Dipeptidyl peptidase IV (CD26) on human lymphocytes. Synthetic inhibitors of and antibodies against dipeptidyl peptidase IV suppress the proliferation of pokeweed mitogen-stimulated peripheral blood mononuclear cells, and IL-2 and IL-6 production

Modulating Laying Hens Productivity and Immune Performance in Response to Oxidative Stress Induced by E. coli Challenge Using Dietary Propolis Supplementation

Propolis (PR) is a resin product of bee colonies that has rich bioactive antioxidant and bactericidal compounds. Endotoxin, a byproduct of bacterial growth, is reported to cause progressive induction of endogenous oxidative stress and has negative impacts on individual health and wellbeing. Hereby, we investigated the ability of PR to alleviate the oxidative stress and immunosuppression imposed by avian pathogenic Escherichia coli using laying hen as a based model. In this study, PR was dietary supplemented to hens for 4 weeks at a concentration of 0.1%. At the beginning of the 4th week of the experiment, hens from control and PR treatment were injected with E. coli (O157:H7; 107 colonies/hen) or saline. The results showed significant (p < 0.05) negative impact of E. coli challenge on antioxidant status, immune response and productive performance. PR supplementation reduced (p < 0.05) inflammation markers levels (tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β)) and plasma corticosterone concentration. The antioxidant status was ameliorated with dietary PR supplementation to challenged hens, showing significant (p < 0.05) reduction in malondialdehyde (MDA) levels and increasing total antioxidant capacity (TAC) concentrations. Cell mediated, as well as, humeral immune response improved significantly (p < 0.05) with dietary PR verified by the enhancement of T- and B-lymphocyte proliferation and the positive respond to phytohemagglutinin (PHA). Leucocyte cells viability increased significantly and the apoptotic factor forkhead box O3 (Foxo3) was reduced with PR supplementation. The current study revealed that dietary PR supplementation can effectively be used as an organic feed additive to overcome the endogenous oxidative stress induced by endotoxins challenge.

A potential contribution of dipeptidyl peptidase-4 by the mediation of monocyte differentiation in the development and progression of abdominal aortic aneurysms

OBJECTIVE

Abdominal aortic aneurysms (AAAs) are characterized by the destruction of elastin and collagen in the media and adventitia. Dipeptidyl peptidase-4 (DPP-4, an adipokine known as CD26) influences cell signaling, cell-matrix interactions, and the regulation of the functional activity of incretins in metabolic and inflammatory disorders. Although the role of DPP-4 in AAA evolution has been demonstrated, the underlying mechanisms of DPP-4-regulated AAA development remains unknown.

METHODS

Patients with AAA (n = 93) and healthy controls (CTL, n = 20) were recruited. Based on computed tomography image analyses, 93 patients were divided into two groups: those with a small AAA (SAA, aortic diameter <5 cm, n = 16) and those with a large AAA (LAA, aortic diameter ≥5 cm, n = 77). Plasma DPP-4, glucagon-like peptide-1 levels, and expression of CD26 on mononuclear cells were analyzed. In addition, phorbol 12-myristate 13-acetate (PMA)-induced THP-1 cells and angiotensin II-infused apolipoprotein E^tmlUnc mice were used to explore the underlying mechanisms.

RESULTS

The levels of DPP-4 (μU/μg) increased while active glucagon-like peptide-1 (pM) decreased in patients with AAA in a diameter-dependent manner [CTL: 2.3 ± 1.5 and 3.7 ± 2.4, respectively; SAA: 10.0 ± 10.9 and 2.1 ± 0.9, respectively; LAA: 32.2 ± 15.0 and 1.8 ± 1.1, respectively]. A significant decline in monocyte CD26 expression in patients with AAAs was observed relative to the CTL group. In vitro studies demonstrated that the inhibition of DPP-4 promoted PMA-induced monocytic cells differentiation, with increased CD68 and p21 expression, regulated by extracellular signal-regulated protein kinase 1/2 activation. Furthermore, inhibition of DPP-4 significantly increased the phosphorylation of PYK2 and paxillin in PMA-induced THP-1 cell differentiation. Finally, the animal study was used to confirm the in vitro results that LAA mice showed marked macrophage infiltration in the adventitia with a decreased expression of DPP-4 as compared with SAA mice.

CONCLUSIONS

Increased plasma DPP-4 activity may correlate with aneurysmal development. CD26 on monocytes plays a critical role in cell differentiation, possibly mediated by extracellular signal-regulated protein kinase 1/2-p21 axis signaling pathways and cytoskeletal proteins reassembly. Exploring the role of DPP-4 further may yield potential therapeutic insights.

Dpp4 inhibition as a therapeutic strategy in cardiometabolic disease: Incretin-dependent and -independent function

Cardiometabolic disorders including obesity, diabetes and cardiovascular disease are among the most severe health problems worldwide. DPP4 enzymatic inhibitors were first developed as anti-diabetic reagents which preserve incretin hormones and promote post-prandial insulin secretion. It's been shown in animal studies that incretin-based therapy has a beneficial effect on cardiovascular disease. Recent studies demonstrated novel non-catalytic functions of DPP4 that may play a role in cardiometabolic disease. Although the role of DPP4 inhibition-mediated incretin effects has been well-reviewed, little information of its incretin-independent actions was introduced in cardiometabolic disease. In the current review, we will summarize the catalytic dependent and independent effects of DPP4 inhibition on cardiometabolic disease.

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Discuss the findings from recent large scale clinical trials (EXAMINE and SAVOR-TIMI 53)

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Summarize the catalytic dependent and independent effects of DPP4 inhibition on cardiometabolic disease

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Focus on recent evidence linking DPP4 inhibition therapy with cardiovascular disease

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Provide mechanistic insights into the cardiovascular effect of DPP4

Recent Advances in Dipeptidyl-Peptidase-4 Inhibition Therapy: Lessons from the Bench and Clinical Trials

DPP4 inhibitors (DPP4i) are a class of newly developed antidiabetic drugs which preserve incretin hormones and promote postprandial insulin secretion. Although the cardiovascular effect of DPP4 inhibition has been substantially studied, the exact role of DPP4 in cardiovascular disease especially in humans remains elusive. Previous small studies and meta-analyses have suggested a benefit in both surrogate outcomes and cardiovascular events for these agents. However, there was growing evidence in recent years questioning the cardioprotective effect of DPP4i. Further, a signal of heart failure hospitalization in a recent large scale clinical trial SAVOR-TIMI 53 has called into question the safety of these agents and their utility in the treatment of cardiovascular disease. In this review, we will revisit the physiologic function of DPP4 and discuss its role in cardiometabolic disease based on recent experimental and clinical studies.

Cardiovascular impact of drugs used in the treatment of diabetes

The International Diabetes Federation predicts that by 2035 10% of the population of the world will have been diagnosed with diabetes, raising serious concerns over the resulting elevated morbidity and mortality as well as the impact on health care budgets. It is also well recognized that cardiovascular disease is the primary cause of the high morbidity and mortality associated with diabetes, raising the concern that appropriate drug therapy should not only correct metabolic dysfunction, but also protect the cardiovascular system from the effects of, in particular, the epigenetic changes that result from hyperglycaemia. A number of new classes of drugs for the treatment of diabetes have been introduced in the past decade, providing the opportunity to optimize treatment; however, comparative information of the cardiovascular benefits, or risks, of the newer drugs versus older therapies such as metformin is variable. This review, in addition to summarizing the cellular basis for the therapeutic action of these drugs, addresses the evidence for their cardiovascular benefits and risks. A particular focus is provided on metformin as it is the first choice drug for most patients with type 2 diabetes.

Emerging roles of dipeptidyl peptidase 4 inhibitors: anti-inflammatory and immunomodulatory effect and its application in diabetes mellitus

Dipeptidyl peptidase 4 (DPP4) inhibitors have been widely used in the treatment of type 2 diabetes mellitus. It is well known that DPP4 inhibitors exert their antidiabetes effects mainly by inhibiting the enzymatic degradation of glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. The anti-inflammatory effect of DPP4 inhibitors was proved by preclinical and clinical studies of type 2 diabetes and coronary artery disease. Preclinical data using DPP4 inhibitors-based therapies in studies of nonobese diabetic mice demonstrated additional effects, including immunomodulation, preserving beta-cell mass, promoting beta-cell regeneration and reversing newly diagnosed diabetes. Thus, these data show that DPP4 inhibitors may be effective for type 1 diabetes mellitus. However, their potential clinical benefits for type 1 diabetes remain to be evaluated. This paper will provide an overview of the progress of the anti-inflammatory and immunomodulatory effects of DPP4 inhibitors in treating both type 1 and type 2 diabetes.

Dipeptidyl petidase-IV inhibitor (gemigliptin) inhibits tunicamycin-induced endoplasmic reticulum stress, apoptosis and inflammation in H9c2 cardiomyocytes

The direct effects of dipeptidyl peptidase-IV (DPP-IV) inhibitors on endoplasmic reticulum (ER) stress-induced apoptosis and inflammation in cardiomyocytes have not been elucidated. H9c2 cell viability, which was reduced by tunicamycin, was increased after DPP-IV inhibitor gemigliptin treatment. Gemigliptin significantly decreased the tunicamycin-mediated increase in glucose regulated protein 78 (GRP78) expression and ER stress-mediated signaling molecules such as protein kinase RNA-like endoplasmic reticulum kinase (PERK)/C-EBP homologous protein (CHOP) and inositol-requiring enzyme 1α (IRE1α)/c-Jun N-terminal kinase (JNK)-p38. Furthermore, gemigliptin effectively induced Akt phosphorylation in a dose-dependent manner. Using flow cytometry and Hoechst staining, we showed that treatment with Akt inhibitor significantly blocked the anti-apoptotic effects mediated by gemigliptin. The reduction in tunicamycin-induced GRP78 level and PERK/CHOP pathway activity by gemigliptin was reversed after treatment with Akt inhibitor. In conclusion, gemigliptin effectively inhibited ER stress-induced apoptosis and inflammation in cardiomyocytes via Akt/PERK/CHOP and IRE1α/JNK-p38 pathways, suggesting its direct protective role in cardiovascular diseases.

An emerging role of dipeptidyl peptidase 4 (DPP4) beyond glucose control: potential implications in cardiovascular disease

The introduction of dipeptidyl peptidase 4 (DPP4) inhibitors for the treatment of Type 2 diabetes acknowledges the fundamental importance of incretin hormones in the regulation of glycemia. Small molecule inhibitors of DPP4 exert their effects via inhibition of enzymatic degradation of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). The widespread expression of DPP4 in tissues such as the vasculature and immune cells suggests that this protein may play a role in cardiovascular function. DPP4 is known to exert its effects via both enzymatic and non-enzymatic mechanisms. A soluble form of DPP4 lacking the cytoplasmic and transmembrane domain has also been recently recognized. Besides enzymatic inactivation of incretins, DPP4 also mediates degradation of many chemokines and neuropeptides. The non-enzymatic function of DPP4 plays a critical role in providing co-stimulatory signals to T cells via adenosine deaminase (ADA). DPP4 may also regulate inflammatory responses in innate immune cells such as monocytes and dendritic cells. The multiplicity of functions and targets suggests that DPP4 may play a distinct role aside from its effects on the incretin axis. Indeed recent studies in experimental models of atherosclerosis provide evidence for a robust effect for these drugs in attenuating inflammation and plaque development. Several prospective randomized controlled clinical trials in humans with established atherosclerosis are testing the effects of DPP4 inhibition on hard cardiovascular events.

Enhanced ovalbumin-induced airway inflammation in CD26-/- mice

In this study, we investigated the potential role of CD26 in ovalbumin (OVA)-induced airway inflammation using CD26 gene knockout mice. Compared with WT counterparts, CD26(-/-) mice showed an obviously enhanced tissue response and denser pulmonary infiltrates containing eosinophils around vessels and in the parenchyma after OVA sensitization and challenge. Serum IgG, including subclasses IgG1 and IgG2a, was greatly reduced in CD26(-/-) mice, but serum IgE remained unchanged. CD26(-/-) mice had increased mRNA expression of the Th2 cytokines IL-4, IL-5, and IL-13 in the lungs compared with WT mice, whereas the levels of the pro-Th1 cytokine IL-12p40 were similar in both strains. Consequently, enhanced protein secretion of IL-4, IL-5, and IL-13 was detected in bronchoalveolar lavage (BAL) fluid from CD26(-/-) mice. In agreement with overexpressed Th2 cytokines, both mRNA transcript and protein levels of chemokines eotaxin and RANTES, as well as their receptors CC chemokine receptor 3 (CCR3) and CCR5, were elevated in CD26(-/-) mice. These results suggest a protective role for CD26 in restricting OVA-induced airway inflammation.

Dipeptidyl peptidase IV inhibition improves cardiorenal function in overpacing-induced heart failure

AIMS

Recent studies indicate that brain natriuretic peptide (BNP(1-32)) may be truncated into BNP(3-32) by dipeptidyl peptidase IV (DPP4) and that BNP(3-32) has reduced biological activities compared with BNP(1-32). We investigated if DPP4 contributes to the cardiorenal alterations and to the attenuated response to BNP seen in heart failure.

METHODS AND RESULTS

Haemodynamic and renal assessment was performed in 12 pigs at baseline, 4 weeks after pacing-induced heart failure, and during BNP infusion. They were randomized to either placebo or treatment with a DPP4 inhibitor, sitagliptin. After 4 weeks of pacing, heart rate was reduced compared with baseline in the sitagliptin group (60 ± 2 vs. 95 ± 16 b.p.m., P < 0.01), and an increase in stroke volume was observed in the sitagliptin group compared with placebo (+24 ± 6% vs. -17 ± 7%, P < 0.01). Glomerular filtration rate declined at week 4 compared with baseline in the placebo group (1.3 ± 0.4 vs. 2.3 ± 0.3 mL/kg/min, P < 0.01) but remained preserved in the sitagliptin group [1.8 ± 0.2 vs. 2.0 ± 0.3 mL/kg/min, P = NS (non-significant)]. In the sitagliptin group, BNP infusion improved end-systolic elastance (68 ± 5 vs. 31 ± 4 mmHg/kg/mL, P < 0.05), ventricular-arterial coupling, and mechanical efficiency. Compared with controls (n = 6), myocardial gene expression of BNP, interleukin-6, Na(+)-Ca(2+) exchanger, and calmodulin was up-regulated in the placebo group, but not in the sitagliptin group.

CONCLUSION

In pacing-induced heart failure, DPP4 inhibition preserves the glomerular filtration rate, modulates stroke volume and heart rate, and potentiates the positive inotropic effect of exogenous BNP at no energy expense.

