Isolation and characterization of Abelson murine leukemia virus-transformed mast cell lines from midgestation embryonic placenta

Apoptosis-inducing human-origin Fcepsilon-Bak chimeric proteins for targeted elimination of mast cells and basophils: a new approach for allergy treatment

During the past few years, many chimeric proteins have been developed to specifically target and kill cells expressing specific surface molecules. Generally these molecules carry a bacterial or plant toxin to destroy the unwanted cells. The major obstacle regarding these molecules in their clinical application is the immunogenicity and nonspecific toxicity associated with bacterial or plant toxins. We lately reported a new approach for construction of chimeric proteins: we successfully replaced bacterial or plant toxins with human apoptosis-inducing proteins. The resulting chimeras were shown to specifically induce apoptosis in the target cells. Taking advantage of the human apoptosis inducing proteins Bak and Bax as novel killing components, we have now constructed new chimeric proteins targeted against the human FcepsilonRI, expressed mainly on mast cells and basophils. These cells are the main effectors of the allergic response. Treatment of the target cells with the new chimeric proteins, termed Fcepsilon-Bak/Bax, had a dramatic effect on cell survival, causing apoptosis. The effect was specific to cells expressing the FcepsilonRI of both human and, very unexpectedly, also of mouse origin. Moreover, interaction of the chimeric proteins with the mast cells did not cause degranulation. Fcepsilon-Bak/Bax are new chimeric proteins of human origin and, as such, are expected to be both less immunogenic and less toxic and, thus, may be specific and efficient reagents for the treatment of allergic diseases.

Mast cell degranulating (MCD) peptide: a prototypic peptide in allergy and inflammation

The solid phase synthesis of mast degranulating peptide (MCD peptide) raised the possibility of preparing analogs and examining the pharmacology and the proposed role of this peptide as a potential agent in allergy and inflammation. MCD peptide, a cationic 22-amino acid residue peptide with two disulfide bridges, causes mast cell degranulation and histamine release at low concentrations and has anti-inflammatory activity at higher concentrations. Because of these unique immunologic properties, MCD peptide may serve as a useful tool for studying secretory mechanisms of inflammatory cells such as mast cells, basophils, and leukocytes, leading to the design of compounds with therapeutic potential.

Murine mast cells and monocytes express distinctive sets of CD45 isoforms

CD45 isoform expression patterns were examined in various mast and monocyte cell populations. The reverse transcription-polymerase chain reaction (RT/PCR) and Southern analysis showed these myeloid cells express characteristic sets of CD45 isoforms. Mast cells produce mRNA for two splice variants, one containing exons 5, 7 and 8 of the alternatively expressed exons (therefore lacking exons 4 and 6) and another containing variable exons 7 and 8. Monocytes express three prominent CD45 mRNA species, one which includes exons 5, 7 and 8, another with exons 7 and 8 and the third containing only exon 8 of the variable exons. These results show that there are clear differences within the myeloid lineage sub-populations with respect to CD45 exon usage which appear to delineate mast cell and monocyte specific patterns.

Targeted elimination of cells expressing the high-affinity receptor for IgE (Fc epsilon RI) by a Pseudomonas exotoxin-based chimeric protein

The interaction between IgE and its high-affinity receptor Fc epsilon RI found on mast cells and basophils is the primary effector pathway in allergic response. To achieve a targeted elimination of cells expressing Fc epsilon RI receptors, we constructed a chimeric protein in which a Fc fragment of mouse IgE is attached to a truncated form of Pseudomonas exotoxin (PE). To prepare the targeting moiety, we used a DNA sequence corresponding to amino acids 301-437, representing 30 residues of domain 2 and domain 3 of the mouse IgE constant region. This sequence was fused at the 5' of a cDNA encoding PE40, a truncated form of PE lacking the cell binding domain. The chimeric protein, termed Fc(2'-3)-PE40, was expressed in Escherichia coli and partially purified. The protein is highly cytotoxic to mouse mast cell lines and bone marrow-derived primary mast cells. This cytotoxicity is specific, as it could be blocked upon addition of whole IgE. Moreover, the protein had no effect on other cell lines of hemopoietic origin. The Fc(2'-3)-PE40 chimeric protein offers a new approach to the treatment of allergic disorders.

A novel, erythroid cell-specific murine transcription factor that binds to the CACCC element and is related to the Krüppel family of nuclear proteins

We describe a novel erythroid cell-specific cDNA (EKLF [erythroid Krüppel-like factor]) isolated by enriching for genes expressed in a mouse erythroleukemia cell line but not expressed in a mouse monocyte-macrophage cell line. The complete cDNA sequence is predicted to encode a protein of approximately 38,000 Da that contains a proline-rich amino domain and three TFIIIA-like zinc fingers within the carboxy domain. Additional sequence analyses reveal that the EKLF zinc fingers are most homologous to the Krüppel family of transcription factors and also allow us to predict potential DNA-binding target sites for the EKLF protein. On the basis of this prediction, we show that EKLF is able to bind the sequence CCA CAC CCT, an essential element of the beta-globin promoter. Its tissue distribution establishes that the EKLF transcript is expressed only in bone marrow and spleen, the two hematopoietic organs of the mouse, and analysis of murine cell lines indicates that EKLF expression is limited to erythroid and mast cell lines. Cotransfection assays establish that EKLF transcriptionally activates a target promoter that contains its DNA-binding site. The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKLF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.

A novel, erythroid cell-specific murine transcription factor that binds to the CACCC element and is related to the Krüppel family of nuclear proteins

We describe a novel erythroid cell-specific cDNA (EKLF [erythroid Krüppel-like factor]) isolated by enriching for genes expressed in a mouse erythroleukemia cell line but not expressed in a mouse monocyte-macrophage cell line. The complete cDNA sequence is predicted to encode a protein of approximately 38,000 Da that contains a proline-rich amino domain and three TFIIIA-like zinc fingers within the carboxy domain. Additional sequence analyses reveal that the EKLF zinc fingers are most homologous to the Krüppel family of transcription factors and also allow us to predict potential DNA-binding target sites for the EKLF protein. On the basis of this prediction, we show that EKLF is able to bind the sequence CCA CAC CCT, an essential element of the beta-globin promoter. Its tissue distribution establishes that the EKLF transcript is expressed only in bone marrow and spleen, the two hematopoietic organs of the mouse, and analysis of murine cell lines indicates that EKLF expression is limited to erythroid and mast cell lines. Cotransfection assays establish that EKLF transcriptionally activates a target promoter that contains its DNA-binding site. The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKLF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.

Avian erythroblastosis virus transforms a novel mast cell-basophil precursor target in the Japanese quail

Hematopoietic cells of the Japanese quail were transformed by avian erythroblastosis virus in vivo and in vitro. In both circumstances, the infected hematopoietic tissues exhibited a dual oncogenic response of erythroid and mast cell-basophil elements. The erythroid transformants escaped the avian erythroblastosis virus block in differentiation and progressed to hemoglobinization. Resulting basophilic cells were morphologically, biochemically, and ultrastructurally identical to mast cell-basophils observed in other species. None of the virally transformed cells actively produced reverse transcriptase activity. Nonproducer cell lines synthesized viral RNA and both v-erbA and v-erbB proteins. These results indicate that the Japanese quail has a viral target cell different from that of the chicken. The implications of a single bipotential transformation target yielding both erythroid and mast cell-basophil colonies is discussed.

Establishment of megakaryoblastic cell lines by coinfection of Abelson murine leukemia virus and recombinant SV40-retrovirus

Murine embryonic cells including yolk sac prepared from 8-day embryos were co-infected with Abelson murine leukemia virus (A-MuLV) and/or a recombinant retrovirus containing large T and small t antigens, and early region of simian virus 40 (M-SV40). By coinfection with A-MuLV and M-SV40, megakaryoblastic cells were obtained in addition to mast cells and fibroblastic cells. However, following infection with A-MuLV or M-SV40 alone, no megakaryoblastic cells were detected, although mast cells and/or fibroblastic cells developed. The same results were obtained in several experiments. By single-cell transfer, 6 acetyl-cholinesterase (AchE)-positive clonal cell lines were established. Characteristics of megakaryocytes, such as AchE, glycoproteins IIb and IIIa, and platelet peroxidase were detected in two representative cells (C1 and C8). More significant changes expressing differentiation were observed following treatment with phorbol myristate acetate or pokeweed mitogen-stimulated murine spleen cell conditioned medium, although release of platelets was not observed. This is the first report showing development of megakaryocytic cells as the result of coinfection with retroviruses.

A simple method for simultaneous detection of Fc receptors and differentiation antigens on normal and neoplastic murine hematopoietic cells

Cell surface receptors for immunoglobulin Fc regions can be detected by light microscopy of cytocentrifuge preparations of normal or malignant murine hematopoietic cells. The cells are first incubated in a culture supernate containing a monoclonal anti-hapten antibody, then with heat-killed, haptenated bacteria. Using 2 morphologically distinct strains of bacteria, we can detect both Fc receptors and cell surface differentiation antigens.