Katsuhiko Yamasaki

Interleukin-6 triggers the association of its receptor with a possible signal transducer, gp130.

Interleukin-6 mediates pleiotropic functions in various types of cells through its specific receptor (IL-6-R), the cDNA of which has already been cloned. We report here that an 80 kd single polypeptide chain (IL-6-R) is involved in IL-6 binding and that IL-6 triggers the association of this receptor with a non-ligand-binding membrane glycoprotein, gp130. The association takes place at 37 degrees C within 5 min and is stable for at least 40 min in the presence of IL-6, but does not occur at 0 degree C. Human IL-6-R can associate with a murine gp130 homolog and is functional in murine cells. Mutant IL-6-R lacking the intracytoplasmic portion is functional, suggesting that the two polypeptide chains interact to involve their extracellular portion. In fact, a soluble IL-6-R lacking the transmembrane and intracytoplasmic domains can associate with gp130 in the presence of IL-6 and mediate its function. These findings indicate that the complex of IL-6 and IL-6-R can interact with a non-ligand-binding membrane glycoprotein, gp130, extracellularly and can provide the IL-6 signal.

Molecular structure of human lymphocyte receptor for immunoglobulin E

We have isolated and sequenced a cDNA clone encoding the human lymphocyte receptor for IgE (Fc epsilon R). The deduced protein sequence reveals that Fc epsilon R consists of 321 amino acids, without any signal sequence, and is oriented with its N-terminus on the cytoplasmic side and its C-terminus on the outside of the cell. This molecule shows striking sequence homology with chicken asialoglycoprotein receptor (hepatic lectin), suggesting a possible role for Fc epsilon R in endocytosis. Fc epsilon R mRNA is expressed in B cells, B cell lines, and macrophage cell lines. It is not expressed in T cells or T cell lines, with the exception of an HTLV-transformed T cell line. mRNAs expressed in a macrophage line and in the latter T cell line differ in size from mRNA expressed in B cells. Human BSF-1 (or IL-4) induces the expression of Fc epsilon R mRNA in B cells, but not in T cells.

Structure-function analysis of human IL-6 receptor : dissociation of amino acid residues required for IL-6-binding and for IL-6 signal transduction through gp130

Here, we report the analysis of the structure‐function relationship of the extracellular region of human interleukin 6 receptor (IL‐6R). Upon binding of IL‐6, IL‐6R becomes associated extracellularly with a non‐IL‐6‐binding but signal transducing molecule, gp130, and the IL‐6 signal is generated. In this region, the cytokine receptor family domain, but not the immunoglobulin‐like domain, was responsible both for IL‐6 binding and for signal transduction through gp130. Because a soluble, extracellular portion of IL‐6R (sIL‐6R) could bind IL‐6 and mediate IL‐6 functions through gp130, amino acid substitutions were introduced into sIL‐6R by site‐directed mutagenesis. The results, together with the previously proposed tertiary structure model, suggested that the amino acid residues critical for IL‐6 binding have a tendency to be distributed to the hinge region between the two ‘barrel’‐like fibronectin type III modules and to the same side of these two ‘barrels’. Amino acid residues, of which substitutions barely affected the IL‐6‐binding but did abolish the IL‐6 signalling capability of sIL‐6R, were identified and found to be located mainly in the membrane proximal half of the second barrel. sIL‐6R mutants carrying such substitutions lacked the capacity to associate with gp130 in the presence of IL‐6.

A Multifunctional Cytokine (IL-6/BSF-2) and Its Receptor

Interleukin 6 (IL-6)/B cell stimulatory factor 2 is a multifunctional cytokine produced by both lymphoid and nonlymphoid cells. IL-6 regulates immune response, acute phase reaction, and hematopoiesis. It was found that IL-6 production by T cells is dependent on macrophages, and IL-6 is one of essential factors for pokeweed mitogen induced immunoglobulin production. Both high- and low-affinity IL-6 receptors were identified. The molecular cloning of IL-6 receptors demonstrated that this receptor is a member of the immunoglobulin superfamily. The deregulated production of IL-6 is suggested to be involved in the pathogenesis of autoimmune diseases and in the development of multiple myeloma.

NORMAL AND ABNORMAL REGULATION OF HUMAN B CELL DIFFERENTIATION BY A NEW CYTOKINE, BSF2/IL-6

Antibody molecules play an essential role not only in protection against viral or bacterial infections, but also in the induction of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus, and immediate-type hypersensitivity. Therefore, the study of the mechanism regulating the activation, proliferation and immunoglobulin secretion of B lymphocytes is essential for the normal and abnormal regulations in the antibody response.

Current Concepts of B Cell Modulation

Three interleukins with distinct functions, IL-4, IL-5 and IL-6, are involved in the regulation of B cell response into antibody producing cells. The studies with recombinant interleukins, however, demonstrated that the activities of these interleukins were not restricted to B lineage cells but showed a wide variety of biological functions on various tissues and cells. One of the most typical example of multifunctional interleukins is IL-6. It acts not only on B cells as B cell differentiation factor but also on T cells, hematopoietic stem cells, hepatocytes, nerve cells and myeloma cells. Deregulation of the expression of these interleukins was shown to be responsible for various diseases, such as i) IL-4 vs. immediate type hypersensitivity and ii) IL-6 vs. autoimmunity and multiple myelomas.

Interleukin 6 and Its Receptor in Immune Regulation

Several factors have been shown to be involved in the regulation of B cell responses into antibody producing cells. The cDNAs for three interleukins, IL-4, IL-5 and IL-6, have been molecularly cloned and functions of these molecules in the activation, proliferation and differentiation of B cells were confirmed utilizing recombinant molecules (Kishimoto and Hirano 1988). However, the studies with recombinant molecules also showed that the functions of these molecules are not restricted to B lineage cells but have a wide variety of biological activities on various tissues and cells. One of the typical examples of multifunctional interleukins is IL-6 (Hirano and Kishimoto in press).

Interleukin 6 and its Receptor: Pathological Role in Autoimmunity and Lymphoid Malignancy

Interleukin 6 (BSF-2/26kD protein/IFN-s 2/HPGF/HSF) is a multifunctional cytokine produced by both lymphoid and non-lymphoid cells. Both high and low affinity IL-6 specific receptors were identified and the cDNA encoding IL-6-R was cloned. The data showed that IL-6 receptor is a member of the immunoglobulin superfamily. IL-6 was demonstrated to be an essential factor for immunoglobulin production by B cells. The results suggested that the deregulation is involved in the pathogenesis of autoimmne diseases and the oncogenesis of multiple myeloma.