Dipeptidyl peptidase in autoimmune pathophysiology

CD26 is a 110-kDa surface glycoprotein with intrinsic dipeptidyl peptidase IV (DPPIV) activity that is expressed on various cell types and has many biological functions. An important aspect of CD26 biology is its peptidase activity and its functional and physical association with molecules with key roles in human immunological programs. CD26 role in immune regulation has been extensively characterized, with recent findings elucidating its link age with signaling pathways and structures involved in T cell activation a well as antigen-presenting cell-T cell interaction, being a marker of diseas behavior clinically as well as playing an important role in autoimmune pathogenesis and development. Through the use of various experimental approaches and agents to influence CD26/DPPIV expression and activity, such as anti-CD26 antibodies, CD26/DPPIV chemical inhibitors, siRNAs to inhibit CD26 expression, overexpressing CD26 transfectants, soluble CD26 molecules and proteomic approach, we have shown that CD26 interacts with structures with essential cellular functions in T cell responses. We will review emerging data that suggest CD26 may be an appropriate therapeutic target for the treatment of selected immune disorders.

Soluble CD26 / dipeptidyl peptidase IV enhances human lymphocyte proliferation in vitro independent of dipeptidyl peptidase enzyme activity and adenosine deaminase binding

Human CD26 has dipeptidyl peptidase-4 (DPP IV) enzyme activity and binds to adenosine deaminase (ADA). CD26 is costimulatory for lymphocytes and has a circulating soluble form (sCD26). DPP IV enzyme inhibition is a new successful type 2 diabetes therapy. We examined whether the ADA binding and catalytic functions of sCD26 contribute to its effects on T-cell proliferation. Wildtype soluble recombinant human CD26 (srhCD26), an enzyme inactive mutant (srhCD26E-) and an ADA non-binding mutant (srhCD26A-) were co-incubated in in vitro T-cell proliferation assays with peripheral blood mononuclear cells (PBMC) stimulated with phytohaemagglutinin (PHA), muromonab-CD3 or Herpes simplex virus antigen (HSV Ag). Both srhCD26 and srhCD26E- enhanced PHA-induced T-cell proliferation dose-dependently in all six subjects tested. srhCD26 and srhCD26A- had no overall effect on anti-CD3-stimulated PBMC proliferation in four of five subjects. srhCD26, srhCD26E- and srhCD26A- enhanced HSV Ag induced PBMC proliferation in low responders to HSV Ag, but had no effect or inhibited proliferation in HSV-high responders. Thus, effects of soluble human CD26 on human T-cell proliferation are mechanistically independent of both the enzyme activity and the ADA-binding capability of sCD26.

Modulation of cytokine production and silica-induced lung fibrosis by inhibitors of aminopeptidase N and of dipeptidyl peptidase-IV-related proteases

AIMS

Dipeptidyl peptidase IV (DP IV)-related proteases and aminopeptidase N (APN) are drug targets in various diseases. Here we investigated for the first time the effects of DP-IV-related protease inhibitors and APN inhibitors on chronic inflammatory lung diseases.

MAIN METHODS

A murine model of silica (SiO2)-induced lung fibrosis and in vitro cultures of human lung epithelial cells and monocytes have been used and the influence of silica-treatment and inhibitors on inflammation and fibrosis has been measured.

KEY FINDINGS

We found increased inflammation and secretion of the chemokines IL-6, MCP-1 and MIP-alpha 2 weeks after SiO2 application, and increased lung fibrosis after 3 months. Treatment with the APN inhibitor actinonin reduced chemokine secretion in the lung and bronchoalveolar lavage fluid, and in cell culture, and decreased the level of fibrosis after 3 months. Treatment with inhibitors of DP-IV-related proteases, or a combination of DP IV inhibitors and APN inhibitors, had no significant effect. We found no obvious side effects of long-term treatment with inhibitors of APN and DP IV.

SIGNIFICANCE

Overall, our findings show that actinonin, an inhibitor of aminopeptidase N, might modulate chemokine secretion in the lung and thus attenuate the development of lung fibrosis. Additional targeting of DP-IV-related proteases had no significant effect on these processes.

Dipeptidyl peptidase IV and related enzymes in cell biology and liver disorders

DP (dipeptidyl peptidase) IV is the archetypal member of its six-member gene family. Four members of this family, DPIV, FAP (fibroblast activation protein), DP8 and DP9, have a rare substrate specificity, hydrolysis of a prolyl bond two residues from the N-terminus. The ubiquitous DPIV glycoprotein has proved interesting in the fields of immunology, endocrinology, haematology and endothelial cell and cancer biology and DPIV has become a novel target for Type II diabetes therapy. The crystal structure shows that the soluble form of DPIV comprises two domains, an alpha/beta-hydrolase domain and an eight-blade beta-propeller domain. The propeller domain contains the ADA (adenosine deaminase) binding site, a dimerization site, antibody epitopes and two openings for substrate access to the internal active site. FAP is structurally very similar to DPIV, but FAP protein expression is largely confined to diseased and damaged tissue, notably the tissue remodelling interface in chronically injured liver. DPIV has a variety of peptide substrates, the best studied being GLP-1 (glucagon-like peptide-1), NPY (neuropeptide Y) and CXCL12. The DPIV family has roles in bone marrow mobilization. The functional interactions of DPIV and FAP with extracellular matrix confer roles for these proteins in cancer biology. DP8 and DP9 are widely distributed and indirectly implicated in immune function. The DPL (DP-like) glycoproteins that lack peptidase activity, DPL1 and DPL2, are brain-expressed potassium channel modulators. Thus the six members of the DPIV gene family exhibit diverse biological roles.

CD26/DPPIV and response to hepatitis B vaccination

The prevention of hepatitis B is important, since it is responsible for significant morbidity and mortality around the world. Unfortunately, hepatitis B vaccine does not always induce protective immunity. The lack of immune response to vaccine (non-responders) can depend on individual characteristics. The objective of this study was to correlate the CD26/DPPIV cellular expression and DPPIV serum activity with HBV vaccine response and its possible role as an indicator of immune competence acquisition. We also determined the cellular expression of CD3, CD19, CD56 and CD25 in peripheral blood T lymphocytes. Blood samples were obtained from 28 healthy human volunteers who were enrolled with a vaccination program. There were "responders" (RM = 13) and "non-responders" (NRM = 15), after vaccination. The lymphocyte populations were identified by flow cytometry. DPPIV serum activity was measured fluorimetrically. CD26 expression in responders (55.9 +/- 7.7%) versus in non-responders (51.9 +/- 7.0%) did not show a significant difference. The DPPIV serum activity in responders compared to in non-responder subgroup (59.9 +/- 8.4/50.3 +/- 10.6U/L) showed, however, a significant difference (P < 0.05). The expression of CD3, CD19 and CD56 on peripheral lymphocytes was similar between responders and non-responders. The expression of CD3CD26 (52.2 +/- 8.6%) and CD3CD25 (10.9 +/- 3.8%) in responders versus the expression of CD3CD26 (48.0 +/- 5.7%) and CD3CD25 (8 +/- 4.6%) in non-responders did not show statistically significant difference. CD25 referred as a marker of T lymphocyte activation was increased in responders (15.8 +/- 4.5%) versus in non-responders (10.1 +/- 4.8%), showing a significant difference (P = 0.003). It was, however, impossible to demonstrate an increase in CD3CD25 and CD3CD26 in the responder subgroup. This suggests that different lymphocyte subsets other than T cells are implicated in the response to hepatitis B vaccination.

Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Dipeptidyl-peptidase IV/CD26 (DPP IV) is a cell-surface protease belonging to the prolyloligopeptidase family. It selectively removes the N-terminal dipeptide from peptides with proline or alanine in the second position. Apart from its catalytic activity, it interacts with several proteins, for instance, adenosine deaminase, the HIV gp120 protein, fibronectin, collagen, the chemokine receptor CXCR4, and the tyrosine phosphatase CD45. DPP IV is expressed on a specific set of T lymphocytes, where it is up-regulated after activation. It is also expressed in a variety of tissues, primarily on endothelial and epithelial cells. A soluble form is present in plasma and other body fluids. DPP IV has been proposed as a diagnostic or prognostic marker for various tumors, hematological malignancies, immunological, inflammatory, psychoneuroendocrine disorders, and viral infections. DPP IV truncates many bioactive peptides of medical importance. It plays a role in glucose homeostasis through proteolytic inactivation of the incretins. DPP IV inhibitors improve glucose tolerance and pancreatic islet cell function in animal models of type 2 diabetes and in diabetic patients. The role of DPP IV/ CD26 within the immune system is a combination of its exopeptidase activity and its interactions with different molecules. This enables DPP IV/CD26 to serve as a co-stimulatory molecule to influence T cell activity and to modulate chemotaxis. DPP IV is also implicated in HIV-1 entry, malignant transformation, and tumor invasion.

Transcellular proteolysis demonstrated by novel cell surface-associated substrates of dipeptidyl peptidase IV (CD26)

Proteolytic enzymes contribute to the regulation of cellular functions such as cell proliferation and death, cytokine production, and matrix remodeling. Dipeptidyl peptidase IV (DP IV) catalyzes the cleavage of several cytokines and thereby contributes to the regulation of cytokine production and the proliferation of immune cells. Here we show for the first time that cell surface-bound DP IV catalyzes the cleavage of specific substrates that are associated with the cellular surface of neighboring cells. Rhodamine 110 (R110), a highly fluorescent xanthene dye, was used to synthesize dipeptidyl peptidase IV (DP IV/CD26) substrates Gly(Ala)-Pro-R110-R, thus facilitating a stable binding of the fluorescent moiety on the cell surface. The fixation resulted from the interaction with the reactive anchor rhodamine and allowed the quantification of cellular DP IV activity on single cells. The reactivity, length, and hydrophobicity of rhodamine was characterized as the decisive factor that facilitated the determination of cellular DP IV activity. Using fluorescence microscopy, it was possible to differentiate between different DP IV activities. The hydrolysis of cell-bound substrates Xaa-Pro-R110-R by DP IV of neighboring cells and by soluble DP IV was shown using flow cytometry. These data demonstrate that ectopeptidases such as DP IV may be involved in communication between blood cells via proteolysis of cell-associated substrates.

Involvement of dipeptidyl peptidase IV in immune complex-mediated glomerulonephritis

Dipeptidyl peptidase IV (DPPIV) is widely expressed in many tissues; however, its precise biological function is poorly understood. One of its possible physiologic roles is an involvement in the immune system, which plays a pivotal role in the pathogenesis of glomerulonephritis. The present study focused on the involvement of DPPIV in immune complex-mediated glomerulonephritis. Experimental nephritis was induced by anti-Thy-1.1 monoclonal antibody E30 using Wistar or F344 rats. The application of a new monoclonal antibody against DPPIV, F16, completely suppressed E30-induced proteinuria and mesangial proliferation in Wistar rats, whereas these preventive effects of F16 were not observed in F344 rats, which spontaneously lack DPPIV protein. Treatment with F16 inhibited glomerular deposition of complement C3 and complement C4 after the binding of E30 to the mesangial cell surface. Because the preventive effect of F16 was attributable to suppression of the complement cascade, we examined its influences on complement-dependent mesangial cell lysis in vitro. We discovered that the complement cascade was markedly inactivated in F16-treated Wistar rat serum but not in F16-treated F344 rats. These results indicate that DPPIV may play a somewhat crucial role in regulating the complement cascade and that inhibition of DPPIV may serve as a new target for preventing complement-dependent tissue injury.

Inhibition of human leukocyte function, alanyl aminopeptidase (APN, CD13) and dipeptidylpeptidase IV (DP IV, CD26) enzymatic activities by aqueous extracts of Cistus incanus L. ssp. incanus

Short-boiled aqueous extract from leaves of Cistus incanus L. ssp. incanus (CIT) dose-dependently inhibit the enzymatic activities of both alanyl aminopeptidase (APN, CD13, EC 3.4.11.2) and dipeptidylpeptidase IV (DP IV, CD26, EC 3.4.14.5). This inhibition is not reversible and very likely results from a covalent binding of reactive compounds to the enzymes. Furthermore, we show that aqueous CIT extracts decrease the DNA-synthesis of human T cells and mononuclear cells and inhibit the proliferation rate of the human T cell line KARPAS-299 in a dose-dependent manner. Data are presented suggesting that the antiproliferative effects of CIT extracts are due to their strong cytotoxic activity.

CD26: a multifunctional integral membrane and secreted protein of activated lymphocytes

CD26 has proved interesting in the fields of immunology, endocrinology, cancer biology and nutrition owing to its ubiquitous and unusual enzyme activity. This dipeptidyl aminopeptidase (DPP IV) activity generally inactivates but sometimes alters or enhances the biological activities of its peptide substrates, which include several chemokines. CD26 costimulates both the CD3 and the CD2 dependent T-cell activation and tyrosine phosphorylation of TCR/CD3 signal transduction pathway proteins. CD26 in vivo has integral membrane protein and soluble forms. Soluble CD26 is at significant levels in serum, these levels alter in many diseases and soluble CD26 can modulate in vitro T-cell proliferation. CD26, being an adenosine deaminase binding protein (ADAbp), functions as a receptor for ADA on lymphocytes. The focus of this review is the structure and function of CD26 and the influence of its ligand binding activity on T-cell proliferation and the T cell costimulatory activity of CD26.

Dipeptidyl peptidase IV in inflammatory CNS disease

Current pathogenic concepts of inflammatory demyelinating disorders such as multiple sclerosis (MS) are based on the hypothesis that a T cell-mediated autoimmune response is involved in the disease process. One of the primary goals in the in the development of immunotherapies for autoimmune diseases has been to achieve inactivation of disease-inducing lymphocytes either by direct inhibition or suppression through regulatory cells and/or cytokines. The CD26 antigen is identical with the cell surface ectopeptidase dipeptidyl peptidase IV (DP IV, EC 3.4.14.5) which is involved in regulating T cell activation and growth. Activated T cells, including those specific for myelin antigens, express high levels of CD26/DP IV. In vitro, reversible DP IV inhibitors suppress T cell proliferation and pro-inflammatory cytokine production in response to myelin antigens. Further studies will evaluate the role of DP IV inhibition in T cell-mediated inflammatory disease of the central nervous system.

Post-proline-cleaving peptidases having DP IV like enzyme activity. Post-proline peptidases

DP IV has been studied extensively in disease and in the immune system by the use of enzyme assays which detect hydrolysis of Gly-Pro or Ala-Pro substrate. In addition many studies have used inhibitors of DP IV enzyme activity. The characterisation of a novel DP IV like protein, DPP4R, and of other proteases which have a substrate specificity similar to DP IV or that bind DP IV inhibitors suggests that these studies require further evaluation.

Dipeptidyl peptidase IV (DP IV/CD26) mRNA expression in PWM-stimulated T-cells is suppressed by specific DP IV inhibition, an effect mediated by TGF-beta(1)

Stimulation of human T-cells by pokeweed mitogen (PWM) results in a significant increase of IL-2, IFN-gamma, and DP IV mRNA expression as analyzed by quantitative RT-PCR. Here we show for the first time that the changes observed in cytokine mRNA expression are dose-dependently suppressed by the specific dipeptidyl peptidase IV inhibitor Lys[Z(NO(2))]-thiazolidide. Most interestingly, the inhibition of DP IV activity leads to a decrease in mRNA expression of the enzyme itself. Furthermore, evidence is provided that this suppression is mediated by TGF-beta(1). The presented data fit into the hypothesis that inhibition of DP IV leads to the induction of TGF-beta(1), which in turn provokes an arrest of cell cycle in late G(1).

Down-regulation of T cell activation following inhibition of dipeptidyl peptidase IV/CD26 by the N-terminal part of the thromboxane A2 receptor

Using synthetic inhibitors, it has been shown that the ectopeptidase dipeptidyl peptidase IV (DP IV) (CD26) plays an important role in the activation and proliferation of T lymphocytes. The human immunodeficiency virus-1 Tat protein, as well as the N-terminal nonapeptide Tat(1-9) and other peptides containing the N-terminal sequence XXP, also inhibit DP IV and therefore T cell activation. Studying the effect of amino acid exchanges in the N-terminal three positions of the Tat(1-9) sequence, we found that tryptophan in position 2 strongly improves DP IV inhibition. NMR spectroscopy and molecular modeling show that the effect of Trp(2)-Tat(1-9) could not be explained by significant alterations in the backbone structure and suggest that tryptophan enters favorable interactions with DP IV. Data base searches revealed the thromboxane A2 receptor (TXA2-R) as a membrane protein extracellularly exposing N-terminal MWP. TXA2-R is expressed within the immune system on antigen-presenting cells, namely monocytes. The N-terminal nonapeptide of TXA2-R, TXA2-R(1-9), inhibits DP IV and DNA synthesis and IL-2 production of tetanus toxoid-stimulated peripheral blood mononuclear cells. Moreover, TXA2-R(1-9) induces the production of the immunosuppressive cytokine transforming growth factor-beta1. These data suggest that the N-terminal part of TXA2-R is an endogenous inhibitory ligand of DP IV and may modulate T cell activation via DP IV/CD26 inhibition.

Dipeptidyl peptidase IV (CD26): role in T cell activation and autoimmune disease

The ectoenzyme dipeptidyl peptidase IV (DP IV; EC 3.4.14.5; CD26) has been shown to play a crucial role in T cell activation. In the present study, we show by flow cytometry and by enzymatic DP IV assay that myelin basic protein (MBP)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) express high levels of DP IV/CD26. The enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 hours after PHA stimulation. The DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide suppress in a dose-dependent manner DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulating activation of autoreactive TCC. Further in vivo investigations will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS and/or other autoimmune diseases.

Early phosphorylation events induced by DPIV/CD26-specific inhibitors

Dipeptidyl peptidase IV (DPIV, CD26) is known to be involved in the regulation of T lymphocyte and NK cell activation and proliferation in vitro. The molecular events of lymphocyte activation mediated by this ectopeptidase as well as their physiological ligands are only partly established. Particularly, the necessity of catalytic dipeptidase activity for the costimulatory function of this molecule has been controversial. Here we provide evidence for a direct involvement of DPIV/CD26 in early phosphorylation mechanisms which are known to be essential in the signal transduction cascade of human T lymphocytes. We have found that DPIV-specific inhibitors (Lys[Z(NO2)]-thiazolidide and -piperidide) are capable of inducing intracellular tyrosine phosphorylation in resting human T cells. On the other hand, both inhibitors decreased the PMA-induced tyrosine phosphorylation in human T cells in a dose-dependent manner. Furthermore, a linkage between CD26 and the tyrosine kinase p56(lck) was shown by inhibition of PMA-induced hyperphosphorylation of p56(lck) by means of DPIV-specific inhibitors. The data presented here suggest that the inhibition of DPIV enzymatic activity induces a inhibitory signal transmitted by tyrosine kinases which leads to a block in a PMA-induced downstream pathway. These results support the assumption that DPIV/CD26 is directly involved in early processes of T cell activation via its enzymatic activity.

The significance of hypersialylation of dipeptidyl peptidase IV (CD26) in the inhibition of its activity by Tat and other cationic peptides. CD26: a subverted adhesion molecule for HIV peptide binding

The functionality of DPP-IV, purified from human placenta and isolated from CD4+/CD26+ T cells of noninfected and HIV-1-infected individuals, was investigated as to its ability to bind certain specific peptides. Using isoelectric focusing and the specificity of substrate-impregnated overlay membranes, we found that DPP-IV from term placenta and from T cells of HIV-infected individuals was significantly more sialylated compared with enzyme isozyme patterns of other tissues. We report here that (1) the number of isoforms of DPP-IV and extent of sialylation are critical to function and peptide binding; (2) the number of sialylated isoforms isolated from PBMCs increases significantly with age greater than 40 years; (3) hypersialylation by extreme anionic isoforms is highly associated with HIV infection and pathognomonic to remaining CD4+ cells in overt AIDS; and (4) highly sialylated DPP-IV is more significantly inhibited by Tat and cationic peptides. We conclude that hypersialylation of DPP-IV modifies surface charge of the CD26 antigen, promoting binding of HIV peptides through their cationic domains to the sialic acid residues of DPP-IV, and that certain HIV moieties are likely to engage this phenomenon as an auxiliary adhesion mechanism to fuse with cells. Furthermore, as a consequence of this occurrence, DPP-IV enzymatic activity can be significantly reduced, competitively.

Inhibitors of dipeptidyl peptidase IV/CD26 suppress activation of human MBP-specific CD4+ T cell clones

The ectoenzyme dipeptidyl peptidase IV (DP IV, EC 3.4.14.5, CD26) has been shown to play a crucial role in T cell activation. Specific inhibitors of DP IV suppress DNA synthesis as well as cytokine production (IL-2, IL-10, IL-12, IFN-gamma) of stimulated human and mouse T cells suggesting a potential application of these effectors in transplantations and autoimmune diseases. In the present study, we have examined the expression of DP IV/CD26 on six myelin basic protein (MBP)(87-99)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) as well as the biological effects of the two synthetic DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide on the function of these cells. All TCC expressed high levels of DP IV/CD26, as shown by flow cytometry and by enzymatic DP IV assay. Enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 h after PHA stimulation. The DP IV inhibitors suppress DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulation of activation of autoreactive TCC. Further in-vivo investigations, first in experimental models, will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS or other autoimmune diseases.

Dipeptidyl peptidase IV (DP IV, CD26) is involved in regulation of DNA synthesis in human keratinocytes

Various studies have shown that the membrane ectoenzyme dipeptidyl peptidase IV (DP IV, CD26), expressed on T, NK, and B cells in the human immune system, is involved in the regulation of DNA synthesis and cytokine production. Here, we clearly demonstrate that this enzyme is highly expressed also on human epidermal foreskin and split-skin keratinocytes and that the specific DP IV inhibitors Lys[Z(NO2)]-thiazolidide, Lys[Z(NO2)]-pyrrolidide inhibit the enzymatic activity as well as the DNA synthesis of these cells. These data demonstrate that CD26 plays a role also in regulation of DNA synthesis of epidermal keratinocytes and that the enzymatic activity is required for mediating these effects.

