title: PU.1/Spi-1 binds to the human TAL-1 silencer to mediate its activity.
abstract: The TAL-1/SCL gene encodes a basic helix-loop-helix (bHLH) transcription factor essential for primitive hematopoiesis and for adult erythroid and megakaryocytic development. Activated transcription of TAL-1 as a consequence of chromosomal rearrangements is associated with a high proportion of human T cell acute leukemias, showing that appropriate control of TAL-1 is crucial for the formation and subsequent fate of hematopoietic cells. Hence, the knowledge of the mechanisms, which govern the pattern of TAL-1 expression in hematopoiesis, is of great interest. We previously described a silencer in the 3'-untranslated region of human TAL-1, the activity of which is mediated through binding of a tissue-specific 40 kDa nuclear protein to a new DNA recognition motif, named tal-RE. Here, we show that tal-RE-binding activity, high in immature human hematopoietic progenitors is down regulated upon erythroid and megakaryocytic differentiation. This expression profile helped us to identify that PU.1/Spi-1 binds to the tal-RE sequences in vitro and occupies the TAL-1 silencer in vivo. By expressing a mutant protein containing only the ETS domain of PU.1 in human erythroleukemic HEL cells, we demonstrated that PU.1 mediates the transcriptional repression activity of the silencer. We found that ectopic PU.1 is not able to induce silencing activity in PU.1-negative Jurkat T cells, indicating that PU.1 activity, although necessary, is not sufficient to confer transcriptional repression activity to the TAL-1 silencer. Finally, we showed that the silencer is also active in TAL-1-negative myeloid HL60 cells that express PU.1 at high levels. In summary, our study shows that PU.1, in addition to its positive role in TAL-1 expression in early hematopoietic progenitors, may also act as a mediator of TAL-1 silencing in some hematopoietic lineages.
authors.affiliation: Institut de Génétique Moléculaire-UMR5535-IFR22, CNRS 1919 Route de Mende F-34980 Montpellier, France.
authors.forename: Mikaël
authors.initials: M
authors.lastname: Le Clech
authors.forename: Elias
authors.initials: E
authors.lastname: Chalhoub
authors.forename: Christiane
authors.initials: C
authors.lastname: Dohet
authors.forename: Virginie
authors.initials: V
authors.lastname: Roure
authors.forename: Serge
authors.initials: S
authors.lastname: Fichelson
authors.forename: Françoise
authors.initials: F
authors.lastname: Moreau-Gachelin
authors.forename: Danièle
authors.initials: D
authors.lastname: Mathieu
mesh_terms: D045744:Cell Line, Tumor; D015536:Down-Regulation; D020868:Gene Silencing; D006410:Hematopoiesis / Q000235:genetics; D006801:Humans; D007938:Leukemia / Q000473:pathology; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D020218:Response Elements; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors; D015533:Transcriptional Activation; D014162:Transfection; D044767:Ubiquitin-Protein Ligases / Q000235:genetics*; D000099232:Proto-Oncogene Protein Spi-1
chemical_list: D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; D000099232:Proto-Oncogene Protein Spi-1; C489657:LRSAM1 protein, human