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PubMed1994

Binding of transforming growth factor-beta (TGF-beta) to pregnancy zone protein (PZP). Comparison to the TGF-beta-alpha 2-macroglobulin interaction.

Pregnancy zone protein (PZP) is quantitatively the most important pregnancy-associated plasma protein and it has strong similarity to alpha 2-macroglobulin. Since alpha 2-macroglobulin is a binding protein for transforming growth factors-beta (TGF-beta), it was of interest to test whether the related protein, PZP, also binds to these growth-regulatory proteins. Using affinity-labelling methods, we demonstrate that PZP binds both TGF-beta 1 and TGF-beta 2 and that the binding characteristics are similar to those of the TGF-beta-alpha 2-macroglobulin interaction. TGF-beta 2 and TGF-beta 1 bind to PZP in a predominantly noncovalent manner in vitro. TGF-beta 1 and TGF-beta 2 bind to both the dimeric and tetrameric forms of PZP. Our studies also indicate that PZP binds TGF-beta 2 with higher affinity than TGF-beta 1. Finally, we demonstrate that PZP inhibits the binding of TGF-beta 1 and TGF-beta 2 to their cell surface receptors. The increased level of PZP during pregnancy may affect the action of TGF-beta by regulating the distribution, clearance and/or general availability of TGF-beta. The preferential binding of TGF-beta 2 over TGF-beta 1 by PZP implies that PZP may differentially regulate the action of TGF-beta 1 and TGF-beta 2.

Autoradiography↗

PubMed1995

Alpha 2-macroglobulin receptor mediates binding and cytotoxicity of plant ribosome-inactivating proteins.

It has been proposed that unconjugated type I ribosome-inactivating proteins (RIP) enter cells through passive mechanisms such as fluid-phase pinocytosis. However, some observations, such as the difference in sensitivity to type I RIP among different cell types, and the organ-specific toxicity of type I RIP, indicate a specific mechanism for the entry of these proteins into target cells. The alpha 2-macroglobulin receptor (alpha 2MR) is responsible for the binding and endocytosis of several ligands, including alpha 2-macroglobulin/proteinase complexes, plasminogen-activator-inhibitor complexes, apoE-enriched beta-very low density lipoproteins, and lipoprotein lipase. Here we demonstrate that saporin, a potent type I RIP, binds specifically to purified alpha 2MR and the binding is prevented by some alpha 2MR ligands. Moreover, the occupancy of specific ligand-binding sites on cell surface alpha 2MR decreases the cytotoxicity of saporin. The A chain of ricin, a type II RIP, also interacts with alpha 2MR. This, and the fact that saporin and ricin A chain both interact also with alpha 2-macroglobulin, indicates a general mechanism of complex interactions between RIP and cellular membranes that is mediated by alpha 2-macroglobulin and the alpha 2MR system.

Cell Death↗

PubMed1996

Blockade of the alpha 2-macroglobulin receptor/low-density-lipoprotein-receptor-related protein on rat liver parenchymal cells by the 39-kDa receptor-associated protein leaves the interaction of beta-migrating very-low-density lipoprotein with the lipoprotein remnant receptor unaffected.

The nature of the liver binding site which is responsible for the initial recognition and clearance of chylomicron-remnants and beta-migrating very-low-density lipoprotein (beta-VLDL) is under active dispute. We have investigated the effect of the 39-kDa receptor-associated protein (RAP) on the recognition site for activated alpha 2-macroglobulin and beta-VLDL on rat liver parenchymal cells in vivo and in vitro in order to analyze whether both substrates are recognized and internalized by the same receptor system. Radiolabelled trypsin-activated alpha 2-macroglobulin (alpha 2M-T) was cleared rapidly by the liver (maximal uptake of 80.8 +/- 1.0% of the injected dose). Prior injection of 5, 15, or 50 mg gluthathione-S-transferase-linked RAP (GST-RAP)/kg rat reduced the liver uptake to 62.2 +/- 2.3%, 59.3 +/- 1.1%, or 2.9 +/- 0.1% of the injected dose, respectively. Concurrently the serum decay was strongly delayed after injection of 50 mg GST-RAP/kg rat but this did not affect the serum decay and liver uptake of 125I-beta-VLDL. Binding studies with isolated liver parenchymal cells in vitro demonstrated that the binding of 125I-alpha 2M-T was 98% inhibited by GST-RAP with an IC50 of 0.3 microgram/ml (4.2 nM), whereas the binding of 125I-beta-VLDL and 125I-beta-VLDL + recombinant apolipoprotein E (rec-apoE) was unaffected by GST-RAP up to 50 micrograms/ml (700 nM). Also, the cell association and degradation of alpha 2M-T was blocked by RAP, while the association and degradation of beta-VLDL and beta-VLDL + rec-apoE were not influenced. The inhibitory effect of RAP on the cell association and degradation of alpha 2M-T lasted for 1-2 h of incubation at 37 degrees C. The binding of the radioiodinated RAP to isolated liver parenchymal cells was highly efficiently coupled to lysosomal degradation. Upon in vivo injection into rats, 125I-labeled RAP is rapidly cleared from the serum and taken up by the liver, which is also coupled to efficient degradation. Since RAP blocks binding of all known ligands to the alpha 2-macroglobulin receptor/low-density lipoprotein receptor-related protein (the alpha 2Mr/LRP) and at high concentrations the binding to the LDL receptor, we conclude that the initial binding and internalization of beta-VLDL by rat liver parenchymal cells is not mediated by the alpha 2Mr/LRP. The properties of binding of beta-VLDL to rat liver parenchymal cells points to an apoE-specific recognition site for lipoprotein remnants which differs from the alpha 2Mr/LRP, proteoglycans and the LDL receptor and is tentatively called the lipoprotein remnant receptor.

Animals↗

PubMed1997

Interactions between ovine cathepsin L, cystatin C and alpha 2-macroglobulin. Potential role in the genital tract.

The specific inhibitor of cysteine proteinases, cystatin C, was purified from ram rete testis fluid and the conditioned medium of Sertoli cells. This molecule associated with sheep liver cathepsin L at one of the fastest rates ever described for a proteinase/inhibitor interaction (1.75 +/- 0.20 x 10(8) M-1.s-1). But the association rate constant for the interaction of cathepsin L with alpha 2-macroglobulin, a non-specific inhibitor of proteinases, was also extremely high (8.8 +/- 0.75 x 10(6) M-1.s-1). Cathepsin L complexed with alpha 2-macroglobulin was protected from inhibition by type 2 and type 3 cystatins. The data indicate that cystatin C is the most potent inhibitor of cathepsin L in mammalian male genital tract fluids, whereas alpha 2-macroglobulin may act as a terminal acceptor of this enzyme. These inhibitors could therefore inhibit the activated form of procathepsin L which may appear during the complex process of spermatozoa production and maturation in the testis and epididymis.

Amino Acid Sequence↗

PubMed2002

Increased Trypanosoma cruzi invasion and heart fibrosis associated with high transforming growth factor beta levels in mice deficient in alpha(2)-macroglobulin.

Trypanosoma cruzi proteinases are involved in host cell invasion in human patients and in mouse models. In mice, murine alpha(2)-macroglobulin (MAM) and murinoglobulin are circulating plasma proteinase inhibitors that also have important roles in inflammation and immune modulation. To define their role in experimental Chagas disease, we investigated the susceptibility to T. cruzi infection of mice that are deficient only in alpha2-macroglobulins (AM-KO) or in both MAM and monomeric murinoglobulin-1 (MM-KO), relative to the wild type (WT). Despite the high parasite load, parasitemia was lower in AM-KO and MM-KO mice than in WT mice. Nevertheless, we observed a significantly higher parasite load in the hearts of AM-KO and MM-KO mice, i.e., more amastigote nests and inflammatory infiltrates than in WT mice. This result demonstrates a protective role for MAM in the acute phase of murine T. cruzi infection. We further demonstrated in vitro that human alpha2-macroglobulins altered the trypomastigote morphology and motility in a dose-dependent way, and that also impaired T. cruzi invasion in cardiomyocytes. Finally, we demonstrated that the levels of transforming growth factor beta in AM-KO mice increased significantly in the third week postinfection, concomitant with high amastigote burden and important fibrosis. Combined, these in vivo and in vitro findings demonstrate that the MAM contribute to the resistance of mice to acute myocarditis induced by experimental T. cruzi infection.

Animals↗

PubMed1970

Serum-alpha2-macroglobulin, transferrin, albumin, and IgG levels in preeclampsia.

A radial immunodiffusion technique has been used to measure levels of four serum proteins in preeclampsia with or without proteinuria and in normal pregnant and non-pregnant controls. In preeclampsia unaccompanied by proteinuria, albumin and transferrin levels are similar to those found in the normal pregnant controls, but there are significant falls in alpha(2)-macroglobulin and IgG. When preeclampsia is accompanied by proteinuria there is a marked fall in albumin and an increase in alpha(2)-macroglobulin. Since alpha(2)-macroglobulin has antiplasmin activity it is possible that increased levels of this protein in preeclampsia accompanied by proteinuria contribute to the intravascular coagulation which has been described in this disorder.

Adolescent↗

PubMed1995

alpha 2-Macroglobulin gene expression during hibernation in ground squirrels is independent of acute phase response.

alpha 2-Macroglobulin, a major acute phase reactant in many species, increases in the Richardson's ground squirrel (Spermophilus richarsonii) during hibernation at the level of both mRNA and protein. To determine if the pattern of liver gene expression known as the acute phase response is elicited as a normal part of the physiological adaptation of hibernation, acute phase reactants were identified in the Richardson's ground squirrel and were then assayed for changes in mRNA expression in the livers of active and hibernating ground squirrels. Our data demonstrate that alpha 1-antitrypsin, alpha 2-macroglobulin, ceruloplasmin, C-reactive protein, and serum amyloid A are acute phase reactants in the Richardson's ground squirrel. Of these, only alpha 2-macroglobulin (alpha 2M) mRNA increases during hibernation, demonstrating that the entire acute phase response is not elicited as a part of the adaptation for hibernation. Alternatively, data from blood clotting assays of serum from active and hibernating animals support a role for the increase in alpha 2M protein during hibernation in decreasing the coagulative properties of the blood.

Actins↗

PubMedDate not supplied

Alpha macroglobulins and the low-density-lipoprotein-related protein/alpha-2-macroglobulin receptor in experimental renal fibrosis.

In this study, we evaluated the location of non-specific proteinase inhibitors and their receptor in experimental glomerular and interstitial fibrosis. The alpha macroglobulins alpha-2-macroglobulin (alpha2M) and alpha-1-inhibitor 3 (alpha1I3) are proteinase inhibitors, including metalloproteinases and serine proteases. Using immunohistochemistry, we detected alpha1I3 in the glomerular mesangium in control rats. In acute and chronic fibrosis, the alpha1I3 protein expression was dramatically increased throughout the glomerulus and at sites of increased extracellular matrix deposition in the interstitium. The presence of alpha1I3 in normal and nephrotic kidneys was confirmed by Western blotting. Under chemically reducing conditions, we found that, in contrast to native alpha1I3, kidney-derived alpha1I3 has reacted upon by proteinases, thereby revealing a functional role for this macroglobulin under normal and pathological conditions. Double staining revealed that high amounts of glomerular alpha1I3 were present in sclerotic lesions. alpha2M was absent in glomeruli and interstitium from control rats, but present in small amounts in glomerular mesangial areas of acute nephrotic rats. alpha2M was also present in significant amounts in glomeruli from rats with chronic fibrosis. The receptor mediating the uptake of proteinase inhibitor-proteinase complexes, the low-density-lipoprotein-related protein/alpha-2-macroglobulin receptor, was found in the glomerular mesangium and tubulo-interstitium from control rats. Significant increments in receptor expression were found in glomeruli and interstitium of rats with chronic fibrosis, with a preferential localization in fibrotic areas. Interstitial staining for low-density-lipoprotein-related protein/alpha-2-macroglobulin receptor was attributed to fibroblasts, since double staining ruled out dendritic cells and macrophages. In conclusion, these studies demonstrate the intrarenal presence of plasma-derived proteinase inhibitors together with their receptors. These findings may point to a novel mechanism for renal fibrosis wherein matrix-degrading proteinases are inhibited, resulting in renal fibrosis.

Acute-Phase Proteins↗

PubMed1982

In vitro inhibition of protein catabolism by alpha 2-macroglobulin in plasma from a patient with posttraumatic acute renal failure.

Rapid proteolytic digestion of three subunits of phosphorylase kinase was shown in plasma ultrafiltrates from a patient who was admitted with multiple traumatic injuries, respiratory insufficiency, hemorrhagic shock and acute renal failure. The observed cleavage of phosphorylase kinase may be a consequence of protease-antiprotease imbalance. After an initial determination of 80 mg/dl the alpha 2-macroglobulin values were too low to be detected. Addition of purified alpha 2-macroglobulin to the ultrafiltrates resulted in complete inhibition of phosphorylase kinase digestion in vitro. Aprotinin did not inhibit proteolytic digestion. Daily dialysis did not ameliorate the observed protein catabolism of this patient. These findings may have clinical application in hypercatabolic states, if alpha 2-macroglobulin becomes available in a form suitable for human use.

Acute Kidney Injury↗

PubMed1976

Interrelations between ABO blood group, plasminogen, alpha1-antitrypsin, alpha2-macroglobulin and the platelet count in blood donors.

The level of plasminogen alpha1-antitrypsin, alpha2-macroglobulin and the platelet count were measured in 511 blood donors. The mean level of alpha1-antitrypsin was significantly lower in men of group B compared with that of group O. No other differences between the blood groups reached statistical significance. Woman had higher mean levels of alpha1-antitrypsin and alpha2-macroglobulin and a higher platelet count than men. The levels of plasminogen and alpha1-antitrypsin were significantly higher in women using oral contraceptive compared with those who were not. The level of alpha2-marcoglobulin fell with age until the 60-64 year age-group in men and the 40-49 year age-group in women. A positive correlation existed between the alpha1-antitrypsin and the alpha2-macroglobulin level and between the platelet count and the plasminogen level.

ABO Blood-Group System↗

PubMed1999

Allergen challenge-induced acute exudation of IL-8, ECP and alpha2-macroglobulin in human rhinovirus-induced common colds.

Rhinovirus infections cause exacerbations of eosinophilic airway disease. The acute effects of allergen-challenge on nasal interleukin-8 (IL-8), eosinophil cationic protein (ECP), and alpha2-macroglobulin were examined in atopic subjects with common cold symptoms. Twenty-three patients with seasonal allergic rhinitis were inoculated with human rhinovirus 16 outside the pollen season. Diluent and allergen challenges, followed by nasal lavages, were carried out about 3 months before and 4 days after virus inoculation. Seventeen patients developed significant common cold symptoms with increased nasal lavage fluid levels of alpha2-macroglobulin, IL-8, and ECP at baseline (p<0.001-0.05 versus before inoculation), and were further increased by allergen challenge (p< 0.001-0.05); IL-8 and ECP levels were correlated (r = 0.63, p<0.001). Before inoculation, the six patients who later did not develop common cold symptoms had high levels of IL-8 and myeloperoxidase (MPO), and exhibited strong allergen-induced plasma exudation responses (alpha2-macroglobulin). After inoculation, IL-8 and ECP did not increase in these symptomless subjects. In conclusion, high nasal interleukin-8 and myeloperoxidase levels and exudative hyperresponsiveness may protect against infection. The association between nasal interleukin-8 and eosinophil cationic protein in common cold, particularly that observed in nasal lavage fluids after allergen-induced acute exudation of plasma, suggests the involvement of interleukin-8 in exacerbation of airway mucosal eosinophil activity.

Adolescent↗

PubMed1999

Alpha2-macroglobulin and eosinophil cationic protein in the allergic airway mucosa in seasonal allergic rhinitis.

As previously demonstrated in seasonal allergic rhinitis, increased microvascular permeability and eosinophil activation are key features of allergic airway inflammation. In the present study, the hypothesis that exudation of alpha2-macroglobulin may cause the appearance of eosinophil cationic protein (ECP) in the airway lumen was explored. Nasal lavages were carried out using the nasal pool device before and during the pollen season both at baseline and after histamine challenge in 10 children with allergic rhinitis. Nasal lavage fluid levels of alpha2-macroglobulin and ECP were determined. All patients experienced nasal symptoms of allergic rhinitis during the pollen season (p<0.01-0.05). Baseline nasal lavage fluid levels of alpha2-macroglobulin and ECP were increased during the season (p<0.01-0.05) and were found to be well correlated (p<0.0001). Histamine produced concentration-dependent plasma exudation before and during the pollen season, but it was only during the pollen season that this caused an increase in the lavage fluid levels of ECP (p<0.05). These data suggest that exudation of plasma and increased tissue levels and output of eosinophil cationic protein characterize nasal mucosal inflammation in children with seasonal allergic rhinitis. The plasma exudation process in part may account for lumenal entry of eosinophil cationic protein molecules that have been released in mucosal tissue compartments. A combination of induced exudation and nasal lavage may improve the yield of important markers of inflammation in studies of nasal diseases.

Biomarkers↗

PubMed1995

Identification of transformed alpha 2-macroglobulin as a growth hormone-binding protein in human blood.

We have found that the human GH forms complexes with the purified proteinase inhibitor, alpha 2-macroglobulin. This inhibitor occurs in two different forms in human blood, known as native and transformed alpha 2-macroglobulin. It could be clearly demonstrated by chromatography and electrophoresis combined with autoradiography that the GH binds specifically to the transformed inhibitor, but not to the native protein. The binding was characterized as being mainly noncovalent to specific binding sites present only in the transformed inhibitor molecule. Binding analysis using antibody precipitation technique revealed two different classes of binding sites with dissociation constants of 0.49 +/- 0.12 and 61 +/- 8 mumol/L for high and low affinity binding sites, respectively. Distribution analysis of 125I-labeled GH in whole plasma suggested that the hormone is bound to different proteins: 1) to the high affinity GH-binding protein, and 2) to the low affinity GH-binding protein identified as transformed alpha 2-macroglobulin.

Chromatography, Gel↗

PubMed1978

The elimination in dogs of trypsin-alpha-macroglobulin complexes inactivated by the Kazal or the Kunitz inhibitor.

The elimination of trypsin-alpha-macroglobulin complexes and similar complexes with the trypsin inactivated by low-molecular weight inhibitor was studied in anesthetized dogs. The complex was inactivated either by the Kazal (pancreatic secretory trypsin inhibitor, PSTI) or the Kunitz inhibitor (Trasylol BE). The inhibitors were labelled with 125I and in the case of the trypsin-alpha-macroglobulin complex the trypsin was labelled with 125I. All of the inactivated complexes exhibited a half-life of about 5 min in the dog. The elimination in plasma was exponential until 80 - 85% of the initial dose was cleared in 30 min and nearly negligible thereafter as seen by radioactivity measurements. Simultaneously increasing amounts of dialyzable radioactive substances with a lower molecular weight than the inhibitors were recovered in the urine. No significant differences in the elimination of trypsin-alpha-macroglobulin complexes were detected in plasma or in the urine before and after inactivation with the Kazal inhibitor (PSTI) or the Kunitz inhibitor (Trasylol BE).

Animals↗

PubMed1983

Studies on the interaction between leukocyte elastase, antileukoproteinase and the plasma proteinase inhibitors alpha 1-proteinase inhibitor and alpha 2-macroglobulin.

The dominating inhibitor of leukocyte elastase in human respiratory tract secretions is a low molecular mass inhibitor, designated antileukoproteinase. An equimolar antileukoproteinase-elastase complex was produced and subjected to gel filtration after differing time intervals and was found to be stable. On addition to human serum, however, elastase dissociated from antileukoproteinase and formed a complex with alpha 1-proteinase inhibitor. A small amount of elastase was also found bound to alpha 2-macroglobulin. Antileukoproteinase was capable of inhibiting elastase bound to alpha 2-macroglobulin. This inhibition was more complete and more rapid when the alpha 2-macroglobulin-elastase complex was in a molar ratio of 1:1 than in a ratio of 1:2.

Blood Proteins↗

PubMed1982

Immunoreactive alpha 2-macroglobulin in rheumatoid synovial membrane.

alpha 2-Macroglobulin was demonstrated immunohistochemically in macrophage-like cells of rheumatoid arthritic synovial tissue. It is concluded that these intracellular deposits probably represent phagocytosed protease-alpha 2-macroglobulin complexes. A contributing local production of alpha 2-macroglobulin is, however, not excluded by the present findings.

Adult↗

PubMed1982

The elimination of alpha 2-macroglobulin complexes from the arthritic joint. A clinical study in rheumatoid arthritis.

A phagocytic uptake of labeled elastase-alpha 2-macroglobulin complexes by macrophage-like synovial lining cells was demonstrated in rheumatoid arthritics. The appearance and distribution of these phagocytically active cells were similar to those containing immunoreactive alpha 2-macroglobulin. It was concluded that these deposits represented phagocytosed alpha 2-macroglobulin complexes and that the elimination of complexes from the arthritic joint at least partly was effected via local phagocytosis.

Aged↗

PubMedDate not supplied

Alpha-2-macroglobulin levels in early respiratory distress syndrome.

The vasoactive products of uncontrolled protease activity can play an important role in the pathogenesis of respiratory distress syndrome in newborn infants. In this study alpha-2-macroglobulin, which has antiproteolytic activity, was studied in the first few hours of life in preterm infants with and without respiratory distress syndrome. Mean plasma alpha-2-macroglobulin levels were found to be similar in both groups. These findings implicated that alpha-2-macroglobulin has no significant role in the pathogenesis of respiratory distress syndrome.

Humans↗