title: A functional SUMO-interacting motif in the transactivation domain of c-Myb regulates its myeloid transforming ability.
abstract: c-Myb is an essential hematopoietic transcription factor that controls proliferation and differentiation of progenitors during blood cell development. Whereas sumoylation of the C-terminal regulatory domain (CRD) is known to have a major impact on the activity of c-Myb, no role for noncovalent binding of small ubiquitin-like modifier (SUMO) to c-Myb has been described. Based on the consensus SUMO-interacting motif (SIM), we identified and examined putative SIMs in human c-Myb. Interaction and reporter assays showed that the SIM in the in the transactivation domain of c-Myb (V(267)NIV) is functional. This motif is necessary for c-Myb to be able to interact noncovalently with SUMO, preferentially SUMO2/3. Destroying the SUMO-binding properties by mutation resulted in a large increase in the transactivation potential of c-Myb. Mutational analysis and overexpression of conjugation-defective SUMO argued against intramolecular repression caused by sumoylated CRD and in favor of SUMO-dependent repression in trans. Using both a myeloid cell line-based assay and a primary hematopoietic cell assay, we addressed the transforming abilities of SUMO binding and conjugation mutants. Interestingly, only loss of SUMO binding, and not SUMO conjugation, enhanced the myeloid transformational potential of c-Myb. c-Myb with the SIM mutated conferred a higher proliferative ability than the wild-type and caused an effective differentiation block. This establishes SUMO binding as a mechanism involved in modulating the transactivation activity of c-Myb, and responsible for keeping the transforming potential of the oncoprotein in check.
authors.affiliation: Department of Molecular Biosciences, University of Oslo, Oslo, Norway. thomas.sather@imbv.uio.no
authors.forename: T
authors.initials: T
authors.lastname: Saether
authors.forename: D R
authors.initials: DR
authors.lastname: Pattabiraman
authors.forename: A H
authors.initials: AH
authors.lastname: Alm-Kristiansen
authors.forename: L T
authors.initials: LT
authors.lastname: Vogt-Kielland
authors.forename: T J
authors.initials: TJ
authors.lastname: Gonda
authors.forename: O S
authors.initials: OS
authors.lastname: Gabrielsen
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism; D019556:COS Cells; D002454:Cell Differentiation; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D002522:Chlorocebus aethiops; D016384:Consensus Sequence; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D022423:Myeloid Cells / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020598:Proto-Oncogene Proteins c-myb / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025841:Small Ubiquitin-Related Modifier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D020598:Proto-Oncogene Proteins c-myb; D025841:Small Ubiquitin-Related Modifier Proteins