Sequence and acute phase regulation of rat alpha 1-inhibitor III messenger RNA

Neuroproteomics and Systems Biology Approach to Identify Temporal Biomarker Changes Post Experimental Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) represents a critical health problem of which diagnosis, management, and treatment remain challenging. TBI is a contributing factor in approximately one-third of all injury-related deaths in the United States. The Centers for Disease Control and Prevention estimate that 1.7 million people suffer a TBI in the United States annually. Efforts continue to focus on elucidating the complex molecular mechanisms underlying TBI pathophysiology and defining sensitive and specific biomarkers that can aid in improving patient management and care. Recently, the area of neuroproteomics–systems biology is proving to be a prominent tool in biomarker discovery for central nervous system injury and other neurological diseases. In this work, we employed the controlled cortical impact (CCI) model of experimental TBI in rat model to assess the temporal–global proteome changes after acute (1 day) and for the first time, subacute (7 days), post-injury time frame using the established cation–anion exchange chromatography-1D SDS gel electrophoresis LC–MS/MS platform for protein separation combined with discrete systems biology analyses to identify temporal biomarker changes related to this rat TBI model. Rather than focusing on any one individual molecular entity, we used in silico systems biology approach to understand the global dynamics that govern proteins that are differentially altered post-injury. In addition, gene ontology analysis of the proteomic data was conducted in order to categorize the proteins by molecular function, biological process, and cellular localization. Results show alterations in several proteins related to inflammatory responses and oxidative stress in both acute (1 day) and subacute (7 days) periods post-TBI. Moreover, results suggest a differential upregulation of neuroprotective proteins at 7 days post-CCI involved in cellular functions such as neurite growth, regeneration, and axonal guidance. Our study is among the first to assess temporal neuroproteome changes in the CCI model. Data presented here unveil potential neural biomarkers and therapeutic targets that could be used for diagnosis, for treatment and, most importantly, for temporal prognostic assessment following brain injury. Of interest, this work relies on in silico bioinformatics approach to draw its conclusion; further work is conducted for functional studies to validate and confirm the omics data obtained.

Microdialysis Sampling from Wound Fluids Enables Quantitative Assessment of Cytokines, Proteins, and Metabolites Reveals Bone Defect-Specific Molecular Profiles

Bone healing involves a variety of different cell types and biological processes. Although certain key molecules have been identified, the molecular interactions of the healing progress are not completely understood. Moreover, a clinical routine for predicting the quality of bone healing after a fracture in an early phase is missing. This is mainly due to a lack of techniques to comprehensively screen for cytokines, growth factors and metabolites at their local site of action. Since all soluble molecules of interest are present in the fracture hematoma, its in-depth assessment could reveal potential markers for the monitoring of bone healing. Here, we describe an approach for sampling and quantification of cytokines and metabolites by using microdialysis, combined with solid phase extractions of proteins from wound fluids. By using a control group with an isolated soft tissue wound, we could reveal several bone defect-specific molecular features. In bone defect dialysates the neutrophil chemoattractants CXCL1, CXCL2 and CXCL3 were quantified with either a higher or earlier response compared to dialysate from soft tissue wound. Moreover, by analyzing downstream adaptions of the cells on protein level and focusing on early immune response, several proteins involved in the immune cell migration and activity could be identified to be specific for the bone defect group, e.g. immune modulators, proteases and their corresponding inhibitors. Additionally, the metabolite screening revealed different profiles between the bone defect group and the control group. In summary, we identified potential biomarkers to indicate imbalanced healing progress on all levels of analysis.

Biological effects of static electric field: Plasma/serum proteome analysis of rats

The external static electric field (SEF) of man-made origin brings to the substantially increased SEF background in a human environment the biological activity of which is a moot question. The paper reports on rats blood plasma/serum proteome modifications by means of 1D polyacrilamide gel electrophoresis and clotting process alterations after the short- and long-term SEF exposures of 200 kV/m. The results indicate decrease of fast α1 and α2 globular proteins in plasma coinciding with clotting acceleration after the short-term SEF, and attenuation of clotting-dependent proteome modifications reflected with incomplete coagulation after the long-term SEF exposure. Increased lysozyme activity in serum unlike plasma was observed after both SEF exposures. Applied model of the high-voltage SEF environment indicates dependence of biological systems functioning on the external SEF.

Functionalized self-assembling peptide hydrogel enhance maintenance of hepatocyte activity in vitro

There is a major challenge in maintaining functional hepatocytes in vivo as these cells rapidly lose their metabolic properties in culture. In this work we have developed a bioengineered platform that replaces the use of the collagen I--in the traditional culture sandwich technique--by a defined extracellular matrix analogue, the self-assembling peptide hydrogel RAD16-I functionalized with biologically active motifs. Thus, after examining side by side the two culture systems we have found that in both cases hepatocytes acquired similar parenchymal morphology, presence of functional bile canaliculi structures, CYP3A2 induction by dexamethasone, urea production, secretion of proteins such as apolipoprotein (class A1, E, J), alpha(1)-microglobulin, alpha(1)-macroglobulin, retinol binding protein, fibronectin, alpha(1)-inhibitor III and biotin-dependent carboxylases. Interestingly, by assessing in more detail some other hepatic markers, one of the functionalized matrix analogues--carrying the 67 kD laminin receptor ligand--enhanced the gene expression of albumin, HNF4-alpha, MDR2 and tyrosine aminotransferase. We conclude that the use of a synthetic culture system with designed matrix functionalization has the advantage in controlling specific cellular responses.

