M. Patricia Beckmann

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.

Molecular cloning of a ligand for the flt3 flk-2 tyrosine kinase receptor: A proliferative factor for primitive hematopoietic cells

Cloning of a ligand for the murine flt3/flk-2 tyrosine kinase receptor was undertaken using a soluble form of the receptor to identify a source of ligand. A murine T cell line, P7B-0.3A4, was identified that appeared to express a cell surface ligand for this receptor. A cDNA clone was isolated from an expression library prepared from these cells that was capable, when transfected into cells, of conferring binding to a soluble form of the flt3/flk-2 receptor. The cDNA for this ligand encodes a type I transmembrane protein that stimulates the proliferation of cells transfected with the flt3/flk-2 receptor. A soluble form of the ligand stimulates the proliferation of defined subpopulations of murine bone marrow and fetal liver cells as well as human bone marrow cells that are highly enriched for hematopoietic stem cells and primitive uncommitted progenitor cells.

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.

Molecular and biological characterization of a ligand for CD27 defines a new family of cytokines with homology to tumor necrosis factor

CD27 is a surface antigen found on T and B cells that has homology to a family of molecules including the receptors for tumor necrosis factor (TNF) and nerve growth factor. A cDNA encoding a ligand for CD27 was isolated by a direct-expression cloning strategy using a fusion protein composed of the extracellular domain of CD27 linked to the constant domain of a human immunoglobulin G1 molecule as a probe. The predicted protein product is a type II transmembrane protein whose gene maps to 19p13 and that shows homology to TNF and the ligand for CD40. Biological characterization indicates that the cloned ligand induces the proliferation of costimulated T cells and enhances the generation of cytolytic T cells.

Molecular characterization of receptors for human interleukin-8, GRO/melanoma growth-stimulatory activity and neutrophil activating peptide-2

Interleukin-8 (IL-8), neutrophil activating peptide-2 (NAP-2), and growth regulated gene (GRO, also known as melanoma growth stimulatory activity) are members of a family of peptides which are chemotactic agents for inflammatory cells such as neutrophils. Receptors have been identified for IL-8, GRO and NAP-2 on human neutrophils and granulocytic cell lines, and it has been observed that these cytokines can cross-compete for binding to a common receptor. Using the recently characterized rabbit IL-8 receptor as a probe, two classes of cDNAs, termed type 1 and type 2, were isolated from a human neutrophil library. The type 1 receptor binds only IL-8 while the type 2 receptor binds IL-8, GRO and NAP-2 at high affinity when respective cDNAs are expressed in COS-7 cells. The two cDNAs encode proteins that have an amino acid sequence identity of 77% while the type 1 and 2 receptors have an identity of 84 and 74% with the rabbit IL-8 receptor. These receptors also show significant homology with receptors for other chemotactic agents and with potential coding regions from the human cytomegalovirus genome.

A soluble form of the interleukin 4 receptor in biological fluids

Murine biological fluids and murine cell culture supernatants were analyzed for the presence of soluble murine interleukin 4 receptor (sIL4R) with the use of two monoclonal antibodies directed against the receptor. Mouse urine, serum, ascitic fluid, and cell culture supernatants contained varying levels of immunoreactive protein. All of the immunoreactive protein possessed interleukin 4 (IL 4) binding activity. Following partial purification of ascitic fluid a protein was isolated that binds IL 4 with high affinity. This data is consistent with the fact that murine biological fluids contain a soluble version of the murine IL 4 receptor that arises via secretion of the soluble receptor and/or via shedding of the extracellular portion of the full-length receptor from the cell surface.

Molecular characterization of the interleukin-8 receptor

Recently a rabbit cDNA (F3R) was characterized as binding and causing calcium mobilization induced by the formyl-methionine-leucine-phenylalanine peptide (fMLP). In the study reported here, cloned DNAs were isolated from rabbit genomic DNA by PCR based on the sequence of F3R. The cloned DNAs have several differences in the DNA sequence compared to the reported F3R sequence that alter the predicted protein sequence. COS-7 cells transfected with these clones in a mammalian expression vector bind human IL-8 with high affinity, but do not bind fMLP. We therefore believe that the cDNAs isolated encode the rabbit IL-8 receptor.

Pharmacokinetic Parameters and Biodistribution of Soluble Cytokine Receptors

The potential use of soluble cytokine receptors as therapeutics in disease states when excessive or prolonged cytokine expression leads to pathogenesis is just beginning (Van Brunt, 1989). The inhibitory effects of soluble receptors have been found to be highly potent and specific for their respective cytokines (Maliszewski and Fanslow, 1990; Maliszewski et al., 1990). Recent in vivo data have shown that exogenously administered soluble receptors can function as cytokine antagonists and suppress autoimmune inflammatory responses (Jacobs et al., 1991a), allograft rejection, and alloreactivity (Fanslow et al., 1990b). The proposed frequency of administration and dosage of a therapeutic agent is dependent on the half-life of the agent and the route of administration. The elimination or half-life of a drug usually depends on its physiochemical properties (molecular size, glycosylation, isoelectric point, and hydrophobic/hydrophilic properties) (DiPalma and DiGregorio, 1990; Katzung, 1984). The half-life will also depend on the mechanism of clearance for that specific receptor. Once pharmacokinetic data are available for soluble receptors, the therapeutic potential of these molecules can be better evaluated. Only limited pharmacokinetic data are currently available for soluble cytokine receptors (Jacobs et al., 1991b). For sIL-1R, the majority of an intravenously administered dose was cleared in the second elimination phase, with a reasonably long half-life (6.3 hr), such that the entire dose was not eliminated until 35 hr. If administration is by subcutaneous injection, the half-life was even more prolonged. One explanation for the prolonged half-life is the minimal distribution to liver and kidneys and thus low levels of clearance by these organs. In contrast, elimination of intravenously administered sIL-4R was relatively rapid, with a short half-life (2.3 hr). This appeared mainly due to liver distribution and clearance, which has been the highest observed for any soluble cytokine receptor. Administering sIL-4R by subcutaneous injection significantly prolonged the half-life. This was most likely due to delaying the rate of liver distribution by slowing the rate of sIL-4R absorption into the circulation. Thus, subcutaneous injection would be the recommended route of administration for this receptor. Construction of a larger dimeric sIL-4R fusion protein did not prolong the i.v. half-life compared to that of the monomer, as the sIL-4R fusion protein was distributed to, and was cleared by, the liver to a greater degree.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of Receptors for Interleukin 4 and Interleukin 7 on Human T Cells

Human recombinant interleukin 4 (IL-4) and interleukin 7 (IL-7) have been modified with biotin-N-hydroxysuccinimide and used to examine the expression of human IL-4 and IL-7 receptors (R) on activated peripheral blood T cells by flow cytometry. Freshly isolated T cells expressed only a low level of IL-4R which remained unchanged when cells were cultured in the absence of stimuli. In the presence of IL-4, IL-7, phytohemagglutinin A (PHA) or immobilized CD3 monoclonal antibody the intensity of biotinylated IL-4 staining increased approximately twofold on the majority of cells. A combination of mitogen with either IL-4 or IL-7 caused a considerable increase in IL-4 receptor expression over that seen in the presence of mitogen alone. IL-2 alone failed to induce IL-4R although it was able to cause a significant increase in receptor expression on T cells co-cultured with PHA or CD3. Freshly isolated T cells expressed high levels of IL-7R, as determined by biotinylated IL-7 binding and flow cytometry, which did not change significantly with culture in medium alone. Stimulation with PHA, Concanavalin A (Con A) or CD3 had little effect on the intensity of staining. In contrast, activation with phorbol ester resulted in a decrease in IL-7R expression. Similarly, in the presence of IL-4 or IL-7, but not IL-2, the intensity of staining with biotinylated IL-7 was lowered. Analysis of purified T-cell populations showed that IL-7R were present, and IL-4R could be induced, on both CD4+ and CD8+ populations. Analysis of IL-4 receptor expression by this flow cytometric technique was supported by results from 125I-labeled IL-4 binding and by Northern blot analysis of mRNA levels. Taken together, the results of these studies show that the use of biotinylated cytokines and flow cytometry provides a very sensitive method with which to study the expression and regulation of cytokine receptors.

Assignment of the gene (EPLG2) encoding a high-affinity binding protein for the receptor tyrosine kinase elk to a 200-kilobasepair region in human chromosome Xq12

Elk is a member of the eph family of receptor tyrosine kinases. Elk is expressed only in the brain and testes of the developing and adult rat, and the interaction of elk with its ligand(s) has been suggested to play a role in the development or maintenance of the nervous system. The mouse gene Eplg2 encodes a potential elk ligand that is highly conserved among rat, mouse, and human. Eplg2 has been mapped to the central portion of the mouse X chromosome, tightly linked to the androgen receptor (Ar) locus. Linkage conservation between the mouse and the human X chromosomes suggested that the human homologue (EPLG2) would map near human AR, in the interval Xq11-q12. In the present study, we have confirmed this prediction and have localized EPLG2 to a 200-kb interval in Xq12 by somatic cell hybrid analysis, two-color fluorescence in situ hybridization (FISH), and yeast artificial chromosome (YAC) hybridization. 12 refs., 1 fig.