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

GFI1 regulates hair cell differentiation by acting as an off-DNA transcriptional co-activator of ATOH1, and a DNA-binding repressor

GFI1 is a zinc finger transcription factor that is necessary for the differentiation and survival of hair cells in the cochlea. Deletion of Gfi1 in mice significantly reduces the expression of hundreds of hair cell genes: this is a surprising result, as GFI1 normally acts as a transcriptional repressor by recruiting histone demethylases and methyltransferases to its targets. To understand the mechanisms by which GFI1 promotes hair cell differentiation, we used CUT&RUN to identify the direct targets of GFI1 and ATOH1 in hair cells. We found that GFI1 regulates hair cell differentiation in two distinct ways—first, GFI1 and ATOH1 can bind to the same regulatory elements in hair cell genes, but while ATOH1 directly binds its target DNA motifs in many of these regions, GFI1 does not. Instead, it appears to enhance ATOH1’s transcriptional activity by acting as part of a complex in which it does not directly bind DNA. Second, GFI1 can act in its more typical role as a direct, DNA-binding transcriptional repressor in hair cells; here it represses non-hair cell genes, including many neuronal genes. Together, our results illuminate the function of GFI1 in hair cell development and hair cell reprogramming strategies.

Myc-Interacting Zinc Finger Protein 1 (Miz-1) Is Essential to Maintain Homeostasis and Immunocompetence of the B Cell Lineage

Aging of the immune system is described as a progressive loss of the ability to respond to immunologic stimuli and is commonly referred to as immunosenescence. B cell immunosenescence is characterized by a decreased differentiation rate in the bone marrow and accumulation of antigen-experienced and age-associated B cells in secondary lymphoid organs (SLOs). A specific deletion of the POZ-domain of the transcription factor Miz-1 in pro-B cells, which is known to be involved in bone marrow hematopoiesis, leads to premature aging of the B cell lineage. In mice, this causes a severe reduction in bone marrow-derived B cells with a drastic decrease from the pre-B cell stage on. Further, mature, naïve cells in SLOs are reduced at an early age, while post-activation-associated subpopulations increase prematurely. We propose that Miz-1 interferes at several key regulatory checkpoints, critical during B cell aging, and counteracts a premature loss of immunocompetence. This enables the use of our mouse model to gain further insights into mechanisms of B cell aging and it can significantly contribute to understand molecular causes of impaired adaptive immune responses to counteract loss of immunocompetence and restore a functional immune response in the elderly.

IFNγ suppresses the expression of GFI1 and thereby inhibits Th2 cell proliferation

While IFNγ is a well-known cytokine that actively promotes the type I immune response, it is also known to suppress the type II response by inhibiting the differentiation and proliferation of Th2 cells. However, the mechanism by which IFNγ suppresses Th2 cell proliferation is still not fully understood. We found that IFNγ decreases the expression of growth factor independent-1 transcriptional repressor (GFI1) in Th2 cells, resulting in the inhibition of Th2 cell proliferation. The deletion of the Gfi1 gene in Th2 cells results in the failure of their proliferation, accompanied by an impaired cell cycle progression. In contrast, the enforced expression of GFI1 restores the defective Th2 cell proliferation, even in the presence of IFNγ. These results demonstrate that GFI1 is a key molecule in the IFNγ-mediated inhibition of Th2 cell proliferation.

Targeting Myc Interacting Proteins as a Winding Path in Cancer Therapy

MYC, as a well-known oncogene, plays essential roles in promoting tumor occurrence, development, invasion and metastasis in many kinds of solid tumors and hematologic neoplasms. In tumors, the low expression and the short half-life of Myc are reversed, cause tumorigenesis. And proteins that directly interact with different Myc domains have exerted a significant impact in the process of Myc-driven carcinogenesis. Apart from affecting the transcription of Myc target genes, Myc interaction proteins also regulate the stability of Myc through acetylation, methylation, phosphorylation and other post-translational modifications, as well as competitive combination with Myc. In this review, we summarize a series of Myc interacting proteins and recent advances in the related inhibitors, hoping that can provide new opportunities for Myc-driven cancer treatment.

The transcription factors GFI1 and GFI1B as modulators of the innate and acquired immune response

GFI1 and GFI1B are small nuclear proteins of 45 and 37kDa, respectively, that have a simple two-domain structure: The first consists of a group of six c-terminal C₂H₂ zinc finger motifs that are almost identical in sequence and bind to very similar, specific DNA sites. The second is an N-terminal 20 amino acid SNAG domain that can bind to the pocket of the histone demethylase KDM1A (LSD1) near its active site. When bound to DNA, both proteins act as bridging factors that bring LSD1 and associated proteins into the vicinity of methylated substrates, in particular histone H3 or TP53. GFI1 can also bring methyl transferases such as PRMT1 together with its substrates that include the DNA repair proteins MRE11 and 53BP1, thereby enabling their methylation and activation. While GFI1B is expressed almost exclusively in the erythroid and megakaryocytic lineage, GFI1 has clear biological roles in the development and differentiation of lymphoid and myeloid immune cells. GFI1 is required for lymphoid/myeloid and monocyte/granulocyte lineage decision as well as the correct nuclear interpretation of a number of important immune-signaling pathways that are initiated by NOTCH1, interleukins such as IL2, IL4, IL5 or IL7, by the pre TCR or -BCR receptors during early lymphoid differentiation or by T and B cell receptors during activation of lymphoid cells. Myeloid cells also depend on GFI1 at both stages of early differentiation as well as later stages in the process of activation of macrophages through Toll-like receptors in response to pathogen-associated molecular patterns. The knowledge gathered on these factors over the last decades puts GFI1 and GFI1B at the center of many biological processes that are critical for both the innate and acquired immune system.

Polydatin Inhibits Cell Viability, Migration, and Invasion Through Suppressing the c-Myc Expression in Human Cervical Cancer

Polydatin, an active ingredient from the roots of Polygonum cuspidatum, is considered to have protective effects on the cardiovascular system and liver. In this study, we demonstrated that polydatin has antitumor activity against human cervical cancer. Polydatin efficiently inhibited cervical cancer cell proliferation by regulating cell cycle-related proteins including p21, p27, CDK2, CDK4, Cyclin D1, and Cyclin E1. Furthermore, polydatin suppressed cell invasion and migration by regulating epithelial-mesenchymal transition (EMT) markers, including E-cadherin, N-cadherin, Snail and Slug. The c-Myc, as a proto-oncogene, is considered to be closely associated with the proliferation and metastasis of tumor cells. After polydatin treatment, the protein expression of c-Myc showed a significant decrease. Based on these data, we overexpressed c-Myc in cervical cancer cells and observed that the overexpression of c-Myc rescued the inhibitory effect of polydatin on cell proliferation and metastasis. These results indicated that polydatin can inhibit cell proliferation and metastasis through suppressing the c-Myc expression in human cervical cancer.

Multifaceted Actions of GFI1 and GFI1B in Hematopoietic Stem Cell Self-Renewal and Lineage Commitment

Growth factor independence 1 (GFI1) and the closely related protein GFI1B are small nuclear proteins that act as DNA binding transcriptional repressors. Both recognize the same consensus DNA binding motif via their C-terminal zinc finger domains and regulate the expression of their target genes by recruiting chromatin modifiers such as histone deacetylases (HDACs) and demethylases (LSD1) by using an N-terminal SNAG domain that comprises only 20 amino acids. The only region that is different between both proteins is the region that separates the zinc finger domains and the SNAG domain. Both proteins are co-expressed in hematopoietic stem cells (HSCs) and, to some extent, in multipotent progenitors (MPPs), but expression is specified as soon as early progenitors and show signs of lineage bias. While expression of GFI1 is maintained in lymphoid primed multipotent progenitors (LMPPs) that have the potential to differentiate into both myeloid and lymphoid cells, GFI1B expression is no longer detectable in these cells. By contrast, GFI1 expression is lost in megakaryocyte precursors (MKPs) and in megakaryocyte-erythrocyte progenitors (MEPs), which maintain a high level of GFI1B expression. Consequently, GFI1 drives myeloid and lymphoid differentiation and GFI1B drives the development of megakaryocytes, platelets, and erythrocytes. How such complementary cell type- and lineage-specific functions of GFI1 and GFI1B are maintained is still an unresolved question in particular since they share an almost identical structure and very similar biochemical modes of actions. The cell type-specific accessibility of GFI1/1B binding sites may explain the fact that very similar transcription factors can be responsible for very different transcriptional programming. An additional explanation comes from recent data showing that both proteins may have additional non-transcriptional functions. GFI1 interacts with a number of proteins involved in DNA repair and lack of GFI1 renders HSCs highly susceptible to DNA damage-induced death and restricts their proliferation. In contrast, GFI1B binds to proteins of the beta-catenin/Wnt signaling pathway and lack of GFI1B leads to an expansion of HSCs and MKPs, illustrating the different impact that GFI1 or GFI1B has on HSCs. In addition, GFI1 and GFI1B are required for endothelial cells to become the first blood cells during early murine development and are among those transcription factors needed to convert adult endothelial cells or fibroblasts into HSCs. This role of GFI1 and GFI1B bears high significance for the ongoing effort to generate hematopoietic stem and progenitor cells de novo for the autologous treatment of blood disorders such as leukemia and lymphoma.

Gfi1 upregulates c-Myc expression and promotes c-Myc-driven cell proliferation

Gfi1 is a zinc-finger transcriptional repressor that plays an important role in hematopoiesis. When aberrantly activated, Gfi1 may function as a weak oncoprotein in the lymphoid system, but collaborates strongly with c-Myc in lymphomagenesis. The mechanism by which Gfi1 collaborates with c-Myc in lymphomagenesis is incompletely understood. We show here that Gfi1 augmented the expression of c-Myc protein in cells transfected with c-Myc expression constructs. The N-terminal SNAG domain and C-terminal ZF domains of Gfi1, but not its transcriptional repression and DNA binding activities, were required for c-Myc upregulation. We further show that Gfi1 overexpression led to reduced polyubiquitination and increased stability of c-Myc protein. Interestingly, the levels of endogenous c-Myc mRNA and protein were augmented upon Gfi1 overexpression, but reduced following Gfi1 knockdown or knockout, which was associated with a decline in the expression of c-Myc-activated target genes. Consistent with its role in the regulation of c-Myc expression, Gfi1 promoted Myc-driven cell cycle progression and proliferation. Together, these data reveal a novel mechanism by which Gfi1 augments the biological function of c-Myc and may have implications for understanding the functional collaboration between Gfi1 and c-Myc in lymphomagenesis.

MYC Oncogene Contributions to Release of Cell Cycle Brakes

Promotion of the cell cycle is a major oncogenic mechanism of the oncogene c-MYC (MYC). MYC promotes the cell cycle by not only activating or inducing cyclins and CDKs but also through the downregulation or the impairment of the activity of a set of proteins that act as cell-cycle brakes. This review is focused on the role of MYC as a cell-cycle brake releaser i.e., how MYC stimulates the cell cycle mainly through the functional inactivation of cell cycle inhibitors. MYC antagonizes the activities and/or the expression levels of p15, ARF, p21, and p27. The mechanism involved differs for each protein. p15 (encoded by CDKN2B) and p21 (CDKN1A) are repressed by MYC at the transcriptional level. In contrast, MYC activates ARF, which contributes to the apoptosis induced by high MYC levels. At least in some cells types, MYC inhibits the transcription of the p27 gene (CDKN1B) but also enhances p27's degradation through the upregulation of components of ubiquitin ligases complexes. The effect of MYC on cell-cycle brakes also opens the possibility of antitumoral therapies based on synthetic lethal interactions involving MYC and CDKs, for which a series of inhibitors are being developed and tested in clinical trials.

Gfi-1 promotes proliferation of human cervical carcinoma via targeting of FBW7 ubiquitin ligase expression

Background

The independent growth factor 1 (Gfi-1) is a transcription factor essential for several diverse hematopoietic functions and developments. However, the role and molecular mechanism of Gfi-1 in the development and progression of cervical cancer remains unclear.

Purpose

The present study investigates the relation of expression of Gfi-1 with prognoses in patients with cervical cancer.

Methods

We used Western blot and reverse transcription polymerase chain reaction (RT-PCR) and the inhibition of proliferation and metastasis of cervical cancer cells in vitro.

Results

This study confirms that the expression of Gfi-1 in cervical cancer tissues was higher than that in adjacent normal tissues. The level of Gfi-1 mRNA in human cervical cancer tissues was significantly higher than that in normal tissues adjacent to cancer. Furthermore, overexpression of Gfi-1 promoted cell proliferation, colony formation, and migration of cervical cancer cells. The increased expression of Gfi-1 promotes the proliferation of cervical cancer cells targeting the tumor suppressor F-box and WD repeat domain containing 7 (FBW7). Clinically, our data suggest that overexpression of Gfi-1 is associated with poor prognosis in patients with cervical cancer. In a tumor xenograft model, knockdown of Gfi-1 inhibited the tumor growth of Hela cells in vivo.

Conclusion

Our results reveal that Gfi-1 plays an important role in cervical cancer and Gfi-1/FBW7 axis serves as a potential therapeutic target for cervical cancer.

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

The most aggressive of four medulloblastoma (MB) subgroups are cMyc-driven group 3 (G3) tumors, some of which overexpress EZH2, the histone H3K27 mono-, di-, and trimethylase of polycomb-repressive complex 2. Ezh2 has a context-dependent role in different cancers as an oncogene or tumor suppressor and retards tumor progression in a mouse model of G3 MB. Engineered deletions of Ezh2 in G3 MBs by gene editing nucleases accelerated tumorigenesis, whereas Ezh2 re-expression reversed attendant histone modifications and slowed tumor progression. Candidate oncogenic drivers suppressed by Ezh2 included Gfi1, a proto-oncogene frequently activated in human G3 MBs. Gfi1 disruption antagonized the tumor-promoting effects of Ezh2 loss; conversely, Gfi1 overexpression collaborated with Myc to bypass effects of Trp53 inactivation in driving MB progression in primary cerebellar neuronal progenitors. Although negative regulation of Gfi1 by Ezh2 may restrain MB development, Gfi1 activation can bypass these effects.

Characterization of Lgr5+ Progenitor Cell Transcriptomes after Neomycin Injury in the Neonatal Mouse Cochlea

Lgr5+ supporting cells (SCs) are enriched hair cell (HC) progenitors in the cochlea. Both in vitro and in vivo studies have shown that HC injury can spontaneously activate Lgr5+ progenitors to regenerate HCs in the neonatal mouse cochlea. Promoting HC regeneration requires the understanding of the mechanism of HC regeneration, and this requires knowledge of the key genes involved in HC injury-induced self-repair responses that promote the proliferation and differentiation of Lgr5+ progenitors. Here, as expected, we found that neomycin-treated Lgr5+ progenitors (NLPs) had significantly greater HC regeneration ability, and greater but not significant proliferation ability compared to untreated Lgr5+ progenitors (ULPs) in response to neomycin exposure. Next, we used RNA-seq analysis to determine the differences in the gene-expression profiles between the transcriptomes of NLPs and ULPs from the neonatal mouse cochlea. We first analyzed the genes that were enriched and differentially expressed in NLPs and ULPs and then analyzed the cell cycle genes, the transcription factors, and the signaling pathway genes that might regulate the proliferation and differentiation of Lgr5+ progenitors. We found 9 cell cycle genes, 88 transcription factors, 8 microRNAs, and 16 cell-signaling pathway genes that were significantly upregulated or downregulated after neomycin injury in NLPs. Lastly, we constructed a protein-protein interaction network to show the interaction and connections of genes that are differentially expressed in NLPs and ULPs. This study has identified the genes that might regulate the proliferation and HC regeneration of Lgr5+ progenitors after neomycin injury, and investigations into the roles and mechanisms of these genes in the cochlea should be performed in the future to identify potential therapeutic targets for HC regeneration.

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

In multiple myeloma, osteolytic lesions rarely heal because of persistent suppressed osteoblast differentiation resulting in a high fracture risk. Herein, chromatin immunoprecipitation analyses reveal that multiple myeloma cells induce repressive epigenetic histone changes at the Runx2 locus that prevent osteoblast differentiation. The most pronounced multiple myeloma-induced changes were at the Runx2-P1 promoter, converting it from a poised bivalent state to a repressed state. Previously, it was observed that multiple myeloma induces the transcription repressor GFI1 in osteoblast precursors, which correlates with decreased Runx2 expression, thus prompting detailed characterization of the multiple myeloma and TNFα-dependent GFI1 response element within the Runx2-P1 promoter. Further analyses reveal that multiple myeloma-induced GFI1 binding to Runx2 in osteoblast precursors and recruitment of the histone modifiers HDAC1, LSD1, and EZH2 is required to establish and maintain Runx2 repression in osteogenic conditions. These GFI1-mediated repressive chromatin changes persist even after removal of multiple myeloma. Ectopic GFI1 is sufficient to bind to Runx2, recruit HDAC1 and EZH2, increase H3K27me3 on the gene, and prevent osteogenic induction of endogenous Runx2 expression. Gfi1 knockdown in MC4 cells blocked multiple myeloma-induced recruitment of HDAC1 and EZH2 to Runx2, acquisition of repressive chromatin architecture, and suppression of osteoblast differentiation. Importantly, inhibition of EZH2 or HDAC1 activity in pre-osteoblasts after multiple myeloma exposure in vitro or in osteoblast precursors from patients with multiple myeloma reversed the repressive chromatin architecture at Runx2 and rescued osteoblast differentiation.Implications: This study suggests that therapeutically targeting EZH2 or HDAC1 activity may reverse the profound multiple myeloma-induced osteoblast suppression and allow repair of the lytic lesions. Mol Cancer Res; 15(4); 405-17. ©2017 AACR.

The Interaction of Myc with Miz1 Defines Medulloblastoma Subgroup Identity

Four distinct subgroups of cerebellar medulloblastomas (MBs) differ in their histopathology, molecular profiles, and prognosis. c-Myc (Myc) or MycN overexpression in granule neuron progenitors (GNPs) induces Group 3 (G3) or Sonic Hedgehog (SHH) MBs, respectively. Differences in Myc and MycN transcriptional profiles depend, in part, on their interaction with Miz1, which binds strongly to Myc but not MycN, to target sites on chromatin. Myc suppresses ciliogenesis and reprograms the transcriptome of SHH-dependent GNPs through Miz1-dependent gene repression to maintain stemness. Genetic disruption of the Myc/Miz1 interaction inhibited G3 MB development. Target genes of Myc/Miz1 are repressed in human G3 MBs but not in other subgroups. Therefore, the Myc/Miz1 interaction is a defining hallmark of G3 MB development.

Two ZNF509 (ZBTB49) isoforms induce cell-cycle arrest by activating transcription of p21/CDKN1A and RB upon exposure to genotoxic stress

ZNF509 is unique among POK family proteins in that four isoforms are generated by alternative splicing. Short ZNF509 (ZNF509S1, -S2 and -S3) isoforms contain one or two out of the seven zinc-fingers contained in long ZNF509 (ZNF509L). Here, we investigated the functions of ZNF509 isoforms in response to DNA damage, showing isoforms to be induced by p53. Intriguingly, to inhibit proliferation of HCT116 and HEK293 cells, we found that ZNF509L activates p21/CDKN1A transcription, while ZNF509S1 induces RB. ZNF509L binds to the p21/CDKN1A promoter either alone or by interacting with MIZ-1 to recruit the co-activator p300 to activate p21/CDKN1A transcription. In contrast, ZNF509S1 binds to the distal RB promoter to interact and interfere with the MIZF repressor, resulting in derepression and transcription of RB. Immunohistochemical analysis revealed that ZNF509 is highly expressed in normal epithelial cells, but was completely repressed in tumor tissues of the colon, lung and skin, indicating a possible role as a tumor suppressor.

GFI1 is repressed by p53 and inhibits DNA damage-induced apoptosis

GFI1 is a transcriptional repressor that plays a critical role in hematopoiesis and has also been implicated in lymphomagenesis. It is still poorly understood how GFI1 expression is regulated in the hematopoietic system. We show here that GFI1 transcription was repressed by the tumor suppressor p53 in hematopoietic cells. Knockdown of p53 resulted in increased GFI1 expression and abolished DNA damage-induced GFI1 downregulation. In contrast, GFI1 expression was reduced and its downregulation in response to DNA damage was rescued upon restoration of p53 function in p53-deficient cells. In luciferase reporter assays, wild type p53, but not a DNA binding-defective p53 mutant, repressed the GFI1 promoter. Chromatin immunoprecipitation (ChIP) assays demonstrated that p53 bound to the proximal region of the GFI1 promoter. Detailed mapping of the GFI1 promoter indicated that GFI1 core promoter region spanning from -33 to +6 bp is sufficient for p53-mediated repression. This core promoter region contains a putative p53 repressive response element, mutation of which abolished p53 binding to and repression of GFI1 promoter. Significantly, apoptosis induced by DNA damage was inhibited upon Gfi1 overexpression, but augmented following GFI1 knockdown. Our data establish for the first time that GFI1 is repressed by p53 and add to our understanding of the roles of GFI1 in normal hematopoiesis and lymphomagenesis.

