Protein Kinase N Family Negatively Regulates Constitutive Androstane Receptor-mediated Transcriptional Induction of Cytochrome P450 2b10 in the Livers of Mice.

In receptor-type transcription factors-mediated cytochrome P450 (P450)s induction, few studies have attempted to clarify the roles of protein kinase N (PKN) in the transcriptional regulation of P450s. This study aimed to examine the involvement of PKN in the transcriptional regulation of P450s by receptor-type transcription factors, including the aryl hydrocarbon receptor, constitutive androstane receptor (CAR), and pregnane X receptor. The mRNA and protein levels, and metabolic activity, of P450s in the livers of wild-type (WT) and double-mutant (D) mice harboring both PKN1 kinase-negative knock-in and PKN3 knockout mutations [PKN1 T778A/T778A; PKN3 -/-] were determined following treatment with activators for receptor-type transcription factors. mRNA and protein levels, and metabolic activity, of CYP2B10 were significantly higher in D mice treated with the CAR activator phenobarbital (PB), but not with 1,4-bis((3,5-dichloropyridin-2-yl)oxy)benzene, compared with WT mice. We examined the CAR-dependent pathway regulated by PKN following PB treatment, because the extent of CYP2B10 induction in WT and D mice was notably different in response to treatment with different CAR activators. The mRNA levels of Cyp2b10 in primary hepatocytes from WT and D mice treated with PB alone or in combination with SKI-1 (a Src inhibitor), or U0126 (a MEK inhibitor), were evaluated. Treatment of hepatocytes from D mice with the combination of PB with U0126, but not SKI-1, significantly increased the mRNA levels of Cyp2b10 compared with those from the corresponding WT mice. These findings suggest that PKN may have inhibitory effects on the Src-RACK1 pathway in the CAR-mediated induction of Cyp2b10 in mice livers. Significance Statement This is the first report of involvement of PKN in the transcriptional regulation of P450s. The elucidation of mechanisms responsible for induction of P450s could help optimize the pharmacotherapy and improve drug development. We examined whether the mRNA and protein levels, and activities of P450s were altered in double-mutant mice harboring both PKN1 kinase-negative knock-in and PKN3 knockout mutations. PKN1/3 negatively regulates CAR-mediated induction of Cyp2b10 through phosphorylation of a signaling molecule in the Src-RACK1 pathway.