TCDD Reduces Rat Hepatic Epidermal Growth Factor Receptor: Comparison of Binding, Immunodetection, and Autophosphorylation

Administration of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), a potent tumor promoter, to rats resulted in a dose-dependent decrease in hepatic plasma membrane epidermal growth factor receptor (EGFR). The present study is the first to quantify and compare alterations in hepatic EGFR levels in female Sprague-Dawley rats 7 days after a single oral gavage dose of TCDD (0, 1, 5, 25, and 50 μg/kg) using three different techniques: (1)equilibrium receptor binding, (2) EGF induced receptor autophosphorylation, and (3) Western blot detection with a rabbit anti-rat EGFR polyclonal antibody. All three methods similarly demonstrated that the level of hepatic EGFR is significantly decreased at a dose of TCDD as low as 1 μg/kg. We showed that the immunoblot technique is a sensitive and quantitative alternative to radioligand binding assays. It is concluded that TCDD decreased total EGFR protein and maximum binding capacity without altering ligand binding affinity ( K d ). The results demonstrated that ligand-induced autophosphorylation capacity and basal phosphotyrosine residues of plasma membrane EGFR were both decreased parallel with the decrease in EGFR protein, suggesting no TCDD-related alteration in the inherent functional ability of the receptor to undergo activation. Furthermore, it was found that the dose-response curve for EGFR protein level determined by Western blot analysis was similar for both male and female Sprague-Dawley rats.