A NOVEL 3T3-L1 PREADIPOCYTE VARIANT THAT EXPRESSES PPAR-GAMMA-2 AND RXR-ALPHA BUT DOES NOT UNDERGO DIFFERENTIATION

This report describes a novel adipocyte-like cell Line termed 3T3-L1/R B1 that tvas derived from preadipocyte cell line, 3T3-L1. The 3T3-L1/R B1 cells continued to divide after reaching confluence, formed foci, a nd constitutively expressed a low level of adipose fatty acid binding protein (A-FABP) mRNA However, 3T3L-1/RB cells did not undergo termina l differentiation as indicated by the failure of insulin and thiazolid endiones to induce the expression of A-FABP, lipoprotein lipase, and f atty acid synthase. We hypothesized that the 3T3-L1/RB1 variant did no t respond to differentiation stimuli because it did not express either peroxisomal proliferator activated receptor gamma 2 (PPAR gamma 2) or its heterodimer partner, retinoid X receptor alpha (RXR alpha). Surpr isingly, Western blots revealed that 3T3-L1/RB1 cells contained both P PAR gamma 2 and RXR alpha proteins at levels equal to or greater than that of the parent cell line. However, gel retardation assays using th e adipose response element from A-FABP and nuclear protein extracts fr om 3T3-L1/RB1 cells treated with insulin or pioglitazone revealed that nuclear protein extracts from 3T3-L1/RB1 cells had very little abilit y to bind the PPAR gamma 2 recognition sequence of the A-FABP gene. Th ese data suggest that the 3T3-L1/RB1 variant contains a mutation that may prevent ligand activation of PPAR gamma 2, and the subsequent conv ersion of 3T3-L1/RB1 cells to mature fat cells.