expression was positively correlated to both disease progression and outcome. However, the mechanism of legumain expression is currently unknown. Legumain overexpression was found to occur at the level of post transcriptional gene regulation. In situ prediction algorithms identified legumain as a putative target of miR-3978. MiR-3978 was significantly decreased in peritoneal metastatic tissue specimens and in MKN45 cells that mimic peritoneal metastasis features. Reporter assays using LGMN (encoding legumain) 3′ untranslated region (UTR) showed that miR-3978 interacted with the wild-type but not miR-3978-seed mutant. Ectopic expression of miR-3978 mimic in the MKN45 cell line significantly decreased proliferation and suppressed in vitro migration and invasion. The miR-3978 mimic inhibited gastric carcinoma and metastatic progression in a mice model by regulating legumain protein expression. Inverse correlation of LGMN mRNA and miR-3978 levels in 20 gastric patients at different stages of metastatic disease confirmed the same. Cumulatively, our results indicate that loss of miR-3978 leads to increased expression of legumain, which indicates that miR-3978might be a biomarker for peritoneal metastasis in patients with gastric cancer.

Asparaginyl endopeptidase promotes the invasion and metastasis of gastric cancer through modulating epithelial-to-mesenchymal transition and analysis of their phosphorylation signaling pathways

Asparaginyl endopeptidase (AEP) is a lysosomal protease often overexpressed in gastric cancer. AEP was expressed higher in peritoneal metastatic loci than in primary gastric cancer. Then we overexpressed AEP or knocked it down with a lentiviral vector in gastric cancer cell lines and detected the cell cycle arrest and the changes of the invasive and metastatic ability in vitro and in vivo. When AEP was knocked-down, the proliferative, invasive and metastatic capacity of gastric cancer cells were inhibited, and the population of sub-G1 cells increased. AEP knockdown led to significant decrease of expression of transcription factor Twist and the mesenchymal markers N-cadherin, ß-catenin and Vimentin and to increased expression of epithelial marker E-cadherin. These results showed that AEP could promote invasion and metastasis by modulating EMT. We used phosphorylation-specific antibody microarrays to investigate the mechanism how AEP promotes gastric cancer invasion and metastasis, and found that the phosphorylation level of AKT and MAPK signaling pathways was decreased significantly if AEP was knocked-down. Therefore, AKT and MAPK signaling pathways took part in the modulation.

Expression of both poly r(C) binding protein 1 (PCBP1) and miRNA-3978 is suppressed in peritoneal gastric cancer metastasis

The expression of legumain which has been shown overexpressed in patients with metastatic gastric cancer is positively correlated to both disease progression and outcome, and negatively correlated to microRNA (miR)-3978 expression. The RNA-binding protein, poly r(C) binding protein 1 (PCBP1) was the most downregulated protein in the metastatic tissue specimens. Quantitative real-time PCR showed that PCBP1 expression is transcriptionally downregulated in peritoneal metastasis tissues. RNA immunoprecipitation experiments showed that PCBP1 and miR-3978 are sequestered in normal peritoneal tissue, but the complex is disrupted following metastatic progression. PCBP1 expression mimicked miR-3978 expression across gastric cancer patients. Finally, replenishment of PCBP1 or miR-3978 expression in the peritoneal metastasis cell line MKN45 decreased legumain protein expression and chemosensitized the cells to treatment with docetaxel. However, replenishment of one and concomitant depletion of the other failed to induce chemosensitivity to docetaxel. Replenishment of miR-3978 also resulted in induction of PCBP1 protein expression, potentially indicating that miR-3978 expression might downregulate a negative regulator targeting PCBP1. Our current study reveals PCBP1 as an additional biomarker in peritoneal metastasis. PCBP1 and miR-3978 expression were correlated and suggests a potential interplay of differential miRNA biogenesis and RNA binding protein during metastatic progression.

Blockade of Asparagine Endopeptidase Inhibits Cancer Metastasis

Asparagine endopeptidase (AEP), also called legumain, is highly expressed in various solid tumors, promoting cancer cell invasion, migration, and metastasis. It has been proposed to be a prognostic marker and therapeutic target for cancer treatment. However, an effective nonpeptide, small-molecule inhibitor against this protease has not yet been identified. Here we show that a family of xanthine derivatives selectively inhibit AEP and suppress matrix metalloproteinase (MMP) cleavage, leading to the inhibition of cancer metastasis. Through structure-activity relationship (SAR) analysis, we obtained an optimized lead compound (38u) that represses breast cancer invasion and migration. Chronic treatment of nude mice, which had been inoculated with MDA-MB-231 cells, with inhibitor 38u via oral administration robustly inhibits breast cancer lung metastasis in a dose-dependent manner, associated with blockade of MMP-2 by AEP. Therefore, our study supports that 38u might act as a potent and specific AEP inhibitor useful for cancer treatment.

Kaposi's sarcoma-associated herpesvirus infection promotes differentiation and polarization of monocytes into tumor-associated macrophages

Tumor associated macrophages (TAMs) promote angiogenesis, tumor invasion and metastasis, and suppression of anti-tumor immunity. These myeloid cells originate from monocytes, which differentiate into TAMs upon exposure to the local tumor microenvironment. We previously reported that Kaposi's sarcoma-associated herpes virus (KSHV) infection of endothelial cells induces the cytokine angiopoietin-2 (Ang-2) to promote migration of monocytes into tumors. Here we report that KSHV infection of endothelial cells induces additional cytokines including interleukin-6 (IL-6), interleukin-10 (IL-10), and interleukin-13 (IL-13) that drive monocytes to differentiate and polarize into TAMs. The KSHV-induced TAMs not only express TAM-specific markers such as CD-163 and legumain (LGMN) but also display a gene expression profile with characteristic features of viral infection. More importantly, KSHV-induced TAMs enhance tumor growth in nude mice. These results are consistent with the strong presence of TAMs in Kaposi's sarcoma (KS) tumors. Therefore, KSHV infection of endothelial cells generates a local microenvironment that not only promotes the recruitment of monocytes but also induces their differentiation and polarization into TAMs. These findings reveal a new mechanism of KSHV contribution to KS tumor development.

Silencing PPA1 inhibits human epithelial ovarian cancer metastasis by suppressing the Wnt/β-catenin signaling pathway

Inorganic pyrophosphatase (PPA1) activity is a key determinant of cellular inorganic pyrophosphate levels, and its expression is correlated with growth of several solid tumors. To investigate this relationship, we first examined PPA1 expression in human epithelial ovarian cancer (EOC) samples, and found that PPA1 was overexpressed in tumors from EOC patients. Higher PPA1 levels correlated with advanced grades, stages, and poor survival in EOC patients. Examination of PPA1 function in EOC revealed that silencing PPA1 inhibited EOC migration, epithelial-mesenchymal transition (EMT), and metastasis in vitro and in vivo. In addition, PPA1 may promote the dephosphorylation and translocation of β-catenin. These results demonstrate that silencing PPA1 inhibits EOC metastasis by suppressing the Wnt/β-catenin signaling pathway. Strategies for downregulating PPA1 may have therapeutic potential for the prevention and treatment of EOC.

Legumain-cleavable 4-arm poly(ethylene glycol)-doxorubicin conjugate for tumor specific delivery and release

Traditional chemotherapy strategy exists undesirable toxic side-effects to normal tissues due to the low selectively to cancer cells of micromolecule cytotoxic drugs. One considered method to realizing the targeted delivery and increasing the specificity to tumor tissues of the cytotoxic drug is to transporting and discharging it through an environment-sensitive mechanism. In this study, a novel enzyme-sensitive polymer-doxorubicin conjugate was designed to delivery chemotherapeutic drug in a tumor-specific behavior and selectively activated in tumor tissue. Briefly, doxorubicin (DOX) was conjugated to carboxyl-terminated 4-arm poly(ethylene glycol) through a tetrapeptide linker, alanine-alanine-asparagine-leucine (AANL), which was one of the substrates of legumain, an asparaginyl endopeptidase that was found presented in plants, mammals and also highly expressed in human tumor tissues. Hereinafter, the polymer-DOX conjugate was termed as 4-arm PEG-AANL-DOX. Dynamic laser scattering (DLS) and transmission electron microscopy (TEM) measurements indicated that the 4-arm PEG-AANL-DOX could self-assemble into micelles in aqueous solution. Drug release and in vitro cytotoxicity studies revealed that the 4-arm PEG-AANL-DOX could be cleaved by legumain. Ex vivo DOX fluorescence imaging measurements demonstrated that the 4-arm PEG-AANL-DOX had an improved tumor-targeting delivery as compared with the free DOX·HCl. In vivo studies on nude mice bearing MDA-MB-435 tumors revealed that the 4-arm PEG-AANL-DOX had a comparable anticancer efficacy with the free DOX·HCl but without DOX-related toxicities to normal tissues as measured by body weight change and histological assessments, indicating that the 4-arm PEG-AANL-DOX had an improved therapeutic index for cancer therapy.

STATEMENT OF SIGNIFICANCE

Herein we describe the construction of a novel tumor environment-sensitive delivery system through the instruction of a legumain-cleavable linkage to a polymer-DOX conjugate (4-arm PEG-AANL-DOX). This particular design strategy allows for polymer-DOX conjugates to be delivered in a tumor-specific manner and selectively activable in tumor microenvironment so that it can combine the advantages of tumor-specific delivery and tumor intracellular microenvironment-triggered release systems.

Molecular imaging of the tumor microenvironment

The tumor microenvironment plays a critical role in tumor initiation, progression, metastasis, and resistance to therapy. It is different from normal tissue in the extracellular matrix, vascular and lymphatic networks, as well as physiologic conditions. Molecular imaging of the tumor microenvironment provides a better understanding of its function in cancer biology, and thus allowing for the design of new diagnostics and therapeutics for early cancer diagnosis and treatment. The clinical translation of cancer molecular imaging is often hampered by the high cost of commercialization of targeted imaging agents as well as the limited clinical applications and small market size of some of the agents. Because many different cancer types share similar tumor microenvironment features, the ability to target these biomarkers has the potential to provide clinically translatable molecular imaging technologies for a spectrum of cancers and broad clinical applications. There has been significant progress in targeting the tumor microenvironment for cancer molecular imaging. In this review, we summarize the principles and strategies of recent advances made in molecular imaging of the tumor microenvironment, using various imaging modalities for early detection and diagnosis of cancer.

Asparaginyl endopeptidase improves the resistance of microtubule-targeting drugs in gastric cancer through IQGAP1 modulating the EGFR/JNK/ERK signaling pathway

PURPOSE

In recent years, understanding of the role of asparaginyl endopeptidase (AEP) in tumorigenesis has steadily increased. In this study, we investigated whether AEP expression correlates with sensitivity to chemotherapeutic drugs in gastric cancer and explored the mechanism.

PATIENTS AND METHODS

AEP expression in the serum of patients' peripheral blood was measured by enzyme-linked immunosorbent assay. Patient survival time was evaluated using univariate and multivariate analyses. Mass spectrometry and co-immunoprecipitation assays were utilized to discover proteins that interact with AEP. Gastric cancer cell lines were established, in which AEP was overexpressed or knocked out using lentiviral CRISPR. The proliferative abilities of these cell lines in response to chemotherapy agents were evaluated using the Cell Counting Kit-8 method. Gene expression changes in these lines were assessed by real-time polymerase chain reaction and Western blot.

RESULTS

Patients with low expression of AEP were significantly more likely to have a good prognosis and experience complete response or partial response after treatment with docetaxel/S-1 regimen. Mass spectrum analysis showed that several proteins in the focal adhesion and mitogen-activated protein kinase signaling pathways interacted with AEP. IQGAP1 was confirmed to be one of the proteins interacting with AEP, and its protein level increased when AEP was knocked out. AEP knockout decreased resistance to microtubule inhibitors, including paclitaxel, docetaxel, and T-DM1. The expression levels of MDR1, p-EGFR, p-JNK, p-ERK, and p-Rac1/cdc42 were decreased in AEP knockout gastric cancer cell lines, and inhibitors of both JNK and ERK could block AEP-induced expression of MDR1.

CONCLUSION

AEP was not only a prognostic factor but also a predictive marker. AEP knockout could inhibit the activity of the EGFR/JNK/ERK signaling pathway and improve sensitivity to microtubule inhibitors through interacting with IQGAP1.

Legumain Regulates Differentiation Fate of Human Bone Marrow Stromal Cells and Is Altered in Postmenopausal Osteoporosis

Secreted factors are a key component of stem cell niche and their dysregulation compromises stem cell function. Legumain is a secreted cysteine protease involved in diverse biological processes. Here, we demonstrate that legumain regulates lineage commitment of human bone marrow stromal cells and that its expression level and cellular localization are altered in postmenopausal osteoporotic patients. As shown by genetic and pharmacological manipulation, legumain inhibited osteoblast (OB) differentiation and in vivo bone formation through degradation of the bone matrix protein fibronectin. In addition, genetic ablation or pharmacological inhibition of legumain activity led to precocious OB differentiation and increased vertebral mineralization in zebrafish. Finally, we show that localized increased expression of legumain in bone marrow adipocytes was inversely correlated with adjacent trabecular bone mass in a cohort of patients with postmenopausal osteoporosis. Our data suggest that altered proteolytic activity of legumain in the bone microenvironment contributes to decreased bone mass in postmenopausal osteoporosis.

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Legumain determines differentiation fate of BMSCs in vitro and in vivo

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Legumain regulates BMSC proliferation independent of its enzymatic activity

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Inhibition of legumain leads to precocious bone formation in zebrafish

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Legumain is overexpressed in bone marrow adipocytes of osteoporotic patients

Protease activity of legumain is inhibited by an increase of cystatin E/M in the DJ-1-knockout mouse spleen, cerebrum and heart

Legumain (EC 3.4.22.34) is an asparaginyl endopeptidase. Legumain activity has been detected in various mouse tissues including the kidney, spleen and epididymis. Legumain is overexpressed in the majority of human solid tumors and transcription of the legumain gene is regulated by the p53 tumor suppressor in HCT116 cells. The legumain activity is also increased under acid conditions in Alzheimer's disease brains. DJ-1/PARK7, a cancer- and Parkinson's disease-associated protein, works as a coactivator to various transcription factors, including the androgen receptor, p53, PSF, Nrf2, SREBP and RREB1. Recently, we found that legumain expression, activation and cleavage of annexin A2 are regulated by DJ-1 through p53. In this study, we found that the expression levels of legumain mRNA were increased in the cerebrum, kidney, spleen, heart, lung, epididymis, stomach, small intestine and pancreas from DJ-1-knockout mice, although legumain activity levels were decreased in the cerebrum, spleen and heart from DJ-1-knockout mice. Furthermore, we found that cystatin E/M expression was increased in the spleen, cerebrum and heart from DJ-1-knockout mice. These results suggest that reduction of legumain activity is caused by an increase of cystatin E/M expression in the spleen, cerebrum and heart from DJ-1-knockout mice.

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Legumain is strongly activated in the epididymis from DJ-1-knockout mice.

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Expression level of legumain mRNA is increased but activity is decreased in the spleen, cerebrum and heart from DJ-1-knockout mice.

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Expression level of cystatin E/M is increased in the spleen, cerebrum and heart from DJ-1-knockout mice.

The High Mobility Group A1 (HMGA1) Transcriptome in Cancer and Development

BACKGROUND & OBJECTIVES

Chromatin structure is the single most important feature that distinguishes a cancer cell from a normal cell histologically. Chromatin remodeling proteins regulate chromatin structure and high mobility group A (HMGA1) proteins are among the most abundant, nonhistone chromatin remodeling proteins found in cancer cells. These proteins include HMGA1a/HMGA1b isoforms, which result from alternatively spliced mRNA. The HMGA1 gene is overexpressed in cancer and high levels portend a poor prognosis in diverse tumors. HMGA1 is also highly expressed during embryogenesis and postnatally in adult stem cells. Overexpression of HMGA1 drives neoplastic transformation in cultured cells, while inhibiting HMGA1 blocks oncogenic and cancer stem cell properties. Hmga1 transgenic mice succumb to aggressive tumors, demonstrating that dysregulated expression of HMGA1 causes cancer in vivo. HMGA1 is also required for reprogramming somatic cells into induced pluripotent stem cells. HMGA1 proteins function as ancillary transcription factors that bend chromatin and recruit other transcription factors to DNA. They induce oncogenic transformation by activating or repressing specific genes involved in this process and an HMGA1 "transcriptome" is emerging. Although prior studies reveal potent oncogenic properties of HMGA1, we are only beginning to understand the molecular mechanisms through which HMGA1 functions. In this review, we summarize the list of putative downstream transcriptional targets regulated by HMGA1. We also briefly discuss studies linking HMGA1 to Alzheimer's disease and type-2 diabetes.

CONCLUSION

Further elucidation of HMGA1 function should lead to novel therapeutic strategies for cancer and possibly for other diseases associated with aberrant HMGA1 expression.