scholarly journals The Leucine Zipper Motif of the Drosophila AF10 Homologue Can Inhibit PRE-Mediated Repression: Implications for Leukemogenic Activity of Human MLL-AF10 Fusions

2003 ◽  
Vol 23 (1) ◽  
pp. 119-130 ◽  
Author(s):  
Laurent Perrin ◽  
Sébastien Bloyer ◽  
Conchita Ferraz ◽  
Namita Agrawal ◽  
Pradip Sinha ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Transcriptional Repression ◽  
Fusion Proteins ◽  
Leucine Zipper ◽  
Full Length ◽  
Fusion Partner ◽  
Leucine Zipper Motif ◽  
Dominant Mutation ◽  
Leucine Zipper Domain ◽  
Phd Domain

ABSTRACT In a screen for Drosophila genes that interfere with transcriptional repression mediated by the Polycomb group of genes, we identified a dominant mutation affecting the Alhambra (Alh) gene, the fly homologue of the human AF10 gene. AF10 has been identified as a fusion partner of both MLL and CALM in infant leukemias. Both fusion proteins retain the leucine zipper domain of AF10 but not its PHD domain. We show here that, while the full-length ALH protein has no activity on Polycomb group-responsive elements (PREs), overexpression of the isolated ALH leucine zipper domain activates several PREs. Within the ALH full-length protein, the PHD domain inhibits the PRE deregulation mediated by the leucine zipper domain. This deregulation is conserved in the human AF10 leucine zipper domain, which confers the same activity on an oncogenic MLL-AF10 fusion protein expressed in Drosophila melanogaster. These data reveal new properties for the leucine zipper domain and thus might provide new clues to understanding the mechanisms by which AF10 fusion proteins in which the PHD domain is lost might trigger leukemias in humans.

scholarly journals A Role for Groucho Tetramerization in Transcriptional Repression

1998 ◽  
Vol 18 (12) ◽  
pp. 7259-7268 ◽  
Author(s):  
Guoqing Chen ◽  
Pierre H. Nguyen ◽  
Albert J. Courey
Keyword(s):  
Transcriptional Repression ◽  
Fusion Proteins ◽  
Leucine Zipper ◽  
Point Mutations ◽  
Cross Linking ◽  
Transcriptional Repressors ◽  
Terminal Domain ◽  
Tetramerization Domain ◽  
Repeat Domain ◽  
Eukaryotic Organisms

ABSTRACT The Drosophila Groucho (Gro) protein is a corepressor required by a number of DNA-binding transcriptional repressors. Comparison of Gro with its homologues in other eukaryotic organisms reveals that Gro contains, in addition to a conserved C-terminal WD repeat domain, a conserved N-terminal domain, which has previously been implicated in transcriptional repression. We determined, via a variety of hydrodynamic measurements as well as protein cross-linking, that native Gro is a tetramer in solution and that tetramerization is mediated by two putative amphipathic α-helices (termed leucine zipper-like motifs) found in the N-terminal region. Point mutations in the leucine zipper-like motifs that block tetramerization also block repression by Gro, as assayed in cultured Drosophila cells with Gal4-Gro fusion proteins. Furthermore, the heterologous tetramerization domain from p53 fully substitutes for the Gro tetramerization domain in transcriptional repression. These findings suggest that oligomerization is essential for Gro-mediated repression and that the primary function of the conserved N-terminal domain is to mediate this oligomerization.

scholarly journals Homotypic dimerization of the actin-binding protein p57/coronin-1 mediated by a leucine zipper motif in the C-terminal region

2005 ◽  
Vol 387 (2) ◽  
pp. 325-331 ◽  
Author(s):  
Teruaki OKU ◽  
Saotomo ITOH ◽  
Rie ISHII ◽  
Kensuke SUZUKI ◽  
William M. NAUSEEF ◽  
...  
Keyword(s):  
Leucine Zipper ◽  
Fluorescent Protein ◽  
Binding Protein ◽  
Coiled Coil ◽  
Terminal Region ◽  
Full Length ◽  
Actin Binding ◽  
Leucine Zipper Motif ◽  
Actin Binding Protein ◽  
Coiled Coil Domain

The actin-binding protein p57/coronin-1, a member of the coronin protein family, is selectively expressed in immune cells, and has been implicated in leucocyte migration and phagocytosis by virtue of its interaction with F-actin (filamentous actin). We previously identified two sites in the N-terminal region of p57/coronin-1 by which it binds actin, and in the present study we examine the role of the leucine zipper motif located in the C-terminal coiled-coil domain in mediating the homotypic association of p57/coronin-1. Recombinant p57/coronin-1 protein in solution formed a homodimer, as analysed by Superose 12 column chromatography and by sucrose density gradient centrifugation. In vivo, a truncated form consisting of the C-terminal coiled-coil domain co-precipitated with full-length p57/coronin-1 when both were co-expressed in COS-1 cells. A chimaeric construct composed of the C-terminal domain of p57/coronin-1 (which lacks the actin-binding sites) fused with green fluorescent protein co-localized with cortical F-actin-rich regions in COS-1 cells only when full-length p57/coronin-1 was expressed simultaneously in the cells, suggesting that the C-terminal region is required for the homotypic association of p57/coronin-1. Furthermore, p57LZ, a polypeptide consisting of the C-terminal 90 amino acid residues of p57/coronin-1, was sufficient for dimerization. When two leucine residues out of the four that constitute the leucine zipper structure in p57LZ or full-length p57 were replaced with alanine residues, the mutants failed to form homodimers. Taken together, these results demonstrate that p57/coronin-1 forms homodimers, that the association is mediated by the leucine zipper structure in the C-terminal region, and that it plays a role in the cross-linking of F-actin in the cell.

Interaction of the Leukemogenic CALM/AF10 Fusion Protein with the Hematopoietic Key Regulator Ikaros.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2365-2365
Author(s):  
Philipp A. Greif ◽  
Belay Tizazu ◽  
Elisabeth Kremmer ◽  
Alexandre Krause ◽  
Stefan K. Bohlander
Keyword(s):  
Transcription Factor ◽  
Fusion Protein ◽  
Myeloid Leukemia ◽  
Leucine Zipper ◽  
Similar Distribution ◽  
Fusion Partner ◽  
Aberrant Expression ◽  
Hematopoietic Stem ◽  
Leucine Zipper Domain ◽  
The Impact

Abstract The focus of our research group is the study of the t(10;11)(p13;q14) translocation that leads to the fusion of the proteins CALM and AF10. This translocation can be found in acute lymphoblastic leukemia (ALL), acute myeloid leukemia (ALL) and also in malignant lymphomas. In some patients the t(10;11) is the only cytogenetic abnormality which indicates that the CALM/AF10 fusion is a causal event during leukemogenesis. Previous studies of our group have shown that the expression of CALM/AF10 in hematopoietic stem cells triggers the development of an aggressive leukemia in a murine bone marrow transplantation model. CALM (Clathrin Assembly Lymphoid Myeloid leukemia gene) has a function in Clathrin mediated endocytosis. AF10, a putative transcription factor with a PHD-Motive (Plant Homeo Domain) and a Leucine Zipper domain, was initially identified as fusion partner of MLL. The underlying mechanism of CALM/AF10 dependent leukemogenesis, however, remains mostly unknown. Recently we could show that AF10 interacts with the transcription factor Ikaros (ZNFN1A1) in yeast-two-hybrid assays. Interestingly, Ikaros is a key regulator of hematopoesis, required for normal differentiation and proliferation of B- and T-lymphocytes. The structure of the protein is characterized by a DNA-binding and an oligomerisation domain. Through interaction with many factors in the cell nucleus, Ikaros can act both as activator and repressor of transcription. In various forms of ALL as well as chronic myeloid leukemia (CML) an aberrant expression pattern of Ikaros has been found. In a murine model the expression of a dominant negative isoform of Ikaros causes leukemias and lymphomas. Using various AF10 deletion mutants in the yeast, the Ikaros interaction domain of AF10 was mapped to the Leucine Zipper domain of AF10 which has also been shown to be required for malignant transformation by the MLL/AF10 fusion protein. Overexpression of fluorescently labelled proteins reveals a similar distribution pattern of AF10 and Ikaros in the nucleus, whereas in the presence of CALM/AF10 Ikaros appears to be localized predominately in the cytoplasm. The interaction between AF10 and Ikaros has been confirmed by GST-pull-down assays. In order to further study this interaction and its role in leukemogenesis we have raised monoclonal antibodies against the C-terminus of AF10. These antibodies are currently established for Western Blot analysis and Immunoprecipitation experiments. Reporter gene assays are carried out to measure the impact of CALM/AF10 on Ikaros’ function as repressor or activator of transcription. These studies may provide new insights into the mechanism of CALM/AF10 induced leukemia and thereby facilitate the development of new therapies.

scholarly journals The leucine zipper of c-Myc is required for full inhibition of erythroleukemia differentiation.

1990 ◽  
Vol 10 (10) ◽  
pp. 5333-5339 ◽  
Author(s):  
M J Smith ◽  
D C Charron-Prochownik ◽  
E V Prochownik
Keyword(s):  
Leucine Zipper ◽  
Point Mutations ◽  
Leucine Zipper Motif ◽  
Wild Type ◽  
Protein Dimerization ◽  
Leucine Zipper Domain ◽  
Close Relationship ◽  
Type C ◽  
Murine Erythroleukemia

The leucine zipper motif has been observed in a number of proteins thought to function as eucaryotic transcription factors. Mutation of the leucine zipper interferes with protein dimerization and DNA binding. We examined the effect of point mutations in the leucine zipper of c-Myc on its ability to dimerize in vitro and to inhibit Friend murine erythroleukemia (F-MEL) differentiation. Glutaraldehyde cross-linking studies failed to provide evidence for homodimerization of in vitro-synthesized c-Myc protein, although it was readily demonstrated for c-Jun. Nevertheless, whereas transfected wild-type c-myc sequences strongly inhibited F-MEL differentiation, those with single or multiple mutations in the leucine zipper were only partially effective in this regard. Since the leucine zipper domain of c-Myc is essential for its cooperative effect in ras oncogene-mediated transformation, this study emphasizes the close relationship that exists between transformation and hematopoietic commitment and differentiation. c-Myc may produce its effects on F-MEL differentiation through leucine zipper-mediated heterodimeric associations rather than homodimeric ones.

The leucine zipper of c-Myc is required for full inhibition of erythroleukemia differentiation

1990 ◽  
Vol 10 (10) ◽  
pp. 5333-5339
Author(s):  
M J Smith ◽  
D C Charron-Prochownik ◽  
E V Prochownik
Keyword(s):  
Leucine Zipper ◽  
Point Mutations ◽  
Leucine Zipper Motif ◽  
Wild Type ◽  
Protein Dimerization ◽  
Leucine Zipper Domain ◽  
Close Relationship ◽  
Type C ◽  
Murine Erythroleukemia

The leucine zipper motif has been observed in a number of proteins thought to function as eucaryotic transcription factors. Mutation of the leucine zipper interferes with protein dimerization and DNA binding. We examined the effect of point mutations in the leucine zipper of c-Myc on its ability to dimerize in vitro and to inhibit Friend murine erythroleukemia (F-MEL) differentiation. Glutaraldehyde cross-linking studies failed to provide evidence for homodimerization of in vitro-synthesized c-Myc protein, although it was readily demonstrated for c-Jun. Nevertheless, whereas transfected wild-type c-myc sequences strongly inhibited F-MEL differentiation, those with single or multiple mutations in the leucine zipper were only partially effective in this regard. Since the leucine zipper domain of c-Myc is essential for its cooperative effect in ras oncogene-mediated transformation, this study emphasizes the close relationship that exists between transformation and hematopoietic commitment and differentiation. c-Myc may produce its effects on F-MEL differentiation through leucine zipper-mediated heterodimeric associations rather than homodimeric ones.

scholarly journals Mating Type in Chlamydomonas Is Specified by mid, the Minus-Dominance Gene

Genetics ◽  
1997 ◽  
Vol 146 (3) ◽  
pp. 859-869 ◽  
Author(s):  
Patrick J Ferris ◽  
Ursula W Goodenough
Keyword(s):  
Transcription Factor ◽  
Mating Type ◽  
Codon Bias ◽  
Leucine Zipper ◽  
Laboratory Strain ◽  
Leucine Zipper Motif ◽  
Type Locus ◽  
Diploid Cells ◽  
Necessary And Sufficient

Diploid cells of Chlamydomonas reinhardtii that are heterozygous at the mating-type locus (mt  +/mt  –) differentiate as minus gametes, a phenomenon known as minus dominance. We report the cloning and characterization of a gene that is necessary and sufficient to exert this minus dominance over the plus differentiation program. The gene, called mid, is located in the rearranged (R) domain of the mt  – locus, and has duplicated and transposed to an autosome in a laboratory strain. The imp11 mt  – mutant, which differentiates as a fusion-incompetent plus gamete, carries a point mutation in mid. Like the fus1 gene in the mt  + locus, mid displays low codon bias compared with other nuclear genes. The mid sequence carries a putative leucine zipper motif, suggesting that it functions as a transcription factor to switch on the minus program and switch off the plus program of gametic differentiation. This is the first sex-determination gene to be characterized in a green organism.

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