Chromatin Organization By SATB1 Regulates HSP70 Induction in Early Erythropoiesis and Lost in Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome. The disease usually presents within the first year of life and is associated with anemia, congenital abnormalities, and an increased risk of developing cancer. The most prevalent mutations are found in the ribosomal protein RPS19, accounting for over 25% of cases but approximately 70% of DBA patients carry mutations in ribosomal genes. Downregulation of GATA1 has been attributed to the disease, but the upstream mechanisms leading to aberrant erythropoiesis is only beginning to be elucidated.

SATB1 is highly upregulated in lymphocytes (especially thymocytes) and steadily downregulated in all myeloid ineages during differentiation. However the more modest expression of SATB1 in early progenitors is required for self-renewal of HSCs and globin switching in early erythropoiesis. Using transcriptomics, we identified SATB1 expression is prematurely lost in RPS19-insufficient erythropoiesis and that over a third (16/42) of RPS19-sensitive early erythroid genes were rescued upon SATB1 re-expression. One of the most deregulated transcripts encode the chaperone HSP70.

GATA1 is an essential master regulator in erythroid differentiation and high GATA1 protein levels are required for efficient erythropoiesis. In DBA, GATA1 protein expression is drastically diminished. Two mechanisms contribute to this. At the translational level, GATA1 transcripts fail to be translated adequately due to ribosomal inefficiency at binding short, unstructured 5'UTRs. At the protein level,HSP70 loss leads to reduced GATA1 protein stability. During healthy erythropoiesis HSP70 genes are drastically upregulated (3.21, 4.18 and 1.37- fold) and this is lost in RPS19 insufficiency. Here we report that upregulation of HSP70 in healthy erythropoiesis requires SATB1. SATB1 binds to 3 sites within a 40kb region surrounding the HSP70 gene loci and recruits a distal predicted enhancer element to the proximal promoters via formation of two chromatin loops. During RPS19-insufficiency this chromatin organization is lost, but SATB1 re-expression restores chromatin looping and HSP70 expression, stabilizing GATA1 and promoting efficient erythropoiesis. As with HSP70, it is likely that permissive chromatin organization is essential for other RPS19-sensitive erythroid genes rescued by SATB1 re-expression.