title: IRE1α-XBP1 is a novel branch in the transcriptional regulation of Ucp1 in brown adipocytes.
abstract: The unfolded protein response (UPR) not only resolves endoplasmic reticulum (ER) stress, but also regulates cellular physiological functions. In this study, we first linked the UPR to the physiological roles of brown adipose tissue (BAT). BAT is one of the tissues that control energy homeostasis in the body. Brown adipocytes are able to dissipate energy in the form of heat owing to their mitochondrial protein, uncoupling protein 1 (UCP1). We found that one of the UPR branches, the IRE1α-XBP1 pathway, was activated during the transcriptional induction of Ucp1. Inhibiting the IRE1α-XBP1 pathway reduced the induction of Ucp1 expression. However, the activation of the IRE1α-XBP1 pathway by ER stress never upregulated Ucp1. On the other hand, the activation of protein kinase A (PKA) induced Ucp1 transcription through the activation of IRE1α-XBP1. The inhibition of PKA abrogated the activation of IRE1α-XBP1 pathway, while the inhibition of a p38 mitogen activated protein kinase (p38 MAPK), which is one of the downstream molecules of PKA, never suppressed the activation of IRE1α-XBP1 pathway. These data indicate that PKA-dependent IRE1α-XBP1 activation is crucial for the transcriptional induction of Ucp1 in brown adipocytes, and they demonstrate a novel, ER stress -independent role of the UPR during thermogenesis.
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Asada
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Soshi
authors.initials: S
authors.lastname: Kanemoto
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Matsuhisa
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Hino
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Min
authors.initials: M
authors.lastname: Cui
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Xiang
authors.initials: X
authors.lastname: Cui
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kaneko
authors.affiliation: Department of Biochemistry, Institute of Biomedical &Health Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Imaizumi
mesh_terms: D052437:Adipocytes, Brown / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D004722:Endoribonucleases / Q000502:physiology*; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008810:Mice, Inbred C57BL; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D000071701:Regulatory Factor X Transcription Factors; D015398:Signal Transduction; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000071256:Uncoupling Protein 1; D056811:Unfolded Protein Response; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; C000604372:Ucp1 protein, mouse; D000071256:Uncoupling Protein 1; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse; C510185:Ern1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D004722:Endoribonucleases