Regulation of expression of cytochrome P-450 by hormonal factor in primary cultured rat hepatocytes.

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SummaryWe used primary culture of hepatocytes to investigate a direct effect of hormonal factors on the expression at the molecular level of rat hepatic cytochrome P-450. The levels of a variety of hepatic cytochrome P-450 are rapidly decreased during primary culture of hepatocytes. We used, therefore,matrigel to prevent the decrease of P-450s and we successed induction of P-450 2B1(CYP2B1)by phenobarbital(PB)in the hepatocytes. Thyroid hormone showed a marked inhibition of PB induction. In addition,growth hormone showed synergistic inhibition with thyroid hormone of PB induction. On the other hand,dehydroepiandrosterone antagonized the induction by growth hormone. By using derivatives of phenobarbital, we showed the structure specificity of barbiturates on the potency of induction of each cytochrome P-450,such as CYP2B1, CYP2B2 and CYP3A. We succeeded in an effective transfection of P-450 gene by Ca^<++>-coprecipition method. We used chloramphenicol-acetyltransferase gene as a receptor gene and the mechanism of induction with phenobarbital was investigated. We revealed one position,which is related with PB induction and locates near TATA box of CYP2B1 gene. Moreover,we observed five sequences of glucocorticoid responsive element(GRE)in CYP3A2 gene 6betaA and two sequences related with hepatic nuclear factor 4(HNF-4). The mechanism of expression of by dexamethasone is now under investigation by using a variety of lengthes of CYP3A2(6betaA)-CAT fusion gene.