title: Transforming growth factor beta 1 inhibits epidermal growth factor receptor endocytosis and down-regulation in cultured fetal rat hepatocytes.
abstract: Incubation of fetal rat hepatocytes (FRH) with transforming growth factor beta 1 (TGF-beta 1) resulted in growth arrest and a biphasic effect on epidermal growth factor (EGF) receptor. After 2 h of exposure, EGF receptor (EGFR) was reduced by 43%. From 6 to 24 h, TGF-beta 1 exposure resulted in progressive increase in EGFR up to 74% over control. The increased binding was due to increase in high affinity EGF binding sites. FRH grown in medium containing EGF exhibited down-regulated EGFR with loss of high affinity EGF binding sites. With TGF-beta 1 exposure, high affinity EGFR was not down-regulated by EGF. Since down-regulation of EGFR involves internalization, the kinetics of EGF receptor-mediated endocytosis were examined. In TGF-beta 1-exposed FRH, EGF endocytosis was inhibited, with a reduction in the first order rate constant for the process from 0.078 to 0.043 min-1. Despite inhibition of growth, receptor down-regulation, and EGF endocytosis after TGF-beta 1 exposure, EGF-induced receptor autophosphorylation was preserved as demonstrated by [32P]phosphate-labeling of immunoprecipitated EGFR. These observations provide direct evidence that TGF-beta 1 regulates growth of fetal cells. Further, they suggest that TGF-beta 1 regulates endocytosis of EGF and possibly of other ligands.
authors.affiliation: Department of Medicine, University of Texas Health Science Center, San Antonio 78284-7878.
authors.forename: G
authors.initials: G
authors.lastname: Baskin
authors.forename: S
authors.initials: S
authors.lastname: Schenker
authors.forename: T
authors.initials: T
authors.lastname: Frosto
authors.forename: G
authors.initials: G
authors.lastname: Henderson
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects*; D004705:Endocytosis / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D005333:Fetus; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D010710:Phosphates; D016212:Transforming Growth Factor beta; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases