title: c-Myc inhibits Ras-mediated differentiation of pheochromocytoma cells by blocking c-Jun up-regulation.
abstract: Although mutant Ras proteins were originally described as transforming oncoproteins, they induce growth arrest, senescence, and/or differentiation in many cell types. c-Myc is an oncogenic transcription factor that cooperates with Ras in cellular transformation and oncogenesis. However, the Myc-Ras relationship in cellular differentiation is largely unknown. Here, we have analyzed the effects of c-Myc on PC12-derived cells (UR61 cell line), harboring an inducible N-Ras oncogene. In these cells, Ras activation induces neuronal-like differentiation by a process involving c-Jun activation. We found that c-Myc inhibited Ras-mediated differentiation by a mechanism that involves the blockade of c-Jun induction in response to Ras signal. Accordingly, ectopically expressed c-Jun could bypass c-Myc impediment of Ras-induced differentiation and activator protein 1 activation. Interestingly, it did not rescue the proliferative arrest elicited by Ras and did not enhance the differentiation-associated apoptosis. The blockade of Ras-mediated induction of c-Jun takes place at the level of c-Jun proximal promoter. Mutational analysis revealed that c-Myc regions involved in DNA binding and transactivation are required to block differentiation and c-Jun induction. c-Myc does not seem to require Miz-1 to inhibit differentiation and block c-Jun induction. Furthermore, Max is not required for c-Myc activity, as UR61 cells lack a functional Max gene. c-Myc-inhibitory effect on the Ras/c-Jun connection is not restricted to UR61 cells as it can occur in other cell types as K562 or HEK293. In conclusion, we describe a novel interplay between c-Myc and c-Jun that controls the ability of Ras to trigger the differentiation program of pheochromocytoma cells.
authors.affiliation: Grupo de Biología Molecular del Cáncer, Dpto. de Biología Molecular and Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria-CSIC-IDICAN, Santander, Spain.
authors.forename: José P
authors.initials: JP
authors.lastname: Vaqué
authors.forename: Belén
authors.initials: B
authors.lastname: Fernández-García
authors.forename: Pablo
authors.initials: P
authors.lastname: García-Sanz
authors.forename: Nuria
authors.initials: N
authors.lastname: Ferrandiz
authors.forename: Gabriel
authors.initials: G
authors.lastname: Bretones
authors.forename: Fernando
authors.initials: F
authors.lastname: Calvo
authors.forename: Piero
authors.initials: P
authors.lastname: Crespo
authors.forename: María C
authors.initials: MC
authors.lastname: Marín
authors.forename: Javier
authors.initials: J
authors.lastname: León
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D004789:Enzyme Activation; D004790:Enzyme Induction; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D017434:Protein Structure, Tertiary; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics; D015854:Up-Regulation; D018631:ras Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D018808:Transcription Factor AP-1; D018631:ras Proteins