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)
Mesh Terms:
Animals, CDC2-CDC28 Kinases, Cell Cycle Proteins, Cyclin A, Cyclin A1, Cyclin-Dependent Kinase 2, Cyclin-Dependent Kinases, DNA-Binding Proteins, Gene Expression Regulation, Hematopoietic Stem Cells, Humans, Macromolecular Substances, Male, Mice, Neoplastic Stem Cells, Organ Specificity, Peptide Mapping, Phosphorylation, Phosphoserine, Phosphothreonine, Promoter Regions, Genetic, Protein Processing, Post-Translational, Protein-Serine-Threonine Kinases, Trans-Activators, Transcription, Genetic, U937 Cells
Animals, CDC2-CDC28 Kinases, Cell Cycle Proteins, Cyclin A, Cyclin A1, Cyclin-Dependent Kinase 2, Cyclin-Dependent Kinases, DNA-Binding Proteins, Gene Expression Regulation, Hematopoietic Stem Cells, Humans, Macromolecular Substances, Male, Mice, Neoplastic Stem Cells, Organ Specificity, Peptide Mapping, Phosphorylation, Phosphoserine, Phosphothreonine, Promoter Regions, Genetic, Protein Processing, Post-Translational, Protein-Serine-Threonine Kinases, Trans-Activators, Transcription, Genetic, U937 Cells
Blood
Date: Apr. 01, 2001
PubMed ID: 11264176
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