Transcriptional Control of Hemoglobin Synthesis and Erythrocyte Development

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PROJECT SUMMARY Hemoglobin synthesis and erythrocyte development are often studied independently, yet their mechanisms are inextricably linked. Differentiation defects yield immature precursors, and impaired hemoglobin synthesis causes ineffective erythropoiesis. A common thread of these mechanisms is GATA transcription factor involvement. Many questions remain regarding how GATA factor networks instruct progenitors to generate vast numbers of erythrocytes, which broadly informs molecular/cellular biology and hematology. We discovered: 1) locus-specific coregulator utilization by GATA1 to control differentiation; 2) GATA factor/regeneration-activated enhancer confers expression of an unstudied sterile alpha motif domain protein that controls erythrocyte regeneration; 3) GATA factor-regulated zinc transporter switch governs differentiation; 4) mechanism of heme targeting chromatin genome-wide; 5) GATA factor-regulated solute carrier protein (SLC) cohort transports diverse small molecules to control erythropoiesis. Our multi-omic work supports the aims to analyze how GATA factors establish small molecule ensembles that target the genome and regulate the GATA factor to ensure differentiation. Aim 1 will dissect a multi-component mechanism by which GATA1 and heme control genome function and erythrocyte development. GATA1 activates genes mediating heme biosynthesis, heme facilitates or restricts GATA1 function and heme downregulates GATA1. Heme regulates transcription by downregulating the repressor Bach1, and we discovered a Bach1-independent heme-regulated mechanism. We hypothesize that Bach1-dependent and -independent mechanisms establish critical erythroid functions, and these mechanisms provide translational opportunities. Using all heme target genes and a gene-specific approach, we will establish the mechanisms. Aim 2 will elucidate a GATA factor-dependent small molecule transporter axis that regulates erythroid differentiation. We hypothesize that diverse small molecules function in GATA factor mechanisms and discovering GATA factor-regulated solute carrier (Slc) transporters will unveil new dimensions to these mechanisms. We defined a GATA1/2-regulated Slc cohort that transports diverse small molecules. We prioritized a subset with GATA factor-occupied predicted enhancers and will elucidate mechanisms that link GATA factors with small molecule ensembles and differentiation. Aim 3 will test models for how GATA1 instigates a sphingolipid-dependent regulatory network. GATA1-regulated Slcs included sphingolipid transporters. Lipidomics revealed GATA1-induced sphingolipid remodeling. Ceramide synthase inhibition blocks GATA1-mediated GATA2 downregulation, β-globin induction and erythroid maturation. Sphingolipid signaling controls apoptosis, proliferation and migration, high S1P is deleterious in sickle cell disease, and human ceramide deficiency involves disrupted erythropoiesis. We hypothesize that sphingolipidome regulation by GATA1 is vital in biology and pathology. We will develop basic and translational insights into GATA factor mechanisms governing small molecules that control GATA factors, globin synthesis and differentiation.