Targeted transcriptional repression of Gfi1 by GFI1 and GFI1B in lymphoid cells

Abstract

Growth factor independence-1 (GFI1) and GFI1B are closely related, yet differentially expressed transcriptional repressors with nearly identical DNA binding domains. GFI1 is upregulated in the earliest thymocyte precursors, while GFI1B expression is restricted to T lymphopoiesis stages coincident with activation. Transgenic expression of GFI1 potentiates T-cell activation, while forced GFI1B expression decreases activation. Both mice and humans with mutant Gfi1 display lymphoid abnormalities. Here we describe autoregulation of Gfi1 in primary mouse thymocytes and a human T-cell line. GFI1 binding to cis-element sequences conserved between rat, mouse and human Gfi1 mediates direct and potent transcriptional repression. In addition, dramatic regulation of Gfi1 can also be mediated by GFI1B. These data provide the first example of a gene directly targeted by GFI1 and GFI1B. Moreover, they support a role for auto- and trans-regulation of Gfi1 by GFI1 and GFI1B in maintaining the normal expression patterns of Gfi1, and suggest that GFI1B may indirectly affect T-cell activation through repression of Gfi1.

Ajuba Functions as a Histone Deacetylase-dependent Co-repressor for Autoregulation of the Growth Factor-independent-1 Transcription Factor

“…In agreement with the low level of Gfi1 in 293T cells (15), transfected B30 ϫ 2 TK reporters demonstrate modest endogenous Gfi1 repression activity (Fig. 1, B, C, and G).…”

“…293T cells are human epithelial kidney cells that express a low level of Gfi1 (15). 293T cells were co-transfected with reporter constructs with or without "B30" (18) high affinity Gfi1 binding sites (Fig.…”

“…To determine if Ajuba and Gfi1 are bound to similar target genes in vivo, we first determined whether Ajuba is bound to Gfi1 target genes in a human myeloid cell line. Gfi1 target genes GFI1B (16,17), GFI1 (15,17), and CSF1 (14) were analyzed by chromatin immunoprecipitation (ChIP) analysis for the presence of both Gfi1 and Ajuba. The ␤-ACTIN gene was included as control, because it was not bound by Gfi1 in similar ChIP analyses (14).…”

“…Plasmids and Subcloning-Chloramphenicol acetyl transferase (CAT) reporter constructs and Gfi1 expression plasmids used in transient transcription assays were described previously (15,19). Luciferase versions were generated by cloning the B30 ϫ 2TK promoter and TK promoter fragments into the pGL3 vector (Promega, Madison, WI).…”

Gfi1 and Gfi1b: key regulators of hematopoiesis

“…In many hematopoietic subsets, the expression of the Gfi1 and Gfi1b genes can be autoregulated by the Gfi1 and Gfi1b proteins themselves. [13][14][15] Gfi1 may control the expression of the Gfi1b gene and vice versa, [16][17][18] although the biological relevance of this crossregulation is poorly understood as both proteins are expressed in certain cell types. Gfi1 and Gfi1b gene expression is co-regulated by other transcription factors such as Ajuba 19 and Ikaros 20 for Gfi1 and GATA1, NF-Y, Oct1 and HMGB2 for Gfi1b.…”