concanavalin-a and Leukemia--T-Cell

Telomerase activity and telomerase reverse transcriptase (hTERT), the key component of the telomerase complex, are tightly proliferation regulated in normal and malignant cells both in vitro and in vivo; however, underlying mechanisms are unclear. In the present study, we identified mitogen-activated protein kinase (MAPK) cascade-mediated histone H3 ser10 phosphorylation to be a molecular link between proliferation and induction of hTERT/telomerase activity. In normal human T lymphocytes and fibroblasts, growth or stress stimuli known to drive H3 phosphorylation through the MAPK signaling induce hTERT expression and/or telomerase activity that was preceded by phosphorylated histone H3 (ser10) at the hTERT promoter. Blockade of the MAPK-triggered H3 phosphorylation significantly abrogates hTERT induction and ser10 phosphorylation at this promoter. However, H3 ser10 phosphorylation alone resulted in low, transient hTERT induction, as seen in fibroblasts, whereas H3 phosphorylation followed by its acetylation at lys14 robustly trans-activated the hTERT gene accompanying constitutive telomerase activity in normal and malignant T cells. H3 acetylation without phosphorylation similarly exerted weak effects on hTERT expression. These results define H3 phosphorylation as a key to hTERT transactivation induced by proliferation and reveal a fundamental mechanism for telomerase regulation in both normal human cells and transformed T cells.

Topics: Acetylation; Cell Cycle; Cell Proliferation; Cells, Cultured; Concanavalin A; DNA-Binding Proteins; Enzyme Activation; Fibroblasts; Gene Expression Regulation; Histones; Humans; Jurkat Cells; Leukemia, T-Cell; Mitogen-Activated Protein Kinases; Phosphorylation; Promoter Regions, Genetic; RNA, Messenger; Serine; T-Lymphocytes; Telomerase; Transcriptional Activation; Up-Regulation

ICSAT (Interferon Consensus Sequence binding protein for Activated T cells) is a lymphocyte-specific member of the interferon regulatory factor (IRF) family of transcription factors, originally identified through Southwestern screening of the ATL(Adult T-cell leukemia)-16T expression library. In this study, we created transgenic mice overexpressing ICSAT in lymphocytes. Although spontaneous tumorigenesis was not observed, IL-2 production with Concanavalin A stimulation was significantly increased in transgenic mice overexpressing ICSAT. ICSAT overexpression in lymphocytes seems insufficient for the leukemogenesis of ATL or multiple myeloma (MM), however, it may regulate T cell activation and its overexpression may lead to leukemogenesis via controlling IL-2 production.

Topics: Adult; Animals; Concanavalin A; DNA-Binding Proteins; Humans; Immunoglobulin G; Interferon Regulatory Factors; Interleukin-2; Leukemia, T-Cell; Lymphocytes; Mice; Mice, Transgenic; Multiple Myeloma; Thymus Gland; Transcription Factors

Lymphocytes respond to mitogens, viruses and other activation agents with hydrogen peroxide or reactive oxygen bursts which may originate at or near the cell membrane. It has been shown that a very small increase in the ratio of Con A cells results in a rapid switchover from mitogenicity to cytotoxicity. It is hypothesized that the change from mitogenicity to cytotoxicity correlates with the strength and duration of the hydrogen peroxide or reactive oxygen bursts which in turn depends on the number of molecules of the activation agent bound per cell. This hypothesis is presented and discussed in the context of the apoptosis (programmed cell death) and pro-oxidant-antioxidant hypothesis of CD4+ T-cell and B-cell subpopulation depletion in AIDS.

Topics: Acquired Immunodeficiency Syndrome; Antioxidants; Apoptosis; B-Lymphocyte Subsets; CD4-Positive T-Lymphocytes; Concanavalin A; HIV Envelope Protein gp120; Humans; Hydrogen Peroxide; Leukemia, T-Cell; Lymphocytes; Measles virus; Mitosis; Models, Biological; Oxidants; Oxidative Stress; Reactive Oxygen Species; Signal Transduction; Tumor Cells, Cultured

We established IL-2-dependent T cells from an adult T-cell leukaemia (ATL) patient whose leukaemic cells changed from CD4 single-positive in the initial phase to double-negative (CD4- CD8-) at the time of exacerbation. The cells termed SO-4 were of ATL cell origin and showed the double-negative TCR alpha beta/CD3+ T-cell phenotype. SO-4 cells acquired CD4 antigen expression following stimulation with concanavalin A (ConA) or immobilized anti-CD3 antibody. The induction was inhibited by herbimycin A, an inhibitor of protein tyrosine kinase (PTK) activity. No CD4 mRNA was detectable in unstimulated SO-4 cells but a 3.0 kb signal specific for CD4 mRNA was detected after stimulation. These findings indicate that SO-4 cells return to their original phenotype (CD4 single-positive) by stimulation involving PTK. The results indicate that there is a pathway of phenotypic cycling between CD4 single-positive and double-negative T cells.

Topics: Benzoquinones; Blotting, Northern; Blotting, Southern; CD3 Complex; CD4 Antigens; CD8 Antigens; Concanavalin A; Female; Gene Expression; Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; Humans; Interleukin-2; Lactams, Macrocyclic; Leukemia, T-Cell; Middle Aged; Protein-Tyrosine Kinases; Quinones; Receptors, Antigen, T-Cell, alpha-beta; Rifabutin; RNA, Messenger; T-Lymphocyte Subsets; Tumor Cells, Cultured

The effect of TBG on the functional activity of different cell lines, spontaneous and Con A induced proliferation of PBL was studied. If concentration of TBG is higher than 50 mu kg/ml it suppresses the proliferation in many used cell lines, except choriocarcinoma and cancer of uterus. The reliable increasing of spontaneous proliferation of PBL, Jurkat and K-562 cells may be observed if concentration is more lower (0.5-15 mu kg/ml). However proliferation of other cell lines corresponds to control level, and Con A induced proliferation of PBL is inhibited. The effect was more marked at 48, as compared to 24 hours of cell incubation with TBG.

Topics: Biomarkers, Tumor; Cell Division; Cell Line; Choriocarcinoma; Concanavalin A; Female; HeLa Cells; Humans; Leukemia, Erythroblastic, Acute; Leukemia, Myeloid; Leukemia, T-Cell; Lymphocytes; Lymphoma, B-Cell; Lymphoma, T-Cell; Pregnancy-Specific beta 1-Glycoproteins; Tumor Cells, Cultured; Uterine Neoplasms