Hormonal Regulation of Gene Expression in Cultured Adipocytes1

Abstract

Cultured adipocytes provide a convenient system to examine the molecular basis of tissue-specific hormonal control of gene expression. We have examined the regulation of the S14 protein (17 kDa, 4.9 pI) in cultured adipocytes. The S14 protein serves as a model for lipogenic gene expression. Whereas both glucocorticoids (GC) and retinoic acid (RA) induce S14 gene transcription in adipocytes, neither hormone activates S14 gene transcription in preadipocytes. To investigate the molecular basis for this tissue-specific hormonal control, 3T3-L1 preadipocytes were stably transfected with S14-chloramphenicol acetyl transferase (CAT) fusion genes. Both GC and RA induced S14CAT activity in adipocytes, but not in preadipocytes, indicating that cis-linked targets for GC, RA, and tissue-specific control were located upstream from the 5′ end of the S14 gene. Analysis of the expression of CAT fusion genes containing canonical GC and RA response elements showed that endogenous GC and RA receptors activated these genes in both preadipocyte and adipocyte phenotypes. Thus, the GC and RA regulatory networks were operative in both cell types. Deletion analysis of the S14CAT fusion genes showed that the cis-linked elements that conferred the GC, RA, and tissue-specific control were located between −1,381 and −1,588 bp upstream from the 5′ end of the S14 gene. Gel shift and DNase I footprint analysis indicated that nuclear proteins interacting with this region were under tissue-specific control. We speculate that tissue-specific proteins modulate the activity of GC/RA regulated proteins that interact with the S14 GC/RA response region.