THE EFFECTS OF HYDROCORTISONE ON FOS, MYC AND RAS EXPRESSION IN IMR-90 FIBROBLASTS

摘要

The effects of hydrocortisone on several aspects of macromolecular biosynthesis were analyzed in human IMR-90 fibroblasts. These studies were undertaken to determine if the quantity of accumulated mRNA of the cellular oncogenes myc, fos, and ras could be altered by hydrocortisone, an agent which can increase or decrease cellular proliferation depending on the cells being investigated. Hydrocortisone is known to increase cellular proliferation of IMR-90 human fetal fibroblasts by acting during the G(,1) phase of the cell cycle.;Serum-deprived IMR-90 fibroblasts were treated with serum and/or hydrocortisone. DNA synthesis, as measured by tritiated thymidine uptake, increased with the addition of both hydrocortisone and fetal calf serum (10%, v/v) with a maximal stimulation occuring at a concentration of 10 micromolar hydrocortisone. The observed increase in thymidine incorporation of hydrocortisone plus serum was 40% greater than the maximum thymidine incorporation of fibroblasts stimulated with serum alone. There was no stimulation of thymidine uptake with hydrocortisone alone.;The expression of fos mRNA was determined by Northern blotting of total RNA. In fibroblasts stimulated with serum alone, there were two time periods or peaks of increased fos expression during the G(,1) phase of the cell cycle. There was no significant difference between cells treated with serum plus hydrocortisone, and cells treated with serum alone with respect to fos expression. Quiescent cells showed no change in fos expression during the G(,1) phase of the cell cycle. However, both peaks of fos expression do occur when cells are treated with hydrocortisone alone.;The results obtained show that hydrocortisone, in the absence of serum, stimulates fos expression in a manner similar to that of serum, but the activation is not amplified when serum and hydrocortisone are added together. Simulation of fos by hydrocortisone alone is insufficient to initiate DNA synthesis in IMR-90 fibroblasts, but hydrocortisone's stimulation of fos expression is similar in quantity to that of serum. Hydrocortisone has no detectable effect on myc or ras expression in the presence or absence of serum in synchronized fibroblasts. Therefore, increased transcription of the nuclear oncogenes myc and fos, and the cytoplasmic oncogenes ras are independently controlled and hydrocortisone may enhance DNA synthesis by increasing fos expression. The means by which fos expression is increased is unknown but may involve the control mechanism by the glucocorticoid-receptor complex at the level of transcription.