title: Muscle regulatory factor MRF4 activates differentiation in rhabdomyosarcoma RD cells through a positive-acting C-terminal protein domain.
abstract: Rhabdomyosarcoma (RMS) has deregulated proliferation and is blocked in the differentiation program despite Myf-5, MyoD and myogenin expression. Here we show that ectopic expression of MRF4, which is not subject to an autoregulatory pathway but regulated by the other MRFs protein family, induces growth arrest and terminal differentiation in RD cells. Deletion mapping identified a positive-acting C-terminal domain in MRF4 as the mediator of transcriptional activity, revealing a conserved motif with helix III in MyoD previously found to initiate expression of endogenous skeletal muscle genes. By using chimeric MyoD/MRF4 proteins, we observe that the C-terminal motif of MRF4 rescues MyoD activity in RD cells. Moreover, comparative induction of muscle-specific genes following activation of MyoD, through the expression of a constitutively activated MKK6 either in the absence or presence of MRF4, shows that MyoD and MRF4 can differently regulate muscle genes expression. Together, these results demonstrate that the MRF4 C-terminus functions as specification as well as activation domain in tumor cells. They provide a basis to identify gene products necessary for b-HLH-mediated differentiation versus tumor progression.
authors.affiliation: Laboratoire de Génétique oncologique, CNRS UMR 8125, Institut Gustave Roussy, 39 rue Camille Desmoulins, 94800 Villejuif, France.
authors.forename: Valentina
authors.initials: V
authors.lastname: Sirri
authors.forename: Marie Pierre
authors.initials: MP
authors.lastname: Leibovitch
authors.forename: Serge Alexandre
authors.initials: SA
authors.lastname: Leibovitch
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002454:Cell Differentiation; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D016213:Cyclins / Q000502:physiology; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology*; D017570:MyoD Protein / Q000502:physiology; D018006:Myogenic Regulatory Factors / Q000737:chemistry / Q000502:physiology*; D018008:Myogenin / Q000502:physiology; D009687:Nuclear Proteins / Q000502:physiology; D012208:Rhabdomyosarcoma / Q000473:pathology*
chemical_list: C493956:CDKN1A protein, human; C493964:CDKN1C protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D016213:Cyclins; C503799:MYOG protein, human; D017570:MyoD Protein; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D009687:Nuclear Proteins; C063403:myogenic factor 6