A novel consensus motif in fibronectin mediates dipeptidyl peptidase IV adhesion and metastasis

The impacts of dipeptidyl- peptidase 4 (DPP-4) inhibitors on common female malignancies: A systematic review

The inhibition of dipeptidyl- peptidase 4 (DPP-4) is an essential therapy for controlling hyperglycemia in patients with type 2 diabetes (T2DM). However, the role of DPP-4 in cancer is not yet clear, with some studies suggesting that it may either promote or suppress tumors. This makes it crucial to have personalized treatment for diabetic women with cancer to effectively manage their diabetes whilst and preventing cancer mortality. To address this issue, we conducted an integrative in-silico analysis and systematic review of the literature to comprehensively examine the relationship between DPP-4 expression and the effects of its inhibitors on prevalent female malignancies. We specifically chose studies that examined the effects of DPP-4 expression and DPP-4 inhibition (DPP-4i) on prevalent cancers in women, such as breast cancer (BC), ovarian cancer (OV), cervical cancer (CC), and endometrial cancer (EC). These studies comprised those conducted both in vivo and in vitro. The review of the literature indicated that DPP-4i may worsen aggressive traits such as metastasis, Epithelial-to-mesenchymal transition (EMT), and chemotherapy resistance in BC cells. However, cohort studies on diabetic and BC patients did not confirm these findings. In vitro studies indicate that on OV, DPP-4 upregulation has been shown to prevent metastasis, while CCappears to be influenced by DPP-4 expression in terms of cell migration. sitagliptin, a pharmaceutical inhibitor of DPP-4, had a significant impact on reducing adhesion in CC cells in vitro. Overexpression of DPP-4 increased cell migration and proliferation in CC and EC cells, and hence the application of sitagliptin is expected to prevent this effect. On the other hand, the result of in-silico data confirmed that a significant correlation exists between DPP-4 expression and immune cell infiltration in breast, ovarian, cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) as well as downregulated in these cancers compared to their normal tissue samples. Furthermore, a significant (p < 0.05) effect on OS of BC and CESC patients has been reported due to the elevation of DPP-4 methylation on a specific CPG Island. These findings could aid in creating specialized treatments for diabetic women with specific malignancies, but caution should be exercised when considering the patient's medical history and cancer type.

Dipeptidyl Peptidase-4-Mediated Fibronectin Processing Evokes a Profibrotic Extracellular Matrix

Fibronectin serves as a platform to guide and facilitate deposition of collagen and fibrillin microfibrils. During development of fibrotic diseases, altered fibronectin deposition in the extracellular matrix (ECM) is generally an early event. After this, dysregulated organization of fibrillins and fibrillar collagens occurs. Because fibronectin is an essential orchestrator of healthy ECM, perturbation of its ECM-organizational capacity may be involved in development of fibrosis. To investigate this, we employed recessive dystrophic epidermolysis bullosa as a disease model with progressive, severe dermal fibrosis. Fibroblasts from donors with recessive dystrophic epidermolysis bullosa in 2-dimensional and 3-dimensional cultures displayed dysregulated fibronectin deposition. Our analyses revealed that increase of profibrotic dipeptidyl peptidase-4-positive fibroblasts coincides with altered fibronectin deposition. Dipeptidyl peptidase-4 inhibitors normalized deposition of fibronectin and subsequently of fibrillin microfibrils and collagen I. Intriguingly, proteomics and inhibitor and mutagenesis studies disclosed that dipeptidyl peptidase-4 modulates ECM deposition through the proteolysis of the fibronectin N-terminus. Our study provides mechanistic insights into the observed profibrotic activities of dipeptidyl peptidase-4 and extends the understanding of fibronectin-guided ECM assembly in health and disease.

Bidirectional relation between dipeptidyl peptidase 4 and angiotensin II type I receptor signaling

Cardiometabolic diseases are often associated with heightened levels of angiotensin II (Ang II), which accounts for the observed oxidative stress, inflammation, and fibrosis. Accumulating evidence indicates a parallel upregulation of dipeptidyl dipeptidase 4 (DPP4) activity in cardiometabolic diseases, with its inhibition shown to mitigate oxidative stress, inflammation, and fibrosis. These findings highlight an overlap between the pathophysiological mechanisms used by Ang II and DPP4. Recent evidence demonstrates that targeted inhibition of DPP4 prevents the rise in Ang II and its associated molecules in experimental models of cardiometabolic diseases. Similarly, inhibitors of the angiotensin I-converting enzyme (ACE) or Ang II type 1 receptor (AT1R) blockers downregulate DPP4 activity, establishing a bidirectional relationship between DPP4 and Ang II. Here, we discuss the current evidence supporting the cross talk between Ang II and DPP4, along with the potential mechanisms promoting this cross regulation. A comprehensive analysis of this bidirectional relationship across tissues will advance our understanding of how DPP4 and Ang II collectively promote the development and progression of cardiometabolic diseases.

A Systems Biology Approach Unveils a Critical Role of DPP4 in Upper Gastrointestinal Cancer Patient Outcomes

Gastrointestinal (GI) cancers comprise of cancers that affect the digestive system and its accessory organs. The late detection and poor prognosis of GI cancer emphasizes the importance of identifying reliable and precise biomarkers for early diagnosis and prediction of prognosis. The membrane-bound glycoprotein dipeptidyl-peptidase 4 (DPP4), also known as CD26, is ubiquitously expressed and has a wide spectrum of biological roles. The role of DPP4/CD26 in tumor progression in different types of cancers remains elusive. However, the link between DPP4 and tumor-infiltrating cells, as well as its prognostic significance in malignancies, still require further investigation. This study was intended to elucidate the correlation of DPP4 expression and survival along with prognosis, followed by its associated enriched molecular pathways and immune cell marker levels in upper GI cancers. Results demonstrated a strong correlation between increased DPP4 expression and a worse prognosis in esophageal and gastric cancer and the co-expressed common genes with DPP4 were associated with crucial molecular pathways involved in tumorigenesis. Additionally, DPP4 was shown to be significantly linked to several immune infiltrating cell marker genes, including Macrophages (M1, M2 and Tumor Associated Macrophages), neutrophils, Treg, T-cell exhaustion, Th1 and Th2. Overall, our findings suggest that DPP4 may serve as a substantial prognostic biomarker, a possible therapeutic target, as well as it can play a critical role in the regulation of immune cell invasion in patients with gastroesophageal (esophageal, gastroesophageal junction and gastric) cancer. KEY WORDS: DPP4, integrated analysis, GI cancer, gastroesophageal cancer, gastroesophageal junction, prognosis.

Biochemical features and therapeutic potential of α-Mangostin: Mechanism of action, medicinal values, and health benefits

α-Mangostin (α-MG) is a natural xanthone obtained from the pericarps of mangosteen. It exhibits excellent potential, including anti-cancer, neuroprotective, antimicrobial, antioxidant, and anti-inflammatory properties, and induces apoptosis. α-MG controls cell proliferation by modulating signaling molecules, thus implicated in cancer therapy. It possesses incredible pharmacological features and modulates crucial cellular and molecular factors. Due to its lesser water solubility and pitiable target selectivity, α-MG has limited clinical application. As a known antioxidant, α-MG has gained significant attention from the scientific community, increasing interest in extensive technical and biomedical applications. Nanoparticle-based drug delivery systems were designed to improve the pharmacological features and efficiency of α-MG. This review is focused on recent developments on the therapeutic potential of α-MG in managing cancer and neurological diseases, with a special focus on its mechanism of action. In addition, we highlighted biochemical and pharmacological features, metabolism, functions, anti-inflammatory, antioxidant effects and pre-clinical applications of α-MG.

Multivalent dipeptidyl peptidase IV fragment-nanogold complex inhibits cancer metastasis by blocking pericellular fibronectin

Inhibition of cancer metastasis is a fundamental challenge in cancer treatment. We have previously shown that metastasis of cancer cells in the lung is critically promoted by the interaction between the superficial dipeptidyl peptidase IV (DPP IV) expressed on lung endothelial cells and the pericellular polymeric fibronectin (polyFN) of circulating cancer cells. In the present study, we aimed to search for DPP IV fragments with high avidity to polyFN and develop FN-targeted gold nanoparticles (AuNPs) conjugated with DPP IV fragments for treating cancer metastasis. We first identified a DPP IV fragment encompassing amino acids 29-130 of DPP IV, designated DP4A, which contained FN-binding sites and could specifically bind to FN immobilized on gelatin agarose beads. Furthermore, we conjugated maltose binding protein (MBP)-fused DP4A proteins to AuNPs for fabricating a DP4A-AuNP complex and evaluated its FN-targeted activity in vitro and anti-metastatic efficacy in vivo. Our results show that DP4A-AuNP exhibited higher binding avidity to polyFN than DP4A by 9 folds. Furthermore, DP4A-AuNP was more potent than DP4A in inhibiting DPP IV binding to polyFN. In terms of polyFN-targeted effect, DP4A-AuNP interacted with FN-overexpressing cancer cells and was endocytosed into cells 10 to 100 times more efficiently than untargeted MBP-AuNP or PEG-AuNP with no noticeable cytotoxicity. Furthermore, DP4A-AuNP was superior to DP4A in competitive inhibition of cancer cell adhesion to DPP IV. Confocal microscopy analysis revealed that binding of DP4A-AuNP to pericellular FN induced FN clustering without altering its surface expression on cancer cells. Notably, intravenous treatment with DP4A-AuNP significantly reduced metastatic lung tumor nodules and prolonged the survival in the experimental metastatic 4T1 tumor model. Collectively, our findings suggest that the DP4A-AuNP complex with potent FN-targeted effects may have therapeutic potential for prevention and treatment of tumor metastasis to the lung.

Depletion of polyfunctional CD26highCD8+ T cells repertoire in chronic lymphocytic leukemia

BACKGROUND

CD8⁺ T cells play an essential role against tumors but the role of human CD8⁺CD26⁺ T cell subset against tumors, in particular, haematological cancers such as chronic lymphocytic leukemia (CLL) remains unknown. Although CD4⁺CD26^high T cells are considered for adoptive cancer immunotherapy, the role of CD8⁺CD26⁺ T cells is ill-defined. Therefore, further studies are required to better determine the role of CD8⁺CD26⁺ T cells in solid tumors and haematological cancers.

METHODS

We studied 55 CLL and 44 age-sex-matched healthy controls (HCs). The expression of CD26 on different T cell subsets (e.g. naïve, memory, effector, and etc.) was analyzed. Also, functional properties of CD8⁺CD26⁺ and CD8⁺CD26^- T cells were evaluated. Finally, the plasma cytokine/chemokine and Galectin-9 (Gal-9) levels were examined.

RESULTS

CD26 expression identifies three CD8⁺ T cell subsets with distinct immunological properties. While CD26^negCD8⁺ T cells are mainly transitional, effector memory and effectors, CD26^lowCD8⁺ T cells are mainly naïve, stem cell, and central memory but CD26^high T cells are differentiated to transitional and effector memory. CD26⁺CD8⁺ T cells are significantly reduced in CLL patients versus HCs. CD26^high cells are enriched with Mucosal Associated Invariant T (MAIT) cells co-expressing CD161TVα7.2 and IL-18Rα. Also, CD26^high cells have a rich chemokine receptor profile (e.g. CCR5 and CCR6), profound cytokine (TNF-α, IFN-γ, and IL-2), and cytolytic molecules (Granzyme B, K, and perforin) expression upon stimulation. CD26^high and CD26^low T cells exhibit significantly lower frequencies of CD160, 2B4, TIGIT, ICOS, CD39, and PD-1 but higher levels of CD27, CD28, and CD73 versus CD26^neg cells. To understand the mechanism linked to CD26^high depletion, we found that malignant B cells by shedding Galectin-9 (Gal-9) contribute to the elevation of plasma Gal-9 in CLL patients. In turn, Gal-9 and the inflammatory milieu (IL-18, IL-12, and IL-15) in CLL patients contribute to increased apoptosis of CD26^high T cells.

CONCLUSIONS

Our results demonstrate that CD26⁺ T cells possess a natural polyfunctionality to traffic and exhibit effector functions and resist exhaustion. Therefore, they can be proposed for adoptive cancer immunotherapy. Finally, neutralizing and/or inhibiting Gal-9 may preserve CD26^highCD8⁺ T cells in CLL.

Human Coronavirus Cell Receptors Provide Challenging Therapeutic Targets

Coronaviruses interact with protein or carbohydrate receptors through their spike proteins to infect cells. Even if the known protein receptors for these viruses have no evolutionary relationships, they do share ontological commonalities that the virus might leverage to exacerbate the pathophysiology. ANPEP/CD13, DPP IV/CD26, and ACE2 are the three protein receptors that are known to be exploited by several human coronaviruses. These receptors are moonlighting enzymes involved in several physiological processes such as digestion, metabolism, and blood pressure regulation; moreover, the three proteins are expressed in kidney, intestine, endothelium, and other tissues/cell types. Here, we spot the commonalities between the three enzymes, the physiological functions of the enzymes are outlined, and how blocking either enzyme results in systemic deregulations and multi-organ failures via viral infection or therapeutic interventions is addressed. It can be difficult to pinpoint any coronavirus as the target when creating a medication to fight them, due to the multiple processes that receptors are linked to and their extensive expression.

Apigenin directly interacts with and inhibits topoisomerase 1 to upregulate CD26/DPP4 on colorectal carcinoma cells

Introduction: CD26/dipeptidyl peptidase IV (DPP4) is a cell-surface glycoprotein present on most epithelial cells that modulates the local response to external signals. We have previously shown that the dietary flavone apigenin (4',5,7-trihydroxyflavone) upregulates cell-surface CD26/DPP4 on human colorectal carcinoma (CRC) cells and regulates its activities. We observed a unique synergistic interaction with the CRC chemotherapeutic agent irinotecan, which through its metabolite SN38 elevates CD26 at doses that are sub-cytotoxic. As SN38 interacts with topoisomerase 1 (Topo1) we evaluated whether apigenin influences Topo1 activity. Methods: We used a radioimmunoassay to selectively measure CD26 at the cell surface of HT-29 cells following various treatments. Topoisomerase 1 mRNA expression was measured by q-RT-PCR and protein abundance by western blot analysis. Direct inhibition of topoisomerase activity was measured using an assay of DNA supercoil relaxation with recombinant human Topo1. The role of Topo1 in the effect of apigenin was shown both pharmacologically and by siRNA silencing of Topo1. Molecular docking analysis was done with SBD computational software using the CDOCKER algorithm. Results: The interplay between apigenin and irinotecan was not observed when apigenin was combined with other chemotherapeutic drugs including the topoisomerase 2 inhibitors doxorubicin or etoposide. There was no enhancement of irinotecan action if apigenin was replaced with its hydroxylated metabolite luteolin (3',4',5,7-tetrahydroxyflavone) or emodin (6-methyl-1,3,8-trihydroxyanthraquinone), which is an inhibitor of the principal kinase target of apigenin, casein kinase 2 (CK2). Apigenin did not alter Topo1 mRNA expression, but siRNA knockdown of functional Topo1 eliminated the effect of apigenin and itself increased CD26 levels. Apigenin inhibited Topo1 activity in intact HT-29 cells and showed comparable inhibition of purified recombinant human Topo1 enzyme activity to that of SN-38, the active metabolite of irinotecan. Apigenin fits into the complex of Topo1 with DNA to directly inhibit Topo1 enzyme activity. Discussion: We conclude that apigenin has a unique fit into the Topo1-DNA functional complex that leads to direct inhibition of Topo1 activity, and suggest that this is the basis for the exceptional interaction with the CRC drug irinotecan. A combined action of these two agents may therefore exert a role to limit local signals that facilitate tumour progression.

Alpha-Mangostin Reduces Pericellular Fibronectin on Suspended Tumor Cells and Therapeutically, but Not Prophylactically, Suppresses Distant Metastasis

Major cancer deaths can be ascribed to distant metastasis to which the assembly of pericellular fibronectin (periFN) on suspended tumor cells (STCs) in the bloodstream that facilitate endothelial attachment can lead. Even though mangosteen pericarps (MP) extracts and the major component α-mangostin (α-MG) exhibit potent cancer chemopreventive properties, whether they can prophylactically and therapeutically be used as dietary nutraceuticals to prevent distant metastasis by suppressing periFN assembly on STCs within the circulation remains obscure. Immunofluorescence staining, MTT assays, flow cytometric assays, immunoblotting, and experimental metastasis mouse models were used to detect the effects of MP extracts or α-MG on periFN on STCs, tumor cell proliferation and apoptosis, the AKT activity, and tumor lung metastasis. The periFN assembly on STCs was significantly diminished upon treatments of STCs with either α-MG or MP extracts in a dose-dependent manner without inhibiting cell proliferation and viability due to increased AKT activity. Pretreatment of STCs with α-MG appeared to suppress tumor lung metastasis and prolong mouse survival rates. Oral gavage with MP extracts could therapeutically, but not prophylactically, prevent lung metastasis of STCs. We concluded that MP extracts or the major component α-MG may therapeutically serve as a potent anti-metastatic nutraceutical.

Dipeptidyl peptidase 4 expression is not associated with an activated fibroblast phenotype in idiopathic pulmonary fibrosis

Dipeptidyl peptidase 4 (DPP4) has been proposed as a marker for activated fibroblasts in fibrotic disease. We aimed to investigate whether a profibrotic DPP4 phenotype is present in lung tissue from patients with idiopathic pulmonary fibrosis (IPF). The presence of DPP4⁺ fibroblasts in normal and IPF lung tissue was investigated using flow cytometry and immunohistology. In addition, the involvement of DPP4 in fibroblast activation was examined in vitro, using CRISPR/Cas9 mediated genetic inactivation to generate primary DPP4 knockout lung fibroblasts. We observed a reduced frequency of primary DPP4⁺ fibroblasts in IPF tissue using flow cytometry, and an absence of DPP4⁺ fibroblasts in pathohistological features of IPF. The in vivo observations were supported by results in vitro showing a decreased expression of DPP4 on normal and IPF fibroblasts after profibrotic stimuli (transforming growth factor β) and no effect on the expression of activation markers (α-smooth muscle actin, collagen I and connective tissue growth factor) upon knockout of DPP4 in lung fibroblasts with or without activation with profibrotic stimuli.

Does DPP-IV Inhibition Offer New Avenues for Therapeutic Intervention in Malignant Disease?

Simple Summary

There is growing interest in identifying the effects of antidiabetic agents on cancer risk, progression, and anti-cancer treatment due to the long-term use of these medications and the inherently increased risk of malignancies in diabetic patients. Tumor development and progression are affected by multiple mediators in the tumor microenvironment, several of which may be proteolytically modified by the multifunctional protease dipeptidyl peptidase-IV (DPP-IV, CD26). Currently, low-molecular-weight DPP-IV inhibitors (gliptins) are used in patients with type 2 diabetes based on the observation that DPP-IV inhibition enhances insulin secretion by increasing the bioavailability of incretins. However, the DPP-IV-mediated cleavage of other biopeptides and chemokines is also prevented by gliptins. The potential utility of gliptins in other areas of medicine, including cancer, is therefore being evaluated. Here, we critically review the existing evidence on the role of DPP-IV inhibitors in cancer pathogenesis, their potential to be used in anti-cancer treatment, and the possible perils associated with this approach.

Abstract

Dipeptidyl peptidase IV (DPP-IV, CD26) is frequently dysregulated in cancer and plays an important role in regulating multiple bioactive peptides with the potential to influence cancer progression and the recruitment of immune cells. Therefore, it represents a potential contributing factor to cancer pathogenesis and an attractive therapeutic target. Specific DPP-IV inhibitors (gliptins) are currently used in patients with type 2 diabetes mellitus to promote insulin secretion by prolonging the activity of the incretins glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Nevertheless, the modulation of the bioavailability and function of other DPP-IV substrates, including chemokines, raises the possibility that the use of these orally administered drugs with favorable side-effect profiles might be extended beyond the treatment of hyperglycemia. In this review, we critically examine the possible utilization of DPP-IV inhibition in cancer prevention and various aspects of cancer treatment and discuss the potential perils associated with the inhibition of DPP-IV in cancer. The current literature is summarized regarding the possible chemopreventive and cytotoxic effects of gliptins and their potential utility in modulating the anti-tumor immune response, enhancing hematopoietic stem cell transplantation, preventing acute graft-versus-host disease, and alleviating the side-effects of conventional anti-tumor treatments.

Emerging Role of Dipeptidyl Peptidase-4 in Autoimmune Disease

Dipeptidyl-peptidase IV (DPP4), originally identified as an aminopeptidase in 1960s, is an ubiquitously expressed protease presented as either a membrane-bound or soluble form. DPP4 cleaves dipeptide off from the N-terminal of its substrates, altering the bioactivity of its substrates. Subsequent studies reveal that DPP4 is also involved in various cellular processes by directly binding to a number of ligands, including adenosine deaminase, CD45, fibronectin, plasminogen, and caveolin-1. In recent years, many novel functions of DPP4, such as promoting fibrosis and mediating virus entry, have been discovered. Due to its implication in fibrotic response and immunoregulation, increasing studies are focusing on the potential role of DPP4 in inflammatory disorders. As a moonlighting protein, DPP4 possesses multiple functions in different types of cells, including both enzymatic and non-enzymatic functions. However, most of the review articles on the role of DPP4 in autoimmune disease were focused on the association between DPP4 enzymatic inhibitors and the risk of autoimmune disease. An updated comprehensive summary of DPP4’s immunoregulatory actions including both enzymatic dependent and independent functions is needed. In this article, we will review the recent advances of DPP4 in immune regulation and autoimmune rheumatic disease.

Sitagliptin Is More Effective Than Gliclazide in Preventing &nbsp;Pro-Fibrotic and Pro-Inflammatory Changes in a Rodent Model of Diet-Induced Non-Alcoholic Fatty Liver Disease

A diet-induced non-alcoholic fatty liver disease (NAFLD) model causing obesity in rodents was used to examine whether sitagliptin and gliclazide therapies have similar protective effects on pathological liver change. Methods: Male mice were fed a high-fat diet (HFD) or standard chow (Chow) ad libitum for 25 weeks and randomly allocated to oral sitagliptin or gliclazide treatment for the final 10 weeks. Fasting blood glucose and circulating insulin were measured. Inflammatory and fibrotic liver markers were assessed by qPCR. The second messenger ERK and autophagy markers were examined by Western immunoblot. F4/80, collagens and CCN2 were assessed by immunohistochemistry (IHC). Results: At termination, HFD mice were obese, hyperinsulinemic and insulin-resistant but non-diabetic. The DPP4 inhibitor sitagliptin prevented intrahepatic induction of pro-fibrotic markers collagen-IV, collagen-VI, CCN2 and TGF-β1 and pro-inflammatory markers TNF-α and IL-1β more effectively than sulfonylurea gliclazide. By IHC, liver collagen-VI and CCN2 induction by HFD were inhibited only by sitagliptin. Sitagliptin had a greater ability than gliclazide to normalise ERK-protein liver dysregulation. Conclusion: These data indicate that sitagliptin, compared with gliclazide, exhibits greater inhibition of pro-fibrotic and pro-inflammatory changes in an HFD-induced NAFLD model. Sitagliptin therapy, even in the absence of diabetes, may have specific benefits in diet-induced NAFLD.

The Multiple Biological Functions of Dipeptidyl Peptidase-4 in Bone Metabolism

Dipeptidyl peptidase-4 (DPP4) is a ubiquitously occurring protease involved in various physiological and pathological processes ranging from glucose homeostasis, immunoregulation, inflammation to tumorigenesis. Recently, the benefits of DPP4 inhibitors as novel hypoglycemic agents on bone metabolism have attracted extensive attraction in many studies, indicating that DPP4 inhibitors may regulate bone homeostasis. The effects of DPP4 on bone metabolism are still unclear. This paper thoroughly reviews the potential mechanisms of DPP4 for interaction with adipokines, bone cells, bone immune cells, and cytokines in skeleton system. This literature review shows that the increased DPP4 activity may indirectly promote bone resorption and inhibit bone formation, increasing the risk of osteoporosis. Thus, bone metabolic balance can be improved by decreasing DPP4 activities. The substantial evidence collected and analyzed in this review supports this implication.

Recent Insights into Human Endometrial Peptidases in Blastocyst Implantation via Shedding of Microvesicles

Blastocyst implantation involves multiple interactions with numerous molecules expressed in endometrial epithelial cells (EECs) during the implantation window; however, there is limited information regarding the molecular mechanism underlying the crosstalk. In blastocysts, fibronectin plays a major role in the adhesion of various types of cells by binding to extracellular matrix proteins via the Arg-Gly-Asp (RGD) motif. In EECs, RGD-recognizing integrins are important bridging receptors for fibronectin, whereas the non-RGD binding of fibronectin includes interactions with dipeptidyl peptidase IV (DPPIV)/cluster of differentiation (CD) 26. Fibronectin may also bind to aminopeptidase N (APN)/CD13, and in the endometrium, these peptidases are present in plasma membranes and lysosomal membranes. Blastocyst implantation is accompanied by lysosome exocytosis, which transports various peptidases and nutrients into the endometrial cavity to facilitate blastocyst implantation. Both DPPIV and APN are released into the uterine cavity via shedding of microvesicles (MVs) from EECs. Recently, extracellular vesicles derived from endometrial cells have been proposed to act on trophectoderm cells to promote implantation. MVs are also secreted from embryonal stem cells and may play an active role in implantation. Thus, crosstalk between the blastocyst and endometrium via extracellular vesicles is a new insight into the fundamental molecular basis of blastocyst implantation.

Leukocyte Membrane Enzymes Play the Cell Adhesion Game

For a long time, proteins with enzymatic activity have not been usually considered to carry out other functions different from catalyzing chemical reactions within or outside the cell. Nevertheless, in the last few years several reports have uncovered the participation of numerous enzymes in other processes, placing them in the category of moonlighting proteins. Some moonlighting enzymes have been shown to participate in complex processes such as cell adhesion. Cell adhesion plays a physiological role in multiple processes: it enables cells to establish close contact with one another, allowing communication; it is a key step during cell migration; it is also involved in tightly binding neighboring cells in tissues, etc. Importantly, cell adhesion is also of great importance in pathophysiological scenarios like migration and metastasis establishment of cancer cells. Cell adhesion is strictly regulated through numerous switches: proteins, glycoproteins and other components of the cell membrane. Recently, several cell membrane enzymes have been reported to participate in distinct steps of the cell adhesion process. Here, we review a variety of examples of membrane bound enzymes participating in adhesion of immune cells.

The Serine Protease CD26/DPP4 in Non-Transformed and Malignant T Cells

Simple Summary

The transmembrane serine protease CD26/Dipeptidylpeptidase 4 modulates T-cell activation, proliferation, and effector function. Due to their remarkable tumoricidal properties CD26-positive T cells are considered promising candidates for T cell-based immunotherapies while in cutaneous T cell lymphoma CD26/DPP4 expression patterns are established markers for diagnosis and possibly prognosis. With a focus on T cells, we review current knowledge on the regulation of CD26/DPP4 expression and release, its implication in T-cell effector function and the suitability CD26/DPP4 as a diagnostic and/or prognostic factor in T-cell malignancies.

Abstract

CD26/Dipeptidylpeptidase 4 is a transmembrane serine protease that cleaves off N-terminal dipeptides. CD26/DPP4 is expressed on several immune cell types including T and NK cells, dendritic cells, and activated B cells. A catalytically active soluble form of CD26/DPP4 can be released from the plasma membrane. Given its wide array of substrates and interaction partners CD26/DPP4 has been implicated in numerous biological processes and effects can be dependent or independent of its enzymatic activity and are exerted by the transmembrane protein and/or the soluble form. CD26/DPP4 has been implicated in the modulation of T-cell activation and proliferation and CD26/DPP4-positive T cells are characterized by remarkable anti-tumor properties rendering them interesting candidates for T cell-based immunotherapies. Moreover, especially in cutaneous T-cell lymphoma CD26/DPP4 expression patterns emerged as an established marker for diagnosis and treatment monitoring. Surprisingly, besides a profound knowledge on substrates, interaction partners, and associated signal transduction pathways, the precise role of CD26/DPP4 for T cell-based immune responses is only partially understood.

A molecular link between diabetes and breast cancer: Therapeutic potential of repurposing incretin-based therapies for breast cancer

Female breast cancer recently surpassed lung cancer and became the most commonly diagnosed cancer worldwide. As per the recent data from WHO, breast cancer accounts for one out of every 8 cancer cases diagnosed among an estimated 2.3 million new cancer cases. Breast cancer is the most prevailing cancer type among women causing the highest number of cancer-related mortality. It has been estimated that in 2020, 68,5000 women died due to this disease. Breast cancers have varying degrees of molecular heterogeneity; therefore, they are divided into various molecular clinical sub types. Recent reports suggest that type 2 diabetes (one of the common chronic diseases worldwide) is linked to the higher incidence, accelerated progression, and aggressiveness of different cancers; especially breast cancer. Breast cancer is hormone-dependent in nature and has a cross-talk with metabolism. A number of antidiabetic therapies are known to exert beneficial effects on various types of cancers, including breast cancer. However, only a few reports are available on the role of incretin-based antidiabetic therapies in cancer as a whole and in breast cancer in particular. The present review sheds light on the potential of incretin based therapies on breast cancer and explores the plausible underlying mechanisms. Additionally, we have also discussed the sub types of breast cancer as well as the intricate relationship between diabetes and breast cancer.

The mechanism of sitagliptin inhibition of colorectal cancer cell lines' metastatic functionalities

The cell membrane glycoprotein CD26 with peptidase activity (DPP4) and/or its soluble CD26/DPP4 counterpart expression and/or activity are altered in several cancers. Its role in metastasis development was recently highlighted by the discovery of CD26⁺ cancer stem cell subsets and the fact that clinical DPP4 inhibitors showed antimetastatic effects in animal models. Also, diabetic patients treated with the DPP4 inhibitor sitagliptin showed greater overall survival after colorectal or lung cancer surgery than patients under other diabetic therapies. However, the mechanism of action of these inhibitors in this context is unclear. We studied the role of CD26 and its DPP4 enzymatic activity in malignant cell features such as cell-to-cell homotypic aggregation, cancer cell motility, and invasion in a panel of human colorectal cancer (CRC) cell lines, avoiding models that include the physiological role of DPP4 in chemotaxis. Present results indicate that CD26 participates in the induction of cell invasion, motility, and aggregation of CD26-positive CRC cell lines. Moreover, only invasion and motility assays, which are collagen matrix-dependent, showed a decrease upon treatment with the DPP4 inhibitor sitagliptin. Sitagliptin showed opposite effects to those of transforming growth factor-β1 on epithelial-to-mesenchymal transition and cell cycle, but this result does not explain its CD26/DPP4-dependent effect. These results contribute to the elucidation of the molecular mechanisms behind sitagliptin inhibition of metastatic traits. At the same time, this role of sitagliptin may help to define areas of medicine where DPP4 inhibitors might be introduced. However, they also suggest that additional tools against CD26 as a target might be used or developed for metastasis prevention in addition to gliptins.

Diagnostic significance of apical membranous and cytoplasmic dot-like CD26 expression in encapsulated follicular variant of papillary thyroid carcinoma: a useful marker for capsular invasion

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and invasive encapsulated follicular variant of papillary thyroid carcinoma (EFV-PTC) are indistinguishable preoperatively. CD26 expression in follicular tumor-uncertain malignant potential (FT-UMP) is reported to be clearly higher than in that without capsular invasion. To verify the diagnostic significance of CD26 immunostaining in EFV-PTC, we examined the expression pattern of CD26 in non-invasive EFV-PTC (NIFTP) and invasive EFV-PTC. We performed immunohistochemical analysis using CD26 antibody for 37 NIFTPs and 54 EFV-PTCs (34 minimally invasive EFV-PTCs and 20 widely invasive EFV-PTCs). Most NIFTP samples showed an apical membranous pattern or a cytoplasmic diffuse pattern of expression. Invasive EFV-PTCs more frequently showed a cytoplasmic dot-like pattern, and the labeling indices of tumor cells with cytoplasmic dot-like patterns were significantly higher than those in NIFTPs. The sizes of dots seen in NIFTPs (mean: 1.12 μm) were significantly smaller than in invasive EFV-PTCs (1.33 μm), minimally invasive EFV-PTC (1.27 μm), and widely invasive EFV-PTC (1.38 μm). We, therefore, conclude that cytoplasmic diffuse and/or cytoplasmic dot-like CD26 expression, particularly the larger CD26-positive dots, could be useful markers for capsular invasion in EFV-PTC. CD26 immunostaining, using cell blocks or cytological specimens, may preoperatively distinguish between NIFTP and invasive EFV-PTC.

MicroRNA-146a suppresses tumor malignancy via targeting vimentin in esophageal squamous cell carcinoma cells with lower fibronectin membrane assembly

Background

Esophageal squamous cell carcinoma (ESCC) is widely prevalent in Taiwan, and high metastatic spread of ESCC leads to poor survival rate. Fibronectin (FN) assembly on the cell membrane may induce ESCC mobility. MicroRNAs (MiRNAs) are abundant in and participate in tumorigenesis in many cancers. However, the role of MiRNA in FN assembly-related ESCC mobility remains unexplored.

