title: Max and inhibitory c-Myc mutants induce erythroid differentiation and resistance to apoptosis in human myeloid leukemia cells.
abstract: We have used the human leukemia cell line K562 as a model to study the role of c-myc in differentiation and apoptosis. We have generated stable transfectants of K562 constitutively expressing two c-Myc inhibitory mutants: D106-143, that carries a deletion in the transactivation domain of the protein, and In373, that carries an insertion in the DNA-interacting region. We show here that In373 is able to compete with c-Myc for Max binding and to inhibit the transformation activity of c-Myc. K562 cells can differentiate towards erythroid or myelomonocytic lineages. K562 transfected with c-myc mutants showed a higher expression of erythroid differentiation markers, without any detectable effects in the myelomonocytic differentiation. We also transfected K562 cells with a zinc-inducible max gene. Ectopic Max overexpression resulted in an increased erythroid differentiation, thus reproducing the effects of c-myc inhibitory mutants. We also studied the role of c-myc mutants and max in apoptosis of K562 induced by okadaic acid, a protein phosphatases inhibitor. The expression of D106-143 and In373 c-myc mutants and the overexpression of max reduced the apoptosis mediated by okadaic acid. The common biochemical activity of D106-143 and In373 is to bind Max and hence to titrate out c-Myc to form non-functional Myc/Max dimers. Similarly, Max overexpression would decrease the relative levels of c-Myc/Max with respect to Max/Max. The results support a model where a threshold of functional c-Myc/Max is required to maintain K562 cells in an undifferentiated state and to undergo drug-mediated apoptosis.
authors.affiliation: Departamento de Biología Molecular, Facultad de Medicina, Santander, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Cañelles
authors.forename: M D
authors.initials: MD
authors.lastname: Delgado
authors.forename: K M
authors.initials: KM
authors.lastname: Hyland
authors.forename: A
authors.initials: A
authors.lastname: Lerga
authors.forename: C
authors.initials: C
authors.lastname: Richard
authors.forename: C V
authors.initials: CV
authors.lastname: Dang
authors.forename: J
authors.initials: J
authors.lastname: León
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000166:cytology; D004920:Erythropoiesis / Q000235:genetics*; D015870:Gene Expression; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics* / Q000473:pathology; D019319:Okadaic Acid / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; 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; D019319:Okadaic Acid; D010744:Phosphoric Monoester Hydrolases