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S Pontremoli

Publications and source records attributed to S Pontremoli.

At least 91 records · Page 5Linked to original sources
PubMed1987

Decreased level of calpain inhibitor activity in kidney from Milan hypertensive rats.

Rat kidney contains two different calpain isozymes distinguishable on the basis of their Ca2+ requirement and of their activation mechanisms. The two calpain isozymes are present in comparable amounts in kidney of normotensive and hypertensive rats of the Milan strain. Conversely, the level of the natural inhibitor of calpain is significantly decreased in kidney of hypertensive rats as compared to control normotensive rats. This deficiency is more pronounced in the cortical region than in other kidney fractions. These results taken together with previous observations indicating the existence of an identical defect in red cells from the same hypertensive rat strain, (Pontremoli, S., Melloni, E., Salamino, F., Sparatore, B., Viotti, P., Michetti, M., Duzzi, L., and Bianchi, G. (1986) Biochem. Biophys. Res. Commun. 138, 1370-1375) emphasize the possible role of an unbalanced intracellular proteolytic system in the development of genetically determined hypertension.

Animals↗
PubMed1987

Increased phosphorylation in red cell membranes of subjects affected by essential hypertension.

In hemolysates of red cells from hypertensive patients the proteolytic activity of calpain is expressed at a rate approximately three fold higher than in red cells of normotensive subjects. Susceptibility to lysis upon exposure to ionophore A23187 and calcium, conditions that increase intracellular calpain activity, is also significantly enhanced in erythrocytes of hypertensive patients. In inside-out vesicles prepared from erythrocytes of these patients band 3 region undergoes a high extent of phosphorylation which is 1.5 fold higher than that occurring in control red cells from normotensive subjects. This increased phosphorylation can be reproduced in inside-out vesicles from erythrocytes of normal subjects following pretreatment with calpain. Taken together, these results suggest that the presence in erythrocytes of hypertensive subjects of an unregulated calpain dependent proteolytic activity may affect the structure of plasma membranes and determine an increased phosphorylation of intrinsic membrane proteins.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1987

Phosphorylation and proteolytic modification of specific cytoskeletal proteins in human neutrophils stimulated by phorbol 12-myristate 13-acetate.

Stimulation of intact human neutrophils with phorbol 12-myristate 13-acetate results in the selective phosphorylation of two cytoskeletal protein components with molecular masses of 20 and 48 kDa. After phosphorylation the 48-kDa protein is no longer recovered as a component of the cytoskeletal fraction but is present as a fully soluble phosphoprotein. Phosphorylation of the 20-kDa protein (probably myosin light chains) signals a proteolytic conversion, catalyzed by calpain, to a smaller species having a molecular mass of approximately 15 kDa. Phosphorylation of both the 48- and 20-kDa proteins is related to the conversion of protein kinase C, also catalyzed by calpain, to the soluble fully active form. Leupeptin, an inhibitor of calpain, blocks both the phosphorylation of the target proteins and the proteolytic modification of the 20-kDa polypeptide. Thus, phosphorylation of cytoskeletal proteins and signal-directed proteolysis appear to be related processes that follow stimulation of human neutrophils by phorbol esters. The resulting changes in cytoskeletal organization may be involved in the expression of some neutrophil functions, such as exocytosis of specific granules.

Cytoskeletal Proteins↗
PubMed1987

Protein kinase C activity and hexamethylenebisacetamide-induced erythroleukemia cell differentiation.

Hexamethylenebisacetamide (HMBA) is a potent inducer of murine erythroleukemia (MEL) cell differentiation. The mechanism of action of HMBA is not known. In this study we provide evidence that protein kinase C has a role in inducer-mediated MEL cell differentiation: (i) HMBA induces the formation of a soluble, proteolytically activated form of protein kinase C that is catalytically active in the absence of Ca2+ and phospholipid; (ii) the protease inhibitor leupeptin blocks formation of this activated form of the kinase and inhibits HMBA-induced MEL cell hemoglobin accumulation; (iii) phorbol 12-myristate 13-acetate (PMA) inhibits HMBA-induced MEL differentiation and causes depletion of total protein kinase C activity; (iv) MEL cells depleted in protein kinase C activity by culture with PMA are resistant to induction by HMBA; (v) upon removal of PMA, restoration of MEL cell sensitivity to HMBA is correlated with reaccumulation of protein kinase C activity; and (vi) MEL cells grown to density arrest are both depleted of protein kinase C activity and resistant to HMBA. Together, these results suggest that HMBA-mediated MEL cell differentiation involves a protein kinase C-related mechanism and the proteolytically activated form of the kinase, which does not require Ca2+ or phospholipid for its catalytic activity.

Acetamides↗
PubMed1987

Phosphorylation by protein kinase C of a 20-kDa cytoskeletal polypeptide enhances its susceptibility to digestion by calpain.

Incubation of the cytoskeletal fraction from human neutrophils with the proteolytically activated form of protein kinase C results in the phosphorylation of several components, including a 20-kDa polypeptide, probably consisting of myosin light chains. The 20-kDa polypeptide is also specifically phosphorylated by activated protein kinase C in a solubilized 20-kDa/80-kDa complex that was obtained after sonication of the insoluble cytoskeletal fraction. Phosphorylation of this polypeptide, in either the insoluble cytoskeletal fraction or the soluble 20-kDa/80-kDa complex, greatly enhances its susceptibility to digestion by the Ca2+-requiring proteinase (calpain, EC 3.4.22.17) of human neutrophils. Thus, signals that activate calpain by mobilizing intracellular calcium would lead to proteolytic activation of protein kinase C, phosphorylation of cytoskeletal proteins, and remodeling of the cytoskeleton by proteolysis of at least one cytoskeletal component.

Calpain↗
PubMed1986

Activation of NADPH oxidase and phosphorylation of membrane proteins in human neutrophils: coordinate inhibition by a surface antigen-directed monoclonal antibody.

Exposure of human neutrophils to low concentrations of phorbol myristate acetate (PMA) results, after a brief lag, in the production of superoxide anion and the phosphorylation of membrane proteins. Evidence that these responses are linked has now been obtained using a monoclonal antibody directed against an undefined macrophage surface antigen. The addition of this antibody, which recognizes a 90 kDa neutrophil membrane protein, caused dose-dependent delays in the onset of both phosphorylation of neutrophil membrane proteins and in the appearance of superoxide anion, following addition of PMA to the cell suspensions. For each response the lag period increased with increasing concentrations of antibody, but the onset of phosphorylation always preceded by a few minutes the initial appearance of superoxide anion.

Antibodies, Monoclonal↗
PubMed1986

ATP induces the release of a neutral serine proteinase and enhances the production of superoxide anion in membranes from phorbol ester-activated neutrophils.

Plasma membranes isolated from human neutrophils after brief exposure to phorbol 12-myristate 13-acetate contain a large portion (30-40%) of the total cellular protein kinase C (Melloni, E., Pontremoli, S., Michetti, M., Sacco, O., Sparatore, B., Salamino, F., and Horecker, B. L. (1986) Biochem. Biophys. Res. Commun. 136, 228-234) and also retain almost 90% of their content of neutral serine proteinase (Pontremoli, S., Melloni, E., Michetti, M., Sacco, O., Sparatore, B., Salamino, F., Damiani, G., and Horecker, B. L. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 1685-1689). When ATP is added to the isolated membranes, a substantial amount (approximately 25%) of the intrinsic proteinase is released into the incubation medium. The addition of ATP in the presence of NADPH also caused a significant enhancement of the production of O2 radicals. These effects of ATP were not observed with membranes isolated from untreated neutrophils. The release of the serine proteinase is almost fully dependent on the addition of ATP and is correlated with the phosphorylation of membrane proteins. It is also markedly inhibited by the addition of retinal or trifluoperazine inhibitors of native protein kinase C. The results represent the first direct demonstration of a role for membrane-bound protein kinase C activity in the release of neutral proteinase and the production of O2 radicals, responses related to the cytotoxic effects of activated neutrophils.

Adenosine Triphosphate↗
PubMed1986

Characterization of the defective calpain-endogenous calpain inhibitor system in erythrocytes from Milan hypertensive rats.

In mature red cells of rats from Milan normal (MNS) and hypertensive strains (MHS), the soluble Ca2+ dependent neutral proteinase (calpain) is present in similar amounts with identical Mr of 110 kDa and a dimeric structure composed of two unequal subunits of Mr of 84 and 26 kDa. Conversely, the amount of the endogenous inhibitor is now confirmed by analysis of the specific activity to be approximately 10 times less in red cells of MHS rats. The inhibitor is present in red cells of both strains in three different oligomeric forms of Mr of 240, 120 and 64 kDa. This last molecular species corresponds to the single basic constituent subunit which is the reacting inhibitor form. The apparent equilibrium between the three oligomeric structures is Ca2+-dependent. The high (0.1 mM) Ca2+ requirement for the activity of calpain from erythrocytes of both strains is reduced to 1-5 microM in the presence of plasma membrane phospholipids. Activation of the enzyme in these conditions is prevented by the natural inhibitor. These results strongly support and further emphasize the hypothesis that the structural and functional abnormalities in MHS rats red cells result from an impairment in the modulation of intracellular calpain activity by interaction with its endogenous inhibitor.

Animals↗
PubMed1986

Decreased level of calpain inhibitor activity in red blood cells from Milan hypertensive rats.

In mature red cells of rats from Milan Normal (MNS) and Hypertensive Strains (MHS), the soluble Ca2+-dependent neutral proteinase (calpain) is present in similar amounts as the form requiring 0.1-0.2 mM Ca2+ for maximum catalytic activity. The amount of the endogenous calpain inhibitor, however, differs greatly in the red cells of the two strains. In red cells from hypertensive rats the activity of the inhibitor is 10 times less with a ratio of inhibitor to calpain activity (unit/unit) of 0.2; compared to red cells from normal rats, in which this ratio is approximately 2. This is the first demonstration of the existence, in a mammalian cell, of such a low ratio of calpain to inhibitor and implies the occurrence of a potentially "unregulated" intracellular soluble proteinase. This abnormal condition may be responsible for some of the structural and metabolic changes reported in rats of the genetically determined MHS strain.

Animals↗
PubMed1986

Biochemical responses in activated human neutrophils mediated by protein kinase C and a Ca2+-requiring proteinase.

Low concentrations of phorbol 12-myristate 13-acetate (PMA) elicit a specific response in human neutrophils, characterized by the production of oxygen radicals and the release into the medium of a membrane-bound serine proteinase (Pontremoli, S., Melloni, E., Michetti, M., Sacco, O., Sparatore, B., Salamino, F., Damiani, G. and Horecker, B. L. (1986) Proc. Natl. Acad. Sci. U. S. A., 83, 1685-1689). The following evidence indicates that this response is mediated by membrane-bound protein kinase C: 1) it is blocked by inhibitors of protein kinase C; and 2) it is enhanced in cells preloaded with leupeptin which prevents proteolysis of protein kinase C and its subsequent dissociation from the cell membrane. This response is not accompanied by significant exocytosis of granule enzymes. With higher concentrations of PMA, and more particularly on stimulation with formylmethionyl-leucyl-phenylalanine (fMLP) plus cytochalasin B, a substantial exocytosis of constituents of both specific and azurophil granules is observed. With fMLP, exocytosis of granule enzymes is the predominant event, with little production of H2O2 and negligible release of membrane-bound serine proteinase. Exocytosis promoted either by a high concentration of PMA or by fMLP is inhibited by leupeptin, indicating that it is due to the action of an intracellular Ca2+-dependent thiol proteinase (calpain), either directly or by conversion by calpain of membrane-bound protein kinase C to the soluble Ca2+/phospholipid-independent form. Intracellular mobilization of Ca2+ is also observed following stimulation with either PMA or fMLP, but only the latter results in a net increase in the intracellular concentration of free Ca2+; under these conditions maximum exocytosis of granule contents is observed.

Calpain↗
PubMed1986

Differential mechanisms of translocation of protein kinase C to plasma membranes in activated human neutrophils.

Three classes of activators of human neutrophils that induce the intracellular translocation of protein kinase C from the cytosol to the particulate fraction were compared for their effects on the properties of the particulate (membrane-bound) enzyme. In cells stimulated with 10 ng/ml of phorbol-12-myristate-13-acetate (PMA) the particulate enzyme is almost fully active in the absence of added Ca2+ or phospholipids and this activity is not released by the Ca2+-chelator EDTA. In contrast, binding of protein kinase C to the particulate fraction in cells treated with the chemotactic factor f-Met-Leu-Phe (fMLF) or with the ionophore A-23187 plus Ca2+ is observed only when the cells are lysed in the presence of 1 mM Ca2+. With these stimuli the particulate enzyme retains a nearly absolute requirement for Ca2+ and phospholipids. Thus only the full intercalation of protein kinase C caused by PMA, which is resistant to removal by chelators stabilizes an active form of protein kinase C in the neutrophil membrane. In confirmation of this conclusion, in isolated plasma membranes loaded with partially purified protein kinase C by incubation with 5 microM Ca2+ further incubation with PMA, but not with fMLF, caused a significant fraction of the bound PKC to become resistant to removal by chelators, and to be nearly fully active in the absence of added activators.

Biological Transport, Active↗
PubMed1986

The involvement of calpain in the activation of protein kinase C in neutrophils stimulated by phorbol myristic acid.

The Ca2+/phospholipid-dependent protein kinase (protein kinase C) of human neutrophils is converted to a proteolytically modified Ca2+/phospholipid-independent form (Inoue, M., Kishimoto, A., Takai, Y.U., and Nishizuka, Y. (1977) J. Biol. Chem. 252, 7610-7616) on incubation with neutrophil membranes in the presence of micromolar concentrations of Ca2+ and an endogenous Ca2+-requiring proteinase (Melloni, E., Pontremoli, S., Michetti, M., Sacco, O., Sparatore, B., Salamino, F., and Horecker, B. L. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 6435-6439). We have now demonstrated the appearance of a similar Ca2+/phospholipid-independent kinase in intact human neutrophils stimulated by phorbol 12-myristate 13-acetate (PMA). The following evidence supports the conclusion that the Ca2+/phospholipid-independent protein kinase recovered from the PMA-treated cells is a proteolytically modified form of the "native" protein kinase C. 1) In cells exposed to PMA, the rate of disappearance of Ca2+/phospholipid-dependent protein kinase C activity is correlated with the rate of appearance of the Ca2+/phospholipid-independent kinase. 2) The chromatographic behavior of the new protein kinase and its molecular size (approximately 65 kDa) are identical to those previously reported for the proteolytically modified form of protein kinase C. 3) The modified protein kinase no longer binds to the cell membrane and is recovered almost entirely in the cytosol fraction. 4) In neutrophils preloaded with inhibitors of the Ca2+-requiring proteinase, stimulation with PMA results in translocation of protein kinase C from the cytosol fraction to the particulate fraction, but the appearance of the soluble, Ca2+/phospholipid-dependent form is prevented. We conclude that binding of protein kinase C to the plasma membrane and its proteolytic conversion are related, but independent, processes both elicited by exposure of neutrophils to the phorbol ester. Proteolytic cleavage of the membrane-bound protein kinase C provides an alternative mechanism for its activation and may account for certain of the cellular responses observed in PMA-stimulated neutrophils.

Calpain↗
PubMed1986

Phosphorylation of proteins in human neutrophils activated with phorbol myristate acetate or with chemotactic factor.

In human neutrophils stimulated with phorbol myristate acetate (PMA) or with the chemotactic factor N-formyl-methionyl-leucyl-phenylalanine (fMLF) a number of proteins are phosphorylated, including proteins recovered in the membrane fraction corresponding to molecular masses of 130, 78, 46, 40, and 34 kDa and proteins recovered in the cytosol fraction corresponding to molecular masses of 65, 55, 48, 38, 36, 30, and 22 kDa. Phosphorylation of the membrane proteins was fourfold greater in cells stimulated with PMA, as compared to cells stimulated with fMLF, whereas both activators induced similar phosphorylation of proteins recovered in the cytosol fraction. Phosphorylation of membrane proteins appeared to be mediated by native protein kinase C (PKC) translocated from the cytosol to the plasma membrane. Thus phosphate incorporation was inhibited by retinal and a similar pattern of incorporation was reproduced in a reconstituted system composed of isolated cell membranes and purified PKC. Phosphorylation of cytosol proteins, on the other hand, appeared to be mediated by the proteolytically modified form of PKC. In this case, phosphate incorporation was inhibited by leupeptin, which prevents the conversion of native PKC to the proteolytically modified form, The phosphorylation pattern was reproduced when isolated cytosol fractions were incubated with the proteolytically modified form of the enzyme but not with the native PKC. These results demonstrate that responses to stimuli such as PMA or fMLF are mediated by different forms of PKC and that the proteolytically modified form is responsible for the major responses elicited by fMLF.

Blood Proteins↗
PubMed1986

Cytolytic effects of neutrophils: role for a membrane-bound neutral proteinase.

A neutral serine proteinase, purified 250-fold from the plasma membrane fraction of human neutrophils, differs in its catalytic and molecular properties from the well-known neutral proteinases present in azurophil (primary) granules. Stimulation of neutrophils with low concentrations of phorbol 12-myristate 13-acetate (PMA) results in the release into the medium of the membrane-bound proteinase and the concomitant production of oxygen radicals. These concentrations of PMA also induce full cytolytic activity measured with 51Cr-labeled ox erythrocytes. A role for the neutral serine proteinase in the cytolytic activity of PMA-stimulated neutrophils is supported by the following observations: (i) the lytic activity of the stimulated neutrophils is correlated with the quantity of neutral proteinase present in the membranes; (ii) the extracellular medium from PMA-stimulated neutrophils causes the cytolysis of 51Cr-labeled erythrocytes that have been exposed to nonlytic concentrations of H2O2; (iii) cytolysis of H2O2-treated erythrocytes is also observed with the crude proteinase solubilized from neutrophil membranes or with the purified proteinase from the same source; and (iv) in each case the cytolytic activity is proportional to the proteinase activity present and is prevented by the addition of serine proteinase inhibitors. We conclude that cytolysis of target cells by PMA-activated neutrophils can result from the cooperative effects of oxygen radicals and the membrane-bound neutral serine proteinase. The participation of enzymes from specific (secondary) granules is excluded because, with the low concentrations of PMA employed, very little release of secondary granule constituents is observed.

Cytotoxicity, Immunologic↗
PubMed1985

Purification and properties of rabbit liver cathepsin M and cathepsin B.

Cathepsins M and B from rabbit liver lysosomes were separated by chromatography on Ultrogel AcA34 at low ionic strength and purified to homogeneity, and their catalytic and molecular properties were compared. Cathepsin M was relatively inactive with synthetic peptide substrates. Thus, it hydrolyzed benzoyl arginine naphthylamide at only one-fifth the rate observed with cathepsin B, and no activity was detected with Gly-Phe naphthylamide which is a relatively good substrate for cathepsin B. On the other hand, cathepsin M exhibited a preference for protein substrates. It was more active than cathepsin B in catalyzing the inactivation of the following enzymes: rabbit muscle or liver fructose-1,6-bisphosphate aldolases, rabbit liver fructose-1,6-bisphosphatase and pyruvate kinase, yeast glucose-6-phosphate dehydrogenase, and rabbit muscle glyceraldehyde-3-phosphate dehydrogenase. With glucagon as substrate, both enzymes showed similar peptidyl dipeptidase activities with some minor differences in peptide bond specificity. Cathepsins M and B are similar in size, with apparent molecular weights of 30,200 for cathepsin M and 28,800 for cathepsin B, and in amino acid composition and carbohydrate content. Each contains approximately 2-3 equivalents/mol glucosamine, 3 equivalents/mol mannose, and no fucose or galactosamine. They also show similar microheterogeneity in sodium dodecylsulfate-gel electrophoresis and isoelectric focusing; this microheterogeneity is probably related to differences in glycosylation. Extensive homology in primary structure for the two proteins was indicated by the similar patterns of peptides formed on digestion with trypsin.

Amino Acids↗
PubMed1985

Following association to the membrane, human erythrocyte procalpain is converted and released as fully active calpain.

When exposed to inside-out human erythrocyte vesicles, in the presence of micromolar Ca2+, the 80 kDa catalytic subunit of procalpain is processed through three successive and sequential steps. These include binding to the cytosolic surface of the membrane, followed by a very rapid conversion into the 75 kDa active subunit, and ultimately by spontaneous and complete release of this active proteinase form. Binding to the membranes is competitively inhibited by the endogenous natural inhibitor through the formation of the proteinase-inhibitor complex, in which form the 80 kDa subunit can no longer be associated to the membranes. Calcium ions and the natural endogenous inhibitor appear to be crucially involved in the modulation of this novel membrane-bound mediated activation of human red cell procalpain.

Calpain↗
PubMed1985

Role of phospholipids in the activation of the Ca2+-dependent neutral proteinase of human erythrocytes.

Activation of the Ca2+-dependent neutral proteinase of human erythrocytes in the presence of Ca2+ and a digestible substrate (Pontremoli, S., Sparatore, B., Melloni, E., Michetti, M. and Horecker, B.L. 1984, Biochem. Biophys. Res. Communs. 123, 331-337) is promoted by phospholipids such as phosphatidylcholine, phosphatidylinositol and phosphatidylserine. The presence of at least one unsaturated fatty acid chain is essential and metabolic derivatives such as dioleylglycerol, phosphorylserine and free fatty acids are ineffective. The most effective promoter was a freshly prepared mixture of phospholipids from human erythrocyte membranes. Activation involves conversion of the 80 kDa proenzyme (procalpain) subunit to the 75 kDa active proteinase and is irreversible. Phospholipids act by producing a large decrease in the concentration of Ca2+ required for the conversion of procalpain to active calpain.

Calcium↗