title: Phosphorylation-dependent down-regulation of c-Myb DNA binding is abrogated by a point mutation in the v-myb oncogene.
abstract: The viral Myb (v-Myb) oncoprotein of the avian myeloblastosis virus (AMV) is an activated form of the cellular transcription factor c-Myb causing acute monoblastic leukemia in chicken. Oncogenic v-Myb alterations include N- and C-terminal deletions as well as point mutations. Whereas truncations in Myb cause loss of various protein modifications, none of the point mutations in v-Myb has been directly linked to protein modifications. Here we show that the DNA-binding domain of c-Myb can be phosphorylated on serine 116 by the catalytic subunit of protein kinase A. Phosphorylation of Ser(116) differentially destabilizes a subtype of c-Myb-DNA complexes. The V117D mutation of the AMV v-Myb oncoprotein abolishes phosphorylation of the adjacent Ser(116) residue. Modification of Ser(116) was also detected in live cells in c-Myb, but not in AMV v-Myb. Phosphorylation-mimicking mutants of c-Myb failed to activate the resident mim-1 gene. Our data imply that protein kinase A or a kinase with similar specificity negatively regulates c-Myb function, including collaboration with C/EBP, and that the leukemogenic AMV v-Myb version evades inactivation by a point mutation that abolishes a phosphoacceptor consensus site. This suggests a novel link between Myb, a signal transduction pathway, cooperativity with C/EBP, and a point mutation in the myb oncogene.
authors.affiliation: Department of Biochemistry, University of Oslo, Norway.
authors.forename: Kristin Brevik
authors.initials: KB
authors.lastname: Andersson
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kowenz-Leutz
authors.forename: Elen Margrethe
authors.initials: EM
authors.lastname: Brendeford
authors.forename: Ann-Helen Herwig
authors.initials: AH
authors.lastname: Tygsett
authors.forename: Achim
authors.initials: A
authors.lastname: Leutz
authors.forename: Odd S
authors.initials: OS
authors.lastname: Gabrielsen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D015536:Down-Regulation; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017354:Point Mutation; D011485:Protein Binding; D020598:Proto-Oncogene Proteins c-myb / Q000737:chemistry / Q000378:metabolism*; D011784:Quail; D017386:Sequence Homology, Amino Acid
chemical_list: D020598:Proto-Oncogene Proteins c-myb; D004247:DNA; D017868:Cyclic AMP-Dependent Protein Kinases