Mechanism of action
Hemgn, a gene with anti-apoptotic properties, is a key downstream target of GFI1 (growth factor independence 1), a transcriptional repressor involved in hematopoiesis. GFI1 plays a crucial role in protecting hematopoietic cells from stress-induced apoptosis. The Hemgn gene is regulated by GFI1 through a 16-bp promoter region located between +47 and +63 bp relative to the transcription start site (TSS). This regulation is dependent on GFI1's interaction with the histone demethylase LSD1. GFI1 activates Hemgn expression through promoter binding, and this activation is enhanced by LSD1-mediated epigenetic modifications that promote transcription of Hemgn.
Hemgn expression is further increased through the synergistic action of Ikaros, another transcription factor. [9] Although Ikaros enhances Hemgn expression, it is not strictly required for GFI1-mediated upregulation. [10] Together, GFI1 and Ikaros cooperate to maximize transcriptional activation of Hemgn.
Hemgn is negatively regulated by PU.1, a transcription factor that functions as a repressor of its expression. [11] GFI1 represses PU.1 expression, [12] leading to derepression and subsequent upregulation of Hemgn. In the absence of PU.1, such as in knockdown or deficiency models, Hemgn expression is enhanced, demonstrating that GFI1 promotes Hemgn expression indirectly by inhibiting PU.1.
Hemgn upregulation contributes significantly to the anti-apoptotic function of GFI1, enabling hematopoietic cells to survive under stress conditions. This protective effect is independent of the p53 pathway and instead relies specifically on Hemgn-mediated mechanisms. [10]
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