title: Regulated expression of telomerase activity in human T lymphocyte development and activation.
abstract: Telomerase, a ribonucleoprotein that is capable of synthesizing telomeric repeats, is expressed in germline and malignant cells, and is absent in most normal human somatic cells. The selective expression of telomerase has thus been proposed to be a basis for the immortality of the germline and of malignant cells. In the present study, telomerase activity was analyzed in normal human T lymphocytes. It was found that telomerase is expressed at a high level in thymocyte subpopulations, at an intermediate level in tonsil T lymphocytes, and at a low to undetectable level in peripheral blood T lymphocytes. Moreover, telomerase activity is highly inducible in peripheral T lymphocytes by activation through CD3 with or without CD28 costimulation, or by stimulation with phorbol myristate acetate (PMA)/ionomycin. The induction of telomerase by anti-CD3 plus anti-CD28 (anti-CD3/CD28) stimulation required RNA and protein synthesis, and was blocked by herbimycin A, an inhibitor of S pi protein tyrosine kinases. The immunosuppressive drug cyclosporin A selectively inhibited telomerase induction by PMA/ionomycin and by anti-CD3, but not by anti-CD3/CD28. Although telomerase activity in peripheral T lymphocytes was activation dependent and correlated with cell proliferation, it was not cell cycle phase restricted. These results indicate that the expression of telomerase in normal human T lymphocytes is both developmentally regulated and activation induced. Telomerase may thus play a permissive role in T cell development and in determining the capacity of lymphoid cells for cell division and clonal expansion.
authors.affiliation: Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: N P
authors.initials: NP
authors.lastname: Weng
authors.forename: B L
authors.initials: BL
authors.lastname: Levine
authors.forename: C H
authors.initials: CH
authors.lastname: June
authors.forename: R J
authors.initials: RJ
authors.lastname: Hodes
mesh_terms: D015703:Antigens, CD / Q000276:immunology; D018106:CD28 Antigens / Q000276:immunology; D017252:CD3 Complex / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D005434:Flow Cytometry; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007223:Infant; D015759:Ionomycin / Q000494:pharmacology; D008213:Lymphocyte Activation; D014066:Palatine Tonsil / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology*; D019098:Telomerase / Q000096:biosynthesis*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013950:Thymus Gland / Q000276:immunology
chemical_list: D015703:Antigens, CD; D018106:CD28 Antigens; D017252:CD3 Complex; D015759:Ionomycin; D019098:Telomerase; D013755:Tetradecanoylphorbol Acetate