Characterization of the Cytosolic Translocation of the CYP3A2 Protein with Ubiquitination in Male and Female Rats

The cytosolic translocation of the membrane-associated CYP3A2 protein was examined in male and female rats to evaluate the ubiquitin-dependent protein degradation. In the experiments, the cytosol and membrane fractions were prepared from pooled rat liver tissues, and the amount of CYP3A2 protein in those fractions was determined by Western immunoblotting. The CYP3A2 protein detected in the cytosol fraction was shown to be ubiquitinated, and the apparent translocation ratio of the CYP3A2 protein from the membrane to the cytosol was calculated to be 0.58 in male control rats. The translocation ratio was then evaluated in male rats undergoing CYP3A2 induction. When male rats were treated with 80 mg/kg of dexamethasone (DEX), the translocation ratio decreased to 0.05, but the ratio was barely affected in male rats treated with 1.6 mg/kg of DEX, indicating that the cytosolic translocation of the CYP3A2 protein had a saturable nature. After that, the CYP3A2 translocation was examined in female rats with induced CYP3A2 protein, as the protein was known to be expressed in a male-specific manner. In female rats treated with 80 mg/kg of DEX, the translocation ratio was 0.04, but in those treated with 1.6 mg/kg of DEX, the ratio increased to 1.24, approximately 2 times larger than that in male control rats. It appeared that the DEX-induced CYP3A2 protein in female rats underwent expeditious degradation, presumably reflecting a difference in the mechanisms regulating the hepatic expression of the CYP3A2 protein in male and female rats.