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This report describes a novel adipocyte-like cell line termed 3T3-L1/RB1 that was derived from preadipocyte cell line, 3T3-L1. The 3T3-L1/RB1 cells continued to divide after reaching confluence, formed foci, and constitutively expressed a low level of adipose fatty acid binding protein (A-FABP) mRNA. However, 3T3L-1/RB cells did not undergo terminal differentiation as indicated by the failure of insulin and thiazolidendiones to induce the expression of A-FABP, lipoprotein lipase, and fatty acid synthase. We hypothesized that the 3T3-L1/RB1 variant did not respond to differentiation stimuli because it did not express either peroxisomal proliferator activated receptor γ2 (PPARγ2) or its heterodimer partner, retinoid X receptor α (RXRα). Surprisingly, Western blots revealed that 3T3-L1/RB1 cells contained both PPARγ2 and RXRα proteins at levels equal to or greater than that of the parent cell line. However, gel retardation assays using the adipose response element from A-FABP and nuclear protein extracts from 3T3-L1/RB1 cells treated with insulin or pioglitazone revealed that nuclear protein extracts from 3T3-L1/RB1 cells had very little ability to bind the PPARγ2 recognition sequence of the A-FABP gene. These data suggest that the 3T3-L1/RB1 variant contains a mutation that may prevent ligand activation of PPARγ2, and the subsequent conversion of 3T3-L1/RB1 cells to mature fat cells.—Baillie, R. A., X. Sha, P. Thuillier, and S. D. Clarke. A novel 3T3-L1 preadipocyte variant that expresses PPARγ2 and RXRα but does not undergo differentiation. J. Lipid Res. 1998. 39: 2048–2053. |