The N-terminal structure of HIV-1 Tat is required for suppression of CD26-dependent T cell growth

Evidence exists that the human immunodeficiency virus-1 (HIV-1) transactivator Tat occurs extracellularly and is involved in the immunosuppression of non-HIV-1-infected T cells of acquired immunodeficiency syndrome (AIDS) patients. The mechanism of this immunosuppressive activity of Tat has been controversially discussed. Interestingly, Tat binds to the T cell activation marker CD26, which has been shown to play a key role in the regulation of growth of lymphocytes and to inhibit its dipeptidyl peptidase IV (DP IV) activity. Here we show that the N-terminal nonapeptide MDPVDPNIE of Tat is a competitive inhibitor of DP IV and suppresses DNA synthesis of tetanus toxoid-stimulated peripheral blood mononuclear cells. Amino acid exchanges at positions 5 and 6 strongly weaken these effects. 1H nuclear magnetic resonance and molecular dynamics simulations of Tat(1-9), I5-Tat(1-9), and L6-Tat(1-9) suggest a similar backbone conformation for Tat(1-9) and L6-Tat(1-9). The solution conformation of I5-Tat(1-9) considerably differs from the other two. However, Tat(1-9) fits into our previously proposed active site model of DP IV in contrast to I5-Tat(1-9) and L6-Tat(1-9). Conformational alterations with regard to the parent peptide and spatial hindrances between these both compounds and DP IV can explain the loss of inhibitory activity. Our data suggest that the N-terminal residues of HIV-1 Tat do interact directly with the active site of DP IV and that DP IV does mediate Tat's immunosuppressive effects.

CD26/dipeptidyl peptidase IV in lymphocyte growth regulation

DP IV/CD26 is involved in regulation of DNA synthesis and proliferation as well as production of cytokines of hematopoietic cells under various conditions. Inhibition of DNA synthesis in T lymphocytes, B lymphocytes, NK cells and myelomonocytic cells as well as of the production of IL-2, IL-6 TNF alpha, IL-1, IL-10, IL-12, IL-13, IFN-gamma, GM-CSF are not due to apoptosis of these cells. DP IV/CD26 inhibitors induce TGF-beta 1 mRNA synthesis and latent protein release demonstrating a crucial role of TGF-beta 1 in mediating CD26 function. X-X-Pro peptides as HIV-Tat protein strongly inhibit DP IV enzymatic activity and suppress DNA synthesis. This group of peptides may represent a class of natural DP IV/CD26 ligands and effectors, respectively. Hyperphosphorylation of p56lck as well as protein tyrosine phosphorylation of a number of proteins in T lymphocytes can be modulated by DP IV inhibitors. These data suggest that enzymatic activity or, at least in part, the active site of DP IV are both essential for its regulatory function in lymphocytes. Further work is required to determine the natural ligands, i.e. substrates and effectors, which are play the central role in DP IV/CD26 action in T cell growth and to understand the molecular mechanism of the early steps of this fundamental process.

In vivo inhibition of dipeptidyl peptidase IV activity by pro-pro-diphenyl-phosphonate (Prodipine)

Dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5), also known as CD26, is a membrane-bound serine protease that cleaves off aminoterminal dipeptides from peptides with a penultimate proline (or, at a much slower rate, a penultimate alanine). Recently, we synthesized and characterized a number of dipeptide-derived diphenylphosphonates. Out of the resulting series of slow-binding irreversible inhibitors of DPP IV, diphenyl 1-(S)-prolylpyrrolidine-2(R,S)-phosphonate hydrochloride (Pro-Pro-diphenylphosphonate or Prodipine) was selected for further study. We investigated the in vivo applicability of Prodipine. Male rabbits weighing 3-4 kg received a single intravenous injection with 10 mg Prodipine or saline. After 1 hr, plasma DPP IV activity had decreased to less than 20% of the preinjection value and remained unchanged during a 24-hr observation period. In a next step, we aimed to study (i) the dose dependency and (ii) the duration of the effect after a single intravenous dose of Prodipine. A profound and long-lasting inhibition of plasma DPP IV activity was observed in the treated animals (1, 5 or 10 mg). It took 5 to 8 days to reach half of the pretreatment DPP IV activity and generally more than 20 days for a complete recovery. Systemic treatment with Prodipine not only led to inhibition of plasma DPP IV activity but also decreased tissue DPP IV activity in circulating mononuclear cells, kidney cortex, thymus, spleen, lung, and liver. No differences in activities of the related peptidases aminopeptidase P (APP, EC 3.4.11.9), prolyl oligopeptidase (PO, EC 3.4.21.26), or aminopeptidase M (mAAP, EC 3.4.11.2) were detected between Prodipine-treated and control rabbits. The in vivo applicability of this chemically stable, irreversible inhibitor of DPP IV opens new possibilities, not only to further unravel the biological functions of this intriguing ectopeptidase, but also to explore this enzyme as a new target in various fields of pharmacological research.

Inhibitors of dipeptidyl peptidase IV induce secretion of transforming growth factor-beta 1 in PWM-stimulated PBMC and T cells

Various studies have shown that the membrane ectoenzyme dipeptidyl peptidase IV (DP IV; CD26), expressed on T, natural killer (NK) and B cells in the immune system, is involved in the regulation of DNA synthesis and cytokine production. We show that the specific DP IV inhibitors Lys[Z(NO2)]-thiazolidide, Lys[Z(NO2)]-piperidide, and Lys[Z(NO2)]-pyrrolidide inhibit DNA synthesis as well as production of interleukin-2 (IL-2), IL-10, IL-12, and interferon-gamma (IFN-gamma) of pokeweed mitogen (PWM)-stimulated purified T cells. Most importantly, these inhibitors induce a three- to fourfold increased secretion of latent transforming growth factor-beta 1 (TGF-beta 1) by PWM-stimulated peripheral blood mononuclear cells (PBMC) and T cells, as measured with a specific TGF-beta 1 enzyme-linked immunosorbent assay and in the Mv1Lu bioassay. As we could demonstrate previously, TGF-beta 1 exhibits the same inhibitory effects as DP IV inhibitors on DNA synthesis and cytokine production (Cytokine 1994, 6, 382-8; J Interferon Cytokine Res 1995, 15, 685-90). A neutralizing chicken anti-TGF-beta 1 antibody was capable of abolishing the DP IV inhibitor-induced suppression of DNA synthesis of PWM-stimulated PBMC and T cells. These data suggest that TGF-beta 1 might have key functions in the molecular action of DP IV/CD26 in regulation of DNA synthesis and cytokine production.

Histochemical evaluation of placental dipeptidyl peptidase IV (CD26) in pre-eclampsia: enzyme activity in villous trophoblast indicates an enhanced likelihood of gestational hypertensive disorders

PROBLEM

To determine whether differences in placental dipeptidyl peptidase IV (DPP IV, CD26) activities occurred in hypertensive complicated pregnancies as compared with uncomplicated pregnancies.

METHOD

DPP IV activity was detected with H-Gly-Pro-4M2NA as the substrate in placental cryostat sections from 65 patients with gestational hypertension and 67 patients with uncomplicated pregnancies. The graduated intensities of the reaction product in the villous trophoblast were scored semiquantitatively by light microscopy and were related to the relative frequencies of hypertensive disorders (proportional odds model). After detection of enzyme activity, the same tissue samples were homogenized and used for kinetic fluorometric measurements.

RESULTS

Enhanced villous trophoblastic DPP IV activity was significantly associated with an increased frequency of proteinuric hypertension in pregnant women (cumulative odds ratio theta1 = 1.6; P < 0.01).

CONCLUSION

This study demonstrates for the first time that increased villous trophoblastic DPP IV activity indicates an increased likelihood of the presence and of the severity of hypertensive disorders in pregnancy.

Inhibitors of dipeptidyl peptidase IV (DP IV, CD26) induces secretion of transforming growth factor-beta 1 (TGF-beta 1) in stimulated mouse splenocytes and thymocytes

Various studies have shown that the ectoenzyme dipeptidyl peptidase IV (DP IV, CD26), expressed on T, NK and B cells in the human immune system, is involved in the regulation of DNA synthesis and cytokine production. The DP IV/CD26 was found also on mouse splenocytes and thymocytes. Here, we show that the specific DP IV inhibitors Lys[Z(NO2)]-thiazolidide, Lys[Z(NO2)]-pyrrolidide inhibit DNA synthesis as well as production of IL-2, IL-6 and IL-10 of PHA-stimulated mouse splenocytes and Con A-stimulated mouse thymocytes. Most importantly, these inhibitors induce a three to fourfold increased secretion of latent transforming growth factor beta 1 (TGF-beta 1) by mitogen-stimulated mouse immune cells, as measured with a specific TGF-beta 1 enzyme-linked immunosorbent assay (ELISA). These data demonstrate that CD26 plays a role also in regulation of DNA synthesis and cytokine production by murine immune cells, that the enzymatic activity is required for mediating these effects, and that TGF-beta 1 might have key functions in these processes.

Induction of interleukin-1 and glucocorticoid hormones by HIV promotes viral replication and links human chromosome 2 to AIDS pathogenesis: genetic mechanisms and therapeutic implications

Human immunodeficiency virus may regulate its replication by stimulating the synthesis of interleukin-1. Interleukin-1, in turn, has the ability to stimulate the human immunodeficiency virus enhancer region. The human genes responsible for interleukin-1 and interleukin-1 receptor antagonist synthesis are located on the long arm of chromosome 2. Coincidentally, the trans-activation responsive ribonucleic acid element in the R region of the long terminal repeat of human immunodeficiency virus-1 has been found to interact directly with a factor present on the long arm of chromosome 2 to facilitate transactivation by the human immunodeficiency virus Tat protein. The human CD26 gene is also located on the long arm of chromosome 2. CD26 is a lymphocyte cell surface antigen that is stimulated by interleukin-1 and serves with CD4 as a coreceptor that interacts with the V3 loop in gp120 of human immunodeficiency virus. The human immunodeficiency virus-induced interleukin-1 excess, thus, serves human immunodeficiency virus by enhancing replication, and by increasing human immunodeficiency virus infectivity via activation of CD26. IL-1 also adversely affects acquired immune deficiency syndrome-related Kaposi's sarcoma. Several genetic treatments for human immunodeficiency virus infection are proposed.

Effects of substance P on human T cell function and the modulatory role of peptidase inhibitors

Evidence has been presented for a modulatory role of surface peptidases on substance P-mediated immune responses. In this study, we first characterized the effects of substance P and its carboxy- and amino-terminal fragments on human lymphocyte proliferative responses to investigate whether peptidase inhibitors influence the effects of the neuropeptide. Substance P at 10(-7) M and the carboxy-terminal fragment SP(4-11) slightly enhanced the lymphocyte responses to phytohemagglutinin and concanavalin A. In contrast, the amino-terminal fragment SP(1-4) failed to have any positive effect. However, in the presence of dipeptidylpeptidase IV/CD26 and neutral endopeptidase/CD10 inhibitors (diprotin A and thiorphan, respectively), the effect of substance P on mitogen-induced proliferation was significantly increased. These data support the hypothesis that lymphocyte surface peptidases play a modulatory role in the effects of substance P on T cell function.

Induction of the membrane alanyl aminopeptidase gene and surface expression in human T-cells by mitogenic activation

The metal-dependent membrane alanyl aminopeptidase (amino-peptidase N, APN, CD13; EC 3.4.11.2) is a well-established marker of normal and malignant cells of the myelo-monocytic lineage. It is also expressed by leukaemic blasts of a small group of patients suffering from acute or chronic lymphoid leukaemia. CD13-specific monoclonal antibodies do not bind to the surface of normal B lymphocytes, and APN mRNA was not detectable by Northern analysis in normal lymphocytes or in T-cell lines. Recently the expression of the APN gene in T-cell lines as well as the ability of these cells to cleave chromogenic substrates preferred by APN have been demonstrated [Lendeckel, Wex, Kähne, Frank, Reinhold and Ansorge (1994) Cell. Immunol. 153, 214-226]. Here, by means of dot-blot hybridization and RNase protection assay, evidence is provided that human peripheral T-cells as well as derived cell lines contain significant amounts of APN mRNA, comparable to that in the promyeloic cell line U937, and that mitogenic activation of peripheral human T-cells leads to a more than 4-fold increase in their APN mRNA content. In the course of activation, T-cells increase their total alanine p-nitroanilide-hydrolysing activity to approx. 7-fold that of resting cells. Furthermore these cells become immunoreactive towards CD13 to a significant extent (up to 51%) as shown by surface staining and confirmed by activity staining and immunostaining after isoelectric focusing (pI of T-cell APN = 4.6). In addition it is demonstrated by fluorescence microscopy that viable, activated T-cells effectively cleave the fluorogenic aminopeptidase substrate bis-glycyl-rhodamine 110 and that the corresponding aminopeptidase activity is associated with the cell surface. We show that specific inhibitors of APN, probestin and actinonin, strongly decrease DNA synthesis in phytohaemagglutinin (PHA)-stimulated T-cells. In summary, evidence is presented that in the course of mitogenic activation human peripheral T-cells increase the expression of APN both at the transcriptional level and at the cell surface. This has been demonstrated both at the APN mRNA level and at the protein level with respect to aminopeptidase enzymic activity and CD13 immunoreactivity.

Dipeptide-derived diphenyl phosphonate esters: mechanism-based inhibitors of dipeptidyl peptidase IV

A number of dipeptide diphenyl phosphonate esters were studied as inhibitors of dipeptidyl peptidase IV, focusing on the role of the P2 residue in the inactivation process. The active compounds were slow irreversible inhibitors of the catalytic activity of the enzyme. With proline (or alanine) in the P1 position, the rate constants of inactivation correlated with the acylation rate constants reported for homologous dipeptide derived substrates. The kinetic data indicate that the mechanism of inhibition consists of the formation of a fairly weak initial complex, followed by a slow irreversible inactivation step. This indicates that, as in the case of trypsin-like proteinases, dipeptide diphenyl phosphonate esters form a covalent adduct with the catalytic site of DPP IV, even though this enzyme belongs to a completely distinct class of serine peptidases. Enantioselectivity and secondary specificity further support the evidence that diphenyl phosphonate esters are mechanism-based inhibitors. The dipeptide diphenyl phosphonate esters had a half-life of 3-10 h at 37 degrees C in Tris buffer. The inhibitors were degraded in human plasma, depending on the type of amino-terminal amino acid. The compound with proline in the P2 position was the most resistant to degradation in plasma. Due to their stability and the irreversible nature of the inhibition, the diphenyl phosphonate esters promise to be useful tools in the continuing investigation of the physiological function of dipeptidyl peptidase IV.

