T-leukemia Cells Research Articles

Control of β1 Integrin Function: LOCALIZATION OF STIMULATORY EPITOPES

The beta1 integrins can be expressed on the surface of cells in a latent form, which is activated by a variety of stimuli. As an approach to examining the transition to an active receptor, a panel of stimulatory antibodies to beta1 were produced and characterized. These antibodies induced adherence of the T-leukemic cell line Jurkat to collagen and fibronectin. Competitive antibody binding assays indicated the existence of at least three distinct epitope clusters A (B3B11, JB1B, 21C8), B (B44, 13B9), and C(N29) defined by the indicated antibodies. Two antibodies to the A site, JB1B and B3B11, were shown to localize to positions 671-703 and 657-670, respectively, of the beta1. This region is located in an area encompassing a predicted disulfide bond between linearly distant cysteines in beta1 (Cys415-Cys671). The homologous region of the beta3 integrin (490 690 and 602 690) has been shown to be one of the sites recognized by stimulatory antibodies to ligand-induced binding sites. The present results indicate the existence of multiple stimulatory regions and suggest considerable homology between the locations of beta1 and beta3 regulatory sites.

Differential expression of opioid receptor genes in human lymphoid cell lines and peripheral blood lymphocytes

The existence of receptors for opioid compounds on cells of the immune system has long been hypothesized, but has been very difficult to demonstrate unequivocally. We have used reverse-transcription polymerase chain reaction to obtain cDNA clones from the human MOLT-4 and CEM-3 T-leukemic cell lines which are nearly identical to portions of the δ and κ opioid receptor cDNAs recently isolated from human brain and placenta, respectively. Northern analyses with riboprobes derived from the δ and κ opioid receptor clones indicate these sequences are expressed at low levels in human peripheral blood lymphocytes and in several human lymphoid cell lines. Sequences corresponding to the μ opioid receptor cDNA were not detected in this study. These results suggest that δ and κ opioid receptors may be responsible for mediating some direct effects of opioids in immune cells.

Potent growth inhibitory activity of a novel Ornithogalum cholestane glycoside on human cells: Induction of apoptosis in promyelocytic leukemia HL-60 cells

Growth inhibitory activities of a novel 22-homo-23-norcholestane glycoside found in bulbs of Ornithogalum saundersiae were examined in vitro using human promyelocytic leukemia HL-60 cells, human T-lymphocytic leukemia MOLT-4 cells, and mitogen-stimulated human peripheral-blood mononuclear cells (PBMC). The growth of HL-60 cells and MOLT-4 cells was strongly suppressed in the presence of the glycoside; the IC 50s of which were 21.0 and 18.0 nM, respectively. Suppressive effect of the glycoside on HL-60 cell growth appears to be mediated partially through induction of apoptosis which was demonstrated by the presence of DNA fragmentation of the leukemic cells. Flow cytometric analysis of glycosidetreated HL-60 cells also demonstrated apoptotic cells with low DNA content and showed a decrease of G0 G1 cells and a concomitant increase of S and/or G2 M cells. The growth inhibiting effect of the glycoside on HL-60 cells was promoted by calcium and was inhibited in the presence of zinc, which support involvement of endonuclease activation in the glycoside-induced apoptosis. The glycoside also inhibited mitogenstimulated blastogenesis of PBMC, the IC 50 of which was 6.2 nM. These results provided the first evidence ever for the potent growth inhibitory activity of Ornithogalum glycoside on human leukemia cell lines and PBMC.

Molecular Cloning and Tissue Expression ofFAT,the Human Homologue of theDrosophila fatGene That Is Located on Chromosome 4q34–q35 and Encodes a Putative Adhesion Molecule

FAT,a new member of the human cadherin superfamily, has been isolated from the T-leukemia cell line J6. The predicted protein closely resembles theDrosophilatumor suppressor fat, which is essential for controlling cell proliferation duringDrosophiladevelopment. The gene has the potential to encode a large transmembrane protein of nearly 4600 residues with 34 tandem cadherin repeats, five EGF-like repeats, and a laminin A–G domain. The cytoplasmic sequence contains two domains with distant homology to the cadherin catenin-binding region. Northern blotting analysis of J6 mRNA demonstrated full-length, approximately 15-kb,FATmessage in addition to several 5′-truncated transcripts. In addition to its presence in J6 cells, insituhybridization revealedFATmRNA expression in epithelia and in some mesenchymal compartments. Furthermore, higher levels of expression were observed in fetal, as opposed to adult, tissue, suggesting that its expression may be developmentally regulated in these tissues. FAT shows homologies with a number of proteins important in developmental decisions and cell:cell communication and is the first fat-like protein reported in vertebrates. The gene encodingFATwas located byin situhybridization on chromosome 4q34–q35. We propose that this family of molecules is likely to be important in mammalian developmental processes and cell communication.

