GFI1B and LSD1 repress myeloid traits during megakaryocyte differentiation
Mutations in transcription factor Growth Factor Independence 1B (GFI1B) cause inherited bleedings with varying intensity possibly caused by different effects on the transcriptional function of GFI1B. We studied transcriptomic changes of normal and GFI1BT174N,H181Y,R184P,Q287* mutants in megakaryoblast MEG01 cells using RNA-sequencing. Compared to normal GFI1B each variant affected different gene modules with limited overlap between variants. Remarkably, GFI1BQ287* specifically activated a myeloid-associated gene module. Based on this finding we studied megakaryocyte differentiation using normal and GFI1BQ287* patient-derived induced pluripotent stem cells (IPSC) followed by single cell RNA-sequencing. This revealed a 45-fold decrease in the megakaryocyte/myeloid cell ratio in the GFI1BQ287* versus control condition. Moreover, myeloid specific genes were expressed within GFI1BQ287* but not normal megakaryocytes. Finally, we studied how megakaryocyte development was affected by inhibiting binding of GFI1B to Lysine Specific Demethylase 1 (LSD1), an interaction required for megakaryocyte development. Treatment of both MEG01 cells and normal IPSC-derived developing megakaryocytes with the small-molecule inhibitor GSK-LSD1 resulted in profound activation of myeloid gene programs within megakaryocytes, while the IPSC-derived megakaryocyte/myeloid ratio dropped two-fold. We conclude that GFI1B and LSD1 suppress myeloid differentiation allowing for proper megakaryocyte development. LSD1 inhibitor and GFI1BQ287*-mediated perturbation of this function causes myeloid skewing during megakaryocyte development. Overall design: To determine transcriptomic changes induced by GFI1B variants we retrovirally expressed GFI1BT174N, H181Y, R184P, Q287* next to normal GFI1B and an empty vector in megakaryoblast MEG01 cells followed by RNA-isolation and in triplicate RNA-sequencing 4 days later.