title: Regulation of SREBP1c gene expression in skeletal muscle: role of retinoid X receptor/liver X receptor and forkhead-O1 transcription factor.
abstract: Sterol regulatory element binding protein 1c (SREBP1c) is a master regulator of lipogenic gene expression in liver and adipose tissue, where its expression is regulated by a heterodimer of nuclear receptor-type transcription factors retinoid X receptor-alpha (RXRalpha) and liver X receptor-alpha (LXRalpha). Despite the potential importance of SREBP1c in skeletal muscle, little is known about the regulation of SREBP1c in that setting. Here we report that gene expression of RXRgamma is markedly decreased by fasting and is restored by refeeding in mouse skeletal muscle, in parallel with changes in gene expression of SREBP1c. RXRgamma or RXRalpha, together with LXRalpha, activate the SREBP1c promoter in vitro. Moreover, transgenic mice overexpressing RXRgamma specifically in skeletal muscle showed increased gene expression of SREBP1c with increased triglyceride content in their skeletal muscles. In contrast, transgenic mice overexpressing the dominant-negative form of RXRgamma showed decreased SREBP1c gene expression. The expression of Forkhead-O1 transcription factor (FOXO1), which can suppress the function of multiple nuclear receptors, is negatively correlated to that of SREBP1c in skeletal muscle during nutritional change. Moreover, transgenic mice overexpressing FOXO1 specifically in skeletal muscle exhibited decreased gene expression of both RXRgamma and SREBP1c. In addition, FOXO1 suppressed RXRalpha/LXRalpha-mediated SREBP1c promoter activity in vitro. These findings provide in vivo and in vitro evidence that RXR/LXR up-regulates SREBP1c gene expression and that FOXO1 antagonizes this effect of RXR/LXR in skeletal muscle.
authors.affiliation: Department of Molecular Medicine and Metabolism, Medical Research Institute, Tokyo Medical and Dental University, 2-3-10 Kanda-surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
authors.forename: Yasutomi
authors.initials: Y
authors.lastname: Kamei
authors.forename: Shinji
authors.initials: S
authors.lastname: Miura
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Suganami
authors.forename: Fumiko
authors.initials: F
authors.lastname: Akaike
authors.forename: Sayaka
authors.initials: S
authors.lastname: Kanai
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sugita
authors.forename: Aki
authors.initials: A
authors.lastname: Katsumata
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Aburatani
authors.forename: Terry G
authors.initials: TG
authors.lastname: Unterman
authors.forename: Osamu
authors.initials: O
authors.lastname: Ezaki
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ogawa
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D004435:Eating / Q000502:physiology; D005215:Fasting / Q000378:metabolism; D005260:Female; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D000071518:Liver X Receptors; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D009928:Organ Specificity; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D047491:Retinoid X Receptor gamma / Q000502:physiology*; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D047491:Retinoid X Receptor gamma; D051780:Sterol Regulatory Element Binding Protein 1