Epigenetic Control of SPI1 Gene by CTCF and ISWI ATPase SMARCA5

Abstract

CCCTC-binding factor (CTCF) can both activate as well as inhibit transcription by forming chromatin loops between regulatory regions and promoters. In this regard, Ctcf binding on non-methylated DNA and its interaction with the Cohesin complex results in differential regulation of the H19/Igf2 locus. Similarly, a role for CTCF has been established in normal hematopoietic development; however its involvement in leukemia remains elusive. Here, we show that Ctcf binds to the imprinting control region of H19/Igf2 in AML blasts. We also demonstrate that Smarca5, which also associates with the Cohesin complex, facilitates Ctcf binding to its target sites on DNA. Furthermore, Smarca5 supports Ctcf functionally and is needed for enhancer-blocking effect at ICR. We next asked whether CTCF and SMARCA5 control the expression of key hematopoiesis regulators. In normally differentiating myeloid cells both CTCF and SMARCA5 together with members of the Cohesin complex are recruited to the SPI1 gene, a key hematopoiesis regulator and leukemia suppressor. Due to DNA methylation, CTCF binding to the SPI1 gene is blocked in AML blasts. Upon AZA-mediated DNA demethylation of human AML blasts, CTCF and SMARCA5 are recruited to the −14.4 Enhancer of SPI1 gene and block its expression. Our data provide new insight into complex SPI1 gene regulation now involving additional key epigenetic factors, CTCF and SMARCA5 that control PU.1 expression at the −14.4 Enhancer.

The ISWI ATPase Smarca5 (Snf2h) Is Required for Proliferation and Differentiation of Hematopoietic Stem and Progenitor Cells

“…The erythroid phenotype of Smarca5 deficiency is consistent with the previously reported SMARCA5 knockdown experiment that caused an inhibition of early erythroid differentiation and led to downregulation of β‐globin expression in human CD34+ progenitors and K562 cells . Interestingly, compared with erythropoiesis, the myelopoiesis in the Smarca5 mutant is affected less severely, consistent with SMARCA5 being a negative regulator of the myeloid transcriptional activator PU.1 . As downregulation of Gata1 does not directly induce apoptosis , we think that the cell death and cell cycle arrest of the Smarca5‐deficient erythroblasts is rather a result of the loss of Smarca5 function in cellular pathways other than Gata1 promoted differentiation.…”

Loss of ISWI ATPase SMARCA5 (SNF2H) in Acute Myeloid Leukemia Cells Inhibits Proliferation and Chromatid Cohesion

“…We recently showed that SMARCA5 (together with the CTCF/cohesin complex) represses PU.1-mediated myeloid differentiation [7] and similarly, we noted that SMARCA5 regulates GATA1-mediated erythropoiesis [1]. We therefore next decided to analyze the levels of SPI1/PU.1 and GATA-1 transcripts with respect to SMARCA5.…”

Chromatin Dynamics during Differentiation of Myeloid Cells

“…Recently, a functional interplay of CTCF with the cohesin complex was reported to control PU.1 gene expression in myeloid cells 143 .…”

“…Moreover, CTCF knockdown led to derepression of PU.1 expression, suggesting that CTCF is a negative regulator of PU.1. Interestingly, the CTCF binding site within the PU.1 URE enhancer was cooccupied by the SWI/SNF complex member SMARCA5, leading to the idea that CTCF may cooperate with the SWI/SNF complex to act on nucleosomal remodeling at this locus 143 .…”