title: p53-inducible human homologue of Drosophila seven in absentia (Siah) inhibits cell growth: suppression by BAG-1.
abstract: The Drosophila seven in absentia (sina) gene is required for R7 photoreceptor cell formation during Drosophila eye development, where it functions within the Ras/Raf pathway and targets other proteins for degradation via associations with a ubiquitin-conjugating enzyme. Recently, a mammalian sina homologue was reported to be a p53-inducible gene in a myeloid leukemia cell line. To explore the function of human SINA-homologous (Siah) proteins, expression plasmids encoding Siah-1A were transiently transfected into 293 epithelial cells and GM701 fibroblast cells, resulting in growth arrest without induction of apoptosis. We discovered that BAG-1, a ubiquitin-like Hsp70/Hsc70-regulating protein, is a negative regulator of Siah-1A. Siah-1A was identified as a BAG-1-binding protein via yeast two-hybrid methods. Specific interaction of BAG-1 with Siah-1A was also demonstrated by in vitro binding experiments using glutathione S-transferase fusion proteins and co-immunoprecipitation studies. Siah-1A-induced growth arrest in 293 and GM701 cells was abolished by co-transfection of wild-type BAG-1 with Siah-1A but not by a C-terminal deletion mutant of BAG-1 that fails to bind Siah-1A. Over-expression of BAG-1 significantly inhibited p53-induced growth arrest in 293 cells without preventing p53 transactivation of reporter gene plasmids. BAG-1 also prevented growth arrest following UV-irradiation-induced genotoxic injury without interfering with accumulation of p53 protein or p21(waf-1) expression. BAG-1 functions downstream of p53-induced gene expression to inhibit p53-mediated suppression of cell growth, presumably by suppressing the actions of Siah-1A. We suggest that Siah-1A may be an important mediator of p53-dependent cell-cycle arrest and demonstrate that Siah-1A is directly inhibited by BAG-1.
authors.affiliation: Burnham Institute, La Jolla, CA 92037, USA.
authors.forename: S
authors.initials: S
authors.lastname: Matsuzawa
authors.forename: S
authors.initials: S
authors.lastname: Takayama
authors.forename: B A
authors.initials: BA
authors.lastname: Froesch
authors.forename: J M
authors.initials: JM
authors.lastname: Zapata
authors.forename: J C
authors.initials: JC
authors.lastname: Reed
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004268:DNA-Binding Proteins; D004330:Drosophila; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D014157:Transcription Factors; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D014466:Ultraviolet Rays; D000098563:Seven in Absentia Proteins
chemical_list: C091732:BCL2-associated athanogene 1 protein; C493956:CDKN1A protein, human; D002352:Carrier Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D004247:DNA; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins