title: PIAS1 interacts with FLASH and enhances its co-activation of c-Myb.
abstract: BACKGROUND
  FLASH is a huge nuclear protein involved in various cellular functions such as apoptosis signalling, NF-κB activation, S-phase regulation, processing of histone pre-mRNAs, and co-regulation of transcription. Recently, we identified FLASH as a co-activator of the transcription factor c-Myb and found FLASH to be tightly associated with active transcription foci. As a huge multifunctional protein, FLASH is expected to have many interaction partners, some which may shed light on its function as a transcriptional regulator.
  
  
  RESULTS
  To find additional FLASH-associated proteins, we performed a yeast two-hybrid (Y2H) screening with FLASH as bait and identified the SUMO E3 ligase PIAS1 as an interaction partner. The association appears to involve two distinct interaction surfaces in FLASH. We verified the interaction by Y2H-mating, GST pulldowns, co-IP and ChIP. FLASH and PIAS1 were found to co-localize in nuclear speckles. Functional assays revealed that PIAS1 enhances the intrinsic transcriptional activity of FLASH in a RING finger-dependent manner. Furthermore, PIAS1 also augments the specific activity of c-Myb, and cooperates with FLASH to further co-activate c-Myb. The three proteins, FLASH, PIAS1, and c-Myb, are all co-localized with active RNA polymerase II foci, resembling transcription factories.
  
  
  CONCLUSIONS
  We conclude that PIAS1 is a common partner for two cancer-related nuclear factors, c-Myb and FLASH. Our results point to a functional cooperation between FLASH and PIAS1 in the enhancement of c-Myb activity in active nuclear foci.
authors.affiliation: Department of Molecular Biosciences, University of Oslo, N-0316 Oslo, Norway.
authors.forename: Anne Hege
authors.initials: AH
authors.lastname: Alm-Kristiansen
authors.forename: Petra I
authors.initials: PI
authors.lastname: Lorenzo
authors.forename: Ann-Kristin
authors.initials: AK
authors.lastname: Molværsmyr
authors.forename: Vilborg
authors.initials: V
authors.lastname: Matre
authors.forename: Marit
authors.initials: M
authors.lastname: Ledsaak
authors.forename: Thomas
authors.initials: T
authors.lastname: Sæther
authors.forename: Odd S
authors.initials: OS
authors.lastname: Gabrielsen
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D002843:Chromatin / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D011485:Protein Binding; D050828:Protein Inhibitors of Activated STAT / Q000378:metabolism*; D021381:Protein Transport; D020598:Proto-Oncogene Proteins c-myb / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C485604:CASP8AP2 protein, human; D002135:Calcium-Binding Proteins; D002843:Chromatin; C106529:PIAS1 protein, human; D050828:Protein Inhibitors of Activated STAT; D020598:Proto-Oncogene Proteins c-myb; D025841:Small Ubiquitin-Related Modifier Proteins; D012319:RNA Polymerase II