RESUMO
High fetal hemoglobin (HbF, α2 γ2 ) levels ameliorate the clinical manifestations of sickle cell disease and ß thalassemia. The mechanisms that repress HbF expression and silence γ-globin genes in adults are incompletely characterized and only a single HbF inducer, hydroxyurea, is approved for treatment, and only in patients with sickle cell disease. We identified SIRT1, a protein deacetylase, as a new inducer of γ-globin. SIRT1 knockdown decreased, while SIRT1 ectopic expression upregulated γ-globin gene (HBG) expression in primary human erythroid cells and in K562 cells. The small molecule SIRT1 activators SRT2104 and SRT1720 enhanced HBG expression in cord blood human erythroblasts and reactivated silenced HBG in adult human erythroblasts. Furthermore, SIRT1 binds in the ß-globin gene cluster locus control region (LCR) and HBG promoters, promotes the looping of the LCR to HBG promoter, and increases the binding of RNA polymerase II and H4K16Ac in the HBG promoter. SIRT1 suppressed the expression of the HBG suppressors BCL11A, KLF1, HDAC1 and HDAC2. Lastly, SIRT1 did not change the proliferation of human erythroid progenitor cells or the expression of differentiation marker CD235a. These data suggest that SIRT1 activates HBG expression through facilitating LCR looping to the HBG promoter, inhibiting the expression of transcriptional suppressors of HBG, and indirectly increasing histone acetylation in the HBG promoter. SIRT1 is a potential therapeutic target for γ-globin gene induction, and small molecule SIRT1 activators might serve as a lead compound for the development of new HbF inducers.
Assuntos
Hemoglobina Fetal/genética , Regulação da Expressão Gênica , Sirtuína 1/metabolismo , Ativação Transcricional , gama-Globinas/genética , Diferenciação Celular/genética , Proliferação de Células/genética , Expressão Ectópica do Gene , Eritroblastos/metabolismo , Células Precursoras Eritroides/metabolismo , Eritropoese/genética , Hemoglobina Fetal/metabolismo , Técnicas de Silenciamento de Genes , Inativação Gênica , Humanos , Células K562 , Região de Controle de Locus Gênico , Especificidade de Órgãos/genética , Regiões Promotoras Genéticas , Ligação Proteica , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Sirtuína 1/genética , gama-Globinas/metabolismoRESUMO
Contact inhibition keeps cell proliferation in check and serves as a built-in protection against cancer development by arresting cell division upon cell-cell contact. Yet the complete mechanism behind this anti-cancer process remains largely unclear. Here we present SIRT1 as a novel regulator of contact inhibition. SIRT1 performs a wide variety of functions in biological processes, but its involvement in contact inhibition has not been explored to date. We used NIH3T3 cells, which are sensitive to contact inhibition, and H460 and DU145 cancer cells, which lack contact inhibition, to investigate the relationship between SIRT1 and contact inhibition. We show that SIRT1 overexpression in NIH3T3 cells overcomes contact inhibition while SIRT1 knockdown in cancer cells restores their lost contact inhibition. Moreover, we demonstrate that p27 protein expression is controlled by SIRT1 in contact inhibition. Overall, our findings underline the critical role of SIRT1 in contact inhibition and suggest SIRT1 inhibition as a potential strategy to suppress cancer cell growth by restoring contact inhibition.
