Isolation of an IL-13-dependent subclone of the B9 cell line useful for the estimation of human IL-13 bioactivity

A novel sub-clone of the B9 hybridoma cell line (B9-1-3) has been selected by cloning following continuous culture in rhIL-13. This cell line shows an increased sensitivity to both hIL-13 and mIL-4 compared to the parental B9 cell line. The proliferative response to IL-13 can be blocked with an anti-IL-4 receptor monoclonal antibody but not with the soluble IL-4 receptor, suggesting that IL-13- and IL-4-binding receptor subunits are distinct but form part of a common receptor complex. Although the B9-1-3 cell line is still sensitive to picogrammes of IL-6, it can be used to measure IL-13 in the presence of IL-6 by inclusion of excess neutralizing IL-6 antibody. This cell line should thus prove useful both in measuring the IL-13 bioactivity and for the dissection of the molecular nature of the IL-13:IL-4 receptor complex.

High-level production of a human membrane protein in yeast: the peripheral-type benzodiazepine receptor

The human peripheral-type benzodiazepine receptor (PBR) has been produced in Saccharomyces cerevisiae where it retains its pharmacological properties [Riond et al., Eur. J. Pharmacol. 208 (1991) 307-312]. As the rate of production was low, we analysed the mRNA level, the effect of variation of the 5' sequence and the production in mitochondria. Translation rather than transcription or targeting was found to be the main limiting factor. We were able to produce a chimeric PBR, with an N-terminal extension, to a very high level in the yeast mitochondrial membrane.

Evidence for the presence of beta 3-adrenergic receptor mRNA in the human brain

The beta 3-adrenergic receptor (AR) is widely distributed in peripheral tissues, but up to now it has not been detected in the central nervous system. By using the polymerase chain reaction (PCR) technique, we found the beta 3-AR mRNA to be present in all the regions of the human brain we investigated. The quantities found were very low compared to those of the beta 1-AR and beta 2-AR mRNAs, being hardly detectable in adult brain. In contrast, the brain of very young infants contained about 100 times more beta 3-AR mRNA than the adult brain, whereas the amounts of beta 1-AR and beta 2-AR transcripts were essentially the same. In addition, using PCR we have cloned a central beta 3-AR coding region from a human frontal cortex cDNA library and have found it to be identical to the corresponding peripheral sequence.

Safety of echo-dipyridamole test in elderly patients with coronary artery disease

The authors prospectively studied the feasibility and safety of high-dose dipyridamole echocardiography in 166 patients (77 younger and 89 elderly patients) referred for clinical evaluation of coronary artery disease. Echocardiographic examinations were adequate for analysis of parameters considered in 135 of the 166 patients (81.3%; 73 elderly, 62 younger patients). The feasibility of dipyridamole echocardiography test was 80.5% in young and 82% in elderly patients (P = ns). The incidence of side effects during dipyridamole echocardiography was similar in the two groups, except for dyspnea, which was observed in 20.5% of older and 3.2% of younger patients (p < 0.05). These data demonstrate that the dipyridamole test combined with echocardiographic monitoring of regional myocardial contractility may be considered a valid noninvasive method of evaluating coronary artery disease in the elderly.

Interleukin-13 inhibits protein kinase C-triggered respiratory burst in human monocytes. Role of calcium and cyclic AMP

Interleukin-13 (IL-13), a novel cytokine produced by activated lymphocytes modulates some monocyte functions, but no data is available concerning the signal transduction pathway. We show here, the inhibitory effect of IL-13 on 12-O-tetradecanoylphorbol-13-acetate (TPA)-triggered reactive oxygen intermediate production in human monocytes and the signals involved in this response. Our results show that IL-13 produces rapid and transient phosphoinositide hydrolysis and intracellular Ca2+ mobilization. Furthermore, IL-13 induces intracellular cAMP accumulation through inositol 1,4,5-trisphosphate-dependent Ca2+ mobilization. Metabolic inhibitors were used to relate the first steps in signaling pathways to the inhibitory effect of IL-13 on TPA-triggered reactive oxygen intermediate production. Indeed, inhibitors of phospholipase C (neomycin), intracellular Ca2+ mobilization (8-[N,N-diethylamino]-octyl 3,4,5-trimethoxybenzoate hydrochloride), adenylate cyclase (delta 9-tetrahydrocannabinol), and protein kinase A (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) impair the IL-13 inhibitory response. Altogether these observations indicate that modulatory effect of IL-13 on the TPA-induced oxidative burst is the result of the intracellular cAMP accumulation through an inositol 1,4,5-trisphosphate-induced Ca2+ mobilization-dependent pathway.

Characterization and comparison of the interleukin 13 receptor with the interleukin 4 receptor on several cell types

We describe here the characterization of the interleukin (IL) 13 receptor and a comparison with the IL-4 receptor on different cell types. Several, but not all, of the IL-4 receptor-positive cells showed specific IL-13 binding, which was always completely displaced by IL-4. In the IL-13 receptor-positive cells, the IL-13 either completely or partially displaced the labeled IL-4. Further characterization of the IL-13 receptor in two cell lines, COS-3 and A431, representative of the groups of complete and partial displacement of IL-4 by IL-13, respectively, showed that the IL-13 binds with high affinity (Kd approximately 300 pM) to both cells and that the number of binding sites is, in COS-3 cells, equivalent to that for IL-4 and, in A431 cells, is smaller than that for IL-4. Cross-linking of labeled IL-13 yielded, on COS-3 cells, two affinity-labeled complexes of 220 and 70 kDa, and on A431 cells, one complex of 70 kDa; labeled IL-4 yielded on both cells the same pattern of three complexes of 220, 145, and 70 kDa. Altogether, these results suggest that the IL-13 receptor may be constituted by a subset of the IL-4 receptor complex associated with at least one additional protein.

An amino-terminal variant of the central cannabinoid receptor resulting from alternative splicing

The cDNA sequences encoding the central cannabinoid receptor, CB1, are known for two species, rat and human. However, little information concerning the flanking, noncoding regions is presently available. We have isolated two overlapping clones from a human lung cDNA library with CB1 cDNA inserts. One of these, cann7, contains a short stretch of the CB1 coding region and 4 kilobase pairs (kb) of the 3'-untranslated region (UTR), including two polyadenylation signals. The other, cann6, is identical to cann7 upstream from the first polyadenylation signal, and in addition, it contains the whole coding region and extends for 1.8 kb into the 5'-UTR. Comparison of cann6 with the published sequence (Gérard, C. M., Mollereau, C., Vassart, G., and Parmentier, M. (1991) Biochem. J. 279, 129-134) shows the coding regions to be identical, but reveals important differences in the flanking regions. Notably, the cann6 sequence appears to be that of an immature transcript, containing 1.8 kb of an intronic sequence in the 5'-UTR. In addition, polymerase chain reaction amplification of the CB1 coding region in the IM-9 cell line cDNA resulted in two fragments, one containing the whole CB1 coding region and the second lacking a 167-base pair intron within the sequence encoding the amino-terminal tail of the receptor. This alternatively spliced form would translate to an NH2-terminal modified isoform (CB1A) of the receptor, shorter than CB1 by 61 amino acids. In addition, the first 28 amino acids of the putative truncated receptor are completely different from those of CB1, containing more hydrophobic residues. Rat CB1 mRNA is similarly alternatively spliced. A study of the distribution of the human CB1 and CB1A mRNAs by reverse transcription-polymerase chain reaction analysis showed the presence of both CB1 and CB1A throughout the brain and in all the peripheral tissues examined, with CB1A being present in amounts of up to 20% of CB1.

Reduced aerobic metabolic efficiency in postischemic myocardium dysfunction in rats: role of aging

It has been suggested that aging may enhance the deleterious effects of myocardial ischemia-reperfusion. This study evaluates the relationship between oxygen consumption and functional impairment during reperfusion following myocardial ischemia in adult and senescent rat hearts. Global ischemia induced a marked impairment of contractile function which was significantly higher in senescent than in adult hearts. During reperfusion postischemic dysfunction was more evident in senescent hearts: at the 10th minute, the developed pressure recovered less (p < 0.05) and end-diastolic pressure increased more (p < 0.05) in senescent than in adult hearts. However, oxygen consumption per unit of work was significantly higher throughout 60 min of reperfusion when compared to controls with no significant difference between adult and senescent hearts. This study demonstrates that following ischemia and reperfusion depression of function and inappropriately high oxygen consumption were observed in both adult and senescent hearts. However, aging was associated with greater contractile impairment, which occurred in the absence of further deterioration of metabolic efficiency of contraction.

Function of the interleukin-2 (IL-2) receptor gamma-chain in biologic responses of X-linked severe combined immunodeficient B cells to IL-2, IL-4, IL-13, and IL-15

The interleukin-2 (IL-2) receptor gamma-chain is a common component of several members of the cytokine receptor superfamily including those for IL-2, IL-4, IL-7, IL-9, IL-15, and possibly IL-13, and has recently been renamed the common gamma-chain (gamma c-chain). Transfection experiments have shown that the gamma c-chain participates in signal transduction by IL-2, IL-4 and IL-7, but a functional role for the gamma c-chain in biological responses by normal T cells and B cells to these cytokines has not been established. In this study, we have used X-linked severe combined immunodeficiency (X-SCID) as a naturally occurring gamma c-chain gene disruption model to examine the role of the gamma c-chain in human B-cell responses to IL-2, IL-4, IL-13, and IL-15. Our experiments show that B cells from two X-SCID patients with characterized gamma c-chain gene mutations do not respond to IL-2 or IL-15, but respond as well or better than normal B cells to both IL-4 and IL-13 in assays for B-cell activation, proliferation, and IgE secretion. This finding raises important questions about the function of the gamma c-chain in receptors for IL-4 and IL-13, and the nature of the immune defect in X-SCID.

Site-directed mutagenesis of the peripheral benzodiazepine receptor: identification of amino acids implicated in the binding site of Ro5-4864

The peripheral benzodiazepine receptor (PBR) is an 18-kDa protein present in the outer mitochondrial membrane. The human PBR can be labeled with the benzodiazepine Ro5-4864 and with the isoquinoline carboxamide PK11195. The two ligands compete with each other in binding experiments, with previous results suggesting overlapping but not identical binding sites. To define the regions of the receptor interacting with PK11195 and Ro5-4864 and to address the question of the topology of the molecule in the membrane, we generated mutant human PBRs with amino- and carboxyl-terminal deletions and with point mutations in potentially accessible cytoplasmic regions. The mutant genes were expressed in yeast and analyzed in binding experiments using radiolabeled PK11195 and Ro5-4864. The results showed that, whereas deletions in the amino-terminal sequence had marked consequences for the binding affinity of both ligands, the final 13 amino acids at the carboxyl terminus could be deleted with no effect on the binding of either Ro5-4864 or PK11195. The site-directed mutagenesis experiments pinpointed four amino acids as participating in the binding site of Ro5-4864. Three of these, Glu-29, Arg-32, and Lys-39, which are located in the first putative cytoplasmic loop, are conserved in human, bovine, rat, and mouse PBRs. The remaining residue, Val-154, which is found at the interface between the putative fifth transmembrane region and the cytoplasm, is present in the human, rat, and mouse sequences but is replaced by methionine in the bovine sequence. The exchange of Met-154 for valine in the bovine PBR introduced a binding site for Ro5-4864, which is absent in the native PBR. These four amino acids played a minor role, if any, in the binding site of PK11195. We also showed that the histidines previously suggested to be part of the binding site of PK11195 are not directly involved in the interaction of the human receptor with either PK11195 or Ro5-4864.

IL-4 and IL-13 induce Lsk, a Csk-like tyrosine kinase, in human monocytes

Lsk is a protein tyrosine kinase with homology to the COOH-terminal Src kinase (Csk). Unlike Csk that is ubiquitously expressed, Lsk has limited tissue distribution. Here we have examined the expression and regulation of Lsk and Csk in peripheral human monocytes. We have found that Lsk mRNA and protein were not expressed in resting monocytes but were induced by treatment with interleukin 4 (IL-4) or IL-13 but not by interferon gamma (IFN-gamma) or IL-2. In fact, IFN-gamma, but not IL-2, efficiently blocked Lsk induction by IL-4 or IL-13. In contrast, Csk was constitutively present in human monocytes and was upregulated by IFN-gamma but not by IL-4 or IL-13. These results suggest that despite their structural similarities, Lsk and Csk may play distinct regulatory roles in monocyte functions elicited by cytokines, with Lsk functioning specifically within the context of a Th2-type immune response.

Macrophage-inactivating IL-13 suppresses experimental autoimmune encephalomyelitis in rats

Experimental autoimmune encephalomyelitis (EAE) is initiated by myelin basic protein (MBP)-specific CD4+ T cells of the Th1 phenotype that subsequently trigger the invasion of monocytes/macrophages into the brain. In this study, we evaluated the potential of human recombinant (hr) IL-13 to exert a protective effect on the development of EAE in Lewis rats. hrIL-13 is found to be a potent in vitro modulator of various rat macrophage functions, including an inhibition of the production of the proinflammatory cytokines IL-1 beta and TNF, and a simultaneous enhancement of MHC class II and CD4 receptor expression. Furthermore, hrIL-13 displayed a slight, but highly reproducible, inhibitory effect on the in vitro proliferative responses of encephalitogenic MBP-specific T cells stimulated in the presence of thymic APCs. Upon in vivo application of hrIL-13-secreting vector cells into MBP-immunized animals, the cytokine was capable of markedly suppressing the development of EAE, as assessed by a reduction of the mean duration, severity, and incidence of disease. This suppression of disease coincided with an only minimal reduction of MBP-directed T cell autoreactivity and no alteration in MBP-specific autoantibody production. We infer from these results that a strictly Th1-initiated immune disease can be attenuated efficiently by the administration of a cytokine that primarily targets cells of the macrophage/monocyte lineage and seems to exert no undesirable general suppression on either T cell or B cell immunoreactivity in vivo.

Macrophage-inactivating IL-13 suppresses experimental autoimmune encephalomyelitis in rats

Experimental autoimmune encephalomyelitis (EAE) is initiated by myelin basic protein (MBP)-specific CD4+ T cells of the Th1 phenotype that subsequently trigger the invasion of monocytes/macrophages into the brain. In this study, we evaluated the potential of human recombinant (hr) IL-13 to exert a protective effect on the development of EAE in Lewis rats. hrIL-13 is found to be a potent in vitro modulator of various rat macrophage functions, including an inhibition of the production of the proinflammatory cytokines IL-1 beta and TNF, and a simultaneous enhancement of MHC class II and CD4 receptor expression. Furthermore, hrIL-13 displayed a slight, but highly reproducible, inhibitory effect on the in vitro proliferative responses of encephalitogenic MBP-specific T cells stimulated in the presence of thymic APCs. Upon in vivo application of hrIL-13-secreting vector cells into MBP-immunized animals, the cytokine was capable of markedly suppressing the development of EAE, as assessed by a reduction of the mean duration, severity, and incidence of disease. This suppression of disease coincided with an only minimal reduction of MBP-directed T cell autoreactivity and no alteration in MBP-specific autoantibody production. We infer from these results that a strictly Th1-initiated immune disease can be attenuated efficiently by the administration of a cytokine that primarily targets cells of the macrophage/monocyte lineage and seems to exert no undesirable general suppression on either T cell or B cell immunoreactivity in vivo.

A short-term infusion regimen of Cisplatin, 5-Fluorouracil and L-folinic Acid in advanced head and neck-carcinoma

Treatment of advanced head and neck cancer is still a matter of controversy. Although current chemotherapy regimens are able to induce high response rates, they have not shown improved survival. We employed a combination of cisplatin (CDDP), 5-fluorouracil (5FU) and 1-folinic acid (1-FA) in a 6-hour infusion schedule easy to administer on an outpatient basis. 49 patients have been included to date. The treatment plan consists of 5-FU (375 mg/m(2)) plus 1-FA (100 mg/m(2)) in a 4-hour i.v. infusion followed by a 2-hour i.v. administration of CDDP (20 mg/m(2)). This therapy was repeated for five consecutive days and recycled every 3-4 weeks. Out of 46 evaluable patients there were 6 complete responses (CR) and 23 partial responses (PR) for an overall response rate of 63%. Overall survival was 10.2 months (mean). Untreated patients had a higher probability of response as well as patients with naso-oropharyngeal primary tumor. Toxicity was generally mild with leukopenia, anemia and vomiting being the most frequent side effects. In conclusion, this combination appears well tolerated and active in the palliation of advanced head and neck cancer. However we think that increasing dose intensity of standard regimens and experimental new therapeutic approaches are needed to improve the clinical outcome of this disease.

Interleukin-13 gene expression by malignant and EBV-transformed human B lymphocytes

Expression of the IL-13 gene in malignant tissues from 26 human B-cell lymphoid malignancies was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). A positive signal was detected in 16 cases, which included high grade B lymphomas, follicular lymphomas and B-cell chronic lymphocytic leukemias. IL-13 mRNA was also detected in the 9 malignant B cell lines and in the 6 lymphoblastoid cell lines tested, as well as in freshly isolated malignant B cells from 2 patients with a Burkitt's lymphoma. Two of 8 T-cell lymphomas and 2 of 4 T-cell lines expressed the IL-13 gene. In contrast, IL-13 gene expression was not detected in any of the 5 non-lymphoid cell lines tested. No specific binding of radiolabeled IL-13 was detected on B cell lines, suggesting an absence of IL-13 receptors on such cells. This conclusion was also supported by the inability of IL-13 or anti-IL-13 antibodies to affect the growth of malignant B cells. Taken together, these results show that both malignant and EBV-transformed B lymphocytes, either freshly isolated or maintained as cell lines, express the IL-13 gene. This raises the question of the role of B lymphocyte-derived IL-13, a B lymphocyte stimulating cytokine, on the in vivo function of normal B lymphocytes as well as on the in vivo behaviour of B lymphoid malignancies.

Quantitative evaluations of gap junctions in old rat brown adipose tissue after cold acclimation: a freeze-fracture and ultra-structural study

The morphological and functional modifications of brown adipose tissue (BAT), the tissue responsible for non-shivering thermogenesis, are well established during the phases of active stimulation (i.e. neonatal period and cold acclimation) in young animals. The 'active' brown adipocytes are filled with numerous small lipid vacuoles and large mitochondria packed with cristae rich in the protonophore uncoupling protein (UCP), whereas the 'quiescent' cell shows larger, confluent vacuoles and smaller mitochondria with rarefied cristae poor of the uncoupling protein. It is well known from literature that also gap junctions (gjs), responsible for the electrical coupling among adjacent adipocytes, modify their size following the physiological stimulus in young animals. This is in agreement with the morphology of the functionally active brown adipocyte, i.e. the multilocular, UCP-positive cell. Although the presence of the BAT in old animals is well documented, less is known about its reactivity to physiological stimuli. The present work demonstrates that after cold acclimation brown adipocytes of old rats (2 years) change their ultrastructure in a similar way as in young rats. A quantitative analysis of gap junction areas on replicas obtained by the freeze fracture technique, showed that gj increase in size (mean area 53.2 vs 110.4 x 10(-3) microns2, p = 0.003). All these morphological modifications are quite similar to those observed in BAT of young and young adult rats, supporting the hypothesis of a physiological role of brown adipose tissue at every age.

Regulation of endothelial and mesothelial cell function by interleukin-13: selective induction of vascular cell adhesion molecule-1 and amplification of interleukin-6 production

The present study was designed to explore the interaction of interleukin-13 (IL-13) with vascular endothelial cells (EC). In vitro exposure to IL-13 of human umbilical vein EC induced surface expression of vascular cell adhesion molecule-1 (VCAM-1). At optimal concentrations (10 to 50 ng/mL) and exposure times (24 hours), IL-13 was a twofold to threefold less effective inducer of VCAM-1 than IL-1, which was used as reference EC activator. When IL-13 was combined with IL-1, an almost additive induction of VCAM-1 was observed. Induction of VCAM-1 by IL-13 was selective in that E-selectin and intercellular adhesion molecule-1 (ICAM-1) were unaffected. IL-13 caused a modest reduction of IL-1 induction of E-selectin and ICAM-1. Surface expression of VCAM-1 on IL-13-treated cells was associated with mRNA induction (as assessed by Northern analysis and reverse transcriptase-polymerase chain reaction), with predominance of transcripts encoding the 7 Ig domain form of this molecule. In agreement with previous reports, IL-13 inhibited cytokine production in human monocytes. In contrast, IL-13 was a weak inducer and an amplifier (in concert with IL-1) of IL-6 expression in EC. Mesothelial cells, which share properties with EC and regulate the traffic and function of leukocytes in serosal cavities, were stimulated to express VCAM-1 and IL-6 by IL-13. Thus, IL-13 elicits a spectrum of responses in vascular endothelium remarkably similar to that of IL-4 and IL-10. Interaction of these cytokines with vascular endothelium may play an important role in the induction and expression of Th2-dependent responses.

IL-4 and IL-13 have overlapping but distinct effects on HIV production in monocytes

In HIV-1-infected monocytes and monocytoid cell lines, viral expression can be observed as high-level production, restricted (chronic low-level) expression, and latency (no viral expression). Interleukin-13 (IL-13) and IL-4, which have remarkedly similar deactivating effects on inflammatory monocyte functions, were studied for their regulation of HIV expression in monocytes. Pretreatment of peripheral monocytes for 48-72 h with IL-13 markedly decreased acute HIV infection, whereas IL-4 increased it. Similar effects were seen when the U1 and R-THP-1 monocytoid cell lines with restricted HIV expression were treated with these cytokines. However, when these continuously producing cell lines were chronically treated with cytokines, IL-13 increased HIV production. Neither IL-4 nor IL-13 stimulated HIV expression in latently infected cells. In chronically infected cells, several cytokines reduced viral mRNA. Both IL-4 and IL-13 increased monocyte aggregate formation, but only IL-4 ultimately stimulated cytolysis of HIV-infected monocytes as well as increased apoptosis of U1. In the presence of tumor necrosis factor alpha or IL-6, which upregulate HIV expression, IL-13 could no longer suppress HIV expression. These results indicate that IL-4 and IL-13, although closely related in modulating monocyte function, can have divergent effects on HIV expression in monocytes. Collectively, these data suggest that there exists a complex cytokine tissue environment with positive regulators of HIV expression able to override negative regulators.

The two soluble forms of the lipopolysaccharide receptor, CD14: characterization and release by normal human monocytes

CD14, a glycolipid-anchored membrane glycoprotein, acts as a high affinity lipopolysaccharide receptor on leukocytes. We previously reported that the Mono-Mac-6 cell line releases two different soluble forms of CD14 (sCD14) (Labeta et al., Eur. J. Immunol. 1993. 23: 2144). Here we show that the two sCD14, which we now refer to as sCD14 alpha (low M(r)) and sCD14 beta (high M(r)), are also synthesized and released by normal human monocytes and present in normal plasma. Their mechanism of release was examined by using the Mono-Mac-6 cell line, chinese hamster ovary cell (CHO)/CD14+ transfectants and plasma from paroxysmal nocturnal hemoglobinuria (PNH) patients. It was found that: (1) sCD14 beta is released faster than sCD14 alpha and that the release of the latter is a lengthy process. (2) Monensin blocked the biosynthesis of membrane-bound CD14 (mCD14) and sCD14, additionally, a 50-kDa CD14 polypeptide accumulated in the cell lysate, suggesting that the different forms of CD14 may have a common precursor. (3) Monensin also blocked the release of sCD14 alpha from surface-labeled cells, suggesting that conversion of mCD14 to sCD14 alpha involves a mechanism of endocytosis followed by exocytosis. Interestingly, (4) sCD14 alpha and sCD14 beta were detected in PNH plasma, indicating that sCD14 alpha may also derive from an endogenous pathway. (5) Phospholipase C-released CD14 was identical in size to mCD14, thus differed from sCD14 beta by approximately 2000, indicating that release of sCD14 beta involves further processing. (6) CHO cells transfected with a CD14 cDNA coding for an eight C-terminal amino acids shorter product released an sCD14 beta-like form; thus absence of the eight C-terminal amino acids prevented mCD14 expression but not the secretion of sCD14 beta. The characterization of sCD14 alpha and sCD14 beta reported here may be useful for better understanding of variations in sCD14 levels in pathological conditions and the contribution of each sCD14 in sepsis and other, as yet unknown functions.

