Enhancement of beta-globin locus control region-mediated transactivation by mitogen-activated protein kinases through stochastic and graded mechanisms.

Forsberg EC, Zaboikina TN, Versaw WK, Ahn NG, Bresnick EH
Mol Cell Biol. 1999 19 (8): 5565-75

PMID: 10409746 · PMCID: PMC84409 · DOI:10.1128/mcb.19.8.5565

Activation of the mitogen-activated protein kinase (MAPK) pathway enhances long-range transactivation by the beta-globin locus control region (LCR) (W. K. Versaw, V. Blank, N. M. Andrews, and E. H. Bresnick, Proc. Natl. Acad. Sci. USA 95:8756-8760, 1998). The enhancement requires tandem recognition sites for the hematopoietic transcription factor NF-E2 within the hypersensitive site 2 (HS2) subregion of the LCR. To distinguish between mechanisms of induction involving the activation of silent promoters or the increased efficacy of active promoters, we analyzed basal and MAPK-stimulated HS2 enhancer activity in single, living cells. K562 erythroleukemia cells stably transfected with constructs containing the human Agamma-globin promoter linked to an enhanced green fluorescent protein (EGFP) reporter, with or without HS2, were analyzed for EGFP expression by flow cytometry. When most cells in a population expressed EGFP, MAPK augmented the activity of active promoters. However, under conditions of silencing, in which cells reverted to a state with no measurable EGFP expression, MAPK activated silent promoters. Furthermore, studies of populations of EGFP-expressing and non-EGFP-expressing cells isolated by flow cytometry showed that MAPK activation converted nonexpressing cells into expressing cells and increased expression in expressing cells. These results support a model in which MAPK elicits both graded and stochastic responses to increase HS2-mediated transactivation from single chromatin templates.

MeSH Terms (22)

5' Untranslated Regions Calcium-Calmodulin-Dependent Protein Kinases DNA-Binding Proteins Enhancer Elements, Genetic Erythroid-Specific DNA-Binding Factors Erythropoiesis Gene Expression Regulation Genes, Reporter Globins Humans K562 Cells NF-E2 Transcription Factor NF-E2 Transcription Factor, p45 Subunit Promoter Regions, Genetic Signal Transduction Stochastic Processes Templates, Genetic Tetradecanoylphorbol Acetate Thymidine Kinase Transcriptional Activation Transcription Factors Transfection

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