The role of C/EBPbeta in regulating UCP1 expressions in 3T3-L1 adipocytes

Liu, Qian (2012) The role of C/EBPbeta in regulating UCP1 expressions in 3T3-L1 adipocytes. PhD thesis, University of Nottingham.

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Abstract

Uncoupling protein 1 (UCP1) is essential for non-shivering thermogenesis in brown adipose tissue (BAT) by dissipating proton-motive force to stimulate maximum mitochondrial respiration. cAMP-dependent protein kinase induction of UCP1, as well as the PPAR coactivator1α (PGC1α), is a typical characteristic in BAT but not in white adipose tissue (WAT). Previous work demonstrated that the overexpression of CCAAT/Enhancer Binding Protein β (C/EBPβ) could rescue the cAMP-induced PGC1α and UCP1 expression in white preadipocytes 3T3-L1 cell line, indicating a key regulatory role of C/EBPβ in brown adipogenesis. The overall aim of this study was to examine the role of C/EBPβ overexpression in regulating the transcription of UCP1 in 3T3-L1 white preadipocytes to transform them to a more brown-like cell phenotype.

Tetracycline inducible (Tet on) lentiviral, adipose-specific expression vectors for overexpressing C/EBPβ (or the control Luciferase-GFP) gene were constructed with the pLenti6 lentiviral vector backbone with TRE tight and rtTA advance regulatory elements. In the absence of doxycycline there was low basal expression from the vectors and a dose-dependent, doxycycline-induced transient, adipose-specific overexpression was observed in 3T3-L1 preadipocytes. Transduction of the pLenti6 positive control luciferase-RFP vector was successfully achieved but the C/EBPβ or LucGFP vectors constructed failed to produce highly infectious lentiviral particles, possibly due to the large size of insert which challenged the limit of the pLenti6 vector backbone. Therefore a stable inducible, adipose-specific, 3T3-L1 line overexpressing C/EBPβ was not achieved.

Transient overexpression of C/EBPβ and PRDM16 significantly increased the transcriptional activity of UCP1 promoter in the presence of forskolin in 3T3-L1 cells without stimulating PGC1α promoter activity, implying a PGC1α-independent manner of activating UCP1 transcription in 3T3-L1s. C/EBPβ overexpression alone activated the PGC1α promoter in HIB-1B and Cos7 cells but not in 3T3-L1 cells, indicating the lack of some activators in 3T3-L1 or a potential 3T3-L1 specific repressive mechanism. Co-overexpression of C/EBPβ and PPARγ in 3T3-L1 markedly stimulated the PGC1α promoter in response to rosiglitazone and increased the UCP1 promoter activity in the presence of rosiglitazone and forskolin. This result suggests that PPARγ could make up for the lack of activator or release the 3T3-L1 repressive mechanism and mediated a PGC1α-dependent manner of activating UCP1 together with C/EBPβ in 3T3-L1 cells. Further studies demonstrated that both CRE and PPRE elements were indispensible in this PGC1α-dependent pathway of activating UCP1 promoter in 3T3-L1 cells. The results suggest that C/EBPβ and PPARγ cooperate to induce UCP1 expression in 3T3-L1 cells stimulated by PPARγ agonist and cAMP.

Item Type:Thesis (PhD)
Supervisors:Lomax, M.
Hill, P.J.
Faculties/Schools:UK Campuses > Faculty of Science > School of Biosciences
ID Code:2469
Deposited By:Dr Qian Liu
Deposited On:16 Nov 2012 11:28
Last Modified:16 Nov 2012 11:30

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