title: Regulation of c-Myc and Max in megakaryocytic and monocytic-macrophagic differentiation of K562 cells induced by protein kinase C modifiers: c-Myc is down-regulated but does not inhibit differentiation.
abstract: We have studied the regulation and role of c-Myc and Max in the differentiation pathways induced in K562 cells by 12-O-tetradecanoyl phorbol-13 acetate (TPA) and staurosporine, an activator and inhibitor, respectively, of protein kinase C (PKC). We found that staurosporine induced megakaryocytic differentiation, as revealed by the cellular ultrastructure, platelet formation, and DNA endoreduplication. In contrast, TPA induced a differentiated phenotype that more closely resembled that of the monocyte-macrophage lineage. c-myc expression was down-regulated in K562 differentiated by both TPA and staurosporine, whereas max expression did not change in either case. Although PKC enzymatic activity was low in cells terminally differentiated with TPA and staurosporine, inhibition of PKC activity by itself did not induce c-myc down-regulation. We conclude that the c-myc gene is switched off as a consequence of the differentiation process triggered by these drugs in a manner independent from PKC. Ectopic overexpression of c-Myc in K562 cells did not affect the monocytic-macrophagic and megakaryocytic differentiation, indicating that c-Myc suppression is not required for these processes in K562. Similarly, both differentiation pathways were not affected by Max overexpression or by concomitant overexpression of c-Myc and Max. This result is in contrast with the inhibition of erythroid differentiation of K562 exerted by c-Myc, suggesting divergent roles for c-Myc/Max, depending on the differentiation pathway.
authors.affiliation: Departamento de Biología Molecular-Unidad Asociada al Centro de Investigaciones Biológicas del CSIC, Santander, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Lerga
authors.forename: P
authors.initials: P
authors.lastname: Crespo
authors.forename: M
authors.initials: M
authors.lastname: Berciano
authors.forename: M D
authors.initials: MD
authors.lastname: Delgado
authors.forename: M
authors.initials: M
authors.lastname: Cañelles
authors.forename: C
authors.initials: C
authors.lastname: Calés
authors.forename: C
authors.initials: C
authors.lastname: Richard
authors.forename: E
authors.initials: E
authors.lastname: Ceballos
authors.forename: P
authors.initials: P
authors.lastname: Gutierrez
authors.forename: N
authors.initials: N
authors.lastname: Ajenjo
authors.forename: S
authors.initials: S
authors.lastname: Gutkind
authors.forename: J
authors.initials: J
authors.lastname: León
mesh_terms: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002273:Carcinogens / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006801:Humans; D020014:K562 Cells; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism; D010641:Phenotype; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics* / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002273:Carcinogens; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C499330:MAX protein, human; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate