Expression profiling of dipeptidyl peptidase 8 and 9 in breast and ovarian carcinoma cell lines

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 9 regulates the dynamics of tumorigenesis and metastasis in breast cancer

The cytosolic dipeptidyl-aminopeptidase 9 (DPP9) cleaves protein N-termini post-proline or -alanine. Our analysis of DPP9 mRNA expression from the TCGA 'breast cancer' data set revealed that low/intermediate DPP9 levels are associated with poor overall survival of breast cancer patients. To unravel the impact of DPP9 on breast cancer development and progression, the transgenic MMTV-PyMT mouse model of metastasizing breast cancer was used. In addition, tissue- and time-controlled genetic deletion of DPP9 by the Cre-loxP recombination system was done. Despite a delay of tumor onset, a higher number of lung metastases were measured in DPP9-deficient mice compared to controls. In human mammary epithelial cells with oncogenic RAS pathway activation, DPP9 deficiency delayed tumorigenic transformation and accelerated TGF-β1 induced epithelial-to-mesenchymal transition (EMT) of spheroids. For further analysis of the mechanism, primary breast tumor cells were isolated from the MMTV-PyMT model. DPP9 deficiency in these cells caused cancer cell migration and invasion accompanied by EMT. In absence of DPP9, the EMT transcription factor ZEB1 was stabilized due to insufficient degradation by the proteasome. In summary, low expression of DPP9 appears to decelerate mammary tumorigenesis but favors EMT and metastasis, which establishes DPP9 as a novel dynamic regulator of breast cancer initiation and progression.

DPP9 Stabilizes NRF2 to Suppress Ferroptosis and Induce Sorafenib Resistance in Clear Cell Renal Cell Carcinoma

The KEAP1-NRF2 axis is the principal regulator of cellular responses to oxidative and electrophilic stressors. NRF2 hyperactivation is frequently observed in many types of cancer and promotes cancer initiation, progression, metastasis, and resistance to various therapies. Here, we determined that dipeptidyl peptidase 9 (DPP9) is a regulator of the KEAP1-NRF2 pathway in clear cell renal cell carcinoma (ccRCC). DPP9 was markedly overexpressed at the mRNA and protein levels in ccRCC, and high DPP9 expression levels correlated with advanced tumor stage and poor prognosis in patients with ccRCC. Protein affinity purification to identify functional partners of DPP9 revealed that it bound to KEAP1 via a conserved ESGE motif. DPP9 disrupted KEAP1-NRF2 binding by competing with NRF2 for binding to KEAP1 in an enzyme-independent manner. Upregulation of DPP9 led to stabilization of NRF2, driving NRF2-dependent transcription and thereby decreasing cellular reactive oxygen species levels. Moreover, DPP9 overexpression suppressed ferroptosis and induced resistance to sorafenib in ccRCC cells, which was largely dependent on the NRF2 transcriptional target SLC7A11. Collectively, these findings indicate that the accumulation of DPP9 results in hyperactivation of the NRF2 pathway to promote tumorigenesis and intrinsic drug resistance in ccRCC.

SIGNIFICANCE

DPP9 overcomes oxidative stress and suppresses ferroptosis in ccRCC by binding to KEAP1 and promoting NRF2 stability, which drives tumor development and sorafenib resistance.

Dipeptidyl-Aminopeptidases 8 and 9 Regulate Autophagy and Tamoxifen Response in Breast Cancer Cells

The cytosolic dipeptidyl-aminopeptidases 8 (DPP8) and 9 (DPP9) belong to the DPPIV serine proteases with the unique characteristic of cleaving off a dipeptide post-proline from the N-termini of substrates. To study the role of DPP8 and DPP9 in breast cancer, MCF-7 cells (luminal A-type breast cancer) and MDA.MB-231 cells (basal-like breast cancer) were used. The inhibition of DPP8/9 by 1G244 increased the number of lysosomes in both cell lines. This phenotype was more pronounced in MCF-7 cells, in which we observed a separation of autophagosomes and lysosomes in the cytosol upon DPP8/9 inhibition. Likewise, the shRNA-mediated knockdown of either DPP8 or DPP9 induced autophagy and increased lysosomes. DPP8/9 inhibition as well as the knockdown of the DPPs reduced the cell survival and proliferation of MCF-7 cells. Additional treatment of MCF-7 cells with tamoxifen, a selective estrogen receptor modulator (SERM) used to treat patients with luminal breast tumors, further decreased survival and proliferation, as well as increased cell death. In summary, both DPP8 and DPP9 activities confine macroautophagy in breast cancer cells. Thus, their inhibition or knockdown reduces cell viability and sensitizes luminal breast cancer cells to tamoxifen treatment.

FAP is critical for ovarian cancer cell survival by sustaining NF-κB activation through recruitment of PRKDC in lipid rafts

Fibroblast activation protein (FAP) is tumor-specific and plays an important role in tumorigenecity. However, agents against its enzymatic activity or extracellular presence were unsuccessful in the clinic for undefined reasons. Here we show that FAP expression is higher in advanced ovarian cancer and is only detected in invasive ovarian cancer cells. Silencing FAP induces apoptosis and FAP's enzymatic activity is dispensable for cell survival. To elucidate the cause of apoptosis, we find that NF-κB activity is diminished when FAP is depleted and BIRC5 (survivin) acts downstream of FAP-NF-κB axis to promote cell survival. To uncover the link between FAP and NF-κB activation, we reveal that PRKDC (DNA-PK, DNA-dependent protein kinase) forms complex with FAP and is required for NF-κB activation and cell survival. Remarkably, FAP-PRKDC interaction occurs only in lipid rafts, and depleting FAP prevents lipid raft localization of PRKDC. Given the known ability of PRKDC to direct NF-κB activation, these results suggest that FAP recruits PRKDC in lipid rafts for NF-κB activation. FAP's non-enzymatic role and functioning from lipid rafts for cell survival also offer an explanation on the failure of past FAP-targeted therapies. Finally, we demonstrate that EpCAM aptamer-delivered FAP siRNA impeded intraperitoneal xenograft development of ovary tumors.

The amino-dipeptidyl peptidases DPP8 and DPP9: Purification and enzymatic assays

Proline residues highly impact protein stability when present either in the first or second N-terminal position. While the human genome encodes for more than 500 proteases, only few proteases are capable of hydrolyzing a proline-containing peptide bond. The two intra-cellular amino-dipeptidyl peptidases DPP8 and DPP9 are exceptional as they possess the rare ability to cleave post-proline. By removing N-terminal Xaa-Pro dipeptides, DPP8 and DPP9 expose a neo N-terminus of their substates, which can consequently alter inter- or intra-molecular interactions of the modified protein. Both DPP8 and DPP9 play key roles in the immune response and are linked to cancer progression, emerging as attractive drug targets. DPP9 is more abundant than DPP8 and is rate limiting for cleavage of cytosolic proline-containing peptides. Only few DPP9 substrates have been characterized; these include Syk, a central kinase for B-cell receptor mediated signaling; Adenylate Kinase 2 (AK2) which is important for cellular energy homeostasis; and the tumor suppressor Breast cancer type 2 susceptibility protein (BRCA2) that is critical for repair of DNA double strand breaks. N-terminal processing of these proteins by DPP9 triggers their rapid turn-over by the proteasome, highlighting a role for DPP9 as upstream components of the N-degron pathway. Whether N-terminal processing by DPP9 leads to substrate-degradation in all cases, or whether additional outcomes are possible, remains to be tested. In this chapter we will describe methods for purification of DPP8 and DPP9 as well as protocols for biochemical and enzymatic characterization of these proteases.

New insights into the role of dipeptidyl peptidase 8 and dipeptidyl peptidase 9 and their inhibitors

Dipeptidyl peptidase 8 (DPP8) and 9 (DPP9) are widely expressed in mammals including humans, mainly locate in the cytoplasm. The DPP8 and DPP9 (DPP8/9) belong to serine proteolytic enzymes, they can recognize and cleave N-terminal dipeptides of specific substrates if proline is at the penultimate position. Because the localization of DPP8/9 is different from that of DPP4 and the substrates for DPP8/9 are not yet completely clear, their physiological and pathological roles are still being further explored. In this article, we will review the recent research advances focusing on the expression, regulation, and functions of DPP8/9 in physiology and pathology status. Emerging research results have shown that DPP8/9 is involved in various biological processes such as cell behavior, energy metabolism, and immune regulation, which plays an essential role in maintaining normal development and physiological functions of the body. DPP8/9 is also involved in pathological processes such as tumorigenesis, inflammation, and organ fibrosis. In recent years, related research on immune cell pyroptosis has made DPP8/9 a new potential target for the treatment of hematological diseases. In addition, DPP8/9 inhibitors also have great potential in the treatment of tumors and chronic kidney disease.

