EKLF Is Recruited to the γ-Globin Gene Promoter as a Co-Activator and Is Required for γ-Globin Gene Induction by Short-Chain Fatty Acids.

Abstract

The erythroid Kruppel-like factor, EKLF, is an essential transcription factor for mammalian β-type globin gene switching, and specifically activates transcription of the adult β-globin gene through binding of its zinc finger domain to the β-globin promoter. We report now that EKLF is also required for activation of the γ-globin gene by short-chain fatty acid (SCFA) derivatives. We found that specific knockdown of EKLF levels by siRNA prevents SCFA induced-expression of an integrated γ-globin promoter in a stably-expressed mLCRβprRlucAγprFluccassette, and prevents induction of the endogenous γ-globin gene in primary human erythroid progenitors. In chromatin immunoprecipitation (ChIP) assays, EKLF was found to be actively recruited to the endogenous γ-globin gene promoter with exposure of human erythroid progenitors, and hematopoietic cell lines, to SCFA derivatives. The human SWI/WNF complex is a ubiquitous multimeric complex that regulates gene expression by remodeling nucleosomal structure in an ATP-dependent manner. We found that the SWI/SNF complex chromatin-modifying core ATPase BRG1 is also required for γ-globin gene induction by SCFA derivatives. Furthermore, BRG1 is actively recruited to the endogenous γ-globin promoter of human erythroid progenitors with exposure to SCFA derivatives, and this recruitment is dependent upon the presence of EKLF. These findings all demonstrate that EKLF, and the co-activator BRG1, previously demonstrated to be required for definitive or adult erythropoietic patterns of globin gene expression, are co-opted by SCFA derivatives to activate the fetal globin genes. Recently. we also identified a γ-globin-specific repressor complex, consisting of NCoR and HDAC3, which is displaced from the proximal γ-globin promoter by exposure to SCFA derivatives prior to activation of transcription (Blood , 108:3179–86, 2006). Collectively, these studies identify critical activating and repressing cofactors regulating γ-globin gene expression, and provide new targets for therapeutic interventions.