Effects of transforming growth factor-α on cytochorme P450 expression in mouse primary hepatocytes

Abstract

TGF-$\alpha$ (transforming growth factor-$\alpha$) suppressed TCDD (2,3,7,8-tetrachloro dibenzo-p-dioxine)-induced EROD activity in a dose dependent manner in primary culture of mouse hepatocytes. As a result of comparison with a similar growth factor, EGF (epidermal growth factor), TGF-$\alpha$ appeared to have higher potency than EGF. Immunoblot analysis and RNA slot blot analysis also showed reduced P450 induction in the level of apoprotein and mRNA. These results indicated that suppression of TCDD-induced P450 IA1 by TGF-$\alpha$ was performed in mRNA level. The effect of TGF-$\alpha$ was also observed in PB-induced BROD activity. This result demonstrates that TGF-$\alpha$ can suppress several P450 activities as well as P450 IA1 activity. The suppressive effect of TGF-$\alpha$ was also showed as hepatocytes were pretreated with TGF-$\alpha$ for short time before TCDD addition. This result indicates that the initial signaling by TGF-$\alpha$ stimulation was crucial for suppression of P450 induction. To explore the relation between suppression of TCDD-induced P450 IA1 and initial signal transduction, the effects of various inhibitors which inhibit the key proteins that participated in signal transduction were examined. The G protein modulating agent, pertussis toxin (PT), was effective in recovery of suppressed EROD activity out of three kinds of inhibitors, those for PKC, Tyrosine kinase, and G protein. This observation indicates that PT-sensitive G protein may be engaged in signal transduction pathway for suppression of P 450 IA1 induction.