A novel human monoclonal antibody, TONO-1, reactive with T-lymphocytic leukemia cells.

Mononuclear cells from the peripheral blood of patients with systemic lupus erythematosus (SLE) were transformed with the Epstein-Barr virus (EBV) and the resultant polyclonal B-lymphoblastoid cell lines were tested for antibody activity to membrane antigens of certain T-cell lines. B lymphoblastoid cell lines secreting specific antibodies were fused with (mouse x human) heteromyeloma SHM-D33 cells. Among the large number of hybridomas generated, one which produced a human monoclonal antibody (MAb) TONO-1 (IgM, lambda) was selected. MAb TONO-1 proved to be reactive with 4 human T-cell lines, HPB-MLT, L-MAT, MOLT-3 and MOLT-4F, but not with B-leukemia, Burkitt's lymphoma, myelomonocytic leukemia, erythroleukemia or non-hematopoietic malignant cell lines. MAb TONO-1 reacted positively with fresh leukemia cells from 2 of 7 patients with acute T-lymphocytic leukemia, but no reaction was observed in non-T-cell leukemia cases. Normal lymphocytes, monocytes, granulocytes, red blood cells and platelets in the peripheral blood did not demonstrate remarkable binding. Neither thymocytes nor bone-marrow cells from healthy volunteers were reactive. The antigens defined by MAb TONO-1 were polypeptides of 57 kDa and 68 kDa. Immunohistological studies revealed no staining of thymocytes in the thymus of a 6-month-old child, but showed epithelial reticular cells and Hassall's corpuscles to stain positively. These results suggest that MAb TONO-1 is directed to T-leukemic cells and some components of thymus tissue.

Transcription Factors and Hematopoietic Development

Transcription Factors and Hematopoietic Development

Alterations in the prooxidant and antioxidant status of human leukemic T-lymphocyte MOLT4 cells treated with potassium chromate.

The involvement of reactive oxygen species in chromate-induced genotoxicity has been postulated. Because intracellular antioxidants help in eliminating the reactive species of oxygen, we have investigated both the prooxidant and antioxidant status of human leukemic T-lymphocyte MOLT4 cells exposed to nontoxic levels of chromium(VI) in culture. The cells treated with 0-->200 microM potassium chromate in a salts/glucose medium for 2 h were found to contain significantly lower levels of both small molecular weight and macromolecular antioxidants. In particular, the levels of glutathione and ascorbate were found to decrease with increased doses of chromate exposure in a dose-dependent manner. As little as 10 microM chromate was found to decrease these small molecular weight antioxidants significantly (p < 0.01). The macromolecular antioxidants, such as glutathione peroxidase, catalase, glutathione reductase, glucose-6-phosphate dehydrogenase and superoxide dismutase were also significantly (p < 0.01) decreased by exposing the cells to as little as 10 microM chromate. Concomitantly, there was a dose-dependent increase in intracellular H2O2 accumulation in cells exposed to chromium(VI). These results indicate that chromate-induced genotoxicity may be due, at least in part, to decreased levels of intracellular antioxidants in conjunction with an increased production of the reactive oxygen species.

Mobilization of intracellular Ca2+ by adenine nucleotides in human T-leukaemia cells: evidence for ADP-specific and P2y-purinergic receptors.

The expression of purinergic receptors on human T-cells was investigated and the receptors were shown to be functionally coupled to intracellular signals in two out of eight T-leukaemia cell-lines. Addition of adenine nucleotides resulted in mobilization of intracellular Ca2+ in HPB-ALL cells and a cell line (CB1) recently isolated from a patient with T-acute lymphoblastic leukaemia. Of a range of nucleotides tested only ADP and ATP elevated intracellular levels of Ca2+, with ADP being the more potent agonist. Ca2+ mobilization by ATP was accompanied by increased inositol phosphate production and was blocked by the purinergic receptor antagonist, Reactive Blue 2, indicating that ATP was interacting with a P2y receptor. Intracellular Ca2+ release triggered by ADP was independent of both inositol phosphate production and protein tyrosine phosphorylation. Expression of the transmembrane phosphotyrosine phosphatase, CD45, had no effect on ADP-stimulated Ca2+ mobilization. Our results show that functional P2y receptors can be expressed on T-cells, and also identify a novel T-cell ADP receptor. Signals mediated by these purinergic receptors could play important roles in modulating T-cell function.

Detection of intracellular lymphoid differentiation antigens by flow cytometry in acute lymphoblastic leukemia.

The value of flow cytometric detection of the intracellular lymphoid differentiation antigens CD3 and CD22 in the differential diagnosis of acute leukemia was assessed in cases of acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and leukemic cell lines. Cells were fixed in 0.25% paraformaldehyde at 4 degrees C for 60 min, permeabilized with 0.2% Tween 20 at 37 degrees C for 15 min, then stained with CD3 or CD22 monoclonal antibodies by indirect immunofluorescence. Cytoplasmic CD22 was detected on greater than 20% (mean 55%; range 20-87%) of blasts from all 20 cases of precursor-B ALL analyzed. The percentage of cells with cytoplasmic CD22 was greater than that with membrane CD22 in all except 2 cases of precursor-B ALL. Cytoplasmic CD22 was not detected in 8 cases of precursor-T ALL, 4 T-leukemia cell lines, or in 7 cases of AML. In contrast, cytoplasmic CD3 was detectable by flow cytometry in all 8 cases of precursor-T ALL, but not in precursor-B ALL, pre-B leukemia cell lines, or in AML. These results confirm that cytoplasmic CD3 and CD22 are excellent markers of the early T and B lineages in ALL and can be reliably detected by flow cytometry. This technique should be a valuable addition to routine immunophenotyping for classification of acute leukemia.

Detection of the Human Platelet-Activating Factor Receptor mRNA in Human B Lymphocytes by Polymerase Chain Reaction on Reverse Transcripts (RT-PCR)

The platelet activating factor receptor (hPAFR) is a GTP binding protein linked receptor of the rhodopsin family. The hPAFR gene maps to chromosome 1 and is characterized by the absence of introns in its coding region. Because PAF demonstrates unique properties as a growth factor in human B lymphoblastoid cell lines, we developed an RT-PCR in order to detect the presence of hPAFR mRNA. We examined the presence of the hPAFR in a series of B lymphoblastoid cell lines, as well as on fresh human B cells and the T-leukemia cell line Jurkat. All cells of B lineage expressed hPAFR mRNA, including a B cell line not previously shown to express functional hPAFR. In contrast, the T-leukemia cell line Jurkat expressed very low levels of hPAFR mRNA. We discuss the methodology and its validation in developing an RT-PCR for intronless genes such as the hPAFR.

Preparation and characterization of a new monoclonal antibody CAF7 specific for a leukocyte activation antigen.

A new murine hybridoma, CAF7, is raised using as an antigen the T-leukemic cell line CEM. It produces a monoclonal antibody (mAb) specific for an activation antigen on human lymphocytes. CAF7 stains monocytes, very weakly resting lymphocytes, and granulocytes, part of the thrombocytes, but not erythrocytes. After activation with phytohemagglutinin (PHA), CAF7 expression on peripheral lymphocytes rises as early as 5 hr post stimulation and 72-hr blasts express it at a considerable level. The cell lines Jurkat, CEM, MOLT4, Raji, Reh, K562, and MONOMAC6 are positive for CAF7. CAF7 immunoprecipitated an antigen, which when subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions migrated as a single band with a molecular weight of 120-140 kD. Under reducing conditions, it appears as two bands at 90-100 and 40 kD. The pattern of expression and the biochemical characteristics of CAF7 do not match any of the clusters defined in the Leukocyte Typing Workshops, but do resemble that of a previously described antigen, 4F2.

The natural tyrosine kinase inhibitor genistein produces cell cycle arrest and apoptosis in Jurkat T-leukemia cells

Genistein, a natural isoflavonoid phytoestrogen, is a strong inhibitor of protein tyrosine kinases. We analyzed the effects of genistein on in vitro growth, cell-cycle progression and chromatin structure of Jurkat cells, a T-cell leukemia line with a constitutively increased tyrosine phosphorylation pattern. Exposure of in vitro cultured Jurkat cells to genistein resulted in a dose-dependent, growth inhibition. Cell-cycle analysis of genistein-treated cells revealed a G 2/M arrest at low genistein concentrations (5–10 μg/ml), while at higher doses (20–30 μg/ml) there was also a perturbation in S-phase progression. The derangements in cell-cycle control were followed by apoptosic death of genistein-treated cells. Immunocytochemical analysis of cells stained with a FITC-conjugated anti-phosphotyrosine monoclonal antibody showed that 30 μ/ml genistein effectively inhibit tyrosine kinase activity in cultured Jurkat cells. Our results indicate that the natural isoflavone genistein antagonizes tumor cell growth through both cell-cycle arrest and induction of apoptosis and suggest that it could be a promising new agent in cancer therapy.

Differential activation-dependent regulation of integrin function in cultured human T-leukemic cell lines

T lymphocytes isolated from human peripheral blood express beta 1 (VLA) and LFA-1 integrins, but strong binding to integrin ligands occurs only after the delivery of an activation stimulus to the T cell. To gain further insight into activation-dependent regulation of integrin function, we have analyzed integrin activity on three different T- leukemic cell lines: Jurkat, CEM, and H9. This analysis shows important mechanistic differences in integrin regulation. First, phorbol ester treatment results in increased beta 1 integrin-dependent adhesion of both Jurkat and CEM cells to fibronectin, but decreased adhesion of H9 cells. Second, certain activation stimuli that upregulate beta 1 integrin activity in peripheral T cells are nonfunctional in these T-cell lines. Third, analysis of a panel of Jurkat mutants lacking surface expression of CD2 and/or CD3 shows that CD2-mediated upregulation of beta 1 integrin activity is dependent on expression of CD3, whereas CD28-mediated upregulation is not dependent on either CD2 or CD3 expression. Fourth, all T-cell lines tested show an inability to adhere to purified ICAM-1 via LFA-1. The selective alterations in integrin regulation in these cell lines relative to peripheral blood T cells provide important insights into the intracellular processes involved in integrin activation.

Differential Activation-Dependent Regulation of Integrin Function in Cultured Human T-Leukemic Cell Lines

AbstractT lymphocytes isolated from human peripheral blood express β1 (VLA) and LFA-1 integrins, but strong binding to integrin ligands occurs only after the delivery of an activation stimulus to the T cell. To gain further insight into activation-dependent regulation of integrin function, we have analyzed integrin activity on three different T-leukemic cell lines: Jurkat, CEM, and H9. This analysis shows important mechanistic differences in integrin regulation. First, phorbol ester treatment results in increased β1 integrindependent adhesion of both Jurkat and CEM cells to fibronectin, but decreased adhesion of H9 cells. Second, certain activation stimuli that upregulate β1 integrin activity in peripheral T cells are nonfunctional in these T-cell lines. Third, analysis of a panel of Jurkat mutants lacking surface expression of CD2 and/or CD3 shows that CD2-mediated upregulation of β1 integrin activity is dependent on expression of CD3, whereas CD28-mediated upregulation is not dependent on either CD2 or CD3 expression. Fourth, all T-cell lines tested show an inability to adhere to purified ICAM-1 via LFA-1. The selective alterations in integrin regulation in these cell lines relative to peripheral blood T cells provide important insights into the intracellular processes involved in integrin activation.

Oxysterol-induced cell death in human leukemic T-cells correlates with oxysterol binding protein occupancy and is independent of glucocorticoid-induced apoptosis

In eukaryotic cells oxysterols inhibit cholesterol biosynthesis and cell growth. A potent oxysterol, 25-hydroxycholesterol, was used to investigate the biological effects of oxysterols on three clonal lines of either glucocorticoid-sensitive or -resistant CEM cells, human leukemic T-lymphocytes. In addition, the glucocorticoid sensitivity of an oxysterol-resistant CEM cell line was tested. Oxysterols blocked growth and caused the lysis of cells regardless of their glucocorticoid response. All cells studied herein possessed an oxysterol binding protein with high affinity for 25-hydroxycholesterol. For all clones grown in serum-free medium, the half-maximal cytolytic concentration of 25-hydroxycholesterol (20–40 nM) correlated with its affinity ( K d = ∼ 31 nM) for this oxysterol binding protein. Both cholesterol and mevalonate reversed 25-hydroxycholesterol cytotoxicity; 3–6 μM cholesterol or 0.1 mM mevalonate decreased 60 nM 25-hydroxycholesterol cytotoxicity by 50%. This cholesterol or mevalonate reversal appeared possible even after several days of 60 nM oxysterol treatment. The protective effect of cholesterol could be overcome by increasing 25-hydroxycholesterol concentrations. Cholesterol and mevalonate did not prevent glucocorticoid-mediated lymphocytolysis. Furthermore, the oxysterol-resistant line was sensitive to dexamethasone lysis. These data support the hypothesis that oxysterols and glucocorticoids act independently to block the growth of human leukemic lymphoblasts.

Dimerization of NF-KB2 with RelA(p65) regulates DNA binding, transcriptional activation, and inhibition by an I kappa B-alpha (MAD-3).

Inducible expression of human immunodeficiency virus (HIV) is regulated by a cellular transcription factor, nuclear factor kappa B (NF-kappa B). NF-kappa B is composed of distinct subunits; five independent genes, NFKB1(p105), NFKB2(p100), RelA(p65), c-rel and relB, that encode related proteins that bind to kappa B DNA elements have been isolated. We have previously found that NFKB2(p49/p52) acts in concert with RelA(p65) to stimulate the HIV enhancer in Jurkat T-leukemia cells. Here we examine the biochemical basis for the transcriptional regulation of HIV by NFKB2. Using Scatchard analysis, we have determined the dissociation constants of homodimeric p49 and heterodimeric p49/p65 for binding to the HIV kappa B site. p49 has a approximately 18-fold-lower affinity for the HIV kappa B site (KD = 69.1 pM) than does the approximately 50-kDa protein NFKB1(p50) derived from p105 (KD = 3.9 pM). In contrast, the affinity of heterodimeric NFKB2(p49)/RelA(p65) for this site is approximately 6-fold higher (KD = 11.8 pM) than that of p49 alone. Consistent with these findings, in vitro transcription was stimulated 18-fold by the addition of preformed, heterodimeric NFKB2(p49)/RelA(p65) protein. Transcriptional activation of the HIV enhancer was also subject to regulation by recently cloned I kappa B-alpha(MAD-3). Recombinant I kappa B-alpha(MAD-3) inhibited the DNA binding activity of p65, p49/p65, and p50/p65 but stimulated the binding of NFKB2(p49) or NFKB1(p50). Functional activation of an HIV reporter plasmid by p49/p65 in transiently transfected Jurkat T-leukemia cells was also inhibited by coexpression of MAD-3. These data suggest that binding of the NFKB2 subunit to the HIV enhancer is facilitated by RelA(p65) and that this NFKB2(p49)/p65 heterodimeric complex mediates transcriptional activation which is subject to regulation by MAD-3.

Dimerization of NF-KB2 with RelA(p65) regulates DNA binding, transcriptional activation, and inhibition by an I kappa B-alpha (MAD-3).

Inducible expression of human immunodeficiency virus (HIV) is regulated by a cellular transcription factor, nuclear factor kappa B (NF-kappa B). NF-kappa B is composed of distinct subunits; five independent genes, NFKB1(p105), NFKB2(p100), RelA(p65), c-rel and relB, that encode related proteins that bind to kappa B DNA elements have been isolated. We have previously found that NFKB2(p49/p52) acts in concert with RelA(p65) to stimulate the HIV enhancer in Jurkat T-leukemia cells. Here we examine the biochemical basis for the transcriptional regulation of HIV by NFKB2. Using Scatchard analysis, we have determined the dissociation constants of homodimeric p49 and heterodimeric p49/p65 for binding to the HIV kappa B site. p49 has a approximately 18-fold-lower affinity for the HIV kappa B site (KD = 69.1 pM) than does the approximately 50-kDa protein NFKB1(p50) derived from p105 (KD = 3.9 pM). In contrast, the affinity of heterodimeric NFKB2(p49)/RelA(p65) for this site is approximately 6-fold higher (KD = 11.8 pM) than that of p49 alone. Consistent with these findings, in vitro transcription was stimulated 18-fold by the addition of preformed, heterodimeric NFKB2(p49)/RelA(p65) protein. Transcriptional activation of the HIV enhancer was also subject to regulation by recently cloned I kappa B-alpha(MAD-3). Recombinant I kappa B-alpha(MAD-3) inhibited the DNA binding activity of p65, p49/p65, and p50/p65 but stimulated the binding of NFKB2(p49) or NFKB1(p50). Functional activation of an HIV reporter plasmid by p49/p65 in transiently transfected Jurkat T-leukemia cells was also inhibited by coexpression of MAD-3. These data suggest that binding of the NFKB2 subunit to the HIV enhancer is facilitated by RelA(p65) and that this NFKB2(p49)/p65 heterodimeric complex mediates transcriptional activation which is subject to regulation by MAD-3.

