Specific recognition of cruciform DNA by nuclear protein HMG1.

Cruciform DNA, a non-double helix form of DNA, can be generated as an intermediate in genetic recombination as well as from palindromic sequences under the effect of supercoiling. Eukaryotic cells are equipped with a DNA-binding protein that selectively recognizes cruciform DNA. Biochemical and immunological data showed that this protein is HMG1, an evolutionarily conserved, essential, and abundant component of the nucleus. The interaction with a ubiquitous protein points to a critical role for cruciform DNA conformations.

Transglutaminase-mediated modifications of the rat sperm surface in vitro.

Two transglutaminase-mediated modifications of the rat epididymal spermatozoon surface were demonstrated in vitro. Transglutaminase was effective in promoting the binding of spermidine to the sperm. Moreover, the enzyme, by reacting with one of the major proteins secreted by the rat seminal vesicle epithelium, produced a modified form of the protein with a higher molecular weight and the capability of binding to the sperm cells. A specific physiological role for the enzyme, bringing about modifications of the rat sperm surface in the seminal fluid environment, is suggested.

Induction of interleukin-6 (IL-6) autoantibodies through vaccination with an engineered IL-6 receptor antagonist.

Neutralization of cytokine activity by monoclonal antibodies or receptor antagonists is beneficial in the treatment of immune and neoplastic diseases, but the necessity for continuous parenteral delivery of these anticytokine agents poses considerable practical limitations. A viable alternative is to induce a neutralizing antibody response. Using transgenic mice with high circulating levels of human interleukin-6 (hIL-6), we show that injection of the hIL-6 receptor antagonist Sant1 (an IL-6 variant with seven amino-acid substitutions) induces a strong anti-hIL-6 antibody response. The elicited antibodies bind circulating hIL-6 with very high affinity, totally masking it, and neutralize hIL-6 bioactivity both in vitro and in vivo.

Development of humanized mice for the study of hepatitis C virus infection.

The development of a small animal model for hepatitis C virus (HCV) infection is a critical issue for the development of novel anti-HCV drugs. To this aim, we have tried many different approaches for generating mice carrying humanized liver. Main efforts were focused on the transplantation of human hepatocytes into immunocompromised mice (SCID-/-, Bg-/-) carrying a genetic lethal liver disease (Alb-uPA). Survival of homozygotic animals should largely depend on early transplantation with healthy hepatocytes. In parallel to establishing a colony of Alb-uPA/SCID/Bg mice, we developed a microsurgical procedure for intrasplenic xenotransplantation of healthy hepatocytes in 1-week-old mice. So far, we generated several chimeras by xenotransplanting human hepatocytes in Alb-uPA+/+/SCID-/-/Bg-/- mice at 1 week after birth. In a first step, identification of successfully engrafted animals is possible by quantification of human serum albumin and human alpha 1 antitrypsin in mouse sera. Additional preliminary histomorphological analysis of liver sections from chimeric animals was also carried out. One of the mice was transiently infected with HCV, reaching viremia levels of approximately 10(5) genomes/mL. However, the efficiency of this system to generate chimeric mice is still very limited. We are currently exploring the use of more robust models of hepatic disease. Moreover, we have been also exploring novel strategies for the generation of chimeric mice by xenotransplanting human adult stem cells, instead of human hepatocytes, at preimmune stages of development.

Down-regulation of interleukin 6 receptor alpha chain in interleukin 6 transduced melanoma cells causes selective resistance to interleukin 6 but not to oncostatin M.

The cytokines interleukin 6 (IL-6) and oncostatin M are able to inhibit the growth of cell lines obtained from early but not advanced melanomas. Resistant cell lines have frequently been found to produce IL-6. Acquisition of IL-6 resistance and the relationship between resistance and endogenous IL-6 production are poorly defined phenomena. We have characterized a panel of melanoma cell lines for susceptibility to IL-6 and oncostatin M and have generated lines that acquired resistance to IL-6 by IL-6 cDNA transduction. These lines retained the previous oncostatin M sensitivity, suggesting that the alpha chain of IL-6 receptor (IL-6R alpha) is involved in the acquisition of resistance. In fact transduced cells lost the ability to bind 125I-IL-6 and to release soluble IL-6R alpha in culture. Moreover, addition of soluble recombinant IL-6R alpha were able to restore IL-6 sensitivity in association with IL-6 production. On the contrary, naturally IL-6 resistant melanoma cell lines were not inhibited by treatment with recombinant soluble IL-6R alpha in association with endogenously produced or recombinant IL-6. These results demonstrate that down-regulation of IL-6 receptor is only one of different mechanisms that are responsible of IL-6 resistance in melanoma cells.

In vitro binding of ciliary neurotrophic factor to its receptors: evidence for the formation of an IL-6-type hexameric complex.

Ciliary neurotrophic factor (CNTF) is a cytokine sharing structural and functional similarities with interleukin-6 (IL-6) and other helical cytokines that utilize the common signalling chain gp130. While IL-6 induces gp130 dimerization, CNTF, after the initial interaction with the specific, non-signalling receptor subunit, CNTFR, induces the formation of gp130/LIF-receptor heterodimers. Through immunoprecipitation experiments with tagged soluble receptor molecules, we recently demonstrated that IL-6 drives the formation of a hexameric receptor complex with a defined topology and composed of two IL-6, two IL-6R alpha and two gp130 molecules. Here, we apply the same strategy to study the assembly in vitro of the CNTF receptor complex. We present evidence that both the cytokine and the specific binding chain undergo dimerization in the presence of gp130. Furthermore, although gp130 and LIFR are able to bind independently to the CNTF/CNTFR sub-complex, they never form homodimers but only heterodimers. We propose that CNTF assembles a hexameric receptor complex composed of two CNTF, two CNTFR, one gp130 and one LIFR molecule, and present a model of the reciprocal interaction of these molecules based on similarities with the IL-6 hexameric complex.

Monovalent phage display of human interleukin (hIL)-6: selection of superbinder variants from a complex molecular repertoire in the hIL-6 D-helix.

Phage display of proteins can be used to study ligand-receptor interaction and for the affinity-maturation of binding sites in polypeptide hormones and/or cytokines. We have expressed human interleukin-6 (hIL-6) on M13 phage in a monovalent fashion as a fusion protein with the phage coat protein, pIII. Phage-displayed hIL-6 is correctly folded, as judged by its ability to interact with conformation-specific anti-hIL-6 monoclonal antibodies (mAb) and with the hIL-6 receptor complex in vitro. We set up an experimental protocol for the efficient affinity selection of hIL-6 phage using the extracellular portion of the hIL-6 receptor alpha (hIL-6R alpha) fixed on a solid phase. This system was used to affinity-purify from a library of hIL-6 variants, in which four residues in the predicted D-helix of the cytokine were fully randomized, mutants binding hIL-6R alpha with higher efficiency than the wild type. When the best-binder variant Q175I/Q183A was combined with a previously identified superbinder S176R [Savino et al., Proc. Natl. Acad. Sci. 90 (1993) 4067-4071], a triple-substitution mutant Q175I/S176R/Q183A (hIL-6IRA) was obtained with a fivefold increased hIL-6R alpha binding and a 2.5-fold enhanced biological activity.

Alu sequences transcription in X. laevis oocytes: nuclear-cytoplasmic partitioning and evidence for 3' end processing reactions.

A large Alu-family cluster in the 5' flanking region of a human alpha 1-acid glycoprotein gene has been identified and sequenced. Individual members microinjected into X. laevis oocytes are transcribed only when canonical box A and B components of the split pol III promoter are present. Alu transcripts accumulate in the nucleus. An unusually short Alu transcript, able to assume a stable secondary structure, undergoes a 3' end processing reaction similar to the one required for tRNA 3' end maturation.

Two distinct factors interact with the promoter regions of several liver-specific genes.

A segment of the human alpha 1-antitrypsin (alpha 1AT) 5'-flanking region comprising nucleotides -137 to -37 from the start of transcription is sufficient to drive liver-specific transcription from the homologous alpha 1AT promoter and from the heterologous SV40 promoter. In this paper we characterize two proteins, LF-A1 and LF-B1, whose ability to bind wild-type and mutant alpha 1AT promoter segments correlates with the ability of these segments to activate transcription in vivo. DNase I protection and methylation interference analysis reveals that LF-A1 recognizes sequences present in the regulatory region of the human alpha 1-antitrypsin, apolipoprotein A1 and haptoglobin-related genes. These sequences share a common 5' TGG/A A/C CC 3' motif. LF-B1 binds to the palindrome 5' TGGTTAAT/ATTCACCA 3' which is present in the human alpha 1-antitrypsin gene between positions -78 and -62 from the start of transcription. LF-B1 also recognizes a related sequence present in the human albumin gene between -66 and -50. These results suggest that LF-A1 and LF-B1 are common positive trans-acting factors which are required for the expression of several genes in the hepatocyte.

Purification of a NF1-like DNA-binding protein from rat liver and cloning of the corresponding cDNA.

NF1-like proteins play a role in transcription of liver-specific genes. A DNA-binding protein, recognizing half of the canonical NF1 binding site (TGGCA) present on the human albumin and retinol-binding protein genes, has been purified from rat liver. Several peptides deriving from a tryptic digest of the purified protein were sequenced and the sequence was used to synthesize specific oligonucleotides. Two overlapping cDNA clones were obtained from a rat-liver cDNA library; their sequence reveals an open reading frame coding for 505 amino acids, including all the peptides sequenced from the purified protein. The DNA-binding domain, most likely located within the first 250 amino acids, is highly homologous to the sequence of CTF/NF1 purified from HeLa cells. Northern analysis reveals several mRNA species present in different combinations in various rat tissues.

Functional expression of soluble human interleukin-11 (IL-11) receptor alpha and stoichiometry of in vitro IL-11 receptor complexes with gp130.

The interleukin-6 (IL-6) family of cytokines activates signaling through the formation of either gp130 homodimers, as for IL-6, or gp130-leukemia inhibitory factor receptor (LIFR) heterodimers as for ciliary neurotrophic factor (CNTF), leukemia inhibitory factor, oncostatinM, and cardiotrophin-1. Recent in vitro studies with IL-6 and CNTF have demonstrated that higher order hexameric receptor complexes are assembled in which signaling chain dimerization is accompanied by the dimerization of both the cytokine molecule and its specific receptor alpha subunits (IL-6Ralpha or CNTFRalpha, respectively). IL-11 is a member of the IL-6 family and known to require gp130 but not LIFR for signaling. In this study we investigate the functional and biochemical composition of the IL-11 receptor complex. The human IL-11 receptor alpha-chain was cloned from a human bone marrow cDNA library. IL-11Ralpha was shown to confer IL-11 responsiveness to human hepatoma cells either by cDNA transfection or by adding a soluble form of the receptor (sIL11Ralpha) expressed in the baculovirus system to the culture medium. In vitro immunoprecipitation experiments showed that sIL11Ralpha specifically binds IL-11 and that binding is enhanced by gp130. Similarly to IL-6 and CNTF, gp130 is able to induce dimerization of the IL-11.IL-11Ralpha subcomplex, the result of which is the formation of a pentameric receptor complex. However, in contrast to the other two cytokines, IL-11 was unable to induce either gp130 homodimerization or gp130/LIFR heterodimerization. These results strongly suggest that an as yet unidentified receptor beta-chain is involved in IL-11 signaling.

The 11S rat seminal vesicle mRNA directs the in vitro synthesis of two precursors of the major secretory protein IV.

The 11s mRNA extracted from the rat seminal vesicles directs the synthesis of two different precursors of the major secretory protein RSV-IV. These two precursors are not interconvertible and seemingly originate from different translational events. Sucrose gradients, polyacrylamide gel electrophoresis and positive hybridization translation experiments do not allow the separation of the two putatively different mRNAs. It is concluded that the two RSV-IV precursors either derive from two extremely similar, but physically not separable mRNA species, or from two different modes of translation of the same mRNA molecule.

Definition of a composite binding site for gp130 in human interleukin-6.

The helical cytokine interleukin-6 (IL-6) assembles a multiprotein receptor complex. The starting event in the activation of intracellular signaling is the binding of the IL-6/IL-6R alpha subcomplex to two gp130 chains. The homodimerization of gp130 is triggered by two distinct and independent regions of IL-6 called sites 2 and 3. Several IL-6 antagonists have been obtained that affect signaling, but not IL-6 IL-6R alpha subcomplex formation. In this paper, we analyze in detail the impact of these antagonists on gp130 binding and dimerization and show that each signaling variant affects gp130 dimerization in vitro and that biological activity on cells decreases in precise parallel to the decrease in gp130 dimerization in vitro. All IL-6 antagonists can be classified into two groups, mapping at either site 2 or 3 in correspondence to their mode of interaction with gp130. We found that site 3 is a large region, which includes residues at the beginning of helix D spatially flanked by residues in the putative AB loop and located at one extremity of the cytokine 4-helix bundle. Interestingly, in leukemia inhibitory factor, another cytokine that signals through gp130, site 3, is topologically conserved but has evolved to bind leukemia inhibitory factor receptor.

Production and structural characterization of amino terminally histidine tagged human oncostatin M in E. coli.

Oncostatin M is a cytokine that acts as a growth regulator on a wide variety of cells and has diverse biological activities including acute phase protein induction, LDL receptor up-regulation and cell-specific gene expression. In order to gather information about the Onc M structure, we established a protocol for large scale production and single step purification of this functional cytokine from bacterial cells. The cDNA of human Onc M was cloned by RT-PCR from total RNA of PMA induced U937 cells. After the addition of a six histidine tag at the N-terminus, the coding region of mature Onc M was cloned in the pT7.7 expression vector. Histidine tagged Onc M was overexpressed in bacterial cells and purified to homogeneity in one step on a metal chelating column. We found that recombinant 6xHis-OncM remains fully active in a growth inhibition assay. Structural characterization of the purified protein was performed by electrospray mass spectrometry, automated Edman degradation and peptide mapping by high-pressure liquid chromatography/fast-atom-bombardment mass spectrometry. Thermal and pH stability dependence of Onc M was assessed by circular dichroism spectroscopy; the helical content is about 50%, in agreement with the four helix bundle fold postulated for cytokines that bind haematopoietic receptors of type I.

Nonradioactive receptor binding assay for ciliary neurotrophic factor.

A nonradioactive receptor binding assay for ciliary neurotrophic factor (CNTF) is described. The assay is based on the interaction between biotinylated human CNTF, soluble gp130, and soluble myc-tagged CNTF receptor captured on a microtiter plate via an antibody against the myc epitope tag. Bound cytokine is revealed by alkaline phosphatase-conjugated avidin. Purified human and rat CNTF competed with biotinylated CNTF for receptor binding, with IC50 values of 29 and 2 nM, respectively. Since the higher affinity of rat vs human CNTF has been previously shown to be conferred by the arginine residue at position 63 of the rat protein, we also tested a human CNTF mutant carrying a Q63R substitution. Secreted forms of wild-type and mutant CNTF were expressed in Escherichia coli, and the amount of cytokines in periplasmic extracts was determined by quantitative Western blotting analysis. The human CNTF mutant (Q63R, N137S) was found to compete with biotinylated CNTF for binding to soluble CNTF receptor with an eightfold higher apparent affinity than wild-type human CNTF. The present method thus faithfully reproduces the relative activities of CNTF analogs determined in other assay systems. The possibility of assaying cytokines in crude bacterial extracts makes the new technique particularly suitable for rapidly determining the receptor binding potencies of genetically engineered CNTF variants.

Interleukin-6 (IL-6) antagonism by soluble IL-6 receptor alpha mutated in the predicted gp130-binding interface.

Interleukin-6 (IL-6) triggers the formation of a high affinity receptor complex constituted by the ligand-binding subunit IL-6 receptor alpha (IL-6R alpha) and the signal-transducing beta chain gp130. Since the cytoplasmic region of IL-6R alpha is not required for signal transduction, soluble forms of IL-6R alpha (sIL-6R alpha) show agonistic properties because they are still able to originate IL-6.sIL-6R alpha complexes, which in turn associate with gp130. A three-dimensional model of the human IL-6.IL-6R alpha.gp130 complex has been constructed and verified by site-directed mutagenesis of regions in shIL-6R alpha (where "h" is human) anticipated to contact hgp130, with the final goal of generating receptor variants with antagonistic properties. In good agreement with our structural model, substitutions at Asn-230, His-280, and Asp-281 selectively impaired the capability of shIL-6R alpha to associate with hgp130 both in vitro and on the cell surface, without affecting its affinity for hIL-6. Moreover, the multiple substitution mutant A228D/N230D/H280S/D281V expressed as a soluble protein partially antagonized hIL-6 bioactivity on hepatoma cells.

