Histochemical and biochemical studies of dipeptidyl peptidase I (DPP I) in laboratory rodents

Dipeptidyl peptidase II (DPPII), a review

An increasing number of biological processes appear to be regulated by Pro-specific N-terminal processing. The proline-specific dipeptidyl peptidases (DPPs) like DPPIV, fibroblast activation protein alpha (FAP), DPPII, DPP8 and DPP9, because of their preference for cleavage after X-Pro in vitro, are likely to be involved in many of these processes. These DPPs are emerging as an important protease family with roles in the regulation of signaling by peptide hormones. Dipeptidyl peptidase II (DPPII, E.C. 3.4.14.2) is an intracellular protease that localizes to the vesicular system. It releases, preferably at acidic pH, N-terminal dipeptides from oligopeptides with Pro or Ala in the penultimate position. Despite the fact that the physiological role of DPPII still has not been elucidated, several suggestions were made on possible functions of the enzyme depending on its localization in different cells, body fluids and organs. DPPII was a.o. suggested to be involved in the processes of cell differentiation and in the protection from cell death, and to have a role in the degradation of collagen fragments, myofibrillar proteins and short neuropeptides. Moreover, changes in the level and distribution of the enzyme provided clues indicating additional roles in disease-related processes. Here we review the DPPII literature, aiming to bring more clarity in the disperse data on this subject and give a state of the art on DPPII research.

Granzyme N, a Novel Granzyme, Is Expressed in Spermatocytes and Spermatids of the Mouse Testis1

We cloned a cDNA for a novel granzyme, granzyme N (Gzmn), from a mouse testes cDNA library. The testes contained two distinct species of Gzmn mRNA, one of which codes for a complete protein of 248 amino acids with three essential residues required for catalytic activity. The Gzmn mRNA was specifically expressed in the testes of adult mice. The Gzmn expression was found to initiate in the testes at 3 wk of age and to become more prominent as the animal reached sexual maturity. In situ hybridization analysis revealed that both spermatocytes and spermatids of the adult mouse testes express Gzmn mRNA. Consistent with these findings, the protein was immunohistochemically detected in the spermatocytes and spermatids, although some of the germ cells showed no positive staining. Gzmn was demonstrated to be a secretory and N-glycosylated protein that exists in two protein forms in the testes extract. In the cryptorchid testes, the expression of Gzmn transcript was drastically reduced on Postoperative Day 10, whereas the protein level was gradually decreased starting on Day 6. The local heating (43 degrees C, 20 min) of the testes did not change the Gzmn expression level at either 8 or 16 h after treatment. These results suggest that Gzmn is not involved in the process of germ cell apoptosis induced by heat shock, but that it may be involved in spermatogenesis in the mouse testes.

Cloning and characterization of dipeptidyl peptidase 10, a new member of an emerging subgroup of serine proteases

Two dipeptidyl peptidase IV (DPPIV, DPP4)-related proteins, DPP8 and DPP9, have been identified recently [Abbott, Yu, Woollatt, Sutherland, McCaughan, and Gorrell (2000) Eur. J. Biochem. 267, 6140-6150; Olsen and Wagtmann (2002) Gene 299, 185-193; Qi, Akinsanya, Riviere, and Junien (2002) Patent application WO0231134]. In the present study, we describe the cloning of DPP10, a novel 796-amino-acid protein, with significant sequence identity to DPP4 (32%) and DPP6 (51%) respectively. We propose that DPP10 is a new member of the S9B serine proteases subfamily. The DPP10 gene is located on the long arm of chromosome 2 (2q12.3-2q14.2), close to the DPP4 (2q24.3) and FAP (2q23) genes. The active-site serine residue is replaced by a glycine residue in DPP10, resulting in the loss of DPP activity. The serine residue is also replaced in DPP6, which lacks peptidase activity. DPP8 and DPP9 share an identical active site with DPP4 (Gly-Trp-Ser-Tyr-Gly). In contrast with the previous results suggesting that DPP9 is inactive, we show that DPP9 is a DPP, hydrolysing Ala-Pro-(7-amino-4-methyl-coumarin) with similar pH-specificity and protease-inhibitor-sensitivity to those of DPP4 and DPP8. Northern-blot analysis shows that whereas DPP8 and DPP9 are widely expressed, DPP10 is expressed mainly in the brain and pancreas. DPP6, which has the highest amino acid identity with DPP10, has been shown previously [Nadal, Ozaita, Amarillo, de Miera, Ma, Mo, Goldberg, Misumi, Ikehara, Neubert et al. (2003) Neuron 37, 449-461] to associate with A-type K(+) channel subunits, modulating their transport and function in somatodendritic compartments of neurons. It is possible that DPP10 is involved in similar functions in the brain. Elucidation of the physiological or pathophysiological role of DPP8, DPP9 and DPP10 and characterization of their structure-function relationships will add impetus to the development of inhibitor molecules for pharmacological or therapeutic use.

Molecular cloning, chromosomal localization, and expression of murine dipeptidyl peptidase I

Dipeptidyl peptidase I (DPPI) is a lysosomal cysteine protease that catalyzes the sequential removal of dipeptides from the amino termini of various protein substrates. We have isolated a cDNA coding for murine DPPI from mouse thymus and spleen cDNA libraries. The deduced amino acid sequence codes for a protein of 462 amino acid residues; comparison of this deduced sequence with that of rat and human DPPI revealed 90.1% and 77.8% identity, respectively. Using DPPI cDNA, we obtained two BAC (Bacterial Artificial Chromosome) clones that contained the murine DPPI locus. The DPPI gene consists of seven exons and 6 introns, and spans approximately 20 kilobases. Using fluorescence in situ chromosome hybridization, we localized murine DPPI to chromosome 7D3-E1.1. We determined that DPPI protein is widely distributed in mouse tissues, although its relative abundance varies from tissue to tissue. In contrast to previous reports, we show here that DPPI mRNA and protein levels and enzymatic activity are unchanged during in vitro T cell activation, implying that this enzyme is not rate-limiting for granzyme processing.

Enzyme histochemistry of the regressing rat decidua and metrial gland

In order to understand more about participation of the basal placental zones in processes of regression and degradation as well as separation on the cellular level, the cell metabolism of the rat decidua and metrial gland was investigated enzyme histochemically in cryosections for activities of oxyradical-forming enzymes and hydrolyzing enzymes. Additionally, plastic sections were studied to facilitate the recognition of cell types. Decidual stromal cells and fibroblasts formed the vast majority amongst many cell types in the decidua and metrial gland. High activities of enzymes involved in purine degradation and oxyradical generation were demonstrated in decidual stromal cells and fibroblasts. Microsomal alanyl aminopeptidase and various acid hydrolases were shown to be extremely active in decidual stromal cells. The abundance of these enzyme activities in the decidua and metrial gland in contrast to other placental areas suggests, that these enzymes may have specialized functions in connection with regression and degradation processes finally contributing to placental separation.

Interference of Substrate Quenching with the Kinetics of Placental Peptidases

The study was undertaken to clarify the putative presence and influence of substrate inhibition and substrate quenching on the kinetic analysis of placental peptidases using naphthylamide substrates in a fluorometric assay. Using the appropriate naphthylamide substrates, we analysed microsomal alanine aminopeptidase (EC 3.4.11.2) and angiotensinase A (EC 3.4.11.7) in the presence or absence of inhibitors (1,10'-phenanthroline, EDTA) or activators (calcium) in the human and rat placenta. All substrates were shown to quench the fluorescence of the enzymatically released unspecific moiety. Since Michaelis-Menten-derived kinetic equations do not include quenching phenomena, we deduced a mathematical model integrating enzyme kinetics and quenching kinetics, thereby allowing simultaneous analysis of both processes from the same raw data. Curves derived from this expanded kinetic model fitted significantly better to velocity data than those derived from Michaelis-Menten-equation. According to the presented data, we assume that substrate inhibition for both enzymes, as previously proposed in the literature, in contrast may be due to formerly unconsidered substrate quenching. The presented kinetic model could serve as a useful tool in the study of putative physiological substrates of the investigated placental peptidases, characterizing the physiologic substrates by their competitive interaction with the synthetic naphthylamides. Additionally, this model may not only be important in fluorometric analysis of peptidases, but also of other enzymes which are analysed fluorometrically with synthetic substrates.