RESUMO
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.
Assuntos
Epigênese Genética/efeitos dos fármacos , Deficiência de Glucosefosfato Desidrogenase/genética , Glucosefosfato Desidrogenase/biossíntese , Glucosefosfato Desidrogenase/genética , Inibidores de Histona Desacetilases/farmacologia , Transcrição Gênica/efeitos dos fármacos , Células Cultivadas , Imunoprecipitação da Cromatina , Deficiência de Glucosefosfato Desidrogenase/enzimologia , Humanos , Reação em Cadeia da Polimerase em Tempo RealRESUMO
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.
Assuntos
Fatores Ativadores da Transcrição/química , Linfócitos B/química , Linfócitos B/metabolismo , Ilhas de CpG/genética , Glicosilfosfatidilinositóis/deficiência , Hemoglobinúria Paroxística/genética , Manosiltransferases/genética , Proteínas do Grupo Polycomb/metabolismo , Fatores Ativadores da Transcrição/genética , Fatores Ativadores da Transcrição/metabolismo , Sequência de Bases , Células Cultivadas , Metilação de DNA , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica , Genes Essenciais , Glicosilfosfatidilinositóis/genética , Glicosilfosfatidilinositóis/metabolismo , Hemoglobinúria Paroxística/metabolismo , Histonas/química , Histonas/metabolismo , Humanos , Manosiltransferases/metabolismo , Dados de Sequência Molecular , Nucleossomos/metabolismo , Mutação Puntual , Proteínas do Grupo Polycomb/química , Proteínas do Grupo Polycomb/genética , Regiões Promotoras Genéticas , Ligação Proteica , ConvulsõesRESUMO
Co-operative interaction of transcription factors (TF) with epigenetic processes, such as chromatin remodeling and modification (acetylation or methylation), as well as DNA methylation, determine transcriptional activity, activation or repression of a given gene. Mutations disrupting binding of TF to their cognate DNA motifs would be expected to alter the epigenetic landscape of the promoter and selectively affect transcription of the given gene. We review here the transcriptional, epigenetic, biochemical, and clinical consequences of a constitutional mutation in the promoter of PIGM, a housekeeping gene that disrupts binding of the general TF, SP1, thus causing the autosomal recessive disease, inherited glycosylphosphatidylinositol (GPI) deficiency. We suggest that detailed dissection of the function of the mutated PIGM promoter provides important lessons pertinent to the transcriptional and epigenetic control of housekeeping genes as a whole and might have wider therapeutic implications.
Assuntos
Erros Inatos do Metabolismo dos Carboidratos/genética , Erros Inatos do Metabolismo dos Carboidratos/metabolismo , Glicosilfosfatidilinositóis/deficiência , Histonas/metabolismo , Acetilação , Animais , Erros Inatos do Metabolismo dos Carboidratos/tratamento farmacológico , Desenvolvimento Embrionário/genética , Desenvolvimento Embrionário/fisiologia , Epigênese Genética , Feminino , Genes Recessivos , Glicosilfosfatidilinositóis/biossíntese , Glicosilfosfatidilinositóis/fisiologia , Inibidores de Histona Desacetilases/uso terapêutico , Histonas/química , Humanos , Masculino , Manosiltransferases/deficiência , Manosiltransferases/genética , Manosiltransferases/metabolismo , Proteínas de Membrana/deficiência , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Modelos Biológicos , Mutação , Gravidez , Regiões Promotoras Genéticas , Fator de Transcrição Sp1/metabolismoRESUMO
The purpose of this study was to evaluate the sTfR-F index and hypochromic erythrocytes (HYPO%) as potential predictors of response to recombinant human erythropoietin (r-HuEPO) of anemic patients with multiple myeloma (MM) before treatment, as well as early in the course of treatment. Twenty-six newly diagnosed anemic MM patients received r-HuEPO 30,000 IU/wk sc, for six weeks. The sTfR-F index and HYPO% were determined at baseline and at weeks 2 and 6. Patients were classified in 1 of 4 categories of a diagnostic plot, according to erythropoietic state (ES I-IV), defined by the combination of sTfR-F index and HYPO%. Sixteen of 20 patients in ES I and II before treatment responded to r-HuEPO, whereas none of the 6 patients in ES III and IV responded (P < .001). At week 2, 44% of patients who responded and 60% of the nonresponders were in functional iron deficiency (FID) and the proportion increased to 69% and 80%, respectively, by week 6. Seven of the patients who did not respond received in addition 200 mg iron sucrose IV weekly, for the next 4 weeks, and 6 of them responded. These results suggest that combination of sTfR-F index and HYPO% in a diagnostic plot can be used as a predictive model to recognize patients who will benefit from r-HuEPO and identify FID requiring iron supplementation, before treatment and early in the course of treatment, contributing thus to optimization of r-HuEPO therapy.
