Studies on glucocorticoid-induced cytolysis in cultured mouse lymphoma cells, L5178Y : I. Glucocorticoid specificity and cytoplasmic receptors in sensitive and resistant cells

1. 1. The cytolytic action of glucocorticoids such as dexamethasone was studied in a murine cultured lymphoma L5178Y cell.

2. 2. Dexamethasone-resistant cells, which could grow even in a culture medium containing 2 × 10^?5 M dexamethasone, were selected from hormone-sensitive L5178Y lymphoma cells by stepwise increasing concentrations of dexamethasone in culture medium.

3. 3. The synthetic activities of macromolecules corresponded closely with the viabilities and with the resistibilities at various concentrations of dexamethasone in both cells.

4. 4. Studies of binding of dexamethasone to lymphoma L5178Y cells in vivo demonstrated that (1) equilibrium of binding at 37 °C was established within 5 min in both cells; (2) the specific binding to either whole cell or the subcellular fractions was, in sensitive cells, about double that in resistant cells.

5. 5. The cytoplasm of L5178Y lymphoma cells contains specific binding sites for dexamethasone and its binding sites (5.7 × 10^?10 mmol/mg protein) were about 2.5-fold more than that of dexamethasone-resistant cells (2.3 × 10^?10 mmol/mg protein).

6. 6. Studies on the dissociation constant, competition of various steroids for the specific binding with dexamethasone, and the sedimentation constant of steroid-receptor complex, suggested that the nature of cytoplasmic binding in resistant cells might be the same as that in sensitive cells.

7. 7. The nuclear binding of dexamethasone was extremely dependent on the affinity of cytoplasm to steroid. Studies suggested an equal level of nuclear association sites for cytoplasmic steroidreceptor complex in the two cell types.