Transcuprein is a macroglobulin regulated by copper and iron availability

Transcuprein is a high-affinity copper carrier in the plasma that is involved in the initial distribution of copper entering the blood from the digestive tract. To identify and obtain cDNA for this protein, it was purified from rat plasma by size exclusion and copper-chelate affinity chromatography, and amino acid sequences were obtained. These revealed a 190-kDa glycosylated protein identified as the macroglobulin alpha(1)-inhibitor III, the main macroglobulin of rodent blood plasma. Albumin (65 kDa) copurified in variable amounts and was concluded to be a contaminant (although it can transiently bind the macroglobulin). The main macroglobulin in human blood plasma (alpha(2)-macroglobulin), which is homologous to alpha(1)-inhibitor III, also bound copper tightly. Expression of alpha(1)I3 (transcuprein) mRNA by the liver was examined in rats with and without copper deficiency, using quantitative polymerase chain reaction methodology and Northern blot analysis. Protein expression was examined by Western blotting. Deficient rats with 40% less ceruloplasmin oxidase activity and liver copper concentrations expressed about twice as much alpha(1)I3 mRNA, but circulating levels of transcuprein did not differ. Iron deficiency, which increased liver copper concentrations by threefold, reduced transcuprein mRNA expression and circulating levels of transcuprein relative to what occurred in rats with normal or excess iron. We conclude that transcupreins are specific macroglobulins that not only carry zinc but also carry transport copper in the blood, and that their expression can be modulated by copper and iron availability.

Substance P induces localization of MIF/alpha1-inhibitor-3 complexes to umbrella cells via paracellular transit through the urothelium in the rat bladder

BACKGROUND

Macrophage migration inhibitory factor (MIF) is released into the intraluminal fluid during bladder inflammation in the rat complexed to alpha1-inhibitor-3 (A1-I3; a rodent proteinase inhibitor in the alpha-macroglobulin family). The location of A1-I3 in the bladder had not been investigated. Therefore, we examined the location of A1-I3 and MIF/A1-I3 complexes in the bladder and changes due to experimental inflammation.

METHODS

Anesthetized male rats had bladders removed with no treatment (intact) or were injected with Substance P (SP; s.c.; saline vehicle). After one hour intraluminal fluid was removed, bladder was excised and MIF and A1-I3 levels were determined using ELISA and/or western-blotting. MIF co-immunoprecipitation determined MIF/A1-I3 complexes in the bladder. Bladder sections were immunostained for A1-I3 and MIF/A1-I3.

RESULTS

A1-I3 immunostaining was observed in interstitial spaces throughout the bladder (including submucosa) but not urothelium in intact and saline-treated rats. RT-PCR showed that the bladder does not synthesize A1-I3, therefore, A1-I3 in the interstitial space of the bladder must be plasma derived. In SP-treated rats, A1-I3 in the bladder increased and A1-I3 was observed traversing through the urothelium. Umbrella cells that do not show MIF and/or A1-I3 immunostaining in intact or saline-treated rats, showed co-localization of MIF and A1-I3 after SP-treatment. Western blotting demonstrated that in the bladder MIF formed non-covalent interactions and also binds covalently to A1-I3 to form high molecular weight MIF/A1-I3 complexes (170, 130 and 75-kDa, respectively, verified by co-immunoprecipitation). SP-induced inflammation selectively reduced 170-kDa MIF/A1-I3 in the bladder while increasing 170 and 130-kDa MIF/A1-I3 in the intraluminal fluid.

CONCLUSION

A1-I3 and MIF/A1-I3 complexes are resident in bladder interstitium. During SP-induced inflammation, MIF/A1-I3 complexes are released from the bladder into the lumen. Binding of MIF/A1-I3 complexes to urothelial cells during inflammation suggests these complexes participate in the inflammatory reaction through activation of receptors for MIF and/or for A1-I3.

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 of genes specific to “oval cells” in the rat 2-acetylaminofluorene/partial hepatectomy model

Under certain conditions liver regeneration can be accomplished by hepatic progenitor cells ("oval cells"). So far, only few factors have been identified to be uniquely regulated by the "oval cell" compartment. Using macroarray analysis in a rat model of oval cell proliferation (treatment with 2-acetylaminofluorene and partial hepatectomy, AAF + PH), we identified 12 differentially expressed genes compared to appropriate control models (AAF treatment and sham operation or AAF treatment alone). Further analysis in models of normal liver regeneration (ordinary PH) and acute phase response (turpentine oil-treated rats) revealed that three out of 12 genes (thymidine kinase 1, Jun-D and ADP-ribosylation factor 4) were not affected by the hepatic acute phase reaction but similarly overexpressed in both "oval cell"-dependant and normal liver regeneration. We characterized Jun-D and ADP-ribosylation factors as novel factors upregulated in oval cells and in non-parenchymal liver cells of normally regenerating livers. However, two out of 12 differentially expressed genes were specifically expressed in oval cells: ras-related protein Rab-3b and Ear-2. On protein level, Rab-3b was increased in total liver homogenates and demonstrated only in clusters of oval cells. We postulate that Ear-2 and Rab-3b may represent novel regulatory factors specifically activated in "oval cells".

Localization of carbohydrate attachment sites and disulfide bridges in limulus alpha 2-macroglobulin. Evidence for two forms differing primarily in their bait region sequences

The primary structure determination of the dimeric invertebrate alpha(2)-macroglobulin (alpha(2)M) from Limulus polyphemus has been completed by determining its sites of glycosylation and disulfide bridge pattern. Of seven potential glycosylation sites for N-linked glycosylation, six (Asn(275), Asn(307), Asn(866), Asn(896), Asn(1089), and Asn(1145)) carry common glucosamine-based carbohydrates groups, whereas one (Asn(80)) carries a carbohydrate chain containing both glucosamine and galactosamine. Nine disulfide bridges, which are homologues with bridges in human alpha(2)M, have been identified (Cys(228)-Cys(269), Cys(456)-Cys(580), Cys(612)-Cys(799), Cys(657)-Cys(707), Cys(849)-Cys(876), Cys(874)-Cys(910), Cys(946)-Cys(1328), Cys(1104)-Cys(1155), and Cys(1362)-Cys(1475)). In addition to these bridges, Limulus alpha(2)M contains three unique bridges that connect Cys(361) and Cys(382), Cys(1370) and Cys(1374), respectively, and Cys(719) in one subunit with the same residue in the other subunit of the dimer. The latter bridge forms the only interchain disulfide bridge in Limulus alpha(2)M. The location of this bridge within the bait region is discussed and compared with other alpha-macroglobulins. Several peptides identified in the course of determining the disulfide bridge pattern provided evidence for the existence of two forms of Limulus alpha(2)M. The two forms have a high degree of sequence identity, but they differ extensively in large parts of their bait regions suggesting that they have different inhibitory spectra. The two forms (Limulus alpha(2)M-1 and -2) are most likely present in an approximately 2:1 ratio in the hemolymph of each animal, and they can be partially separated on a Mono Q column at pH 7.4 by applying a shallow gradient of NaCl.

New member of the trefoil factor family of proteins is an alpha-macroglobulin protease inhibitor

The amino acid sequence of the monomeric alpha-macroglobulin (alphaM) from the American bullfrog, Rana catesbiana, was determined. The mature protein consisted of 1469 amino acid residues and shared sequence identity with other members of the alphaM family of protein. The central portion of the frog monomeric alphaM contained Cys residues positioned analogously to the Cys residues in human alpha(2)-macroglobulin (alpha(2)M), known to be involved in disulfide bridges. Additionally, the frog monomeric alphaM contained six Cys residues in a approximately 60 residue COOH-terminal extension not present in previously characterized alphaMs. The spacing of the Cys residues and the overall sequence identity of this COOH-terminal extension were consistent with a trefoil motif. This is the first time a member of the trefoil factor family has been identified in the circulatory system. The "bait region" was located between Arg(675)-Lys(685) and contained mainly basic amino acid residues. The COOH-terminal receptor-binding domain was not exposed prior to proteolysis of this highly susceptible region. The proximity of the receptor-binding and trefoil domains implied that the trefoil domain is similarly concealed before bait region cleavage.

Monitoring the effects of drug treatment in rat models of disease by serum protein analysis

In this review we list from literature investigations on rat serum proteins using electrophoretic techniques in connection with drug testing. From our own research work, we provide annotated two-dimensional maps of rat serum proteins under control and experimental conditions. Emphasis is on species-specific components and on the effects of acute and chronic inflammation. We discuss our project of structural proteomics on rat serum as a minimally invasive approach to pharmacological investigation, and we outline a typical experimental plan for drug testing according to the above guidelines. We then report in detail on the results of our trials of anti-inflammatory drugs on adjuvant arthritis, an animal model of disease resembling in many aspects human rheumatoid arthritis. We demonstrate a correlation between biochemical parameters and therapeutic findings and outline the advantages of the chosen methodological approach, which proved also sensitive in revealing "side effects" of the test drugs. In an appendix we describe our experimental protocol when performing two-dimensional electrophoresis of rat serum.

A high affinity binding site for the polypyrimidine tract binding protein (PTB) is located in the 5'-untranslated region of the rat proteinase alpha1-inhibitor 3 variant I gene

As a first step towards understanding the mechanism underlying the differential gene expression of the two variants of the rat proteinase-inhibitor alpha1-inhibitor 3 (alpha1-I3) corresponding genomic clones were isolated. The 100% similarity between the sequence of one genomic clone and that of the alpha1-13 variant I cDNA strongly suggested that its 5'-sequence represented the upstream region of the corresponding gene. Several putative cis-regulatory elements were identified as well as a polypyrimidine tract located between the transcription start site of the alpha1-I3 variant I mRNA and the AUG codon. The polypyrimidine tract functions as a positive cis-element in a heterologous promoter. By electrophoretic mobility shift assays (EMSA) we have shown that a GST (glutathione S-transferase) fusion of the rat polypyrimidine tract binding protein (PTB) has a high affinity for the pyrimidine-rich sense strand but not for the complementary sequence of the 5'-untranslated region of the alpha1-I3 variant I gene.

Proteins of rat serum: III. Gender-related differences in protein concentration under baseline conditions and upon experimental inflammation as evaluated by two-dimensional electrophoresis

We have previously described the major components of rat serum (Electrophoresis 1998, 19, 1484-1492 and 1493-1500). In this report we examine sex-related differences in protein concentrations, both in control animals and upon experimentally induced inflammation. Under baseline conditions approximately one third of the spots resolved in serum by two-dimensional electrophoresis (2-DE) are expressed at levels > or =25% higher in female rats than in male rats and a further 10% at levels > or =25% lower. Inflammation increases the expression of the positive acute-phase reactants: hemopexin, ceruloplasmin, alpha1-antitrypsin (all approximately 2-fold), C-reactive protein (3- to 5-fold), serine protease inhibitor-3 (4- to 5-fold), thiostatin (> 5-fold in females, >20-fold in males), clusterin, orosomucoid, haptoglobin chains and alpha2-macroglobulin. The baseline level of the last four markers is below the detection limit, hence no percent increase can be computed. Conversely, negative acute-phase reactants are reduced on inflammation: alpha1-inhibitor III, alpha2-HS-glycoprotein, kallikrein-binding protein and transthyretin (all reduced to between 1/2 to 1/3 of the baseline levels), retinol-binding protein (to about 1/2 to 1/4) and albumin (to 2/3). Except for thiostatin, the changes in acute-phase protein levels are similar in male and female rats.

Inhibition of a snake venom hemorrhagic metalloproteinase by human and rat alpha-macroglobulins

Jararafibrase I is a hemorrhagic metalloproteinase purified from Bothrops jararaca venom, which induces local hemorrhage by degrading the basement membrane components. The present study was undertaken to investigate the inhibition of jararafibrase I by human and rat serum proteinase inhibitors. The proteolytic activity of jararafibrase I was completely inhibited by human and rat sera. In particular, rat serum displayed a greater inhibitory capacity. The inhibitory capacities of both sera were dependent on alpha-macroglobulins. SDS-PAGE analysis revealed that jararafibrase I formed complexes with alpha-macroglobulins that were present in normal sera. The proteolytic activity of jararafibrase I was completely inhibited by alpha1-macroglobulin and murinoglobulin in rat serum, and by human alpha2-macroglobulin. The inhibition molar ratios of alpha-macroglobulin/jararafibrase I were 1.5 for rat alpha1-macroglobulin and human alpha2-macroglobulin, and 2.4 for rat murinoglobulin. SDS-PAGE under reducing conditions demonstrated that the bait region of human alpha2-macroglobulin and rat murinoglobulin was cleaved by jararafibrase I. The bait region cleavage sites were identified as being situated at the 696Arg-697Leu peptide bond in human alpha2-macroglobulin, and at the 686Ala-687Val peptide bond in rat murinoglobulin.

Crystal structure of the receptor-binding domain of alpha 2-macroglobulin

BACKGROUND

The large plasma proteinase inhibitors of the alpha 2-macroglobulin superfamily inhibit proteinases by capturing them within a central cavity of the inhibitor molecule. After reaction with the proteinase, the alpha-macroglobulin-proteinase complex binds to the alpha-macroglobulin receptor, present in the liver and other tissues, and becomes endocytosed and rapidly removed from the circulation. The complex binds to the receptor via recognition sites located on a separate domain of approximately 138 residues positioned at the C terminus of the alpha-macroglobulin subunit.

RESULTS

The crystal structure of the receptor-binding domain of bovine alpha 2-macroglobulin (bRBD) has been determined at a resolution of 1.9 A. The domain primarily comprises a nine-strand beta structure with a jelly-roll topology, but also contains two small alpha helices.

CONCLUSIONS

The surface patch responsible for receptor recognition is thought to involve residues located on one of the two alpha helices of the bRBD as well as residues in two of the beta strands. Located on this alpha helix are two lysine residues that are important for receptor binding. The structure of bRBD is very similar to the approximately 100-residue C-terminal domain of factor XIII, a transglutaminase from the blood coagulation system.

Critical role of asparagine 1065 of human alpha2-macroglobulin in formation and reactivity of the thiol ester

It has been shown that the relative reaction preference of the C4 thiol ester toward oxygen and nitrogen nucleophiles upon activation by proteinase depends on whether residue 1106 is aspartate or histidine (Dodds, A. W., Ren, X.-D., Willis, A. C., and Law, S. K. A. (1996) Nature 379, 177-179). To determine if the equivalent residue in the related thiol ester-containing protein human alpha2-macroglobulin (alpha2M), asparagine 1065, plays a similar role, we have expressed and characterized four alpha2M variants in which this asparagine has been replaced by aspartate, alanine, histidine, or lysine. The change from asparagine resulted in an altered ability to form the thiol ester. This ranged from failure to form the thiol ester (Asn --> Asp) to a maximum extent of formation of about 50% (Asn --> Ala). For the three variants that were able to form the thiol ester, the rates of thiol ester cleavage by a given amine were found to be different from one another and slower in nearly all cases than plasma alpha2M, but with the same relative reactivity of methylamine > ethylamine > ammonia. The rate of conformational change that follows cleavage of thiol esters in a functional half-molecule was also found to differ between the variants and to be slower than plasma alpha2M. TNS emission spectra indicated that the conformations of the transformed variants differed measurably from transformed plasma alpha2M. These findings suggest that residue 1065 plays a critical role in human alpha2M, for formation of the thiol ester, for its subsequent reaction with nucleophiles, and for the conformational change induced by this reaction. By analogy with C4, where this residue influences the nucleophile preference through direct interaction with the thiol ester, residue 1065 in alpha2M is expected to be located in or very close to the thiol ester region in alpha2M.

Molecular cloning of Limulus alpha 2-macroglobulin

The American horseshoe crab Limulus polyphemus contains alpha 2-macroglobulin (alpha 2M) in the hemolymph plasma and hemocytes. alpha 2M from Limulus shows many of the typical characteristics of mammalian alpha 2M, including the presence of an internal thiol-ester, reactivity with a diversity of endopeptidases, a unique proteinase-trapping mechanism, and reactivity with the mammalian alpha 2M receptor. Additionally, Limulus alpha 2M has the unique property that it regulates the limulin-based hemolytic system of the plasma. A cDNA encoding Limulus alpha 2M has been obtained from a hemocyte cDNA library. The open reading frame encodes an N-terminal signal sequence of 25 amino acid residues and a mature protein of 1482 residues. The entire amino acid sequence is similar to those of the mammalian alpha 2Ms (28-29% identity) and contains common features found in mammalian alpha 2Ms. a bait region, an internal thiol-ester site, and a receptor-binding domain. However, the N-terminal portion (positions 24-105) has no sequence similarity with those of mammalian alpha 2Ms, and it is structurally related to that of the human complement factor C8 chain, consistent with a role for Limulus alpha 2M in host defense. The component sugar analysis of Limulus alpha 2M showed the existence of a complex type of oligosaccharide chain similar to those of mammalian alpha 2M. However, unlike mammalian alpha 2M, no sialic acid was detected in Limulus alpha 2M and it contained approximately 3 mol/mol N-acetylgalactosamine, suggesting the presence of O-linked sugar chains, which have not been found in mammalian alpha 2M. Expression of alpha 2M was detected in hemocytes, but not in hepatopancreas, heart, stomach, intestine, coxal gland, brain and skeletal muscle. Furthermore, immunoblotting of large and small granules of the hemocytes with antiserum against alpha 2M indicated the presence of the alpha 2M in large granules. Trypsin-treated Limulus alpha 2M, but not the native alpha 2M, displaced methylamine-treated human 125I-alpha 2M from the human alpha 2M receptor with a Kd of 30 nM, suggesting conservation of the proteinase-clearance mechanisms between mammalian and arthropod evolutionary lineages.

Identification of residues in alpha-macroglobulins important for binding to the alpha2-macroglobulin receptor/Low density lipoprotein receptor-related protein

Variants of the receptor binding domain of both human alpha2-macroglobulin and the corresponding domain of hen egg white ovomacroglobulin have been expressed in Escherichia coli and refolded in vitro. Competition experiments with methylamine-treated alpha2-macroglobulin for binding to the multifunctional alpha2-macroglobulin receptor identify two Lys residues (residues 1370 and 1374 in human alpha2-macroglobulin) spaced by three amino acid residues as crucial for receptor binding. From this result and mutational evidence from other ligands for the alpha2-macroglobulin receptor, a tentative sequence motif for receptor binding is proposed.

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.

Accelerated evolution in inhibitor domains of porcine elafin family members

Through the analysis of the porcine gene encoding the elastase inhibitor elafin, we demonstrated that there are at least three closely related members of the elafin family, and their genes have arisen by accelerated evolution. A porcine genomic DNA library was screened with a previously cloned human elafin cDNA probe, and several positive clones were obtained that can be distinguished by a combination of restriction enzymes. Sequence analysis of these clones revealed the presence of three homologous members whose genes, all consisting of three exons and two introns, are almost identical except the exon 2 sequences encoding the inhibitor domain called "WAP motif"; the intron sequences are related to each other with sequence similarities of 93-98%, whereas the exon 2 sequences exhibited only 60-77% similarities among the three members. The extreme divergence in the exon 2 sequences compared to the highly conserved intron sequences may be generated by accelerated mutations confined in a short stretch of the genes following recent duplication events of a single ancestral gene. An RNase protection assay indicated that the messages of the elafin family members are abundantly expressed in the trachea and intestine, suggesting that the most likely selective forces for the accelerated evolution are extrinsic proteinases produced by invasive microorganisms.

The reaction mechanism of the internal thioester in the human complement component C4

A key step in the elimination of pathogens from the body is the covalent binding of complement proteins C3 and C4 to their surfaces. Proteolytic activation of these proteins results in a conformational change, and an internal thioester is exposed which reacts with amino or hydroxyl groups on the target surface to form amide or ester bonds, or is hydrolysed. We report here that the binding of the human C4A isotype involves a direct reaction between amino-nucleophiles and the thioester. A two-step mechanism is used by the C4B isotype. The histidine at position 1,106(aspartic acid in C4A) first attacks the thioester to form an acyl-imidazole intermediate. The released thiol then acts as a base to catalyse the transfer of the acyl group to amino- and hydroxyl-nucleophiles, including water.

Posttranslational folding of alpha 1-inhibitor 3. Evidence for a compaction process

alpha 1-inhibitor 3 (alpha 1 I3) is a rodent-specific proteinase inhibitor of about 190 kDa belonging to the alpha 2-macroglobulin family. It consists of five globular domains, three of which are connected by disulfide bridges, and contains an intramolecular thiol ester which can react with attacking proteinases. To explore the folding of newly synthesized alpha 1 I3, we have used rat hepatocytes and pulsechase experiments. In one of the analyses, the radiolabeled protein was isolated from cell lysates by immunoprecipitation and its Asp-Pro bonds cleaved by treatment with formic acid. The size of the major fragment, as assessed by electrophoresis under nonreducing conditions, was found to increase from 100 to 150 kDa upon the chasing. This result, together with knowledge of the positions of the cleavage sites and the disulfide arrangement, indicates that one of the interdomain disulfide bonds is formed after the synthesis of the polypeptide. Analysis of the same material by limited proteolysis and by velocity centrifugation showed that the folded regions became larger and that the protein became more compact; the thiol ester was found to be formed after these conformational changes. These results suggest that the domains of alpha 1 I3 are only partially developed directly after the synthesis of the polypeptide and that they acquire their final structure as the protein condenses and the domains interact with one another.

