Kinetics of dipeptidyl peptidase IV proteolysis of growth hormone-releasing factor and analogs

CD26/DPP4 as a Therapeutic Target in Nonalcoholic Steatohepatitis Associated Hepatocellular Carcinoma

Simple Summary

CD26/DPP4 has been reported to attenuate anticancer immunity via chemokine cleavage and to promote insulin resistance and inflammation in the liver and/or adipose tissue via dysregulation of macrophage M1/M2 polarization. These results suggest the promotive roles of CD26/DPP4 especially in nonalcoholic steatohepatitis (NASH) associated hepatocellular carcinoma (HCC). In this review, we discuss the biological roles of CD26/DPP4 in the development and progression of NASH associated HCC and the potential of DPP4 inhibitors as therapeutic agents for HCC.

Abstract

Hepatocellular carcinoma (HCC) is generally considered an “immune-cold” cancer since T cells are not observed abundantly in HCC tumor tissue. Combination therapy with immune checkpoint inhibitors and vascular endothelial growth factor (VEGF) inhibitors is currently recognized as a first-line systemic treatment for advanced-stage HCC. Immunologically, immune checkpoint inhibitors influence the recognition of cancer cells by T cells, and VEGF inhibitors influence the infiltration of T cells into tumors. However, no drugs that facilitate the trafficking of T cells toward tumors have been developed. Chemokines are promising agents that activate T cell trafficking. On the other hand, metabolic factors such as obesity and insulin resistance are considered risk factors for HCC development. CD26/dipeptidyl peptidase 4 (DPP4) functions as a serine protease, selectively cleaving polypeptides with a proline or alanine at the penultimate N-terminal position, such as chemokines. Recently, CD26/DPP4 has been reported to attenuate anticancer immunity via chemokine cleavage and to promote insulin resistance and inflammation in the liver and/or adipose tissue via dysregulation of macrophage M1/M2 polarization. In this review, we discuss the promotive roles of CD26/DPP4 in HCC development and progression and the potential of DPP4 inhibitors as therapeutic agents for HCC.

High DPP4 expression predicts poor prognosis in patients with low-grade glioma

Dipeptidyl peptidase-IV (DPP4) plays a key role in tumor development; however, its role in glioma pathogenesis has not been determined. Here, we aimed to investigate the expression pattern of DPP4 and explore the association between expression and patient prognosis in glioma. DPP4 levels were investigated using qRT-PCR, immunohistochemistry and western blot in a rat model of glioma and also in patient samples. The relationship between DPP4 levels, WHO pathological grade gliomas, and isocitrate dehydrogenase 1 and 2 (IDH1/2) status was assessed in patient samples. Our data indicated that DPP4 levels were markedly increased in a rat model of glioma (p < 0.05, p < 0.01) and aslo in patient samples. Furthermore, the elevation of DPP4 levels in the samples obtained from pateints was associated with the pathogical grade of glioma and the IDH1/2 status (p < 0.01, p < 0.001). High DPP4 levels decreased the survival probability of patients with low-grade glioma (LGG). The data from patient samples showed that DPP4 expression increased with the pathological grade. Increased expression of DPP4 could be a promising index for determining the prognosis of glioma.

Dipeptidyl Peptidase 4 Inhibitors Reduce Hepatocellular Carcinoma by Activating Lymphocyte Chemotaxis in Mice

BACKGROUND & AIMS

CD26, a multifunctional transmembrane glycoprotein, is expressed in various cancers and functions as dipeptidyl peptidase 4 (DPP4). We investigated whether CD26 expression is associated with hepatocellular carcinoma (HCC) progression and whether DPP4 inhibitors exert antitumor effects against HCC.

METHODS

CD26 expression was examined in 41 surgically resected HCC specimens. The effects of DPP4 inhibitors on HCC were examined by using HCC cell lines (Huh-7 and Li-7), xenograft tumors in nude mice, and a nonalcoholic steatohepatitis-related HCC mouse model.

RESULTS

CD26 expression in HCC specimens was associated with increased serum DPP4 activity, as well as a more advanced stage, less tumor immunity, and poorer prognosis in HCC patients. The HCC cell lines and xenograft tumors exhibited CD26 expression and DPP4 activity. The DPP4 inhibitors did not exhibit antitumor effects in vitro, but natural killer (NK) and/or T-cell tumor accumulation suppressed growth of xenograft tumor and HCC in vivo. The antitumor effects of DPP4 inhibitors were abolished by the depletion of NK cells or the neutralization of CXCR3, a chemokine receptor on NK cells. EZ-TAXIScan, an optical horizontal chemotaxis apparatus, identified enhanced NK and T-cell chemotaxis by DPP4 inhibitors ex vivo in the presence of Huh-7 cells and the chemokine CXCL10, which binds to CXCR3. The DPP4 inhibitors prevented the biologically active form of CXCL10 from being truncated by Huh-7 cell DPP4 activity. DPP4 inhibitors also suppressed tumor angiogenesis.

CONCLUSIONS

These results provide a rationale for verifying whether DPP4 inhibitors clinically inhibit the progression of HCC or augment the antitumor effects of molecular-targeting drugs or immunotherapies against HCC.

Degradation of Incretins and Modulation of Blood Glucose Levels by Periodontopathic Bacterial Dipeptidyl Peptidase 4

Severe periodontitis is known to aggravate diabetes mellitus, though molecular events related to that link have not been fully elucidated. Porphyromonas gingivalis, a major pathogen of periodontitis, expresses dipeptidyl peptidase 4 (DPP4), which is involved in regulation of blood glucose levels by cleaving incretins in humans. We examined the enzymatic characteristics of DPP4 from P. gingivalis as well as two other periodontopathic bacteria, Tannerella forsythia and Prevotella intermedia, and determined whether it is capable of regulating blood glucose levels. Cell-associated DPP4 activity was found in those microorganisms, which was effectively suppressed by inhibitors of human DPP4, and molecules sized 73 kDa in P. gingivalis, and 71 kDa in T. forsythia and P. intermedia were immunologically detected. The k_cat/K_m values of recombinant DPP4s ranged from 721 ± 55 to 1,283 ± 23 μM^-1s^-1 toward Gly-Pro-4-methylcoumaryl-7-amide (MCA), while those were much lower for His-Ala-MCA. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis showed His/Tyr-Ala dipeptide release from the N termini of incretins, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide, respectively, with the action of microbial DPP4. Moreover, intravenous injection of DPP4 into mice decreased plasma active GLP-1 and insulin levels, accompanied by a substantial elevation in blood glucose over the control after oral glucose administration. These results are the first to show that periodontopathic bacterial DPP4 is capable of modulating blood glucose levels the same as mammalian DPP4; thus, the incidence of periodontopathic bacteremia may exacerbate diabetes mellitus via molecular events of bacterial DPP4 activities.

Regulation and roles of CD26/DPPIV in hematopoiesis and diseases

Dipeptidyl peptidase IV (DPPIV),¹ on the surface of certain cells, where it is also referred to as CD26, is involved in a vast majority of biological and pathological processes. CD26/DPPIV function contributes to cancer and tumor metastasis as well as inhibition of its expression which alters the expression of immune response-related genes. CD26/DPPIV is a widely distributed multifunctional integral membrane and secreted protein that is defined as early predictive biomarker in HIV, cancer and autoimmunity diseases like diabetes and multiple sclerosis. CD26/DPPIV-chemokine interaction may have a functional role in T-cells and overall immune function. It is expressed at low density on resting T cells, but is upregulated with T cell activation. In this review, we summarize valuable information about detailed biological aspects and pharmacokinetic characteristics of CD26/DPPIV and its clinical efficacy, focusing particularly on the role of CD26/DPPIV in immunological and non-immunological diseases. We also describe our recent work about umbilical cord blood (UCB)² hematopoietic stem cell transplantation strategies in which identified CD26+ cells can be differentiated to immune cells under certain culture condition.

Inhibition of Dipeptidyl-Peptidase IV Does Not Increase Circulating IGF-1 Concentrations in Growing Pigs

The enzyme dipeptidyl peptidase-IV (DPP-IV) inactivates a variety of bioactive peptides, including glucagon-like peptide-1 (GLP-1) and growth hormone releasing hormone (GHRH). Inhibiting DPP-IV in order to increase circulating GLP-1 is of interest as a treatment for Type II diabetes. Inactivation of DPP-IV may also increase circulating GHRH, potentially enhancing growth in domestic animals. To test the hypothesis that inhibition of DPP-IV activity will influence the growth hormone/IGF-1 axis, growing pigs (Sus scrofa domesticus, 78 kg) were treated with a DPP-IV inhibitor (Compound 1, the 2,5-difluorophenyl analog of the triazolopiperazine MK0431, sitagliptin), and plasma concentrations of IGF-1 were monitored. Pigs were administered either sterile saline (0.11 ml/kg followed by a continuous infusion at 2 ml/hr for 72 hrs, controls, n = 2), Compound 1 (2.78 mg/kg followed by a continuous infusion at 0.327 mg/kg·hr for 72 hrs, n = 4) or GHRH (0.11 ml/kg sterile saline, followed by a continuous infusion of GHRH at 2.5 μg/kg hr for 48 hrs, n = 4). Plasma concentrations of Compound 1 were maintained at 1 μM, which resulted in a 90% inhibition of circulating DPP-IV activity. Relative to the predose 24-hr period, area under the IGF-1 concentration curve (AUC) tended to be lower (P = 0.062) with Compound 1 (–79 ± 130 ng/ml hr) than controls (543 ± 330 ng/ml hr). GHRH treatment increased the IGF-1 AUC (1210 ± 160 ng/ml hr, P = 0.049 vs. controls and P = 0.001 vs. Compound 1). We conclude that inhibition of DPP-IV does not alter the circulating levels of IGF-1 in the growing pig.

Inhibition of DPP4 activity in humans establishes its in vivo role in CXCL10 post-translational modification: prospective placebo-controlled clinical studies

Biochemical experiments, animal models, and observational studies in humans all support a role of dipeptidyl peptidase 4 (DPP4) in the N‐terminal truncation of CXCL10, which results in the generation of an antagonist form of the chemokine that limits T‐cell and NK cell migration. Motivated by the ability to regulate lymphocyte trafficking in vivo, we conducted two prospective clinical trials to test the effects of DPP4 inhibition on CXCL10 processing in healthy donors and in chronic hepatitis C patients, a disease in which DPP4 levels are found to be elevated. Participants were treated daily with 100 mg sitagliptin, a clinically approved DPP4 inhibitor. Plasma samples were analyzed using an ultrasensitive single‐molecule assay (Simoa) to distinguish the full‐length CXCL10_1–77 from the NH₂‐truncated CXCL10_3–77, as compared to the total CXCL10 levels. Sitagliptin treatment resulted in a significant decrease in CXCL10_3–77 concentration, a reciprocal increase in CXCL10_1–77, with only minimal effects on total levels of the chemokine. These data provide the first direct evidence that in vivo DPP4 inhibition in humans can preserve the bioactive form of CXCL10, offering new therapeutic opportunities for DPP4 inhibitors.

Mass spectrometry-assisted confirmation of the inability of dipeptidyl peptidase-4 to cleave goldfish peptide YY(1-36) and the lack of anorexigenic effects of peptide YY(3-36) in goldfish (Carassius auratus)

Dipeptidyl peptidase-4 (DPP4) is a serine protease of great interest because it has been shown to modulate the activity of several peptidergic factors including peptide YY (PYY) and glucagon-like peptide-1/2. While PYY(1-36) is orexigenic in mammals, PYY(3-36) recently garnered interest as a potent anorexigen. In silico phylogenetic analysis found that the DPP4 cleavage sites are absent in fish PYY sequences. However, no studies were conducted to show that indeed PYY(3-36) is not produced by DPP4 in fish. If DPP4 does not cleave PYY(1-36), is PYY(3-36) an anorexigen in fish? The objectives of this research were to (1) test whether DPP4 cleaves goldfish PYY(1-36) and (2) determine whether PYY(3-36) is an anorexigen in goldfish. First, we identified the highly conserved catalytic region of DPP4 in goldfish. Abundant expression of DPP4 mRNA was found within the gastrointestinal tract. We also report the first MALDI-MS cleavage analysis of DPP4 effects on PYY(1-36) in a non-mammalian vertebrate. Our novel results indicate that DPP4 is unable to cleave goldfish PYY(1-36) to PYY(3-36) in vitro. It also confirms a previously held hypothesis that DPP4 is unable to cleave fish PYY(1-36) that contains N-terminal proline-proline residues. PYY(3-36) had no effects on food intake of goldfish. The appetite inhibitory effects of intraperitoneal and intracerebroventricular injections of 10 ng/g body weight gfPYY(1-36) were abolished by coinjections of BIBP3226, a Y1 receptor antagonist. These results are significant because it shows the lack of generation of endogenous PYY(3-36) and its anorectic effects in goldfish.

In Vivo Models to Study Chemokine Biology

Chemokines are essential mediators of leukocyte movement in vivo. In vitro assays of leukocyte migration cannot mimic the complex interactions with other cell types and matrix needed for cells to extravasate and migrate into tissues. Therefore, in vivo strategies to study the effects and potential relevance of chemokines for the migration of particular leukocyte subsets are necessary. Here, we describe methods to study the effects and endogenous role of chemokine in mice. Advantages and pitfalls of particular models are discussed and we focus on description in model's joint and pleural cavity inflammation and the effects and relevance of CXCR2 and CCR2 ligands on cell migration.

Dipeptidylpeptidase 4 inhibition enhances lymphocyte trafficking, improving both naturally occurring tumor immunity and immunotherapy

The success of antitumor immune responses depends on the infiltration of solid tumors by effector T cells, a process guided by chemokines. Here we show that in vivo post-translational processing of chemokines by dipeptidylpeptidase 4 (DPP4, also known as CD26) limits lymphocyte migration to sites of inflammation and tumors. Inhibition of DPP4 enzymatic activity enhanced tumor rejection by preserving biologically active CXCL10 and increasing trafficking into the tumor by lymphocytes expressing the counter-receptor CXCR3. Furthermore, DPP4 inhibition improved adjuvant-based immunotherapy, adoptive T cell transfer and checkpoint blockade. These findings provide direct in vivo evidence for control of lymphocyte trafficking via CXCL10 cleavage and support the use of DPP4 inhibitors for stabilizing biologically active forms of chemokines as a strategy to enhance tumor immunotherapy.

Dipeptidyl peptidase IV as a potential target for selective prodrug activation and chemotherapeutic action in cancers

The efficacy of chemotherapeutic drugs is often offset by severe side effects attributable to poor selectivity and toxicity to normal cells. Recently, the enzyme dipeptidyl peptidase IV (DPPIV) was considered as a potential target for the delivery of chemotherapeutic drugs. The purpose of this study was to investigate the feasibility of targeting chemotherapeutic drugs to DPPIV as a strategy to enhance their specificity. The expression profile of DPPIV was obtained for seven cancer cell lines using DNA microarray data from the DTP database, and was validated by RT-PCR. A prodrug was then synthesized by linking the cytotoxic drug melphalan to a proline-glycine dipeptide moiety, followed by hydrolysis studies in the seven cell lines with a standard substrate, as well as the glycyl-prolyl-melphalan (GP-Mel). Lastly, cell proliferation studies were carried out to demonstrate enzyme-dependent activation of the candidate prodrug. The relative RT-PCR expression levels of DPPIV in the cancer cell lines exhibited linear correlation with U95Av2 Affymetrix data (r(2) = 0.94), and with specific activity of a standard substrate, glycine-proline-p-nitroanilide (r(2) = 0.96). The significantly higher antiproliferative activity of GP-Mel in Caco-2 cells (GI₅₀ = 261 μM) compared to that in SK-MEL-5 cells (GI₅₀ = 807 μM) was consistent with the 9-fold higher specific activity of the prodrug in Caco-2 cells (5.14 pmol/min/μg protein) compared to SK-MEL-5 cells (0.68 pmol/min/μg protein) and with DPPIV expression levels in these cells. Our results demonstrate the great potential to exploit DPPIV as a prodrug activating enzyme for efficient chemotherapeutic drug targeting.

Proteome-wide reactivity profiling identifies diverse carbamate chemotypes tuned for serine hydrolase inhibition

Serine hydrolases are one of the largest and most diverse enzyme classes in Nature. Inhibitors of serine hydrolases are used to treat many diseases, including obesity, diabetes, cognitive dementia, and bacterial and viral infections. Nonetheless, the majority of the 200+ serine hydrolases in mammals still lack selective inhibitors for their functional characterization. We and others have shown that activated carbamates, through covalent reaction with the conserved serine nucleophile of serine hydrolases, can serve as useful inhibitors for members of this enzyme family. The extent to which carbamates, however, cross-react with other protein classes remains mostly unexplored. Here, we address this problem by investigating the proteome-wide reactivity of a diverse set of activated carbamates in vitro and in vivo, using a combination of competitive and click chemistry (CC)-activity-based protein profiling (ABPP). We identify multiple classes of carbamates, including O-aryl, O-hexafluoroisopropyl (HFIP), and O-N-hydroxysuccinimidyl (NHS) carbamates that react selectively with serine hydrolases across entire mouse tissue proteomes in vivo. We exploit the proteome-wide specificity of HFIP carbamates to create in situ imaging probes for the endocannabinoid hydrolases monoacylglycerol lipase (MAGL) and α-β hydrolase-6 (ABHD6). These findings, taken together, designate the carbamate as a privileged reactive group for serine hydrolases that can accommodate diverse structural modifications to produce inhibitors that display exceptional potency and selectivity across the mammalian proteome.

[Dipeptidyl peptidase IV in inflammatory bowel diseases (DPP IV/CD26)]

Inflammatory bowel diseases (Crohn's disease, ulcerative colitis, undetermined colitis) are a group of chronic autoimmune inflammatory diseases distinguished by recurrent inflammation of various parts of the gastrointestinal (GI) system and presenting a significant public health problem. Despite large basic and clinical research, the aetiology of these diseases and the pathogenesis of inflammation itself remain elusive. Previous studies have confirmed a causal relationship between mediators of inflammatory response and molecules involved in the regulation of their biological activity, especially proteases. The aim of this review is to summarise earlier findings on different aspects of inflammatory bowel diseases, paying particular attention to the involvement of dipeptidyl peptidase IV (CD26 molecule, DPP IV/CD26) in the etiopathogenesis of inflammatory processes in the GI tract. Animal studies of colitis have significantly contributed to the understanding and treatment of these diseases, investigations of ulcerative colitis (DSS-colitis) and Crohn's disease (TNBS-colitis) on the murine model in particular.

Loss of CD26 protease activity in recipient mice during hematopoietic stem cell transplantation results in improved transplant efficiency

BACKGROUND

A firm understanding of the biology of hematopoietic stem and progenitor cell (HSC/HPC) trafficking is critical to improve transplant efficiency and immune reconstitution during hematopoietic stem cell transplantation (HSCT). Our earlier findings suggested that suppression of CD26 (dipeptidyl peptidase IV) proteolytic activity in the donor cell population can be utilized as a method for increasing transplant efficiency. However, factors in the recipient should not be overlooked, given the potential for the bone marrow (BM) microenvironment to regulate HSCT.

STUDY DESIGN AND METHODS

We first evaluated CD26 expression and then investigated the effects of the CD26 inhibitor diprotin A and the absence of CD26 (CD26-/-) in recipient mice on HSC/HPC homing and engraftment using an in vivo congenic mouse model of HSCT.

RESULTS

A significant increase in donor cell engraftment into the peripheral blood (PB), and to a lesser extent homing into the BM, was observed in CD26-/- mice or CD26 inhibitor-treated mice. Increased PB engraftment of CD26-/- mice was significant at 3 and 6 months, but not 1 month, after transplant. It was noted that the increased homing was statistically greater with donor cell manipulation (CD26-/- donor cells) than with recipient manipulation (CD26-/- recipient mice). Conversely, donor and recipient manipulation both worked well to increase PB engraftment at 6 months.

CONCLUSION

These results provide preclinical evidence of CD26, in the HSCT recipient, as a major regulator of HSC/HPC engraftment with minor effects on HSC/HPC homing and suggest the potential use of CD26 inhibitors in HSCT patients to improve transplant efficiency.

CD26 protease inhibition improves functional response of unfractionated cord blood, bone marrow, and mobilized peripheral blood cells to CXCL12/SDF-1

Hematopoietic stem cell transplantation (HSCT) is an important treatment option for patients with malignant and nonmalignant hematologic diseases. Methods to improve transplant efficiency are being explored with the intent to improve engraftment and immune reconstitution post-HSCT. A current approach under investigation involves treatment of donor cells with inhibitors that target the protease CD26, a negative regulator of the chemokine CXCL12/stromal cell-derived factor-1. CD26 inhibitor treatment has been shown to improve the functional response of CD34(+) cord blood (CB) cells, but not CD34(+) granulocyte colony-stimulating factor-mobilized peripheral blood stem cells, to CXCL12/stromal cell-derived factor-1. The effect of CD26 inhibitors on unfractionated CB, bone marrow, or granulocyte colony-stimulating factor-mobilized peripheral blood mononuclear cells has not been evaluated previously. We observed that although CB had greater CD26 expression than bone marrow or mobilized peripheral blood, treatment with a CD26 inhibitor (Diprotin A) resulted in increased responsiveness to stromal cell-derived factor-1 for all three mononuclear cell sources tested. This suggests that clinical therapeutic benefit might be gained by using CD26 inhibitors as a strategy to improve engraftment of unfractionated mobilized peripheral blood cells as well as CB cells.

The pharmacological landscape and therapeutic potential of serine hydrolases

Serine hydrolases perform crucial roles in many biological processes, and several of these enzymes are targets of approved drugs for indications such as type 2 diabetes, Alzheimer's disease and infectious diseases. Despite this, most of the human serine hydrolases (of which there are more than 200) remain poorly characterized with respect to their physiological substrates and functions, and the vast majority lack selective, in vivo-active inhibitors. Here, we review the current state of pharmacology for mammalian serine hydrolases, including marketed drugs, compounds that are under clinical investigation and selective inhibitors emerging from academic probe development efforts. We also highlight recent methodological advances that have accelerated the rate of inhibitor discovery and optimization for serine hydrolases, which we anticipate will aid in their biological characterization and, in some cases, therapeutic validation.

Neuropeptide Y, B-type natriuretic peptide, substance P and peptide YY are novel substrates of fibroblast activation protein-α

Fibroblast activation protein-α (FAP) is a cell surface-expressed and soluble enzyme of the prolyl oligopeptidase family, which includes dipeptidyl peptidase 4 (DPP4). FAP is not generally expressed in normal adult tissues, but is found at high levels in activated myofibroblasts and hepatic stellate cells in fibrosis and in stromal fibroblasts of epithelial tumours. FAP possesses a rare catalytic activity, hydrolysis of the post-proline bond two or more residues from the N-terminus of target substrates. α(2)-antiplasmin is an important physiological substrate of FAP endopeptidase activity. This study reports the first natural substrates of FAP dipeptidyl peptidase activity. Neuropeptide Y, B-type natriuretic peptide, substance P and peptide YY were the most efficiently hydrolysed substrates and the first hormone substrates of FAP to be identified. In addition, FAP slowly hydrolysed other hormone peptides, such as the incretins glucagon-like peptide-1 and glucose-dependent insulinotropic peptide, which are efficient DPP4 substrates. FAP showed negligible or no hydrolysis of eight chemokines that are readily hydrolysed by DPP4. This novel identification of FAP substrates furthers our understanding of this unique protease by indicating potential roles in cardiac function and neurobiology.

In vivo expansion of the megakaryocyte progenitor cell population in adult CD26-deficient mice

OBJECTIVE

Megakaryopoiesis involves commitment of hematopoietic stem cells (HSC) toward the myeloid lineage in combination with the proliferation, maturation, and terminal differentiation of progenitors into megakaryocytes. The exact mechanism of megakaryocyte development from HSC is unknown, but growth factors such as thrombopoietin have been identified as critical. Additionally, it has been suggested that the chemokine CXCL12/stromal-cell derived factor-1α has a role in regulating megakaryopoiesis and thrombopoiesis. We recently reported the importance of the extracellular protease CD26 (dipeptidylpeptidase IV) in regulating HSC responses to CXCL12, as well as modulating HSC trafficking into and out of the bone marrow. However, the importance of CD26 for megakaryopoiesis has not been reported. We therefore compared megakaryocyte development between CD26-deficient (CD26(-/-)) mice and C57BL/6 control mice.

MATERIALS AND METHODS

Adult CD26(-/-) mice and C57BL/6 control mice were evaluated using blood differentials, histological analysis, flow cytometric analysis, and progenitor colony assays.

RESULTS

Bone marrow from CD26(-/-) mice has a significantly expanded megakaryocyte and megakaryocyte progenitor population compared to control C57BL/6 mice bone marrow.

CONCLUSIONS

Our results indicate that endogenous CD26 normally suppresses megakaryopoiesis and that loss of CD26 activity results in expansion of the megakaryocyte progenitor population in vivo. This suggests the potential use of CD26 inhibitors to improve megakaryocyte progenitor function and/or reconstitution of the megakaryocyte cell population.

CD26 inhibition on CD34+ or lineage- human umbilical cord blood donor hematopoietic stem cells/hematopoietic progenitor cells improves long-term engraftment into NOD/SCID/Beta2null immunodeficient mice

Given the tremendous need for and potential of umbilical cord blood (CB) to be utilized as a donor source for hematopoietic stem cell (HSC) transplantation in adults, there is a strong push to overcome the constraints created by the limited volumes and subsequent limited HSC and hematopoietic progenitor cell (HPC) numbers available for HSC transplantation from a single collection. We have previously described the use of CD26 inhibitor treatment of donor cells as a method to increase the transplant efficiency of mouse HSCs and HPCs into a mouse recipient. To study the use of CD26 inhibitors as a method of improving the transplantation of human CB HSCs and HPCs, we utilized the nonobese diabetic/severe combined immunodeficient/beta 2 microglobulin null (NOD/SCID/B2m(null)) immunodeficient mouse model of HSC transplantation. We report here significant improvements in the engraftment of long-term repopulating cells following the treatment of either CD34(+) or lineage negative (lin()) donor CB with the CD26 inhibitor, Diprotin A, prior to transplant. These results establish a basis on which to propose the use of CD26 inhibitor treatment of donor CB units prior to transplantation for the purpose of improving transplant efficiency and subsequently patient outcome.

Site-Specific PEGylation for High-Yield Preparation of Lys21-Amine PEGylated Growth Hormone-Releasing Factor (GRF) (1−29) using a GRF(1−29) Derivative FMOC-Protected at Tyr1 and Lys12

PEGylation has been viewed as an effective means of overcoming the therapeutic restriction of growth hormone-releasing factor (1-29) (GRF(1-29)) due to its short biological lifetime caused by severe proteolysis and rapid glomerular filtration. Of three isomers according to the PEGylation sites (Tyr1, Lys12, or Lys21), PEGylated GRF(1-29) at Lys21-amine (Lys21-PEG-GRF(1-29)) was shown to have the highest bioactivity. In this report, we propose a unique two-step site-specific PEGylation method capable of producing only Lys21-PEG-GRF(1-29) with a single composition in high yield using a GRF(1-29) derivative protected at Tyr1 and Lys12 and remained available at Lys21 (FMOC1,12-GRF(1-29)). The first step of this reaction involved the PEG attachment to FMOC1,12-GRF(1-29), and the second step involved the removal of FMOC moieties. This PEGylation process was optimized at the following conditions: 0.2-0.3% (v/v) triethylamine concentration, 5.0-6.0-fold molar amount of PEG, reaction temperature of 25-45 degrees C, and reaction time of 30 min. Under these conditions, the maximum yield of Lys21-PEG-GRF(1-29) produced was ca. approximately 95%, 6.3-fold higher than that by nonspecific PEGylation at pH 8.5. Significantly, this site-specific Lys21-PEG-GRF(1-29) was found to have greatly increased resistance to rat plasma, liver, and kidney homogenates, with 7.0-, 25.4-, and 16.4-fold longer half-lives vs GRF(1-29), respectively. Furthermore, 125I-Lys21-PEG-GRF(1-29) displayed significantly reduced liver and kidney distributions and extended blood presence vs 125I-GRF(1-29) in rats. Due to these benefits, Lys21-PEG-GRF(1-29) displayed an enhanced initial growth hormone release in vivo despite having 15% remaining activity in vitro. This devised PEGylation method using an FMOC-protection/deprotection strategy would provide great usefulness for PEGylating bioactive peptides in terms of improved biological potency, elevated production yield, and a uniform composition.

