title: Loss of TAL-1 protein activity induces premature apoptosis of Jurkat leukemic T cells upon medium depletion.
abstract: Transcriptional activation of the tal-1 gene occurs in -30% of patients with T cell Acute Lymphoblastic Leukemia and is therefore likely to be involved in human T cell leukemogenesis. However, the TAL-1 protein functional properties involved in this process have not been assessed so far. We have derived a clonal subline of the Jurkat T cell line which produced solely a mutant truncated form of TAL-1 protein. Sequencing of genomic DNA and cDNAs showed that the only transcribed tal-1 allele of this mutant subline harbored a G nucleotide insertion at codon 270. The resulting frameshift modifies TAL-1 residues 272-278 and creates a stop at codon 279. Although the deletion of the 53 carboxy-terminal residues of the TAL-1 protein did not directly affect the TAL-1 basic helix-loop-helix domain (residues 185-243), it had drastic effects on TAL-1 functional properties, since the mutant subline exhibited a dramatic decrease of protein binding activity to the TAL-1 DNA consensus sequence. Growth curves indicated that the mutant subline exhibited premature apoptosis upon medium depletion or serum reduction when compared with the parental cells. However, no difference between Jurkat and the mutant subline was observed in etoposide- or Fas/APO-1-triggered apoptosis. Stable expression of the mutant TAL-1 protein in Jurkat cells resulted in a phenotype that was similar to that of the mutant Jurkat subline, indicating that the TAL-1 mutant protein behaved like a dominant negative mutant and that the premature apoptosis of the mutant subline upon medium depletion was the consequence of the loss of TAL-1 protein activity.
authors.affiliation: INSERM U.91, Hôpital Henri Mondor, Créteil, France.
authors.forename: K
authors.initials: K
authors.lastname: Leroy-Viard
authors.forename: M A
authors.initials: MA
authors.lastname: Vinit
authors.forename: N
authors.initials: N
authors.lastname: Lecointe
authors.forename: H
authors.initials: H
authors.lastname: Jouault
authors.forename: U
authors.initials: U
authors.lastname: Hibner
authors.forename: P H
authors.initials: PH
authors.lastname: Roméo
authors.forename: D
authors.initials: D
authors.lastname: Mathieu-Mahul
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D002453:Cell Cycle / Q000235:genetics; D002471:Cell Transformation, Neoplastic; D002999:Clone Cells; D003470:Culture Media; D004268:DNA-Binding Proteins / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D018257:Helix-Loop-Helix Motifs / Q000235:genetics*; D015458:Leukemia, T-Cell / Q000209:etiology / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010641:Phenotype; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D017384:Sequence Deletion; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
chemical_list: D003470:Culture Media; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors