Coordinate activation of multidrug‐resistance (P‐glycoprotein) genes mdr2 and mdr3 during mouse liver regeneration

We previously reported that only one of the three mouse multidrug‐resistance (mdr) genes, mdr3, is activated in hepatocellular carcinomas (HCCs). The present study examined the expression of mdr family members during mouse liver regeneration after partial hepatectomy to determine whether the regeneration that occurs during hepatic tumorigenesis is responsible for mdr3 elevation in HCC. We demonstrated that in both C3H/HeN and B6C3/F1 mice strains, the levels of both mdr2 and mdr3 mRNAs coordinately increased five‐ to sevenfold 24 h after partial hepatectomy, whereas the levels of mdr1 mRNA were not statistically different from those in the controls. Forty‐eight hours after partial hepatectomy, mdr mRNA levels decreased and in most cases returned to normal levels after 72 h. These results indicate that mdr3 induction during hepatocarcinogenesis is not due to liver regeneration alone.