Down-regulation of c-Myc following MEK/ERK inhibition halts the expression of malignant phenotype in rhabdomyosarcoma and in non muscle-derived human tumors.
BACKGROUND
Expression of c-myc proto-oncogene is inappropriate in a wide range of human tumors, and is a downstream target of Ras/Raf/ERK pathway, which promotes c-Myc stability by enhancing c-Myc expression and activity. The aim of this study was to investigate whether the oncogenic phenotype in the human muscle-derived Rhabdomyosarcoma (RD) cell line and in non muscle-derived human tumor cell lines (SW403, IGR39 and PC3) can be blocked by disrupting the c-Myc pathway either by means of pharmacological MEK/ERK inhibition or by direct inactivation of the c-Myc protein.


RESULTS
We demonstrate that, in all the tumor cell lines used, the MEK/ERK inhibitor U0126 rapidly induces c-Myc de-phosphorylation, which is followed by a marked reduction in its expression level, by inhibition of proliferation and by reversion of anchorage-independent growth. These data suggest that the targeting of pathways controlling c-Myc expression or stability reverses deregulated growth of different tumor-derived cell lines. Indeed, in RD cells, we found a marked down-regulation of cyclins E2, A and B and CDK2, all of which are known to be targets of c-Myc. Moreover, ectopic MadMyc chimera, a c-Myc function antagonist, causes dramatic growth arrest, CDK and cyclin modulation as well as inhibition of anchorage-independent growth in RD cells, as occurs in U0126-treated cells. In particular, we found that the mere inhibition of c-Myc by MadMyc chimera rescues the myogenic program, MHC expression and the acquisition of the myogenic-like phenotype in RD cells.


CONCLUSIONS
Our data provide evidence of the key role played by the MEK/ERK pathway in the growth arrest and transformation phenotype of Rhabdomyosarcoma and of non muscle-derived tumor cell lines. In fact, MEK/ERK inhibitor, U0126, induces growth arrest, anchorage-dependent growth of these cell lines. In addition, the results of this study demonstrate that the direct inactivation of c-Myc by Mad/Myc chimera rescues myogenic program and leads to the reversal of the Rhabdomyosarcoma phenotype. In conclusion these data strongly suggest that the targeting of c-Myc by means of the MEK inhibitor can be tested as a promising strategy in anti-cancer therapy.
Marampon
Francesco
F
Department of Experimental Medicine, University of L'Aquila, L'Aquila, Italy. f.marampon@virgilio.it
Ciccarelli
Carmela
C
Zani
Bianca M
BM
D002070:Butadienes / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D015151:Immunoblotting / Q000379:methods; D047468:Immunoprecipitation / Q000379:methods; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019042:Muscle Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009570:Nitriles / Q000494:pharmacology; D010641:Phenotype; D010957:Plasmids / Q000235:genetics; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D018233:Rhabdomyosarcoma, Embryonal / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection
D002070:Butadienes; D004791:Enzyme Inhibitors; C000715470:MAS1 protein, human; D009570:Nitriles; D000090063:Proto-Oncogene Mas; D016271:Proto-Oncogene Proteins c-myc; C113580:U 0126; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases