Murinoglobulin, a novel protease inhibitor from murine plasma. Isolation, characterization, and comparison with murine alpha-macroglobulin and human alpha-2-macroglobulin

Activated Alpha-2 Macroglobulin Improves Insulin Response via LRP1 in Lipid-Loaded HL-1 Cardiomyocytes

Activated alpha-2 Macroglobulin (α₂M*) is specifically recognized by the cluster I/II of LRP1 (Low-density lipoprotein Receptor-related Protein-1). LRP1 is a scaffold protein for insulin receptor involved in the insulin-induced glucose transporter type 4 (GLUT4) translocation to plasma membrane and glucose uptake in different types of cells. Moreover, the cluster II of LRP1 plays a critical role in the internalization of atherogenic lipoproteins, such as aggregated Low-density Lipoproteins (aggLDL), promoting intracellular cholesteryl ester (CE) accumulation mainly in arterial intima and myocardium. The aggLDL uptake by LRP1 impairs GLUT4 traffic and the insulin response in cardiomyocytes. However, the link between CE accumulation, insulin action, and cardiac dysfunction are largely unknown. Here, we found that α₂M* increased GLUT4 expression on cell surface by Rab4, Rab8A, and Rab10-mediated recycling through PI₃K/Akt and MAPK/ERK signaling activation. Moreover, α₂M* enhanced the insulin response increasing insulin-induced glucose uptake rate in the myocardium under normal conditions. On the other hand, α₂M* blocked the intracellular CE accumulation, improved the insulin response and reduced cardiac damage in HL-1 cardiomyocytes exposed to aggLDL. In conclusion, α₂M* by its agonist action on LRP1, counteracts the deleterious effects of aggLDL in cardiomyocytes, which may have therapeutic implications in cardiovascular diseases associated with hypercholesterolemia.

Protein profiles in mucosal and systemic compartments in response to Vibrio cholerae in a mouse pulmonary infection model

We have recently shown that a mouse lung infection model resulting in acute pneumonia could be used for evaluating the protective immunity induced by mucosal vaccines against Vibrio cholerae. In order to gain insight and better understanding of the pathogenicity of V. cholerae infection, we identified and compared proteins induced by V. cholerae in nasal washes, bronchoalveolar lavages (BAL), and sera. Intranasal administration of V. cholerae increased the concentration of total proteins in nasal washes and BAL fluids, but not in sera. LTQ-Orbitrap hybrid Fourier transform mass spectrometry showed that cytoskeletal proteins, protease inhibitors and anti-inflammatory mediators were present in nasal washes from uninfected mice. The distinctly expressed proteins in nasal washes in response to V. cholerae mainly consisted of protease inhibitors, anti-inflammatory proteins, and anti-microbial proteins. A number of protease inhibitors and anti-inflammatory proteins were selectively expressed in BAL fluids from V. cholerae-infected mice, while cytoskeletal proteins and heat shock proteins were mainly observed in BAL fluids from uninfected mice. A large number of serum complements, protease inhibitors, and acute phase proteins were expressed in V. cholerae-infected mice. Collectively, these results suggest that intranasal administration of V. cholerae leading to acute pneumonia elicited alterations of protein profiles associated with immune homeostasis and host protection in both the mucosal and systemic compartments.

Transcriptomes of purified gastric ECL and parietal cells: identification of a novel pathway regulating acid secretion

The gastric entero-chromaffin-like (ECL) cell plays a key regulatory role in peripheral regulation of acid secretion due to the release of histamine that stimulates acid secretion by the parietal cell. Studies in intact animals, gastric glands, and isolated cells after short-term culture have shown expression of stimulatory CCK2 and PAC1 and inhibitory SST2 and Gal1 receptors as well as histidine decarboxylase. However, the pattern of its gene expression as a neuroendocrine cell has not been explored. Comparison of gene expression by 95% pure ECL cells obtained by density gradient, elutriation, and fluorescence-assisted cell sorting with isolates of the intact fundic gastric epithelium (i.e., "subtractive hybridization") identified a variety of additional expressed gene families characteristic of this neuroendocrine cell. These include genes 1) involved in neuropeptide synthesis and secretory vesicle exocytosis, 2) involved in control of inflammation, 3) implicated in healing of the epithelium, 4) encoding inhibitory Gi protein-coupled receptors, 5) playing a role in neuroendocrine regulation of food intake, and 6) encoding proteins likely involved in maintenance of circadian rhythm, in addition to the ECL cell-specific genes histidine decarboxylase and monoamine transporter. Particularly, the inhibitory apelin receptor gene, APJ, was highly expressed in the ECL cell preparation. Because parietal cells express apelin, immunohistochemical and functional studies showed that there is an inhibitory feed back loop between the parietal and ECL cell during gastrin stimulation, providing evidence for a novel pathway of downregulation of acid secretion due to interaction between these two cell types.

A novel protease inhibitor of the alpha2-macroglobulin family expressed in the human epidermis

In the course of a large scale analysis of late-expressed genes in the human epidermis, we identified a new member of the alpha(2)-macroglobulin (alpha2M) protease inhibitor family, A2ML1 (for alpha(2)-macroglobulin-like 1). Like A2M and PZP, A2ML1 is located on chromosome 12p13.31. A2ML1 encodes a protein of 1454 amino acids, which fits the characteristics of alpha2Ms: 1) strong conservation in amino acid sequence including most of cysteine positions with alpha2M; 2) a putative central bait domain; 3) a typical thiol ester sequence. Northern blot and reverse transcriptase-PCR studies revealed a single 5-kb A2ML1 mRNA, mainly in the epidermis granular keratinocytes. A2ML1 is also transcribed in placenta, thymus, and testis. By Western blot analysis, alpha2ML1 is detected as a monomeric, approximately 180-kDa protein in human epidermis. In vitro keratinocyte differentiation is associated with increased expression levels. By immunohistochemistry, alpha2ML1 was detected within keratinosomes in the granular layer of the epidermis, and as a secreted product in the extracellular space between the uppermost granular layer and the cornified layer. Recombinant alpha2ML1 displayed inhibitory activity toward chymotrypsin, papain, thermolysin, subtilisin A, and to a lesser extent, elastase but not trypsin. Incubation with chymotrypsin and the chymotrypsin-like kallikrein 7 protease indicated that alpha2ML1 binds covalently to these proteases, a feature shared with other members of the family. Therefore, alpha2ML1 is the first alpha2M family member detected in the epidermis. It may play an important role during desquamation by inhibiting extracellular proteases.

Identification and characterization of CPAMD8, a novel member of the complement 3/alpha2-macroglobulin family with a C-terminal Kazal domain

We have identified and characterized a novel member of the complement 3/alpha(2)-macroglobulin (C3/alpha(2)M) family named CPAMD8 (complement 3 and pregnancy zone protein-like, alpha2-macroglobulin domain-containing 8). The gene maps to chromosome 19p13.2-p13.3 and spans approximately 130 kb. The gene partially overlaps with the protease-activated receptor-4 (PAR4) gene in the reverse orientation. The cDNA consists of 40 exons ( approximately 6 kb) and encodes a protein of 1885 amino acids. Similar to other proteins in this family, CPAMD8 contains a signal sequence, an RXXR processing site, and a thioester motif. In addition, CPAMD8 has a Kazal-type serine proteinase inhibitor/follistatin-like domain at the C-terminus. The intact CPAMD8 protein generated by in vitro transcription and translation resolved as a single band of about 200 kDa on SDS-PAGE. RT-PCR and immunoblot assays showed that CPAMD8 is expressed in a number of human tissues, most abundantly in the kidney, brain, and testis and at lower levels in heart, liver, and small intestine. CPAMD8 is also expressed in several types of cells in culture, in which it is proteolytically processed into two chains of about 70 and 130 kDa. The Kazal domain of CPAMD8 binds to heparin, and subcellular fractionation shows that CPAMD8 is membrane associated via ionic interaction. In response to immune stimulants, CPAMD8 expression is markedly up-regulated in cells in culture. Thus, CPAMD8 may, like other members of the C3/alpha(2)M family, function in innate immunity but in a localized manner.

Vascular endothelial cell injury induced by Bothrops jararaca venom; non-significance of hemorrhagic metalloproteinase

To examine the effect of Bothrops jararaca venom and its major hemorrhagic metalloproteinase, jararafibrase I (JF I), on vascular endothelial cells, B. jararaca crude venom and JF I were infused intravenously into rabbits. The degree of endothelial cell injury was estimated from the plasma level of soluble thrombomodulin (TM). The fibrinogen level, prothrombin time (PT), JF I antigen level and macroglobulin activity of the plasma were also measured. The TM level was not increased even by a large quantity of JF I, while the crude venom caused an increase in TM level suggesting the occurrence of endothelial cell injury. No alterations of fibrinogen level and PT were noted with a high amount of JF I, and no systemic bleeding was observed. Macroglobulin, which is the main inhibitor of metalloproteinase in rabbit plasma, was not significantly reduced despite a high dose of JF I. The elevation of TM level in the rabbit plasma after infusion of crude venom was totally suppressed by pretreatment with heparin. These findings suggest that the endothelial cell injury caused by B. jararaca venom is not due to the hemorrhagic metalloproteinase but to the coagulating factors in the venom. Plasma macroglobulin appears to be efficient enough to neutralize the circulating hemorrhagic metalloproteinases inoculated by B. jararaca.

Serine proteinase inhibitor 3 and murinoglobulin I are potent inhibitors of neuropsin in adult mouse brain

Extracellular serine protease neuropsin (NP) is expressed in the forebrain limbic area of adult brain and is implicated in synaptic plasticity. We screened for endogenous NP inhibitors with recombinant NP (r-NP) from extracts of the hippocampus and the cerebral cortex in adult mouse brain. Two SDS-stable complexes were detected, and after their purification, peptide sequences were determined by amino acid sequencing and mass spectrometry, revealing that target molecules were serine proteinase inhibitor-3 (SPI3) and murinoglobulin I (MUG I). The addition of the recombinant SPI3 to r-NP resulted in an SDS-stable complex, and the complex formation followed bimolecular kinetics with an association rate constant of 3.4 +/- 0.22 x 10(6) M(-1) s(-1), showing that SPI3 was a slow, tight binding inhibitor of NP. In situ hybridization histochemistry showed that SPI3 mRNA was expressed in pyramidal neurons in the hippocampal CA1-CA3 subfields, as was NP mRNA. Alternatively, the addition of purified plasma MUG I to r-NP resulted in an SDS-stable complex, and MUG I inhibited degradation of fibronectin by r-NP to 24% at a r-NP/MUG I molar ratio of 1:2. Immunofluorescence histochemistry showed that MUG I localized in the hippocampal neurons. These findings indicate that SPI3 and MUG I serve to inactivate NP and control the level of NP in adult brain, respectively.

Comparative studies on the cysteine proteinase inhibitory capacity of mammalian blood

The inhibition of cysteine proteinase (papain) by human, bovine, horse, rabbit, guinea pig, rat, hamster, and mouse plasma, and pig, sheep, goat, and dog sera was investigated. The rat and mouse plasma and the pig serum showed such high inhibitory capacity as 813, 380, and 508%, respectively, of the human plasma. On the other hand, the horse, guinea pig, and rabbit plasma indicated 36, 40, and 54%, respectively, of the human plasma. A cysteine proteinase inhibitor (s) was separated from alpha-macroglobulin by Sephacryl S-300, and the inhibitory activity of all of the mammalian plasma/sera except for the guinea pig plasma appeared at around the 50-150-kDa region. The guinea pig plasma exhibited well-resolved two peaks of 100 and 200 kDa.

alpha2-macroglobulin- and murinoglobulin-1- deficient mice. A mouse model for acute pancreatitis

Mice deficient in either or both mouse alpha2-macroglobulin (MAM) and murinoglobulin-1 (MUG1) were generated and proved phenotypically normal under standard conditions. Acute pancreatitis was induced with a diet deficient in choline and methionine, supplemented with ethionine. The mortality was less than 25% in wild-type mice, as opposed to at least 56% in knockout mice, and was highest (70%) in MAM-/- mice, with earliest onset at 2 days. Plasma amylase and lipase levels were increased, but pancreatic tissue appeared histologically variable in individual mice. The clinical symptoms were most severe in MAM-/- mice and, surprisingly, were not aggravated in the double knockout mice, suggesting that the lack of proteinase inhibition capacity was not the major problem. Therefore, we analyzed the expression of 21 different cytokines and polypeptide factors in the pancreas of all experimental groups of mice. Interleukin-1-receptor antagonist mRNA was consistently induced by the diet in the pancreas of MAM-/- mice, and transforming growth factor-beta, tumor necrosis factor-alpha, tumor necrosis factor-beta, beta-lymphotoxin, and interferon-gamma mRNA levels were also increased. The data demonstrate the important role of alpha2-macroglobulin (A2M) in acute pancreatitis as both a proteinase inhibitor and a cytokine carrier. Mice deficient in MAM and/or MUG thus offer new experimental models for defining in vivo the role of the macroglobulins in pancreatitis and in other normal and pathological processes.

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

Binding of rat alpha 1-inhibitor-3-methylamine to the alpha 2-macroglobulin signaling receptor induces second messengers

Binding of receptor-recognized forms of tetrameric human alpha 2-macroglobulin (alpha 2M*) to a macrophage signaling receptor induces cAMP synthesis, increases in inositol 1,4,5-triphosphate (IP3) synthesis, and a concomitant rise in cytosolic free calcium ([Ca2+]i). The alpha 2M* signaling receptor is coupled to a pertussis-toxin insensitive G protein. Binding of alpha 2M* also occurs to the low density lipoprotein receptor-related protein/alpha 2M receptor (LRP/alpha 2MR), but this binding does not induce signal transduction. Rat alpha 1-inhibitor-3 (alpha 1I3) is a monomeric member of the alpha-macroglobulin/complement superfamily. Like alpha 2M, it can react with proteinases or methylamine which induces a conformational change causing activated alpha 1I3 to bind to LRP/alpha 2MR. We now report that alpha 1I3-methylamine binds to the macrophage alpha 2M* signaling receptor inducing a rapid rise in the synthesis of IP3 with a subsequent 1.5- to 3-fold rise in [Ca2+]i. alpha 1I3-methylamine binding to macrophages also caused a statistically significant elevation in cAMP. Native alpha 1I3, like alpha 2M, was unable to induce signal transduction. alpha 1I3 forms a complex with alpha 1-microglobulin, which has a distinct conformation from alpha 1I3 and is recognized by LRP/alpha 2MR. This complex also induces an increase in [Ca2+]i comparable to the effect of alpha 1I3-methylamine on macrophages. It is concluded that activation of alpha 1I3 by methylamine or binding of alpha 1-microglobulin causes similar conformational changes in the inhibitor, exposing the receptor recognition site for the alpha 2M* signaling receptor, as well as for LRP/alpha 2MR.

Targeted inactivation of the mouse alpha 2-macroglobulin gene

The mouse alpha 2-macroglobulin gene was inactivated in embryonic stem cells by homologous recombination. Liver alpha 2-macroglobulin mRNA and plasma protein was absent in homozygotes and reduced to 50% in heterozygotes. alpha 2-Macroglobulin-deficient mice were viable and produced normally sized litters with normal sex ratio over 3 generations. Characterization of adult homozygotes included diets with different fat content, treatments with endotoxin, bleomycin, carbon tetrachloride, and ethionine to test for immune system, lung, liver, and pancreas toxicity, respectively. Knock-out mice were more resistant to endotoxin but more sensitive to a choline-free diet supplemented with ethionine. Regulation of murinoglobulin mRNA expression during pregnancy was analyzed as a possible back-up mechanism for the deficiency in alpha 2-macroglobulin. In addition, expression of mRNA was studied, coding for alpha 2-macroglobulin receptor/lipoprotein receptor-related protein, low density lipoprotein receptor, and very low density lipoprotein receptor and for some common ligands, i.e. apolipoprotein E, lipoprotein lipase, and the 44-kDa heparin binding protein. Their differential regulation in the knock-out mice relative to C57B1 mice was evident and is discussed. The impressive 15-fold increase in maternal liver murinoglobulin mRNA at partum in the knock-out mice indicated increased consumption, compared to only 4-fold in normal mice. Thus, murinoglobulin appears as the major proteinase inhibitor around partum, obviously solicited to a much greater extend in alpha 2-macroglobulin-deficient mice.

Distribution of mRNA coding for alpha-2-macroglobulin, the murinoglobulins, the alpha-2-macroglobulin receptor and the alpha-2-macroglobulin receptor associated protein during mouse embryogenesis and in adult tissues

The distribution of mRNA coding for the members of the wide-spectrum proteinase scavenging system of the alpha-2-macroglobulin family was examined in the mouse: Alpha-2-macroglobulin (MAM), the murinoglobulins (MUG), the alpha-2-macroglobulin receptor (alpha 2MR) and the receptor associated protein, the heparin binding protein-44 (alpha 2MRAP/HBP-44), a component of unknown function. The results demonstrate that MAM is expressed in the mouse embryo exclusively in the liver and not before day 13 of gestation. MUG mRNA was never detected during embryogenesis. On the other hand, both the alpha 2MR and the alpha 2MRAP/HBP-44 messages were present throughout all embryonal stages examined. The distribution of the alpha 2MR mRNA was widespread in most tissues, with stronger signals observed in developing mouse brain, in whisker follicles and in the perifollicular mesenchyme, in lung, liver, kidney, intestine and placenta. The alpha 2MRAP/HBP-44 mRNA was detected predominantly in brain, lung, liver, kidney and placenta. Interestingly, within each tissue the cellular distribution of the alpha 2MR and alpha 2MRAP/HBP-44 mRNA was quite different with the most remarkable extremes observed in kidney and in placenta. The implication of these observations for receptor expression and function are discussed. Northern analysis of adult tissues extended these observations: major signals for MAM and MUG were seen only in liver, while the expression of the alpha 2MR and the alpha 2MRAP/HBP-44 was widespread with highest levels of the 15-kb alpha 2MR mRNA in liver. Kidney was the most abundant source of alpha 2MRAP/HBP-44 mRNA with the 1.8- and 3.6-kb mRNAs, derived from the same gene by alternative mRNA splicing, present in nearly constant ratios in most tissues, except in testis. The notable absence of expression of MAM in the first half of gestation indicates that during this period the receptor is scavenging for proteinases complexed to MAM derived from the maternal circulation or is being used for endocytosis of the other documented ligands, such as plasminogen activator complexes or apolipoprotein E-containing lipoprotein particles.

The primary sequence and the subunit structure of mouse alpha-2-macroglobulin, deduced from protein sequencing of the isolated subunits and from molecular cloning of the cDNA

Mouse plasma alpha-2-macroglobulin (m alpha 2M) was isolated and the N-terminal amino-acid sequences determined after separation of the 165-kDa and 35-kDa subunits. These sequences were compared to the protein sequence predicted by the cDNA, which was cloned from a mouse liver library and sequenced. From these data it is evident that both subunits are encoded by one mRNA of approximately 5 kb expressed predominantly in liver. The smaller subunit, with the N-terminal sequence DLSSSDLT, comprises the C-terminal 257 residues of m alpha 2M and is derived from a single-chain precursor probably by proteolytic processing at an arginine residue in the sequence PTRDLSS. Analysis of the predicted protein further showed all the salient features of a proteinase inhibitor of the macroglobulin family: a bait region that deviates from all known sequences in this family, a very conserved internal thiolester site and conserved cysteine residues and putative N-glycosylation sites. The synthesis of m alpha 2M in adult liver was demonstrated by Northern blotting and in fetal liver by in-situ hybridization. Transient transfection of COS cells with the cDNA under control of a viral promoter demonstrated the secretion and partial processing of m alpha 2M in the culture medium. In plasma the level of m alpha 2M was found to be stable as expected for the murine counterpart of human plasma alpha-2-macroglobulin. The possibilities of using the mouse as a genetic model to study this proteinase inhibitor in vivo are discussed.

Ultrastructure of alpha 2-macroglobulins

New results concerning the ultrastructure of human alpha 2-macroglobulin (alpha 2M) molecules are presented in connection and comparison with the historical, the current and our own most recent, even unpublished results on the structure and function of alpha 2M and related proteins. The electron microscopic approach uses classical negative staining, combined with the new imaging mode "Electron Energy Loss Spectroscopy", which provides unusual contrast, resolution and readability of the electron micrographs. Immuno- and cryoelectron microscopy, as well as image processing has provided new data necessary to the building of tentative 3D models of the molecule. A model for the native tetrameric alpha 2M is described for the first time, and tries to explain and gather the various observations, sometimes contradictory, taken from different laboratories. A revised version for a model of the methylamine- and proteinase-transformed forms of alpha 2M is also shown. The probable positions of the bait regions and the thiol esters are given on both models. We confirm that alpha 2M is a twin trap capable of inactivating one or two proteinases by partial immobilization. Preliminary results on the production of crystals of alpha 2M-chymotrypsin complexes are also presented. A critical analysis of our models is presented in comparison with others. The technical limitations reached with some techniques and some possible extensions of future research in the field are also presented.

Intracellular modifications of rat alpha 1 inhibitor3. Formation of disulphides, internal thiolester and sulphation

alpha 1 Inhibitor3 (alpha 1I3) is a monomeric protease inhibitor of about 190 kDa which is secreted by rodent hepatocytes. We have studied intracellular modifications of this protein in [35]methionine-labelled rat hepatocytes by pulse/chase experiments followed by immunoprecipitation and gel electrophoresis under reducing and nonreducing conditions. Directly after the pulse, most of the unreduced alpha 1I3 migrated faster than the reduced form, indicating that disulphide bridges are formed during or shortly after synthesis yielding a compact structure. With increasing chase time however, an increasing portion of the unreduced alpha 1I3 migrated with a mobility lower than that of the reduced protein, half-maximal conversion occurring after about 10 min. This finding suggests that alpha 1I3 undergoes a conformational change in the endoplasmic reticulum, possibly becoming more elongated. During 10-30 min of chase, the protein acquired the capacity to undergo autolytic cleavage upon heating, a property due to the existence of an internal thiolester bond [Howard, J. B., Vermeulen, M. & Swenson, R. P. (1980) J. Biol. Chem. 255, 3820-3823; Esnard, F., Gutman, N., El Moujahed, A. & Gauthier, F. (1985) FEBS Lett. 182, 125-129]. Analysis by subcellular fractionation indicated that this bond is formed in the endoplasmic reticulum. Finally, we show that secreted alpha 1I3 is sulphated, presumably at Tyr618.

Purification, characterization, and acute phase response of plasma alpha-1-antiproteinase in the hamster, Mesacricetus auratus

1. alpha-1-Antiproteinase (also called alpha-1-antitrypsin or alpha-1-proteinase inhibitor) with a molecular mass of 60 kDa was purified to apparent homogeneity from hamster plasma. 2. It inhibited elastase, chymotrypsin and trypsin, but did not significantly affect pancreatic kallikrein, plasma kallikrein or plasmin. 3. It has the same N-terminal heptapeptide sequence as that of rat alpha-1-antiproteinase. 4. Its plasma level decreased after injection of bacterial lipopolysaccharide.

Sertoli cell synthesizes and secretes a protease inhibitor, alpha 2-macroglobulin

The mechanism by which the seminiferous epithelium limits the damaging effects of proteases that are released from degenerating late spermatids does not depend upon protease inhibitors in the systemic circulation since these proteins are excluded from the seminiferous tubule by the blood-testis barrier. The purpose of this study was to identify the major protease inhibitor of the testis and determine its cellular origin. Sertoli cells, the major epithelial component of the seminiferous epithelium, release a protease inhibitor, testicular alpha 2-macroglobulin, in vitro. Immunoprecipitation using [35S]methionine and a monospecific polyclonal antibody prepared against purified testicular alpha 2-macroglobulin establishes that this protein is actively synthesized and secreted by Sertoli cells. Measurements of immunoreactive protease inhibitors in tubular and rete testis fluids collected by micropuncture suggest that alpha 2-macroglobulin rather than alpha 1-antitrypsin is the major protease inhibitor in the seminiferous tubules in vivo. The ability of alpha 2-macroglobulin to inactivate proteases and growth factors such as TGF-beta by a common mechanism suggests that this protein may have a dual function in the testis.

Electron microscopic demonstration of a common structural motif in human complement factor C3 and rat alpha 1-inhibitor 3 (murinoglobulin)

Electron microscopy of two homologous giant proteins revealed that complement factor C3 and alpha 1-inhibitor 3 have a common structural motif of a semicircularly bent string 18-20 nm long with two or three bumps indicating globular domains. C3 had a structure similar to the letter C with a small but distinct hole in the center. alpha 1-Inhibitor 3 was a more complete ring sometimes ajar at one corner. When the latter was treated with a proteinase, it became slightly flattened and adopted a squarish C-shape.

In vivo catabolism of heparin cofactor II and its complex with thrombin: evidence for a common receptor-mediated clearance pathway for three serine proteinase inhibitors

The plasma clearance of 125I-labeled human heparin cofactor II and its complex with thrombin was studied in mice to determine whether a specific mechanism exists for the catabolism of the inhibitor-proteinase complex. Initial studies demonstrated that murine plasma contains a heparin cofactor II-like inhibitor as shown by the presence of a dermatan sulfate-sensitive thrombin inhibitor. Human heparin cofactor II cleared from the circulation of mice with an apparent half-life of 80 min while heparin cofactor II-thrombin complexes cleared with an apparent half-life of only 10 min. The specificity of the clearance mechanism was investigated by clearance competition studies involving coinjection of excess unlabeled heparin cofactor II-alpha-thrombin, antithrombin III-alpha-thrombin, or alpha 1-proteinase inhibitor-elastase, and by tissue distribution studies. The results demonstrated that the clearance of 125I-labeled heparin cofactor II-alpha-thrombin is a receptor-mediated process, and that the same hepatocyte receptor system recognizes complexes containing heparin cofactor II, antithrombin III, and alpha 1-proteinase inhibitor.

Amino acid sequence of a 32-residue region around the thiol ester site in duck ovostatin

To obtain the amino acid sequence at the thiol ester site in duck ovostatin for comparisons with other proteins, the native ovostatin was labeled with 14CH3NH2 at the reactive thiol ester site. The modified protein was reduced, carboxymethylated, and digested with trypsin. 14C-labeled peptides isolated by gel filtration with Sephadex G-50, ion-exchange chromatography on DEAE-cellulose and HPLC were subjected to automated sequence analysis, and the stretch of 32 amino acid residues containing the 14CH3NH2-binding site were determined. A comparison of this sequence with the corresponding sequences in alpha 2-macroglobulin, and complement components C3 and C4 revealed 72, 31 and 34% homology, respectively. The results indicate that ovostatin is a close relative to plasma alpha-macroglobulins and may share a common ancestor with C3 and C4.

Open quaternary structure of the hagfish proteinase inhibitor with similar properties to human alpha-2-macroglobulin

A homologous protein to human plasma alpha-2-macroglobulin (alpha-2-M) was purified from the blood plasma of hagfish (Eptatretus buergeri) and its structure and function were studied. The hagfish protein inhibited several proteinases and its inhibitory activity was blocked with methylamine as in the case of human alpha-2-M. The molecular weight and sedimentation coefficient of the hagfish inhibitor were 390,000 +/- 20,000 and 11.0 S, respectively, as determined by sedimentation studies. The frictional ratio calculated from these parameters was 1.75. The Stokes radius estimated from HPLC gel chromatography was 8.8-8.9 nm, which was similar to that of human alpha-2-M despite the fact that the hagfish inhibitor was only one-half as large as human alpha-2-M in molecular weight. The hagfish inhibitor was expected to be more asymmetric and/or more hydrated than the human inhibitor. The electron micrographs of the negatively stained hagfish inhibitor showed that it had an open, rectangular quaternary structure of 15 +/- 1.5 X 19 +/- 2 nm in which two semiglobular units were located at the two shorter sides with a gap of 8 +/- 1 nm in width. Each semiglobular unit had an approximate width of 5 +/- 0.5 nm. The thickness of the unit was estimated to be 3 to 3.5 nm from the result of fixed-angle shadowing experiments. Although the two semiglobular units must be connected by some structure, very little material could be seen between them. Such an open quaternary structure may explain the high frictional ratio and large Stokes radius of this protein. The structural change of the inhibitor after reaction with proteinases or methylamine could be detected by electron microscopy and gel chromatography.

Guinea pig plasma murinoglobulin. Purification and some properties

Murinoglobulin, a newly identified mouse plasma protein resembling alpha-macroglobulins [Saito, A. & Sinohara, H. (1985) J. Biol. Chem. 260, 775-781], was also found in guinea pig plasma, and purified to homogeneity. Guinea pig murinoglobulin consisted of a single 180-kDa polypeptide chain containing about 18% carbohydrate. It inhibited the proteolytic activities of trypsin and thermolysin towards Remazol brilliant blue hide powder, but stimulated the amidolytic activities of trypsin and Staphylococcus aureus V8 protease towards small synthetic substrates. Heat treatment of murinoglobulin completely abolished the former activities, but partially retained the latter activities. The ability of guinea pig murinoglobulin to inhibit the proteolysis was much weaker than that of the mouse homologue. On interaction with trypsin, murinoglobulin underwent cleavage of one susceptible bond with concomitant unmasking of one thiol group. Methylamine treatment also released one thiol group per molecule.

Isolation and characterization of influenza C virus inhibitor in rat serum

Two hemagglutination inhibitors for influenza C virus were isolated from pooled sera of normal rats by sequential chromatography on Blue Sepharose CL 6B, Ultrogel AcA 22, and DEAE-cellulose. The two inhibitors were identified as alpha 1-macroglobulin and murinoglobulin by comparison with the authentic samples. These inhibitors abolished the hemagglutination by influenza C virus strains but did not affect the hemagglutination by influenza A and B virus strains. Hemagglutination inhibition activity of both inhibitors was completely destroyed by incubation with influenza C virus at 37 degrees C but not with the other types of influenza virus, indicating that the inhibitors are specific for influenza C virus. The inhibitory activity was also destroyed by incubation with neuraminidase from Arthrobacter ureafaciens. By contrast, no activity was lost after treatment with neuraminidase from Vibrio cholerae. These results suggest that the sialic acid residue(s) which is cleavable by the former neuraminidase but not by the latter is essential for the hemagglutination inhibition. The two inhibitors were inactivated by treating with sodium hydroxide and methylamine but not with sodium metaperiodate.

Isolation and characterization of influenza C virus inhibitors in rat serum

Two inhibitors against haemagglutination by influenza C virus were isolated from pooled sera of normal rats by sequential chromatography on Blue Sepharose CL 6B, Ultrogel AcA 2, and DEAE-cellulose. The two inhibitors were identified as alpha 1-macroglobulin and murinoglobulin by comparison with the authentic samples. These inhibitors abolished the haemagglutination by influenza C virus strains but did not affect the haemagglutination by influenza A and B virus strains. Haemagglutination inhibition activity of both inhibitors was completely destroyed by incubation with neuraminidase from Arthrobacter ureafaciens. By contrast, no activity was lost after treatment with neuraminidase from Vibrio cholerae. These results suggest that the sialic acid residue(s) which is excised by the former neuraminidase but not by the latter is essential for the haemagglutination inhibition. The two inhibitors were inactivated by treating with sodium hydroxide and methylamine but not with sodium metaperiodate.