Effects of soluble interleukin-1 type II receptor on rabbit antigen-induced arthritis: clinical, biochemical and histological assessment

OBJECTIVES

To investigate the effects of soluble interleukin-1 (IL-1) type II receptor (sIL-1RII) on a number of clinical, biochemical and histological parameters in rabbit antigen-induced arthritis.

METHODS

Arthritis was induced by intra-articular injection of methylated bovine serum albumin (mBSA) into rabbits pre-sensitized to the same antigen. An initial i.v. bolus of sIL-1RII was administered, followed by s.c. mini-pump dosing for 14 days, starting at the time of the arthritis induction. Animals received vehicle (saline 500 microl + 5 microl/h), low-dose sIL-1RII (13.4 microg + 1.34 microg/h) or high-dose sIL-1RII (40.2 microg + 4.02 microg/h).

RESULTS

Marked, dose-related inhibition of joint diameter, plasma prostaglandin E2 (PGE2), and synovial fluid IL-1alpha and IL-1beta concentrations were seen after administration of sIL-1RII. However, synovial fluid PGE2 concentrations and synovial fluid cell counts were not affected. A significant inhibitory effect was also seen histologically on soft-tissue swelling and joint damage with high-dose sIL-1RII.

CONCLUSIONS

These results demonstrate that IL-1 plays an important role in the pathogenesis of rabbit antigen-induced arthritis, thus confirming it as an excellent animal model with respect to evaluating anti-cytokine therapies for rheumatoid arthritis.

Increased mature interleukin-1beta (IL-1beta) secretion from THP-1 cells induced by nigericin is a result of activation of p45 IL-1beta-converting enzyme processing

Perregaux and Gabel (Perregaux, D., and Gabel, C. A. (1994) J. Biol. Chem. 269, 15195-15203) reported that potassium depletion of lipopolysaccharide-stimulated mouse macrophages induced by the potassium ionophore, nigericin, leads to the rapid release of mature interleukin-1beta (IL-1beta). We have now shown a similar phenomenon in lipopolysaccharide-stimulated human monocytic leukemia THP-1 cells. Rapid secretion of mature, 17-kDa IL-1beta occurred, in the presence of nigericin (4-16 microM). No effects on the release of tumor necrosis factor-alpha, IL-6, or proIL-1beta were seen. Addition of the irreversible interleukin-1beta-converting enzyme (ICE) inhibitor, Z-Val-Ala-Asp-dichlorobenzoate, or a radicicol analog, inhibited nigericin-induced mature IL-1beta release and activation of p45 ICE precursor. The radicicol analog itself did not inhibit ICE, but markedly, and very rapidly depleted intracellular levels of 31-kDa proIL-1beta. By contrast, dexamethasone, cycloheximide, and the Na+/H+ antiporter inhibitor, 5-(N-ethyl-N-isopropyl)amiloride, had no effect on nigericin-induced release of IL-1beta. We have therefore shown conclusively, for the first time, that nigericin-induced release of IL-1beta is dependent upon activation of p45 ICE processing. So far, the mechanism by which reduced intracellular potassium ion concentration triggers p45 ICE processing is not known, but further investigation in this area could lead to the discovery of novel molecular targets whereby control of IL-1beta production might be effected.

Induction of rapid IL-1 beta mRNA degradation in THP-1 cells mediated through the AU-rich region in the 3'UTR by a radicicol analogue

A radicicol analogue (analogue A) was found to inhibit interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF-alpha) secretion from THP-1 cells. If added to cells activated by interferon gamma and lipopolysaccharide, radicicol analogue A not only inhibited the secretion of IL-1 beta but also induced an extremely rapid degradation of IL-1 beta, IL-6 and TNF-alpha mRNA to undetectable levels within 5-8 h. This degradation is independent of translation and of the signal inducing transcription. The common feature of these genes is the inclusion of one or more copies of the mRNA-instability sequence, AUUUA, in the 3' untranslated region. Indeed, no destabilizing effect of radicicol analogue A could be observed on mRNA derived from the expression of an IL-1 beta construct lacking the AUUUA motifs of the 3'UTR. The effect of radicicol analogue A on protein/mRNA interaction and on post-translational modifications of cytoplasmic proteins is described. This class of compound constitutes a valuable tool for the further elucidation of the mechanism of mRNA degradation of cytokines and proto-oncogenes.

Expression, refolding, and autocatalytic proteolytic processing of the interleukin-1 beta-converting enzyme precursor

The interleukin-1 beta-converting enzyme is a heterodimeric cysteine protease that is produced as a 45-kDa precursor. The full-length precursor form of the enzyme was expressed in Escherichia coli as insoluble inclusion bodies. Following solubilization and refolding of the 45-kDa protein, autoproteolytic conversion to a heterodimeric form containing 10- and 20-kDa subunits was observed. This enzyme had catalytic activity against both natural (interleukin-1 beta precursor) and synthetic peptide substrates. The inclusion of a specific inhibitor (SDZ 223-941) of the converting enzyme in the refolding mixture prevented proteolytic processing to the 10-/20-kDa form. Similarly, refolding under nonreducing conditions also prevented processing. Time course experiments showed that the 10-kDa subunit was released from the 45-kDa precursor before the 20-kDa subunit, implying that the N-terminal portion of the precursor is released last and may play a regulatory role.

Cell-free transcription directed by the 422 adipose P2 gene promoter: activation by the CCAAT/enhancer binding protein

Previous investigations have shown that CCAAT/enhancer binding protein (C/EBP) can function as a trans-activator of the promoters of several adipocyte-specific genes--i.e., the 422 adipose P2 (422/aP2), stearoyl-CoA desaturase 1 (SCD1), and glucose transporter 4 (GLUT4) genes, in 3T3-L1 mouse preadipocytes. We now describe a cell-free system prepared from nuclei of 3T3-L1 cells that carries out transcription directed by these promoters. To measure transcript formation, we employed a polymerase chain reaction-assisted analysis. Nuclear extract from 3T3-L1 adipocytes that express C/EBP supports a higher rate of transcription of chimeric 422(aP2) promoter-chloramphenicol acetyltransferase (CAT) reporter gene constructs than nuclear extract from preadipocytes that lack C/EBP. A competitor oligonucleotide containing the C/EBP binding site sequence and antibodies raised against C/EBP inhibit transcription directed by the 422(aP2) promoter. The factor limiting transcription by nuclear extract from preadipocytes appears to be C/EBP, since recombinant C/EBP (rC/EBP) markedly activates transcription of the 422(aP2) promoter-CAT gene with preadipocyte extract but not with adipocyte extract. rC/EBP also activates cell-free transcription of SCD1 promoter-CAT and GLUT4 promoter-CAT chimeric genes. Point mutations within the C/EBP binding site in the 422(aP2) promoter markedly decrease transcription activated by rC/EBP. Consistent with activation by cAMP of the 422(aP2) promoter in intact preadipocytes, cAMP-dependent protein kinase activates transcription through this promoter with the cell-free system, this effect being independent of C/EBP. Thus, regulation of transcription directed by the 422(aP2) promoter in the cell-free system resembles that which occurs in intact 3T3-L1 cells.

The upstream stimulatory factor binds to and activates the promoter of the rat class I alcohol dehydrogenase gene

The gene encoding rat class I alcohol dehydrogenase (ADH) is expressed primarily in the liver. Recent studies in our laboratories indicate that multiple cellular factors present in the rat liver interact with various regions of the promoter of this gene. One of the regions contains the sequence 5'-CACATG-3' that has an "E box" homology to which a number of transcription factors containing the basic helix-loop-helix motif bind. We now demonstrate that the human transcription factor, upstream stimulatory factor (USF), a basic helix-loop-helix-containing protein, binds to and activates the promoter of the rat class I ADH gene. Electrophoretic mobility shift assays of labeled oligonucleotide containing the 5'-CACATG-3' sequence within the ADH promoter revealed the formation of multiple DNA-protein complexes when nuclear extracts obtained from adult rat liver were used. The binding of proteins to the DNA could be competed away with an oligonucleotide specifying a sequence within the adenovirus major late promoter (MLP) that had previously been shown to bind USF. Similar complexes were observed when electrophoretic mobility shift assays of labeled MLP oligonucleotide were performed with rat liver nuclear extracts. Conversely, nuclear extracts isolated from HeLa cells, cells known to have abundant USF, contain factors that interact with the sequence present in the ADH promoter. This interaction could be competed efficiently by the MLP oligonucleotide. USF synthesized in an in vitro transcription and translation system also binds to the ADH promoter as well as to the MLP. In addition, antiserum directed against USF recognizes factors present in the rat liver nuclear extracts that interact with the ADH promoter. Furthermore, transcription directed from both the ADH and the adenovirus major late promoters was inhibited by an oligonucleotide representing the USF-binding site within the ADH promoter in a cell-free in vitro transcription system. Lastly, an ADH promoter-reporter gene construct was transactivated by an eukaryotic expression vector containing USF in HepG2 cells co-transfected with the two constructs. These experiments demonstrate that USF is present in the rat liver and that it binds to and activates the promoter of the rat class I ADH gene in a sequence-specific manner.

A spin-label electron spin resonance study of the binding of mitochondrial creatine kinase to cardiolipin

The binding of the mitochondrial creatine kinase to aqueous dispersions of beef heart cardiolipin has been studied via the perturbation of the mobility of spin-labelled cardiolipin, using electron spin resonance (ESR) spectroscopy. In the presence of creatine kinase (1:1 protein/lipid ratio, by mass), the ESR spectra of cardiolipin labelled in a single acyl chain [n-(4,4-dimethyl-oxazolidinyl-N- oxy)stearoylcardiolipin] indicate a restriction of motion both at the C-5 and C-14 positions (n = 5, 14) of the lipid chains. The restriction in mobility was reversed by addition of phosphate or adriamycin, which are thought to inhibit the binding of creatine kinase to the mitochondrial membrane or to displace it from its binding site on the membrane. The effect of the protein on the chain mobility is consistent with surface binding of the protein; no positive evidence was obtained for penetration of the protein into the hydrophobic region of the membrane.

Identification and primary structure of the cardiolipin-binding domain of mitochondrial creatine kinase

It was recently shown that the mitochondrial isozyme of heart creatine kinase binds to cardiolipin on the outer half of the inner membrane [Müller, M., et al. (1985) J. Biol. Chem. 260, 3839-3843]. The enzyme has now been extracted and purified to homogeneity from rat heart mitochondria, and cleaved with CNBr. The fragments have been separated on an FPLC system using a Mono Q HR 5/5 column. Only one of these binds to cardiolipin-containing liposomes and has thus been identified as the cardiolipin-binding domain of the enzyme. Its amino acid sequence has been determined. The fragment contains 25 amino acids and corresponds to the N-terminal region of the protein. The binding of the fragment of cardiolipin-containing liposomes was inhibited by adriamycin. Another and larger CNBr fragment could be specifically labelled with periodate-oxidized (di-aldehyde) ATP and has thus been identified as the ATP-binding domain. Chemical modification of the basic amino acids Lys and Arg of the enzyme abolished its binding to cardiolipin.

Adriamycin as a probe for the transversal distribution of cardiolipin in the inner mitochondrial membrane

The ability of adriamycin to complex cardiolipin was used to determine the distribution of cardiolipin across the inner membrane of rat liver and heart mitochondria. In both mitochondrial types, about 57 +/- 5% of the total cardiolipin was found to be located in the cytoplasmic face of the inner membrane. Mitochondria and mitoplasts were used to study the cytoplasmic face of the inner membrane, purified submitochondrial vesicles with inverted membrane orientation for the matrix face. The cardiolipin amount titrated by adriamycin in the latter was found to be complementary to the amount titrated in the cytoplasmic face. The adriamycin association constant determined for the first saturation level of mitochondria was in good agreement with the value published by Goormaghtigh et al. (Goormaghtigh, E., Chatelain, P., Caspers, J., and Ruysschaert, J. M. (1980) Biochim. Biophys. Acta 597, 1-14) for cardiolipin in artificial membranes. Two binding plateaus were observed when increasing amounts of adriamycin were added to mitochondria. The plateau at higher concentrations is conveniently explained by the penetration of adriamycin into mitochondria and the titration of cardiolipin in the matrix face. Scatchard plot analysis of the binding curves leading to the two plateaus produced almost identical association constants. The total amount of cardiolipin in mitochondria calculated from curves of this type corresponded to the total amount of cardiolipin determined by phosphate analysis of extracts, analyzed by thin layer chromatography.

