Effects of glucocorticoids on deoxyribonucleic acid(DNA) synthesis stimulated by growth factors in cultured rat skin fibroblasts.

Abstract

The effects of glucocorticoids on deoxyribonucleic acid (DNA) synthesis were studied by using confluent cultured rat skin fibroblasts prepared by enzymatic dispersion and expanded up to passage 3. Dexamethasone caused the inhibition of the DNA synthesis stimulated by 10% fetal calf serum (FCS) in a dose dependent manner. Maximum inhibition (90%-100%) was achieved by the concentration of 10(-7)M. A similar dose dependent inhibition was also obtained in the experiment using epidermal growth factor (EGF) (1 ng/ml) as a stimulant. Dexamethasone (10(-7)M) also inhibited the DNA synthesis stimulated by somatomedin C (100 ng/ml) or platelet derived growth factor (1 half-maximum unit/ml) almost to control levels. Binding studies with 125I-labeled EGF suggested that dexamethasone caused this inhibitory action without modulation of cell surface receptors for EGF. Furthermore, the effects of a variety of glucocorticoids on the DNA synthesis were studied to clarify the structural requirement of glucocorticoids for the inhibition of the DNA synthesis. The results showed that 11 beta-hydroxyl and 21-hydroxyl groups on the steroid nucleus were necessary for the inhibition of the growth factor-stimulated DNA synthesis. Meanwhile, the inhibitory action on the DNA synthesis was markedly diminished by the replacement of a 16 alpha-methyl group by a 16 beta-methyl group in the presence of a bulky group at C-17 (e.g. 17 alpha-valerate). For further elucidation of mechanisms of action of glucocorticoids on the inhibition of the growth factor-stimulated DNA synthesis, the relationships between the structural features of glucocorticoids and their binding ability to the glucocorticoid receptor ([3H]-dexamethasone-binding receptor) were studied.(ABSTRACT TRUNCATED AT 250 WORDS)