Effect and Mechanism of Growth Factors and Their Interactions on the Expression of c-fos and c-myc Proto-oncogenes in Cultured Normal Rat Thyroid Cell Line (FRTL-5)

Yoo, Hwan Young; Oh, Seung Keun

Abstract

Oncogenes are known to be involved in normal cellular growth and proliferation as well as in carcinogenesis. It is reported that stimulation of quiescent cells with growth factors makes the oncogenes produce protein products as an early and immediate response, and these protein products induce or control the cell growth. Among those oncogenes, c-fos and c-myc are well known for its generalized expressions. An experiment was performed in order to prove the hypothesis that oncogene expressions would have the same pattern with that of cellular growth by growth factors in cultured normal rat thyroid cell line(FRTL-5). Ribonucleic acids of FRTL-5 cells were extracted time-sequentially at 15, 30, 60 and 120 minutes after administration of growth factors to the media of quiescent FRTL-5 cells. Extracted ribonucleic acids were blotted to the nitrocellulose membrane, and then hybridized with radiolabelled c-fos and c-myc oligonucleotide probes, and -actin probes. Hybridized dot blots on nitrocellulose membrane were autoradiographed on X-ray films, and the amount of radioactivity were measured by densitometry. Densitometric readings were used as the indices of oncogene expressions. The concentrations of TSH, IGF-I and IgG from patients with Graves' disease, which showed the maximum expressions of c-fos and c-myc in quiescent FRTL-5 cells, were TSH 10 mU/ml, IGF-I 100 ng/ml and IgG from patients with Graves' disease 1 mg/ml, respectively. Expressions of c-fos and c-myc were more prominent in combined administrations of TSH and IGF-I, or IgG from patients with Graves' disease and IGF-I than in case of TSH and IgG from patients with Graves' disease. IgG from patients with primary myxedema suppressed oncogene expressions provoked by TSH or IgG from patients with Graves' disease, but not by IGF-I. Expressions of c-fos and c-myc were more prominent by the combined administration of TSH with TPA which stimulated the phosphoinositide turnover-protein kinase C-calcium system than by those of TSH with dBcAMP, forskolin, IBMX or cholera toxin which stimulated adenylate cyclase system. From the above results, following conclusions were obtained. 1) Expressions of c-fos and c-myc by growth factors have similar patterns with those of cell growth by growth factors in FRTL-5 cells. 2) It is suggested that the actions of TSH and IgG from patients with Graves' disease would be manifested through the same signal transduction system, and that of IGF-I would be manifested through its own, but the oncogenes would be expressed mainly through adenylate cyclase system.