Specific Glucocorticoid-Binding Macromolecules from Mouse Fibroblasts Growing in Vitro

Abstract

Mouse fibroblasts growing in vitro (L cells) contain a binding component for triamcinolone acetonide which is apparently distributed intracellularly, largely as a cytoplasmic soluble macromolecule. The structure-activity relationships of steroids active in growth inhibition are exactly paralleled by their ability to displace ³H-triamcinolone acetonide from this binding component. The binding component is saturated between 10^-8 and 5 x 10^-8 M triamcinolone acetonide. The macromolecules bind unchanged triamcinolone acetonide noncovalently, and the steroid is released from binding by brief digestion with a proteolytic enzyme. Cells which are resistant to glucocorticoids bind much less triamcinolone acetonide in a specific manner (i.e., displaceable by glucocorticoids) than do sensitive cells. The binding component therefore satisfies many of the rigorous criteria necessary for assignment as a "receptor" for the growth-inhibitory action of glucocorticoids on mouse fibroblasts. In addition, triamcinolone acetonide bound to the 105,000 x g supernatant fraction remains bound under conditions of frozen storage for at least 1 month.