Inhibition of dipeptidyl peptidase IV activity as a therapy of Type 2 diabetes

Dipeptidyl peptidase IV (DPP IV) is a ubiquitous, multifunctional, serine protease enzyme and receptor with roles in the control of endocrine and immune function, cell metabolism, growth and adhesion. As an enzyme, DPP IV cleaves the N-terminal dipeptide from the incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. This inactivates the hormones, thereby cancelling their prandial insulinotropic effect. One approach to restore incretin activity as a therapy for Type 2 diabetes has been the development of DPP IV inhibitors. Inhibitors of DPP IV have shown efficacy and tolerability when used to control the hyperglycaemia of noninsulin-dependent animal models and human Type 2 diabetes. These DPP IV inhibitors prolong active incretin hormone concentrations and may exert additional antidiabetic effects. If long-term clinical trials confirm sustained and safe control of blood glucose, DPP IV inhibitors (known as 'gliptins') may be expected to provide a new treatment modality for Type 2 diabetes.

G-CSF- and GM-CSF-induced upregulation of CD26 peptidase downregulates the functional chemotactic response of CD34+CD38− human cord blood hematopoietic cells

OBJECTIVE

Cytokine treatment with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) is a mainstay of current and future clinical and research protocols for peripheral blood stem cell mobilization, therapeutic care after hematopoietic stem cell transplantation (HSCT), and ex vivo hematopoietic stem and progenitor cell (HSC/HPC) expansion. We have previously shown that the peptidase CD26 (DPPIV/dipeptidylpeptidase IV) negatively regulates HSC/HPC and that inhibition of CD26 improves the chemotactic ability and trafficking of HSC/HPC. We set out to establish whether short-term in vitro G-CSF, GM-CSF, or SCF treatment upregulates CD26 and thereby has a detrimental effect on the chemotactic potential of HSC/HPC that could be reversed by CD26 inhibitor treatment.

MATERIALS AND METHODS

CD34+ or CD34+CD38- cells, a population enriched in HSC, were isolated from human umbilical cord blood and subjected to G-CSF, GM-CSF, or SCF treatment. We then evaluated CD26 expression, CD26 activity, and CXCL12 (SDF-1)-induced migration in the presence or absence of a CD26 inhibitor, Diprotin A.

RESULTS

Treatment with G-CSF and GM-CSF but not SCF upregulates CD26 expression and activity resulting in a CD26 inhibitor-reversible downregulation of CXCL12-induced chemotactic response.

CONCLUSIONS

Short-term in vitro G-CSF and GM-CSF treatment upregulates the peptidase CD26, resulting in downregulation of the functional ability of CD34+CD38- cells to respond to the chemokine CXCL12. This suggests that current and future clinical protocols utilizing G-CSF and GM-CSF may have unforeseen detrimental effects on the trafficking of HSC/HPC during HSCT that can be overcome through the use of CD26 inhibitors.

Synthesis, kinetic evaluation, and utilization of a biotinylated dipeptide proline diphenyl phosphonate for the disclosure of dipeptidyl peptidase IV-like serine proteases

In this study, we report on the synthesis, kinetic characterisation, and application of a novel biotinylated and active site-directed inactivator of dipeptidyl peptidase IV (DPP-IV). Thus, the dipeptide-derived proline diphenyl phosphonate NH(2)-Glu(biotinyl-PEG)-Pro(P)(OPh)(2) has been prepared by a combination of classical solution- and solid-phase methodologies and has been shown to be an irreversible inhibitor of porcine DPP-IV, exhibiting an over all second-order rate constant (k(i)/K(i)) for inhibition of 1.57 x 10(3) M(-1) min(-1). This value compares favourably with previously reported rates of inactivation of DPP-IV by dipeptides containing a P(1) proline diphenyl phosphonate grouping [B. Boduszek, J. Oleksyszyn, C.M. Kam, J. Selzler, R.E. Smith, J.C. Powers, Dipeptide phophonates as inhibitors of dipeptidyl peptidase IV, J. Med. Chem. 37 (1994) 3969-3976; B.F. Gilmore, J.F. Lynas, C.J. Scott, C. McGoohan, L. Martin, B. Walker, Dipeptide proline diphenyl phosphonates are potent, irreversible inhibitors of seprase (FAPalpha), Biochem, Biophys. Res. Commun. 346 (2006) 436-446.], thus demonstrating that the incorporation of the side-chain modified (N-biotinyl-3-(2-(2-(3-aminopropyloxy)-ethoxy)-ethoxy)-propyl) glutamic acid residue at the P(2) position is compatible with inhibitor efficacy. The utilisation of this probe for the detection of both purified dipeptidyl peptidase IV and the disclosure of a dipeptidyl peptidase IV-like activity from a clinical isolate of Porphyromonas gingivalis, using established electrophoretic and Western blotting techniques previously developed by our group, is also demonstrated.

SDF-1/CXCL12 enhances survival and chemotaxis of murine embryonic stem cells and production of primitive and definitive hematopoietic progenitor cells

Understanding embryonic stem cell (ESC) regulation is important for realizing how best to control their growth and differentiation ex vivo for potential therapeutic benefit. Stromal cell-derived factor-1 (SDF-1/CXCL12) and its receptor, CXCR4, have been implicated as important regulators of a number of fetal and adult cell functions, including survival/antiapoptosis and migration/homing of hematopoietic stem and progenitor cells. We hypothesized that the SDF-1/CXCL12-CXCR4 axis would also be important for regulation of murine ESC functions. ESCs secreted low levels of SDF-1/CXCL12 and expressed low levels of CXCR4; however, both increased with differentiation of ESCs. Endogenously produced/released SDF-1/CXCL12 enhanced survival/antiapoptosis of ESCs in the presence of leukemia inhibitory factor but absence of serum, and survival/antiapoptosis was further enhanced by exogenous administration of SDF-1/CXCL12. Furthermore, SDF-1/CXCL12 induced chemotaxis of ESCs, and chemotaxis could be enhanced by diprotin A inhibition of CD26/dipeptidylpeptidase IV. Endogenous and exogenous SDF-1/CXCL12 enhanced embryoid body production of primitive and definitive erythroid, granulocyte-macrophage, and multipotential progenitors. SDF-1/CXCL12 did not noticeably affect production of hemangioblasts. These results demonstrate functional activities of SDF-1/CXCL12 on survival, chemotaxis, and hematopoietic differentiation of murine ESCs that may be relevant for their ex vivo manipulation.

Rigidity and Flexibility of Dipeptidyl Peptidase IV: Crystal Structures of and Docking Experiments with DPIV

Dipeptidyl peptidase IV (DPIV) is an alpha,beta-hydrolase-like serine exopeptidase, which removes dipeptides, preferentially with a C-terminal l-Pro residue, from the N terminus of longer peptide substrates. Previously, we determined the tetrameric 1.8A crystal structure of native porcine DPIV. Each monomer is composed of a beta-propeller and a catalytic domain, which together embrace an internal cavity housing the active centre. This cavity is connected to the bulk solvent by a "propeller opening" and a "side opening". Here, we analyse DPIV complexes with a t-butyl-Gly-Pro-Ile tripeptide, Pro-boroPro, a piperazine purine compound, and aminoethyl phenyl sulfonylfluoride. The latter two compounds bind to the active-site groove in a compact and a quite bulky manner, respectively, causing considerable shifts of the catalytic Ser630 side-chain and of the Tyr547 phenolic group, which forms the oxyanion hole. The tripeptide, mimicking a peptide substrate, is clamped to the active site through tight interactions via its N-terminal alpha-ammonium group, the P2 carbonyl group, the P1-l-Pro side-chain, the C-terminal carboxylate group, and the stable orthoacid ester amide formed between the scissile peptide carbonyl group and Ser630 O(gamma). This stable trapping of the tripeptide could be due to stabilization of the protonated His740 imidazolium cation by the adjacent negatively charged C-terminal carboxylate group, preventing proton transfer to the leaving group nitrogen atom. Docking experiments with the compact rigid 58 residue protein aprotinin, which had been shown to be processed by DPIV, indicate that the Arg1-Pro2 N terminus can access the DPIV active site only upon widening of its side openings, probably by separation of the first and the last propeller blades, and/or of the catalytic and the propeller domain.

Clinical and oncologic implications in epigenetic down-regulation of CD26/dipeptidyl peptidase IV in adult T-cell leukemia cells

CD26/dipeptidyl peptidase IV (DPPIV), a T-cell-activation antigen, is a 110-kD type II surface glycoprotein expressed on various types of normal cells. CD26/DPPIV is considered a multifunction housekeeping protein. Malignant cells often show altered CD26/DPPIV expression or no CD26/DPPIV expression, thus suggesting a useful marker for assessing some T-cell malignancies. In this study, cell surface protein and messenger RNA expression profiles for CD26/DPPIV were examined in 49 patients with adult T-cell leukemia (ATL), 10 carriers of human T-lymphotropic virus I (HTLV-I), and 4 HTLV-I-infected cell lines to assess the utility of CD26/DPPIV expression as a useful molecular marker for ATL pathology. In contrast to normal lymphocytes, ATL cells and HTLV-I-infected cell lines apparently down-regulated or completely lost the CD26/DPPIV antigen. Furthermore, the positive rate and antigen density for CD26/DPPIV in ATL cells gradually declined along with the advancement of ATL stage. Analysis of genomic DNA and the CD26/DPPIV transcript showed that CD26- ATL cells possessed faintly detected transcripts of the gene that were aberrantly methylated at the CpG islands within the promoter region in parallel with the advancement of ATL, a finding supported by a rescue experiment for transcript reexpression using 5-azacytidine as demethylation agent. Moreover, there was no relationship between loss of CD26/DPPIV and HTLV-I tax expression. These results indicate that ATL cells down-regulate CD26 antigens by means of epigenetic machinery and that this antigen abnormality is a useful molecular marker for the pathology of ATL.

Chromatographic separation and mass spectrometric identification of positional isomers of polyethylene glycol-modified growth hormone-releasing factor (1-29)

A one-step chromatographic method capable of separating all isomers of polyethylene glycol (PEG)-growth hormone-releasing factor (GRF) (1-29) conjugates was developed. The unmodified GRF (1-29) and seven different isomers of PEG-GRF (1-29) conjugates were separated by using a simple reversed-phase HPLC method depending on the differences of hydrophobicity due to the number and site of PEG attachment. The PEGylation sites of all isomers of PEG-GRF (1-29) conjugates were identified by determining the molecular masses of the Lys-C digested fragments with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This study is a first report for the separation of all PEG-conjugate isomers and would be useful for further studies to find the promising conjugate by evaluating biological activity and stability of each isomer.

Crystal structure of human dipeptidyl peptidase IV in complex with a decapeptide reveals details on substrate specificity and tetrahedral intermediate formation

Dipeptidyl peptidase IV (DPPIV) is a member of the prolyl oligopeptidase family of serine proteases. DPPIV removes dipeptides from the N terminus of substrates, including many chemokines, neuropeptides, and peptide hormones. Specific inhibition of DPPIV is being investigated in human trials for the treatment of type II diabetes. To understand better the molecular determinants that underlie enzyme catalysis and substrate specificity, we report the crystal structures of DPPIV in the free form and in complex with the first 10 residues of the physiological substrate, Neuropeptide Y (residues 1-10; tNPY). The crystal structure of the free form of the enzyme reveals two potential channels through which substrates could access the active site-a so-called propeller opening, and side opening. The crystal structure of the DPPIV/tNPY complex suggests that bioactive peptides utilize the side opening unique to DPPIV to access the active site. Other structural features in the active site such as the presence of a Glu motif, a well-defined hydrophobic S1 subsite, and minimal long-range interactions explain the substrate recognition and binding properties of DPPIV. Moreover, in the DPPIV/tNPY complex structure, the peptide is not cleaved but trapped in a tetrahedral intermediate that occurs during catalysis. Conformational changes of S630 and H740 between DPPIV in its free form and in complex with tNPY were observed and contribute to the stabilization of the tetrahedral intermediate. Our results facilitate the design of potent, selective small molecule inhibitors of DPPIV that may yield compounds for the development of novel drugs to treat type II diabetes.

Cell-surface peptidases

The cell surface has various functions: communicating with other cells, integrating into the tissue, and interacting with the extracellular matrix. Proteases play a key role in these processes. This review focuses on cell-surface peptidases (ectopeptidases, oligopeptidases) that are involved in the inactivation or activation of extracellular regulatory peptides, hormones, paracrine peptides, cytokines, and neuropeptides. The nomenclature of cell-surface peptidases is explained in relation to other proteases, and information is provided on membrane anchoring, catalytic sites, regulation, and, in particular, on their physiological and pharmacological importance. Furthermore, nonenzymatic (binding) functions and participation in intracellular signal transduction of cell surfaces peptidases are described. An overview on the different cell-surface peptidases is given, and their divergent functions are explained in detail. An example of actual pharmacological importance, dipeptidyl-peptidase IV (CD26), is discussed.

Differential processing of stromal-derived factor-1alpha and stromal-derived factor-1beta explains functional diversity

The chemokine stromal-derived factor-1 (SDF-1), which is constitutively expressed in most tissues as SDF-1alpha and SDF-1beta resulting from alternative gene splicing, regulates hematopoiesis, lymphocyte homing, B-lineage cell growth, and angiogenesis. Because SDF-1alpha and SDF-1beta are constitutively and ubiquitously expressed, their degradation must serve an important regulatory role. Here we show that SDF-1alpha and SDF-1beta are secreted as full-length molecules. When exposed to human serum, full-length SDF-1alpha (1-68) undergoes processing first at the COOH terminus to produce SDF-1alpha 1-67 and then at the NH2 terminus to produce SDF-1alpha 3-67. By contrast, full-length SDF-1beta (1-72) is processed only at the NH2 terminus to produce SDF-1beta 3-72. CD26/dipeptidyl peptidase is responsible for serum cleavage of SDF-1alpha and SDF-1beta at the NH2 terminus. Serum processing of SDF-1alpha at the COOH terminus, which has not been previously reported, reduces the ability of the polypeptide to bind to heparin and to cells and to stimulate B-cell proliferation and chemotaxis. The additional processing at the NH2 terminus renders both forms of SDF-1 unable to bind to heparin and to activate cells. The differential processing of SDF-1alpha and SDF-1beta provides biologic significance to the existence of 2 splice forms of the chemokine and adds a tool to precisely regulate SDF-1's biologic activity by changes in specific activity.