Methods

We divided ESCC CE81T cells into high-FN assembly (CE81^FN+) and low-FN assembly (CE81^FN−) groups by flow cytometry. MiRNA microarray analysis identified miR-146a expression as the most down-regulated miRNA in comparison of CE81^FN+ and CE81^FN− cells.

Results

Cell proliferation and migration were decreased when CE81^FN+ cells overexpressed transgenic miR-146a compared to the parental cells, indicating an inverse correlation between low miR-146a expression and high proliferation as well as motility of FN assembly ESCC cells. Furthermore, vimentin is the target gene of miR-146a involved in ESCC tumorigenesis. MiR-146a suppressed cell proliferation, migration and invasion of CE81^FN+ cells through the inhibition of vimentin expression, as confirmed by real-time PCR, Western blotting and Transwell™ assay. Analysis of one hundred and thirty-six paired ESCC patient specimens revealed that low miR-146a and high vimentin levels were frequently detected in tumor, and that the former was associated with late tumor stages (III and IV). Notably, either low miR-146a expression or high vimentin level was significantly associated with poor overall survival rate among ESCC patients.

Conclusions

This is the first report to link FN assembly in the cell membrane with miR-146a, vimentin and ESCC tumorigenesis both in vitro and in ESCC patients.

Depleting RhoA/Stress Fiber-Organized Fibronectin Matrices on Tumor Cells Non-Autonomously Aggravates Fibroblast-Driven Tumor Cell Growth

Fibronectin (FN) expressed by tumor cells has been known to be tumor suppressive but the pericellular FN (periFN) assembled on circulating tumor cells appears to evidently promote distant metastasis. Whereas the regulation of periFN assembly in suspended cells has currently been under investigation, how it is regulated in adherent tumor cells and the role of periFN in primary tumor growth remain elusive. Techniques of RNAi, plasmid transfections, immunoblotting, fluorescence/immunohistochemistry staining, cell proliferation assays, and primary tumor growth in C57BL6 mice and Fischer 344 rats were employed in this study. We found that endogenously synthesized FN in adherent tumor cells was required for periFN assembly which was aligned by RhoA-organized actin stress fiber (SF). Depleting periFN on adherent tumor cells congruently promoted in vivo tumor growth but surprisingly did not autonomously impact on in vitro tumor cell proliferation and apoptosis, suggestive of a non-autonomous role of periFN in in vivo tumor growth. We showed that the proliferative ability of shFN-expressing tumor cells was higher than shScramble cells did in the presence of fibroblasts. Altogether, these results suggested that depriving RhoA/SF-regulated periFN matrices non-autonomously promotes fibroblast-mediated tumor cell growth.

Angiogenesis is promoted by exosomal DPP4 derived from 5-fluorouracil-resistant colon cancer cells

Cancer cells can communicate with the tumor microenvironment and contribute to tumor progression. However, the effects of drug-resistant tumor cells on angiogenesis are unclear. Current anti-angiogenic strategies also have limitations and it would be useful to develop novel targets and treatment strategies. Here, our study showed that the conditioned medium and exosomes from 5-FU-resistant colon cancer cells promoted angiogenesis, and we observed that exosomal dipeptidyl peptidase IV (DPP4) was a potent inducer of this angiogenesis. DPP4-enriched exosomes increased periostin (POSTN) expression in human umbilical vein endothelial cells via Twist1 nuclear translocation or activating Smad signaling pathway, while silencing or inhibition of DPP4 neutralized those effects. The in vivo and clinical data indicated that high DPP4 expression was related to tumor progression. These findings indicate that DPP4 may be a target for inhibiting angiogenesis in 5-FU-resistant colon cancer. Furthermore, exosomal DPP4 concentrations may be a useful prognostic marker for colon cancer.

Apigenin upregulation of CD26/DPPIV on colon epithelial cells requires inhibition of casein kinase 2

CD26/DPPIV is a cell surface glycoprotein found on cells of the intestinal epithelium including those of the colon. We have previously shown that the dietary flavone apigenin (4',5,7-trihydroxyflavone) upregulates CD26/DPPIV on colon cells. Flavonoids such as apigenin interfere with the action of multiple cellular protein kinases and have the capacity to modulate the cell exterior and its ability to interface with the local environment through different signaling pathways. We show here that the ability of apigenin to upregulate CD26/DPPIV is exerted through and requires the activity of casein kinase 2 (CK2). Inhibitors of CK2 that are distinct from apigenin (emodin, 6-methyl-1,3,8-trihydroxyanthraquinone; TBB, 4,5,6,7-tetrabromobenzotriazole; and DRB, 5,6-dichlorobenzimidazole 1-β-D-ribofuranoside) showed a dose-dependent ability to increase CD26/DPPIV and had the same maximal effect when combined with apigenin at submaximal concentrations. Knockdown of CK2 with siRNA abrogated the ability of apigenin to upregulate CD26/DPPIV. Apigenin treatment of cells had no effect on the levels of CK2 protein, consistent with an inhibition of activity of the enzyme. Apigenin's upregulation of CD26/DPPIV in differentiated human colon epithelial cells depends upon inhibition of CK2 activity. This is a key step in enabling apigenin's ability to regulate the functions of intestinal epithelial cells.

Vildagliptin, a CD26/DPP4 inhibitor, ameliorates bleomycin-induced pulmonary fibrosis via regulating the extracellular matrix

BACKGROUND

Idiopathic pulmonary fibrosis is a debilitating lung disease. CD26/DPP4 plays promotive roles in pulmonary damage and fibrosis. This study aimed to explore the roles of vildagliptin in bleomycin-induced pulmonary fibrosis, and to address its ameliorative effect on the extracellular matrix (ECM).

METHODS

Idiopathic pulmonary fibrosis mice models were induced by intratracheal injection of bleomycin. DPP4 activity was evaluated, and the fibrosis was investigated by Hematoxylin-eosin, Masson's trichrome staining and hydroxyproline assay. Expression of extracellular matrix proteins including α-SMA, collagen IV, collagen I, FN and TGF-β were analyzed by immunochemistry and western blot. Percentages of the numbers of monocytes, leukocytes, basophils and lymphocytes were classified, and inflammatory factors in plasma as well as lung tissues were examined by enzyme-linked immunosorbent assay and western blot. The influences of vildagliptin on TGF-β1-induced cell proliferation, differentiation and inflammatory factors in MRC-5 cells were detected.

RESULTS

Vildagliptin effectively attenuated inflammation and fibrosis in bleomycin-induced pulmonary tissue via inhibiting the activity of CD26/DPP4. extracellular matrix proteins were suppressed by vildagliptin. Thus, lung tissue fibrosis was efficiently alleviated by vildagliptin.

CONCLUSION

As an inhibitor of CD26/DPP4, Vildagliptin could be a promising therapeutic candidate for idiopathic pulmonary fibrosis.

Involvement of Integrin-Activating Peptides Derived from Tenascin-C in Cancer Aggression and New Anticancer Strategy Using the Fibronectin-Derived Integrin-Inactivating Peptide

Matricellular proteins, which exist in association with the extracellular matrix (ECM) and ECM protein molecules, harbor functional sites within their molecular structures. These functional sites are released through proteolytic cleavage by inflammatory proteinases, such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS), and the peptides containing these functional sites have unique biological activities that are often not detected in the parent molecules. We previously showed that tenascin-C (TNC) and plasma fibronectin (pFN), examples of matricellular proteins, have cryptic bioactive sites that have opposite effects on cell adhesion to the ECM. A peptide containing the bioactive site of TNC, termed TNIIIA2, which is highly released at sites of inflammation and in the tumor microenvironment (TME), has the ability to potently and persistently activate β1-integrins. In the opposite manner, the peptide FNIII14 containing the bioactive site of pFN has the ability to inactivate β1-integrins. This review highlights that peptide TNIIIA2 can act as a procancer factor and peptide FNIII14 can act as an anticancer agent, based on the regulation on β1-integrin activation. Notably, the detrimental effects of TNIIIA2 can be inhibited by FNIII14. These findings open the possibility for new therapeutic strategies based on the inactivation of β1-integrin by FNIII14.

Impact of DPP4 Inhibitors in Survival of Patients With Prostate, Pancreas, and Breast Cancer

Background: Dipeptidyl peptidase-4 (DPP4), a cell surface protein, exhibits a crucial role in tumor biology and regulation of the immune system. We aim to study the impact of DPP4 inhibitors (DPP4i) in patients with prostate cancer (PRC), pancreatic cancer (PC) and breast cancer (BC).

Methods: Using the SEER and Medicare linked database, we identified patients with PRC or PC or BC with coexisting type II diabetes mellitus between 2007 and 2015. Patients were classified into four groups: (1) not on either DPP4i or metformin (reference group), this group included patient that were on anti-diabetic agents other than metformin or DPP4i (2) metformin only, (3) DPP4i only, and (4) DPP4i along with metformin (combination group). Overall survival (OS) analyses were performed using SAS®, version 9.4.

Results: We identified 15,330 patients with PRC, 5,359 patients with PC and 16,085 patients with BC. In PRC cohort, patients on DPP4i had significant survival advantage with HR 0.77 (95% CI: 0.64–0.93), P = 0.005 when compared to the reference group. Patients taking metformin also had significant OS benefit with HR 0.87 (95% CI: 0.81–0.93), P < 0.0001 when compared to the reference group. However, in BC cohort, OS did not favor the patients taking DPP4i with HR 1.07 (95% CI: 0.93–1.25, P = 0.33). Similarly, in PC cohort, OS was indifferent for the patients on DPP4i with HR 1.07 (95% CI: 0.93–1.24, P = 0.68). Upon subgroup analyses of PRC patients, the survival favored the group taking DPP4i, irrespective of stage, use of chemotherapy, androgen-deprivation therapy, and prostatectomy or radiation therapy.

Conclusions: DPP4i seems to improve survival in PRC patients; however, not in PC or BC patients. While the exact mechanism involved remains to be elucidated, a prospective clinical trial would help to confirm these findings.

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

Dipeptidyl peptidase-4 is increased in the abdominal aortic aneurysm vessel wall and is associated with aneurysm disease processes

BACKGROUND

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disease, and until today there is no other treatment available than surgical intervention. Dipeptidyl peptidase-4 (DPP4)-inhibitors, used clinically to treat type 2 diabetes, have in murine models been shown to attenuate aneurysm formation and decrease aortic wall matrix degradation, inflammation and apoptosis. Our aim was to investigate if DPP4 is present, active and differentially expressed in human AAA.

METHODS AND RESULTS

DPP4 gene expression was elevated in both media and adventitia of AAA tissue compared with control tissue, as measured by microarrays and qPCR, with consistent findings in external data. The plasma activity of DPP4 was however lower in male patients with AAA compared with age- and gender-matched controls, independently of comorbidity or medication. Immunohistochemical double staining revealed co-localization of DPP4 with cells positive for CD68, CD4 and -8, CD20, and SMA. Gene set enrichment analysis demonstrated that expression of DPP4 in AAA tissue correlated with expression of biological processes related to B- and T-cells, extracellular matrix turnover, peptidase activity, oxidative stress and angiogenesis whereas it correlated negatively with muscle-/actin-related processes.

CONCLUSION

DPP4 is upregulated in both media and adventitia of human AAA and correlates with aneurysm pathophysiological processes. These results support previous murine mechanistic studies and implicate DPP4 as a target in AAA disease.

Fibronectin in Cancer: Friend or Foe

The role of fibronectin (FN) in tumorigenesis and malignant progression has been highly controversial. Cancerous FN plays a tumor-suppressive role, whereas it is pro-metastatic and associated with poor prognosis. Interestingly, FN matrix deposited in the tumor microenvironments (TMEs) promotes tumor progression but is paradoxically related to a better prognosis. Here, we justify how FN impacts tumor transformation and subsequently metastatic progression. Next, we try to reconcile and rationalize the seemingly conflicting roles of FN in cancer and TMEs. Finally, we propose future perspectives for potential FN-based therapeutic strategies.

Dynamic cell–cell adhesion mediated by pericellular matrix interaction – a hypothesis

Cell–cell adhesion strength, measured as tissue surface tension, spans an enormous 1000-fold range when different cell types are compared. However, the examination of basic mechanical principles of cell adhesion indicates that cadherin-based and related mechanisms are not able to promote the high-strength adhesion experimentally observed in many late embryonic or malignant tissues. Therefore, the hypothesis is explored that the interaction of the pericellular matrices of cells generates strong adhesion by a mechanism akin to the self-adhesion/self-healing of dynamically cross-linked hydrogels. Quantitative data from biofilm matrices support this model. The mechanism links tissue surface tension to pericellular matrix stiffness. Moreover, it explains the wide, matrix-filled spaces around cells in liquid-like, yet highly cohesive, tissues, and it rehabilitates aspects of the original interpretation of classical cell sorting experiments, as expressed in Steinberg's differential adhesion hypothesis: that quantitative differences in adhesion energies between cells are sufficient to drive sorting.

DynOVis: a web tool to study dynamic perturbations for capturing dose-over-time effects in biological networks

Background

The development of high throughput sequencing techniques provides us with the possibilities to obtain large data sets, which capture the effect of dynamic perturbations on cellular processes. However, because of the dynamic nature of these processes, the analysis of the results is challenging. Therefore, there is a great need for bioinformatics tools that address this problem.

Results

Here we present DynOVis, a network visualization tool that can capture dynamic dose-over-time effects in biological networks. DynOVis is an integrated work frame of R packages and JavaScript libraries and offers a force-directed graph network style, involving multiple network analysis methods such as degree threshold, but more importantly, it allows for node expression animations as well as a frame-by-frame view of the dynamic exposure. Valuable biological information can be highlighted on the nodes in the network, by the integration of various databases within DynOVis. This information includes pathway-to-gene associations from ConsensusPathDB, disease-to-gene associations from the Comparative Toxicogenomics databases, as well as Entrez gene ID, gene symbol, gene synonyms and gene type from the NCBI database.

Conclusions

DynOVis could be a useful tool to analyse biological networks which have a dynamic nature. It can visualize the dynamic perturbations in biological networks and allows the user to investigate the changes over time. The integrated data from various online databases makes it easy to identify the biological relevance of nodes in the network. With DynOVis we offer a service that is easy to use and does not require any bioinformatics skills to visualize a network.

CD26 in autoimmune diseases: The other side of "moonlight protein"

Dipeptidyl peptidase 4 (DPP-4) is a serine protease, which has enzymatic activity to selectively clean the N-terminal dipeptide of peptides and proteins with proline or alanine in the second position. DPP-4 inhibitor has been widely used for the treatment of type 2 diabetes by increasing the level of the glucagon-like peptide-1 and decreasing the glucose level. DPP-4, also known as lymphocyte cell surface protein CD26, plays a core role of T cell immunity. Many roles of CD26 in other immune cells have been found. As a "moonlight protein", the effect of CD26 in autoimmune diseases has attracted more and more attention. The paper reviewed the function and potential effect of CD26 in autoimmune diseases, which shows CD26 may be a new target of autoimmune diseases deserved further study.

CD26 and Asthma: a Comprehensive Review

Asthma is a heterogeneous and chronic inflammatory family of disorders of the airways with increasing prevalence that results in recurrent and reversible bronchial obstruction and expiratory airflow limitation. These diseases arise from the interaction between environmental and genetic factors, which collaborate to cause increased susceptibility and severity. Many asthma susceptibility genes are linked to the immune system or encode enzymes like metalloproteases (e.g., ADAM-33) or serine proteases. The S9 family of serine proteases (prolyl oligopeptidases) is capable to process peptide bonds adjacent to proline, a kind of cleavage-resistant peptide bonds present in many growth factors, chemokines or cytokines that are important for asthma. Curiously, two serine proteases within the S9 family encoded by genes located on chromosome 2 appear to have a role in asthma: CD26/dipeptidyl peptidase 4 (DPP4) and DPP10. The aim of this review is to summarize the current knowledge about CD26 and to provide a structured overview of the numerous functions and implications that this versatile enzyme could have in this disease, especially after the detection of some secondary effects (e.g., viral nasopharyngitis) in type II diabetes mellitus patients (a subset with a certain risk of developing obesity-related asthma) upon CD26 inhibitory therapy.

Surface expression marker profile in colon cancer cell lines and sphere-derived cells suggests complexity in CD26+ cancer stem cells subsets

Taking advantage of eight established cell lines from colorectal cancer patients at different stages of the disease and the fact that all of them could form spheres, cell surface biomarkers of cancer stem cells and epithelial-mesenchymal transition were tested. The aim was to investigate cancer stem cells and metastatic stem cells in order to provide functional characterization of circulating tumor cells and promote the development of new anti-metastatic therapies. Our model showed an important heterogeneity in EpCAM, CD133, CD44, LGR5, CD26 and E-cadherin expression. We showed the presence of a subset of E-cadherin⁺ (some cells being E-cadherin^high) expressing CD26⁺ (or CD26^high) together with the well-known CSC markers LGR5 and EpCAM^high, sometimes in the absence of CD44 or CD133. The already described CD26⁺/E-cadherin^low or ^negative and CD26⁺/EpCAM⁻/CD133⁻ subsets were also present. Cell division drastically affected the expression of all markers, in particular E-cadherin, so new-born cells resembled mesenchymal cells in surface staining. CD26 and/or dipeptidyl peptidase 4 inhibitors have already shown anti-metastatic effects in pre-clinical models, and the existence of these CD26⁺ subsets may help further research against cancer metastasis.

Summary: In our model of eight established cell lines from colorectal cancer patients we show the presence of different putative cancer stem cell (CSC) subsets with expression of CD26/DPP4.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

Oxidized LDL upregulates macrophage DPP4 expression via TLR4/TRIF/CD36 pathways

Background

We and others have shown that dipeptidyl peptidase-IV (DPP4) expression is increased in obesity/atherosclerosis and is positively correlated with atherosclerotic burden. However, the mechanism by which DPP4 expression is regulated in obesity remains unclear. In this study, we investigated the pathways regulating the expression of DPP4 on macrophages.

Methods

Flowsight® Imaging Flow Cytometry was employed for the detection of DPP4 and immunophenotyping. DPP4 enzymatic activity was measured by a DPPIV-Glo™ Protease Assay kit.

Findings

Human monocytes expressed a moderate level of membrane-bound DPP4. Obese patients with body mass index (BMI) ≥ 30 had a higher level of monocyte DPP4 expression, in parallel with higher levels of HOMA-IR, blood glucose, triglycerides, and non-HDL cholesterol, compared to those in the non-obese (BMI < 30) patients. Oxidized low-density lipoprotein (oxLDL), but not native LDL, up-regulated DPP4 expression on macrophages with a preferential increase in CD36⁺ cells. OxLDL mediated DPP4 up-regulation was considerably diminished by Toll-like receptor-4 (TLR4) knockdown and CD36 deficiency. TRIF deficiency, but not MyD88 deficiency, attenuated oxLDL-induced DPP4 increase.

Interpretation

Our study suggests a key role for oxLDL and downstream CD36/TLR4/TRIF in regulating DPP4 expression. Increased DPP4 in response to oxidized lipids may represent an integrated mechanism linking post-prandial glucose metabolism to lipoprotein abnormality-potentiated atherosclerosis.

PDGF-A suppresses contact inhibition during directional collective cell migration

The leading-edge mesendoderm (LEM) of the Xenopus gastrula moves as an aggregate by collective migration. However, LEM cells on fibronectin in vitro show contact inhibition of locomotion by quickly retracting lamellipodia upon mutual contact. We found that a fibronectin-integrin-syndecan module acts between p21-activated kinase 1 upstream and ephrin B1 downstream to promote the contact-induced collapse of lamellipodia. To function in this module, fibronectin has to be present as puncta on the surface of LEM cells. To overcome contact inhibition in LEM cell aggregates, PDGF-A deposited in the endogenous substratum of LEM migration blocks the fibronectin-integrin-syndecan module at the integrin level. This stabilizes lamellipodia preferentially in the direction of normal LEM movement and supports cell orientation and the directional migration of the coherent LEM cell mass.

The Establishment of a Lung Colonization Assay for Circulating Tumor Cell Visualization in Lung Tissues

Metastasis is the major cause of cancer death. The role of circulating tumor cells (CTCs) in promoting cancer metastasis, in which lung colonization by CTCs critically contributes to early lung metastatic processes, has been vigorously investigated. As such, animal models are the only approach that captures the full systemic process of metastasis. Given that problems occur in previous experimental designs for examining the contributions of CTCs to blood vessel extravasation, we established an in vivo lung colonization assay in which a long-term-fluorescence cell-tracer, carboxyfluorescein succinimidyl ester (CFSE), was used to label suspended tumor cells and lung perfusion was performed to clear non-specifically trapped CTCs prior to lung removal, confocal imaging, and quantification. Polymeric fibronectin (polyFN) assembled on CTC surfaces has been found to mediate lung colonization in the final establishment of metastatic tumor tissues. Here, to specifically test the requirement of polyFN assembly on CTCs for lung colonization and extravasation, we performed short term lung colonization assays in which suspended Lewis lung carcinoma cells (LLCs) stably expressing FN-shRNA (shFN) or scramble-shRNA (shScr) and pre-labeled with 20 μM of CFSE were intravenously inoculated into C57BL/6 mice. We successfully demonstrated that the abilities of shFN LLC cells to colonize the mouse lungs were significantly diminished in comparison to shScr LLC cells. Therefore, this short-term methodology may be widely applied to specifically demonstrate the ability of CTCs within the circulation to colonize the lungs.

DPP4/CD26 overexpression in urothelial carcinoma confers an independent prognostic impact and correlates with intrinsic biological aggressiveness

Urothelial carcinoma (UC) is common cancer worldwide. The molecular aberrations regarding tumor progression remain unclear. Pericellular proteolysis is crucial in tumorigenesis, but its significance is unexplored in UC. By data mining the datasets in Gene Expression Omnibus, specifically focus on the proteolysis pathway, and followed by a preliminary validation in a pilot batch of tumor samples, we identified that the upregulation of dipeptidyl peptidase 4 (DPP4) was most significantly associated with clinical aggressiveness of UCs. Quantitative RT-PCR confirmed upregulation of DPP4 mRNA in advanced stage UCs. The clinical significance of DPP4 expression was validated in our large cohort consists of 635 UCs from upper urinary tract and urinary bladder. Univariate and multivariate analyses show that DPP4 is an independent prognosticatory biomarker for disease-specific survival and metastasis-free survival. Comparing the DPP4 expression level of three urothelial cell lines with normal urothelial cells, J82 and RTCC-1 showed a significantly increased in transcript and protein expression. DPP4 knockdown as conducted by using short-hairpin RNA resulted in a significantly decreased cell viability, proliferation, migration, and invasion in J82 and RTCC-1 cells. These findings implicate that DPP4 plays a role in the aggressiveness of UCs, and can serve as a novel prognostic marker and therapeutic target.

Apoptotic and Nonapoptotic Activities of Pterostilbene against Cancer

Cancer is a major cause of death. The outcomes of current therapeutic strategies against cancer often ironically lead to even increased mortality due to the subsequent drug resistance and to metastatic recurrence. Alternative medicines are thus urgently needed. Cumulative evidence has pointed out that pterostilbene (trans-3,5-dimethoxy-4-hydroxystilbene, PS) has excellent pharmacological benefits for the prevention and treatment for various types of cancer in their different stages of progression by evoking apoptotic or nonapoptotic anti-cancer activities. In this review article, we first update current knowledge regarding tumor progression toward accomplishment of metastasis. Subsequently, we review current literature regarding the anti-cancer activities of PS. Finally, we provide future perspectives to clinically utilize PS as novel cancer therapeutic remedies. We, therefore, conclude and propose that PS is one ideal alternative medicine to be administered in the diet as a nutritional supplement.

α1-antitrypsin promotes lung adenocarcinoma metastasis through upregulating fibronectin expression

α1-antitrypsin (AAT) has been recognized to be associated with lung adenocarcinoma metastasis. However, the mechanisms by which AAT promotes tumor metastasis remain to be investigated. Herein, we first examined AAT expression in a panel of formalin-fixed paraffin-embedded tumor tissues from 88 lung adenocarcinoma patients undergoing curative resection, using immunohistochemical methods. Lung adenocarcinoma patients with high AAT expression showed a significantly shorter overall survival compared to those with low AAT expression by Kaplan-Meier method (P=0.008). High AAT expression was also identified as an independent prognostic factor by Cox regression analysis (adjusted hazard ratio: 2.05; P=0.04). Second, the role of AAT in lung adenocarcinoma cell migration was evaluated in vitro using wound healing and Transwell assays, by transfecting the lentivirus vector with interfering sequence or coding sequence of AAT. The migration property of A549 and SPC-A1 cells was significantly diminished by downregulating AAT expression. Conversely, the migration of both cell lines was significantly increased through upregulating AAT. Furthermore, AAT could increase the expression of fibronectin (FN). FN down-regulation reversed AAT-induced promotion of adenocarcinoma cell migration. Third, a cancer cell/endothelial cell co-culture model was established to investigate the effect of AAT on adenocarcinoma cell adhesion using immunofluorescence examination. The results showed that downregulation of AAT inhibited adhesion between lung adenocarcinoma cells and human umbilical vein endothelial cells whereas upregulation of AAT promoted adhesion, which may attribute to interactions between FN and integrin α5. Finally, AAT also showed the regulation effect on the metastatic behavior of lung adenocarcinoma cells in a mouse model, which may be through regulating FN expression. This study suggested that high AAT expression might be a negative prognostic marker for lung adenocarcinoma. AAT promoted lung adenocarcinoma metastasis, whose functional target may be FN. Our findings provide new insight into the mechanisms of lung adenocarcinoma metastasis.

