LOCALIZATION OF A POLYUNSATURATED FATTY-ACID RESPONSE REGION IN STEAROYL-COA DESATURASE GENE-1

Polyunsaturated fatty acids (PUFA) repress stearoyl-CoA desaturase gen e 1 (SCD1) expression in liver and adipose tissues. We used HepG2 cell s to localize genetic regulatory elements for PUFA in the SCD1 5'-flan king region. A chimeric reporter gene construct containing the 4.3 kb SCD1 putative promoter was transiently transfected into HepG2 cells, w hich were then treated with various fatty acids. We observed greater t han 60% repression of transcription with 18:3n - 3 and 75% repression with 20:4n - 6 and 20:5n - 3. No significant change was seen with 18:0 . Using smaller SCD1 chimeric constructs, we localized the genetic reg ulatory region to a 237 bp sequence within the SCD1 proximal promoter. DNA mobility shift analysis with HepG2 and mouse liver nuclear extrac ts demonstrated specific binding of nuclear proteins to this region. M obility shift analysis with nuclear extract from 3T3-L1 adipocytes sho wed a similar pattern of protein binding. Competitive DNA mobility shi ft analysis identified a 60 bp region containing sites that specifical ly bind and compete for nuclear proteins. This region conferred respon siveness to PUFA when placed in a heterologous promoter. A homologous region in the stearoyl-CoA desaturase gene 2 (SCD2) promoter also medi ated PUFA-specific repression in transfection experiments, These data suggest that a common transcriptional mechanism may exist in liver and adipose tissues for inhibition of lipogenesis by PUFA. (C) 1997 Elsev ier Science B.V.