HEXIM1 Overexpression Alters GATA1 Activity and Promotes Fetal Globin Expression

Erythropoiesis is a highly organized process whereby multipotent HSCs become committed to the erythroid linage and mature into enucleate erythrocytes. Recent work from our lab demonstrated that HEXIM1 is essential in the regulation of erythroid proliferation, viability and gene expression, and also promotes the expression of GATA1 target genes. New analyses of HEXIM1 overexpression (OE) in HUDEP2 cells revealed a significant increase of gamma globin production, with a higher proportion of cells expressing fetal hemoglobin. To gain insights into the mechanisms underlying the increased fetal globin expression, we performed CUT&RUN assays for Ser5 phosphorylated and total RNPII in HEXIM1 OE and control cells. Surprisingly, OE of HEXIM1 had only modest impacts on RNPII pausing, but instead lead to changes in the genes occupied by RNPII. Our results support a model where elevated HEXIM1 levels promote the pioneer activity of GATA1, and facilitate the expression of a fetal transcriptional program in adult cells in a pTEFb-dependent manner. CUT&RUN assays for total and Ser5 phophorylated RNA Polymerase II, and GATA1 in HUDEP-2 cells. CUT&RUN assays for HEXIM1 and ATAC-seq in HUDEP-2 cells.