Steroid Hormones Mediate Reversible Phenotypic Transition between Transformed and Untransformed States in Mouse Fibroblasts

Hydrocortisone at physiological concentrations reversibly inhibits DNA synthesis in ST1 cells (a line of mouse fibroblasts possessing 40 chromosomes and derived from Swiss 3T3 cells). This inhibitory activity is a property of glucocorticoids, but the β -OH of C-11 of glucocorticoids is not essential for the inhibition. The steroid hormone restores to ST1 cells dependency on serum, density, and anchorage for growth. When injected into nude mice, ST1 cells generated malignant invasive fibrosarcoma. Injections of dexamethasone into tumor-bearing animals blocked tumor growth. The steroid hormone seems to induce a reversible transition between a transformed and a ``normal'' phenotype. ST1 cells treated or untreated with hydrocortisone are not responsive to fibroblast growth factor, epidermal growth factor, or prostaglandin F2αwhereas they are responsive to a factor that is a contaminant in bovine serum albumin.