IDENTIFICATION OF A TRANSCRIPTIONAL REPRESSOR DOWN-REGULATED DURING PREADIPOCYTE DIFFERENTIATION

During differentiation of 3T3-L1 preadipocytes into adipocytes, the transcription of adipocyte genes, including the stearoyl-CoA desaturase 2 (SCD2) gene, is activated. Transfection experiments with chimeric SCD2 promoter-chloramphenicol acetyltransferase (CAT) reporter gene constructs revealed a preadipocyte repressor element (PRE) capable of repressing transcription of the reporter gene in preadipocytes but not in adipocytes. DNase I protection and gel retardation analyses were used to localize the PRE site between nucleotides -435 and -410 of the SCD2 promoter and to identify a nuclear PRE binding protein present at high levels in preadipocytes and HeLa cells but lacking or inactive in adipocytes. Southwestern blot analysis indicated that the PRE binding protein has an apparent molecular mass of almost-equal-to 58 kDa. A single copy of the PRE site, inserted upstream of the simian virus 40 enhancer/promoter of pSV2CAT, was capable of strongly repressing transcription of the reporter gene in preadipocytes and HeLa cells but not in adipocytes. Taken together these results suggest that the PRE site and binding protein may regulate transcription of SCD2 and possibly other adipocyte genes by inhibiting their transcription in preadipocytes.