title: Effects of cytochrome P1-450 inducers on the cell-surface receptors for epidermal growth factor, phorbol 12,13-dibutyrate, or insulin of cultured mouse hepatoma cells.
abstract: Hepa-1c1c7, a mouse hepatoma cell line, was used to study the effect of cytochrome P1-450 inducers on the binding of 125I-epidermal growth factor (EGF), 125I-insulin, or [20-3H]phorbol 12,13-dibutyrate each to its specific cell-surface receptor. After a 24-h exposure to the cultured cells, several polycyclic hydrocarbon P1-450 inducers decrease the binding of EGF to EGF receptors much more than phenobarbital does. There appears to be a selectivity in the inhibitory effects: whereas EGF binding to EGF receptors is blocked, the binding of either phorbol ester or insulin each to its specific cell-surface receptors remains unaffected. The rank order of binding affinities of these chemicals to the cytosolic Ah receptor (2,3,7,8-tetrachlorodibenzo-p-dioxin much greater than benzo[a]pyrene greater than benzo[a]anthracene greater than 6-aminochrysene much greater than phenobarbital) is not correlated with their effects on EGF binding capacity. The effect of polycyclic hydrocarbons on EGF binding takes 24 h at 37 degrees C to be maximal, whereas phorbol 12-myristate 13-acetate, a potent tumor-promoting compound, inhibits EGF binding in less than 30 min. Removal of benzo[a]anthracene from the growth medium after 24 h results in a gradual recovery in EGF binding, indicating that the effect is reversible. Benzo[a]pyrene and benzo[a]anthracene are relatively ineffective at decreasing EGF binding to the EGF receptors in Hepa-1 mutant clones c2 and c4, which lack a normally functioning Ah receptor and inducible aryl hydrocarbon hydroxylase activity (P1-450). The very toxic metabolite (+)-7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, when added directly to the growth medium of c4 cells, however, is effective at decreasing EGF binding. These data suggest that electrophilic metabolites of polycyclic aromatic compounds, formed by P1-450 induced during the exposure of Hepa-1 cells to these chemicals, are important in decreasing EGF binding to the EGF cell-surface receptor. Occupancy of the Ah receptor per se does not affect EGF binding.
mesh_terms: D000818:Animals; D001551:Benz(a)Anthracenes / Q000494:pharmacology; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002460:Cell Line; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004790:Enzyme Induction; D066246:ErbB Receptors; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate; D010703:Phorbol Esters / Q000378:metabolism*; D010704:Phorbols / Q000378:metabolism*; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D011493:Protein Kinase C; D011972:Receptor, Insulin / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011955:Receptors, Drug
chemical_list: D001551:Benz(a)Anthracenes; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D010703:Phorbol Esters; D010704:Phorbols; D000072317:Polychlorinated Dibenzodioxins; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D015240:Phorbol 12,13-Dibutyrate; D003577:Cytochrome P-450 Enzyme System; C030935:benz(a)anthracene; D066246:ErbB Receptors; D011972:Receptor, Insulin; D011493:Protein Kinase C