title: Identification of the TBX5 transactivating domain and the nuclear localization signal.
abstract: TBX5 is a member of the T-box gene family and encodes a transcription factor involved in cardiac and limb development. Mutations of TBX5 cause Holt-Oram syndrome (HOS), an autosomal-dominant condition with congenital cardiac defects and forelimb anomalies. Here, we used a GAL4-TBX5 fusion protein in a modified yeast-one hybrid system to elucidate the TBX5 transactivating domain. Using a series of deletion mutations of TBX5, we narrowed down its functional domain to amino acids 339-379 of its C-terminal half; point mutagenesis analysis then showed that the loss of amino acids 349-351 abolished transactivation. This result was confirmed in mammalian cells. Furthermore, wild-type TBX5, but not TBX5 with mutations at the amino acids 349-351, has ability to inhibit NCI-H1299 cell growth also suggesting that these amino acids are crucial for the TBX5 function in mammalian cells. In addition, to identify the nuclear localization signal of TBX5, we searched for cluster of basic amino acids. We found that the deletion of the KRK sequence at amino acids 325-327 mislocalizes TBX5 to cytoplasm, suggesting that these amino acids serve as a nuclear localization signal. These studies enhance our understanding of the structure-function relationship of TBX5 and suggest that truncation mutations of TBX5 could cause HOS through the loss of its transactivating domain and/or the nuclear localization signal.
authors.affiliation: Department of Pediatrics, Division of Human Genetics, University of California, Irvine, CA 92697, USA.
authors.forename: Michael V
authors.initials: MV
authors.lastname: Zaragoza
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Lewis
authors.forename: Guifeng
authors.initials: G
authors.lastname: Sun
authors.forename: Eric
authors.initials: E
authors.lastname: Wang
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.forename: Ilham
authors.initials: I
authors.lastname: Said-Salman
authors.forename: Laura
authors.initials: L
authors.lastname: Feucht
authors.forename: Taosheng
authors.initials: T
authors.lastname: Huang
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D020825:T-Box Domain Proteins / Q000235:genetics* / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology; D015533:Transcriptional Activation / Q000235:genetics* / Q000502:physiology; D014162:Transfection
chemical_list: D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; D015534:Trans-Activators; D049452:Green Fluorescent Proteins