Hormonal Regulation of the S14 Gene in 3T3-F442A Cells

Abstract

3T3-F442A cells differentiate from preadipocytes to adipocytes when cultured in medium containing fetal calf serum and insulin. We examined the regulation of the S14 gene in 3T3-F442A preadipocytes and adipocytes to determine whether these cells would be a good in vitro model to define the regulation and function of the S14 protein (17,000 Mr; 4.9 pI). Expression of mRNAs14 (1.12 kilobases) in mouse liver is regulated by both thyroid hormone (T3) and glucocorticoids. Accordingly, we examined the T3 and glucocorticoid regulation of S14 gene expression in 3T3-F442A cells. Neither T3 or the glucocorticoid agonist, dexamethasone (DEX) induced mRNAs14 in 3T3-F442A fibroblasts. While DEX induced mRNAs14 greater than 60-fold in 3T3-F442A adipocytes after a 72-h treatment, T3 was found to have no effect on S14 gene expression in adipocytes. These results indicate: 1) that S14 gene expression is dependent on the differentiation state of 3T3-F442A cells; and 2) that of the two hormones regulating mRNAs14 expression in vivo, only the glucocorticoid regulatory mechanism is operative in 3T3-F442A adipocytes. Characterization of the glucocorticoid-mediated regulation of S14 gene expression showed that DEX induced mRNAs14 significantly within 30 min, but required 72 h of hormone treatment to reach maximal levels of expression. The glucocorticoid-mediated increase in mRNAs14 was due to activation of S14 gene transcription. While glucocorticoid analogs induced mRNAs14, mineralocorticoids and sex steroids failed to induce mRNAs14 in adipocytes. These studies suggest that glucocorticoids act directly on the S14 gene through the glucocorticoid receptor to regulate S14 gene expression in 3T3-F442A.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyunsaturated fatty acids inhibit S14 gene transcription in rat liver and cultured hepatocytes.

“…S14 gene transcription is induced by 3,5,3'-triiodothyronine (T3) (10,11), glucocorticoids (12,13), retinoic acid (14,15), insulin, carbohydrate (16)(17)(18)(19), and tissue-specific factors (20) and suppressed by factors that elevate hepatic cAMP levels (16). While the molecular basis for PUFA-mediated inhibition of gene transcription remains unclear, our understanding of the regulation of S14 gene expression makes this an attractive model to…”

“…Liver, epididymal fat, and hepatocyte total RNA were isolated (24) and used for measurement of mRNAs coding for S14, 1-actin, and phosphoenolpyruvate carboxykinase (PepCk) by Northern and dotblot analyses (10,12). Hepatic nuclei were isolated for run-on gene transcription analysis (17 (18,26).…”

The CCAAT Box Binding Factor, NF-Y, Is Required for Thyroid Hormone Regulation of Rat Liver S14 Gene Transcription

“…T 3 induces mRNA S14 in liver, lactating mammary gland, and white adipose tissue but not cultured 3T3-L1 or 3T3-F442A adipocytes (25,33,34). Instead, glucocorticoids and retinoic acid replace T 3 as the major transcriptional activator of S14 in cultured fat cells (33,34). In brain, heart, kidney, lung, spleen, testes, and pituitary, mRNA S14 is expressed at Ͻ1% of the liver level and is not regulated by T 3 (14).…”

“…Hepatic S14 gene transcription is induced by T 3 , dietary carbohydrate, and insulin (14,15,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). Starvation, diabetes, polyunsaturated fatty acids, and elevation of intracellular cAMP suppress hepatic S14 gene transcription (26,31,32).…”

“…Starvation, diabetes, polyunsaturated fatty acids, and elevation of intracellular cAMP suppress hepatic S14 gene transcription (26,31,32). T 3 induces mRNA S14 in liver, lactating mammary gland, and white adipose tissue but not cultured 3T3-L1 or 3T3-F442A adipocytes (25,33,34). Instead, glucocorticoids and retinoic acid replace T 3 as the major transcriptional activator of S14 in cultured fat cells (33,34).…”