Glucocorticoid-binding components in an irradiation-induced thymoma of the C57BL/6J mouse

Preliminary experiments on thymocyte suspensions derived from normal thymus and γ-irradiation-induced thymomas of the C57BL/6J mouse indicated the presence of macromolecular species capable of binding triamcinolone acetonide-3H specifically with high affinity. Retention of labeled steroid by isolated tumor cells varied considerably among thymomas. Using cell-free preparations and a dextran-coated charcoal procedure, tumor cytosols bound triamcinolone acetonide-3H with a dissociation constant of 3 x 10-9 M; the number of binding sites was 354 fmoles/mg cytosol protein. Cytosols contained binding components that sedimented at 7 to 8 S on low-salt gradients and at 4 to 5 S on gradients containing 0.4 M KCl. These cytoplasmic components bound principally hormones with glucocorticoid activity as indicated by the competition of triamcinolone acetonide-3H binding in the presence of 5 x 10-5 M cortisol, dexamethasone, and cortexolone as well as by progesterone and aldosterone. Neither estradiol-17β, estriol, testosterone, nor dihydrotestosterone at 5 x 10-5 M inhibited specific binding of triamcinolone acetonide-3H. Generally, the binding properties of isolated thymocytes were similar to those determined on cell-free preparations. (U.S.)