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Insulin Suppresses the Induction of CYP2B1 and CYP2B2 Gene Expression by Phenobarbital in Adult Rat Cultured Hepatocytes

https://doi.org/10.1006/bbrc.1996.1777Get rights and content

Abstract

The effect of insulin on the phenobarbital (PB)-induced gene expression of CYP2B1 and CYP2B2 (CYP2B1/2B2) in adult rat hepatocytes was investigated. Insulin, which has been regarded as an essential hormone for primary hepatocytes, was found to strongly suppress the induction of CYP2B1/2B2 gene expression in hepatocytes cultured on EHS-gel. Although the induction by PB was not seen in monolayer hepatocytes cultured on type I collagen under standard culture conditions, the induced expression of the CYP2B1/2B2 gene was observed in monolayer hepatocytes by removing insulin from the medium. Further, we succeeded in maintaining the prolonged induction of CYP2B1/2B2 by PB in monolayer hepatocytes by using a medium containing dexamethasone but not insulin. Since the PB-induced UDP-glucuronosyltransferase gene expression was not reduced by insulin, the suppressive effect of insulin was considered to be specific to the CYP2B1/2B2 gene. These results demonstrate that insulin in media masks the PB-induced expression of the CYP2B1/2B2 gene in conventional monolayer hepatocytes and that the use of insulin-free media with primary hepatocytes provides a useful tool for investigating the molecular mechanism of CYP2B1/2B2 gene expression.

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Abbreviations: apo, apolipoprotein; ANOVA, analysis of variance; CYP, cytochrome P-450; Dex, dexamethasone; EHS, Engelbreth-Holm-Swarm; IRS, insulin responsive sequence; IRS1, insulin receptor substrate 1; PB, phenobarbital; PEPCK, phosphoenolpyruvate carboxykinase; PI-3 kinase, phosphatidylinositol-3 kinase; TAT, tyrosine aminotransferase; TIC, type I collagen; UGT, UDP-glucuronosyltransferase.

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To whom correspondence and reprint requests should be addressed. Fax: +81-52-789-5050. E-mail: hirooda@ agr.nagoya-u.ac.jp.

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