Abstract

Coimmunoprecipitation was used to investigate protein-protein interactions between several UDP-glucuronosyltransferase (UGT) isoforms and cytochrome P450 3A4. Solubilized human liver microsomes were incubated with specific antibodies to UGT2B7, UGT1A6, UGT1A1, and CYP3A4, and the immunoprecipitates were run on SDS-polyacrylamide gel electrophoresis. Western blots showed that UGT2B7, UGT1A6, UGT1A1, and CYP3A4 were successfully immunoprecipitated with the specific antibodies for each enzyme. Upon immunoprecipitating UGT2B7, the corresponding immunoblot showed that UGT1A6, UGT1A1, and CYP3A4 were immunoprecipitated. Similar studies found that different UGT isoforms or CYP3A4 immunoprecipitated along with the original immunoprecipitating enzyme. These data suggest that UGT isoforms may form complexes (dimers, tetramers, etc.) with each other in the endoplasmic reticulum and nuclear envelope. In addition, the UGT isoforms tested here may have interacted with CYP3A4 in the endoplasmic reticulum, suggesting that these enzymes may cooperate in the excretion of compounds in a multistep metabolic process.