Myogenesis and MyoD down-regulate Sp1. A mechanism for the repression of GLUT1 during muscle cell differentiation.
Muscle cell differentiation caused a reduction of glucose transport, GLUT1 glucose transporter expression, and GLUT1 mRNA levels. A fragment of 2.1 kilobases of the rat GLUT1 gene linked to chloramphenicol acetyltransferase drove transcriptional activity in myoblasts, and differentiation caused a decrease in transcription. Transient transfection of 5' and 3' deletion constructs showed that the fragment -99/-33 of the GLUT1 gene drives transcriptional activity of the GLUT1 gene and participates in the reduced transcription after muscle differentiation. Electrophoretic mobility shift assays showed the binding of Sp1 protein to the fragment -102/-37 in the myoblast state but not in myotubes, and Sp1 was found to transactivate the GLUT1 promoter. Western blot analysis indicated that Sp1 was drastically down-regulated during myogenesis. Furthermore, the forced over-expression of MyoD in C3H10T1/2 cells mimicked the effects observed during myogenesis, Sp1 down-regulation and reduced transcriptional activity of the GLUT1 gene promoter. In all, these data suggest a regulatory model in which MyoD activation during myogenesis causes the down-regulation of Sp1, which contributes to the repression of GLUT1 gene transcription and, therefore, leads to the reduction in GLUT1 expression and glucose transport.
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Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, 08028 Barcelona, Spain.
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Santalucia
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Ferré
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002454:Cell Differentiation; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D051272:Glucose Transporter Type 1; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D009154:Mutation; D017570:MyoD Protein / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism
D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; D017570:MyoD Protein; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C495679:Slc2a1 protein, rat