Topography of the Leydig cell mitochondrial peripheral-type benzodiazepine receptor

Native MA-10 mouse Leydig tumor cell mitochondrial preparations were examined by transmission electron (TEM) and atomic force (AFM) microscopic procedures in order to investigate the topography and organization of the peripheral-type benzodiazepine receptor (PBR). Mitochondria were immunolabeled with an anti-PBR antiserum coupled to gold-labeled secondary antibodies. Results obtained indicate that the 18,000 MW PBR protein is organized in clusters of 4-6 molecules. Moreover, on many occasions, the interrelationship among the PBR molecules was found to favor the formation of a single pore. Taking into account recent observations that the 18,000 MW PBR protein is functionally associated with the pore forming 34,000 MW voltage-dependent anion channel (VDAC) these results suggest that (i) the mitochondrial PBR complex could function as a pore, thus allowing the translocation of cholesterol and other molecules to the inner mitochondrial membrane, and (ii) the native receptor is a multimeric complex of an approximate 140,000 MW composed on an average of five 18,000 PBR subunits, one 34,000 VDAC subunit, and associated lipids.

Interleukin 13: novel role in direct regulation of proliferation and differentiation of primitive hematopoietic progenitor cells

The recently cloned interleukin 13 (IL-13) shares most investigated biological activities on B lymphocytes and monocytes with IL-4. In this study we investigated for the first time the potential role of IL-13 in the regulation of the growth of hematopoietic progenitor cells. IL-13 enhanced stem cell factor (SCF)-induced proliferation of Lin-Sca-1+ bone marrow progenitor cells more potently than IL-4. The effect of IL-13 was purely synergistic, since IL-13 alone stimulated no colony formation. Single cell experiments suggested that the synergistic effect of IL-13 on Lin-Sca-1+ progenitors was directly mediated. In contrast, IL-13 had no synergistic activity on SCF-induced proliferation of the more mature Lin-Sca-1- progenitor cells. Thus, the cloning frequency in response to SCF + IL-13 was at least 20-fold higher in the Lin-Sca-1+ than the Lin-Sca-1- progenitor cell population. Furthermore, IL-13 but not IL-4 synergistically enhanced colony formation of Lin-Sca-1+ progenitors in response to granulocyte/macrophage colony-stimulating factor (GM-CSF) (threefold), whereas both IL-4 and IL-13 enhanced G-CSF-induced colony formation (threefold), and neither of the two significantly affected CSF-1 and IL-3-induced proliferation. Finally, whereas stimulation of Lin-Sca-1+ progenitors by SCF + G-CSF resulted in the formation of 90% granulocytes, the addition of IL-13 resulted in the production of macrophages exclusively. This novel effect on differentiation was directly mediated, shared with IL-4, and could not be observed on Lin-Sca-1- progenitor cells. Collectively, these findings indicate a novel role of IL-13 in early myelopoiesis, partially overlapping but also different from that of IL-4.

Interleukin-13 is a monocyte chemoattractant

Recombinant human IL-13 is chemotactic for purified human peripheral blood monocytes Cell migration is stimulated with a typical bell-shaped concentration curve and is maximal at 10 ng/ml. Migration is the result of chemotaxis, and not chemokinesis, as shown by checkerboard experiments. The chemotactic activity of IL-13 on monocytes is not inhibited by preincubation of the cells with pertussis toxin but is diminished by preincubation with protein kinase inhibitors. The related cytokine, IL-4, also stimulates migration of monocytes in the Boyden chamber assays at concentrations similar to those effective for IL-13. Human IL-13 is capable of attracting rabbit peripheral blood monocytes at those concentrations active on human monocytes. On the other hand, no neutrophil migration was induced by IL-13, even at 1 microM concentrations.

Rat platelets contain glycosylated and non-glycosylated forms of platelet factor 4. Identification and characterization by mass spectrometry

Platelet factor 4 is a heparin-binding protein released from the alpha granules of activated platelets. This study describes the purification and identification of two forms of rat platelet factor 4, the previously characterized non-glycosylated form of 7 kDa and an additional glycosylated form of molecular mass 9 kDa. The two proteins both neutralized the antithrombin-III-dependent inhibitory activity of heparin. Although their amino acid composition was found to be the same, in the N-terminal sequence of the 9-kDa protein, the second threonine residue could not be detected and a difference of 976Da was determined by mass spectrometry. After digestion with O-glycanase and sialidase, the two proteins showed the same molecular mass. Overall consideration of these data led to identification of the higher-molecular-mass protein as a glycosylated form of rat platelet factor 4 with O-glycosylation at the second N-terminal amino acid, while the structure of the oligosaccharide core was established by mass spectrometry and sugar differentiation with lectins. The two forms of platelet factor 4 are both present in platelets and secreted after platelet activation.