p38 Mitogen–Activated Protein Kinase Regulates Nuclear Receptor CAR that Activates the CYP2B6 Gene

Abstract

The constitutive active/androstane receptor (CAR) regulates hepatic drug metabolism by activating genes, such as cytochrome P450, and certain transferases. p38 Mitogen-activated protein kinase (MAPK) is highly activated in human primary hepatocytes but barely in human hepatoma cell lines including HepG2 cells. Liganded-CAR induced CYP2B6 mRNA in human primary hepatocytes far more effectively than in HepG2 cells ectopically expressing CAR. In the present study, we found that activation of p38 MAPK by anisomycin potentiated induction of CYP2B6 mRNA by CAR ligand in HepG2 cells to levels observed in ligandtreated human primary hepatocytes. siRNA knockdown of p38 MAPK abrogated the ability of anisomycin to synergistically induce CYP2B6 mRNA. In addition to CYP2B6, anisomycin cotreatment potentiated an increase in CYP2A7 and CYP2C9 mRNAs but not CYP3A4 or UDP-glucuronosyltransferase 1A1 mRNAs. Thus, activated p38 MAPK is required for liganded-CAR to selectively activate a set of genes that encode drug-metabolizing enzymes. Our present results suggest that CAR-mediated induction of these enzymes cannot be understood by ligand binding alone because the specificity and magnitude of induction are codetermined by a given cell signaling, such as p38 MAPK; both physiologic and pathophysiological states of cell signaling may have a strong impact in hepatic drug-metabolizing capability during treatments.

p38 MAP Kinase Links CAR Activation and Inactivation in the Nucleus via Phosphorylation at Threonine 38

“…1A). The results of a previous experiment with small-interfering RNA confirmed that this synergy was, in fact, mediated by p38 MAPK (Saito et al, 2013b). Upon activation, CAR binds the DNA sequence called PBREM within the CYP2B6 promoter to activate it.…”

“…In liver cells, phosphorylated p38 MAPK is accumulated in the nucleus to activate various transcription factors and protein kinases. We have recently demonstrated that p38 MAPK is essential for CAR to activate the cytochrome P450 2B6 (CYP2B6) gene in human hepatoma HepG2-derived cells (Saito et al, 2013b). In the present study, we revealed that p38 MAPK forms a complex with CAR to promote the CAR-mediated transcription in the nucleus.…”

Phenobarbital Meets Phosphorylation of Nuclear Receptors

“…CAR requires p38 MAPK activity to activate the CYP2B6 gene in HepG2 cells (Saito et al, 2013). Our recent study with mouse CARexpressing HepG2 cells and mouse primary hepatocytes demonstrated that, in the nucleus, p38 MAPK recruits CAR to the PBREM of the CYP2B promoter for activation and subsequently phosphorylates threonine 38 for inactivation (Hori et al, 2016).…”

Deciphering the roles of the constitutive androstane receptor in energy metabolism

“…lytic subunits, PPP1R16A, interacts with CAR at the cell membrane and prevents nuclear translocation of CAR, which is dependent on phosphatase activity [22] . Moreover, the mitogenactivated protein kinase (MAPK) p38 also regulates human CAR activity on the CYP2B6 gene [23] . This additional evidence adds further complexity to the phosphorylation-dependent nuclear translocation of CAR.…”