Calpain 3 is activated through autolysis within the active site and lyses sarcomeric and sarcolemmal components.
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Calpain 3 (Capn3) is known as the skeletal muscle-specific member of the calpains, a family of intracellular nonlysosomal cysteine proteases. This enigmatic protease has many unique features among the calpain family and, importantly, mutations in Capn3 have been shown to be responsible for limb girdle muscular dystrophy type 2A. Here we demonstrate that the Capn3 activation mechanism is similar to the universal activation of caspases and corresponds to an autolysis within the active site of the protease. We undertook a search for substrates in immature muscle cells, as several lines of evidence suggest that Capn3 is mostly in an inactive state in muscle and needs a signal to be activated. In this model, Capn3 proteolytic activity leads to disruption of the actin cytoskeleton and disorganization of focal adhesions through cleavage of several endogenous proteins. In addition, we show that titin, a previously identified Capn3 partner, and filamin C are further substrates of Capn3. Finally, we report that Capn3 colocalizes in vivo with its substrates at various sites along cytoskeletal structures. We propose that Capn3-mediated cleavage produces an adaptive response of muscle cells to external and/or internal stimuli, establishing Capn3 as a muscle cytoskeleton regulator. (+info)
Elongation factor 1 (EF1alpha) promoter in a lentiviral backbone improves expression of the CD20 suicide gene in primary T lymphocytes allowing efficient rituximab-mediated lysis.
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BACKGROUND AND OBJECTIVES: CD20 has been proposed as a novel suicide gene system for the treatment of graft-versus-host disease (GVHD), a fatal complication of allogeneic bone marrow transplantation: indeed expression of the human non-immunogenic exogenous CD20 protein allows positive immunoselection of transduced cells as well as their killing in vitro with rituximab. Lentiviral vectors are promising tools in the field of gene therapy. We therefore searched for a lentivector giving good efficiency of transduction of human T lymphocytes activated by the sole addition of interleukin (IL)-2 and high expression levels of the CD20 transgene. DESIGN AND METHODS: The T cell line CEM and peripheral T lymphocytes activated by phytohemagglutinin (PHA) and/or IL-2 were transduced with two different vectors carrying the CD20 transgene driven by either the phosphoglycerate kinase (PGK) or elongation factor 1alpha (EF1alpha) promoter, and using different multiplicities of infection (MOIs). RESULTS: Both the PGK- and EF1alpha-CD20 vectors allowed efficient transduction of the CEM cell line and PHA-activated T cells, reaching 99 and 90% in the different targets, respectively. However EF1alpha-CD20 led to much higher expression levels of the transgene (mean fluorescence intensity 588-618 compared to 53 for PGK-CD20). Furthermore lymphocytes activated with IL-2 alone could be efficiently transduced with EF1alpha-CD20, reaching 10-25% positivity for CD20 (mean fluorescence intensity 409-424), allowing adequate immunoselection and strong complement-mediated lysis. INTERPRETATION AND CONCLUSIONS: EF1alpha-CD20 may represent a good candidate vector for gene therapy with the CD20 suicide system in the setting of allogeneic bone marrow transplants. (+info)
On the sequential determinants of calpain cleavage.
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The structural clues of substrate recognition by calpain are incompletely understood. In this study, 106 cleavage sites in substrate proteins compiled from the literature have been analyzed to dissect the signal for calpain cleavage and also to enable the design of an ideal calpain substrate and interfere with calpain action via site-directed mutagenesis. In general, our data underline the importance of the primary structure of the substrate around the scissile bond in the recognition process. Significant amino acid preferences were found to extend over 11 residues around the scissile bond, from P(4) to P(7)'. In compliance with earlier data, preferred residues in the P(2) position are Leu, Thr, and Val, and in P(1) Lys, Tyr, and Arg. In position P(1) ', small hydrophilic residues, Ser and to a lesser extent Thr and Ala, occur most often. Pro dominates the region flanking the P(2)-P(1)' segment, i.e. positions P(3) and P(2)'-P(4)'; most notable is its occurrence 5.59 times above chance in P(3)'. Intriguingly, the segment C-terminal to the cleavage site resembles the consensus inhibitory region of calpastatin, the specific inhibitor of the enzyme. Further, the position of the scissile bond correlates with certain sequential attributes, such as secondary structure and PEST score, which, along with the amino acid preferences, suggests that calpain cleaves within rather disordered segments of proteins. The amino acid preferences were confirmed by site-directed mutagenesis of the autolysis sites of Drosophila calpain B; when amino acids at key positions were changed to less preferred ones, autolytic cleavage shifted to other, adjacent sites. Based on these preferences, a new fluorogenic calpain substrate, DABCYLTPLKSPPPSPR-EDANS, was designed and synthesized. In the case of micro- and m-calpain, this substrate is kinetically superior to commercially available ones, and it can be used for the in vivo assessment of the activity of these ubiquitous mammalian calpains. (+info)
A simple method for the prevention of endometrial autolysis in hysterectomy specimens.
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AIMS: Uteri are among the most common surgical pathology specimens. Assessment of the endometrium is often difficult because of pronounced tissue autolysis. This study describes a simple method to prevent endometrial autolysis and aid in interpretation of the endometrium. METHODS: Sixty uteri were injected with formalin using a needle and syringe directed alongside a probe, which was inserted through the external cervical os into the endometrial cavity. Injection was performed on the same day as removal of the uterus. As controls, 60 uteri that were not injected with formalin were examined. The degree of endometrial autolysis was assessed on a four point scale (0-3), with a score of 0 representing no or minimal autolysis and a score of 3 representing extensive autolysis, such that histological interpretation of the endometrium was impossible. RESULTS: In the injected group, the number of cases with scores of 0, 1, 2, and 3 was 42, 13, four, and one, respectively. The corresponding values for the control group were 17, 23, eight, and 12, respectively. This was highly significant (p < 0.001) CONCLUSIONS: There was significantly less endometrial autolysis in uteri injected with formalin. The use of this simple procedure should be encouraged in hysterectomy specimens. (+info)
Controlled autolysis and enzyme release in a recombinant lactococcal strain expressing the metalloendopeptidase enterolysin A.
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This study concerns the exploitation of the lytic enzyme enterolysin A (EntL), produced by Enterococcus faecalis strain DPC5280, to elicit the controlled autolysis of starter lactococci. EntL, a cell wall metalloendopeptidase secreted by some E. faecalis strains, can kill a wide range of gram-positive bacteria, including lactococci. The controlled expression of entL, which encodes EntL, was achieved using a nisin-inducible expression system in a lactococcal host. Zymographic analysis of EntL activity demonstrated that active enzyme is produced by the recombinant lactococcal host. Indeed, expression of EntL resulted in almost complete autolysis of the host strain 2 h after induction with nisin. Model cheese experiments using a starter strain in addition to the inducible enterolysin-producing strain showed a 27-fold increase in activity with respect to the release of lactate dehydrogenase in the strain overexpressing EntL, demonstrating the potential of EntL production in large-scale cheese production systems. Indeed, the observation that a wide range of lactic bacteria are sensitive to EntL suggests that EntL-induced autolysis has potential applications with a variety of lactic acid bacteria and could be a basis for probiotic delivery systems. (+info)
Mapping and characterization of multiple chromosomal factors involved in methicillin resistance in Staphylococcus aureus.
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Chromosomal factors, termed fem or aux factors, are needed for the expression of methicillin resistance in methicillin-resistant (Mcr) Staphylococcus aureus; also needed is the mec-encoded low-affinity penicillin-binding protein PBP 2'. These factors make up part of the normal set of genes present in susceptible and resistant strains of S. aureus and can be identified by Tn551-mediated insertional inactivation of the methicillin resistance. In this study, we characterized different Tn551 inserts and mapped them into four distinct loci on the SmaI chromosomal map of S. aureus NCTC 8325, thereby identifying two new loci which code for fem factors. The largest fragment, SmaI-A, carries three loci, two coding for both closely linked factors femA and femB and a novel third locus (femC) that is not linked to the other two. An additional, fourth, locus, femD, was identified in fragment SmaI-I. femA and femB inactivation reduced overall methicillin resistance, whereby femB had less of an influence on the resistance level. femC and femD inactivation reduced mainly the basal resistance level in heterogeneously Mcr strains and had less of an impact on the subpopulation with high-level resistance. Inactivation of either of these factors was shown to have no influence on the production of PBP 2', the main factor mediating methicillin resistance. In addition, no changes were observed in the banding patterns of the major autolysins in whole-cell extracts of the fem mutants, suggesting that the reduced cell wall turnover and autolysis observed in some of the insertionally inactivated strains were due to changes either of the substrate or in the autolysin control. (+info)
Effects of autolysis on properties of mu- and m-calpain.
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Although the biochemical changes that occur during autolysis of mu- and m-calpain are well characterized, there have been few studies on properties of the autolyzed calpain molecules themselves. The present study shows that both autolyzed mu- and m-calpain lose 50-55% of their proteolytic activity within 5 min during incubation at pH 7.5 in 300 mM or higher salt and at a slower rate in 100 mM salt. This loss of activity is not reversed by dialysis for 18 h against a low-ionic-strength buffer at pH 7.5. Proteolytic activity of the unautolyzed calpains is not affected by incubation for 45 min at ionic strengths up to 1000 mM. Size-exclusion chromatography shows that ionic strengths of 100 mM or above cause dissociation of the two subunits of autolyzed calpains and that the dissociated large subunits (76- or 78-kDa) aggregate to form dimers and trimers, which are proteolytically inactive. Hence, instability of autolyzed calpains is due to aggregation of dissociated heavy chains. Autolysis removes the N-terminal 19 (m-calpain) or 27 (mu-calpain) amino acids from the large subunit and approximately 90 amino acids from the N-terminus of the small subunit. These regions form contacts between the two subunits in unautolyzed calpains, and their removal leaves only contacts between domain IV in the large subunit and domain VI in the small subunit. Although many of these contacts are hydrophobic in nature, ionic-strength-induced dissociation of the two subunits in the autolyzed calpains indicates that salt bridges have an important, possibly indirect, role in the domain IV/domain VI interaction. (+info)
Blocking of human immunodeficiency virus type-1 virion autolysis by autologous p2(gag) peptide.
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Our previous study suggested that the p2(gag) peptide, AEAMSQVTNTATIM, inhibits human immunodeficiency virus type 1 (HIV-1) protease (PR) activity in vitro. In this study, Ala substitutions (Met4Ala and Thr8Ala) and deletion of amino acid Asn9 within the nona p2(gag) peptide (AEAMSQVTN) were found to decrease the inhibitory effect on HIV-1 PR activity. Furthermore, treatment of PMA-activated latently infected T lymphocytes, ACH-2 cells, with the p2(gag) peptide (100 and 250 micro M) resulted in a decrease in the amount of p24(gag )in the resultant viral lysates derived from the cell-free supernatant. In addition, the HIV-1-Tat-p2(gag) fusion peptide was synthesized to effectively deliver the p2(gag) peptide into the cells. The fusion peptide was incorporated into chronically infected T lymphocytes, CEM/LAV-1 cells, as detected on indirect immunofluorescence analysis using anti-p2(gag) peptide monoclonal antibodies, which recognize the nona peptide (AEAMSQVTN) derived from the N-terminus of the p2(gag) peptide, and cleaved by HIV-1 PR in vitro. Treatment of CEM/LAV-1 cells with the fusion peptide also resulted in a decrease in the amount of p24(gag )in the resultant viral lysate derived from the cell-free supernatant. Taken together, these data suggest that the p2(gag) peptide consequently blocks the autolysis of HIV-1 virions for the conservation of viral species. (+info)