Smarca5 Regulates Ctcf Recruitment to Chromatin, Including to Regulatory Loci Involved In Control of Globin Gene Expression In Erythroleukemia

Abstract 5159

Transcription factor Ctcf (CCCTC-binding factor) represents a major regulatory component of epigenetic regulation by recognizing its unmethyled DNA binding sites, resulting in changes in expression of neighboring genes. Ctcf plays an important role in transgenerational genetic imprinting. Very little is known about its role in hematologic malignancies. Ctcf has been described to promote differentiation of human erythroleukemia K562 cells (Torano 2005). We studied Ctcf in mouse erythroleukemia (MEL) cells and found it is expressed at both the mRNA and protein levels. Using chromatin immunoprecipitation (ChIP), we found that Ctcf is recruited to the H19/Igf2 imprinting control region (ICR) and also to the promoters of the alpha globin genes (Hba-a1, Hba-a2) as well as the beta globin locus control region (LCR) in MEL cells. To determine the mechanism by which Ctcf interacts with chromatin, we tested its interaction with chromatin remodeling proteins that associate with these DNA targets, including the well known Imitation Switch (ISWI class) ATPase Smarca5 (Snf2h). Using coimmunopreciptiation and ChIP experiments we found that Smarca5 and Ctcf interact on DNA. Next, we used MEL cells expressing an inducible Smarca5 shRNA. Doxycycline induction of Smarca5 shRNA led to a 5-fold decrease in Smarca5 mRNA and protein levels within 48hrs. ChIP experiments demonstrated that depletion of Smarca5 was accompanied by loss of Ctcf from the aforementioned loci indicating Ctcf requires Smarca5 for its association with chromatin. Furthermore, this was followed by significantly decreased levels H19 RNA. Our data provide evidence that Smarca5 regulates Ctcf recruitment to chromatin, including to regulatory loci involved in controlling globin gene expression. (Grants # IGA 10310-3, MSMT 2B06077, GAUK 251070 45410, SVV-2010-254260507, NIH R01CA154239).