Impaired conversion of procollagen to collagen by fibroblasts and bone treated with tunicamycin, an inhibitor of protein glycosylation

Glycosylation Modulates the Structure and Functions of Collagen: A Review

Collagens are fundamental constituents of the extracellular matrix and are the most abundant proteins in mammals. Collagens belong to the family of fibrous or fiber-forming proteins that self-assemble into fibrils that define their mechanical properties and biological functions. Up to now, 28 members of the collagen superfamily have been recognized. Collagen biosynthesis occurs in the endoplasmic reticulum, where specific post-translational modification-glycosylation-is also carried out. The glycosylation of collagens is very specific and adds β-d-galactopyranose and β-d-Glcp-(1→2)-d-Galp disaccharide through β-O-linkage to hydroxylysine. Several glycosyltransferases, namely COLGALT1, COLGALT2, LH3, and PGGHG glucosidase, were associated the with glycosylation of collagens, and recently, the crystal structure of LH3 has been solved. Although not fully understood, it is clear that the glycosylation of collagens influences collagen secretion and the alignment of collagen fibrils. A growing body of evidence also associates the glycosylation of collagen with its functions and various human diseases. Recent progress in understanding collagen glycosylation allows for the exploitation of its therapeutic potential and the discovery of new agents. This review will discuss the relevant contributions to understanding the glycosylation of collagens. Then, glycosyltransferases involved in collagen glycosylation, their structure, and catalytic mechanism will be surveyed. Furthermore, the involvement of glycosylation in collagen functions and collagen glycosylation-related diseases will be discussed.

Arsenic trioxide promotes ERK1/2-mediated phosphorylation and degradation of BIMEL to attenuate apoptosis in BEAS-2B cells

Inorganic arsenic is highly toxic, widely distributed in the human environment and may result in multisystem diseases and several types of cancers. The BCL-2-interacting mediator of cell death protein (BIM) is a key modulator of the intrinsic apoptosis pathway. Interestingly, in the present study, we found that arsenic trioxide (As₂O₃) decreased BIM_EL levels in human bronchial epithelial cell line BEAS-2B and increased BIM_EL levels in human lung carcinoma cell line A549 and mouse Sertoli cell line TM4. Mechanismly, the 26S proteasome inhibitors MG132 and bortezomib could effectively inhibit BIM_EL degradation induced by As₂O₃ in BEAS-2B cells. As₂O₃ activated extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways, but only the ERK1/2 MAPK inhibitor PD98059 blocked BIM_EL degradation induced by As₂O₃. Furthermore, As₂O₃ induced-phosphorylation of BIM_EL at multiple sites was inhibited by ERK1/2 MAPK inhibitor PD98059. Inhibition of As₂O₃-induced ERK1/2 MAPK phosphorylation increased the levels of BIM_EL and cleaved-caspase-3 proteins and decreased BEAS-2B cell viability. As₂O₃ also markedly mitigated tunicamycin-induced apoptosis of BEAS-2B cells by increasing ERK1/2 phosphorylation and BIM_EL degradation. Our results suggest that As₂O₃-induced activation of the ERK1/2 MAPK pathway increases phosphorylation of BIM_EL and promotes BIM_EL degradation, thereby alleviating the role of apoptosis in As₂O₃-induced cell death. This study provides new insights into how to maintain the survival of BEAS-2B cells before malignant transformation induced by high doses of As₂O₃.

Insights into auto-S-fatty acylation: targets, druggability, and inhibitors

Posttranslational S-fatty acylation (or S-palmitoylation) modulates protein localization and functions, and has been implicated in neurological, metabolic, and infectious diseases, and cancers. Auto-S-fatty acylation involves reactive cysteine residues in the proteins which directly react with fatty acyl-CoA through thioester transfer reactions, and is the first step in some palmitoyl acyltransferase (PAT)-mediated catalysis reactions. In addition, many structural proteins, transcription factors and adaptor proteins might possess such "enzyme-like" activities and undergo auto-S-fatty acylation upon fatty acyl-CoA binding. Auto-S-fatty acylated proteins represent a new class of potential drug targets, which often harbor lipid-binding hydrophobic pockets and reactive cysteine residues, providing potential binding sites for covalent and non-covalent modulators. Therefore, targeting auto-S-fatty acylation could be a promising avenue to pharmacologically intervene in important cellular signaling pathways. Here, we summarize the recent progress in understanding the regulation and functions of auto-S-fatty acylation in cell signaling and diseases. We highlight the druggability of auto-S-fatty acylated proteins, including PATs and other proteins, with potential in silico and rationalized drug design approaches. We also highlight structural analysis and examples of currently known small molecules targeting auto-S-fatty acylation, to gain insights into targeting this class of proteins, and to expand the "druggable" proteome.

Elucidation of brefeldin A-induced ER and Golgi stress responses in Neuro2a cells

Brefeldin A (BFA) disrupts the structure of the Golgi apparatus to trigger ER stress signaling pathways. On the other hand, treatment with BFA induces the activation of CREB3, the protein structure of which is similar to that of ATF6. In this study, we established Neuro2a cells in which three different transcription factors, namely, ATF4, ATF3 and CREB3, were deficient using the CRISPR/Cas9 approach, and we investigated the BFA-induced ER and Golgi stress response in these cells. BFA treatment rapidly induced ATF4, ATF3, Herp and GADD153 protein expression in Neuro2a cells. ATF4-deficient Neuro2a cells exhibited significantly decreased mRNA and protein expression of ATF3 and Herp but not GADD153; however, cells deficient in ATF3 exhibited minimal effects on GADD34, GADD153 and Herp expression. The cleavage of CREB3 in Neuro2a cells was triggered by BFA; however, the expression of several ER and Golgi stress-related factors was hardly influenced by the CREB3 deficiency in these Neuro2a cells. This study shows that CREB3 minimally associates with typical ER stress-inducible responses in Neuro2a cells. Therefore, identification and characterization of the downstream transcriptional targets of CREB3 is required to clarify not only Golgi stress response but also its relationship with ER stress signaling pathways.

Myo-inositol oxygenase accentuates renal tubular injury initiated by endoplasmic reticulum stress

Besides oxidant stress, endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of various metabolic disorders affecting the kidney. These two forms of stresses are not mutually exclusive to each other and may operate by a feedback loop in worsening the cellular injury. To attest to this contention, studies were performed to assess whether in such a setting, there is worsening of tubulointerstitial injury. We employed tunicamycin as a model of ER stress and used tubular cells and mice overexpressing myo-inositol oxygenase (MIOX), an enzyme involved in glycolytic events with excessive generation of ROS. Concomitant treatment of tunicamycin and transfection of cells with MIOX-pcDNA led to a marked generation of ROS, which was reduced by MIOX-siRNA. Likewise, an accentuated expression of ER stress sensors, GRP78, XBP1, and CHOP, was observed, which was reduced with MIOX-siRNA. These sensors were markedly elevated in MIOX-TG mice compared with WT treated with tunicamycin. This was accompanied with marked deterioration of tubular morphology, along with impairment of renal functions. Interestingly, minimal damage and elevation of ER stressors was observed in MIOX-KO mice. Downstream events that were more adversely affected in MIOX-TG mice included accentuated expression of proapoptogenic proteins, proinflammatory cytokines, and extracellular matrix constituents, although expression of these molecules was unaffected in MIOX-KO mice. Also, their tunicamycin-induced accentuated expression in tubular cells was notably reduced with MIOX-siRNA. These studies suggest that the biology of MIOX-induced oxidant stress and tunicamycin-induced ER stress are interlinked, and both of the events may feed into each other to amplify the tubulointerstitial injury.

A novel splice variant of the protein tyrosine phosphatase PTPRJ that encodes for a soluble protein involved in angiogenesis

PTPRJ is a receptor protein tyrosine phosphatase with tumor suppressor activity. Very little is known about the role of PTPRJ ectodomain, although recently both physiological and synthetic PTPRJ ligands have been identified. A putative shorter spliced variant, coding for a 539 aa protein corresponding to the extracellular N-terminus of PTPRJ, is reported in several databases but, currently, no further information is available.

Here, we confirmed that the PTPRJ short isoform (named sPTPRJ) is a soluble protein secreted into the supernatant of both endothelial and tumor cells. Like PTPRJ, also sPTPRJ undergoes post-translational modifications such as glycosylation, as assessed by sPTPRJ immunoprecipitation. To characterize its functional activity, we performed an endothelial cell tube formation assay and a wound healing assay on HUVEC cells overexpressing sPTPRJ and we found that sPTPRJ has a proangiogenic activity. We also showed that sPTPRJ expression down-regulates endothelial adhesion molecules, that is a hallmark of proangiogenic activity. Moreover, sPTPRJ mRNA levels in human high-grade glioma, one of the most angiogenic tumors, are higher in tumor samples compared to controls. Further studies will be helpful not only to clarify the way sPTPRJ works but also to supply clues to circumvent its activity in cancer therapy.

Tunicamycin-induced endoplasmic reticulum stress reduces in vitro subpopulation and invasion of CD44+/CD24- phenotype breast cancer stem cells

Tunicamycin is an inhibitor of glycosylation that disturbs protein folding machinery in eukaryotic cells. Tunicamycin causes accumulation of unfolded proteins in cell endoplasmic reticulum (ER) and induces ER stress. ER stress is an essential mechanism for cellular homeostasis has role in cell death via reprogramming of protein processing, regulation of autophagy and apoptosis. In this study we show effect of tunicamycin on subpopulation and invasion of CD44+/CD24- MCF7 breast cancer stem cells. CD44+/CD24- cells were isolated from MCF7 cell line by fluorescence activated cell sorting (FACS) and treated with tunicamycin. ER stress was monitored by evaluation of X-box binding protein 1(XBP-1) mRNA splicing, cleaved activating transcription factor 6 (ATF6) nuclear translocation and CCAAT/enhancer-binding protein homologous protein (CHOP) expression. CD44+/CD24- subpopulation was analyzed using flow cytometry. Invasion was investigated by scratch assay, trypan blue staining, 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation and in vitro migration assays. Increased level of spliced XBP-1, ATF6 nuclear translocation and CHOP protein expression were detected in CD44+/CD24- and original MCF7 cells treated with tunicamycin. Also, a significant decline in CD44+/CD24- cell subpopulation was determined in the cells treated with tunicamycin. The results also showed inhibited invasion, increased cell death, suppressed proliferation and reduced migration in the CD44+/CD24- and CD44+/CD24- rich MCF7 cell culture, under effect of tunicamycin. Our results indicate that CD44+/CD24- phenotype MCF7 cells are susceptible to tunicamycin. The results showed that tunicamycin-induced ER stress suppresses CD44+/CD24- phenotype cell subpopulation and in vitro invasion and accelerates tumorosphore formation. These results suggest that tunicamycin-induced ER stress inhibits CD44+/CD24- phenotype MCF7 breast cancer stem cells. We conclude that using ER-targeting chemicals like tunicamycin is an interesting approach to target breast cancer stem cells inside tumor.

Regulation of human Dicer by the resident ER membrane protein CLIMP-63

The ribonuclease Dicer plays a central role in the microRNA pathway by catalyzing the formation of microRNAs, which are known to regulate messenger RNA (mRNA) translation. In order to improve our understanding of the molecular context in which Dicer functions and how it is regulated in human cells, we sought to expand its protein interaction network by employing a yeast two-hybrid screening strategy. This approach led to the identification and characterization of cytoskeleton-linking endoplasmic reticulum (ER) membrane protein of 63 kDa (CLIMP-63) as a novel Dicer-interacting protein. CLIMP-63 interacts with Dicer to form a high molecular weight complex, which is electrostatic in nature, is not mediated by RNA and is catalytically active in pre-microRNA processing. CLIMP-63 is required for stabilizing Dicer protein and for optimal regulation of a reporter gene coupled to the 3′ untranslated region of HMGA2 mRNA in human cells. Interacting with a portion of the luminal domain of CLIMP-63 and within minutes of its synthesis, our results suggest that Dicer transits through the ER, is glycosylated and can be secreted by cultured human cells with CLIMP-63. Our findings define CLIMP-63 as a novel protein interactor and regulator of Dicer function, involved in maintaining Dicer protein levels in human cells.

Clarin-1, encoded by the Usher Syndrome III causative gene, forms a membranous microdomain: possible role of clarin-1 in organizing the actin cytoskeleton

Clarin-1 is the protein product encoded by the gene mutated in Usher syndrome III. Although the molecular function of clarin-1 is unknown, its primary structure predicts four transmembrane domains similar to a large family of membrane proteins that include tetraspanins. Here we investigated the role of clarin-1 by using heterologous expression and in vivo model systems. When expressed in HEK293 cells, clarin-1 localized to the plasma membrane and concentrated in low density compartments distinct from lipid rafts. Clarin-1 reorganized actin filament structures and induced lamellipodia. This actin-reorganizing function was absent in the modified protein encoded by the most prevalent North American Usher syndrome III mutation, the N48K form of clarin-1 deficient in N-linked glycosylation. Proteomics analyses revealed a number of clarin-1-interacting proteins involved in cell-cell adhesion, focal adhesions, cell migration, tight junctions, and regulation of the actin cytoskeleton. Consistent with the hypothesized role of clarin-1 in actin organization, F-actin-enriched stereocilia of auditory hair cells evidenced structural disorganization in Clrn1(-/-) mice. These observations suggest a possible role for clarin-1 in the regulation and homeostasis of actin filaments, and link clarin-1 to the interactive network of Usher syndrome gene products.

