Dipeptidyl peptidase-IV inhibits glioma cell growth independent of its enzymatic activity.

Malignant gliomas exhibit abnormal expression of proteolytic enzymes that may participate in the uncontrolled cell proliferation and aberrant interactions with the brain extracellular matrix. The multifunctional membrane bound serine aminopeptidase dipeptidyl peptidase (DPP)-IV has been linked to the development and progression of several malignancies, possibly both through the enzymatic and nonenzymatic mechanisms. In this report we demonstrate the expression of DPP-IV and homologous proteases fibroblast activation protein, DPP8 and DPP9 in primary cell cultures derived from high-grade gliomas, and show that the DPP-IV-like enzymatic activity is negatively associated with their in vitro growth. More importantly, the DPP-IV positive subpopulation isolated from the primary cell cultures using immunomagnetic separation exhibited slower proliferation. Forced expression of the wild as well as the enzymatically inactive mutant DPP-IV in glioma cell lines resulted in their reduced growth, migration and adhesion in vitro, as well as suppressed glioma growth in an orthotopic xenotransplantation mouse model. Microarray analysis of glioma cells with forced DPP-IV expression revealed differential expression of several candidate genes not linked to the tumor suppressive effects of DPP-IV in previous studies. Gene set enrichment analysis of the differentially expressed genes showed overrepresentation of gene ontology terms associated with cell proliferation, cell adhesion and migration. In conclusion, our data show that DPP-IV may interfere with several aspects of the malignant phenotype of glioma cells in great part independent of its enzymatic activity.

Coupled expression of dipeptidyl peptidase-IV and fibroblast activation protein-α in transformed astrocytic cells.

Dipeptidyl peptidase-IV (DPP-IV) and fibroblast activation protein-α (FAP) are speculated to participate in the regulation of multiple biological processes, because of their unique enzymatic activity, as well as by non-hydrolytic molecular interactions. At present, the role of DPP-IV and FAP in the development and progression of various types of tumors, including glioblastoma, is intensively studied, and their functional crosstalk is hypothesized. In this article, we describe the correlative expression of DPP-IV and FAP mRNA in primary cell cultures derived from human glioblastoma and associated expression dynamics of both molecules in astrocytoma cell lines depending on culture conditions. Although the molecular mechanisms of DPP-IV and FAP co-regulations remain unclear, uncoupled expression of transgenic DPP-IV and the endogenous FAP suggests that it occurs rather at the transcriptional than at the posttranscriptional level. Understanding of the expressional and functional coordinations of DPP-IV and FAP may help clarify the mechanisms of biological roles of both molecules in transformed astrocytic cells.

Expression of dipeptidyl peptidase-IV activity and/or structure homologs in human meningiomas.

Meningiomas are tumors derived from arachnoid cap cells that represent approximately 30% of all intracranial tumors. In this study, we investigated 22 human meningiomas for the expression of dipeptidyl peptidase (DPP)-IV activity and/or structure homologs (DASH), including canonical DPP-IV/CD26, fibroblast activation protein-alpha (FAPalpha), DPP8 and DPP9. DPP-IV-like enzymatic activity, including all enzymatically-active DASH molecules, was found in all 18 benign meningiomas WHO grade I and IV atypical meningiomas WHO grade II by continuous rate fluorimetric assay in tissue homogenates and catalytic enzyme histochemistry in situ. In atypical meningiomas, this activity was significantly higher and was associated with higher cell proliferation as detected by Ki67 antigen immunohistochemistry. The expression of DPP-IV/CD26 and FAPalpha demonstrated by real-time RT-PCR and immunohistochemistry was low. As shown histochemically, it occurred most often on the surface of fibrous bundles and whorls rich in extracellular matrix. Compared to DPP-IV/CD26 and FAPalpha, the expression of DPP8 and DPP9 was higher and, in addition, it was present also in the cells inside these structures. Expression of CXCR4, the receptor of pro-proliferative chemokine stromal cell-derived factor-1alpha (SDF-1alpha), DPP-IV substrate, was found in all tumors, suggesting higher values in atypical grade II samples. This is the first report on the expression status of dipeptidyl peptidase-IV and related molecules in meningiomas. It shows that DPP8 and DPP9 prevail over canonical DPP-IV/CD26 and FAPalpha in all examined patients. In addition, the study suggests an increase of DPP-IV-like enzymatic activity in these tumors of WHO grade II.

Dipeptidyl peptidase-IV and related molecules: markers of malignancy?

BACKGROUND: The dipeptidyl peptidase-IV (DPP-IV) family has outgrown its humble origins as a simple enzymatic activity cleaving dipeptides from peptides with an accessible N-terminal penultimate proline with no clear role in metabolism. It is now understood to play a critical role in regulating signaling capacity of chemokines, neuropeptides and other extracellular messengers in addition to playing direct roles by means of non-enzymatic interactions to regulate the local extracellular proliferative environment. Consequently, examination of DPP-IV family representation and activity in immune and oncogenic processes has become a major focus. OBJECTIVES: To review the evidence for DPP-IV family members as markers of malignancy. METHODS: Overview of published data. RESULTS/CONCLUSION: The DPP-IV family, which is probably linked directly to the pathogenesis of cancer, holds significant promise for exploitation in the diagnostic arena.

Dipeptidyl peptidase-IV enzymatic activity bearing molecules in human brain tumors--good or evil?

Dipeptidyl peptidase-IV (DPP-IV) represents a unique proteolytic activity cleaving N-terminal X-Pro dipeptides. In addition to canonical DPP-IV/CD26, a number of other molecules have been discovered which exhibit DPP-IV-like enzymatic activity and various degree of structural similarity. These comprise enzymatically active fibroblast activation protein-alpha, DPP-II, DPP8, DPP9 and enzymatically inactive DPP6 and DPP10 that have been grouped as "DPP-IV activity and/or structure homologues" (DASH). Because the enzymatically active DASH can share similar sets of biologically active substrates and are frequently coexpressed within single cell or on tissue level, it is tempting to consider their participation on biological function(s) previously attributed to DPP-IV/CD26. It is speculated that disrupted expression and enzymatic activity of some DASH might corrupt the message carried by their substrates, with consequent promotion of abnormal cell behavior. Thus, modulation of activity of a particular enzyme using e.g. inhibitors, specific antibodies or modifying its expression may be an attractive therapeutic concept in cancer treatment. This review summarizes current knowledge of the expression and possible function of DPP-IV enzymatic activity bearing molecules in human brain tumors.

Expression and enzymatic activity of dipeptidyl peptidase-IV in human astrocytic tumours are associated with tumour grade.

Alterations in dipeptidyl peptidase-IV (DPP-IV) enzymatic activity are characteristic of malignant transformation. Through its well-characterized functionality in regulating the activity of bioactive peptides by removal of the N-terminal dipeptide, DPP-IV activity may have profound effects upon metastatic potential and cell growth. Although DPP-IV/CD26 (EC 3.4.14.5) is the canonical representative of the group, a number of other proteins including DPP-7, 8, 9, and seprase/fibroblast activation protein-alpha (FAP-alpha) have been shown to have similar enzymatic activity. This study was set up to address the relative representation and enzymatic activity of plasma membrane localized DPP-IV/CD26 and FAP-alpha in human brain and astrocytic tumours. In parallel, expression of CXCR4, receptor for glioma cell growth stimulator chemokine SDF-1alpha known to be a DPP-IV substrate, was investigated. This is the first report showing that non-malignant brain tissue contains a DPP-IV-like enzymatic activity attributable mostly to DPP-8/9, while the substantial part of the activity in glioma is due to increased DPP-IV/CD26, localized in both the vascular and parenchymal compartments. DPP-IV enzymatic activity increased dramatically with tumour grade severity. A grade-related increase in CXCR4 receptor paralleled the rise in DPP-IV expression and activity. These data might support a role for DPP-IV regulation of the CXCR4-SDF-1alpha axis in glioma development.