LOCALIZATION OF A NEGATIVE THYROID HORMONE-RESPONSE REGION IN HEPATICSTEAROYL-COA DESATURASE GENE-1

The effect of thyroid hormone on stearoyl-CoA desaturase gene 1 (SCD1) expression was investigated in mouse liver. Daily injections of 15 mu g triiodothyronine (T-3)/100 g body weight to hypothyroid mice result ed in repression of SCD1 mRNA levels by more than 50% in 48 hours and up to 65% in 6 clays. Transient cotransfections were performed with an expression vector for T-3 receptor alpha (T3R alpha) in HepG2 cells u sing chimeric reporter gene constructs of the SCD1 5'-flanking region. Transcriptional repression of the SCD1 putative promoter was observed upon treatment with 100 nM: Ts when cotransfected with T3R alpha, but not without cotransfection of receptor. Transient gene expression stu dies localized a T-3 response region to a 70-bp sequence in the SCD1 p utative promoter. Eliminating the TATA box and an AP-2 binding site, D NA mobility shift analysis demonstrated specific binding of in vivo nu clear protein from mouse liver nuclear extract to a 43-bp sequence. DN A mobility shift with purified T3R alpha confirmed the presence of a T -3 receptor binding site in this thyroid hormone-responsive region, Th ese data indicate that SCD1 contains a negative T-3 response region in its proximal promoter. (C) 1997 Academic Press.