Distinctive effects of hydrocortisone on the modulation of EGF binding and cell growth in HeLa cells grown in defined medium

Abstract

Hydrocortisone modulates the binding capacity of HeLa cells for 125I-labeled epidermal growth factor (EGF). A twofold increase in 125I-labeled EGF binding is observed within 24 hours after the addition of pharmacological concentration of hydrocortisone (5 X 10(-8) - 1 X 10(-6) M). This enhancement of binding is reversible, and occurs when the cells are cultured in either serum-supplemented or completely defined, serum-free, hormone-supplemented medium. Scatchard analysis of the binding data indicates that the number of 125I-EGF binding sites is increased, and that no appreciable change in the affinity of the EGF receptor for labeled EGF occurs. In the serum-free condition hydrocortisone stimulates the growth of HeLa cells, but we have observed no connection between this growth stimulation and the enhancement of EGF binding. The growth response to hydrocortisone is independent of EGF, and the concentration dependency of the growth response to EGF is unaltered by the addition of hydrocortisone to the medium. Hydrocortisone elicits the growth response at a concentration as low as 5 X 10(-9) M, while a concentration higher than 5 X 10(-6) M is required to affect the binding capacity for 125-EGF. These effects are specific for glucocorticoid steroids. Similar concentrations of progesterone, testosterone, or estradiol produce no measurable response. Although the elevation of EGF receptor levels in the serum-supplemented medium is similar to that observed in the serum-free cultures, hydrocortisone is growth-inhibitory under these conditions. This growth inhibition occurs at pharmacological concentrations of hydrocortisone with a concentration dependency that is similar to that of the EGF receptor modulation.