A role of Miz-1 in Gfi-1-mediated transcriptional repression of CDKN1A

Abstract

Zinc-finger (ZF) transcriptional repressor Gfi-1 plays an important role in hematopoiesis and inner ear development, and also functions as an oncoprotein that cooperates with c-Myc in lymphomagenesis. Gfi-1 represses transcription by directly binding to conserved sequences in the promoters of its target genes. CDKN1A encoding p21Cip1 has been identified as a Gfi-1 target gene and shown to contain Gfi-1 binding sites in the upstream promoter region. We show here that Gfi-1 represses CDKN1A in a manner that is independent of its DNA binding activity. Gfi-1 interacts with POZ-ZF transcription factor Miz-1, originally shown to be a c-Myc interacting partner, and via Miz-1 binds to CDKN1A core promoter. Interestingly, Gfi-1 and c-Myc, through Miz-1, form a ternary complex on the CDKN1A promoter, and act in collaboration to repress CDKN1A. Gfi-1 knockdown results in enhanced levels of p21Cip1 and attenuated cell proliferation. Notably, similar to c-Myc, the expression of Gfi-1 is downregulated by TGFβ and the level of Gfi-1 influences the response of cell to the cytostatic effect of TGFβ. Our data reveal an important mechanism by which Gfi-1 regulates cell proliferation and may also have implications for understanding the role of Gfi-1 in lymphomagenesis.

Inactivation of Ezh2 Upregulates Gfi1 and Drives Aggressive Myc-Driven Group 3 Medulloblastoma

“…Gfil can bind directly to promoter-proximal sequences at a consensus motif (Duan and Horwitz, 2003), where it can recruit histone deacetylases and Ezh2 to generate repressive H3K27me3 chromatin modifications (Duan et al, 2005; McGhee et al, 2003; Saleque et al, 2007; Vassen et al, 2006). Gfi1 can also be recruited to promoters independently of its direct DNA binding activity to enforce gene repression by Myc/Miz1 complexes (Liu et al, 2010), a feature particularly relevant in G3 MBs in which Myc/Miz repressive functions are key determinants of the G3 subtype (Vo et al, 2016). Importantly, Gfi1 overexpression is sufficient to induce mouse G3 MBs in collaboration with Myc, even in cells that maintain wild type Trp53 (Northcott et al, 2014).…”

EZH2 or HDAC1 Inhibition Reverses Multiple Myeloma–Induced Epigenetic Suppression of Osteoblast Differentiation

“…GFI1 recruitment of histone methyltransferase G9a (EHMT2) and histone deacetylase 1 (HDAC1) through the intermediate domain represses the promoter of cell cycle regulator CDKN1A (21). GFI1 can also repress gene expression independently of its DNA binding capability, as shown by its binding to and cooperation with the POZ-ZF transcription factor MIZ-1 (ZBTB17) at the CDKN1A and CDKN2B gene promoters (11, 22). Additionally, GFI1 binding to other transcription factors can interfere with their DNA binding or transactivation properties, thereby repressing their targets without GFI1 DNA binding.…”

Transcriptional Repression: The Dark Side of Myc

“…In contrast, the Gfi-1 repressor forms a ternary complex with Myc and Miz1 at the cdkn2b, cdkn1a, and cdkn1b promoter to repress transcription. 32,33 Whether interactions of Myc with Sp1 or Miz1 are required for recruitment of Myc to repressed promoters or whether these interactions are required for the establishment of a repressed promoter state is an open question. Binding of Myc to the cdkn2b promoter, for example, depends on heterodimerization with Max, arguing that binding of Myc to DNA may contribute to targeting Myc to repressed promoters.…”