Changes in expression of the oligosaccharides in the human fetal skin

Lectin histochemistry was used to investigate the glycoconjugate saccharidic moieties in the skin of human fetuses ranging in age from the 8th to the 13th week of gestation. For this purpose, seven HRP-conjugated lectins were employed (Con A, WGA, PNA, DBA, SBA, UEAI and LTA). The distribution and changes of the sugar residues of glycoconjugates at the level of the various layers of the fetal epidermis, as well of the underlying mesenchyme were studied. We have shown that UEAI reactivity is a characteristic finding of the cells of the intermediate layer at the 11th and 12th week of gestation. LTA reactivity was detected only at the free border of the peridermal cells from the 10th to the 13th week of gestation. We demonstrated the presence of PNA binding sites at both the basal and peridermal cells from the 8th week of gestation, whereas other authors have stated that the appearance of PNA reactivity coincides with the onset of fetal skin stratification (11th-12th week of gestation). Moreover, some typical features in lectin reactivity at the level of the mesenchymal cells and fibres have been pointed out.

Posttranscriptional aspects of the biosynthesis of type 1 collagen pro-alpha chains: the effects of posttranslational modifications on synthesis pauses during elongation of the pro alpha 1 (I) chain

Early studies indicated that chain elongation pauses were prominent during the in vivo synthesis of type I procollagen chains, and it was postulated [Kirk et al., (1987): J Biol Chem 262:5540-5545.] that these might have a role in the coordination of procollagen I molecular assembly. To examine this postulate, polysomes isolated from [(14)C]-Pro-labeled 3T6 cells were subjected to SDS-PAGE. The resulting gels were Western blotted and screened with a monoclonal antibody (SP1 .D8) directed against the N-terminal region of the pro alpha 1 (I) chain. The blots were fluorographed, which also permitted analysis of the pro alpha 2 (I) chain. There was a prominent pro alpha1 synthesis pause near the completion of full-length chain elongation, not matched by a pro alpha 2 pause. The amount of labeled polysome-associated near-full length pro alpha 1 (I) chains increased in parallel with labeling time. After 24 h in culture -[(14)C-Pro], collagen synthesis ceased but unlabeled polysome-associated pro alpha1 chains were readily detected by SP1 .D8. Change to fresh culture medium +[(14)C-Pro] reinitiated synthesis and permitted tracing of the newly synthesized labeled pro a chains through the polysome and intracellular compartments. The secreted procollagen molecules had a 2:1 pro alpha 1 (1):pro alpha 2 (I) chain ratio but the polysome-bound peptides did not. Pulse-chase experiments showed that near-full length pro alpha 1 (I) chains remained bound to polysomes as long as 4 h after reinitiation of translation but there was no evidence for pro alpha 2 (I) chain accumulation. The hydroxylation inhibitor alpha, alpha'-dipyridyl, and triple-helix inhibitors cis-hydroxyproline and 3,4 dehydroproline had minimal effects on the buildup of polysome-associated pro al chains. The glycosylation inhibitor tunicamycin also failed to change the final pro alpha 1 chain pausing, but it did cause the appearance of several discrete lower molecular weight pro alpha 1-related polypeptides that could not be accounted for simply as the result of lack of N-linked glycosylation in the C-propeptide regions. Disulfide bond experiments showed that some of the paused nascent polysome-associated pro alpha 1 (I) chains were disulfide bonded. Thus, while synthesis of pro alpha 1 (I) and pro alpha 2 (I) chains proceeds in parallel within the same ER compartments, their elongation rates are not coordinated. Interactions leading to heterotrimer formation are a late event which may affect the rate of release of the completed pro alpha 1 (I) chain from the polysome. The release of completed nascent pro alpha 1 (I) chains from their polysomal complexes is regulated by a mechanism not operating in the synthesis of pro alpha 2 (I) chains. The pro alpha 1 (I) chain release process is not connected directly with hydroxylation, glycosylation or triple-helix formation.

The type I collagen pro alpha 1(I) COOH-terminal propeptide N-linked oligosaccharide. Functional analysis by site-directed mutagenesis

The C-propeptides of the pro alpha 1(I) and pro alpha 2(I) chains of type I collagen are each substituted with a single high-mannose N-linked oligosaccharide. Conservation of this motif among the fibrillar collagens has led to the proposal that the oligosaccharide has structural or functional importance, but a role in collagen biosynthesis has not been unambiguously defined. To examine directly the function of the pro alpha 1(I) C-propeptide N-linked oligosaccharide, the acceptor Asn residue was changed to Gln by site-directed mutagenesis. In transfected mouse Mov13 and 3T6 cells, unglycosylated mutant pro alpha 1(I) folded and assembled normally into trimeric molecules with pro alpha 2(I). In biosynthetic pulse-chase experiments mutant pro alpha 1(I) were secreted at the same rate as wild-type chains; however, following secretion, the chains were partitioned differently between the cell layer and medium, with a greater proportion of the mutant pro alpha 1(I) being released into the medium. This distribution difference was not eliminated by the inclusion of yeast mannan indicating that the high-mannose oligosaccharide itself was not binding to the matrix or the fibroblast surface after secretion. Subtle alterations in the tertiary structure of unglycosylated C-propeptides may have decreased their affinity for a cell-surface component. Further support for a small conformational change in the mutant C-propeptides came from experiments suggesting that unglycosylated pro alpha 1(I) chains were cleaved in vitro by the purified C-proteinase slightly less efficiently than wild-type chains. Mutant and normal pro alpha 1(I) were deposited with equal efficiency into the 3T6 cell accumulated matrix, thus the reduced cleavage by C-proteinase and altered distribution in the short pulse-chase experiments were not functionally significant in this in vitro extracellular matrix model system.

In vivo effects of tunicamycin on chondrocytes of rat mandibular condyles as revealed by lectin cytochemistry

The in vivo effects of tunicamycin on the glycosylation of proteoglycans and link protein in rat mandibular condylar chondrocytes were studied by ultrastructural lectin histochemistry. The binding of wheat-germ agglutinin was shown by using anti-lectin antibody followed by protein A-gold complex. In normal rats, wheat-germ agglutinin labeling was restricted to trans cisternae and vacuoles of the Golgi complex, whereas it was observed in neither the cis region of the Golgi complex nor in the rough endoplasmic reticulum. By 3 h after the drug administration, wheat-germ agglutinin binding sites on the disorganized Golgi vacuoles were dramatically reduced in number. At 6 h after the drug administration, the lectin binding sites on the Golgi vacuoles were restored. These results demonstrate that the in vivo use of tunicamycin in combination with histochemical analysis using lectin probes is of significant value for the study of protein glycosylation in chondrocytes of the rat mandibular condyle.

