title: Identification of a regulatory function for an orphan receptor in muscle: COUP-TF II affects the expression of the myoD gene family during myogenesis.
abstract: COUP-TF II is an 'orphan steroid receptor' that binds a wide variety of AGGTCA repeats and represses thyroid hormone (T3) and retinoid dependent trans-activation; however, very little is known of its functional and/or developmental role during mammalian cell differentiation. T3 and retinoids have been demonstrated to promote terminal muscle differentiation via activation of the muscle specific myoD gene family (myoD, myogenin, myf-5 and MRF-4). The myoD gene family can direct the fate of mesodermal cell lineages, repress proliferation, activate differentiation and the contractile phenotype. Hence, we investigated the expression and functional role of COUP-TF II during muscle differentiation. Proliferating C2C12 myoblasts expressed COUP-TF II mRNA which was repressed when cells were induced to differentiate into post-mitotic multinucleated myotubes by serum withdrawal. Concomitant with the decrease of COUP-TF II mRNA was the appearance of muscle specific mRNAs (e.g. myogenin, alpha-actin). We show that Escherichia coli expressed full length and truncated COUP-TF II bound in a sequence specific manner to the T3 response elements (TREs) in the myoD and myogenin regulatory HLH genes [Olson (1992) Dev. Biol. 154, 261-272]; and the TRE in the skeletal alpha-actin contractile protein gene. COUP-TF II diminished the homodimeric binding of the thyroid hormone receptor and the heterodimeric binding of thyroid hormone and retinoid X receptor complexes to these TREs. Constitutive over-expression of COUP-TF II cDNA in mouse C2C12 myogenic cells suppressed the levels of myoD mRNA and blocked the induction of myogenin mRNA, whereas constitutive expression of anti-sense COUP-TF II cDNA significantly increased the steady state levels of myoD mRNA and hyper-induced myogenin mRNA. These studies demonstrate for the first time (i) that COUP-TF II, functions as a physiologically relevant antagonistic regulator of myogenesis via direct effects on the myoD gene family and (ii) direct evidence for the developmental role of COUP-TF II during mammalian cell differentiation.
authors.affiliation: University of Queensland, Centre for Molecular and Cellular Biology, Ritchie Research Laboratories, St Lucia, Australia.
authors.forename: G E
authors.initials: GE
authors.lastname: Muscat
authors.forename: S
authors.initials: S
authors.lastname: Rea
authors.forename: M
authors.initials: M
authors.lastname: Downes
mesh_terms: D000199:Actins / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D051836:COUP Transcription Factors; D002454:Cell Differentiation; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000166:cytology* / Q000196:embryology; D009154:Mutation; D017570:MyoD Protein / Q000096:biosynthesis / Q000235:genetics*; D018008:Myogenin / Q000096:biosynthesis / Q000235:genetics*; D009218:Myosins / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D011956:Receptors, Cell Surface / Q000502:physiology*; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D047488:Retinoid X Receptors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D000199:Actins; D051836:COUP Transcription Factors; D004268:DNA-Binding Proteins; C503799:MYOG protein, human; D017570:MyoD Protein; C503801:Myog protein, mouse; D018008:Myogenin; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018168:Receptors, Retinoic Acid; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D014157:Transcription Factors; D004247:DNA; D009218:Myosins