c-myc gene expression and activation of human thymocytes.
The relationship between c-myc expression and thymocyte activation was studied in freshly isolated human thymocytes and in thymocytes activated with various inducing agents. In freshly isolated thymocytes c-myc mRNA is expressed at low levels, while thymocytes activated with Concanavalin A (Con A), the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), Con A in combination with TPA or interleukin 2 (IL-2) are induced to express higher levels of c-myc mRNA. The expression of c-myc is increased within 3 h of stimulation with these inducing agents; the amount of c-myc mRNA which is accumulated is not correlated with the rate of thymocyte proliferation. Dexamethasone and Cyclosporin A (CsA) which inhibit early events of T cell activation and the expression of the interleukin-2 (IL-2) and gamma-interferon (gamma-IFN) genes also markedly suppress the expression of c-myc mRNA in Con A, and Con A + TPA-activated thymocytes. We conclude that activation of c-myc gene expression is an early event observed in activated human thymocytes. The level of c-myc expression is dependent on the mode of thymocyte activation rather than on the rate of thymocyte proliferation. Since freshly isolated thymocytes express low levels of c-myc mRNA it is possible that IL-2 induces c-myc expression at least in a responsive subpopulation of thymocytes during ontogeny.
D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002648:Child; D003208:Concanavalin A; D003524:Cyclosporins / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D006801:Humans; D007223:Infant; D008213:Lymphocyte Activation; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000235:genetics*; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000276:immunology; D013950:Thymus Gland / Q000276:immunology; D014158:Transcription, Genetic
D003524:Cyclosporins; D012333:RNA, Messenger; D003208:Concanavalin A; D003907:Dexamethasone