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 activators of protein kinases or phosphatases were assessed for their ability to modulate PB-induction of CYP2B and CYP3A mRNA expression. Rat hepatocytes 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 (cAMP)/protein kinase A pathway and the positive role of some serine/threonine protein phosphatases in the mechanism of PB-induction. The present data further suggested that Ca2+/calmodulin-dependent protein kinases II (independently of Ca2+) and extracellular signal-regulated kinases 1/2 (ERK1/2) might function respectively as positive and negative regulator in the PB-induction of CYP2B and CYP3A. In contrast, protein kinases C and phosphatidylinositol-3-kinase did not appear to be involved, while the role of tyrosine kinases remained unclear. We conclude that a complex network of phosphorylation/dephosphorylation events might be crucial for PB-induction of rat CYP2B and CYP3A.