Human immunodeficiency viruses containing heterologous enhancer/promoters are replication competent and exhibit different lymphocyte tropisms.

The human immunodeficiency virus (HIV) type 1 long terminal repeat (LTR) contains binding sites for nuclear factor kappa B (NF-kappa B) and the constitutively expressed transcription factor Sp1, both of which are highly conserved in HIV and simian immunodeficiency virus isolates. To delineate the effects of these motifs on the replicative capacity of HIV and to explore the possibility of extending the virus host range, known heterologous enhancer/promoters were inserted into the HIV-1 LTR in place of the NF-kappa B and Sp1 binding sites. The effects of these substitutions on viral replication in transfected HeLa cells and on HIV infection of human peripheral blood lymphocytes or continuous T-leukemia cell lines were evaluated. HIVs in which the NF-kappa B/Sp1 enhancer plus the downstream TATA element were replaced with heterologous enhancer/promoters were also constructed. Viruses containing the human cytomegalovirus immediate-early enhancer exhibited infectious kinetics similar to that of wild-type HIV in activated human peripheral blood lymphocytes and AA2 cells but replicated less efficiently in H9 and CEM cells. These studies indicate that heterologous enhancer elements are capable of restoring Tat responsiveness to the HIV LTR in the context of directing reporter gene expression as well as in the production of infectious progeny virions.

G-proteins are not directly involved in the CD3-antigen-mediated production of inositol phosphates in HPB-ALL T-leukaemia cells expressing phospholipase C isoforms gamma 1 and beta 3.

The possible involvement of G-proteins in T cell antigen-receptor complex (TCR)-mediated inositol phosphate production was investigated in HPB-ALL T-cells, which were found to express the phospholipase C gamma 1 and beta 3 isoforms. Cross-linking the CD3 antigen on streptolysin-O-permeabilized cells stimulated a dose-dependent increase in inositol phosphate production, as did addition of guanosine 5'-[gamma-thio]triphosphate (GTP[S]) or vanadate, a phosphotyrosine phosphatase inhibitor. It was possible, therefore, that the CD3-antigen-mediated production of inositol phosphates was either via a G-protein-dependent mechanism or by stimulation of protein tyrosine phosphorylation. The CD3-induced inositol phosphate production was potentiated by addition of vanadate, but not by addition of GTP[S]. Guanosine 5'-[beta-thio]diphosphate (GDP[S]) inhibited the rise in inositol phosphates induced by GTP[S], vanadate or cross-linking the CD3 antigen. The increase in protein tyrosine phosphorylation stimulated by vanadate or the OKT3 monoclonal antibody was not observed in the presence of GDP[S], showing that in permeabilized HPB-ALL cells, GDP[S] inhibits the actions of tyrosine kinases as well as G-protein function. Addition of either ADP[S] or phenylarsine oxide inhibited CD3- and vanadate-mediated increases in both tyrosine phosphorylation and inositol phosphate production, but did not inhibit GTP[S]-stimulated inositol phosphate production. On the other hand, pretreatment of cells with phorbol 12,13-dibutyrate inhibited subsequent GTP[S]-stimulated inositol phosphate production but did not inhibit significantly inositol phosphate production stimulated by either OKT3 F(ab')2 fragments or vanadate. Our results are consistent with the CD3 antigen stimulating inositol phosphate production by increasing the level of protein tyrosine phosphorylation, but not by activating a G-protein.

Isolation of a cDNA Clone Encoding a Zinc Finger Protein Highly Expressed in T-Leukemia Lines

AbstractA cDNA clone encoding a novel zinc finger protein expressed in lymphoid cells has been isolated. This protein contains 5 repeats of the C2H2 motif previously described in the Drosophila gap gene, Kruppel, which is involved in embryo segmentation. Northern blot analysis showed that the messenger RNA (mRNA) encoding this protein is expressed at high levels in a variety of T-leukemia cell lines, at lower levels in some B cells, but is not observed in nonlymphoid cells. Within the T lineage, the mRNA is found at high levels in both alpha beta and gamma delta T cells. These data suggest that this cDNA, designated Hkr-T1, represents a gene that may contribute to the determination of the differentiation and the specificity within lymphoid cells.