Previous investigations have indicated that de novo protein synthesis is a critical requirement for phenobarbital (PB) induction. We reexamined this issue in PBresponsive primary rat hepatocyte cultures using a broader array of protein synthesis inhibitors and experimental end points. Anisomycin, cycloheximide, emetine, puromycin, and puromycin aminonucleoside, a negative analog, were evaluated for their respective effects on protein synthesis and the PB-induction process. All of the inhibitors

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... effectively repressed de novo protein synthesis in the cells in a concentration-dependent manner. However, anisomycin only minimally effected PB induction, ascertained though the measure of CYP2B1, CYP2B2, and CYP3A1 mRNA levels. The inactive agent, puromycin aminonucleoside, produced marked repression of the PB-induction response. Results from further experiments demonstrated that these protein synthesis inhibitors stimulated rapid and differential phosphorylation of the stress-activated protein kinase/c-Jun kinase (SAPK/JNK) pathway, indicating nonselective actions on cellular processes. Puromycin aminonucleoside was without effect on these pathways, despite its efficacy as an inhibitor of PB induction. These results demonstrate that de novo protein synthesis is not a requirement for PB induction, nor is activation of the SAPK/JNK kinase cascade responsible for down-regulating PB responsiveness in primary hepatocytes.