Endrin inhibits adipocyte differentiation by selectively altering expression pattern of CCAAT enhancer binding protein-alpha in 3T3-L1 cells

The effects of selected chlorinated cyclodiene pesticides on the adipocyte differentiation process were examined using the 3T3-L1 adipocyte model in v itro. Endrin was found to cause a dose-dependent inhibition of adipocyte di fferentiation in 3T3-L1 cells. Aldrin and dieldrin were less potent than en drin in interfering with the adipogenic process. Endrin's inhibitory effect was effective only when the pesticide was present in the medium during the first 48 h after exposure of 3T3-L1 cells to adipogenic inducers. Immunobl ots analysis revealed that endrin caused a dose-dependent, selective inhibi tion of the intracellular levels of CCAAT enhancer binding protein (C/EBP)a lpha without altering the expression patterns of C/EBP beta or C/EBP delta along the differentiation. Supershift analysis showed that DNA-binding capa city of C/EBP alpha was affected most by endrin treatment. Endrin also caus ed a decrease in the elevation of the adipogenic factor peroxisome prolifer ator-activated receptor (PPAR)gamma elicited by the adipogenic inducers. Ho wever, the cotreatment with troglitazone, a thiazolidinedione known to acti vate PPAR gamma, did not suppress the antiadipogenic action of endrin, indi cating that its direct action site is not PPAR gamma receptor. Endrin also altered the pattern of activation of nuclear factor-kappa B, a factor activ ated by 12-O-tetradecanoylphorbol-13-acetate and tumor necrosis factor-alph a, which are known to interfere with adipocyte differentiation. Thus, endri n inhibited the normal decrease in nuclear factor-kappa B-DNA binding obser ved as cells are acquiring the adipocyte phenotype at a late stage of diffe rentiation. Our results suggest that endrin inhibits adipocyte differentiat ion through the specific suppression of C/EBP alpha.