The role of dipeptidyl peptidase IV in the cleavage of glucagon family peptides: in vivo metabolism of pituitary adenylate cyclase activating polypeptide-(1-38)

Dipeptidyl peptidase IV (DP-IV) is a cell surface serine dipeptidase that is involved in the regulation of the incretin hormones, glucagon-like peptide (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). There is accumulating evidence that other members of the glucagon family of peptides are also endogenous substrates for this enzyme. To identify candidate substrates for DP-IV, a mass spectrometry-based protease assay was developed that measures cleavage efficiencies (kcat/Km) of polypeptides in a mixture, using only a few picomoles of each substrate and physiological amounts of enzyme in a single kinetic experiment. Oxyntomodulin and the growth hormone-(1-43) fragment were identified as new candidate in vivo substrates. Pituitary adenylate cyclase-activating polypeptide-(1-38) (PACAP38), a critical mediator of lipid and carbohydrate metabolism, was also determined to be efficiently processed by DP-IV in vitro. The catabolism of exogenously administered PACAP38 in wild type and DP-IV-deficient C57Bl/6 mice was monitored by tandem mass spectrometry. Animals lacking DP-IV exhibited a significantly slower clearance of the circulating peptide with virtually complete suppression of the inactive DP-IV metabolite, PACAP-(3-38). These in vivo results suggest that DP-IV plays a major role in the degradation of circulating PACAP38.

Cell surface peptidase CD26/DPPIV mediates G-CSF mobilization of mouse progenitor cells

CXC ligand 12 (CXCL12; also known as stromal cell-derived factor 1alpha/SDF-1alpha) chemoattracts hematopoietic stem and progenitor cells (HSCs/HPCs) and is thought to play a crucial role in the mobilization of HSCs/HPCs from the bone marrow. CD26 (dipeptidylpeptidase IV [DPPIV]) is a membrane-bound extracellular peptidase that cleaves dipeptides from the N-terminus of polypeptide chains. CD26 has the ability to cleave CXCL12 at its position-2 proline. We found by flow cytometry that CD26 is expressed on a subpopulation of normal Sca-1+c-kit+lin- hematopoietic cells isolated from mouse bone marrow, as well as Sca-1+c-kit-lin- cells, and that these cells possess CD26 peptidase activity. To test the functional role of CD26 in CXCL12-mediated normal HSC/HPC migration, chemotaxis assays were performed. The CD26 truncated CXCL12(3-68) showed an inability to induce the migration of sorted Sca-1+c-kit+lin- or Sca-1+c-kit-lin- mouse marrow cells compared with the normal CXCL12. In addition, CXCL12(3-68) acts as an antagonist, resulting in the reduction of migratory response to normal CXCL12. Treatment of Sca-1+c-kit+lin- mouse marrow cells, and myeloid progenitors within this population, or Sca-1+c-kit-lin- cells with a specific CD26 inhibitor, enhanced the migratory response of these cells to CXCL12. Finally, to test for potential in vivo relevance of these in vitro observations, mice were treated with CD26 inhibitors during granulocyte colony-stimulating factor (G-CSF)-induced mobilization. This treatment resulted in a reduction in the number of progenitor cells in the periphery as compared with the G-CSF regimen alone. This suggests that a mechanism of action of G-CSF mobilization involves CD26.

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.

Different modes of dipeptidyl peptidase IV (CD26) inhibition by oligopeptides derived from the N-terminus of HIV-1 Tat indicate at least two inhibitor binding sites

Dipeptidyl peptidase IV (DP IV, CD26) plays an essential role in the activation and proliferation of lymphocytes, which is shown by the immunosuppressive effects of synthetic DP IV inhibitors. Similarly, both human immunodeficiency virus-1 (HIV-1) Tat protein and the N-terminal peptide Tat(1-9) inhibit DP IV activity and T cell proliferation. Therefore, the N-terminal amino acid sequence of HIV-1 Tat is important for the inhibition of DP IV. Recently, we characterized the thromboxane A2 receptor peptide TXA2-R(1-9), bearing the N-terminal MWP sequence motif, as a potent DP IV inhibitor possibly playing a functional role during antigen presentation by inhibiting T cell-expressed DP IV [Wrenger, S., Faust, J., Mrestani-Klaus, C., Fengler, A., Stöckel-Maschek, A., Lorey, S., Kähne, T., Brandt, W., Neubert, K., Ansorge, S. & Reinhold, D. (2000) J. Biol. Chem.275, 22180-22186]. Here, we demonstrate that amino acid substitutions at different positions of Tat(1-9) can result in a change of the inhibition type. Certain Tat(1-9)-related peptides are found to be competitive, and others linear mixed-type or parabolic mixed-type inhibitors indicating different inhibitor binding sites on DP IV, at the active site and out of the active site. The parabolic mixed-type mechanism, attributed to both non-mutually exclusive inhibitor binding sites of the enzyme, is described in detail. From the kinetic investigations and molecular modeling experiments, possible interactions of the oligopeptides with specified amino acids of DP IV are suggested. These findings give new insights for the development of more potent and specific peptide-based DP IV inhibitors. Such inhibitors could be useful for the treatment of autoimmune and inflammatory diseases.

The multifunctional or moonlighting protein CD26/DPPIV

CD26/DPPIV can be considered a moonlighting protein because it is a multifunctional protein that exerts its different functions depending on cell type and intra- or extracellular conditions in which it is expressed. In the present review, we summarize all its known functions in relation to physiological and pathophysiological conditions. The protein is a proteolytic enzyme, receptor, costimulatory protein, and is involved in adhesion and apoptosis. The CD26/DPPIV protein plays a major role in immune response. Abnormal expression is found in the case of autoimmune diseases, HIV-related diseases and cancer. Natural substrates for CD26/DPPIV are involved in immunomodulation, psycho/neuronal modulation and physiological processes in general. Therefore, targeting of CD26/ DPPIV and especially its proteolytic activity has many therapeutic potentials. On the other hand, there are homologous proteins with overlapping proteolytic activity, which thus may prevent specific modulation of CD26/DPPIV. In conclusion, CD26/DPPIV is a protein present both in various cellular compartments and extracellularly where it exerts different functions and thus is a true moonlighting protein.

Cell surface peptidase CD26/dipeptidylpeptidase IV regulates CXCL12/stromal cell-derived factor-1 alpha-mediated chemotaxis of human cord blood CD34+ progenitor cells

CD26/dipeptidylpeptidase IV (DPPIV) is a membrane-bound extracellular peptidase that cleaves dipeptides from the N terminus of polypeptide chains. The N terminus of chemokines is known to interact with the extracellular portion of chemokine receptors, and removal of these amino acids in many instances results in significant changes in functional activity. CD26/DPPIV has the ability to cleave the chemokine CXCL12/stromal cell-derived factor 1alpha (SDF-1alpha) at its position two proline. CXCL12/SDF-1alpha induces migration of hemopoietic stem and progenitor cells, and it is thought that CXCL12 plays a crucial role in homing/mobilization of these cells to/from the bone marrow. We found that CD26/DPPIV is expressed by a subpopulation of CD34(+) hemopoietic cells isolated from cord blood and that these cells have DPPIV activity. The involvement of CD26/DPPIV in CD34(+) hemopoietic stem and progenitor cell migration has not been previously examined. Functional studies show that the N-terminal-truncated CXCL12/SDF-1alpha lacks the ability to induce the migration of CD34(+) cord blood cells and acts to inhibit normal CXCL12/SDF-1alpha-induced migration. Finally, inhibiting the endogenous CD26/DPPIV activity on CD34(+) cells enhances the migratory response of these cells to CXCL12/SDF-1alpha. This process of CXCL12/SDF-1alpha cleavage by CD26/DPPIV on a subpopulation of CD34(+) cells may represent a novel regulatory mechanism in hemopoietic stem and progenitor cells for the migration, homing, and mobilization of these cells. Inhibition of the CD26/DPPIV peptidase activity may therefore represent an innovative approach to increasing homing and engraftment during cord blood transplantation.

Human CD26 expression in transgenic mice affects murine T-cell populations and modifies their subset distribution

CD26 is a type II transmembrane glycoprotein with dipeptidyl peptidase (DPPIV) activity, constitutively expressed in different cell types and contributing to T-cell activation by acting as costimulatory molecule. Although data suggest an important role for CD26 within the immune system, the physiologic function of this molecule is still unknown. To investigate the role of CD26 in vivo we have produced transgenic mice expressing the human molecule in T cells. Human CD26 (huCD26) is constitutively expressed in all thymocytes and peripheral T lymphocytes of these transgenic mice and is endowed with an enhanced DPPIV activity. CD26 transgene expression induces major phenotypic changes to T-cell populations within the thymus and in peripheral blood. After the onset of sexual maturity, huCD26 expression induces an age-related overreduction of thymus cellularity accompanied by a relative impairment of thymocyte proliferation following lectin stimulation. Also the peripheral blood T-cell pool is reduced in huCD26 transgenic mice and this is accompanied by an increase of the apoptotic rate of CD4+ and CD8+ subpopulations. Taken together these data suggest that CD26 interferes with transduction pathway(s) needed for the maturation of T cells and plays an important role in T lymphocyte homeostasis in peripheral blood.

Set-up of large laboratory-scale chromatographic separations of poly(ethylene glycol) derivatives of the growth hormone-releasing factor 1-29 analogue

In this paper we report the scale-up of the purification of poly(ethylene glycol) (PEG) derivatives of the growth hormone-releasing factor 1-29, from laboratory scale (100 mg of bulk starting material) to larger scale (3 g of bulk), through the use of a cation-exchange TSK-SP-5PW chromatographic column. A one-step purification process capable of purifying large amounts of mono-PEGylated GRF species from the crude reaction mixture was developed. A simple, straightforward stepwise gradient elution separation was developed at laboratory scale and then scaled up with a larger column packed with a chromatographic resin with the same chemistry which maintained the laboratory-scale separation profile. Active material recovery and material purity remained constant through the scale-up from the 13-microm stationary phase to the 25-microm larger column. Overall, the gram GRF equivalent/batch process scale showed to be quite reproducible, and could be considered as a good platform for scale up to production scale.

Kinetic study of the processing by dipeptidyl-peptidase IV/CD26 of neuropeptides involved in pancreatic insulin secretion

Dipeptidyl-peptidase IV (DPPIV/CD26) metabolizes neuropeptides regulating insulin secretion. We studied the in vitro steady-state kinetics of DPPIV/CD26-mediated truncation of vasoactive intestinal peptide (VIP), pituitary adenylyl cyclase-activating peptide (PACAP27 and PACAP38), gastrin-releasing peptide (GRP) and neuropeptide Y (NPY). DPPIV/CD26 sequentially cleaves off two dipeptides of VIP, PACAP27, PACAP38 and GRP. GRP situates between the best DPPIV/CD26 substrates reported, comparable to NPY. Surprisingly, the C-terminal extension of PACAP38, distant from the scissile bond, improves both PACAP38 binding and turnover. Therefore, residues remote from the scissile bond can modulate DPPIV/CD26 substrate selectivity as well as residues flanking it.

Kinetic investigation of chemokine truncation by CD26/dipeptidyl peptidase IV reveals a striking selectivity within the chemokine family

Chemokines coordinate many aspects of leukocyte migration. As chemoattractants they play an important role in the innate and acquired immune response. There is good experimental evidence that N-terminal truncation by secreted or cell surface proteases is a way of modulating chemokine action. The localization of CD26/dipeptidyl peptidase IV on cell surfaces and in biological fluids, its primary specificity, and the type of naturally occurring truncated chemokines are consistent with such a function. We determined the steady-state catalytic parameters for a relevant selection of chemokines (CCL3b, CCL5, CCL11, CCL22, CXCL9, CXCL10, CXCL11, and CXCL12) previously reported to alter their chemotactic behavior due to CD26/dipeptidyl peptidase IV-catalyzed truncation. The results reveal a striking selectivity for stromal cell-derived factor-1alpha (CXCL12) and macrophage-derived chemokine (CCL22). The kinetic parameters support the hypothesis that CD26/dipeptidyl peptidase IV contributes to the degradation of certain chemokines in vivo. The data not only provide insight into the selectivity of the enzyme for specific chemokines, but they also contribute to the general understanding of CD26/dipeptidyl peptidase IV secondary substrate specificity.

Reference values for plasma dipeptidyl-peptidase IV activity and their association with other laboratory parameters

In blood, the exopeptidase dipeptidyl-peptidase IV (DPPIV; EC 3.4.14.5) is predominantly present in a soluble form in plasma/serum and as an activation antigen on the membrane of lymphocytes (CD26). It modifies some important biologically active peptides (neuropeptides, chemokines), and a regulatory role for DPPIV/CD26 in immune and endocrine processes has been demonstrated. The aim of this study was to determine reference values for plasma/serum DPPIV activity and to study the association of this activity with a series of biochemical and hematological parameters and baseline characteristics such as age, gender, blood pressure and body mass index. We studied 481 healthy subjects aged between 19 and 61 years. The group consisted of 213 men and 268 women equally divided between the different categories of age. Among the women, 127 were taking hormone therapy (contraception/hormone replacement) and 141 were not. A multiple regression model shows that DPPIV activity decreases significantly with age. The activity in women is slightly lower than in men. We observed an important association with liver, muscle and lipid metabolism-related parameters. In this model, no significant contribution of body mass index, blood pressure or hormone therapy could be stated.

Metabolism of glucagon by dipeptidyl peptidase IV (CD26)

Glucagon is a 29-amino acid polypeptide released from pancreatic islet alpha-cells that acts to maintain euglycemia by stimulating hepatic glycogenolysis and gluconeogenesis. Despite its importance, there remains controversy about the mechanisms responsible for glucagon clearance in the body. In the current study, enzymatic metabolism of glucagon was assessed using sensitive mass spectrometric techniques to identify the molecular products. Incubation of glucagon with purified porcine dipeptidyl peptidase IV (DP IV) yielded sequential production of glucagon(3-29) and glucagon(5-29). In human serum, degradation to glucagon(3-29) was rapidly followed by N-terminal cyclization of glucagon, preventing further DP IV-mediated hydrolysis. Bioassay of glucagon, following incubation with purified DP IV or normal rat serum demonstrated a significant loss of hyperglycemic activity, while a similar incubation in DP IV-deficient rat serum did not show any loss of glucagon bioactivity. Degradation, monitored by mass spectrometry and bioassay, was blocked by the specific DP IV inhibitor, isoleucyl thiazolidine. These results identify DP IV as a primary enzyme involved in the degradation and inactivation of glucagon. These findings have important implications for the determination of glucagon levels in human plasma.

Humoral factors in intestinal adaptation

The small bowel has a remarkable ability to adapt after injury, inflammation or resection. It has long been suggested that humoral factors, particularly enteroglucagon, epidermal growth factor, neurotensin and growth hormone/insulin-like growth factor I, might stimulate bowel growth. Of particular interest is the recent finding that glucagon-like peptide 2 (GLP-2), a product of the gene encoding proglucagon, exerts a trophic effect on the intestinal epithelium via a specific G-protein-coupled receptor. GLP-2 and/or these other trophic peptides might prove to have a role in the treatment of bowel diseases associated with structural or functional loss of the small bowel.