Polymorphism of rat seminal vesicle secretory proteins: characterization of svp-1 and svp-2 and their identification with the major secretory proteins IV and V.

The proteins secreted by the rat seminal vesicle can be separated into five denaturing conditions. Two polymorphic proteins, svp-1 and svp-2, also present in the mouse, are produced by the seminal vesicle as well, but the procedure used for their identification makes it impossible to ascertain whether they correspond to any of the major fractions mentioned above. We show here that, on the basis of molecular weight measurements and of amino acid composition determinations, svp-1 and RSV-V are indeed the same protein. We also show that svp-2 is strictly related to another major secretory protein, RSV-IV, whose amino acid composition is almost identical, but for a few amino acid residues, to that of svp-2. We thus conclude that the latter protein is a variant of RSV-IV that can be expressed only in rats homozygous for a given allele at the svp-2 locus. This paper thus brings together published information on the genetics of the loci coding for svp-1 and for svp-2 and on the molecular biology of RSV-IV and RSV-V and of their corresponding gene.

Oncostatin M binds directly to gp130 and behaves as interleukin-6 antagonist on a cell line expressing gp130 but lacking functional oncostatin M receptors.

Oncostatin M (OM) and interleukin 6 (IL-6) are functionally related cytokines, which trigger similar biological responses because they share gp130 as a common signal transducing transmembrane receptor. While IL-6 recruits gp130 only upon binding to its specific receptor subunit (IL-6R alpha), reconstitution and cross-linking experiments on cell membranes suggest that OM can directly interact with gp130 and that this interaction is necessary but not sufficient to stimulate cells. However, the issue of the direct binding between gp130 and OM, in the absence of any additional membrane component, remained essentially unclarified. In this paper we show that, uniquely among the family of cytokines that transduce through gp130, OM directly binds in vitro with a 10(-8) M affinity sgp130, a soluble form of gp130. Moreover, titration of sgp130 with OM inhibits the formation of a ternary complex comprising IL-6, sIL-6R alpha, and sgp130. These in vitro properties of OM are consistent with the additional finding that on human hepatoma Hep3B cells, which express gp130 but not functional OM receptors, OM does not mimic IL-6 activity, but rather behaves, at high doses, as an IL-6 antagonist.

Cis- and trans-acting elements responsible for the cell-specific expression of the human alpha 1-antitrypsin gene.

The 5' flanking region of the human alpha 1-antitrypsin (alpha 1-AT) gene contains cis-acting signals for liver-specific expression and, when fused to a reporter gene, is able to drive the expression of this gene specifically in liver cells. Here we report the results of a functional dissection of the alpha 1-AT regulatory region. The expression of the bacterial chloramphenicol-transacetylase (CAT) gene, fused to a set of alpha 1-AT 5' flanking regions shortened by progressive deletions or mutated by base pair substitutions, has been compared by transfection in HepG2 (hepatocyte) and HeLa (non-hepatocyte) human cell lines. A minimal tissue-specific element has been identified between the nucleotides -137 and -37 (from the transcriptional start site). This DNA segment activates the heterologous SV40 promoter in hepatoma cell lines but not in HeLa cells. This element contains at least two regions referred to as the A (-125/-100) and B (-84/-70) domains, both essential for transcription. There are at least two other regulatory domains located upstream of the 'minimal element'; the most active of these is located between positions -261 and -210 from the cap site. These upstream elements activate the heterologous SV40 early promoter both in hepatoma cell lines and in HeLa cells. Upon fractionation of rat liver nuclear extracts two proteins have been identified, alpha 1TF-A and alpha 1TF-B, which bind specifically to the A and B domains respectively. Transcriptionally inactive A and B domain mutants are not able to bind these proteins.