We evaluated the role insulin plays in the regulation of hepatic S14 gene transcription using the streptozotocin-induced diabetic rat model. Nuclear run-on activity and mRNAS14 levels were reduced by more than 85% in diabetic rats compared to those in intact animals. After the administration of insulin, both S14 run-on activity and mRNAS14 levels were rapidly induced. Within 1 h of insulin administration, S14 run-on activity and mRNAS14 were induced 5- and 8-fold, respectively. S14 gene expression was restored to intact levels within 4 h, with overall increases in run-on activity and mRNAS14 of 7- and 20-fold, respectively. The full induction of mRNAS14 cannot be accounted for solely by activation of S14 gene transcription, implicating insulin effects at the posttranscriptional level. However, our results show that the principal target for insulin action on the S14 gene is transcriptional. Administration of dibutryl cAMP and theophylline fully blocked the insulin-mediated increase in S14 gene transcription, indicating that hepatic cAMP levels play a dominant negative role in regulating S14 gene transcription in vivo. Fructose administration to starved diabetic rats induced only a marginal 60% increase in mRNAS14 and S14 run-on activity within 4 h, while insulin plus fructose or insulin plus glucose fully restored S14 gene expression to intact levels within the same time period. Thus, dietary fructose or a metabolite generated from fructose alone cannot induce S14 gene transcription or mRNAS14 to intact levels in the starved diabetic rat. Acute effects of dietary carbohydrate on hepatic S14 gene transcription are insulin dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

No 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)

No abstract

No abstract