Inhibition of cytochrome P-450p (P450IIIA1) gene expression during liver regeneration from two-thirds hepatectomy in the rat

Regenerating liver from partial hepatectomy (HPX) is known to exhibit a strong and transient deficiency in both spectrally detectable microsomal cytochrome P-450 (P-450) and related monooxygenase activities. Male Wistar rats (250–300 g) were HPX or sham operated and liver was excised at different times after operation. The time course of accumulation of five different forms of P-450 (including P-450b/e, P-450c, P-450d, P-450p and P-450UT-A) was determined in the regenerating liver, by Western blots developed with specific antibodies. With the exception of P-450c, whose level was not affected, the accumulation of other forms strongly decreased during the first 24 hr after HPX. For P-450b/e and P-450d, 80% of initial level was restored at 96 hr, whereas for P-450p and P-450UT-A, two major forms in control rat liver, the accumulation was only 20–25% of the initial, 1 week after HPX. No significant decrease was observed in sham operated animals. Plasmid pDex 12 containing a cDNA insert coding for P-450p was used to further investigate the effects of HPX on P-450p mRNA level and gene transcription. Northern blot analysis of RNA from regenerating liver (cDNA insert of pDex 12 being used as a probe) demonstrated that P-450p mRNA level decreased strongly to a minimum 12 hr after operation. This was correlated with a strong and transient decrease in P-450p gene transcription determined from nuclear run on experiments, the time course of which, however, did not account for the early decrease in mRNA level. We conclude that P-450p deficiency in the regenerating liver results from a combination of transient inhibition of gene transcription and early increase of mRNA degradation. Time course and amplitude of the decrease in P-450 UT-A accumulation suggest an inhibition of gene transcription as observed with P-450p.