TY - JOUR
T1 - Cytosolic and nuclear distribution of PPAR-γ2 in differentiating 3T3- L1 preadipocytes
AU - Thuillier, Philippe
AU - Baillie, Rebecca
AU - Sha, Xiaoming
AU - Clarke, Steven D.
N1 - Copyright:
Copyright 2007 Elsevier B.V., All rights reserved.
PY - 1998
Y1 - 1998
N2 - In light of the pivotal role that PPARγ2 plays in the expression of fat specific genes (e.g., A-FABP), we have examined the hypothesis that a rise in PPARγ2 protein is required for the expression of A-FABP, and that the acceleration of fat cell differentiation by the thiazolidinedione agent, pioglitazone (PIOG), reflects an increase in the abundance of PPARγ2 mRNA and protein. Western analyses surprisingly revealed that undifferentiated 3T3-L1 fibroblasts contained significant levels of PPARγ2 protein; that the amount of total cellular PPARγ2 only increased 2-fold during differentiation; and that the levels of PPARγ2 protein and mRNA were not increased by PIOG even though fat cell differentiation was accelerated by PIOG as revealed by a 20-fold increase in A-FABP expression. Cell fractionation studies revealed that PPARγ2 was evenly distributed between the cytosolic and nuclear compartments in both undifferentiated and differentiating 3T3-L1 cells. Immunocytochemical studies with a PPARγ2- specific antibody indicated that PPARγ2 was diffusely distributed throughout the cytosol of undifferentiated 3T3-L1 cells, but as the differentiation progressed, the PPARγ2 became focused around the developing lipid droplets. In contrast to PPARγ2, undifferentiated 3T3-L1 cells contained no measurable quantities of RXRα, but once fat cell differentiation was initiated by treatment with IBMX and dexamethasone, the cellular content of RXRα increased several fold. The rise in RXRα content paralleled the induction of A-FABP, but the expression of RXRα was not enhanced by PIOG. Although the amount of PPARγ2 and RXRα was unaffected by PIOG, gel shift assays revealed that PIOG stimulated PPARγ2/RXRα binding to the adipose response element of A-FABP by 5-fold in less than 12 h. Apparently, RXRα rather than PPARγ2 is the pivotal trans-factor essential for the initiation of terminal fat cell differentiation. However, the high cytosolic content of PPARγ2 and its association with the lipid droplet of differentiating 3T3-L1 cells suggests PPARγ2 may possess a cytosolic function in the developing fat cell.
AB - In light of the pivotal role that PPARγ2 plays in the expression of fat specific genes (e.g., A-FABP), we have examined the hypothesis that a rise in PPARγ2 protein is required for the expression of A-FABP, and that the acceleration of fat cell differentiation by the thiazolidinedione agent, pioglitazone (PIOG), reflects an increase in the abundance of PPARγ2 mRNA and protein. Western analyses surprisingly revealed that undifferentiated 3T3-L1 fibroblasts contained significant levels of PPARγ2 protein; that the amount of total cellular PPARγ2 only increased 2-fold during differentiation; and that the levels of PPARγ2 protein and mRNA were not increased by PIOG even though fat cell differentiation was accelerated by PIOG as revealed by a 20-fold increase in A-FABP expression. Cell fractionation studies revealed that PPARγ2 was evenly distributed between the cytosolic and nuclear compartments in both undifferentiated and differentiating 3T3-L1 cells. Immunocytochemical studies with a PPARγ2- specific antibody indicated that PPARγ2 was diffusely distributed throughout the cytosol of undifferentiated 3T3-L1 cells, but as the differentiation progressed, the PPARγ2 became focused around the developing lipid droplets. In contrast to PPARγ2, undifferentiated 3T3-L1 cells contained no measurable quantities of RXRα, but once fat cell differentiation was initiated by treatment with IBMX and dexamethasone, the cellular content of RXRα increased several fold. The rise in RXRα content paralleled the induction of A-FABP, but the expression of RXRα was not enhanced by PIOG. Although the amount of PPARγ2 and RXRα was unaffected by PIOG, gel shift assays revealed that PIOG stimulated PPARγ2/RXRα binding to the adipose response element of A-FABP by 5-fold in less than 12 h. Apparently, RXRα rather than PPARγ2 is the pivotal trans-factor essential for the initiation of terminal fat cell differentiation. However, the high cytosolic content of PPARγ2 and its association with the lipid droplet of differentiating 3T3-L1 cells suggests PPARγ2 may possess a cytosolic function in the developing fat cell.
KW - Fatty acid binding protein
KW - Gene expression
KW - Insulin
KW - PPARγ2
KW - Pioglitazone
KW - RXRα
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M3 - Article
C2 - 9831621
AN - SCOPUS:0032433287
SN - 0022-2275
VL - 39
SP - 2329
EP - 2338
JO - Journal of lipid research
JF - Journal of lipid research
IS - 12
ER -