Low-level internalization of cystatin E/M affects legumain activity and migration of melanoma cells

Type 2 Cystatins and Their Roles in the Regulation of Human Immune Response and Cancer Progression

Cystatins are a family of intracellular and extracellular protease inhibitors that inhibit cysteine cathepsins-a group of lysosomal cysteine proteases that participate in multiple biological processes, including protein degradation and post-translational cleavage. Cysteine cathepsins are associated with the development of autoimmune diseases, tumor progression, and metastasis. Cystatins are categorized into three subfamilies: type 1, type 2, and type 3. The type 2 cystatin subfamily is the largest, containing 10 members, and consists entirely of small secreted proteins. Although type 2 cystatins have many shared biological roles, each member differs in structure, post-translational modifications (e.g., glycosylation), and expression in different cell types. These distinctions allow the type 2 cystatins to have unique biological functions and properties. This review provides an overview of type 2 cystatins, including their biological similarities and differences, their regulatory effect on human immune responses, and their roles in tumor progression, immune evasion, and metastasis.

Non-invasive diagnosis of early cutaneous squamous cell carcinoma

Early cutaneous squamous cell carcinoma (cSCC) can be challenging to diagnose using clinical criteria as it could present similar to actinic keratosis (AK) or Bowen's disease (BD), precursors of cSCC. Currently, histopathological assessment of an invasive biopsy is the gold standard for diagnosis. A non-invasive diagnostic approach would reduce patient and health system burden. Therefore, this study used non-invasive sampling by tape-stripping coupled with data-independent acquisition mass spectrometry (DIA-MS) proteomics to profile the proteome of histopathologically diagnosed AK, BD and cSCC, as well as matched normal samples. Proteomic data were analysed to identify proteins and biological functions that are significantly different between lesions. Additionally, a support vector machine (SVM) machine learning algorithm was used to assess the usefulness of proteomic data for the early diagnosis of cSCC. A total of 696 proteins were identified across the samples studied. A machine learning model constructed using the proteomic data classified premalignant (AK + BD) and malignant (cSCC) lesions at 77.5% accuracy. Differential abundance analysis identified 144 and 21 protein groups that were significantly changed in the cSCC, and BD samples compared to the normal skin, respectively (adj. p < 0.05). Changes in pivotal carcinogenic pathways such as LXR/RXR activation, production of reactive oxygen species, and Hippo signalling were observed that may explain the progression of cSCC from premalignant lesions. In summary, this study demonstrates that DIA-MS analysis of tape-stripped samples can identify non-invasive protein biomarkers with the potential to be developed into a complementary diagnostic tool for early cSCC.

Novel CSF biomarkers for diagnosis and integrated analysis of neuropsychiatric systemic lupus erythematosus: based on antibody profiling

BACKGROUND

Neuropsychiatric systemic lupus erythematosus (NPSLE), with various morbidities and multiple manifestations in the central nervous system, remains a limited standard for diagnosis. Our study was to discover novel biomarkers for improving the diagnostic efficiency for NPSLE.

METHODS

We performed a quantitative planar protein antibody microarray to screen 1000 proteins in cerebrospinal fluid from controls, systemic lupus erythematosus (SLE, non-NPSLE) patients, and NPSLE patients. Differentially expressed proteins (DEPs) as candidate biomarkers were developed into a custom multiplexed protein antibody array for further validation in an independent larger cohort. Subsequently, we used least absolute shrinkage and selection operator regression (LASSO) analysis and multivariable logistic regression analysis for optimizing feature selection and constructing a diagnostic model. A receiver operating characteristic curve (ROC) was generated to assess the effectiveness of the models.

RESULTS

The expression of 29 proteins in CSF was significantly altered in the comparison of the three groups. We selected 17 proteins as candidate biomarkers in accordance with protein interaction analysis. In the larger cohort, we identified 5 DEPs as biomarkers for NPSLE, including TCN2, CST6, KLK5, L-selectin, and Trappin-2. The diagnostic model included 3 hub proteins (CST6, TCN2, KLK5) and was best at discriminating NPSLE from SLE patients. These CSF biomarkers were also highly associated with disease activity. In addition, there were 6 molecules with remarkable changes in NPSLE CSF and hippocampus, which indicated the consistency of the environment in the brain and the promising molecular targets in the pathogenesis of NPSLE.

CONCLUSIONS

The dual-chips screening strategy demonstrated KLK5, L-selectin, Trappin-2, TCN2, and CST6 as CSF biomarkers for diagnosing NPSLE.

CST6 suppresses osteolytic bone disease in multiple myeloma by blocking osteoclast differentiation

Osteolytic bone disease is a hallmark of multiple myeloma (MM). A significant fraction (~20%) of MM patients do not develop osteolytic lesions (OL). The molecular basis for the absence of bone disease in MM is not understood. We combined PET-CT and gene expression profiling (GEP) of purified bone marrow (BM) CD138+ MM cells from 512 newly diagnosed MM patients to reveal that elevated expression of cystatin M/E (CST6) was significantly associated with the absence of OL in MM. An enzyme-linked immunosorbent assay revealed a strong correlation between CST6 levels in BM serum/plasma and CST6 mRNA expression. Both recombinant CST6 protein and BM serum from patients with high CST6 significantly inhibited the activity of the osteoclast-specific protease cathepsin K, and blocked osteoclast differentiation and function. Recombinant CST6 inhibited bone destruction in ex vivo and in vivo myeloma models. Single cell RNA-sequencing identified that CST6 attenuates polarization of monocytes to osteoclast precursors. Furthermore, CST6 protein blocks osteoclast differentiation by suppressing cathepsin-mediated cleavage of NF-κB/p100 and TRAF3 following RANKL stimulation. Secretion by MM cells of CST6, an inhibitor of osteoclast differentiation and function, suppresses osteolytic bone disease in MM and probably other diseases associated with osteoclast-mediated bone loss.

Active legumain promotes invasion and migration of neuroblastoma by regulating epithelial-mesenchymal transition

Neuroblastoma (NB) is a commonly occurring malignancy in children. Epithelial-mesenchymal transition (EMT) is an adaptive change in promoting tumor metastasis. As an important factor in regulating tumor metastasis, whether legumain could promote metastasis of NB by EMT is still unexplored. Legumain is the active form of prolegumain, abundant in tumor plasma. So in the current study, different forms of legumain were identified in NB. Second, correlation analysis of N-cadherin and active legumain was identified by western blot analysis. Third, legumain gene amplification or gene knockdown were proceeded to examine the effect of legumain on EMT by scratch and transwell assay; meanwhile, active mature legumain or its asparagine endopeptidase (AEP) inhibitor was also added in. Finally, legumain can be detected differently in NB cells. Changes in legumain could influence NB metastasis by regulating EMT markers (e.g., N-cadherin, vimentin, and slug). Besides, the effect of legumain on EMT by its AEP activity was proved by intervention experiment of AEP gene transfection and gene knockdown experiments or adding recombinant human legumain suspension or specific inhibitor of AEP in NB cells (p < 0.05). These results suggest that legumain can promote invasion and migration of NB by regulating EMT, and EMT of NB is regulated by AEP activity of legumain, which can be inhibited by a specific AEP inhibitor.

A Pan-Cancer Analysis of Cystatin E/M Reveals Its Dual Functional Effects and Positive Regulation of Epithelial Cell in Human Tumors

Cystatin E/M (CST6), a representative cysteine protease inhibitor, plays both tumor-promoting and tumor-suppressing functions and is pursued as an epigenetically therapeutic target in special cancer types. However, a comprehensive and systematic analysis for CST6 in pan-cancer level is still lacking. In the present study, we explored the expression pattern of CST6 in multiple cancer types across ∼10,000 samples from TCGA (The Cancer Genome Atlas) and ∼8,000 samples from MMDs (Merged Microarray-acquired Datasets). We found that the dynamic expression alteration of CST6 was consistent with dual function in different types of cancer. In addition, we observed that the expression of CST6 was globally regulated by the DNA methylation in its promoter region. CST6 expression was positively correlated with the epithelial cell infiltration involved in epithelial-to-mesenchymal transition (EMT) and proliferation. The relationship between CST6 and tumor microenvironment was also explored. In particular, we found that CST6 serves a protective function in the process of melanoma metastasis. Finally, the clinical association analysis further revealed the dual function of CST6 in cancer, and a combination of the epithelial cell infiltration and CST6 expression could predict the prognosis for SKCM patients. In summary, this first CST6 pan-cancer study improves the understanding of the dual functional effects on CST6 in different types of human cancer.

Externally added cystatin C reduces growth of A375 melanoma cells by increasing cell cycle time

Some secreted cysteine protease inhibitors of the cystatin family appear to affect intracellular proteolysis and growth of human cells, as a result of internalization. Here, we studied the effects of external addition of the most abundant human cystatin, cystatin C, on viability and proliferation of cancer cells in culture. A dose‐dependent decrease in viable cells was seen for A375 melanoma, MCF‐7 breast cancer, and PC‐3 prostate cancer cells cultured in 1–5 µm cystatin C after 24 h. Real‐time assessment of growth rates in A375 cell cultures for 48 h by digital holographic microscopy showed an increased doubling time for cells cultured in the presence of 5 µm cystatin C (20.1 h) compared with control cells (14.7 h). A prolonged doubling time was already observed during the first 12 h, indicating a rapid general decrease in cell proliferation at the population level. Tracking of individual cells in phase holographic images showed that dividing cells incubated with 5 µm cystatin C underwent fewer mitoses during 48 h than control cells. In addition, the time between cell divisions was longer, especially for the first cell cycle. Incubation with the variant W106F‐cystatin C (with high cellular uptake rate) resulted in a lower number of viable cells and a prolonged doubling time than when cells were incubated with wild‐type cystatin C, but no effect was observed for (R24A,R25A)‐cystatin C (low cellular uptake). Thus, cystatin C causes prolonged cell division leading to decreased proliferation of melanoma cells, and internalization seems to be a prerequisite for this effect.

Cystatin M/E (Cystatin 6): A Janus-Faced Cysteine Protease Inhibitor with Both Tumor-Suppressing and Tumor-Promoting Functions

Alongside its contribution in maintaining skin homeostasis and its probable involvement in fetal and placental development, cystatin M/E (also known as cystatin 6) was first described as a tumor suppressor of breast cancer. This review aims to provide an update on cystatin M/E with particular attention paid to its role during tumorigenesis. Cystatin M/E, which is related to type 2 cystatins, displays the unique property of being a dual tight-binding inhibitor of both legumain (also known as asparagine endopeptidase) and cysteine cathepsins L, V and B, while its expression level is epigenetically regulated via the methylation of the CST6 promoter region. The tumor-suppressing role of cystatin M/E was further reported in melanoma, cervical, brain, prostate, gastric and renal cancers, and cystatin M/E was proposed as a biomarker of prognostic significance. Contrariwise, cystatin M/E could have an antagonistic function, acting as a tumor promoter (e.g., oral, pancreatic cancer, thyroid and hepatocellular carcinoma). Taking into account these apparently divergent functions, there is an urgent need to decipher the molecular and cellular regulatory mechanisms of the expression and activity of cystatin M/E associated with the safeguarding homeostasis of the proteolytic balance as well as its imbalance in cancer.

Comprehensive analysis and identification of key genes and signaling pathways in the occurrence and metastasis of cutaneous melanoma

Background

Melanoma is a malignant tumor of melanocytes, and the incidence has increased faster than any other cancer over the past half century. Most primary melanoma can be cured by local excision, but metastatic melanoma has a poor prognosis. Cutaneous melanoma (CM) is prone to metastasis, so the research on the mechanism of melanoma occurrence and metastasis will be beneficial to diagnose early, improve treatment, and prolong life survival. In this study, we compared the gene expression of normal skin (N), primary cutaneous melanoma (PM) and metastatic cutaneous melanoma (MM) in the Gene Expression Omnibus (GEO) database. Then we identified the key genes and molecular pathways that may be involved in the development and metastasis of cutaneous melanoma, thus to discover potential markers or therapeutic targets.

Methods

Three gene expression profiles (GSE7553, GSE15605 and GSE46517) were downloaded from the GEO database, which contained 225 tissue samples. R software identified the differentially expressed genes (DEGs) between pairs of N, PM and MM samples in the three sets of data. Subsequently, we analyzed the gene ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway of the DEGs, and constructed a protein-protein interaction (PPI) network. MCODE was used to seek the most important modules in PPI network, and then the GO function and KEGG pathway of them were analyzed. Finally, the hub genes were calculated by the cytoHubba in Cytoscape software. The Cancer Genome Atlas (TCGA) data were analyzed using UALCAN and GEPIA to validate the hub genes and analyze the prognosis of patients.

Results

A total of 134, 317 and 147 DEGs were identified between N, PM and MM in pair. GO functions and KEGG pathways analysis results showed that the upregulated DEGs mainly concentrated in cell division, spindle microtubule, protein kinase activity and the pathway of transcriptional misregulation in cancer. The downregulated DEGs occurred in epidermis development, extracellular exosome, structural molecule activity, metabolic pathways and p53 signaling pathway. The PPI network obtained the most important module, whose GO function and KEGG pathway were enriched in oxidoreductase activity, cell division, cell exosomes, protein binding, structural molecule activity, and metabolic pathways. 14, 18 and 18 DEGs were identified respectively as the hub genes between N, PM and MM, and TCGA data confirmed the expression differences of hub genes. In addition, the overall survival curve of hub genes showed that the differences in these genes may lead to a significant decrease in overall survival of melanoma patients.

Conclusions

In this study, several hub genes were found from normal skin, primary melanoma and metastatic melanoma samples. These hub genes may play an important role in the production, invasion, recurrence or death of CM, and may provide new ideas and potential targets for its diagnosis or treatment.

Down-regulation of lncRNA PCGEM1 inhibits cervical carcinoma by modulating the miR-642a-5p/LGMN axis

LncRNA PCGEM1 (PCGEM1) has been reported to exert essential effects on the development and progress of various tumors, while the detailed effects and possible mechanisms of PCGEM1 in cervical carcinoma remain unknown. In the present study, PCGEM1 was over-expressed in cervical carcinoma cells as evidenced by real-time quantitative polymerase chain reaction (RT-qPCR) assay. Knockdown of PCGEM1 significantly repressed proliferation, migration, and invasion, while induced G1 arrest in cervical carcinoma cells. In addition, PCGEM1 was predicted to target miR-642a-5p by bioinformatics software, which was further confirmed by luciferase reporter assay. Besides, RT-qPCR assay indicated that miR-642a-5p expression was decreased in cervical carcinoma cells and knockdown of PCGEM1 could accelerate miR-642a-5p expression. Moreover, inhibition of miR-642a-5p partly abolished the functions of PCGEM1 knockdown on proliferation, cell cycle, migration and invasion of cervical carcinoma cells. Furthermore, miR-642a-5p could bind to the 3'-UTR of LGMN, which was over-expressed in the cervical carcinoma cells. Suppression of LGMN partly restored the functions of miR-642a-5p inhibitor on proliferation, cell cycle distribution, migration and invasion in the cervical carcinoma cells treated with the PCGEM1 shRNA. Taken together, our data indicated that knockdown of PCGEM1 inhibited proliferation, migration and invasion in cervical carcinoma by modulating the miR-642a-5p/ LGMN axis.

Secreted cystatins decrease proliferation and enhance apoptosis of human leukemic cells

Cysteine proteases are implicated in proteolysis events favoring cancer cell growth, spread, and death by apoptosis. Herein, we have studied whether the net growth and survival of the leukemic cell lines Jurkat, U937, and HL‐60 are affected by external addition of five proteins acting as natural cysteine protease inhibitors. None of the cystatins examined (A, C, D, and E/M) or chagasin showed consistent effects on Fas‐induced apoptosis when evaluated at 1 µm. In contrast, when the intrinsic apoptosis pathway was activated by hydrogen peroxide, addition of cystatin D augmented caspase‐3‐like activity within all three cell lines. Flow cytometric analysis of U937 cells also showed increased numbers of annexin V‐positive cells when hydrogen peroxide was used to initiate apoptosis and cells were cultured in the presence of cystatin D or C. Moreover, stimulation of hydrogen peroxide‐induced apoptotic U937 cells with either cystatin C or D resulted in a dose‐dependent decrease in the number of cells. Cell viability was also decreased when U937 cells were cultured in the presence of cystatin C or D (1–9 µm) only, demonstrating that these cystatins can reduce cell proliferation by themselves in addition to enhancing apoptosis induced by oxidative stress. These effects on U937 cells were paralleled by internalization of cystatins C and D, indicating these effects are caused by downregulation of intracellular proteolysis. External addition of cystatins C and D to HL‐60 and Jurkat cells demonstrated similar degrees of cystatin D uptake and decreased viability as for U937 cells, indicating that these effects are general for leukemic cells.

Recent advances in the development of legumain-selective chemical probes and peptide prodrugs

Legumain, which is also known as vacuolar processing enzyme (VPE) or asparaginyl endopeptidase (AEP), is a cysteine protease that was first discovered and characterized in the leguminous seeds of the moth bean in the early 1990s. Later, this enzyme was also detected in higher organisms, including eukaryotes. This pH-dependent protease displays the highest activity in acidic endolysosomal compartments; however, legumain also displays nuclear, cytosolic and extracellular activity when stabilized by other proteins or intramolecular complexes. Based on the results from over 25 years of research, this protease is involved in multiple cellular events, including protein degradation and antigen presentation. Moreover, when dysregulated, this protease contributes to the progression of several diseases, with cancer being the well-studied example. Research on legumain biology was undoubtedly facilitated by the use of small molecule chemical tools. Therefore, in this review, I present the historical perspectives and most current strategies for the development of small molecule substrates, inhibitors and activity-based probes for legumain. These tools are of paramount importance in elucidating the roles of legumain in multiple biological processes. Finally, as this enzyme appears to be a promising molecular target for anticancer therapies, the development of legumain-activated prodrugs is also described.

δ-secretase in neurodegenerative diseases: mechanisms, regulators and therapeutic opportunities

Mammalian asparagine endopeptidase (AEP) is a cysteine protease that cleaves its protein substrates on the C-terminal side of asparagine residues. Converging lines of evidence indicate that AEP may be involved in the pathogenesis of several neurological diseases, including Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. AEP is activated in the aging brain, cleaves amyloid precursor protein (APP) and promotes the production of amyloid-β (Aβ). We renamed AEP to δ-secretase to emphasize its role in APP fragmentation and Aβ production. AEP also cleaves other substrates, such as tau, α-synuclein, SET, and TAR DNA-binding protein 43, generating neurotoxic fragments and disturbing their physiological functions. The activity of δ-secretase is tightly regulated at both the transcriptional and posttranslational levels. Here, we review the recent advances in the role of δ-secretase in neurodegenerative diseases, with a focus on its biochemical properties and the transcriptional and posttranslational regulation of its activity, and discuss the clinical implications of δ-secretase as a diagnostic biomarker and therapeutic target for neurodegenerative diseases.

Cystatin C Expression is Promoted by VEGFA Blocking, With Inhibitory Effects on Endothelial Cell Angiogenic Functions Including Proliferation, Migration, and Chorioallantoic Membrane Angiogenesis

Background Vascular development, including vasculogenesis and angiogenesis, is involved in many diseases. Cystatin C ( CST 3) is a commonly used marker of renal dysfunction, and we have previously reported that its expression level is associated with variations in the gerbil circle of Willis. Thus, we hypothesized that CST 3 may affect endothelial function and angiogenic capacity. In the current study, we sought to determine the influence of CST 3 on endothelial function and explore its potential regulatory pathway. Methods and Results We analyzed CST 3 and vascular endothelial growth factor A ( VEGFA) levels in different developmental stages of gerbils using ELISA s and immunofluorescence (to examine the relationship between CST 3 and VEGFA . We used a real-time cell analyzer, cytotoxicity assays, and the chorioallantoic membrane assay to investigate the function of CST 3 in endothelial cells and the chorioallantoic membrane. Additionally, we used Western blotting to explore the downstream targets of CST 3. The expression levels of both CST 3 and VEGFA were at their highest on day 10 of the embryonic stage. CST 3 inhibited endothelial cell proliferation, migration, tube formation, and permeability, as well as vascular development in the chorioallantoic membrane. Blocking of VEGFA dose-dependently increased CST 3 expression in arterial and venous endothelial cells. Furthermore, overexpression and knockdown of CST 3 significantly affected the protein levels of p53 and CAPN10 (calpain 10), suggesting that CST 3 might play a role in vascular development through these proteins. Conclusions CST 3 may be associated with vascular development and angiogenesis, and this effect could be promoted by blocking VEGFA .

Structural and functional analysis of cystatin E reveals enzymologically relevant dimer and amyloid fibril states

Protein activity is often regulated by altering the oligomerization state. One mechanism of multimerization involves domain swapping, wherein proteins exchange parts of their structures and thereby form long-lived dimers or multimers. Domain swapping has been specifically observed in amyloidogenic proteins, for example the cystatin superfamily of cysteine protease inhibitors. Cystatins are twin-headed inhibitors, simultaneously targeting the lysosomal cathepsins and legumain, with important roles in cancer progression and Alzheimer's disease. Although cystatin E is the most potent legumain inhibitor identified so far, nothing is known about its propensity to oligomerize. In this study, we show that conformational destabilization of cystatin E leads to the formation of a domain-swapped dimer with increased conformational stability. This dimer was active as a legumain inhibitor by forming a trimeric complex. By contrast, the binding sites toward papain-like proteases were buried within the cystatin E dimer. We also showed that the dimers could further convert to amyloid fibrils. Unexpectedly, cystatin E amyloid fibrils contained functional protein, which inhibited both legumain and papain-like enzymes. Fibril formation was further regulated by glycosylation. We speculate that cystatin amyloid fibrils might serve as a binding platform to stabilize the pH-sensitive legumain and cathepsins in the extracellular environment, contributing to their physiological and pathological functions.