Sequestration of thermogenic transcription factors in the cytoplasm during development of brown adipose tissue.
Transcription factors that regulate gene expression during adipogenesis also control the expression of genes of thermogenesis in brown adipose tissue, in particular, the mitochondrial uncoupling protein gene (Ucp1). There is evidence that a plasticity exists among adipocytes in which activation of the Ucp1 gene together with mitochondrial biogenesis can increase the brown adipocyte character of white fat. To understand this process, we have characterized the changes in transcription that occur in interscapular brown adipocytes during development. We have found dramatic reductions in both DNA-binding activity to probes and immunoreactive protein for peroxisome proliferator-activated receptor, retinoid X receptor, CCAAT/enhancer binding protein, and cAMP-response element-binding protein regulatory motifs in nuclear extracts when mice reach adulthood. Exposure of adult mice to the cold, which reactivates Ucp1 expression, leads to a re-accumulation of factors in the nucleus. We propose that transcription factors are sequestered in the cytoplasm as mice age under conditions of reduced thermogenesis. Changes in isoform sub-types for peroxisome proliferator-activated receptor-gamma and cAMP-response element-binding proteins indicate an additional level of control on gene expression during thermogenesis. The increased movement of the RIIbeta protein kinase A regulatory subunit into the nucleus with age suggests a mechanism for regulating the phosphorylation of transcription factors in the nucleus in response to the thermogenic requirements of the animal. Nuclear factor-kappaB has been used as a model to demonstrate that the nuclear localization of transcription factors in brown fat are reduced during post-natal development. Furthermore, it was found by immunofluorescence that adrenergic stimulation of primary adipocyte cultures causes an increase of both the protein kinase A catalytic alpha-subunit and nuclear factor-kappaB into the nucleus.
Rim
Jong S
JS
Pennington Biomedical Research Center, Baton Rouge, Louisiana 70808, USA.
Xue
Bingzhong
B
Gawronska-Kozak
Barbara
B
Kozak
Leslie P
LP
D021581:Active Transport, Cell Nucleus; D002001:Adipose Tissue, Brown / Q000378:metabolism*; D000818:Animals; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics; D002478:Cells, Cultured; D003080:Cold Temperature; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D007473:Ion Channels; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D024101:Mitochondrial Proteins; D010766:Phosphorylation; D012333:RNA, Messenger / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis; D022722:Thermogenesis / Q000502:physiology*; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism*; D000071256:Uncoupling Protein 1
D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; C497253:Cebpd protein, mouse; D017362:Cyclic AMP Response Element-Binding Protein; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C000604372:Ucp1 protein, mouse; D000071256:Uncoupling Protein 1; D051743:CCAAT-Enhancer-Binding Protein-delta; D017868:Cyclic AMP-Dependent Protein Kinases