Circulating Dipeptidyl Peptidase Activity Is a Potential Biomarker for Inflammatory Bowel Disease

INTRODUCTION

Dipeptidyl peptidase (DPP)-4 is part of a larger family of proteases referred to as DPPs. DPP4 has been suggested as a possible biomarker for inflammatory bowel disease (IBD). Circulating DPP4 (cDPP4) enzyme activity was investigated as a potential biomarker for IBD. In addition, DPP enzyme activity and gene expression were quantified in colonic tissue of patients with IBD and non-IBD.

METHODS

In study 1, DPP enzyme activity was quantified in plasma samples from 220 patients with IBD (Crohn's disease [CD] n = 130 and ulcerative colitis [UC] n = 90) and non-IBD controls (n = 26) using a colorimetric assay. In study 2, tissue and plasma samples were collected from 26 patients with IBD and 20 non-IBD controls. Plasma C-reactive protein (CRP) was quantified in all patients. Colonic DPP4, DPP8, DPP9, and fibroblast activation protein (FAP) gene expression was determined by quantitative polymerase chain reaction. cDPP and cFAP enzyme activity was also measured. Sensitivity and specificity were determined by receiver operating characteristic curve analysis.

RESULTS

In study 1, total cDPP activity was found to differentiate patients with CD with active disease (n = 18) from those in remission (n = 19; sensitivity 78% and specificity 63%). In study 2, total cDPP and cFAP activity was 28% and 48% lower in patients with elevated CRP (>10 mg/L), respectively, compared with patients with normal CRP. Gene expression of DPP4, FAP, and DPP8 was also significantly higher in colonic biopsies from patients with IBD compared with non-IBD patients (P < 0.05).

DISCUSSION

Our findings implicate the DPP enzyme family in intestinal inflammation and suggest future biomarker applications to differentiate the pathophysiological aspects of IBD.

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

Dipeptidyl peptidase-8 induces Sorafenib resistance via binding with c-Rel to mediate NF-κB signaling in hepatocellular carcinoma

Sorafenib is the important first standard drug for patients with advanced hepatocellular carcinoma (HCC). A major obstacle to successful treatment is Sorafenib resistance. However, the mechanism of Sorafenib resistance is unclear. The present study aimed to determine the involvement of dipeptidyl peptidase-8 (DPP8) in Sorafenib resistance. DPP8 expression was detected using quantitative real-time PCR (qPCR) and western blotting. The effect of DPP8 on Sorafenib resistance was examined using terminal deoxynulceotidyl transferase nick-end-labeling (TUNEL), colony formation, flow cytometry, luciferase reporter, immunofluorescence, and immunoprecipitation (IP) assays. We found that DPP8 mRNA and protein levels were dramatically upregulated in HCC. Gene set enrichment analysis (GSEA) illustrated that DPP8 might be involved in apoptosis regulation. Downregulation of DPP8 substantially promoted the sensitivity of HCC cells to Sorafenib. Further analysis showed that DPP8 might regulate nuclear factor kappa B (NF-κB) signaling, which was confirmed using a luciferase reporter assay. Downregulation of DPP8 decreased the expression levels of downstream genes of the NF-κB pathway. IP showed that DPP8 can interact with NF-κB subunit c-Rel, an important protein of NF-κB signaling. Finally, a drug combination of Sorafenib and Val-boroPro induced higher mortality of HCC cells than Sorafenib alone in DPP8-upregulated cells. Our findings indicated that using the inhibitor Val-boroPro might be a promising method to enhance Sorafenib sensitivity in advanced HCC. This article is protected by copyright. All rights reserved.

RAB5A effect on metastasis of hepatocellular carcinoma cell line via altering the pro-invasive content of exosomes

Tumor microenvironment exerts a critical role in cancer progression and metastasis. Exosomes, cell-cell communicators and major players of the tumor microenvironment are considered as a serious mediator of cancer metastasis. Here, we determined the effect of RAB5A gene on the hepatocellular carcinoma (HCC) cells particularly whether RAB5A could affect HCC metastasis via regulating the pro-invasive content of exosomes. In response to RAB5A knockdown, we analyzed the proliferation rate and migration capability of HCC cells. Then, we estimated changes in the total protein composition of exosomes via analyzing the expression of exosomal markers, CD63 and Alix. Thereafter, alterations of the pro-invasive content of exosomes were functionally evaluated using matrigel invasion assay. Our results revealed that knockdown of RAB5A could decrease HCC cell proliferation rate and migration capability significantly. Moreover, no significant changes in the expression of exosomal CD63 and Alix reflected that no differences might be occurred in protein composition of RAB5A knockdown cell-derived exosomes. Matrigel invasion assay functionally showed that exosomes-derived from RAB5A knockdown cells still had pro-invasive properties and their pro-invasive content was not affected in response to RAB5A knockdown. In conclusion, we believe that our results propose a new explanation about RAB5A and metastatic potentials of exosomes-derived from HCC cells.

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.

Expression and clinical role of the dipeptidyl peptidases DPP8 and DPP9 in ovarian carcinoma

Dipeptidyl peptidase 9 (DPP9) was recently identified as fusion gene in ovarian high-grade serous carcinoma (HGSC). The aim of this study was to analyze the expression and clinical relevance of DPP8 and DPP9 in ovarian carcinoma, with focus on HGSC. mRNA expression by qRT-PCR of DPP8 and DPP9 was analyzed in 232 carcinomas, including 114 effusions and 118 surgical specimens (89 ovarian, 29 solid metastases). DPP8 and DPP9 protein expression was analyzed in 92 effusions. DPP8 and DPP9 mRNA was overexpressed in effusions compared to solid lesions in analysis of all histotypes (p < 0.001 both), as well as in analysis limited to HGSC (p < 0.001 for DPP9, p = 0.002 for DPP8). DPP9 mRNA was additionally overexpressed in HGSC compared to other histotypes (p = 0.021). DPP8 and DPP9 protein was expressed in carcinoma cells in 31/92 (37%) and 81/92 (88%) effusions, respectively. DPP8 protein expression in HGSC effusions was significantly related to better (complete) chemoresponse at diagnosis (p = 0.005). DPP8 and DPP9 mRNA and protein expression was unrelated to survival in analysis of the entire effusion cohort. However, higher DPP9 mRNA levels were significantly related to longer overall survival in pre-chemotherapy effusions (p = 0.049). In conclusion, DPP8 and DPP9 mRNA is frequently expressed in ovarian carcinoma, whereas DPP9 is more frequently expressed at the protein level. DPP8 and DPP9 may be related to less aggressive disease in advanced-stage HGSC.

Targeting dipeptidyl peptidase 8 genes inhibits proliferation, migration and invasion by inhibition of cyclin D1 and MMP2MMP9 signal pathway in cervical cancer

BACKGROUND

DPP8 is a member of the dipeptidyl peptidase IV family, which belongs to the S9b protease subfamily. It regulates cell proliferation, apoptosis, migration and invasion during cancer progression.

METHODS

To investigate the role of DPP8 in cervical cancer, we examined DPP8 levels in cervical cancer tissues and cells. The localization of DPP8 was determined by immunofluorescence staining. Subsequently, SiHa and HeLa cells were treated with small interfering RNA (siRNA)-DPP8. We used cell cycle analysis, an 5-ethyl-2'-deoxyuridine assay proliferation assay and a cellular apoptosis assay to determine the effect of DPP8 on the proliferation and apoptosis of cervical cancer cells. We used a Transwell assay to assess the number of transfection cancer cells migrating through the matrix. A real-time polymerase chain reaction and western blot analysis were used to analyze the expression of related proteins and to determine the phenotype caused by the depletion or overexpression of DPP8 in cervical cancer cells.

