RESUMEN
A rare point mutation in the core promoter -270GC-rich box of PIGM, a housekeeping gene, disrupts binding of the generic transcription factor (TF) Sp1 and causes inherited glycosylphosphatidylinositol (GPI) deficiency (IGD). We show that whereas PIGM messenger RNA levels and surface GPI expression in IGD B cells are low, GPI expression is near normal in IGD erythroid cells. This divergent phenotype results from differential promoter chromatin accessibility and binding of Sp1. Specifically, whereas PIGM transcription in B cells is dependent on Sp1 binding to the -270GC-rich box and is associated with lower promoter accessibility, in erythroid cells, Sp1 activates PIGM transcription by binding upstream of (but not to) the -270GC-rich box. These findings explain intact PIGM transcription in IGD erythroid cells and the lack of clinically significant intravascular hemolysis in patients with IGD. Furthermore, they provide novel insights into tissue-specific transcriptional control of a housekeeping gene by a generic TF.
Asunto(s)
Glicosilfosfatidilinositoles/deficiencia , Hemoglobinuria Paroxística/genética , Manosiltransferasas/genética , Activación Transcripcional , Linfocitos B/metabolismo , Linfocitos B/patología , Eritrocitos/metabolismo , Eritrocitos/patología , Glicosilfosfatidilinositoles/genética , Glicosilfosfatidilinositoles/metabolismo , Hemoglobinuria Paroxística/metabolismo , Hemoglobinuria Paroxística/patología , Humanos , Mutación , Fenotipo , Regiones Promotoras Genéticas , Convulsiones , Factor de Transcripción Sp1/metabolismoRESUMEN
HDAC inhibitors (HDACi) increase transcription of some genes through histone hyperacetylation. To test the hypothesis that HDACi-mediated enhanced transcription might be of therapeutic value for inherited enzyme deficiency disorders, we focused on the glycolytic and pentose phosphate pathways (GPPPs). We show that among the 16 genes of the GPPPs, HDACi selectively enhance transcription of glucose 6-phosphate dehydrogenase (G6PD). This requires enhanced recruitment of the generic transcription factor Sp1, with commensurate recruitment of histone acetyltransferases and deacetylases, increased histone acetylation, and polymerase II recruitment to G6PD. These G6PD-selective transcriptional and epigenetic events result in increased G6PD transcription and ultimately restored enzymatic activity in B cells and erythroid precursor cells from patients with G6PD deficiency, a disorder associated with acute or chronic hemolytic anemia. Therefore, restoration of enzymatic activity in G6PD-deficient nucleated cells is feasible through modulation of G6PD transcription. Our findings also suggest that clinical consequences of pathogenic missense mutations in proteins with enzymatic function can be overcome in some cases by enhancement of the transcriptional output of the affected gene.
Asunto(s)
Epigénesis Genética/efectos de los fármacos , Deficiencia de Glucosafosfato Deshidrogenasa/genética , Glucosafosfato Deshidrogenasa/biosíntesis , Glucosafosfato Deshidrogenasa/genética , Inhibidores de Histona Desacetilasas/farmacología , Transcripción Genética/efectos de los fármacos , Células Cultivadas , Inmunoprecipitación de Cromatina , Deficiencia de Glucosafosfato Deshidrogenasa/enzimología , Humanos , Reacción en Cadena en Tiempo Real de la PolimerasaRESUMEN
How the transcription repressing complex Polycomb interacts with transcriptional regulators at housekeeping genes in somatic cells is not well understood. By exploiting a CpG island (CGI) point mutation causing a Mendelian disease, we show that DNA binding of activating transcription factor (TF) determines histone acetylation and nucleosomal depletion commensurate with Polycomb exclusion from the target promoter. Lack of TF binding leads to reversible transcriptional repression imposed by nucleosomal compaction and consolidated by Polycomb recruitment and establishment of bivalent chromatin status. Thus, within a functional hierarchy of transcriptional regulators, TF binding is the main determinant of Polycomb recruitment to the CGI of a housekeeping gene in somatic cells.