The mouse MRF4 promoter is trans-activated directly and indirectly by muscle-specific transcription factors.
MRF4 is a member of the basic helix-loop-helix (bHLH) family of muscle-specific transcription factors, which also includes MyoD, myogenin, and myf5. The myocyte enhancer binding factor 2 (MEF2) proteins also serve as important muscle-specific transcription factors. In addition to activating the expression of many muscle-specific structural genes, various members of these two classes of proteins activate their own expression and the expression of each other in a complex transcriptional network that results in the establishment and maintenance of the muscle phenotype. To begin to determine how the expression of MRF4 is regulated by other muscle-specific transcription factors, we have isolated a region of the MRF4 gene that confers muscle-specific expression and have analyzed this promoter region for cis-acting elements involved in trans-activation by the myogenic bHLH and MEF2 transcription factors. Here, we show that in 10T1/2 fibroblasts the MRF4 promoter is trans-activated by myogenin, MyoD, myf5, and by the MEF2 factors, but that MRF4 does not activate expression of its own promoter. Myogenin activated the MRF4 promoter directly by an E box-dependent mechanism, while MEF2 factors activated the promoter through an indirect pathway. The E box-dependent regulation of the MRF4 promoter is in contrast to the regulation of the myogenin and MyoD promoters and may represent a mechanism for the differential expression of these factors during myogenesis.
Black
B L
BL
Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Martin
J F
JF
Olson
E N
EN
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002645:Chickens; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D015870:Gene Expression; D015698:Genomic Library; D064326:MEF2 Transcription Factors; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D018006:Myogenic Regulatory Factors / Q000096:biosynthesis / Q000235:genetics*; D018008:Myogenin / Q000096:biosynthesis*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014157:Transcription Factors / Q000096:biosynthesis* / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
D017931:DNA Primers; D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; C503801:Myog protein, mouse; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D011994:Recombinant Proteins; D014157:Transcription Factors; C063403:myogenic factor 6