Abstract
Human globin gene expression during development is modulated by transcription factors in a stage-dependent manner. However, the mechanisms controlling the process are still largely unknown. In this study, we found that a nuclear protein, LYAR (human homologue of mouse Ly-1 antibody reactive clone) directly interacted with the methyltransferase PRMT5 which triggers the histone H4 Arg3 symmetric dimethylation (H4R3me2s) mark. We found that PRMT5 binding on the proximal γ-promoter was LYAR-dependent. The LYAR DNA-binding motif (GGTTAT) was identified by performing CASTing (cyclic amplification and selection of targets) experiments. Results of EMSA and ChIP assays confirmed that LYAR bound to a DNA region corresponding to the 5′-untranslated region of the γ-globin gene. We also found that LYAR repressed human fetal globin gene expression in both K562 cells and primary human adult erythroid progenitor cells. Thus, these data indicate that LYAR acts as a novel transcription factor that binds the γ-globin gene, and is essential for silencing the γ-globin gene.
Highlights
The human -globin locus is composed of five globin genes (⑀, G␥, A␥ - ␦, -globin) located on the short arm of chromosome 11
We found that PRMT5 was co-immunoprecipitated with LYAR protein from K562 cellular extract by anti-LYAR antibody
Using immunoprecipitation followed by mass spectrometry analysis, we determined that LYAR interacted with PRMT5, and participated in suppressing ␥ -globin gene expression through binding directly to the DNA region corresponding to 5 untranslated region (UTR) of the ␥ -globin gene
Summary
The human -globin locus is composed of five globin genes (⑀-, G␥ -, A␥ - ␦-, -globin) located on the short arm of chromosome 11. Globin genes are expressed in a developmentaland tissue-specific manner. The ␥ -globin genes (G␥ , A␥ ) are expressed throughout most of fetal life, and their expression is gradually replaced by -globin after birth [1]. Mutations in the -globin gene can cause -thalassemia and sickle cell disease (SCD) [2]. Reactivation of ␥ -globin gene expression in adulthood has proven to be one of the best strategies to ameliorate the symptoms in these patients. Because of the clinical significance of -globins, numerous studies have focused on the molecular events regulating their expression and the ␥ to  switch [3,4]
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