GSE192972
HMG20B stabilizes interaction of LSD1 with GFI1 on chromatin to confer transcription repression and leukemia cell differentiation block [ChIP-seq I]
Pharmacologic inhibition of LSD1 induces molecular and morphologic differentiation of blast cells in acute myeloid leukaemia (AML) patients harboring MLL gene translocations. In addition to its demethylase activity, LSD1 has a critical scaffolding function at genomic sites occupied by the SNAG domain transcription repressor GFI1. Importantly, inhibitors block both enzymatic and scaffolding activities, in the latter case by disrupting the protein:protein interaction of GFI1 with LSD1. To explore the wider consequences of LSD1 inhibition on the LSD1 protein complex we made use of mass spectrometry approaches. We discovered that the interaction of the HMG-box protein HMG20B with LSD1 was also disrupted by LSD1 inhibition. Downstream investigations revealed that HMG20B is colocated on chromatin genome-wide with GFI1 and LSD1; the strongest HMG20B binding colocates with the strongest GFI1 and LSD1 binding. Functional assays demonstrated that HMG20B depletion induces leukaemia cell differentiation and further revealed that HMG20B is required for the transcription repressor activity of GFI1 through stabilizing the interaction on chromatin of LSD1 with GFI1. Interaction of HMG20B with LSD1 is through its coiled-coil domain. Thus, HMG20B is a critical component of the GFI1:LSD1 transcription repressor complex which contributes to leukaemia cell differentiation block. Overall design: Human THP1 AML cells were infected with lentivirus to induce doxycycline-induced expression of Flag-tagged full HMG20B, or a fusion protein containing the GFI1 DNA binding domain (GFI1-ZNF) fused with the full HMG20B. Cells were grown in the presence or absence of doxycycline for 48 hr. and subsequently ChIP-sequencing for LSD1, GFI1, Flag-HMG20B/GFI1-ZNF-HMG20B or H3K27ac was done.