Small-angle scattering study of alpha 1 inhibitor III from rat blood plasma

The alpha 1 proteinase inhibitor III from rat blood plasma, homologous to the alpha 2-macroglobulin family of proteins, has been studied in solution using small-angle scattering of X-rays and of neutrons: the radius of gyration, Rg, was found to be 4.5 nm, and the largest distance within the molecule, Dmax = 14 nm. When the inhibitor reacts with chymotrypsin or methylamine, the resulting derivatives yield slightly higher Rg-values, 4.7 and 4.85 nm, respectively. The data of the native protein are consistent with a model, the projection of which resembles the letter V and which is formed by the two identical halves of an elliptic cylinder with semi-axes of 2.1 and 5.5 nm and a length of 11 nm. This elliptic cylinder model also explained the scattering from the monomeric complement proteins C3 and C4, as well as that from the monomers of the dimeric and tetrameric alpha 2-macroglobulin family of proteins (Osterberg, R., et al. (1991), Biochemistry 30, 7873-7878). Due to the conformational change occurring when the thiol ester bond is split, the cleft in the V-form seems to be closed; and as a result, the models of the chymotrypsin and methylamine derivatives are more compact than that of the native protein.

Dynamic regulation of intact and C-terminal truncated insulin receptor phosphorylation in permeabilized cells

Using digitonin-permeabilized Chinese hamster ovary (CHO) cells that were transfected with intact human insulin receptors (CHO/HIRc cells), we examined insulin receptor phosphorylation and dephosphorylation using pulse-chase techniques. Insulin activated receptor autophosphorylation on tyrosyl residues to a level severalfold over basal, reaching maximal levels after 2, 5, and 10 min of stimulation at 34, 18, and 6 degrees C, respectively. Phosphopeptide analysis revealed that the triply phosphorylated form of the 1146-kinase domain of the insulin receptor was the major species, which is characteristic of the fully active tyrosine kinase function. The dephosphorylation reaction was time- and temperature-dependent with t1/2 values of 0.67 and 2 min at 18 and 6 degrees C, respectively. Vanadate completely inhibited dephosphorylation. Under similar permeabilization conditions when compared with CHO/HIRc cells, CHO/delta CT cells (CHO cells overexpressing a mutated form of the receptor with a 43 amino acid deletion at the C-terminus) stimulated with insulin exhibited larger increases in receptor autophosphorylation levels and in tyrosine kinase activity toward a synthetic peptide substrate; the rate of CHO/delta CT receptor dephosphorylation was not reduced. There was near-complete absence of insulin receptor substrate 1 (IRS-1) in the cell ghosts after permeabilization. We therefore examined the pattern of tyrosine phosphorylation and dephosphorylation of residual cellular proteins in permeabilized CHO/HIRc cells by Western blot analysis. In addition to the 95-kDa receptor beta-subunit, we detected the phosphorylation of two glycoproteins which included the commonly found 120-kDa protein and a novel 195-kDa protein whose dephosphorylation rate is slower than that of receptor beta-subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid sequence of hen ovomacroglobulin (ovostatin) deduced from cloned cDNA

The complete amino acid sequence of the hen ovomacroglobulin (ovostatin) subunit has been determined from cDNA and partial peptide sequence analysis. Ovostatin is a tetrameric member of the alpha-macroglobulin (alpha M) family of proteins. The 4715 nt ovostatin cDNA encodes a 36- or a 16-residue signal peptide and a 1437-residue mature protein (162.2 kDa). At the protein level the overall score of sequence identity between ovostatin and mammalian alpha Ms is 39-44%, indicating an early divergence from the line leading to the mammalian alpha Ms. Ovostatin contains 56 mol glucosamine per mol subunit, and 12 of its Asn-residues are likely to be N-glycosylated. Including carbohydrate, the size of the ovostatin subunit is approx. 185 kDa. The ovostatin subunit is predicted to contain 12 intrachain disulfide bridges, and two subunits are predicted to be disulfide bound by two interchain bridges. One Cys residue may be unpaired or participate in dimer formation as a third interchain disulfide bridge. Ovostatin contains a unique 40-residue bait region. In contrast to other alpha Ms, ovostatin contains no internal beta-Cys-gamma-Glu thiol ester, as a result of a Cys-to-Asn replacement (TGC or TGT to AAT), but the Gln-moiety of the thiol ester is preserved. By comparing the sequences of the receptor binding domain in alpha Ms with the corresponding region of ovostatin possible determinants for receptor recognition of mammalian alpha Ms are proposed.

Distribution of alpha 2-macroglobulin and alpha 1-acid glycoprotein mRNA shows regional specialization in rat decidua

In situ hybridization histochemistry was used to detect mRNA coding for the plasma proteins alpha 1-acid glycoprotein and alpha 2-macroglobulin in the rat decidua during the period when the chorioallantoic placenta is established. It was found that alpha 1-acid glycoprotein mRNA was localized to a subpopulation of decidual cells predominantly found in the decidua capsularis but extending into the decidua basalis at later times. The highest levels of alpha 2-macroglobulin mRNA were found in the decidua basalis where there was some overlap with regions containing alpha 1-acid glycoprotein mRNA. No alpha 2-macroglobulin mRNA could be found in the inner part of the decidua capsularis where the highest levels of alpha 1-acid glycoprotein mRNA were found. However, a thin outer layer of compressed stromal cells, adjacent to the myometrium expressed the alpha 2-macroglobulin gene which surrounded the cells containing alpha 1-acid glycoprotein mRNA. This distribution of alpha 2-macroglobulin mRNA is consistent with the hypothesis that the protein is produced locally to prevent non-specific proteolysis which may otherwise result from catabolic processes involved in tissue remodelling. The function of alpha 1-acid glycoprotein is unknown but this protein is also likely to be involved in the maintenance of homeostasis during the period when contact between maternal and fetal systems is being established within the chorioallantoic placenta.

Hydrocortisone induces the synthesis of alpha 2-macroglobulin by rat mammary myoepithelial cells

The effects of lactogenic hormones on protein secretion by 25.5-G4.2.3 cells, a rat mammary myoepithelial cell line immortalised with a temperature-sensitive T-antigen, were investigated. Insulin, prolactin, estradiol and progesterone had no effect but hydrocortisone induced the secretion of two proteins with molecular masses of 175 kDa (p175) and 146 kDa (p146), 10-30-fold and 5-fold respectively. The induction of p175 and p146 synthesis by hydrocortisone was greater at 39.5 degrees C than at 33 degrees C reflecting the increased differentiation of 25.5-G4.2.3 cells at the higher temperature. Rat mammary epithelial cells did not synthesise p175. After addition of hydrocortisone to 25.5-G4.2.3 cells, there was a lag phase of 10 h before the synthesis of p175 was induced. Half-maximal induction of p175 synthesis required a hydrocortisone concentration of 0.5 microM. p175 was identified as alpha 2-macroglobulin by N-terminal amino-acid sequence determination and immunoprecipitation with a specific antibody. Hydrocortisone induced a 5-kb alpha 2-macroglobulin-specific mRNA transcript in 25.5-G4.2.3 cells. Myoepithelial cells are responsible for synthesising the basement membrane around the rapidly expanding mammary alveoli during pregnancy. Myoepithelial cells also secrete metalloproteinases which are probably involved in turnover of the basement membrane. We suggest that increased levels of hydrocortisone during pregnancy induce the synthesis of alpha 2-macroglobulin, which is believed to be a potent inhibitor of metalloproteinases, by rat mammary myoepithelial cells to reduce proteolytic degradation of the basement membrane.

Differential expression of the transfected liver-specific alpha 1-inhibitor III gene in normal hepatocytes and hepatoma cells in culture

Normal and malignant hepatocytes were transfected during log phase culture with a nested series of DNA plasmids containing 5'-flanking regions of the rat liver-specific acute phase plasma proteinase alpha 1-inhibitor III (alpha 1 I3) gene. Under these conditions, luciferase reporter gene expression in primary adult rat and mouse hepatocytes was 10-fold higher than luciferase expression in hepatoma lines (human HepG2 and Hep3B; rat FAZA). Optimal expression in primary rat hepatocytes required regions stretching 2214 bp 5'-upstream of the transcription start site. Shorter 5'-flanking sequences were optimal for expression in hepatoma cells (-1025 and -186 bp for rat and human lines, respectively) and primary mouse hepatocytes (-225 bp). In contrast, regions from -186 to -225 bp drove luciferase expression in primary rat hepatocytes, but only 20-75% of optimal levels. Qualitative differences were unaccounted for by non-equivalent uptake of plasmid DNA, suggesting that tissue specific gene expression is regulated differently in normal and malignant cells, and with apparent species specificity.

Differential rates of glycoprotein secretion by isolated rat hepatocytes studied in terms of concanavalin A binding

Using a concanavalin-A-based method which respects cell function, we have shown that the kinetics of glycoprotein secretion appear to depend on the nature of the oligosaccharide moiety. In 37 degrees C pulse/chase experiments using freshly isolated normal rat hepatocytes, we found that except for transferrin, whose rate of secretion was independent of its concanavalin A reactivity, the secretion of the concanavalin-A-retained forms of alpha 1 acid glycoprotein, T-kininogen, alpha 1 protease inhibitor and alpha 1 inhibitor III was slower than that of the concanavalin-A-non-retained forms. When hepatocytes were incubated at 20 degrees C, secretion was blocked with the accumulation of mainly endoglycosidase-H-sensitive forms. The secretion kinetics of the concanavalin-A-differentiated forms were still different when the temperature was shifted back to 37 degrees C. The divergence between the secretion rates of the concanavalin-A-differentiated forms would appear to be due to a late event in intracellular protein trafficking, which may depend on the sugar content and/or the number of carbohydrate chains of the glycoproteins.

Differential regulation of the two mRNA species of the rodent negative acute phase protein alpha 1-inhibitor 3

Screening of two rat liver cDNA libraries, one of which was constructed using an alpha 1-inhibitor 3 (alpha 1-13) specific primer, yielded overlapping cDNA clones which correspond to the full length cDNA for alpha 1-13 mRNA. On the basis of sequence microheterogeneity existing throughout the cDNA sequence we identified two alpha 1-13 mRNA species whose sequences are so grossly different in their bait regions that the amino acid homology therein is only 30%. Using oligonucleotide probes derived from their respective bait regions we investigated the regulation of the two alpha 1 I3 mRNA species and demonstrated that only one of them, alpha 1-I3 variant I, is regulated pretranslationally following experimentally induced inflammation.

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.

Primary structure of pregnancy zone protein. Molecular cloning of a full-length PZP cDNA clone by the polymerase chain reaction

A full-length cDNA clone of the human pregnancy zone protein (PZP) was cloned from the hepatocellular carcinoma cell line Hep3B. Based on the exon sequences of the PZP gene (Devriendt et al. (1989) Gene 81, 325-334; Marynen et al., unpublished data), primer pairs were designed to amplify six overlapping fragments of the PZP cDNA. The obtained cDNA is 4609 bp long and contains an open reading frame coding for 1482 amino acids, including a signal peptide of 25 amino acid residues. Comparison with the published partial PZP amino acid sequence (Sottrup-Jensen et al. (1984) Proc. Natl. Acad. Sci. USA 81, 7353-7357) and the PZP genomic sequences confirmed the identity as a PZP cDNA. 71% of the corresponding amino acid residues in PZP and human alpha 2-macroglobulin (alpha 2M) are identical and all cysteine residues are conserved. A typical internal thiol ester site and a bait domain were identified. A Pro/Thr polymorphism was identified at amino acid position 1180, and an A/G nucleotide polymorphism at bp 4097.

