Flanking sequences modulate the cell specificity of M-CAT elements.
M-CAT elements mediate both muscle-specific and non-muscle-specific transcription. We used artificial promoters to dissect M-CAT elements derived from the cardiac troponin T promoter, whose regulation is highly striated muscle specific. We show that muscle-specific M-CAT-dependent expression requires two distinct components: the core heptameric M-CAT motif (5'-CATTCCT-3'), which constitutes the canonical binding site for TEF-1-related proteins, and specific sequences immediately flanking the core motif that bind an additional factor(s). These factors are found in higher-order M-CAT DNA-protein complexes with TEF-1 proteins. Non-muscle-specific promoters are produced when the sequences flanking the M-CAT motif are removed or modified to match those of non-muscle-specific promoters such as the simian virus 40 promoter. Moreover, a mutation of the 5'-flanking region of the cardiac troponin T M-CAT-1 element upregulated expression in nonmuscle cells. That mutation also disrupts a potential E box that apparently does not bind myogenic basic helix-loop-helix proteins. We propose a model in which M-CAT motifs are potentially active in many cell types but are modulated through protein binding to specific flanking sequences. In nonmuscle cells, these flanking sequences bind a factor(s) that represses M-CAT-dependent activity. In muscle cells, on the other hand, the factor(s) binding to these flanking sequences contributes to both the cell specificity and the overall transcriptional strength of M-CAT-dependent promoters.
Larkin
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SB
Department of Anatomy, University of California San Francisco, California 94143, USA.
Farrance
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IK
Ordahl
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CP
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002642:Chick Embryo; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008745:Methylation; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D009838:Oligodeoxyribonucleotides; D015345:Oligonucleotide Probes; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D000091262:TEA Domain Transcription Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014336:Troponin / Q000096:biosynthesis* / Q000235:genetics*; D020107:Troponin T
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D015345:Oligonucleotide Probes; D000091262:TEA Domain Transcription Factors; C057182:TEAD1 protein, human; D014157:Transcription Factors; D014336:Troponin; D020107:Troponin T