Possible relation of cathepsin C activity and seasonal fluctuation of skin lesions in Papillon-Lefèvre syndrome

Our patient with Papillon–Lefèvre syndrome with a novel p.G430V and recurrent p.G301S missense mutation showing aggravation of skin lesions in wintertime. A temperature-dependent cathepsin C enzymatic activity study indicates a possible association between seasonal fluctuations, minimal dental involvement and temperature.

Dipeptidyl peptidase 1 inhibition as a potential therapeutic approach in neutrophil-mediated inflammatory disease

Neutrophils have a critical role in the innate immune response to infection and the control of inflammation. A key component of this process is the release of neutrophil serine proteases (NSPs), primarily neutrophil elastase, proteinase 3, cathepsin G, and NSP4, which have essential functions in immune modulation and tissue repair following injury. Normally, NSP activity is controlled and modulated by endogenous antiproteases. However, disruption of this homeostatic relationship can cause diseases in which neutrophilic inflammation is central to the pathology, such as chronic obstructive pulmonary disease (COPD), alpha-1 antitrypsin deficiency, bronchiectasis, and cystic fibrosis, as well as many non-pulmonary pathologies. Although the pathobiology of these diseases varies, evidence indicates that excessive NSP activity is common and a principal mediator of tissue damage and clinical decline. NSPs are synthesized as inactive zymogens and activated primarily by the ubiquitous enzyme dipeptidyl peptidase 1, also known as cathepsin C. Preclinical data confirm that inactivation of this protease reduces activation of NSPs. Thus, pharmacological inhibition of dipeptidyl peptidase 1 potentially reduces the contribution of aberrant NSP activity to the severity and/or progression of multiple inflammatory diseases. Initial clinical data support this view. Ongoing research continues to explore the role of NSP activation by dipeptidyl peptidase 1 in different disease states and the potential clinical benefits of dipeptidyl peptidase 1 inhibition.

Pharmacological inhibition of the cysteine protease cathepsin C improves graft function after heart transplantation in rats

BACKGROUND

Heart transplantation (HTX) is the standard treatment for end-stage heart failure. However, reperfusion following an ischemic period can contribute to myocardial injury. Neutrophil infiltration, along with the subsequent release of tissue-degrading neutrophil elastase (NE)-related serine proteases and oxygen-derived radicals, is associated with adverse graft outcomes. The inhibition of cathepsin C (CatC) has been shown to block NE-related protease activation. We hypothesized that the CatC inhibitor BI-9740 improves graft function after HTX.

METHODS

In a rat model of HTX, the recipient Lewis rats were orally administered with either a placebo (n = 12) or BI-9740 (n = 11, 20 mg/kg) once daily for 12 days. Donor hearts from untreated Lewis rats were explanted, preserved in a cardioplegic solution, and subsequently heterotopically implanted. In vivo left-ventricular (LV) graft function was assessed after 1 h of reperfusion. The proteolytic activity of neutrophil serine proteases was determined in bone marrow lysates from BI-9740-treated and control rats. Additionally, myocardial morphological changes were examined, and heart samples underwent immunohistochemistry and western blot analysis.

RESULTS

The NE-related proteolytic activity in bone marrow cell lysates was markedly decreased in the BI-9740-treated rats compared to those of the placebo group. Histopathological lesions, elevated CatC and myeloperoxidase-positive cell infiltration, and nitrotyrosine immunoreactivity with an increased number of poly(ADP-ribose) polymerase (PARP)-1-positive cells were lowered in the hearts of animals treated with BI-9740 compared to placebo groups. Regarding the functional parameters of the implanted graft, improvements were observed in both systolic function (LV systolic pressure 110 ± 6 vs 74 ± 6 mmHg; dP/dtmax 2782 ± 149 vs 2076 ± 167 mmHg/s, LV developed pressure, at an intraventricular volume of 200 µl, p < 0.05) and diastolic function in the hearts of BI-9740 treated animals compared with those receiving the only placebo. Furthermore, the administration of BI-9740 resulted in a shorter graft re-beating time compared to the placebo group. However, this study did not provide evidence of DNA fragmentation, the generation of both superoxide anions and hydrogen peroxide, correlating with the absence of protein alterations related to apoptosis, as evidenced by western blot in grafts after HTX.

CONCLUSIONS

We provided experimental evidence that pharmacological inhibition of CatC improves graft function following HTX in rats.

Cathepsin C promotes colorectal cancer metastasis by regulating immune escape through upregulating CSF1

Since metastasis remains the primary reason for colorectal cancer (CRC) associated death, a better understanding of the molecular mechanism underlying CRC metastasis is urgently needed. Here, we elucidated the role of Cathepsin C (CTSC) in promoting CRC metastasis. The expression of CTSC was detected by real-time PCR and immunohistochemistry in the human CRC cohort. The metastatic capacities of CTSC-mediated metastasis were analyzed by in vivo metastasis model. Elevated CSTC expression was positively associated with tumor differentiation, tumor invasion, lymph node metastasis, and AJCC stage and indicated poor prognosis in human CRC. CTSC overexpression in CRC cells promoted myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) recruitment by the CSF1/CSF1R axis. In contrast, the knockdown of CSF1 reduced CTSC-mediated MDSCs and TAMs infiltration and CRC metastasis. Depletion of either MDSCs or TAMs decreased CTSC-mediated CRC metastasis. In human CRC tissues, CTSC expression was positively associated with intratumoral MDSCs and TAMs infiltration. Furthermore, the combination of CTSC inhibitor AZD7986 and anti-PD-L1 antibody blocked CTSC-induced CRC metastasis. CTSC overexpression promoted MDSCs and TAMs infiltration by CSF1/CSF1R axis. Interruption of this oncogenic loop may provide a promising treatment strategy for inhibiting CTSC-driven CRC metastasis.

Cathepsin C (CTSC) contributes to the antibacterial immunity in golden pompano (Trachinotus ovatus)

Cathepsins, as a class of protein hydrolases, are widely found in the lysosomes of many tissues and play an essential role in various physiological activities. Cathepsin C (CTSC), a lysosomal cysteine protease, is an essential component of the lysosomal hydrolase family. In this study, we identified a CTSC from Trachinotus ovatus (TroCTSC) and analyzed its function. TroCTSC contained an ORF of 1368 bp and encoded 455 amino acids, which included three conserved catalytically active sites (Cys²⁵¹, His³⁹⁷, and Asn⁴¹⁹). It shares high homology (69.47%-90.77%) with the other known CTSC sequences of teleosts, which was most closely related to Seriola dumerili. TroCTSC was most abundant in the muscle, liver, and head kidney. After Vibrio harveyi infection, the expression levels of TroCTSC in liver, spleen, and head kidney were significantly up-regulated. TroCTSC was found in the cytoplasm with some of which were co-located with the lysosome. After V. harveyi stimulation, TroCTSC was translocated to nucleus in golden pompano snout (GPS) cells. In vitro, results revealed that the optimal hydrolase activity of the recombinant protein, rTroCTSC, was at 40 °C and pH 5.5. The activity of rTroCTSC was promoted by Zn²⁺ and Ca²⁺ but inhibited by Fe²⁺ and Cu²⁺. However, three mutant proteins, rTroCTSC-C251A, rTroCTSC-H397A, rTroCTSC-N419A, were dramatically reduced the proteolytic activity. Furthermore, in vivo results showed that overexpression of TroCTSC could significantly enhance body's ability to resist V. harveyi and promote the expression of proinflammatory cytokines, including interleukin 1-beta (IL-1β), IL-6, IL-8, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α). In contrast, the interference of TroCTSC expression induced a significant increase in the number of bacteria after V. harveyi infection. Our results suggested that TroCTSC was an essential effector of the innate immune system and played a pivotal role in antibacterial immunity.

Multi-Design Differential Expression Profiling of COVID-19 Lung Autopsy Specimens Reveals Significantly Deregulated Inflammatory Pathways and SFTPC Impaired Transcription

The transcriptomic profiling of lung damage associated with SARS-CoV-2 infection may lead to the development of effective therapies to prevent COVID-19-related deaths. We selected a series of 21 autoptic lung samples, 14 of which had positive nasopharyngeal swabs for SARS-CoV-2 and a clinical diagnosis of COVID-19-related death; their pulmonary viral load was quantified with a specific probe for SARS-CoV-2. The remaining seven cases had no documented respiratory disease and were used as controls. RNA from formalin-fixed paraffin-embedded (FFPE) tissue samples was extracted to perform gene expression profiling by means of targeted (Nanostring) and comprehensive RNA-Seq. Two differential expression designs were carried out leading to relevant results in terms of deregulation. SARS-CoV-2 positive specimens presented a significant overexpression in genes of the type I interferon signaling pathway (IFIT1, OAS1, ISG15 and RSAD2), complement activation (C2 and CFB), macrophage polarization (PKM, SIGLEC1, CD163 and MS4A4A) and Cathepsin C (CTSC). CD163, Siglec-1 and Cathepsin C overexpression was validated by immunohistochemistry. SFTPC, the encoding gene for pulmonary-associated surfactant protein C, emerged as a key identifier of COVID-19 patients with high viral load. This study successfully recognized SARS-CoV-2 specific immune signatures in lung samples and highlighted new potential therapeutic targets. A better understanding of the immunopathogenic mechanisms of SARS-CoV-2 induced lung damage is required to develop effective individualized pharmacological strategies.

Location of the binding site for chloride ion activation of cathepsin C

Cathepsin C, a tetrameric lysosomal dipeptidyl-peptide hydrolase, is activated by chloride ion. The activation is shown here to be specific and pH-dependent, dissociation constants for chloride being lower at low pH. Bound chloride decreases the Km for the hydrolysis of chromophore labelled substrates without any significant change in Vmax, confirming its involvement in substrate binding. Determination of the kinetic parameters of chloride activation, using unlabelled substrates, has enabled its site of action to be located. The lower Km for the hydrolysis of simple amide substrates in the presence of Cl- shows that the S sites are involved. Possible involvement of the S' sites is excluded by the finding that the Km for the nucleophile in the transferase reaction is unaffected by chloride. The rates of inhibition by E-64 and iodoacetate are both chloride-dependent and, from the structure of the papain-E-64 complex, it is concluded that chloride binds close to the S2 site. The binding of guanidinium ion, a positively charged inhibitor, to the S site is dependent on chloride. Based on these results, a model is proposed to explain the chloride activation of cathepsin C. The possible physiological role of chloride in the regulation of proteolysis in the lysosome is discussed.

Dipeptidyl peptidase I is required for the processing and activation of granzymes A and B in vivo

Dipeptidyl peptidase I (DPPI) is a lysosomal cysteine protease that has been implicated in the processing of granzymes, which are neutral serine proteases exclusively expressed in the granules of activated cytotoxic lymphocytes. In this report, we show that cytotoxic lymphocytes derived from DPPI-/- mice contain normal amounts of granzymes A and B, but these molecules retain their prodipeptide domains and are inactive. Cytotoxic assays with DPPI-/- effector cells reveal severe defects in the induction of target cell apoptosis (as measured by [(125)I]UdR release) at both early and late time points; this defect is comparable to that detected in perforin-/- or granzyme A-/- x B-/- cytotoxic lymphocytes. DPPI therefore plays an essential role in the in vivo processing and activation of granzymes A and B, which are required for cytotoxic lymphocyte granule-mediated apoptosis.

Increased collagenase and dipeptidyl peptidase I activity in leucocytes from healthy elderly people

The incidence of infectious diseases increases with ageing. The enzymatic activity of leucocytes may have a relevant role in the morbidity and mortality due to infections in the elderly. In this study we have compared the activity of enzymes involved in the inflammatory response in leucocytes from young and elderly women. A total of 35 healthy females was studied, 20 volunteers aged 78-98 years (mean 89.1 years) and 15 young controls aged 19-34 years (mean 26 years). All of them were in good clinical condition, without any acute or chronic disease. Intracellular enzyme activity was analysed by flow cytometry in leucocytes from young and elderly women. The enzyme substrates employed were for oxidative burst, L-aminopeptidase, collagenase, cathepsin B, C, D and, G and dipeptidyl peptidase I. The intracellular enzyme activity assessed by flow cytometry in leucocytes from young and elderly women was similar, as far as oxidative burst, L-aminopeptidase, cathepsin B, C, D and G are concerned. An increased collagenase activity was detected in granulocytes from elders. The mean fluorescence channels for this enzyme corresponded to 86 +/- 23 and 60 +/- 15 in cells from elders and controls, respectively (P = 0.01224). An increased dipeptidyl peptidase I activity was detected in lymphocytes from elderly women. The corresponding values for this enzyme in elders and the young were 65.9 +/- 43.3 and 17.3 +/- 5, respectively (P = 0. 0036). The proper functional activity of intracellular enzymes involved in inflammatory responses is likely to be determinant for successful ageing.

Competitive inhibition of cathepsin C by guanidinium ions and reexamination of substrate inhibition

Cathepsin C, a lysosomal dipeptidyl aminopeptidase, is competitively and reversibly inhibited by guanidinium ions with a Ki approximately 1.5 mM. Loss of activity is not the result of conformational change, subunit dissociation or altered mobility of the enzyme, but rather reflects a specific binding of guanidinium ions to the active site. The finding that cathepsin C is not inhibited by substrate has allowed the kinetic parameters in the presence of guanidinium ion to be determined. Guanidinium significantly decreases the Km of substrate hydrolysis, without changing Vmax. In a novel application of the transferase reaction, the Km of the nucleophile substrate has been determined (11 mM) and found not to be affected by guanidinium, indicating its inhibition of substrate binding to the S, but not the S', site. Inhibition is suggested to be the result of shielding a negative charge on the enzyme important for interaction with the substrate.

Removal of N-terminal polyhistidine tags from recombinant proteins using engineered aminopeptidases

We have developed a specific and efficient method for complete removal of polyhistidine purification tags (HisTags) from the N-termini of target proteins. The method is based on the use of the aminopeptidase dipeptidyl peptidase I (DPPI), either alone or in combination with glutamine cyclotransferase (GCT) and pyroglutamyl aminopeptidase (PGAP). In both cases, the HisTag is cleaved off by DPPI, which catalyzes a stepwise excision of a wide range of dipeptides from the N-terminus of a peptide chain. Some sequences, however, are resistant to DPPI cleavage and a number of mature proteins have nonsubstrate N-termini which protects them against digestion. For such proteins, HisTags composed of an even number of residues can be cleaved off by treatment with DPPI alone. When the target protein is unprotected against DPPI, a blocking group is generated enzymatically from a glutamine residue inserted between the HisTag and the target protein. A protein with a HisTag-Gln extension is incubated with both DPPI and GCT. As above, the polyhistidine sequence is cleaved off by DPPI, but when the glutamine residue appears in the N-terminus, it is immediately converted into a pyroglutamyl residue by an excess of GCT and further DPPI digestion is prevented. The desired sequence is finally obtained by excision of the pyroglutamyl residue with PGAP. All the enzymes employed can bind to immobilized metal affinity chromatography (IMAC) matrices, and in this paper we demonstrate a simple and highly effective process combining IMAC purification of His-tagged proteins, our aminopeptidase-based method for specific excision of HisTags and use of subtractive IMAC for removing processing enzymes. Typical recoveries were 75-90% for the enzymatic processing and subtractive IMAC. The integrated process holds promises for use in large-scale production of pharmaceutical proteins because of a simple overall design, use of robust and inexpensive matrices, and use of enzymes of either recombinant or plant origin.

Dipeptidyl peptidase I and III activities of adult schistosomes

Soluble extracts of adult Schistosoma japonicum and S. mansoni were examined for the presence of proteolytic activities ascribable to dipeptidyl peptidases (DPPs) at a range of pH from 4 to 11 using synthetic peptidyl substrates diagnostic of DPPs I, II, III and IV. Activity capable of cleaving the DPP I-specific substrates H-Gly-Arg-NHMec and H-Gly-Phe-NHMec which exhibited a pH optimum of 5.5 was observed in extracts of schistosomes. Female schistosomes exhibited greater DPP I activity than male schistosomes, while female S. japonicum showed substantially more activity than female S. mansoni. The specific activities against H-Gly-Arg-NHMec were 21.5 and 1.9 nmoles NHMec/min/mg protein for female and male S. japonicum and 8.5 and 1.9 nmoles NHMec/min/mg for female and male S. mansoni. The biochemical properties of schistosome DPP I were similar to mammalian DPP I (= cathepsin C) in that schistosome DPP I was only slowly inhibited by the cysteine protease inhibitor trans-epoxysuccinyl-1-leucylamido (4-guanidino)-butane, partly inhibited by the blocked diazomethyl ketones Z-Phe-Ala-CHN2 and Z-Phe-Phe-CHN2, but enhanced by halide ions. At pH 8.5, activity against the DPP III-specific substrate H-Arg-Arg-NHMec was evident in schistosome extracts, and this activity appeared to be due to a zinc metallo-exopeptidase because it was inhibited by 1,10-phenathroline and by EDTA. DPP II or DPP IV activity was not detected in the schistosome extracts.

Cysteine proteases and cysteine protease inhibitors in non-small cell lung cancer

In this study we investigated the levels of two lysosomal cysteine protease proteins cathepsin B (CB) and cathepsin L (CL) and the levels of three cysteine protease inhibitor proteins stefin A (SFA), stefin B (SFB) and cystatin C (CNC) in squamous-cell lung carcinoma (SQCLC) and matched lung parenchyma specimens and examined the inhibition of CB and cathepsin C (CC) activities by endogenous inhibitors in extracts from SQCLC, lung adenocarcinoma (LAC) and lung parenchyma specimens. We found that Stage I SQCLCs contained significantly increased levels of CB protein, CB activity and SFA protein as compared to matched lungs. Neither the levels of CL protein nor the levels of SFB protein nor the levels of CNC protein in Stage I SQCLCs and the lungs were significantly different, but the levels of CB and CL proteins as well as the levels of SFA and SFB proteins showed significant positive correlation in SQCLCs. In SQCLCs as well as in the lungs the level of SFB protein was significantly higher than the level of SFA protein or the level of CNC protein. In the lungs the levels of SFA protein and CNC protein revealed a weak negative correlation trend. In extracts from SQCLCs the level of SFA protein showed a weak negative correlation with the residual CB activity (i.e. the activity remaining after extract preincubation) whereas in extracts from the lungs the level of CNC protein displayed a weak negative correlation trend with the residual CB activity and with the residual CC activity. We observed that SQCLCs and LACs contained not only a significantly increased activity of CB but also a significantly higher inhibitory potential against the activity of endogenous CB as compared to matched lungs. Leupeptin, a small inhibitor of CB, was capable to protect CB in lung carcinoma and lung parenchyma extracts from preincubation-induced inhibition, revealing an active-site directed and competitive nature of CB inhibition by endogenous cystatins. Ultrafiltration passaged protein preparations of nominal Mr < or = 30,000 obtained from extracts of SQCLCs inhibited significantly higher quantities of activity of purified bovine spleen CC than did such protein preparations from matched lungs. Reaction courses of purified bovine spleen CC that had been preincubated with such protein preparations resembled those of endogenous CC from SQCLC and lung extracts showing a slow steady-state approach. These observations and the relaxation kinetics of CC from SQCLC and lung extracts suggest that CC in the extracts may be complexed with some cystatins. In conclusion, our results indicate that quantitatively different combinations of cystatins are the major constituents of the inhibitory potential against CB and CC in SQCLCs and the lungs.

Evidence for protein splicing in the endoplasmic reticulum-Golgi intermediate compartment

We present evidence that the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) is a site for protein splicing of cathepsin C: (i) maturation of the enzyme in COS 7 cells is a two-step process starting within the ERGIC, and (ii) the intermediately processed polypeptide retains both termini of the proenzyme and lacks an internal fragment.

Active recombinant rat dipeptidyl aminopeptidase I (cathepsin C) produced using the baculovirus expression system

An active form of rat dipeptidyl aminopeptidase I (DPPI, cathepsin C) was obtained by heterologous expression in insect cells. Baculoviruses carrying a cDNA sequence encoding the entire rat DPPI precursor was used to infect High Five cells in a serum-free medium. Recombinant DPPI (rDPPI) was secreted into the medium from which it was purified by a combination of ammonium sulfate fractionation, hydrophobic interaction chromatography (HIC), and ion-exchange chromatography. A polyhistidine-tagged form of the enzyme (HT-rDPPI) was purified from the medium by immobilized metal affinity chromatography (IMAC). In vivo activation of native rat DPPI involves at least three chain cleavages per subunit and the ability of the expression system to imitate this processing was investigated. Both rDPPI and HT-rDPPI were secreted into the medium as unprocessed and inactive proenzymes and gradually converted into their active forms in the medium. This process was not completed at the time of harvest but mature enzyme processed similarly to native rat and human DPPI could be obtained by incubating the eluates from the HIC and IMAC columns at pH 4.5 and 5 degrees C for 18-40 h. The yield of purified and matured enzyme was approximately 50 mg/liter, and it was shown that rDPPI and HT-rDPPI were active against both a dipeptide-p-nitroanilide substrate and human growth hormone N-terminally extended with an Ala-Glu dipeptide.

Cathepsin C from Schistosoma japonicum--cDNA encoding the preproenzyme and its phylogenetic relationships

A cDNA encoding preprocathepsin C was isolated from adults of the asian blood fluke Schistosoma japonicum. The deduced amino acid sequence of S. japonicum cathepsin C comprised 458 amino acid residues; 22 NH2-terminal residues corresponding to the signal peptide, 199 residues corresponding to the propeptide and 237 COOH-terminal residues corresponding to the mature enzyme region. The amino acid sequence of this preprocathepsin showed 43% and 50% identity to that of human and rat, respectively. The preproenzyme shared only 59% identity with the sequence for a cathepsin C reported from Schistosoma mansoni, differing from it in active-site residues and in its potential N-glycosylation sites. Northern-blot analysis showed that S. japonicum cathepsin C was expressed in greater quantities in female than in male parasites. Phylogenetic analysis utilizing the mature enzyme sequences of S. japonicum and other cathepsin Cs demonstrated that cathepsin Cs and cathepsin Bs shared a common ancestry. The unusually long prosegment observed in cathepsin C from S. japonicum and from other species was compared to that of cathepsin Bs and cathepsin Ls. The extension contained two blocks of residues which were highly conserved among cathepsin Cs. The COOH terminus of the prosegment exhibited a composite of features present in the prosegments of cathepsin Ls and cathepsin Bs. Most significantly, given the common ancestry of cathepsin B and cathepsin C, the prosegment of cathepsin C included ERFNIN-like motifs and other residues more characteristic of non-cathepsin-B-like members of the papain superfamily such as cathepsin L.

Mistargeting of the lectin ERGIC-53 to the endoplasmic reticulum of HeLa cells impairs the secretion of a lysosomal enzyme

ERGIC-53, a homo-oligomeric recycling protein associated with the ER-Golgi intermediate compartment (ERGIC), has properties of a mannose-selective lectin in vitro, suggesting that it may function as a transport receptor for glycoproteins in the early secretory pathway. To investigate if ERGIC-53 is involved in glycoprotein secretion, a mutant form of this protein was generated that is incapable of leaving the ER. If expressed in HeLa cells in a tetracycline-inducible manner, this mutant accumulated in the ER and retained the endogenous ERGIC-53 in this compartment, thus preventing its recycling. Mistargeting of ERGIC-53 to the ER did not alter the gross morphology of the early secretory pathway, including the distribution of beta'-COP. However, it impaired the secretion of one major glycoprotein, identified as the precursor of the lysosomal enzyme cathepsin C, while overexpression of wild-type ERGIC-53 had no effect on glycoprotein secretion. Transport of two other lysosomal enzymes and three post-Golgi membrane glycoproteins was unaffected by inactivating the recycling of ERGIC-53. The results suggest that the recycling of ERGIC-53 is required for efficient intracellular transport of a small subset of glycoproteins, but it does not appear to be essential for the majority of glycoproteins.

Regulated expression, processing, and secretion of dog mast cell dipeptidyl peptidase I

Dipeptidyl peptidase I (DPPI) is a cysteine protease found predominantly in myelomonocytic cells, cytotoxic T-cells, and mast cells. Recent studies identify an intracellular role for mast cell-DPPI (MC-DPPI) by activating prochymase and protryptase to their mature forms. To better define MC-DPPI and to explore the possibility of extracellular roles, we purified MC-DPPI from mastocytoma cells. We found the dog C2 mastocytoma cell line to be the richest source yet described for DPPI, purifying up to 200 microg of enzyme per g of cells. Dog MC-DPPI has an Mr of approximately 175,000 and consists of four subunits, each composed of a propeptide, light chain, and heavy chain. The heavy chain is N-glycosylated and is heterogeneously processed to three different forms. NH2-terminal sequences of the heavy chain and propeptide are identical to those predicted from a cDNA clone we sequenced from a mastocytoma cDNA library. The dog cDNA-derived sequence is 86% identical to that of human DPPI. Dog mastocytoma cells incubated with 12-O-tetradecanoylphorbol-13-acetate increase expression of MC-DPPI mRNA. MC-DPPI maintains its activity for dipeptide substrates at a neutral to alkaline pH. Cells stimulated with ionophore or substance P secrete MC-DPPI in parallel with the granule-associated mediators tryptase and histamine. Thus, dog mastocytoma cells secrete DPPI that is active at the pH of extracellular fluids, suggesting that MC-DPPI may act outside the cell.

Dipeptidyl peptidase I and granzyme A are coordinately expressed during CD8+ T cell development and differentiation

Dipeptidyl peptidase I (DPPI) is a granule protease that plays a requisite role in processing the proenzyme form of the CTL granule serine proteases (granzymes). This study assesses DPPI mRNA and enzyme expression during T lymphocyte ontogeny and CTL differentiation. The most immature CD3- CD4- CD8- thymocytes were found to express >40-fold higher levels of DPPI mRNA, although levels of DPPI enzymatic activity in CD3- CD4- CD8- thymocytes were only modestly higher than those seen for CD4+ CD8+ or CD4+ CD8- thymocytes. More mature CD8+ CD4- thymocytes and CD8+ splenocytes expressed significantly higher levels of DPPI mRNA and enzymatic activity than CD4+ CD8+ or CD4+ CD8- thymocytes. Granzyme A mRNA expression was observed in DPPI expressing CD3- CD4- CD8- and CD8+ CD4- thymocytes and was also observed in CD8+ CD4- splenocytes; however, expression was not observed in CD4+ CD8+ or CD4+ CD8- thymocytes. Both DPPI mRNA and granzyme A mRNA expression in CD8+ T cells decreased to very low or undetectable levels during the first 48 h after allostimulation in MLCs. However, peak levels of both DPPI and granzyme A expression were observed later in the course of CD8+ T cell responses to alloantigen, with DPPI mRNA expression peaking on either day 3 or day 4 and granzyme A expression peaking at the end of a 5-day MLR. These data indicate that DPPI is expressed at all stages of T cell ontogeny and differentiation in which granzyme A mRNA is detected; consequently, DPPI appears to be available for the processing and activation of granzyme A during both CD8+ T cell development and differentiation.

Activity of lysosomal and nonlysosomal proteases of fibrosarcoma induced by methylcholanthrene

Activity of lysosomal (cathepsins A,B,C,D and E) and nonlysosomal proteases (cathepsin G, elastase, collagenase, prolidase, prolinase) was evaluated in fibrosarcoma induced in rats by methylcholanthrene. No differences were found in the activity of the examined proteases in tumours of different size in the external, intermediate and central spheres of these tumours. Activity of cathepsins A,B,C,D,E and G, prolidase and prolinase was higher in the fibrosarcoma and activity of collagenase and elastase was lower than in the rat skin.

Dipeptidyl aminotransferase activity and in vitro O-glycosylation of MUC5AC mucin motif peptides by human gastric microsomal preparations

The in vitro O-glycosylation reaction of the MUC5AC mucin motif peptide, TTSAPTTS (in one-letter code), was achieved with human gastric microsomal homogenates. The analyses using capillary electrophoresis online coupled with electrospray mass spectrometry and further Edman degradation of the purified products (obtained by capillary electrophoresis at preparative scale) allowed us to distinguish two components at close masses: the addition of a mass of 202 corresponded to an N-terminal elongation of the peptide TTSAPTTS with the dipeptide (TT) and the addition of a mass of 203 corresponded to an N-acetylgalactosamine O-linkage. Using different peptidase inhibitors, a dipeptidyl peptidase/transferase activity was further characterized. A thiol dependence and an inhibition by H-Gly-PheCHN2 (specific to cathepsin C activity) were found. Moreover, besides TTSAPTTS, other MUC5AC motif peptides (GTTPSPVP, TSAPTTS) were also dipeptide donors (GT and TS, respectively) and our results suggested the involvement of a single dipeptidyl peptidase/transferase activity. Finally, this latter activity modified the in vitro GalNAc incorporation rates when using our selected MUC5AC motif peptides. Our study therefore shows that caution must be taken to prevent peptidic substrate elongation while performing in vitro O-glycosylation with microsomal preparations as the enzyme source. In fact, the results of the N-acetylgalactosamine incorporation rates and thus the microsomal N-acetylgalactosamine transferase affinity can be misinterpreted if dipeptidyl peptidase/transferase activity is not inhibited by the thiol inhibitor E-64 or the cathepsin C inhibitor H-Gly-PheCHN2.

The conversion of recombinant human mast cell prochymase to enzymatically active chymase by dipeptidyl peptidase I is inhibited by heparin and histamine

Chymase, a major product of mast cell activation, is secreted as a fully active enzyme. We have prepared recombinant human prochymase and have investigated the conditions under which it may be activated by dipeptidyl peptidase I (DPP I). The gene for human chymase was cloned in a baculovirus vector and expressed in High Five insect cells, and the recombinant protein purified by heparin-agarose and gel-filtration chromatography. The purified prochymase was homogeneous by SDS/PAGE with the same molecular mass as native human chymase, and its identity confirmed by N-terminal sequence analysis and Western blotting with chymase-specific antibodies. Treatment with DPP I to remove the N-terminal dipeptide prosequence resulted in enzymatically active chymase, with substrate and inhibitor profiles very similar to those of the native human enzyme. The activation of prochymase by DPP I was strongly inhibited by heparin (IC50 = 0.5 microg ml[-1]) and histamine (IC50 = 2 mM), though these mast cell products had little effect on the action of DPP I towards a low molecular-mass substrate. The pH optimum of DPP I was also higher and narrower with prochymase. The inhibitory action of heparin was lost at NaCl or KCl concentrations sufficient to elute prochymase from a heparin agarose column. Dextran sulphate was as inhibitory as heparin, whereas chondroitin sulphate C was more than 10-fold less effective. Our findings suggest that the activation of prochymase might be restricted to the early stages of vesicle maturation, when the pH is close to neutrality and the histamine and heparin concentrations are low.

Stoichiometry and heterogeneity of the pro-region chain in tetrameric human cathepsin C

The subunit structure and composition of mature human cathepsin C, an oligomeric cysteine proteinase, has been characterised in detail. The heavy chain, light chain and pro-region peptides are shown to be held together solely by non-covalent interactions, and to be present in equimolar ratio, suggesting an important structural role for the residual pro-region chain which is strongly bound to the enzyme. The mass of the light chain, as determined by mass spectrometry, combined with its N-terminal sequence, determines the position of cleavage from the heavy chain. Amino-acid sequencing has led to definition of the 13.5 kDa N-terminal part of the pro-region which remains in the mature enzyme, the C-terminal moiety of 10 kDa being cleaved out and lost from the pro-peptide on activation. The residual pro-region is heterogeneous, a proportion being intact and the remainder being cleaved at alternative positions 58 or 61, yielding two smaller peptides joined by disulphide bond. The proportion of cleaved form was found to vary with tissue and enzyme preparation but did not affect enzyme activity. The molecular masses of the constituent chains after deglycosylation lead to a protein mass of 158 kDa. All four potential glycosylation sites are glycosylated.

Interactions of proteases and protease inhibitors in Sertoli-germ cell cocultures preceding the formation of specialized Sertoli-germ cell junctions in vitro

The biochemical mechanism(s) by which germ cells can form specialized junctions with Sertoli cells in the seminiferous epithelium at various stages of the spermatogenic cycle is unknown. This study sought to examine the biochemical changes that are involved when germ cells are cocultured with Sertoli cells in vitro preceding the establishment of specialized Sertoli-germ cell junctions. While isolated germ cells were allowed to attach to Sertoli cells, media from both the apical and basal compartments of bicameral units were collected to assess serine and cysteine protease activity. The expression of selected serine and cysteine proteases and their corresponding inhibitors in these Sertoli-germ cell cocultures was also examined by RT-PCR. Using an [125I]-collagen film assay, a transient but significant increase in serine protease activity was noted in both the apical and basal compartments when germ cells began to settle onto the Sertoli cell monolayer preceding the formation of intercellular junctions. A specific tryptase (RNK-Tryp 2, a serine protease formerly cloned from a rat granular lymphocyte leukemia cell line, RNK-16, cDNA expression library) was shown to be expressed exclusively by Sertoli cells and not germ cells. Furthermore, Sertoli cell tryptase expression as well as urokinase plasminogen activator (u-PA, also a serine protease) increased significantly when germ cells were adhering to Sertoli cells. The decline in total serine protease activity when Sertoli-germ cell junctions were being formed was accompanied by a concomitant increase in alpha2-macroglobulin (alpha2-MG, a nonspecific protease inhibitor) expression. No significant changes in cysteine protease activity in either the apical or basal compartment were noted. However, there was a transient but significant increase in cathepsin L expression when germ cells were adhering to Sertoli cells preceding cell junction formation. The subsequent reduction in cathepsin L expression after this transient increase was accompanied by a concomitant increase in cystatin C expression. These results suggest that proteases and their corresponding inhibitors are working synergistically and are likely to be involved in the adherence of germ cells to Sertoli cells and the subsequent formation of intercellular junctions.

Increased production of low molecular weight recombinant proteins in Escherichia coli

A general method for obtaining high-level production of low molecular weight proteins in Escherichia coli is described. This method is based on the use of a novel Met-Xaa-protein construction which is formed by insertion of a single amino acid residue (preferably Arginine or Lysine) between the N-terminal methionine and the protein of interest. The utility of this method is illustrated by examples for achieving high-level production of human insulin-like growth factor-1, human proinsulin, and their analogs. Furthermore, highly produced insulin-like growth factor-1 derivatives and human proinsulin analogs are converted to their natural sequences by removal of dipeptides with cathepsin C.

A selective inhibitor of dipeptidyl peptidase I impairs generation of CD8+ T cell cytotoxic effector function

CTL express high levels of dipeptidyl peptidase I (DPPI), a granule thiol protease able to convert the zymogen precursors of granzymes A and B into active proteases. In the present studies, the effects of specific inhibition of DPPI on generation of CTL effector functions were examined. When T cell DPPI activity was inhibited by >95% throughout 5-day MLC, a significant reduction in the generation of CD8+ T cell BLT esterase activity (<30% of control) and cytolytic activity (<10% of control) was observed. DPPI inhibition during the second to fourth days of 5-day MLC also was associated with reduced proliferation of CD8+ T cells, but had no effect on CD4+ T cell proliferation or IL-2 production by either population. CTL generated in the continuous presence of DPPI inhibition also exhibited impaired lysis of anuclear erythrocyte targets and diminished killing of nucleated targets by perforin-independent pathways. In contrast, inhibition of DPPI during only the last 24 h of 5-day MLC was associated only with reduced generation of BLT esterase activity and reduced lysis of nucleated targets by perforin-dependent pathways. Repeated or delayed inhibition of DPPI in MLC containing granzyme B-deficient responder cells also impaired generation of cytotoxic activity. These results indicate that DPPI or other DPPI-like protease activities not only are required for the activation of granzymes, but also play a role in the expansion and differentiation of full CD8+ T cell cytolytic activity.

alpha-Glucosidase and N-acetylglucosamine-6-sulphatase are the major mannose-6-phosphate glycoproteins in human urine

Most newly synthesized lysosomal enzymes contain a transient carbohydrate modification, mannose 6-phosphate (Man-6-P), which signals their vesicular transport from the Golgi to the lysosome via Man-6-P receptors (MPRs). We have examined Man-6-P glycoproteins in human urine by using a purified soluble fragment of the soluble cation-independent MPR (sCI-MPR) as a preparative and analytical affinity reagent. In a survey of urine samples from seven healthy subjects, the pattern of Man-6-P glycoproteins detected with iodinated sCI-MPR as a probe in a blotting assay was essentially identical in each, regardless of sex or age. Two bands of approx. 100 and 110 kDa were particularly prominent. Man-6-P glycoproteins in human urine were purified by affinity chromatography on immobilized sCI-MPR. Seven distinct bands revealed by SDS/PAGE and Coomassie Blue staining were subjected to N-terminal sequence analysis. The prominent 100 and 110 kDa Man-6-P glycoproteins were identified as N-acetylglucosamine-6-sulphatase and alpha-glucosidase respectively. This identification was confirmed by molecular mass determinations on the two major bands after deglycosylation. Sequence analysis revealed arylsulphatase A and several previously unidentified proteins as minor species. Man-6-P glycoproteins were also purified on an analytical scale to determine the proportion of a number of lysosomal enzyme activities represented by the mannose-6-phosphorylated forms. The lysosomal enzymes in urine containing the highest proportion of mannose-6-phosphorylated form were beta-mannosidase (82%), hexosaminidase (27%) and alpha-glucosidase (24%). The profiles of Man-6-P glycoproteins detected by blotting in urine and plasma were not similar, suggesting that the urinary species are not derived from the bloodstream.

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.

Human dipeptidyl-peptidase I. Gene characterization, localization, and expression

Dipeptidyl-peptidase I, a lysosomal cysteine proteinase, is important in intracellular degradation of proteins and appears to be a central coordinator for activation of many serine proteinases in immune/inflammatory cells. Little is known about the molecular genetics of the enzyme. In the present investigation the gene for dipeptidyl-peptidase I was cloned and characterized. The gene spans approximately 3.5 kilobases and consists of two exons and one intron. The genomic organization is distinct from the complex structures of the other members of the papain-type cysteine proteinase family. By fluorescence in situ hybridization, the gene was mapped to chromosomal region 11q14.1-q14.3. Analysis of the sequenced 5'-flanking region revealed no classical TATA or CCAAT box in the GC-rich region upstream of cap site. A number of possible regulatory elements that could account for tissue-specific expression were identified. Northern analyses demonstrated that the dipeptidyl-peptidase I message is expressed at high levels in lung, kidney, and placenta, at moderate to low levels in many organs, and at barely detectable levels in the brain, suggesting tissue-specific regulation. Among immune/inflammatory cells, the message is expressed at high levels in polymorphonuclear leukocytes and alveolar macrophages and their precursor cells. Treatment of lymphocytes with interleukin-2 resulted in a significant increase in dipeptidyl-peptidase I mRNA levels, suggesting that this gene is subjected to transcriptional regulation. The results provide initial insights into the molecular basis for the regulation of human dipeptidyl-peptidase I.

Cloning and characterization of the cDNA encoding mouse dipeptidyl peptidase I (cathepsin C)

The mouse dipeptidyl peptidase I cDNA has been cloned and sequenced and patterns of DPPI mRNA expression in various tissues characterized. Sequences encoding DPPI are highly conserved among mouse, rat and human and include an unusually long propeptide and a distinctive tyrosine adjacent to the active site cysteine.

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with fibrosarcoma induced by methylcholanthrene

Activity of lysosomal and nonlysosomal proteases and contents of protein and its degradation products in the blood serum of rats with methylcholantrene fibrosarcoma were evaluated. Activity of lysosomal proteases and prolidase and prolinase as well in the blood serum of rats with methylcholanthrene tumour did not differ from the activity of these enzymes in the blood serum of control rats. Only the activity of elastase and collagenase in the blood serum of rats with methylcholanthrene tumour especially with tumour of intermediate and big mass was increased. Content of total protein was decreased in the blood serum of rats with tumour of intermediate and big mass and contents of glycoproteins and alfa-amin nitrogen were increased in comparison to the blood serum of control rats.

Interaction of human cathepsin C with chicken cystatin

Cathepsin C was purified from human spleen by a rapid procedure, which included homogenization, ammonium sulfate precipitation, gel filtration on Sephacryl S-200 and finally affinity chromatography on chicken cystatin-Sepharose. The interaction between cathepsin C and chicken cystatin was further characterized. It was found to be accompanied by a maximum decrease in fluorescence emission intensity at 336 nm. Fluorescence titration showed that human cathepsin C can bind four chicken cystatin molecules. The 4:1 binding stoichiometry was confirmed by titration monitored by the loss of enzyme activity. A non-competitive-competitive type of inhibition was determined from a double-reciprocal Lineweaver-Burk plot with a Ki value of 0.22 nM for the non-competitive inhibition.

Simultaneous isolation of human kidney cathepsins B, H, L and C and their characterisation

A procedure for the simultaneous isolation of four cysteine proteinases, cathepsins B, H, L and C, from human kidney is described. The method includes concentration of the acidified homogenate by ammonium sulphate precipitation. The resuspended and dialysed precipitate was chromatographed on DEAE-cellulose DE-32, to allow separation of cathepsins H and C from cathepsins B and L. The main isoform of cathepsin H was separated from cathepsin C by cation-exchange chromatography on CM-Sephadex C-50. These two enzymes were further purified by covalent chromatography on thiopropyl Sepharose and gel permeation on Sephacryl S-200. The last step allowed separation of cathepsin C and the minor isoform of cathepsin H. Purification of the other two enzymes, cathepsins B and L, was carried out on thiol Sepharose, followed by chromatography on CM-Sepharose C-50. In this step, pure cathepsin L was obtained, while two isoforms of cathepsin B had to be finally purified on Sephacryl S-200 columns. The purity of each enzyme was analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis, isoelectric focusing on polyacrylamide gels and N-terminal sequencing. The activities of the purified cathepsins B, H and L were determined in terms of kcat/KM for three substrates, Z-Phe-Arg-MCA, Z-Arg-Arg-MCA and Arg-MCA. The method produced 25 mg of cathepsin B, 6.5 mg of cathepsin H, 1.5 mg of cathepsin L and 3.8 mg of cathepsin C from 3.5 kg of human kidney.

The human gene FALL39 and processing of the cathelin precursor to the antibacterial peptide LL-37 in granulocytes

The peptide FA-LL-37, previously termed FALL-39, was originally predicted from on ORF of a cDNA clone isolated from a human bone marrow library. This peptide was synthesized and found to have antibacterial activity. We have now characterized and sequenced the complete gene for FA-LL-37, termed FALL39. It is a compact gene of 1963 bp with four exons. Exons 1-3 code for a signal sequence and the cathelin region. Exon 4 contains the information for the mature antibacterial peptide. Our results indicate that FALL39 is the only member of the cathelin gene family present in the human genome. Potential binding sites for acute-phase-response factors are identified in the promoter and in intron 2. A possible role for the cytokine interleukin-6 in the regulation of FALL 39 is discussed. Anti-(FA-LL-37) IgG located the peptide in granulocytes and we isolated the mature peptide from these cells after degranulation. Structural analysis determined the mature peptide to be LL-37. To obtain LL-37 for antibacterial assays, synthetic FA-LL-37 was degraded with dipeptidyl-peptidase I. This analysis showed that mature LL-37 is a potent antibacterial peptide.

Expression of human recombinant granzyme A zymogen and its activation by the cysteine proteinase cathepsin C

Human granzyme A is one of the serine proteinases present in the granules of cytotoxic T lymphocytes and natural killer cells. Granzymes are synthesized as inactive proenzymes with an amino-terminal prodipeptide, which is processed during transport of granzymes to the cytotoxic granules, where they are stored as active proteinases. In this study, we explored the possibility of producing recombinant granzymes. Recombinant human granzyme A zymogen was expressed in several eukaryotic cell lines (HepG2, Jurkat, and COS-1) after infection with a recombinant vaccinia virus containing full-length granzyme A cDNA. Immunoblot analysis of cell lysates showed that all infected cells produced a disulfide-linked homodimer of identical molecular weight as natural granzyme A. Infected HepG2 cells produced the largest amount of this protease (approximately 160 times more than lymphokine activated killer (LAK) cells). The recombinant protein only had high mannose type oligosaccharides as did the natural protein. Although infected HepG2 and COS cells contained high granzyme A antigen levels, lysates from these cells did not show any granzyme A proteolytic activity. However, the inactive proenzyme could be converted into active granzyme A by incubation with the thiol proteinase cathepsin C (dipeptidyl peptidase I). This study is the first to demonstrate expression of an active recombinant human cytotoxic lymphocyte proteinase and conversion of inactive progranzyme A into an active enzyme by cathepsin C. We suggest that a similar approach can be used for the production of other granzymes and related proteinases.

A novel heparin-dependent processing pathway for human tryptase. Autocatalysis followed by activation with dipeptidyl peptidase I

Tryptase is the major protein constituent of human mast cells, where it is stored within the secretory granules as a fully active tetramer. Two tryptase genes (alpha and beta) are expressed by human mast cells at the level of mRNA and protein, each with a 30 amino acid leader sequence. Recombinant precursor forms of human alpha- and beta-tryptase were produced in a baculovirus system, purified, and used to study their processing. Monomeric beta-protryptase first is shown to be intermolecularly autoprocessed to monomeric beta-pro'tryptase at acid pH in the presence of heparin by cleavage between Arg-3 and Val-2 in the leader peptide. The precursor of alpha-tryptase has an Arg-3 to Gln-3 mutation that precludes autoprocessing. this may explain why alpha-tryptase is not stored in secretory granules, but instead is constitutively secreted by mast cells and is the predominant form of tryptase found in blood in both healthy subjects and those with systemic mastocytosis under nonacute conditions. Second, the NH2-terminal activation dipeptide on beta-pro'tryptase is removed by dipeptidyl peptidase I at acid pH in the absence of heparin to yield an inactive monomeric form of tryptase. Conversion of the catalytic portion of beta-tryptase to the active homotetramer at acid pH requires heparin. Thus, beta-tryptase homotetramers probably account for active enzyme detected in vivo. Also, processing of tryptase to an active form should occur optimally only in cells that coexpress heparin proteoglycan, restricting this pathway to a mast cell lineage.

Biosynthesis and processing of proteinase 3 in U937 cells. Processing pathways are distinct from those of cathepsin G

Proteinase 3 is a human polymorphonuclear leukocyte serine proteinase that degrades elastin in vitro and causes emphysema when administered by intratracheal insufflation into hamsters. Proteinase 3, stored in the azurophilic granules, is expressed in progenitor cells of myeloid origin. In the present study, the biosynthesis, processing, and intracellular transport of the enzyme was investigated in the human myelomonocytic cell line U937. Proteinase 3 is initially identified as a 35-kDa precursor and converted into the 29-kDa mature form within 3 h. By using a combination of techniques including amino-terminal sequencing, we identified the 35-kDa form as a zymogen containing an activation dipeptide but lacking the amino-terminal 25 residues, presumably the result of cleavage by a signal peptidase. Tunicamycin treatment and alkalinization of acidic cell compartments with NH4Cl did not prevent the processing of the proteinase 3 zymogen into the mature form, suggesting that the enzyme is targeted to the cytoplasmic granules by a mechanism other than the mannose 6-phosphate receptor. Brefeldin A inhibited the zymogen processing, suggesting that the dipeptide cleavage occurred in a post-Golgi organelle. The enzyme responsible for the removal of the dipeptide is a cysteine proteinase since E-64d, a class-specific inhibitor, prevented processing. However, treatment of cells with a dipeptidyl peptidase I inhibitor, Gly-Phe-diazomethyl ketone and with the lysosomotropic agents, NH4Cl and chloroquine, did not prevent dipeptide cleavage, indicating that the processing enzyme for proteinase 3 is not dipeptidyl peptidase I. In contrast, Gly-Phe-diazomethyl ketone inhibited cleavage of the dipeptide from cathepsin G. This indicates that processing of proteinase 3 is distinct from that of cathepsin G. Proteinase 3 is also processed at the COOH-terminal extension. Cleavage takes place next to Arg-222, suggesting that a trypsin-like proteinase is involved in the COOH-terminal processing.

Oligomeric structure and substrate induced inhibition of human cathepsin C

Cathepsin C has been purified from human kidney by a modified procedure. Human cathepsin C was isolated as pure protein with a pI close to 6.0. The enzyme was shown to have a molecular mass of 200 kDa and to consist of four identical subunits, each composed of three different polypeptide chains, two of them disulfide-bound. Their NH2-terminal amino acid sequences were determined. Two chains showed pronounced similarity with the heavy and light chains of other papain-like cysteine proteinases, whereas the third one corresponded to the prosequence of the enzyme, thus showing that a substantial part of the proregion remains bound in the mature enzyme. The kinetics of substrate hydrolysis deviated substantially from standard Michaelis-Menten kinetics, demonstrating substrate inhibition at higher substrate concentrations. These data are explained by a sequential cooperative interaction model, where an enzyme molecule can bind up to four substrate molecules but where only the binary enzyme-substrate complex is catalytically active. Substrate inhibition was observed over the whole range of pH activity. From the pH activity profile it can be concluded that at least three ionizable groups with pKa values 4.2, 6.8, and 7.7 are involved in substrate hydrolysis. Human cathepsin C thus appears to differ qualitatively from other cysteine proteinases of different origin.

Purification and preliminary characterization of dDAP, a novel dipeptidylaminopeptidase from Dictyostelium discoideum

We have discovered and purified a novel dipeptidylaminopeptidase (DAP) from the cell-free broth of Dictyostelium discoideum Ax3. The enzyme is secreted in parallel with cell growth in axenic broth culture. It shares substrate preferences with both DAP-I and DAP-III enzymes yet is distinct from both in some physical properties. Similar to DAP-I, the D. discoideum enzyme is able to cleave a variety of dipeptides from the amino termini of substrates. In addition, it readily cleaves substrate sequences beginning with RR- and KK-, a property of the DAP-III class. The D. discoideum enzyme has a pH optimum of 3.5, a subunit molecular mass of 66,000 daltons, and a molecular weight of approximately 225,000 and is not significantly inhibited by cysteine or serine protease inhibitors. It is inhibited by leupeptin and trivalent cations. On the basis of enzymological and other data presented here, we conclude the D. discoideum enzyme does not belong to any of the previously reported DAP classes (DAP-I, -II, -III, -IV) and propose that the class DAP-V be established with this D. discoideum enzyme as the first member.

In vitro characterization of Acanthamoeba castellanii cytopathic effect

This study examined the mechanism of the cytopathic effect (CPE) of Acanthamoeba castellanii on human target cells. Pathogenic Acanthamoeba trophozoites were incubated with human ocular melanoma (OCM1) cells for 30 min, 1 hr, and 3 hr. The amoebae were treated with a calcium ionophore (A23187), phorbol myristate ester (PMA), calcium channel blocker (Bepridil), cytochalasin D, and L-leucyl-L-leucine methyl ester (leu-leu-OMe). Cytolysis was quantified using a spectrophotometric assay. Cocultures of amoeba and cells were also observed by transmission electron microscopy at 1, 2, and 3 hr. Results show that trophozoites formed pseudopodia that made intimate contact with the target cell membrane. Neither amebostomes nor phagocytosis was seen. The calcium ionophore A23187 increased the cytopathic effect of the trophozoites on the cultured OCM1. In contrast, cytochalasin D, Bepridil, and PMA reduced the cytopathic effect. Leu-leu-OMe did not result in killing of Acanthamoeba trophozoites. The results suggest that the cytopathic effect of Acanthamoeba trophozoites involves calcium channels and cytoskeletal elements. There was no evidence of trogocytosis or phagocytosis as sometimes occurs in cytolysis by other free-living amoeba. Although Acanthamoeba-mediated CPE in some ways resembles CPE produced by cytotoxic lymphocytes, the mechanisms are not identical.

Expression of recombinant human granzyme B. A processing and activation role for dipeptidyl peptidase I

Human granzyme B (hGrzB) is the key member of a family of granule serine proteases (granzymes) that participate in target cell death inflicted by cytotoxic lymphocytes. The proenzyme activation peptide predicted from the cDNA encoding hGrzB is composed of two residues. We have devised a PCR strategy to delete this activation dipeptide within hGrzB and express active recombinant hGrzB in mammalian COS cells. Lysates of COS cells transfected with modified hGrzB cDNA were able to hydrolyze tert-butyloxycarbonyl-Ala-Ala-Asp-thiobenzyl ester (Boc-Ala-Ala-Asp-SBzl), whereas lysates transfected with unmodified hGrzB cDNA were inactive. Accordingly, active recombinant hGrzB displayed no significant activities toward substrates containing Met-, Lys-, or Phe- at P1. It has been suggested that the mechanism by which the amino-terminal dipeptide is normally cleaved to generate active GrzB involves dipeptidyl peptidase I (DPPI). Our studies demonstrated that lysates of COS cells cotransfected with unmodified hGrzB cDNA (inactive) and rat DPPI cDNA were able to hydrolyze Boc-Ala-Ala-Asp-SBzl. Similarly, lysates of COS cells transfected with unmodified hGrzB cDNA, and devoid of Asp-ase activity, were also activated upon the addition of bovine spleen DPPI in a pH and time-dependent fashion. These results suggest that the activation dipeptide, and more particularly DPPI, may play and important role in the normal post-translational processing and activation of hGrzB in cytotoxic lymphocytes.