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.