title: c-Myc antagonizes the effect of p53 on apoptosis and p21WAF1 transactivation in K562 leukemia cells.
abstract: c-myc protooncogene positively regulates cell proliferation and overexpression of c-myc is found in many solid tumors and leukemias. In the present study we used the K562 human myeloid leukemia cell line as a model to study the functional interaction between c-Myc and p53. Using two different methods, we generated K562 transfectant cell lines with conditional expression of either c-Myc or p53. The cells expressed the p53Vall35 mutant, which adopts a wild-type conformation at 32 degrees C, while c-Myc induction was achieved with a zinc-inducible expression vector. We found that p53 in wild-type conformation induces growth arrest and apoptosis of K562. Expression of c-Myc significantly attenuated apoptosis and impaired the transcriptional activity of p53 on p21WAF1, Bax and cytomegalovirus promoters. The impairment of p21WAF1 transactivation by c-Myc was confirmed by transfection of a c-Myc-estrogen receptor fusion protein and by induction of c-myc by zinc in transfected cells. Also, p53-mediated up-regulation of p21WAF1 mRNA protein were significantly reduced by c-Myc, while Bax levels were unaffected. Consistently, c-Myc increased cyclin-dependent kinase 2 activity in K562 cells expressing p53 in wild-type conformation. These results suggest that c-Myc overexpression may antagonize the pro-apoptotic function of p53, thus providing a molecular mechanism for the frequently observed deregulation of c-myc in human cancer.
authors.affiliation: Departamento de Biologia Molecular, Unidad Asociada al Centro de Investigaciones Biológicas, Universidad de Cantabria, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Ceballos
authors.forename: M D
authors.initials: MD
authors.lastname: Delgado
authors.forename: P
authors.initials: P
authors.lastname: Gutierrez
authors.forename: C
authors.initials: C
authors.lastname: Richard
authors.forename: D
authors.initials: D
authors.lastname: Müller
authors.forename: M
authors.initials: M
authors.lastname: Eilers
authors.forename: M
authors.initials: M
authors.lastname: Ehinger
authors.forename: U
authors.initials: U
authors.lastname: Gullberg
authors.forename: J
authors.initials: J
authors.lastname: León
mesh_terms: D017209:Apoptosis; D001752:Blast Crisis / Q000235:genetics*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics*; D006801:Humans; D020014:K562 Cells; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53