Characterization of epidermal growth factor receptor in a rat thyroid cell line, FRTL-5

A rat thyroid cell line FRTL-5 showed no significant binding of epidermal growth factor(EGF) either in the presence or absence of thyrotropin(TSH). Conditioned medium from FRTL-5 did not inhibit the specific binding of [125I]EGF to HeLa cell which has EGF receptors (EGF-R). Two bands of 170KD and 80KD obtained by immunoprecipitation with solubilized FRTL-5 and anti-EGF-R monoclonal antibody indicated autophosphorylation activity. The activity was enhanced by several thyroid cell growth factors including TSH. dibutyryl-cAMP(db-cAMP), insulin like growth factor I(IGF-I). Interleukin 1 beta (IL-1 beta) and phorbol ester. EGF alone enhanced the autophosphorylation activity. These data indicate that FRTL-5 possesses unique EGF-R with low affinity to EGF and that the tyrosine kinase of the receptor is activated during cell proliferation.