title: Identification of transcriptional targets for Six5: implication for the pathogenesis of myotonic dystrophy type 1.
abstract: Myotonic dystrophy 1 (DM1) is the most common inherited neuromuscular disease in adults. The disorder, characterized by myotonia, muscle wasting and weakness, cataract, insulin resistance, and mental impairment, is caused by the expansion of an unstable CTG repeat located in the 3' untranslated region of DMPK. The repeat expansion suppresses the expression of the homeobox gene SIX5. We describe here an experimental system to identify downstream transcriptional targets of mouse Six5 in order to elucidate the role of SIX5 in the pathogenesis of DM1 and development. By overexpressing a constitutively active Six5 (VP16-Six5wt) using adenovirus-mediated gene transfer in P19 cells and subsequent expression profiling using cDNA arrays, 21 genes, whose expression level increased by the treatment, were identified as potential target genes. Genes expressed in the somites, skeletal muscles, brain and meninges comprised the majority, suggesting the role of Six5 in the development and function of mesodermal tissues and brain. We provide evidence that Igfbp5 encoding a component of IGF signaling is a direct Six5-target. Moreover, the overall expression level of Igfbp5 was decreased in Six5-deficient mouse fibroblasts, and the response of human IGFBP5 to MyoD-induced muscle conversion was altered in cells of DM1 patients. Our results not only identify Six5 as an activator that directs Igfbp5 expression but also suggest that reduced SIX5 expression in DM1 might contribute to specific aspects of the DM1 phenotype.
authors.affiliation: Department of Biology, Jichi Medical School, Minamikawachi, Tochigi 329-0498, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Sato
authors.forename: Miwa
authors.initials: M
authors.lastname: Nakamura
authors.forename: Diane H
authors.initials: DH
authors.lastname: Cho
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Tapscott
authors.forename: Hidenori
authors.initials: H
authors.lastname: Ozaki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kawakami
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D019556:COS Cells / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D005347:Fibroblasts / Q000378:metabolism; D020869:Gene Expression Profiling; D017405:Herpes Simplex Virus Protein Vmw65 / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009223:Myotonic Dystrophy / Q000235:genetics* / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D017931:DNA Primers; D017405:Herpes Simplex Virus Protein Vmw65; D018398:Homeodomain Proteins; D018975:Insulin-Like Growth Factor Binding Protein 5; C106687:SIX5 protein, human; C486344:Six5 protein, mouse; D007335:Insulin-Like Growth Factor II