Sequence similarity between alpha 2-macroglobulin from the horseshoe crab, Limulus polyphemus, and proteins of the alpha 2-macroglobulin family from mammals

1. Purified alpha 2-macroglobulin (alpha 2M) from the American horseshoe crab, Limulus polyphemus was cleaved with trypsin and 20 of the tryptic peptides were sequenced and compared with the sequences of human alpha 2M, rat alpha 1M, alpha 2M, and alpha 1-inhibitor 3, and human complement proteins C3 and C4. 2. Ten of the peptides (233 residues), including that containing the thiol ester site, could be aligned unambiguously with stretches in mammalian alpha 2M, with a degree of identity greater than 30%. 3. The 12-residue thiol ester-containing peptide of Limulus alpha 2M showed 67% identity with the same stretch of human alpha 2M.

A cluster of alpha 2-macroglobulin-related genes (alpha 2 M) on human chromosome 12p: cloning of the pregnancy-zone protein gene and an alpha 2M pseudogene

The characterization of two alpha 2-macroglobulin (alpha 2M)-related genomic clones, isolated from two human genomic libraries by use of alpha 2M cDNA [Kan et al., Proc. Natl. Acad. Sci. USA 82 (1985) 2282-2286] as a probe, is reported. Sequence comparison of the clone EPZP6 with the human alpha 2M cDNA revealed the presence of five exons with the proper splice signals. Alignment of the corresponding amino acid (aa) sequence of these exons with the published partial pregnancy-zone protein (PZP) aa sequence (Sottrup-Jensen et al., Proc. Natl. Acad. Sci. USA 81 (1984) 7353-7357] showed a perfect match, thereby identifying EPZP6 as a PZP genomic clone. The clone MPAM16 showed a considerable degree of sequence conservation when compared to the human alpha 2M cDNA sequence, and several putative exons were identified. However, a frame-shift mutation leading to a premature stop codon was found in the coding sequence, classifying this gene as an alpha 2M pseudogene. Human alpha 2M, PZP and the related pseudogene were mapped to the human chromosome 12p12-13, with the help of gene-specific probes and in situ hybridization. This result was confirmed in Southern-blot experiments with DNA from a human-Ltk- mouse somatic-cell hybrid containing only a human isochromosome 12p in a mouse background.

Amino acid sequence around the thiolester of alpha 2-macroglobulin from plasma of the crayfish, Pacifastacus leniusculus

Alpha 2-Macroglobulin (alpha 2 M) was isolated from plasma of the freshwater crayfish, Pacifastacus leniusculus, using ultracentrifugation, ion-exchange chromatography and gel filtration techniques. The Pacifastacus alpha 2 M molecule (P alpha 2 M) was radio-actively labeled in the thiol ester structure with iodo [14C]acetic acid in the presence of methylamine. After reduction and carboxymethylation of the protein, it was digested with trypsin. A 14C-labeled tryptic peptide was sequenced and contained an amino acid sequence very similar to other known thiol ester sequences from human alpha 2 M and related proteins. The N-terminal sequence of P alpha 2 M was related to that recently determined for lobster alpha 2 M [(1987) J. Biol. Chem. 262, 14606-14611].

Tumor-associated expression of a serum protein, termed aX protein (alpha 1-inhibitor III), and its mRNA in rat liver

A cDNA clone bearing the mRNA sequence for rat alpha X protein (alpha X) was isolated from a cDNA library constructed from rat liver mRNA. The nucleotide sequence of alpha X protein cDNA showed 97% homology with that of the 3'-proximal domain of alpha 1-inhibitor III cDNA. The amino acid sequence deduced from that of alpha X cDNA also exhibited high homology with the primary sequences of alpha 1-inhibitor III and alpha 2-macroglobulin. K231 ascites hepatoma cells were transplanted into male ACI rats, and the level of alpha X mRNA in the liver of the tumor-bearing rats was determined by RNA blot hybridization with the cDNA probe. The serum concentration of alpha X decreased to about 30% of the control value with time after transplantation. The amount of alpha X mRNA in the liver of tumor-bearing rats was proportional to the serum concentration of alpha X. The serum concentrations of transferrin and albumin in the tumor-bearing rats also decreased to about 30 and 60% of the normal levels, respectively. However, the amounts of mRNAs for transferrin and albumin in the liver of tumor-bearing rats did not decrease. These findings indicate that the mechanisms of tumor-associated decrease in the concentrations of different serum proteins in tumor-bearing rats may differ.

Structure of the rat alpha 2-macroglobulin-coding gene

Rat alpha 2-macroglobulin (alpha 2M) is an acute-phase protein, i.e., produced upon tissue inflammation. Genomic DNA clones covering the entire sequence of the alpha 2M gene were isolated and characterized by restriction mapping. Southern blotting and (partial) DNA sequencing. The rat alpha 2M gene is approx. 50 kb in length and consists of 36 exons ranging in size from 21 to 229 bp. Two functional domains, a bait region and a thiol ester site, are encoded by the exon 18 and 24, respectively. Several possible regulatory signals such as a TPA-inducible enhancer core, an identifier sequence, purine-pyrimidine alternative stretches and viral enhancer core sequences were identified. Several genomic DNA clones which cross-hybridized with the alpha 2M cDNA probe were also identified. Sequence analysis showed that they possessed sequences identical to a part of the rat alpha 1-inhibitor III cDNA and that they had a strikingly similar exon organization to the alpha 2M gene.