title: Regulation of FeLV-945 by c-Myb binding and CBP recruitment to the LTR.
abstract: BACKGROUND
  Feline leukemia virus (FeLV) induces degenerative, proliferative and malignant hematologic disorders in its natural host, the domestic cat. FeLV-945 is a viral variant identified as predominant in a cohort of naturally infected animals. FeLV-945 contains a unique sequence motif in the long terminal repeat (LTR) comprised of a single copy of transcriptional enhancer followed by a 21-bp sequence triplicated in tandem. The LTR is precisely conserved among independent cases of multicentric lymphoma, myeloproliferative disease and anemia in animals from the cohort. The 21-bp triplication was previously shown to act as a transcriptional enhancer preferentially in hematopoietic cells and to confer a replicative advantage. The objective of the present study was to examine the molecular mechanism by which the 21-bp triplication exerts its influence and the selective advantage responsible for its precise conservation.
  
  
  RESULTS
  Potential binding sites for the transcription factor, c-Myb, were identified across the repeat junctions of the 21-bp triplication. Such sites would not occur in the absence of the repeat; thus, a requirement for c-Myb binding to the repeat junctions of the triplication would exert a selective pressure to conserve its sequence precisely. Electrophoretic mobility shift assays demonstrated specific binding of c-Myb to the 21-bp triplication. Reporter gene assays showed that the triplication-containing LTR is responsive to c-Myb, and that responsiveness requires the presence of both c-Myb binding sites. Results further indicated that c-Myb in complex with the 21-bp triplication recruits the transcriptional co-activator, CBP, a regulator of normal hematopoiesis. FeLV-945 replication was shown to be positively regulated by CBP in a manner dependent on the presence of the 21-bp triplication.
  
  
  CONCLUSIONS
  Binding sites for c-Myb across the repeat junctions of the 21-bp triplication may account for its precise conservation in the FeLV-945 LTR. c-Myb binding and CBP recruitment to the LTR positively regulated virus production, and thus may be responsible for the replicative advantage conferred by the 21-bp triplication. Considering that CBP is present in hematopoietic cells in limiting amounts, we hypothesize that FeLV-945 replication in bone marrow may influence CBP availability and thereby alter the regulation of CBP-responsive genes, thus contributing to altered hematopoiesis and consequent hematologic disease.
authors.affiliation: Department of Microbiology and Immunology, Program in Molecular and Cellular Biology and Tulane Cancer Center, Tulane University Health Sciences Center, New Orleans, Louisiana, USA. sfinsta1@tulane.edu
authors.forename: Samantha L
authors.initials: SL
authors.lastname: Finstad
authors.forename: Sudha
authors.initials: S
authors.lastname: Prabhu
authors.forename: Karen R
authors.initials: KR
authors.lastname: Rulli
authors.forename: Laura S
authors.initials: LS
authors.lastname: Levy
mesh_terms: D000818:Animals; D050882:CREB-Binding Protein / Q000378:metabolism*; D002415:Cats; D045744:Cell Line, Tumor; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D005256:Leukemia Virus, Feline / Q000235:genetics* / Q000502:physiology*; D009154:Mutation; D011485:Protein Binding; D020598:Proto-Oncogene Proteins c-myb / Q000378:metabolism*; D020079:Terminal Repeat Sequences / Q000235:genetics*; D014779:Virus Replication
chemical_list: D020598:Proto-Oncogene Proteins c-myb; D050882:CREB-Binding Protein