Quantitative analysis of peptide-MHC class II interaction

The tremendous progress in the field of basic immunology and immunochemistry made in the last decade has significantly advanced our understanding of antigen processing and presentation by MHC class I and II proteins. In this review different techniques to study peptide interaction with MHC class II molecules are summarized and their impact on the elucidation of quantitative parameters, like affinities or kinetic data, is discussed. A recently introduced method based on synthetic combinatorial peptide libraries allows to quantify the binding contribution of each amino acid residue in a class II ligand and is presented in more detail. As this knowledge is fundamental for current investigations in modern medicine, e.g. for novel immune system based therapy concepts, further aspects like the design of new high affinity MHC class II ligands and the prediction of peptide antigens are discussed.

Cathepsin L is an intracellular and extracellular protease in Paramecium tetraurelia. Purification, cloning, sequencing and specific inhibition by its expressed propeptide

The ciliate Paramecium tetraurelia secretes large amounts of a cysteine protease into the growth medium, presumably for extracellular food digestion. Two endoprotease isozymes (30 and 33 kDa on SDS/PAGE, respectively), both present in cell homogenates and in spent growth medium, were purified to homogeneity. Peptide sequence analysis revealed that these isozymes share identities at the amino acid level but are probably differently processed. Enzymatic characterization of the isolated proteases and sequencing of the cloned cDNA demonstrated that the enzymes belong to the cathepsin-L protease subfamily. Although the identity with mammalian and other protozoan L cathepsins was only around 30%, all important signature sequences for cathepsin L in the preproregion as well as in the catalyst of the enzyme were fully retained. The cDNA of this cysteine protease codes for a preproregion of 108 amino acids. The putative proregion of 86 amino acids which contained the characteristic conserved ERFNIN motif, was fused with a His6 tag, expressed in Escherichia coli, and purified. Both cathepsin L isozymes of Paramecium tetraurelia were inhibited by their cognate propeptide in the nanomolar concentration range. All other cysteine proteases tested (papain and mammalian cathepsin B, G and H) were unaffected by the propeptide up to 10 microM.

Synthetic analogues of the N-terminal lipid part of bacterial lipoprotein are B-lymphocyte mitogens in vitro and in vivo

Two analogues of the N-terminal part of bacterial lipoprotein, S-[2,3-bis(palmitoyloxy)-(2RS)propyl]-N-palmitoyl-(R)-cysteine methyl ester ("tripalmitoyl cysteine") and S [-2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-cysteinyl-(S)-seryl-(S)-seryl-(S)-asparaginyl-(S)-alanine ("tripalmitoyl pentapeptide") were synthesized and tested for mitogenic activity. The compounds were potent mitogens towards mouse spleen cell cultures, as measured by 3H-thymidine incorporation and by hemolytic plaque assays. This activity was not dependent on the presence of serum. Tripalmitoyl pentapeptide had little, if any, effect on thymocytes. When injected intravenously into Balb/c mice, the synthetic compounds induced splenomegaly and polyclonal B-cell activation, the latter was evident from an increase in the number of plaque-forming cells against trinitrophenylated sheep red blood cells. Thus, a synthetic fragment of a bacterial surface component was shown to exhibit marked biological activity in vitro as well as in vivo.

Incomplete functional differentiation of HL-60 leukemic cells by synthetic lipopeptides. Partial inhibition by pertussis toxin of enhanced superoxide formation

In human neutrophils, the synthetic lipopeptide, N-palmitoyl-S-[2,3- bis(palmitoyloxy-(2RS)-propyl]-(R)-cysteinyl-(S)-seryl-(S)-lysyl-( S)-lysyl-(S) -lysyl-(S)-lysine [Pam3CysSer(Lys)4], activates NADPH-oxidase catalyzed superoxide (O2-) formation through pertussis-toxin-sensitive and pertussis-toxin-insensitive mechanisms (Seifert, R., Schultz, G., Richter-Freund, M., Metzger, J., Wiesmüller, K.-H., Jung, G., Bessler, W. G. & Hauschildt, S. (1990) Biochem. J. 267, 795-802). We studied the effects of lipopeptides on differentiation of HL-60 leukemic cells. Pam3CysSer(Lys)4 enhanced phorbol-12-myristate-13-acetate-induced O2- formation (presumably through the expression of components of NADPH oxidase) in a concentration-dependent manner with a half-maximal effect at 100 ng/ml and a maximum at 1 microgram/ml. The effect of the lipopeptide was evident after 24 h and reached a plateau after 48 h. (2S,6S)-2-Palmitoylamino-6,7- bis(palmitoyloxy)heptanoyl-(S)-seryl-(S)-lysyl-(S)-lysyl-(S) -lysyl-(S)-lysine enhanced O2- formation as well. The effects of Pam3CysSer(Lys)4 were potentiated by dibutyryl cAMP, dimethyl sulfoxide, retinoic acid, 1,25-dihydroxyvitamin D3, interferon-gamma and tumor-necrosis-factor-alpha. Pertussis toxin, but not its B-oligomer, partially inhibited enhanced O2- formation induced by Pam3CysSer(Lys)4. O2- formation induced by arachidonic acid and gamma-hexachlorocyclohexane were more sensitive to inhibition by pertussis toxin than O2- formation induced by phorbol 12-myristate 13-acetate. Enhanced O2- formation induced by dibutyryl cAMP was not affected by pertussis toxin. Unlike ATP, histamine, prostaglandin E1 and the beta-adrenergic agonist, isoproterenol, Pam3CysSer(Lys)4 did not increase cytosolic Ca2+ [( Ca2+]i) in undifferentiated HL-60 cells. Histamine but not lipopeptides stimulated high-affinity GTPase of guanine-nucleotide-binding proteins in membranes of undifferentiated HL-60 cells. In Pam3CysSer(Lys)4-differentiated HL-60 cells, the responsiveness to the [Ca2+]i-increasing agonists, N-formyl-L-methionyl-L-leucyl-L-phenylalanine, C5a and leukotriene B4, was increased, whilst the responsiveness to prostaglandin E1 and isoproterenol was decreased. Pam3CysSer(Lys)4 did not inhibit proliferation of HL-60 cells but decreased transferrin receptor expression and increased C3bi receptor expression. Pertussis toxin did not affect proliferation and expression of transferrin and C3bi receptors. Dibutyryl cAMP was considerably more effective than Pam3CysSer(Lys)4 at inducing alterations in the above parameters. Our results suggest that (a) Pam3CysSer(Lys)4 induces incomplete functional differentiation of HL-60 cells through a mechanism which does not depend on a rise in [Ca2+]i and is different from that of other differentiation-inducing substances and (b) the mechanism by which Pam3CysSer(Lys)4 induces differentiation involves pertussis-toxin-sensitive and pertussis-toxin-insensitive mechanisms.

Structures of lantibiotics studied by NMR

During the last decade, Nuclear Magnetic Resonance has played an important role in the unravelling of the primary and tertiary structures of lantibiotics. A short overview of these studies, together with typical spatial structures obtained, is presented.

Biological activity of bacterial surface components: bacterial extracts and defined bacterial cell wall components as immunomodulators

Bacterial extracts obtained from pathogenic strains occurring in lung infections (Broncho Vaxom) or urogenital infections (Urovaxom) as well as defined surface components of Gram-negative bacteria purified from bacteria or obtained by chemical synthesis were tested for their immunomodulatory properties in a murine system. The bacterial extracts were able to act as immunogens inducing an antigen-specific response. Both the bacterial extracts and the purified bacterial cell wall components constituted polyclonal activators of murine splenic B cells, as demonstrated by proliferation assays measuring the incorporation of [3H]thymidine into DNA. They were also able to act as immunoadjuvants increasing the SRBC and the BSA-TNP specific immune response, and could induce tumor cytotoxicity in bone marrow-derived macrophages. The results show that bacterial extracts and defined bacterial surface components constitute immunogens as well as immunomodulators in vitro and in vivo.

Peptide siderophores

Siderophores are low molecular weight iron chelators, produced by virtually all bacteria, fungi and some plants. They serve to deliver the essential element iron, barely soluble under aerobic conditions, into microbial cells. Siderophores are therefore important secondary metabolites which are very often based on amino acids and their derivatives. Biosynthesis, transport, regulation and chemical synthesis of natural siderophores and their analogues is of considerable interest for the protein and peptide chemist. This review gives an overview of the structural classes of peptidic siderophores, along with data on their biosynthesis. On a number of representative examples, strategies and schemes of their chemical synthesis are described.

Intracellular localization of a lipopeptide macrophage activator: immunocytochemical investigations and EELS analysis on ultrathin cryosections of bone marrow-derived macrophages

Synthetic lipopeptides, structurally derived from the N-terminal part of bacterial lipoprotein, constitute macrophage and B-lymphocyte activators. The molecular mechanism of macrophage activation by lipopeptides still remains unclear. The purpose of our study was to determine the route and kinetics of lipopeptide distribution in bone marrow-derived macrophages. The intracellular localization of the C-terminally biotinylated lipodipeptide Pam3Cys-Ser was investigated on ultrathin cryosections using the biotinstreptavidin-gold system. Our findings indicate that the lipopeptide penetrates the plasma membrane and can already be found within the cytoplasm, the nuclear membrane, and within the nucleus after 2 min of stimulation. The pattern of lipopeptide distribution obtained 2 min after stimulation resembles that obtained after longer incubation times (8 and 20 min). Correlating distribution patterns were observed when using the method of electron energy loss spectroscopy (EELS). These findings are a clear indication for the rapid uptake of lipopeptides into eukaryotic cells, and are of importance for further studies of the immunostimulating properties of the bacterial lipopeptides and vaccines derived therefrom.

Conformational and epitope mapping of herpes-simplex-virus type-1 thymidine kinase using synthetic peptide segments

Adjacent peptide segments covering the complete sequence of herpes-simplex-virus type-1 thymidine kinase (HSV1-TK) of 376 amino acids were synthesized in order to experimentally verify the three-dimensional structure of the HSV1-TK active site, which was previously determined by molecular modeling. 26 peptides have been prepared by multiple solid-phase synthesis using the 9-fluorenylmethoxycarbonyl strategy. The purified peptides were linked covalently to bovine serum albumin. The peptide/ELISA of the synthesized bovine-serum-albumin conjugates using polyclonal rabbit anti(HSV1-TK)serum resulted in ten epitopes, which correlate excellently with the computer-proposed active site of HSV1-TK. CD spectra of the HSV1-TK peptides were recorded in trifluoroethanol/water (9:1 by vol.) An eigenvalue method based on CD spectra of 15 well known protein structures was used to calculate the relative percentage of secondary structures from the CD data. The computer model of the HSV1-TK showed full conformity with the folding pattern determined by CD of the synthetic peptide segments. Therefore, conformational peptide mapping with CD-based secondary structures combined with epitope mapping from the peptide/ELISA is an efficient and reliable method to support computer-aided protein design.

Ligand motif of the autoimmune disease-associated mouse MHC class II molecule H2-A(s)

The MHC class II molecule H2-A(s), expressed in the SJL mouse strain, is the principle restriction element of autoreactive CD4(+) T cells mediating experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. We deduced the H2-A(s) ligand motif from the analysis of naturally processed self peptides and from peptide binding studies. Major anchor residues were identified using various sets of substituted and truncated peptides, derived from natural peptide ligands and known H2-A(s) binders like myelin basic protein 81 - 99. The nine-residue H2-A(s) core binding motif comprises an arrangement of anchors in relative positions P1, P4, P6, P7, and P9. The P1 pocket is relatively unspecific and the P6 pocket favors hydrophobic-aliphatic side chains. The P1 pocket contributes little to peptide binding. Primary anchors were identified in P4, P7, and in particular in P9. The preferred anchor residues are Lys (P4), His/Arg (P7), and Pro (P9), respectively. Ala-polysubstituted peptides containing only one of these dominant anchor residues still retain the capacity to bind to H2-A(s). Thus, the presence of only one suitable anchor side chain in P4, P7, or P9 is sufficient for high-affinity peptide binding, at least in the absence of negatively charged side chains nearby. The identified ligand motif facilitates the analysis of immunogenic peptides interacting with H2-A(s) and will allow a better prediction of pathogenetically relevant peptide antigens in the autoimmune mouse model.

Heterogeneity of linear B cell epitopes of the measles virus fusion protein reacting with late convalescent sera

B cell epitopes of the measles virus fusion protein were mapped, by reacting sera from late convalescent donors with synthetic overlapping pentadecapeptides, segments covering the whole F protein sequence. Unselected individual sera recognized 7 to 20% of the total sequence. Cumulation of the binding patterns of 30 sera identified eight to 10 clusters of antibody-binding peptides spread over most of the sequence. The B cell epitopes included regions of transition between the more hydropathic (including the N-terminal end of the F1 and F2 protein) and hydrophilic sequences. When the regions of antibody binding were compared with the predicted secondary structure of the F protein, no detectable pattern became apparent. Exposed sequences as well as sequences hidden in the viral membrane or in the protein core of both the F1 and F2 polypeptides were recognized by the antibodies. The heterogeneity of the binding patterns was not merely dependent on the anti-measles virus titre. The importance of antibodies recognizing linear epitopes of the measles virus fusion protein for the immune protection is presently not known.

Isolation and analysis of the rat genomic sequence encoding Cu/Zn superoxide dismutase

A rat genomic DNA (SOD1) encoding Cu/Zn superoxide dismutase (SOD1) (superoxide; superoxide oxidoreductase, EC 1.15.1.1) was cloned and sequenced. The rat SOD1 gene consisted of five exons and four introns spanning about 6 kb. The transcription start point (tsp) was observed 93 bp upstream from the ATG codon by primer extension analysis. The 5'-flanking sequence of SOD1 contained two CCAAT box motifs, a TATA box and four GC-like boxes. In the 3'-flanking region of SOD1, a polyadenylation signal, consensus sequence YGTGTTYY, and a G/T cluster were observed. A rat identifier (ID) sequence, a repetitive element of the rat genome, was located at between 569 and 484 bp upstream from the tsp.

Structure activity studies of mast cell activation and hypotension induced by neuropeptide Y (NPY), centrally truncated and C-terminal NPY analogues

1. Neuropeptide-induced histamine release is thought to occur via receptor-independent mechanisms, with net charge and lipophilicity being important factors. 2. In this study, the histamine releasing ability of neuropeptide Y (NPY), two C-terminal segments of NPY and 13 centrally truncated NPY analogues was examined. These results were compared with the ability of the peptides to bind to the Y2 receptor in the rabbit kidney membrane model and with their hypotensive actions in the anaesthetized-rat model. 3. All analogues tested, with the exception of [Glu4,25,33,35]-NPY(1-4)-Ahx-(25-36) and [Asp4,25,33,35]NPY(1-4)-Ahx-(25-36) which were devoid of histamine releasing activity, evoked a dose-dependent histamine release but there were marked differences between the peptides. The native peptide was the least active. 4. Histamine release was not linked to the ability of the peptides to displace NPY from Y2 receptors. There was a statistical correlation between the hypotensive effects expressed as ED10 values (mumol kg-1, which induced a blood pressure decrease of 10 mmHg) and the EC25 for histamine release (r = 0.62, P = 0.04), although histamine release may not be the sole determinant of the alterations in blood pressure. 5. There was a strong negative correlation between EC25 for histamine release and net positive charge (r = -0.93, P = 5.7 x 10(-7), i.e. increasing the net positive charge caused greater histamine release. However, there was a 12 fold difference in activity amongst the most positively charged analogues (+5). Helicity did not correlate with histamine releasing ability. 6. In the development of NPY-related drugs the avoidance of compounds with net positive charge is recommended.

Solvent-dependent structural features of the membrane active peptide trichotoxin A40 as reflected in its dielectric dispersion

The dielectric dispersion of trichotoxin A40 in solvents of diverse lipophilicity (i.e. n-octanol, dioxane and mixtures of these) has been measured between 100 kHz and 50 MHz. In pure octanol also the weight average molecular weight and the concentration dependence of the circular dichroism spectrum were determined. An analysis of the data leads to the conclusion that in octanol an appreciable amount of the solute exists as single monomeric particles which are about 30 A long and 12.5 A in diameter. There is a dipole moment parallel to the long axis. In addition the evidence points at the presence of small aggregates (mainly dimers and trimers) formed by some kind of head-to-tail association. Evidently dioxane added to octanol favors a different structure of the trichotoxin monomer. It is apparently involved in another aggregation process resulting in aggregates of large size but comparatively low dipole moments.

A flow cytometric long-term cytotoxicity assay

A method to evaluate cytotoxic effects applicable over a wide range of incubation times has been developed. It is based on quantification by flow cytometry of dead and viable target cells stained by covalently binding the fluorescent dye fluorescein isothiocyanate (FITC). The staining with FITC did not affect cell viability and growth parameters and was stable enough to identify target cells for at least 2 days. The flow cytometric analysis of the cell mixture was performed in a test system with activated CD8+ lymphocytes as effector cells and melanoma M21 cells as targets in the presence of appropriate bispecific antibodies and revealed a rather complex pattern composed of several distinct cell subsets which were identified by use of antibodies to lymphocyte antigens. The assay compared favourably with results from a conventional 51Cr release assay obtained after 4 h and 8 h of incubation and from a target cell adherence assay obtained after 24 h of incubation. The application of the method described herein is especially advantageous for the evaluation of long-term cytotoxic effects. Furthermore, it provides valuable multi-parameter information which is useful for elucidating mechanisms of cytotoxicity.

Abdominal lymphoma staging: is MR imaging with T2-weighted turbo-spin-echo sequence a diagnostic alternative to contrast-enhanced spiral CT?

PURPOSE

To evaluate the diagnostic value of MR imaging in abdominal lymphoma staging, in comparison with that of the established spiral CT, within the context of a prospective study.

METHODS

50 patients with non-Hodgkin (n = 27) and Hodgkin lymphoma (n = 23) were examined with a plain T2-weighted TSE sequence (parameters: TE 90 ms, TR >2.500 ms, slice thickness 8 mm, slice interval 0.8 mm, ETL 20, NEX 4), and with spiral CT following oral and intravenous administration of contrast agent.

RESULTS

Both CT and MR imaging agreed in showing abdominal lymphomas in 34/50 cases. The size of the detected lymphomas was between 1.5-9 cm (mean: 4.3 +/-2.2 cm). In the analysis of the individual lymph node sites, CT showed involvement of the paraaortic lymph nodes in 29/50 patients, compared with 28/50 in MRI, and involvement of the portal lymph nodes in 15/50, compared with 12/50. Both techniques showed the iliac lymph nodes in 21/50 patients, the inguinal lymph nodes in 10/50, and the mesenteric lymph nodes in 11/50. Both techniques also showed focal organ lesions in 12/50 cases.

CONCLUSIONS

In the staging of abdominal lymphomas, MR imaging with a T2-weighted TSE sequence can be regarded as equal to spiral CT in the detection of lymph adenopathy and the demonstration of focal organ lesions. In addition to the absence of ionizing radiation, the advantage of MR imaging is that there is no necessity for oral or intravenous administration of contrast agent.

Role of target antigen in bispecific-antibody-mediated killing of human glioblastoma cells: a pre-clinical study

Bispecific antibodies (bsAbs) directed to tumor-associated antigens and to receptors mediating T-cell activation, such as the TCR/CD3 complex and the co-stimulatory CD28 molecule, are capable of activating T cells at the surface of tumor cells, resulting in tumor-cell killing. Here we report the pre-clinical characterization of bispecific-antibody fragments (bsFab2) directed to 2 different glioblastoma-associated antigens: the EGF receptor (EGFR) and a chondroitin-sulfate proteoglycan (CSPG). Using cultured glioblastoma cells expressing both target antigens, we found that the ability of anti-tumor x anti-CD28 bsFab2 to mediate "targeted T-cell co-stimulation" is superior for constructs targeting the CSPG molecule, correlating with an approximately 6-fold higher expression level of this antigen on the cell surface. In contrast, bsFab2 triggering CD3 are more effective if they contain EGFR-target specificity. This indicates that the activity of anti-tumor x anti-CD3 constructs critically depends on properties of the antigen other than its expression level on the cell surface, e.g., its mobility in the membrane. These findings prompted us to use EGFR-targeting bsFab2 in an ongoing clinical trial with glioma patients.

C/EBP alpha is a major activator for the transcription of rat Cu/Zn superoxide dismutase gene in liver cell

The rat Cu/Zn superoxide dismutase (SOD1) is expressed in all tissues. Sequence analysis of the SOD1 promoter region showed that none of the cis-elements of hepatocyte-specific nuclear factors (HNF) were observed. The cis-element of C/EBP alpha in the proximal region of the SOD1 promoter and the high level of C/EBP alpha in the liver tissue led us to focus on the transcriptional regulation of the SOD1 gene by C/EBP alpha. Cotransfection assays with the plasmid expressing transcription factor C/EBP alpha showed that C/EBP alpha transactivated SOD1 gene by 27 fold. The marked transactivation and direct binding of C/EBP alpha to the SOD1 promoter were confirmed by deletion analyses and mobility shift assays. These results suggested that C/EBP alpha plays a major role in the tissue distribution of SOD1.

Electropolymerization of a phenol-modified peptide for use in receptor-ligand interactions studied by surface plasmon resonance

The combination of surface plasmon resonance (SPR) with an electrochemical method for surface modification is presented. The SLP1 sequence of the sodium channel protein of rat cardiac muscle cells was N-terminally modified with an electropolymerizable group and immobilized on a gold-coated glass slide by oxidative polymerization. The resulting peptide-functionalized substrate was incubated with a polyclonal-specific anti-SLP1 serum. Growth of the peptide layer and the immunological reaction between ligand and receptor were detected on-line by SPR. The applicability of this approach for the rapid and selective analysis of receptor-ligand interactions is demonstrated.

N-Hydroxy-amide analogues of MHC-class I peptide ligands with nanomolar binding affinities

A novel class of major histocompatibility complex class I (MHC-I) ligands containing an N-hydroxyamide bond was designed on the basis of the natural epitope SIINFEKL, and synthesized on solid phase. The capacity of these compounds to bind to the MHC-I molecule H-2Kb and to induce T cell responses was analysed in comparison with the corresponding glycine containing variant of SIINFEKL. Binding to the MHC molecule was diminished by the N-hydroxy group at positions 2 and 3 of the oligomer and improved in the case of positions 4, 5, 6 and 7. No change was seen for position 1. The efficacy of T cell stimulation was strongly reduced by the modification of all positions except for position 1. A complete loss of activity was found for the N-hydroxy variant in positions 4 and 6. N-Hydroxy amide-containing peptides displayed an enhanced stability to enzymatic degradation. This new class of MHC ligand can become instrumental as immunomodulatory reagent in various disease situations.

Establishment of T cell lines to bovine beta-casein and beta-casein-derived epitopes in patients with type 1 diabetes

Enhanced cellular immune response to bovine beta-casein has been reported in patients with type 1 diabetes. In this study we aimed to establish beta-casein-specific T cell lines from newly diagnosed type 1 diabetic patients and to characterise these cell lines in terms of phenotype and epitope specificity. Furthermore, since sequence homologies exist between beta-casein and putative beta-cell autoantigens, reactivity to the latter was also investigated. T cell lines were generated from the peripheral blood of nine recent onset type 1 diabetic patients with different HLA-DQ and -DR genotypes, after stimulation with antigen pulsed autologous irradiated antigen presenting cells (APCs) and recombinant human interleukin-2 (rhIL-2). T cell line reactivity was evaluated in response to bovine beta-casein, to 18 overlapping peptides encompassing the whole sequence of beta-casein and to beta-cell antigens, including the human insulinoma cell line, CM, and a peptide from the beta-cell glucose transporter, GLUT-2. T cell lines specific to beta-casein could not be isolated from HLA-matched and -unmatched control subjects. beta-Casein T cell lines reacted to different sequences of the protein, however a higher frequency of T cell reactivity was observed towards the C-terminal portion (peptides B05-14, and B05-17 in 5/9 and 4/9 T cell lines respectively). Furthermore, we found that 1 out of 9 beta-casein-specific T cell lines reacted also to the homologous peptide from GLUT-2, and that 3 out of 4 of tested cell lines reacted also to extracts of the human insulinoma cell line, CM. We conclude that T cell lines specific to bovine beta-casein can be isolated from the peripheral blood of patients with type 1 diabetes; these cell lines react with multiple and different sequences of the protein particularly towards the C-terminal portion. In addition, reactivity of beta-casein T cell lines to human insulinoma extracts and GLUT-2 peptide was detected, suggesting that the potential cross-reactivity with beta-cell antigens deserves further investigation.

C/EBP alpha and C/EBPbeta play similar roles in the transcription of the human Cu/Zn SOD gene

Copper/zinc-containing superoxide dismutase (Cu/Zn SOD) is one of the essential enzymes that protects cells in aerobic conditions. To understand the mechanism of transcriptional regulation of the human Cu/Zn SOD gene, the proximal promoter region of Cu/Zn SOD has been investigated. In a previous study, it was found that transcription factors of the Sp1 and C/EBP family are associated with the expression of human Cu/Zn SOD [Seo et al. (1996). Gene, 178, 177-180]. Of the four known C/EBP activators, the effects of C/EBP alpha and C/EBPbeta on the transcription of Cu/Zn SOD were examined. Usually, one of the two C/EBP factors, C/EBP alpha or C/EBPbeta, exclusively stimulates the target gene, but, unexpectedly, C/EBP alpha and C/EBPbeta stimulated the expression of Cu/Zn SOD to a similar extent in our experiments. LIP, a dominant negative regulator of the C/EBP family, inhibited the transcriptional activation of Cu/Zn SOD stimulated by C/EBP alpha and C/EBPbeta. These results suggest that C/EBP alpha and C/EBPbeta can substitute each other and play similar roles on the transcription of Cu/Zn SOD.