Molecular mechanism of 1,25-dihydroxyvitamin D3 inhibition of adipogenesis in 3T3-L1 cells.
We have investigated the molecular mechanism whereby 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] inhibits adipogenesis in vitro. 1,25(OH)2D3 blocks 3T3-L1 cell differentiation into adipocytes in a dose-dependent manner; however, the inhibition is ineffective 24-48 h after the differentiation is initiated, suggesting that 1,25(OH)2D3 inhibits only the early events of the adipogenic program. Treatment of 3T3-L1 cells with 1,25(OH)2D3 does not block the mitotic clonal expansion or C/EBPbeta induction; rather, 1,25(OH)2D3 blocks the expression of C/EBPalpha, peroxisome proliferator-activated receptor-gamma (PPARgamma), sterol regulatory element-binding protein-1, and other downstream adipocyte markers. The inhibition by 1,25(OH)2D3 is reversible, since removal of 1,25(OH)2D3 from the medium restores the adipogenic process with only a temporal delay. Interestingly, although the vitamin D receptor (VDR) protein is barely detectable in 3T3-L1 preadipocytes, its levels are dramatically increased during the early phase of adipogenesis, peaking at 4-8 h and subsiding afterward throughout the rest of the differentiation program; 1,25(OH)2D3 treatment appears to stabilize the VDR protein levels. Consistently, adenovirus-mediated overexpression of human (h) VDR in 3T3-L1 cells completely blocks the adipogenic program, confirming that VDR is inhibitory. Inhibition of adipocyte differentiation by 1,25(OH)2D3 is ameliorated by troglitazone, a specific PPARgamma antagonist; conversely, hVDR partially suppresses the transacting activity of PPARgamma but not of C/EBPbeta or C/EBPalpha. Moreover, 1,25(OH)2D3 markedly suppresses C/EBPalpha and PPARgamma mRNA levels in mouse epididymal fat tissue culture. Taken together, these data indicate that the blockade of 3T3-L1 cell differentiation by 1,25(OH)2D3 occurs at the postclonal expansion stages and involves direct suppression of C/EBPalpha and PPARgamma upregulation, antagonization of PPARgamma activity, and stabilization of the inhibitory VDR protein.
Kong
Juan
J
Dept. of Medicine, Univ. of Chicago, 5841 S. Maryland Ave., Chicago, IL 60637, USA.
Li
Yan Chun
YC
D041721:3T3-L1 Cells; D050156:Adipogenesis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics; D002117:Calcitriol / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002839:Chromans / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D008071:Lipoprotein Lipase / Q000235:genetics; D051379:Mice; D047495:PPAR gamma / Q000819:agonists / Q000235:genetics; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D047488:Retinoid X Receptors / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D045162:Thiazolidinediones / Q000494:pharmacology; D050656:Transcription Factor AP-2 / Q000235:genetics; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology; D000077288:Troglitazone; D014815:Vitamins / Q000494:pharmacology
D000970:Antineoplastic Agents; D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D002839:Chromans; D047495:PPAR gamma; D018167:Receptors, Calcitriol; D047488:Retinoid X Receptors; D045162:Thiazolidinediones; D050656:Transcription Factor AP-2; D014815:Vitamins; D014212:Tretinoin; D008071:Lipoprotein Lipase; D002117:Calcitriol; D000077288:Troglitazone