Mos activates myogenic differentiation by promoting heterodimerization of MyoD and E12 proteins.
The activities of myogenic basic helix-loop-helix (bHLH) factors are regulated by a number of different positive and negative signals. Extensive information has been published about the molecular mechanisms that interfere with the process of myogenic differentiation, but little is known about the positive signals. We previously showed that overexpression of rat Mos in C2C12 myoblasts increased the expression of myogenic markers whereas repression of Mos products by antisense RNAs inhibited myogenic differentiation. In the present work, our results show that the rat mos proto-oncogene activates transcriptional activity of MyoD protein. In transient transfection assays, Mos promotes transcriptional transactivation by MyoD of the muscle creatine kinase enhancer and/or a reporter gene linked to MyoD-DNA binding sites. Physical interaction between Mos and MyoD, but not with E12, is demonstrated in vivo by using the two-hybrid approach with C3H10T1/2 cells and in vitro by using the glutathione S-transferase (GST) pull-down assays. Unphosphorylated MyoD from myogenic cell lysates and/or bacterially expressed MyoD physically interacts with Mos. This interaction occurs via the helix 2 region of MyoD and a highly conserved region in Mos proteins with 40% similarity to the helix 2 domain of the E-protein class of bHLH factors. Phosphorylation of MyoD by activated GST-Mos protein inhibits the DNA-binding activity of MyoD homodimers and promotes MyoD-E12 heterodimer formation. These data support a novel function for Mos as a mediator (coregulator) of muscle-specific gene(s) expression.
Lenormand
J L
JL
Laboratoire de Génétique Oncologique, URA 1967 CNRS, Institut GustaveRoussy, Villejuif, France.
Benayoun
B
B
Guillier
M
M
Vandromme
M
M
Leibovitch
M P
MP
Leibovitch
S A
SA
D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D003402:Creatine Kinase / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D004742:Enhancer Elements, Genetic / Q000235:genetics; D018257:Helix-Loop-Helix Motifs; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000166:cytology*; D009154:Mutation; D017570:MyoD Protein / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins; D017386:Sequence Homology, Amino Acid; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D015533:Transcriptional Activation / Q000502:physiology*; D014162:Transfection
D004268:DNA-Binding Proteins; D017570:MyoD Protein; D011993:Recombinant Fusion Proteins; D051820:TCF Transcription Factors; C544913:Tcf7l1 protein, mouse; C553060:Tcf7l1 protein, rat; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D017231:Proto-Oncogene Proteins c-mos; D003402:Creatine Kinase