Regulation of phenobarbital-induction of CYP2B and CYP3A genes in rat cultured hepatocytes: involvement of several serine/threonine protein kinases and phosphatases

We investigated the involvement of diverse protein kinases and phosphatases in the transduction pathways elicited by phenobarbital (PB), a well-known inducer of some hepatic cytochromes P450 (CYP). Different inhibitors or act ivators of protein kinases or phosphatases were assessed for their ability to modulate PB-induction of CYP2B and CYP3A mRNA expression. Rat hepatocyte s in primary culture were treated with the test compounds one hour prior to , and then continuously, in the absence or presence of 1 mmol/L PB for 24 h . By northern blot analysis of CYP2B1/2 and 3A1/2 gene expression, we first confirmed the negative role of the adenosine 3':5' cyclic monophosphate (c AMP)/protein kinase A pathway and the positive role of some serine/threonin e protein phosphatases in the mechanism of PB-induction. The present data f urther suggested that Ca2+/calmodulin-dependent protein kinases II (indepen dently of Ca2+) and extracellular signal-regulated kinases 1/2 (ERK1/2) mig ht function respectively as positive and negative regulator in the PB-induc tion of CYP2B and CYP3A. In contrast, protein kinases C and phosphatidylino sitol-3-kinase did not appear to be involved, while the role of tyrosine ki nases remained unclear. We conclude that a complex network of phosphorylati on/dephosphorylation events might be crucial for PB-induction of rat CYP2B and CYP3A.