Cardiolipin is the membrane receptor for mitochondrial creatine phosphokinase

Treatment of rat heart mitochondria with phosphate or mersalyl releases a number of proteins, including the mitochondrial creatine kinase (mt-CK). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the released proteins showed that phosphate is more selective than mersalyl in releasing mt-CK. The rebinding of mt-CK to mitochondria was selectively inhibited by adriamycin, which complexes membrane-bound cardiolipin. mt-CK activity and binding experiments have shown that intact mitochondria are able to bind approximately twice the amount of mt-CK they originally contain. Liver mitochondria bound heart mitochondria mt-CK to the same extent as creatine kinase-depleted heart mitochondria. mt-CK was bound by liposomes but only if they contained cardiolipin. The binding of mt-CK to cardiolipin-containing liposomes was inhibited by adriamycin. Phosphatidylcholine liposomes reconstituted with the purified ADP/ATP translocator failed to bind mt-CK.

Doxorubicin inhibits the phosphate-transport protein reconstituted in liposomes. A study on the mechanism of the inhibition

The phosphate transport protein (PTP) has been isolated from beef heart mitochondria in the presence of cardiolipin and reconstituted in asolectin and phosphatidylcholine vesicles. As expected, the activity of the reconstituted PTP is inhibited by N-ethylmaleimide and mersalyl. It is also inhibited by adriamycin and Br-daunomycin. Storage of isolated mitochondria at -80 degrees C prior to the isolation of the PTP decreases the maximal activity of the unidirectional transport of phosphate (Pi) in reconstituted vesicles. The sensitivity of the system to the four inhibitors remains the same. The inhibition of the PTP by adriamycin is reversed by KCl and prevented by MgSO4. Since the interaction between adriamycin and cardiolipin is of ionic type, KCl apparently replaces adriamycin on the negative charges of cardiolipin. By contrast, MgSO4 complexes adriamycin directly, eliminating its inhibitory effect on the PTP. No PTP activity is found after reconstitution in phosphatidylcholine vesicles in the absence of cardiolipin. Addition of buffer-dispersed cardiolipin to the vesicles restores the Pi-transport activity. The addition of adriamycin to the vesicles together with cardiolipin removes the reactivation. Succinylation of the PTP at pH 8.0 eliminates the inhibitory effect of adriamycin in the reconstituted system. The effects of N-ethylmaleimide and mersalyl are not modified. The succinylated preparation reconstituted in phosphatidylcholine vesicles is reactivated by cardiolipin, but in this case the reactivation is not counteracted by adriamycin. Succinylation of the PTP at pH 9.0 results in its complete inhibition. The results indicate, (a) that the sites of interaction of MalNEt /mersalyl and adriamycin with the PTP X cardiolipin complex are different, and (b) that the adriamycin-binding site in the complex is probably on cardiolipin molecules essential to the PTP activity. It is postulated that succinylation of the PTP prevents the interaction of adriamycin with these molecules.

The mitochondrial phosphate carrier reconstituted in liposomes is inhibited by doxorubicin

The phosphate carrier has been isolated from beef heart mitochondria in the presence of cardiolipin and reconstituted in asolectin vesicles. It has been found that 100 microM doxorubicin and 100 microM Br-daunomycin inhibit the unidirectional phosphate uptake in the reconstituted liposomes to the same extent as N-ethylmaleimide. The inhibition by Br-daunomycin is not due to covalent interaction with the carrier. The specific interaction between doxorubicin and cardiolipin is responsible for the inhibition of the phosphate carrier. Br-daunomycin interacts with 3 mitochondrial proteins of apparent Mr approximately 45 000, approximately 35 000 and approximately 30 000.