Pretranslational enhancement of epidermal growth factor receptor by direct effect of testosterone in mouse liver.

The effects of testosterone on the levels of epidermal growth factor receptor (EGFR) in mouse liver were studied. Orchiectomy resulted in 39% and 41% reductions in the levels of EGFR mRNA and EGF binding, respectively, within 2 weeks. Treatment of orchiectomized mice with a sc injection of testosterone propionate (TP; 100 micrograms/mouse.day) for 1 week restored these values to normal male levels. The hepatic levels of EGFR mRNA and EGF binding in females were 37% and 36% of those in males, respectively, and were not affected by ovariectomy, whereas treatment of females with TP (100 micrograms/mouse.day) increased EGFR to normal male levels within 1 week. On the other hand, neither orchiectomy nor androgen treatment affected levels of mRNAs for EGFR in the kidney or mRNAs for the structural protein beta-actin in the liver. To examine whether testosterone directly increased EGFR levels in the liver, TP (1.0 mg) pellets were implanted into the spleen of orchiectomized mice, so that testosterone released from the pellets reached the liver through the portal vein but did not enter the systemic circulation due to rapid clearance by the liver. The heptic levels of EGFR mRNA and EGF binding in orchiectomized mice were restored to normal male levels by intrasplenic implantation of TP (1.0 mg) pellets. This treatment also increased the hepatic levels of EGFR mRNA and EGF binding in female mice by 61% and 68%, respectively. In addition, sialoadenectomy, which reduced plasma EGF, as well as EGF antiserum treatment did not affect the androgen-dependent increase in EGFR levels in the liver, suggesting that endogenous EGF is not involved in the androgenic regulation of hepatic EGFR levels. These results suggest that hepatic EGFR levels are at least in part regulated at a pretranslational level by direct effects of androgens on the liver.