RESULTS

We observed that DPP8 was highly expressed in cervical cancer tissues and cells. DPP8 expression was observed in the cytosol and in the perinuclear area, as well as in the nuclei of cervical cancer cells. Notably, when cells were treated with siRNA-DPP8, the expression of BAX increased, and the expression of cyclin D1, Bcl-2, MMP2 and MMP9 was downregulated. In cervical cancer cell lines, silencing the expression of DPP8 not only suppressed the proliferation, migration and invasion of the cervical cancer cells, but also promoted cervical cancer cell apoptosis.

CONCLUSIONS

The data obtained in the present study reveal that DPP8 promotes the progression of cervical cancer.

Inhibition of dipeptidyl peptidase IV prevents high fat diet-induced liver cancer angiogenesis by downregulating chemokine ligand 2

Obesity is a major risk factor for hepatocellular carcinoma (HCC) and is typically accompanied by higher levels of serum dipeptidyl peptidase 4 (DPP4). However, the role of DPP4 in obesity-promoted HCC is unclear. Here, we found that consumption of a high-fat diet (HFD) promoted HCC cell proliferation and metastasis and led to poor survival in a carcinogen-induced model of HCC in rats. Notably, genetic ablation of DPP4 or treatment with a DPP4 inhibitor (vildagliptin) prevented HFD-induced HCC. Moreover, HFD-induced DPP4 activity facilitated angiogenesis and cancer cell metastasis in vitro and in vivo, and vildagliptin prevented tumor progression by mediating the pro-angiogenic role of chemokine ligand 2 (CCL2). Loss of DPP4 effectively reversed HFD-induced CCL2 production and angiogenesis, indicating that the DPP4/CCL2/angiogenesis cascade had key roles in HFD-associated HCC progression. Furthermore, concomitant changes in serum DPP4 and CCL2 were observed in 210 patients with HCC, and high serum DPP4 activity was associated with poor clinical prognosis. These results revealed a link between obesity-related high serum DPP4 activity and HCC progression. Inhibition of DPP4 may represent a novel therapeutic intervention for patients with HCC.

Hepatocellular carcinoma: Mouse models and the potential roles of proteases

Primary liver cancer is the second most common cause of mortality from cancer. The most common models of hepatocellular carcinoma, which use a chemical and/or metabolic insult, xenograft, or genetic manipulation, are discussed in this review. In the tumour microenvironment lymphocytes, fibroblasts, endothelial cells and antigen presenting cells are important determinants of cell fate. These cells make a range of proteases that modify the biological activity of other proteins, particularly extracellular matrix proteins that alter cell migration of tumour cells, fibroblasts and leucocytes, and chemokines that alter leucocyte migration. The DPP4 family of post-proline peptidase enzymes modifies cell movement and the activities of many bioactive molecules including growth factors and chemokines.

Unravelling the immunological roles of dipeptidyl peptidase 4 (DPP4) activity and/or structure homologue (DASH) proteins

Dipeptidyl peptidase (DPP) 4 (CD26, DPP4) is a multi-functional protein involved in T cell activation by co-stimulation via its association with adenosine deaminase (ADA), caveolin-1, CARMA-1, CD45, mannose-6-phosphate/insulin growth factor-II receptor (M6P/IGFII-R) and C-X-C motif receptor 4 (CXC-R4). The proline-specific dipeptidyl peptidase also modulates the bioactivity of several chemokines. However, a number of enzymes displaying either DPP4-like activities or representing structural homologues have been discovered in the past two decades and are referred to as DPP4 activity and/or structure homologue (DASH) proteins. Apart from DPP4, DASH proteins include fibroblast activation protein alpha (FAP), DPP8, DPP9, DPP4-like protein 1 (DPL1, DPP6, DPPX L, DPPX S), DPP4-like protein 2 (DPL2, DPP10) from the DPP4-gene family S9b and structurally unrelated enzyme DPP2, displaying DPP4-like activity. In contrast, DPP6 and DPP10 lack enzymatic DPP4-like activity. These DASH proteins play important roles in the immune system involving quiescence (DPP2), proliferation (DPP8/DPP9), antigen-presenting (DPP9), co-stimulation (DPP4), T cell activation (DPP4), signal transduction (DPP4, DPP8 and DPP9), differentiation (DPP4, DPP8) and tissue remodelling (DPP4, FAP). Thus, they are involved in many pathophysiological processes and have therefore been proposed for potential biomarkers or even drug targets in various cancers (DPP4 and FAP) and inflammatory diseases (DPP4, DPP8/DPP9). However, they also pose the challenge of drug selectivity concerning other DASH members for better efficacy and/or avoidance of unwanted side effects. Therefore, this review unravels the complex roles of DASH proteins in immunology.

DESC1 and MSPL activate influenza A viruses and emerging coronaviruses for host cell entry

The type II transmembrane serine protease (TTSP) TMPRSS2 cleaves and activates the influenza virus and coronavirus surface proteins. Expression of TMPRSS2 is essential for the spread and pathogenesis of H1N1 influenza viruses in mice. In contrast, H3N2 viruses are less dependent on TMPRSS2 for viral amplification, suggesting that these viruses might employ other TTSPs for their activation. Here, we analyzed TTSPs, reported to be expressed in the respiratory system, for the ability to activate influenza viruses and coronaviruses. We found that MSPL and, to a lesser degree, DESC1 are expressed in human lung tissue and cleave and activate the spike proteins of the Middle East respiratory syndrome and severe acute respiratory syndrome coronaviruses for cell-cell and virus-cell fusion. In addition, we show that these proteases support the spread of all influenza virus subtypes previously pandemic in humans. In sum, we identified two host cell proteases that could promote the amplification of influenza viruses and emerging coronaviruses in humans and might constitute targets for antiviral intervention. Importance: Activation of influenza viruses by host cell proteases is essential for viral infectivity and the enzymes responsible are potential targets for antiviral intervention. The present study demonstrates that two cellular serine proteases, DESC1 and MSPL, activate influenza viruses and emerging coronaviruses in cell culture and, because of their expression in human lung tissue, might promote viral spread in the infected host. Antiviral strategies aiming to prevent viral activation might thus need to encompass inhibitors targeting MSPL and DESC1.

Inhibition of proprotein convertases abrogates processing of the middle eastern respiratory syndrome coronavirus spike protein in infected cells but does not reduce viral infectivity

Middle East respiratory syndrome coronavirus (MERS-CoV) infection is associated with a high case-fatality rate, and the potential pandemic spread of the virus is a public health concern. The spike protein of MERS-CoV (MERS-S) facilitates viral entry into host cells, which depends on activation of MERS-S by cellular proteases. Proteolytic activation of MERS-S during viral uptake into target cells has been demonstrated. However, it is unclear whether MERS-S is also cleaved during S protein synthesis in infected cells and whether cleavage is required for MERS-CoV infectivity. Here, we show that MERS-S is processed by proprotein convertases in MERS-S–transfected and MERS-CoV–infected cells and that several RXXR motifs located at the border between the surface and transmembrane subunit of MERS-S are required for efficient proteolysis. However, blockade of proprotein convertases did not impact MERS-S–dependent transduction of target cells expressing high amounts of the viral receptor, DPP4, and did not modulate MERS-CoV infectivity. These results show that MERS-S is a substrate for proprotein convertases and demonstrate that processing by these enzymes is dispensable for S protein activation. Efforts to inhibit MERS-CoV infection by targeting host cell proteases should therefore focus on enzymes that process MERS-S during viral uptake into target cells.

Characterization of the genomic architecture and mutational spectrum of a small cell prostate carcinoma

We present the use of a series of laboratory, analytical and interpretation methods to investigate personalized cancer care for a case of small cell prostate carcinoma (SCPC), a rare and aggressive tumor with poor prognosis, for which the underlying genomic architecture and mutational spectrum has not been well characterized. We performed both SNP genotyping and exome sequencing of a Virchow node metastasis from a patient with SCPC. A variety of methods were used to analyze and interpret the tumor genome for copy number variation, loss of heterozygosity (LOH), somatic mosaicism and mutations in genes from known cancer pathways. The combination of genotyping and exome sequencing approaches provided more information than either technique alone. The results showed widespread evidence of copy number changes involving most chromosomes including the possible loss of both alleles of CDKN1B (p27/Kip1). LOH was observed for the regions encompassing the tumor suppressors TP53, RB1, and CHD1. Predicted damaging somatic mutations were observed in the retained TP53 and RB1 alleles. Mutations in other genes that may be functionally relevant were noted, especially the recently reported high confidence cancer drivers FOXA1 and CCAR1. The disruption of multiple cancer drivers underscores why SCPC may be such a difficult cancer to manage.

Advances in understanding the expression and function of dipeptidyl peptidase 8 and 9

DPP8 and DPP9 are recently identified members of the dipeptidyl peptidase IV (DPPIV) enzyme family, which is characterized by the rare ability to cleave a post-proline bond two residues from the N-terminus of a substrate. DPP8 and DPP9 have unique cellular localization patterns, are ubiquitously expressed in tissues and cell lines, and evidence suggests important contributions to various biological processes including: cell behavior, cancer biology, disease pathogenesis, and immune responses. Importantly, functional differences between these two proteins have emerged, such as DPP8 may be more associated with gut inflammation whereas DPP9 is involved in antigen presentation and intracellular signaling. Similarly, the DPP9 connections with H-Ras and SUMO1, and its role in AKT1 pathway downregulation provide essential insights into the molecular mechanisms of DPP9 action. The recent discovery of novel natural substrates of DPP8 and DPP9 highlights the potential role of these proteases in energy metabolism and homeostasis. This review focuses on the recent progress made with these post-proline dipeptidyl peptidases and underscores their emerging importance.

Dipeptidyl peptidase-4: A key player in chronic liver disease

Dipeptidyl peptidase-4 (DPP-4) is a membrane-associated peptidase, also known as CD26. DPP-4 has widespread organ distribution throughout the body and exerts pleiotropic effects via its peptidase activity. A representative target peptide is glucagon-like peptide-1, and inactivation of glucagon-like peptide-1 results in the development of glucose intolerance/diabetes mellitus and hepatic steatosis. In addition to its peptidase activity, DPP-4 is known to be associated with immune stimulation, binding to and degradation of extracellular matrix, resistance to anti-cancer agents, and lipid accumulation. The liver expresses DPP-4 to a high degree, and recent accumulating data suggest that DPP-4 is involved in the development of various chronic liver diseases such as hepatitis C virus infection, non-alcoholic fatty liver disease, and hepatocellular carcinoma. Furthermore, DPP-4 occurs in hepatic stem cells and plays a crucial role in hepatic regeneration. In this review, we described the tissue distribution and various biological effects of DPP-4. Then, we discussed the impact of DPP-4 in chronic liver disease and the possible therapeutic effects of a DPP-4 inhibitor.

Identifying natural substrates for dipeptidyl peptidases 8 and 9 using terminal amine isotopic labeling of substrates (TAILS) reveals in vivo roles in cellular homeostasis and energy metabolism

Dipeptidyl peptidases (DP) 8 and 9 are homologous, cytoplasmic N-terminal post-proline-cleaving enzymes that are anti-targets for the development of DP4 (DPPIV/CD26) inhibitors for treating type II diabetes. To date, DP8 and DP9 have been implicated in immune responses and cancer biology, but their pathophysiological functions and substrate repertoire remain unknown. This study utilizes terminal amine isotopic labeling of substrates (TAILS), an N-terminal positional proteomic approach, for the discovery of in vivo DP8 and DP9 substrates. In vivo roles for DP8 and DP9 in cellular metabolism and homeostasis were revealed via the identification of more than 29 candidate natural substrates and pathways affected by DP8/DP9 overexpression. Cleavage of 14 substrates was investigated in vitro; 9/14 substrates for both DP8 and DP9 were confirmed by MALDI-TOF MS, including two of high confidence, calreticulin and adenylate kinase 2. Adenylate kinase 2 plays key roles in cellular energy and nucleotide homeostasis. These results demonstrate remarkable in vivo substrate overlap between DP8/DP9, suggesting compensatory roles for these enzymes. This work provides the first global investigation into DP8 and DP9 substrates, providing a number of leads for future investigations into the biological roles and significance of DP8 and DP9 in human health and disease.