The N-terminal X-X-Pro sequence of the HIV-1 Tat protein is important for the inhibition of dipeptidyl peptidase IV (DP IV/CD26) and the suppression of mitogen-induced proliferation of human T cells

Recent data in the literature suggest that the HIV-1 Tat(1-86) protein exhibits immunosuppressive effects. Moreover, Tat was found to interact with dipeptidyl peptidase IV (DP IV), which is identical to the T cell activation marker CD26. Here we show that the N-terminal amino acid sequence of Tat is essential for the inhibition of DP IV-catalyzed IL-2(1-12) degradation. N-terminal modification of Tat with rhodamine prevented inhibition of enzymatic activity of DP IV as well as suppression of DNA synthesis of mitogen-stimulated human T cells. Moreover, natural peptides containing the X-X-Pro N-terminal motif of Tat also inhibited DP IV activity. These data suggest the existence of endogenous immunomodulatory oligopeptides which influence immune cell proliferation and differentiation via DP IV as does HIV-1 Tat.

A new mechanism in serine proteases catalysis exhibited by dipeptidyl peptidase IV (DP IV)--Results of PM3 semiempirical thermodynamic studies supported by experimental results

Herein we present results of semiempirical molecular orbital calculations employing the PM3 molecular model. The compounds studied are related to substrates of the serine protease dipeptidyl peptidase IV (DP IV). Our goal was the thermodynamic characterization of the DP IV-enzyme-catalyzed reaction pathway. A new mechanism of serine proteases catalysis is presented. We found that a tetrahedral intermediate can be stabilized by the formation of an oxazolidine ring with the nonscissile P2-P1 peptide bond. In this way, the negative charge of the tetrahedral intermediate around the scissile bond is transferred to the carbonyl oxygen atom of the preceding peptide bond. This negative charge can be compensated by a proton transfer from the positively charged N-terminus to this oxygen atom. It is shown that the positively charged N-terminus is the driving force in this particular serine protease mechanism of catalysis. The mechanism is supported by observed secondary hydrogen isotope effects on the C alpha proton for an alanine residue in the P2 position. We suggest a trans-cis isomerisation around the P2-P1 peptide bond in the final step of the acylation and cleavage of the substrates. The results obtained by our theoretical calculations are compared with several experimental findings supporting the suggested mechanism.

A model of the active site of dipeptidyl peptidase IV predicted by comparative molecular field analysis and molecular modelling simulations

A molecular model of the active site of the serine protease dipeptidyl peptidase IV (DPP IV or CD26) has been developed on the basis of comparative molecular field analysis (CoMFA) of competitive inhibitors and by force field calculations. By application of CoMFA experimentally obtained inhibition constants Ki have been successfully predicted. The resulting steric and electrostatic coefficients of CoMFA were used for the development of the molecular model. The main assumptions of the model are the recognition of substrates or inhibitors by the side chains of a tyrosine (S1-position) and a tryptophan residue (S2-position). The model helps us to understand a multitude of experimental data regarding the substrate specificity of this enzyme as well as results obtained by genetic engineering experiments by other authors. General conclusions concerning a new family of serine proteases are drawn and discussed.

Inhibition of dipeptidyl peptidase IV (DP IV) by anti-DP IV antibodies and non-substrate X-X-Pro- oligopeptides ascertained by capillary electrophoresis

Dipeptidyl peptidase IV (DP IV)-catalyzed hydrolysis of the NH2-X-Pro-containing N-terminal dodecapeptide of IL-2 was studied using free zone capillary electrophoresis as an alternative peptidase assay. In contrast to the conventional DP IV substrate glycyl-prolyl-p-nitroanilide (Gly-Pro-pNA), the hydrolysis of this peptide by DP IV was found to be significantly inhibited by anti-DP IV antibodies. Inhibition of DP IV was also observed with a number of non-substrate oligopeptides containing an N-terminal X-X-Pro- structure, including the HIV Tat protein. For Met-IL-2(1-6), we determined a competitive inhibition with an inhibition constant of ca. 100 microM.

An alternative role for the src-homology-domain-containing phosphotyrosine phosphatase (SH-PTP2) in regulating epidermal-growth-factor-dependent cell growth

The association of the src homology 2 (SH2) domain-containing tyrosine phosphatase (SH-PTP2) with the activated epidermal growth factor (EGF) and platelet-derived growth factor receptors, as well as the insulin receptor substrate 1 and growth-factor-receptor-bound protein 2 and its intrinsic tyrosine phosphatase activity suggests an important role for this phosphatase in signal transduction. Previous studies have shown a positive role for SH-PTP2 in growth-factor-mediated cell signaling. We show here that SH-PTP2 can also function to negatively regulate EGF-mediated signal transduction in the human glioma cell line SNB19. We demonstrate this by showing that, in SNB19 cells, which lack the ability to proliferate in response to EGF but retain the ability to bind EGF and also activate the EGF receptor as well as allow for the association of SH-PTP2 with the phosphorylated receptor, stable overexpression of an interfering SH-PTP2 mutant can restore the ability of these cells to proliferate in response to EGF.

Transforming growth factor beta 1 inhibits interleukin-10 mRNA expression and production in pokeweed mitogen-stimulated peripheral blood mononuclear cells and T cells

The multifunctional cytokine transforming growth factor-beta 1 (TGF-beta 1) is known to inhibit the proliferation of lymphocytes. Whether this effect is a result of a direct action of TGF-beta 1 or an involvement of other "immunoinhibitory" cytokines is not yet clear. Here we have analyzed the effects of TGF-beta 1 on IL-10 and IL-1RA production in pokeweed mitogen-stimulated peripheral blood mononuclear cells (PBMC) and purified T lymphocytes. We show in these systems that TGF-beta 1 at a concentration of 10 ng/ml significantly suppresses both IL-10 mRNA expression and IL-10 production. IL-2 and IL-6 were capable of abolishing the effect of TGF-beta 1 on DNA synthesis and production of IL-10 by T lymphocytes in an additive manner. However, TGF-beta 1 did not influence IL-1RA production in PWM-stimulated PBMC. The present data show that the inhibitory effect of TGF-beta 1 on mitogen-activated immune cells is not the consequence of induction of the inhibitory cytokines IL-10 or IL-1RA but rather an inhibitory action on the production of IL-2 and/or IL-6.

Enzymatic activity of DPIV/CD26 is involved in PMA-induced hyperphosphorylation of p56lck

The T-cell activation antigen CD26 (dipeptidyl peptidase IV, DPIV) is a proline specific protease thought to be involved in regulation of the immune response. Several former results characterized this ectoenzyme as a possible accessory molecule of the T-cell surface. The molecular events of lymphocyte activation mediated by this enzyme, as well as the physiological ligands of dipeptidyl peptidase, are only partly established. Here we provide evidence for a direct involvement of DPIV/CD26 in early phosphorylation mechanisms which were known to be essential in the signal transduction cascade of human T lymphocytes. Considering a possible functional linkage between CD26 and the tyrosine kinase p56lck, we have investigated the action of DPIV-specific inhibitors (Lys[Z[NO2)]-thiazolidide and -piperidide) on the PMA-induced hyperphosphorylation of p56lck in human T cells. Interestingly, this hyperphosphorylation of p56lck was strongly suppressed by both inhibitors in a dose-dependent manner. Removal of these inhibitors totally restored the hyperphosphorylation. Therefore, this effect could be considered as reversible. Free thiazolidine and piperidine, used in control experiments, neither inhibit DPIV enzyme activity nor PMA-induced hyperphosphorylation. The data presented here provide evidence that DPIV/CD26 is directly involved in early processes of T-cell activation. Furthermore, these findings strongly support the assumption that the signaling function of CD26 requires its enzymatic activity.