Transcriptional repression: the dark side of myc

The (c-)Myc oncoprotein and its cousins, the N-Myc and L-Myc proteins, show all hallmarks of transcriptional activator proteins: Myc carries a carboxy-terminal DNA binding domain, which mediates sequence-specific binding to DNA. At its amino-terminus, Myc carries a transcriptional regulatory domain that strongly activates transcription when fused to an ectopic DNA binding domain; moreover, the strength of activation of different members of the Myc family correlates with their ability to transform rodent cells. Furthermore, activation of conditional alleles of Myc, either tetracycline or estrogen inducible, upregulates expression of a large number of genes, both in tissue culture and in transgenic animals. Indeed, many of these genes have essential roles in cell proliferation, cell growth, and metabolism; two of them, odc, encoding ornithine decarboxylase, a rate-limiting enzyme of polyamine biosynthesis, and rpl24, encoding a constituent of the large ribosomal subunit, are haploinsufficient for Myc-induced lymphomagenesis but not for normal development, arguing very strongly that upregulation of both genes is critical for Myc-dependent tumor formation. Undoubtedly, therefore, Myc exerts part of its biological activities via transcriptional upregulation of a large number of target genes. One of the key issues in the field is whether there are additional biochemical activities of the Myc protein and, if so, whether and how they contribute to Myc biology. This review summarizes evidence demonstrating that Myc has the ability to repress transcription and that this may be an important function during oncogenic transformation.

Myc and Miz-1 have coordinate genomic functions including targeting Hox genes in human embryonic stem cells

BACKGROUND

A proposed role for Myc in maintaining mouse embryonic stem (ES) cell pluripotency is transcriptional repression of key differentiation-promoting genes, but detail of the mechanism has remained an important open topic.

RESULTS

To test the hypothesis that the zinc finger protein Miz-1 plays a central role, in the present work we conducted chromatin immunoprecipitation/microarray (ChIP-chip) analysis of Myc and Miz-1 in human ES cells, finding homeobox (Hox) genes as the most significant functional class of Miz-1 direct targets. Miz-1 differentiation-associated target genes specifically lack acetylated lysine 9 and trimethylated lysine 4 of histone H3 (AcH3K9 and H3K4me3) 9 histone marks, consistent with a repressed transcriptional state. Almost 30% of Miz-1 targets are also bound by Myc and these cobound genes are mostly factors that promote differentiation including Hox genes. Knockdown of Myc increased expression of differentiation genes directly bound by Myc and Miz-1, while a subset of the same genes is downregulated by Miz-1 loss-of-function. Myc and Miz-1 proteins interact with each other and associate with several corepressor factors in ES cells, suggesting a mechanism of repression of differentiation genes.

CONCLUSIONS

Taken together our data indicate that Miz-1 and Myc maintain human ES cell pluripotency by coordinately suppressing differentiation genes, particularly Hox genes. These data also support a new model of how Myc and Miz-1 function on chromatin.

Growth factor independence 1 (Gfi1) as a regulator of lymphocyte development and activation

T- and B-lymphocytes are important elements in the immune defense repertoire of higher organisms. The development and function of lymphoid cells is regulated at many levels one being the control of gene expression by transcription factors. The zinc finger transcriptional repressor Gfi1 has emerged as a factor that is critically implicated in the commitment of precursor cells for the lymphoid lineage. In addition, Gfi1 controls distinct stages of early T- or B-lymphoid development and is also critical for their maturation, activation and effector function. From many years of work, a picture emerges in which Gfi1 is part of a complicated, but well orchestrated network of interdependent regulators, most of which impinge on lymphoid development and activation by transcriptional regulation. Biochemical studies show that Gfi1 is part of a large DNA binding multi-protein complex that enables histone modifications, but may also control alternative pre mRNA splicing. Many insights into the biological role of Gfi1 have been gained through the study of gene deficient mice that have defects in B- and T-cell differentiation, in T-cell selection and polarization processes and in the response of mature B- and T-cells towards antigen. Most importantly, the defects seen in Gfi1 deficient mice also point to roles of Gfi1 in diseases of the immune system that involve auto-immune responses and acute lymphoid leukemia and lymphoma.