Dynamic Interaction Between TAL1 Oncoprotein And LSD1 Regulates TAL1 Function In Hematopoiesis And Leukemogenesis

TAL1/SCL is a hematopoietic specific member of the basic Helix-Loop-Helix (bHLH) family of transcription factors important for the development of all hematopoietic lineages and pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL). TAL1 is required for specification and self-renewal of hematopoietic stem cells (HSCs), as well as for terminal differentiation of erythrocytes. TAL1 activity is regulated by association with transcriptional coactivators and corepressors, and the dynamic regulation of TAL1 and its associated coregulators may determine the onset of the hematopoietic differentiation program. However, it remains unclear how association of TAL1 with corepressors versus coactivators is properly regulated.Several threonine (Thr) and serine (Ser) residues of TAL1 can be phosphorylated by protein kinase B (Akt), mitogen activated protein kinase (MAPK), and protein kinase A (PKA). In particular, serine 172 is phosphorylated in vitro and in vivo by PKA. Phosphorylation of this residue affects TAL1 target-dependent DNA recognition, therefore, potentially discriminating the DNA binding site selection during differentiation. The phosphorylation of TAL1 regulates its DNA binding and transcriptional activities suggesting that phosphorylation may dictate TAL1's ability to associate with transcriptional corepressors and coactivators.To understand the detailed mechanism that regulates TAL1-associated coregulator complexes and how the dysregulation of this process contributes to T-cell leukemia, we investigated the underlying molecular mechanism that regulates TAL1 and LSD1 interaction. Here we reported that PKA mediated phosphorylation regulates TAL1 interaction with the H3K4 demethylase LSD1. Phosphorylation of serine 172 in TAL1 specifically destabilizes the TAL1-LSD1 interaction that leads to promoter H3K4 hypermethylation and activation of target genes that have been suppressed in normal and malignant hematopoiesis. Knockdown of TAL1 or LSD1 led to a derepression of the TAL1 targets accompanied by reduced recruitment of LSD1 and increased H3K4 methylation at their enhancer/promoter regions. Similarly, treatment of PKA activator forskolin resulted in derepression of target genes by reducing its interaction with LSD1 while PKA inhibitor H89 represses them by suppressing H3K4 methylation levels. Consistent with the dual roles of TAL1 in transcription, TAL1 associated LSD1 is decreased while recruitment of hSET1 is increased at the TAL1 targets during erythroid differentiation. This process is accompanied by a dramatic increase in H3K4 methylation.We summarize that the interaction between TAL1 and LSD1 is modulated by a PKA-mediated serine 172 phosphorylation located at the LSD1 interacting domain of TAL1. Phosphorylation mediated dynamic recruitment of LSD1 complex modulates TAL1 directed transcription of target genes that are essential for hematopoietic progenitor differentiation and T-cell development. Treatment of the PKA activator forskolin stimulates the expression of the TAL1 target genes by reducing its interaction with LSD1 while PKA inhibitor H89 further inhibits the TAL1 targets by suppressing promoter H3K4 methylation levels. Thus, our results suggest that the dynamic regulation of TAL1 and its associated histone demethylase LSD1 by PKA mediated phosphorylation controls the transcription of the TAL1 target genes via modulating the promoter H3K4 methylation.Thus, our data revealed a novel interplay between PKA phosphorylation and TAL1 mediated epigenetic regulation that determines hematopoietic transcription and differentiation programs. Taken together, our study have provided important insights into an underlying mechanism by which phosphorylation regulated demethylase LSD1 recruitment controls the timing of erythroid differentiation and oncogenesis of T-cell leukemia.