Pterostilbene prevents AKT-ERK axis-mediated polymerization of surface fibronectin on suspended lung cancer cells independently of apoptosis and suppresses metastasis

Background

Polymeric fibronectin (polyFN) assembled on suspended breast cancer cells is required for metastasis. Conceivably, drugs that target such polyFN may fight against cancer metastasis. While stilbene analogs trigger pro-apoptotic effect on attached cancer cells, whether they prevent polyFN assembly and metastasis of suspended cancer cells via an apoptosis-independent manner remains unexplored.

Methods

We depleted suspended Lewis lung carcinoma (LLC) cells of polyFN by silencing the endogenous FN expression or pterostilbene (PS) to examine whether metastasis of lung cancer cells could thus be suppressed. We investigated whether PS regulates AKT-ERK signaling axis to suppress polyFN assembly in suspended LLC cells independently of apoptosis. We tested the therapeutic effects of orally administered PS against cancer metastasis.

Results

Both FN-silencing and PS among the three stilbenoids indeed significantly reduced polyFN assembly and lung metastasis of suspended LLC cells in an apoptosis-independent manner. Mechanistically, PS-induced AKT phosphorylation (pAKT) and suppressed ERK phosphorylation (pERK) in suspended LLC cells, whereas pretreatment with a PI3K inhibitor, LY294002, effectively reduced pAKT, rescued pERK, and consequently reversed the PS-suppressed polyFN assembly on LLC cells; these pretreatment effects were then overturned by the ERK inhibitor U0126. Indeed, PS-suppressed lung metastasis was counteracted by LY294002, which was further overruled with U0126. Finally, we found that PS, when orally administered in experimental metastasis assays, both significantly prevented lung colonization and metastasis of LLC cells and reduced the already established tumor growth in the mouse lungs.

Conclusions

PS suppressed AKT/ERK-regulated polyFN assembly on suspended LLC cells and pulmonary metastasis. PS possesses potency in both preventing and treating lung metastasis of lung cancer cells in apoptosis-independent and apoptosis-dependent manners, respectively.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0441-z) contains supplementary material, which is available to authorized users.

The expression of proline-specific enzymes in the human lung

The pathophysiology of lung diseases is very complex and proteolytic enzymes may play a role or could be used as biomarkers. In this review, the literature was searched to make an overview of what is known on the expression of the proline-specific peptidases dipeptidyl peptidase (DPP) 4, 8, 9, prolyl oligopeptidase (PREP) and fibroblast activation protein α (FAP) in the healthy and diseased lung. Search terms included asthma, chronic obstructive pulmonary disease (COPD), lung cancer, fibrosis, ischemia reperfusion injury and pneumonia. Knowledge on the loss or gain of protein expression and activity during disease might tie these enzymes to certain cell types, substrates or interaction partners that are involved in the pathophysiology of the disease, ultimately leading to the elucidation of their functional roles and a potential therapeutic target. Most data could be found on DPP4, while the other enzymes are less explored. Published data however often appear to be conflicting, the applied methods divers and the specificity of the assays used questionable. In conclusion, information on the expression of the proline-specific peptidases in the healthy and diseased lung is lacking, begging for further well-designed research.

Mechanism of Fibronectin Binding to Human Trabecular Meshwork Exosomes and Its Modulation by Dexamethasone

Exosomes are emerging as important mediators of cell-matrix interactions by means of specific adhesion proteins. Changes in the tissue-specific exosomal protein expression may underlie pathological conditions whereby extracellular matrix turnover and homeostasis is disrupted. Ocular hypertension due to extracellular matrix accumulation in the trabecular meshwork is a hallmark of glucocorticoid-induced glaucoma. In the trabecular meshwork, exosomal fibronectin mediates cell matrix interactions at cellular structures called “invadosomes”. Trabecular meshwork cells use invadosomes to turn over their surrounding matrix and maintain passageways for flow of aqueous humor. In this study, we observed that human trabecular meshwork explants treated with dexamethasone released exosomes with significantly reduced amounts of fibronectin bound per exosome. Further, we found that exosome-fibronectin binding is heparan sulfate-dependent, consistent with our observation that trabecular meshwork exosomes are enriched in the heparin/heparan sulfate binding annexins A2 and A6. In this way, dexamethasone-treated explants released exosomes with a significant reduction in annexin A2 and A6 per exosome. Interestingly, we did not detect exosomal matrix metalloproteinases, but we identified abundant dipeptidyl peptidase 4, a serine protease whose activity was reduced on exosomes isolated from dexamethasone-treated explants. Together, our findings demonstrate mechanistically how corticosteroid-induced alterations in exosomal adhesion cargo and properties can account for the pathological matrix accumulation seen in many glaucoma patients.

Cut to the chase: a review of CD26/dipeptidyl peptidase-4's (DPP4) entanglement in the immune system

CD26/DPP4 (dipeptidyl peptidase 4/DP4/DPPIV) is a surface T cell activation antigen and has been shown to have DPP4 enzymatic activity, cleaving-off amino-terminal dipeptides with either L-proline or L-alanine at the penultimate position. It plays a major role in glucose metabolism by N-terminal truncation and inactivation of the incretins glucagon-like peptide-1 (GLP) and gastric inhibitory protein (GIP). In 2006, DPP4 inhibitors have been introduced to clinics and have been demonstrated to efficiently enhance the endogenous insulin secretion via prolongation of the half-life of GLP-1 and GIP in patients. However, a large number of studies demonstrate clearly that CD26/DPP4 also plays an integral role in the immune system, particularly in T cell activation. Therefore, inhibition of DPP4 might represent a double-edged sword. Apart from the metabolic benefit, the associated immunological effects of long term DPP4 inhibition on regulatory processes such as T cell homeostasis, maturation and activation are not understood fully at this stage. The current data point to an important role for CD26/DPP4 in maintaining lymphocyte composition and function, T cell activation and co-stimulation, memory T cell generation and thymic emigration patterns during immune-senescence. In rodents, critical immune changes occur at baseline levels as well as after in-vitro and in-vivo challenge. In patients receiving DPP4 inhibitors, evidence of immunological side effects also became apparent. The scope of this review is to recapitulate the role of CD26/DPP4 in the immune system regarding its pharmacological inhibition and T cell-dependent immune regulation.

Proteolytic Enzymes Clustered in Specialized Plasma-Membrane Domains Drive Endothelial Cells' Migration

In vitro cultured endothelial cells forming a continuous monolayer establish stable cell-cell contacts and acquire a “resting” phenotype; on the other hand, when growing in sparse conditions these cells acquire a migratory phenotype and invade the empty area of the culture. Culturing cells in different conditions, we compared expression and clustering of proteolytic enzymes in cells having migratory versus stationary behavior. In order to observe resting and migrating cells in the same microscopic field, a continuous cell monolayer was wounded. Increased expression of proteolytic enzymes was evident in cell membranes of migrating cells especially at sprouting sites and in shed membrane vesicles. Gelatin zymography and western blotting analyses confirmed that in migrating cells, expression of membrane-bound and of vesicle-associated proteolytic enzymes are increased. The enzymes concerned include MMP-2, MMP-9, MT1-MMP, seprase, DPP4 (DiPeptidyl Peptidase 4) and uPA. Shed membrane vesicles were shown to exert degradative activity on ECM components and produce substrates facilitating cell migration. Vesicles shed by migrating cells degraded ECM components at an increased rate; as a result their effect on cell migration was amplified. Inhibiting either Matrix Metallo Proteases (MMPs) or Serine Integral Membrane Peptidases (SIMPs) caused a decrease in the stimulatory effect of vesicles, inhibiting the spontaneous migratory activity of cells; a similar result was also obtained when a monoclonal antibody acting on DPP4 was tested. We conclude that proteolytic enzymes have a synergistic stimulatory effect on cell migration and that their clustering probably facilitates the proteolytic activation cascades needed to produce maximal degradative activity on cell substrates during the angiogenic process.