Cyclin A1 directly interacts with B-myb and cyclin A1/cdk2 phosphorylate B-myb at functionally important serine and threonine residues: tissue-specific regulation of B-myb function.
Cyclin A1 is tissue-specifically expressed during spermatogenesis, but it is also highly expressed in acute myeloid leukemia (AML). Its pathogenetic role in AML and in the cell cycle of leukemic blasts is unknown. B-myb is essential for G1/S transition and has been shown to be phosphorylated by the cyclin A2/cdk2 complex. Here it is demonstrated that cyclin A1 interacts with the C-terminal portion of B-myb as shown by glutathione S-transferase (GST) precipitation. This interaction is confined to cyclin A1 because binding could not be detected between cyclin A2 and B-myb. Also, cdk2 was not pulled down by GST-B-myb from U937 lysates. In addition, co-immunoprecipitation of cyclin A1 and B-myb in leukemic cells evidenced protein interaction in vivo. Baculovirus-expressed cyclin A1/cdk2 complexes were able to phosphorylate human as well as murine B-myb in vitro. Tryptic phosphopeptide mapping revealed that cyclin A1/cdk2 complexes phosphorylated the C-terminal part of B-myb at several sites including threonine 447, 490, and 497 and serine 581. These phosphorylation sites have been demonstrated to be important for the enhancement of B-myb transcriptional activity. Further studies showed that cyclin A1 cooperated with B-myb to transactivate myb binding site containing promoters including the promoter of the human cyclin A1 gene. Taken together, the data suggest that cyclin A1 is a tissue-specific regulator of B-myb function and activates B-myb in leukemic blasts. (Blood. 2001;97:2091-2097)
Department of Medicine, Hematology, and Oncology, University of Münster, Germany. muellerc@uni-muenster.de
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D000818:Animals; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D019925:Cyclin A / Q000502:physiology*; D056750:Cyclin A1; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008297:Male; D051379:Mice; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D009928:Organ Specificity; D010449:Peptide Mapping; D010766:Phosphorylation; D010768:Phosphoserine / Q000737:chemistry*; D010769:Phosphothreonine / Q000737:chemistry*; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*; D020298:U937 Cells / Q000378:metabolism
C503745:CCNA1 protein, human; C503747:Ccna1 protein, mouse; D018797:Cell Cycle Proteins; D019925:Cyclin A; D056750:Cyclin A1; D004268:DNA-Binding Proteins; C064352:MYBL2 protein, human; D046911:Macromolecular Substances; C499306:Mybl2 protein, mouse; D015534:Trans-Activators; D010769:Phosphothreonine; D010768:Phosphoserine; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases