CCAAT ENHANCER-BINDING PROTEIN-BETA IS NOT AFFECTED BY TETRACHLORODIBENZO-P-DIOXIN (TCDD) INHIBITION OF 3T3-L1 PREADIPOCYTE DIFFERENTIATION/

The differentiation of 3T3-L1 preadipocytes is induced by the coordina te activation of trans-acting factors in response to inducers. Dependi ng on the time of treatment, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD ) was effective in inhibiting 3T3-L1 preadipocyte differentiation and the expression of differentiation-dependent trans-acting factors. Base d on glycerol-3-phosphate dehydrogenase activity, the differentiation of 3T3-L1 cells was decreased by 70% in cells treated with TCDD before the induction of differentiation, 25% during induction, and not at al l after induction. This time-dependent inhibition of cell differentiat ion by TCDD was correlated with the levels of aryl hydrocarbon recepto r (AhR). TCDD treatment decreased the mRNA levels of C/EBP alpha and P PAR gamma 2 but did not affect the mRNA levels of RXR alpha and RAR al pha. Furthermore, TCDD did not change the mRNA or protein levels of C/ EBP beta, which is thought to play a role in inducing C/EBP alpha and PPAR gamma 2 expression. These results suggest that TCDD inhibited 3T3 -L1 preadipocyte differentiation through the AhR pathway, and the chan ge of C/EBP beta mRNA and protein was not involved in reducing mRNA ex pression of C/EBP alpha and PPAR gamma 2.