Partial sequencing and characterization of the tumor cell-derived collagenase stimulatory factor

A tumor cell-derived, collagenase stimulatory factor (TCSF), previously isolated and purified from LX-1 human lung carcinoma cells and judged by immunoblotting and SDS-PAGE to contain a single protein of approximately 58 kDa, has been further analyzed for its biological activity and composition. Three significant new findings have been made. First, the biological activity of TCSF preparations was shown definitively to reside in the 58-kDa protein. This was achieved in two ways: (a) a polyclonal antibody was raised against the 58-kDa protein, after excision from an SDS-PAGE gel, and shown to inhibit the stimulation of fibroblast collagenase production by TCSF preparations; (b) the 58-kDa protein was eluted from a transblot of purified TCSF and shown to stimulate fibroblast collagenase production. Second, partial sequencing of the 58-kDa protein revealed no significant homologies with other known collagenase stimulatory factors. Third, purified TCSF was found, on transblotting to Immobilon, to contain a doublet of 58 kDa (TCSF1) and 54 kDa (TCSF2) proteins; the former was present in higher concentration than the latter. N-terminal amino acid sequencing of the two intact proteins and of four corresponding pairs of tryptic peptides derived from the two proteins showed identity in each case, indicating that TCSF1 and TCSF2 are very similar in composition. However, TCSF1 but not TCSF2 stimulated fibroblast collagenase production, confirming that the 58-kDa protein is the major active component of TCSF preparations.

Type I procollagen C-proteinase from mouse fibroblasts. Purification and demonstration of a 55-kDa enhancer glycoprotein

The enzyme procollagen C-proteinase removes the carboxy-terminal propeptide from procollagen. In the present study we describe an improved procedure for the purification of this enzyme. From the medium of cultured mouse fibroblasts, consisting of ammonium sulfate precipitation, gel filtration and affinity chromatography on a lysyl-Sepharose column, followed by chromatography on a column of Sepharose coupled to the carboxy-terminal propeptide of type I procollagen (PP-Sepharose). This procedure yielded a practically homogeneous, 18,500-fold-purified enzyme preparation and the molecular mass of the purified C-proteinase as determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis was 80 kDa. The lysyl-Sepharose step separated the enzyme from the majority of the contaminating proteins, including a 55-kDa protein which was further purified by PP-Sepharose chromatography and identified as an additional form of the 36-kDa and 34-kDa procollagen C-proteinase enhancer proteins described before [Adar et al. (1986) Collagen Relat. Res. 6,267-277]. It enhanced the C-proteinase activity, bound to the carboxyl propeptide of type I procollagen, cross-reacted immunologically with the 36-kDa as well as the 34-kDa enhancer proteins, and in common with the latter proteins, it was glycosylated. In the course of PP-Sepharose chromatography, a large proportion of the 55-kDa protein disappeared with the concomitant appearance of the smaller enhancer proteins. All these findings suggest that the 55-kDa protein is a precursor of the low molecular mass enhancer proteins. Also suggested from this study is that lysyl-Sepharose chromatography is a highly beneficial purification step which may find use in the purification of the C-proteinase from other sources as well.

Cellular regulation of diphtheria toxin cell surface receptors

The cellular regulation of diphtheria toxin cell surface receptors was studied. Treatment of Vero cells with cycloheximide reduced their diphtheria toxin binding capacity, while cells treated with actinomycin D did not lose their ability to bind diphtheria toxin. A non-toxic analogue of diphtheria toxin, CRM 197, produced a dose-related depletion of cell surface diphtheria toxin binding capacity that was reversible upon washing the cells. Vero cells depleted of toxin receptors by CRM 197 did not restore their ability to bind diphtheria toxin in the presence of cycloheximide. Phospholipase C treatment of Vero cells reduced their diphtheria toxin binding capacity in a dose-dependent manner. The loss of diphtheria toxin binding capacity was recovered within 2 hr after removal of the enzyme. Protein synthesis inhibition blocked this recovery while actinomycin D partially inhibited it. Receptors prebound with toxin were resistant to phospholipase C treatment, suggesting that the action of the enzyme was directly on the receptor. Inhibition of glycosylation with tunicamycin did not prevent reappearance of toxin receptors after CRM 197 or phospholipase C treatment. These data establish the requirement of a continuous protein synthesis for the maintenance of diphtheria toxin cell surface receptors and also suggest that these receptors do not recycle after binding ligand. A hypothesis is put forward that the diphtheria toxin receptor might be a lipid-linked cell surface protein.

In vivo effect of tunicamycin on the expression of rat small intestinal brush border membrane glycoproteins and glycoenzymes

Tunicamycin, a known inhibitor of the lipid-dependent glycosylation of proteins, was used in vivo to study the biosynthesis of rat intestinal brush border membrane aminopeptidase N and dipeptidyl aminopeptidase IV. The incorporation of [3H]glucosamine into newly synthesized total protein of mucosal cell homogenates was inhibited by 60%, whereas incorporation of [3H]leucine was decreased only 21% by tunicamycin. This effect was much more pronounced in the brush border membrane fraction isolated from intestinal mucosal cells where incorporation of radiolabled leucine and glucosamine was reduced to 50 and 82% of control values respectively. An examination of the brush border membrane protein profile by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that there was a marked selective decrease in the amount of glycoproteins of molecular weights greater than 130 kD. In addition, there were decreased levels of assayable aminopeptidase N, dipeptidyl aminopeptidase IV and disaccharidase activity in intestinal mucosal cell homogenates and brush border membranes of tunicamycin-treated rats. Though tunicamycin decreased incorporation of newly synthesized aminopeptidase N and dipeptidyl aminopeptidase IV protein into brush border membranes by 70-75%, the newly synthesized enzyme that was incorporated was indistinguishable from that of controls. Further, non-glycoslyated forms of both enzymes were not detected in any other subcellular fractions. These results show that tunicamycin, an inhibitor of glycosylation, significantly affected the expression of brush border membrane glycoproteins, suggesting that both polypeptide synthesis and degradation of these proteins may be altered in the presence of this drug.

Stimulation of collagen production in vitro by ascorbic acid released from explants of migrating avian neural crest

Embryonic neuronal tissues contain a collagen-stimulating factor, shown to enhance the hydroxylation and secretion of proline-containing macromolecules by cultured muscle cells. Here we report on a similar activity found during avian embryonic development in explants of migrating mesencephalic neural crest. The degree of proline hydroxylation of proteins secreted into the medium was stimulated 2.5-6-fold in neural crest-muscle and neural crest-somite cocultures, as compared with control cultures devoid of crest explants. No such stimulation occurred when cocultures were treated with the enzyme ascorbate oxidase (EC 1.10.3.3), suggesting that the active factor in neural crest explants was ascorbic acid or an ascorbate-like molecule. Further characterization of this molecule was performed in crest explants and other embryonic tissues by using HPLC with amperometric detection: this study revealed that migrating cephalic neural crest contains 1.5 micrograms ascorbic acid per mg protein. Our results suggest that ascorbic acid and/or related molecule(s) could act during development of the nervous system as a trigger for collagen production and subsequent assembly of an extracellular matrix.

Cardiovascular complications in the Ehlers-Danlos syndrome with minimal external findings

Ehlers-Danlos syndrome (EDS) is clinically and genetically a heterogeneous disorder of connective tissue. Eleven different types of EDS have been documented, several of which have major cardiovascular complications as part of their clinical manifestations. The purpose of this report is to call attention to a form of EDS with minimal external features but severe internal vascular complications.

Comparison of rat MHC class I antigens by peptide mapping

Monoclonal antibodies specific for the rat major histocompatibility complex (MHC) class I antigens RT1.An, RT1.Au, and RT1.Eu were used for immunoprecipitation of antigens biosynthetically radiolabeled with 14C- or 3H-labeled arginine, lysine, and tyrosine; with arginine or tyrosine alone; and with or without tunicamycin in the culture medium. Heavy chains of the glycosylated and unglycosylated antigens were purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and their tryptic and chymotryptic peptides were compared by high performance liquid chromatography. The antigens coded by the same locus in two different haplotypes (An and Au) differed by 30%, whereas the products of two different loci in the same haplotype (Au and Eu) differed only by 1-3%. Comparative analysis of the data for samples labeled with single amino acids indicated that two amino acids in Au have been substituted by an arginine and probably by a tyrosine residue, respectively, in Eu. The high degree of homology between the products of the A and E loci in the same haplotype accounts for the difficulty in detecting recombinational events within the MHC of the rat by classical serological approaches.

Effect of tunicamycin on synthesis and secretion of carcinoembryonic antigen by human colonic adenocarcinoma cells

The effect of the glycosylation inhibitor, tunicamycin, on synthesis and secretion of the membrane-associated glycoprotein carcinoembryonic antigen (CEA), was studied in the LS174T human colon cancer cell line. Tunicamycin treatment inhibited total cellular glycoprotein synthesis but did not affect CEA levels of cellular homogenate, membrane or cytosol fractions as determined by enzyme immunoassay. Control cells metabolically labelled with 3H-glucosamine, 3H-leucine or 35S-cysteine exhibited membranous and extracellular (i.e. secreted) CEA with an MW of 200 kDa as judged by SDS-gel electrophoresis following immunoprecipitation. However, in the tunicamycin-treated cells several forms of CEA with lower MWs and representing molecules with decreased glycosylation could be detected in addition to the original CEA molecule of 200 kDa present in control cells. The rates of synthesis, secretion and turnover of the lower-molecular-weight forms of poorly glycosylated CEA that appear after tunicamycin treatment are similar to those of CEA in control cells. These data suggest that the carbohydrate portion of the CEA molecule is not essential in synthesis, incorporation into the membrane, and secretion of CEA by colon cancer cells in vitro.

Partial purification and characterization of a procollagen C-proteinase from the culture medium of mouse fibroblasts

A procollagen C-proteinase was purified about 100-fold from the medium of cultured mouse fibroblasts by a combination of ammonium sulfate precipitation, gel-filtration, and affinity chromatography on a column of Sepharose coupled to the carboxyl propeptide of type I procollagen. The purified enzyme did not exhibit other proteolytic activities, and it cleaved type I, II and III procollagens to produce the corresponding pN alpha chains and carboxyl propeptides as the only products. Amino acid sequencing of the first 14-18 residues at the N-terminus of the carboxyl propeptides generated by the enzyme from human pro alpha 1(I), pro alpha 2(I) and pro alpha 1(III) chains showed that the cleavage occurred at the physiological site, i.e. at the specific Ala-Asp bond in the pro alpha 1(I) and pro alpha 2(I) chains, and at the specific Gly-Asp bond in the pro alpha 1(III) chain. The pH optimum of the enzyme is 8.5 and its molecular weight as estimated by gel-filtration is about 125,000 daltons. The enzyme is inhibited by metal-chelators, various amines, dithiothreitol, N-ethylmaleimide and serum, but it is insensitive to pepstatin, leupeptin and serine proteases inhibitors. The enzyme differs from the C-proteinase described by Njieha et al. (Biochemistry 21:757-764, 1982), and the catheptic activities reported by Davidson et al. (Eur. J. Biochem 100:551-558, 1979) and Helseth and Veis (Proc. Natl. Acad. Sci. USA 81:3302-3306, 1984). The specificity of the enzyme is offered as evidence for a unique, C-proteinase, and its recovery from culture medium supports an extracellular location for procollagen processing.

Evidence for a protein that enhances the activity of type I procollagen C-proteinase

Gel-filtration separated type I procollagen C-proteinase from a glycoprotein that enhanced the enzyme activity by approximately 4-fold. The enhancer was purified by affinity chromatography on a column of Sepharose coupled to the carboxyl propeptide of type I procollagen. Sodium-dodecyl-sulfate- polyacrylamide gel electrophoresis of the affinity-purified enhancer revealed two active major protein bands with molecular weights of 36 and 34 kdal. Both proteins were glycosylated, as shown by binding to concanavalin-A. The enhancer is extremely heat stable (100 degrees C, 15 min) but its activity is totally abolished by treatment with trypsin or bacterial elastase. The enhancer does not alter the digestion intermediates or final products of the enzymatic reaction but it changes the kinetic properties of the reaction, increasing the apparent Km and Vmax values 16- and 20-fold, respectively. It is suggested that the enhancer might play a regulatory role in procollagen processing.

Endothelial cell injury in vitro is associated with increased secretion of an Mr 43,000 glycoprotein ligand

A novel, serum albumin-binding glycoprotein of molecular weight (mw) 43,000 (43K protein) was initially purified from the culture medium of bovine aortic endothelial (BAE) cells (Sage, H., Johnson, C., and Bornstein, P., J. Biol. Chem. 259:3993-4007, 1984). Its secretion by normal mesenchymal cells and by transformed cells of both ectodermal and endodermal origin suggested a general role in cellular function. To examine the effect of sublethal injury in vitro on the biosynthesis of 43K protein, BAE cells were exposed to endotoxin. At concentrations which produced minimal cell detachment and lysis, the cells secreted 70-100% more protein compared to control cultures, and the relative increase in 43K protein over total protein was approximately three-fold. A second type of cellular injury, manifested by rapid cellular proliferation and migration in response to sparse plating density (a condition that we have termed 'culture shock'), was also accompanied by a significant increase in the secretion of 43K protein. Pulse-chase studies revealed that the initial product secreted within 1.5 h was of Mr 38,000, and that between 6 and 21 h this molecule was converted to the final form of Mr 43,000. The 43K protein was not associated with RNA or glycosaminoglycan, but appeared to be linked to complex oligosaccharides containing peripheral sialosyl residues. Treatment with tunicamycin produced lower mw forms that displayed reduced affinity for albumin. By immunologic criteria, peptide mapping, and amino acid analysis, the 43K protein was shown to be structurally distinct from several proteins of Mr 40,000-50,000 associated with endothelium or with serum, including tissue factor, a plasminogen anti-activator, and several apolipoproteins. In addition, the 43K protein was not present in the extracellular matrices of endothelial, fibroblastic, or smooth muscle cells, nor was it found in plasma, serum, platelet releasate, or alveolar lavage fluids. These studies identify a unique Mr 43,000 glycoprotein that is associated with cellular stress or injury in vitro. As a secreted but nonmatrix macromolecule, this protein may be part of a 'survival kit' used by the endothelium to cope with cellular injury.

Maturation and secretion of lipoprotein lipase in cultured adipose cells. II. Effects of tunicamycin on activation and secretion of the enzyme

The effects of N-linked glycosylation on the activation and secretion of lipoprotein lipase were studied in Ob17 cells. The cells were first depleted of any activity and enzyme content by cycloheximide treatment and of precursors of oligosaccharide chains by tunicamycin. The repletion of lipoprotein lipase content was studied in these cells maintained in the presence of tunicamycin after cycloheximide removal. During the repletion phase, the EC50 values of inhibition by tunicamycin (approx. 0.2 microgram/ml) of the incorporation of labeled glucose, mannose or galactose into trichloroacetic acid-insoluble material were found to be identical. Under these conditions, the rate of protein synthesis was maximally decreased by 30%. The results showed clearly that the recovery in lipoprotein lipase activity was parallel to the recovery in hexose incorporation, no activity being recovered in the absence of glycosylation. An inactive form of lipoprotein lipase from tunicamycin-treated cells was detected by competition experiments with mature active lipoprotein lipase for the binding to immobilized antilipoprotein lipase antibodies, as well as by immunofluorescence staining. SDS-polyacrylamide gel electrophoresis and Western blots of cellular extracts and of extracellular media, obtained after tunicamycin-treated cells were exposed to heparin, revealed a single immunodetectable Mr 52 000 protein, whereas a single Mr 57 000 protein was detected in control cells. Therefore, the results indicate that the acquisition by lipoprotein lipase of a catalytically active conformation is linked directly or indirectly to glycosylation. Despite this lack of activation, the lipoprotein lipase molecule was able to migrate intracellularily and to undergo secretion after heparin stimulation of the tunicamycin-treated cells.

Importance of the different steps of glycosylation for the activity and secretion of lipoprotein lipase in rat preadipocytes studied with monensin and tunicamycin

Lipoprotein lipase synthesized by cultured rat preadipocytes is present in three compartments: an intracellular, a surface-related 3-min heparin-releasable, and that secreted into the culture medium. 30 min after addition of 6 microM monensin, the lipoprotein lipase activity in the heparin-releasable compartment starts to decrease; by 4 h of monensin treatment the lipoprotein lipase activity in the heparin-releasable pool and in the culture medium is about 10% of that found in control dishes. The intracellular activity, which had been identified as lipoprotein lipase by an antiserum to lipoprotein lipase, increases slowly and doubles by 24 h. However, since the cellular compartment accounts for 10-25% of total activity, this increase does not account for the missing enzyme activity. To determine whether this enzyme molecule is synthesized but is not active, incorporation of labeled leucine, mannose and galactose into immunoadsorbable lipoprotein lipase was studied in control, monensin- or tunicamycin-treated cells. Addition of tunicamycin (5 micrograms/ml) for 24 h caused a 30-50% reduction in immunoadsorbable lipoprotein lipase, but the enzyme activity was reduced by 90%. On the other hand, 4 h monensin treatment reduced both incorporation of [3H]leucine into immunoadsorbable lipoprotein lipase and heparin-releasable and medium lipoprotein lipase activity by 57 to 77%. The immunoadsorbable lipoprotein lipase in the intracellular compartment has a [14C]mannose to [3H]galactose ratio of 0.15 and this ratio increased 6-fold in monensin-treated cells. The intracellular lipoprotein lipase in monensin-treated cells had the same affinity for both the native and synthetic substrate as the lipoprotein lipase in control cells, yet its spontaneous secretion into the culture medium and its release by 3 min heparin treatment was markedly decreased. The present results indicate that: the presence of asparagine-linked oligosaccharide (formation of which is inhibited by tunicamycin) is mandatory for the expression of lipoprotein lipase activity; lipoprotein lipase is active also in a high mannose form; and terminal glycosylation and oligosaccharide processing, which is inhibited by monensin, may be important for the appearance of heparin-releasable lipoprotein lipase and secretion of lipoprotein lipase into the medium.

Aldosterone-induced proteins: characterization using lectin-affinity chromatography

Aldosterone-stimulated Na+ transport in toad urinary bladder is associated with the synthesis of a specific group of proteins whose induction appears to be related to the natriferic effect of the hormone. These aldosterone-induced proteins (AIPs) occur in two slightly different molecular weight classes (around 70 kDa), each class being composed of several proteins with discrete isoelectric points (range, 5.5-6.0). Because glycosylation is a common cause of such electrophoretic polymorphism and microheterogeneity, we examined whether these proteins are glycoproteins. Tunicamycin (a specific inhibitor of N-linked glycosylation) inhibited aldosterone-stimulated Na+ transport and AIP synthesis without affecting overall protein synthesis. The vast majority of epithelial cell proteins did not bind to the mannose-specific lectin, concanavalin A-sepharose. In contrast, both classes of AIPs bound to concanavalin A-sepharose, but the affinities of the higher and lower molecular weight proteins were markedly different: the former were readily eluted with 0.2 M alpha-methyl-D-mannoside alone, whereas the latter could only be eluted with 0.4 M alpha-methyl-D-mannoside in combination with high concentrations of NaCl (2.5-5.0 M). These studies indicate that 1) glycosylation is important in the natriferic response to aldosterone, 2) the AIPs are N-linked mannose-containing glycoproteins, and 3) the electrophoretic polymorphism of the AIPs is due, at least in part, to differences in glycosylation. Furthermore, concanavalin A-affinity chromatography provides a simple means for the partial purification of these putative "effectors" of the cellular action of aldosterone.

Collagen-stimulating factor from embryonic brain has ascorbate-like activity and stimulates prolyl hydroxylation in cultured muscle cells

Embryonic rat-brain extract contains a collagen-stimulating factor which enhances the production of collagen types I, III, IV and V by cultured rat muscle cells. Here we report on the partial characterization and possible mechanism of action of a low-molecular-mass fraction with ascorbate-like activity isolated from embryonic rat brain extracts. This activity eluted very close to ascorbate when filtered through Bio-Gel P-2 and Sephadex G-10. The peak of biological activity showed properties of a reducing agent. Both the biological and reducing activities were lost when the fraction was treated with the enzyme ascorbate oxidase. This factor enhanced in a time-dependent manner, the secretion of procollagen, pulse-labeled with [3H] proline. Incubation of the muscle cultures with the factor increased by 15-fold the ratio of hydroxyproline to proline residues in secreted macromolecules over controls. A fourfold increase in the above ratio was obtained for the cellular proteins. Crude homogenates from control and factor-stimulated cultures were tested for prolyl hydroxylase activity using [3H](Pro-Gly-Pro)n as a substrate. Cultures treated with the collagen-stimulating factor showed a 5-50-fold increase in prolyl hydroxylation activity compared to controls. No effect on prolyl hydroxylation was found when the factor was added in vitro to either control or stimulated enzyme preparations. Our results suggest that the collagen-stimulating factor contains ascorbate-like activity which promotes the secretion of collagenous proteins by increasing hydroxylation of proline residues in their polypeptide backbone.

A single-step gel-filtration method for the isolation of procollagens from cell culture conditioned medium

Procollagens are the major proteins secreted into the conditioned medium of cultured arterial smooth muscle cells. Methods for the isolation and quantification of these macromolecules have traditionally required preliminary salt precipitation of procollagens from the conditioned medium followed by cellulose ion-exchange chromatography. The method described here exploits the elongated conformation of soluble procollagens and allows the direct recovery of procollagens from culture medium by a single gel-filtration chromatographic step under nondissociating conditions. Procollagens are isolated in high yield and show minimal processing by procollagen N- or C-terminal peptidase activity. This method results in rapid recovery of highly purified procollagens, free of most proteoglycans or other products of smooth muscle cell metabolism.

Effects of hormones, amino acids and specific inhibitors on rat heart heparin-releasable lipoprotein lipase and tissue neutral lipase activities during long-term perfusion

Rat hearts were perfused for long periods in the presence of 14C-labeled amino acids. From these hearts, postheparin-effluent and a tissue homogenate containing lipoprotein lipase and neutral lipase, respectively, were derived. Lipolytic activity and 14C-labeled protein in both preparations were characterized by affinity chromatography, immunoprecipitation and SDS-polyacrylamide gel electrophoresis. Lipase activity and 14C-labeled protein co-eluted from heparin-Sepharose 4B at 1.2 M NaCl and were inhibited and precipitated by preincubation with anti-lipoprotein lipase gamma-globulins. Gel electrophoresis of both preparations showed the presence of 14C-labeled protein with a molecular weight of 35 000. These data strongly suggest similarity between lipoprotein lipase and neutral lipase and their possible precursor-product relationship and indicate that during perfusion continuous synthesis, secretion and vascular binding of lipase molecules occur. Cycloheximide perfusion induced a dramatic decrease of lipoprotein lipase and neutral lipase activity, indicating a half-life of less than 90 min for both enzymes. Tunicamycin present during perfusion also induced a drop in lipoprotein lipase and tissue neutral lipase activity, indicating that glycosylation is necessary for secretion of lipoprotein lipase. Long-term perfusion of rat hearts in the presence of norepinephrine, glucagon or tyrosine leads to reciprocal alterations in lipoprotein lipase and neutral lipase activities, i.e., lipoprotein lipase activity increased and neutral lipase activity decreased, whereas total lipase activity (lipoprotein lipase + neutral lipase) remained unaltered. During perfusion in the presence of insulin, no net change in lipase activities was observed. Also, insulin did not affect the glucagon-induced inverse effects on either lipase activity. The reciprocal changes in lipase activities occurring during norepinephrine perfusion were hampered by colchicine and propranolol, pointing towards beta-receptor and microtubular mediation of tissue lipase processing and endothelial binding. Our data suggest that the tissue flux and vascular binding of lipase protein may be important sites of hormonal regulation of lipoprotein lipase homeostasis.

Homozygosity for autosomal dominant Marfan syndrome

Marfan syndrome is an autosomal dominant condition with varying phenotypic manifestations. Affected persons are usually heterozygotes. A family is presented in which the gene for this syndrome is segregating in a large number of members. Two sibs suffered from unusually severe, identical, and fatal manifestations from birth, their parents having mild cardiovascular and somatic symptoms common in Marfan syndrome. Investigation of collagen biosynthesis in fibroblasts revealed no abnormalities in fibronectin and procollagen I and III synthesis and secretion or in the procollagen to collagen conversion. We suggest that these two sibs are examples of homozygosity for the Marfan syndrome gene, based on the large number of affected members, the absence of additional consanguinity, manifestation of the syndrome in both parents, and the severity of the disease in the two sibs.

Epidermal fucosylation of cell surface glycoprotein

When Ulex europeus agglutinin I (UEA) conjugated with fluorescein isothiocyanate is applied to tissue sections from the cutaneous epidermis of the newborn rat, the lectin binds to the surfaces of cells in the layer immediately above the basal layer but not to the cells in the basal layer itself. The latter cells bind the isolectin I-B4, from Griffonia simplicifolia (GS I-B4). The addition of a fucosyl residue to the oligosaccharide of the glycoprotein found on the surface of the basal cell can account for the change in lectin-binding specificity which occurs as the basal cell moves toward the cutaneous surface and becomes a spinous cell. The epidermis of the newborn rat has the necessary transferase to convert a glycoprotein with binding-specificity for GS I-B4 to binding specificity for UEA by adding a fucosyl residue from GDP-L-fucose.

Epithelial sheet movement: effects of tunicamycin on migration and glycoprotein synthesis

Corneas with central epithelial wounds, 3 mm in diameter, were organ cultured in the presence of tunicamycin (TM) (1 microgram/ml), an antibiotic that inhibits glycosylation of asparagine-linked glycoproteins. Compared with control corneas, which healed in 22 hr, corneas cultured in the presence of TM for the entire culture time or for only the first 6 hr displayed a progressively slower epithelial healing rate that essentially dropped to zero by 24 hr of culture time. At 24 hr, approximately 75% of the wound was covered. After repeated washings with TM-free culture media (6X, 10 min each), this effect could consistently be reversed in corneas exposed to TM for 6 hr. Incorporation of [3H]glucosamine into trichloroacetic acid-precipitable proteins of migrating epithelial sheets was reduced to 14% that of controls after 12 hr of culture with TM, whereas [14C]leucine incorporation was not significantly affected. The decreased glycosylation was reflected on the cell surface after 12 and 20 hr culture in the presence of TM: apical cell membranes of the first six cells of the leading edge of the migrating sheet bound significantly fewer ferritin-concanavalin A particles per micrometer of membrane than did controls. These results indicate that synthesis of asparagine-linked glycoproteins is required for continued migration of corneal epithelial sheets. The asparagine-linked glycoproteins that are required for migration probably include cell-surface glycoproteins.

Role of glycoproteins in neuronal differentiation. Inhibition of neurite outgrowth and the major cell surface glycoprotein of murine neuroblastoma cells by a purified tunicamycin homologue

Mouse neuroblastoma cells in culture can be induced to differentiate morphologically by serum deprivation or by dibutyryl cyclic AMP (db-cAMP), e.g. they appear flattened, adhere more firmly to the culture substratum and extend long neuritic processes, and thus represent a widely used model system for neuronal cells. This differentiation is accompanied by modulation of cell surface components, such as the induction of a high molecular weight (HMW) glycoprotein (200 kD). We have studied the role of glycoproteins in the process of neuronal differentiation, using a purified homologue of the antibiotic tunicamycin (Al-tunicamycin) and neuroblastoma N115 cells grown in culture. Al-tunicamycin markedly inhibited (up to 60-75%) the incorporation of radioactively labelled sugars into cellular proteins of differentiating neuroblastoma cells. Concomitantly, the cells altered their morphology, they became rounded and less adhesive and retracted their neurites. Changes in the appearance, glycosylation and electrophoretic mobility of several cellular and secreted glycoproteins were observed, when cells were incubated in the presence of Al-tunicamycin. The most striking effect of Al-tunicamycin on the composition of cellular glycoproteins was the marked reduction in appearance of the 200 kD glycoprotein. The findings suggest that glycoproteins and in particular the neuron-specific 200 kD glycoprotein, are related to morphological differentiation processes, mainly to cellular adhesion and neurite outgrowth.

Tunicamycin treatment inhibits the antiviral activity of interferon in mice

Earlier we reported that tunicamycin (TM) treatment of L cells in vitro significantly enhances the antiviral activity of interferon (IFN) against viruses (such as vesicular stomatitis, Sindbis, and herpes simplex) which bud from membranes. However, no such enhancement of the antiviral activity of IFN by TM was observed against encephalomyocarditis virus (EMCV) (nonbudding). We were interested to know whether TM would similarly enhance the antiviral activity of IFN and IFN inducers in vivo against Semliki Forest virus (SFV) and EMCV infections in mice. It was observed that TM alone (0.001 to 5.0 micrograms per mouse) did not protect mice against infections of SFV and EMCV; instead, TM-treated mice died with virus-specific paralytic symptoms earlier than untreated animals. The enhanced mortality in TM-treated and SFV- or EMCV-infected mice was associated with the concomitant increase in virus titer in brain tissue. IFN significantly protected mice against SFV and EMCV infections. The antiviral protection of mice by IFN against both the viruses was markedly inhibited by TM administration. IFN inducers (polyinosinic acid-polycytidylic acid, 6-MFA [a mixture of proteins, polysaccharides, and double-stranded DNA isolated from Aspergillus ochraceus ATCC 28706]) protected a significant number of mice against SFV infection. However, no such protection was observed in mice injected with a combination of TM and IFN inducer. These results indicate that TM treatment inhibits the antiviral action of IFN or IFN inducers in vivo.

Effect of tunicamycin on polarized membrane functions of an established kidney epithelial cell line

We have explored the relationship between glycoprotein biosynthesis, cell proliferation and function of a differentiated polarized membrane assessed by dome formation in the MDCK epithelial cell line. At 0.1 microgram/ml tunicamycin, complete inhibition of cell proliferation was observed in either serum-containing or serum-free, hormone-supplemented growth medium. By contrast, no inhibition of either spontaneous dome formation or that triggered by inducers of cell differentiation such as hexamethylene bisacetamide was observed at 0.5 microgram/ml tunicamycin, although total glycosylation of cellular proteins was inhibited by 75%. Our results suggest that the polarized sorting out of epithelial membrane proteins to apical and basolateral surfaces and their functions related to vectorial transepithelial fluid transport, monitored by dome formation, can persist unimpaired despite considerable underglycosylation of cellular glycoproteins and inhibition of cell proliferation.

Tunicamycin enhances the antiviral and anticellular activity of interferon

The inhibitory effects of interferon on virus multiplication and cell growth are significantly enhanced by treatment with tunicamycin. Potentiation of antiviral activity was found only with enveloped viruses and not with nonbudding viruses. Changes in the plasma membrane of treated cells may account for this effect, since enveloped viruses bud from the cell surface as a terminal step.

Tunicamycin inhibits the expression of membrane IgM in the human lymphoblastoid cell line Daudi

Tunicamycin inhibited the synthesis of glycosylated mu-chains and kappa-chains in the human lymphoblastoid cell line, Daudi. Nonglycosylated IgM could not be detected on the surface of tunicamycin-treated cells by cell surface iodination techniques even under conditions where membrane IgM was re-expressed in control cultures following the enzymatic stripping of the existing membrane IgM. Biosynthetic labeling and subsequent immunochemical analysis indicated that the nonglycosylated mu and kappa-chains failed to efficiently assemble into monomeric IgM units. In a previous study (Dulis et al., J. biol. Chem., 1982), we have shown that the nonglycosylated mu- and kappa-chains are rapidly catabolized. The lack of expression of nonglycosylated IgM could be due to the rapid catabolism of the nonglycosylated polypeptide chains and/or to the inability to form functional monomeric IgM molecules. Thus glycosylation may be required to protect the newly synthesized polypeptide chains from intracellular catabolic events and to maintain proper conformational foldings of the polypeptide chains to allow for the assembly of subunits into functional units and their ultimate expression.

Inhibition of protein glycosylation and selective cytotoxicity toward virally transformed fibroblasts caused by B3-tunicamycin

The biological effect of B3-tunicamycin, the only known homologue of tunicamycin which contains a saturated fatty-acid side chain, was examined using chick embryo fibroblasts, a mouse fibroblastic line (3T3) and a virally transformed mouse fibroblastic line (SV40-3T3). This homologue inhibited the transfer of N-acetylglucosamine 1-phosphate from UDP-N-acetylglucosamine to dolichyl phosphate, catalyzed by microsomes from chick liver or from cultured mouse fibroblasts. B3-tunicamycin also inhibited the incorporation of mannose into glycoproteins synthesized by chick or mouse fibroblasts. Incorporation of the amino acids proline and tyrosine was inhibited by B3-tunicamycin to a lesser extent than the incorporation of mannose. The mannose incorporation into glycoproteins synthesized by virally transformed cells was inhibited by B3-tunicamycin to a higher degree than what was achieved in the nontransformed lines or in the chick primary fibroblasts. When the activity of B3-tunicamycin as an inhibitor of protein glycosylation was compared to other homologues of tunicamycin, it was found to be the most active. This homologue caused complete (more than 95%) inhibition of protein glycosylation at a concentration of 50 ng/ml in chick and in mouse fibroblasts and at a concentration of 10 ng/ml in transformed mouse fibroblasts. When the cytotoxic activities of tunicamycin homologues were examined on nontransformed and virally transformed 3T3 cells, it was found that B3-tunicamycin displayed the highest selective cytotoxicity toward the transformed cells. When transformed fibroblasts (10(5) cells/plate) were treated with B3-tunicamycin (100 ng/ml) for 48 h, complete cell death was observed. The viability and the proliferative activity of the nontransformed fibroblast were normal even when treated with concentrations up to 500 ng/ml of B3-tunicamycin. This suggests that B3-tunicamycin may be a suitable candidate for studies of tumor growth in animals.