Regulation of the uncoupling protein-2 gene in INS-1 beta-cells by oleic acid.
Current evidence suggests that uncoupling protein-2 (UCP2) is a regulator of insulin secretion. It is also known that chronic exposure of pancreatic islets to free fatty acids (FFAs) blunts glucose-stimulated insulin secretion and is accompanied by elevated levels of UCP2. However, the mechanisms regulating expression of UCP2 in beta-cells are unknown. Here, we show that UCP2 mRNA and protein levels were increased after a 48-h exposure of INS-1(832/13) beta-cells to oleic acid (0.5 mm) by activation of the UCP2 promoter. Furthermore, progressive deletions of the mouse UCP2 promoter (from -7.3 kb to +12 bp) indicated that an enhancer region (-86/-44) was responsible for both basal and FFA-stimulated UCP2 gene transcription. This enhancer contains tightly clustered Sp1, sterol regulatory element (SRE), and double E-Box elements. While all three sequence motifs were required for basal activity of the UCP2 promoter, the mutations in either the SRE or the E-Box elements eliminated the response to FFAs. The SRE and sterol regulatory element binding protein-1 (SREBP1) appear to be crucial for the response of the UCP2 gene to FFAs, since overexpression of the nuclear forms of the SREBPs increased UCP2 promoter activity by 7-10-fold and restored the ability of E-Box mutants to respond to oleic acid. These data support a model in which SREBP is the major modulator of UCP2 gene transcription by FFA, while E-Box binding factors play a supportive role.
Medvedev
Alexander V
AV
Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina 27710, USA.
Robidoux
Jacques
J
Bai
Xu
X
Cao
Wenhong
W
Floering
Lisa M
LM
Daniel
Kiefer W
KW
Collins
Sheila
S
D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D007473:Ion Channels; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D019301:Oleic Acid / Q000494:pharmacology*; D017354:Point Mutation; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D014162:Transfection; D014475:Uncoupling Agents / Q000378:metabolism; D000071246:Uncoupling Protein 2
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D007473:Ion Channels; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D011994:Recombinant Proteins; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; C000604390:Ucp2 protein, mouse; D014475:Uncoupling Agents; D000071246:Uncoupling Protein 2; D019301:Oleic Acid