Tissue-specific expression of the skeletal alpha-actin gene involves sequences that can function independently of MyoD and Id.
The skeletal alpha-actin gene is a member of the sarcomeric contractile protein gene family and is specifically expressed in differentiated muscle. The skeletal alpha-actin gene is regulated efficiently by enhancer and regulatory sequences between nucleotide positions -1282 and -87. In the present study we have shown that the sequences 3' of nucleotide position -87 can functionally interact with the SV40 enhancer in a tissue-specific manner and can restrict the ubiquitous function of the SV40 enhancer to myogenic cells. Site-specific cassette mutagenesis was used to delimit the sequences upstream of the TATA motif (-32), between nucleotide positions -64 and -37, that mediate efficient expression in myogenic cells in the presence of the SV40 enhancer. The skeletal alpha-actin promoter was trans-activated by the helix-loop-helix (HLH) transcription factors MyoD, MRF-4, and Myogenin, in pluripotential 10T1/2 fibroblasts and trans-repressed by the HLH protein Id (inhibitor of differentiation) in myogenic C2C12 cells. This trans-regulation required sequences upstream of -87 and occurred independently of the two consensus E boxes (CANNTG) at positions +18 and +71. The -64/-37 region interacted with purified Sp1 and an unidentified protein(s), proximal regulatory factor(s) I (PRF-I). We conclude that the muscle-specific expression of the skeletal alpha-actin promoter is not simply determined by MyoD elements and enhancer and regulatory sequences, but that the minimal promoter contains important determinants of cell-specific transcription that can function independently of the helix-loop-helix transcription factors.
Muscat
G E
GE
University of Queensland, Center for Molecular Biology and Biotechnology, Ritchie Research Laboratories, St. Lucia, Australia.
Emery
J
J
Collie
E S
ES
D000199:Actins / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D017570:MyoD Protein; D009206:Myocardium / Q000378:metabolism; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D009928:Organ Specificity; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000378:metabolism; D013539:Simian virus 40 / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation
D000199:Actins; D004268:DNA-Binding Proteins; C497453:ID1 protein, human; C497455:Idb1 protein, mouse; D051798:Inhibitor of Differentiation Protein 1; C503799:MYOG protein, human; D009124:Muscle Proteins; D017570:MyoD Protein; C503801:Myog protein, mouse; D018006:Myogenic Regulatory Factors; D018008:Myogenin; D012097:Repressor Proteins; D014157:Transcription Factors; C063403:myogenic factor 6