David Cosman

A homologue of the TNF receptor and its ligand enhance T-cell growth and dendritic-cell function

Dendritic cells are rare haematopoietic cells that reside in a number of organs and tissues. By capturing, processing and presenting antigens to T cells, dendritic cells are essential for immune surveillance and the regulation of specific immunity. Several members of the tumour necrosis factor receptor (TNFR) superfamily are integral to the regulation of the immune response. These structurally related proteins modulate cellular functions ranging from proliferation and differentiation to inflammation and cell survival or death. The functional activity of dendritic cells is greatly increased by signalling through the TNFR family member CD40 (refs 7, 8). Here we report the characterization of RANK (for receptor activator of NF-κB), a new member of the TNFR family derived from dendritic cells, and the isolation of a RANK ligand (RANKL) by direct expression screening. RANKL augments the ability of dendritic cells to stimulate naive T-cell proliferation in a mixed lymphocyte reaction, and increases the survival of RANK+T cells generated with interleukin-4 and transforming growth factor (TGF)-β. Thus RANK and RANKL seem to be important regulators of interactions between T cells and dendritic cells.

ULBPs, Novel MHC Class I–Related Molecules, Bind to CMV Glycoprotein UL16 and Stimulate NK Cytotoxicity through the NKG2D Receptor

The human cytomegalovirus glycoprotein, UL16, binds to two members of a novel family of molecules, the ULBPs, and to the MHC class I homolog, MICB. The ULBPs are GPI-linked glycoproteins belonging to the extended MHC class I family but are only distantly related to MICB. The ULBP and MICB molecules are ligands for the activating receptor, NKG2D/DAP10, and this interaction is blocked by a soluble form of UL16. The ULBPs stimulate cytokine and chemokine production from NK cells, and expression of ULBPs in NK cell-resistant target cells confers susceptibility to NK cell cytotoxicity. Masking of NK cell recognition of ULBP or MIC antigens by UL16 provides a potential mechanism by which human cytomegalovirus-infected cells might evade attack by the immune system.

Identification of a ligand for the c-kit proto-oncogene

We report the purification and N-terminal amino acid sequence of a novel mast cell growth factor, termed MGF, from the supernatants of a murine stromal cell line. A panel of interleukin 3-dependent cell lines were screened for responsiveness to partially purified MGF in [3H]thymidine incorporation assays; proliferative stimulation of these cells in response to MGF correlated with expression of mRNA for the c-kit protooncogene. MGF was shown to be a ligand for c-kit by cross-linking 125I-labeled MGF to c-kit-expressing cells with subsequent immunoprecipitation of the complex with antiserum specific for the C-terminus of c-kit. This establishes MGF as a ligand for the c-kit protein.

Molecular cloning of mast cell growth factor, a hematopoietin that is active in both membrane bound and soluble forms

We have previously reported the identification of a novel mast cell growth factor (MGF) that was shown to be a ligand for c-kit and is encoded by a gene that maps near the steel locus on mouse chromosome 10. We now report the cloning of cDNAs encoding the MGF protein. The MGF protein encoded by this cDNA can be expressed in a biologically active form as either a membrane bound protein or as a soluble factor. The soluble protein promotes the proliferation of MGF-responsive cell lines and, in the presence of erythropoietin, stimulates the formation of macroscopic [corrected] erythroid and multilineage hematopoietic colonies.

A Novel Immunoglobulin Superfamily Receptor for Cellular and Viral MHC Class I Molecules

The human cytomegalovirus UL18 gene product is a homolog of cellular major histocompatibility (MHC) class I antigens. UL18 has been proposed to protect virus-infected cells against natural killer (NK) cell cytotoxicity by engaging NK cell killer inhibitory receptors (KIR) for MHC class I. UL18 binds to a novel immunoglobulin superfamily glycoprotein, designated Leukocyte Immunoglobulin-like Receptor (LIR-1). This protein is distinct from, but related to, known KIRs and binds cellular MHC class I antigens. The cytoplasmic domain of LIR-1 contains four putative immunoreceptor tyrosine-based inhibitory motifs. Upon tyrosine phosphorylation, LIR-1 associates with the tyrosine phosphatase SHP-1. In contrast to KIRs, LIR-1 is expressed predominantly on monocytic and B lymphoid cell types, suggesting a distinct biological function.

The murine interleukin-4 receptor: Molecular cloning and characterization of secreted and membrane bound forms

Receptors for interleukin-4 (IL-4) are expressed at low levels on a wide variety of primary cells and cultured cell lines. Fluorescence-activated sorting of CTLL-2 cells resulted in the isolation of a subclone, CTLL 19.4, which expressed 10(6) IL-4 receptors per cell. These cells were used for the purification of IL-4 receptor protein and to prepare a hybrid-subtracted cDNA probe for isolation of cDNA clones. Three classes of IL-4 receptor cDNA were identified. The first encoded a 140 kd membrane bound IL-4 receptor containing extracellular, transmembrane, and cytoplasmic domains. The second class lacked the cytoplasmic region, and the third encoded a secreted form of the receptor. All cDNA clones expressed in COS-7 cells had IL-4 binding properties comparable to the native IL-4 receptor. The soluble form of the IL-4 receptor blocked the ability of IL-4 to induce CTLL cell proliferation and may represent a regulatory molecule specific for IL-4-dependent immune responses.

Mast cell growth factor maps near the steel locus on mouse chromosome 10 and is deleted in a number of steel alleles

Many spontaneous, chemical-induced, and radiation-induced dominant white spotting (W) and steel (Sl) mutations have been identified in the mouse. W and Sl mutations have similar phenotypic effects including deficiencies in pigment cells, germ cells, and blood cells, Numerous studies have suggested that W acts within the affected cell while Sl instead exerts its effects in the extracellular environment. Recent findings demonstrating that W encodes the c-kit proto-oncogene, a tyrosine kinase membrane receptor, have suggested that Sl encodes a ligand for c-kit. In the accompanying article we report the identification and purification of mast cell growth factor (MGF), a c-kit ligand. Here we describe the cloning of sequences encoding MGF. Furthermore, we show that Mgf maps near Sl in the distal region of mouse chromosome 10 and is deleted in a number of Sl alleles. These findings strongly support the notion that Sl encodes the mast cell growth factor.

Cloning of the human and murine interleukin-7 receptors: Demonstration of a soluble form and homology to a new receptor superfamily

cDNA clones encoding the human and murine interleukin-7 (IL-7) receptor were isolated and expressed in COS-7 cells. Binding of radiolabeled IL-7 to the recombinant IL-7 receptors produced curvilinear Scatchard plots containing high and low affinity classes. These binding properties, as well as the molecular size of the cloned receptor, were comparable to the native forms of the IL-7 receptor. In addition, several cDNA clones were isolated that encode a secreted form of the human IL-7 receptor capable of binding IL-7 in solution. Analysis of the sequence of the IL-7 receptor revealed significant homology in the extracellular domain to several recently cloned cytokine receptors, demonstrating that the IL-7 receptor is a member of a new receptor superfamily.

A new cytokine receptor superfamily

The amino acid sequences of several, recently cloned cytokine receptors show significant homologies, primarily in their extracellular, ligand-binding domains. With one exception, their cognate cytokines mediate biological activities on a variety of hematopoietic cell types; thus we have designated the receptors as the hematopoietic receptor superfamily.

Dual Oncostatin M (OSM) Receptors CLONING AND CHARACTERIZATION OF AN ALTERNATIVE SIGNALING SUBUNIT CONFERRING OSM-SPECIFIC RECEPTOR ACTIVATION

Oncostatin M (OSM) is a cytokine whose structural and functional features are similar to other members of the interleukin (IL)-6 family of cytokines (IL-6, IL-11, leukemia inhibitory factor (LIF), granulocyte colonystimulating factor, ciliary neurotrophic factor, and cardiotrophin-1), many of which utilize gp130 as a common receptor subunit. A biologically active OSM receptor has been previously described that consists of a heterodimer of leukemia inhibitory factor receptor (LIFR) and gp130. This LIFR·gp130 complex is also a functional receptor for LIF. We have cloned and characterized an alternative subunit (OSMRβ) for an OSM receptor complex (a heterodimer of gp130 and OSMRβ) that is activated by OSM but not by LIF. The signaling capability of specific receptor subunit combinations was analyzed by independent assays measuring cell proliferation or induction of acute phase protein synthesis. Our results demonstrate that both LIF and OSM cause tyrosine phosphorylation and activation of the gp130·LIFR combination, but the gp130·OSMRβ complex is activated by OSM only. OSM-induced cellular responses, initiated through low affinity binding to gp130, are mediated by two heterodimeric receptor complexes that utilize alternative signal transducing subunits that confer different cytokine specificities to the receptor complex.