A splice variant of the ITF-2 transcript encodes a transcription factor that inhibits MyoD activity.
Proteins of the basic helix-loop-helix (bHLH) family are transcription factors that bind DNA containing the E box motif (CANNTG) found in the promoters of many muscle-specific genes. ITF-2 is a bHLH protein with widespread expression that is thought to form active heterodimers with MyoD, a muscle-specific bHLH transcription factor. We have isolated cDNAs derived from two alternatively spliced forms of mouse ITF-2, termed MITF-2A and -2B. These proteins differ in their N termini. Neither MITF-2A nor -2B transactivated the cardiac alpha-actin promoter, which contains an E box, when transfected into nonmuscle cells. In fact, MITF-2B inhibited MyoD activation of the cardiac alpha-actin promoter. This inhibitory activity required the N-terminal 83 amino acids since MITF-2A showed no inhibitory activity, and a mutant MITF-2B with deletion of the N-terminal 83 amino acids failed to inhibit MyoD-mediated transcriptional activation. MyoD activity was also inhibited by Id, a HLH protein, and this inhibition was reversed by the addition of excess E12 or MITF-2A. However, the inhibition of MyoD activity by MITF-2B was not reversed with E12 or MITF-2A. While Id is thought to inhibit MyoD by binding and sequestering potential dimerization partners, MITF-2B appears to inhibit MyoD activity by forming an inactive heterodimer with MyoD. Thus, differentially spliced transcripts of mouse ITF-2 encode different proteins that appear to dimerize with MyoD and activate or repress transcription.
Skerjanc
I S
IS
Department of Biochemistry, Health Sciences Building, University of Western Ontario, London, Ontario N6A 5C1, Canada.
Truong
J
J
Filion
P
P
McBurney
M W
MW
D000199:Actins / Q000235:genetics; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D018236:Carcinoma, Embryonal; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D003001:Cloning, Molecular; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism; D015723:Gene Library; D014644:Genetic Variation; D018257:Helix-Loop-Helix Motifs; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D017570:MyoD Protein / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D009419:Nerve Tissue Proteins; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000096:biosynthesis* / Q000378:metabolism; D000073940:Transcription Factor 4; D014157:Transcription Factors; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D001616:beta-Galactosidase / Q000096:biosynthesis
D000199:Actins; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D017931:DNA Primers; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D017570:MyoD Protein; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; D051820:TCF Transcription Factors; C090743:Tcf4 protein, mouse; D015534:Trans-Activators; D000073940:Transcription Factor 4; D014157:Transcription Factors; D015500:Chloramphenicol O-Acetyltransferase; D001616:beta-Galactosidase