Hormonal effects upon the rate of proliferation of the murine plasmacytoma MOPC 315¹

The growth rate of the transplantable murine plasmacytoma MOPC 315 is decreased by daily injections of 2 mg cortisol. Estradiol injections (0.01 mg/day) have a slight stimulatory effect while testosterone has no detectable effect. Growth rate is unaffected by propylthiouracil, triiodothyronine, and growth hormone. MOPC 315 contains glucocorticoid binding proteins which bind ³H-dexamethasone with high affinity. In intact cells there are 3-4 × 10⁴ dexamethasone binding sites per cell as judged by competition experiments in which cells were incubated with a saturating concentration of ³H-dexamethasone in the presence and absence of a 1,000-fold molar excess of unlabelled dexamethasone. Scatchard analysis of binding data reveals the presence of a class of sites which binds about 2 × 10⁴ molecules of dexamethasone/cell with an equilibrium dissocation constant (Kd) of about 3 × 10⁻⁸M. In intact cells, only half of the saturable dexamethasone binding sites have stereochemical specificity for dexamethasone. This was deduced from the observation that dexamethasone binding to about half of these sites was displaced by the addition of a 1,000-fold molar excess of estradiol. Nuclear binding sites for dexamethasone were detected at a level of about 1 × 10⁴/cell. Nuclear dexamethasone binding sites were not displaced by the addition of a 1,000-fold molar excess of estradiol.