title: Redundant functions of B-Myb and c-Myb in differentiating myeloid cells.
abstract: We show in this report that the human myeloid leukemia cell line GFD8 is a useful model to compare the biological function of the structurally related c-Myb and B-Myb proto-oncogenes and to investigate the c-myb domains required for this function. GFD8 cells are dependent for growth on granulocyte-macrophage colony-stimulating factor and differentiate in response to phorbol myristate acetate (PMA). We have stably transfected this cell line with constructs constitutively expressing c-Myb or B-Myb. Deregulated expression of both c-Myb and B-Myb inhibited the differentiation observed in response to PMA and, in particular, the induction of the CD11b and CD11c antigens on the cell surface, and the induction of adherence. Furthermore, c-Myb and B-Myb enhanced expression of CD13 upon PMA treatment. Although deregulated Myb expression did not alter the growth factor dependence of the cells, it led to an increase in G2 relative to G1 arrest in cells induced to differentiate in response to PMA, whereas control vector-transfected cells were blocked mostly in G1. This decrease in G1 block took place despite normal induction of the cyclin-dependent kinase inhibitor protein p21 (CIP1/WAF1). Thus, GFD8 cells stably expressing the human B-Myb protein behaved in a manner indistinguishable from those stably expressing C-Myb for both differentiation and cell cycle parameters. In agreement with these findings and differently from most previous reports, transactivation assays show that B-myb can indeed act as a strong activator of transcription. Finally, we demonstrated that although the DNA-binding domain of c-myb is required for both the differentiation block and the shift in cell cycle after PMA treatment, phosphorylation by casein kinase II and mitogen-activated protein kinase at positions 11 and 12 or 532 of c-myb, respectively, are not. We conclude that c-Myb and B-Myb may activate a common cellular program in the GFD8 cell line involved in both differentiation and cell cycle control.
authors.affiliation: Department of Immunology and Cell Biology, Istituto Ricerche Farmacologicalhe, Mario Negri, Milano, Italy.
authors.forename: J
authors.initials: J
authors.lastname: Golay
authors.forename: V
authors.initials: V
authors.lastname: Broccoli
authors.forename: G M
authors.initials: GM
authors.lastname: Borleri
authors.forename: E
authors.initials: E
authors.lastname: Erba
authors.forename: M
authors.initials: M
authors.lastname: Faretta
authors.forename: L
authors.initials: L
authors.lastname: Basilico
authors.forename: G G
authors.initials: GG
authors.lastname: Ying
authors.forename: G
authors.initials: G
authors.lastname: Piccinini
authors.forename: L H
authors.initials: LH
authors.lastname: Shapiro
authors.forename: J
authors.initials: J
authors.lastname: Lovrić
authors.forename: M
authors.initials: M
authors.lastname: Nawrath
authors.forename: K
authors.initials: K
authors.lastname: Mölling
authors.forename: A
authors.initials: A
authors.lastname: Rambaldi
authors.forename: M
authors.initials: M
authors.lastname: Introna
mesh_terms: D000943:Antigens, Differentiation / Q000096:biosynthesis; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics*; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000235:genetics*; D005786:Gene Expression Regulation; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000235:genetics*; D020598:Proto-Oncogene Proteins c-myb; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015534:Trans-Activators / Q000187:drug effects / Q000235:genetics*; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000943:Antigens, Differentiation; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; C064352:MYBL2 protein, human; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators; D014157:Transcription Factors; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D013755:Tetradecanoylphorbol Acetate