Myc inhibits p27-induced erythroid differentiation of leukemia cells by repressing erythroid master genes without reversing p27-mediated cell cycle arrest.
Inhibition of differentiation has been proposed as an important mechanism for Myc-induced tumorigenesis, but the mechanisms involved are unclear. We have established a genetically defined differentiation model in human leukemia K562 cells by conditional expression of the cyclin-dependent kinase (Cdk) inhibitor p27 (inducible by Zn(2+)) and Myc (activatable by 4-hydroxy-tamoxifen). Induction of p27 resulted in erythroid differentiation, accompanied by Cdk inhibition and G(1) arrest. Interestingly, activation of Myc inhibited p27-mediated erythroid differentiation without affecting p27-mediated proliferation arrest. Microarray-based gene expression indicated that, in the presence of p27, Myc blocked the upregulation of several erythroid-cell-specific genes, including NFE2, JUNB, and GATA1 (transcription factors with a pivotal role in erythropoiesis). Moreover, Myc also blocked the upregulation of Mad1, a transcriptional antagonist of Myc that is able to induce erythroid differentiation. Cotransfection experiments demonstrated that Myc-mediated inhibition of differentiation is partly dependent on the repression of Mad1 and GATA1. In conclusion, this model demonstrates that Myc-mediated inhibition of differentiation depends on the regulation of a specific gene program, whereas it is independent of p27-mediated cell cycle arrest. Our results support the hypothesis that differentiation inhibition is an important Myc tumorigenic mechanism that is independent of cell proliferation.
Cancer Molecular Biology Group, Department of Molecular Biology, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria-CSIC-IDICAN, Santander, Spain.
Juan C
JC
Acosta
Nuria
N
Ferrándiz
Gabriel
G
Bretones
Verónica
V
Torrano
Rosa
R
Blanco
Carlos
C
Richard
Brenda
B
O'Connell
John
J
Sedivy
M Dolores
MD
Delgado
Javier
J
León
D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics* / Q000502:physiology; D049109:Cell Proliferation; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D004920:Erythropoiesis / Q000235:genetics* / Q000502:physiology; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D020014:K562 Cells; D007938:Leukemia; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
D018797:Cell Cycle Proteins; C501384:MAD1L1 protein, human; D009687:Nuclear Proteins; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases