Sodium molybdate increases the amount of progesterone and estrogen receptor detected in certain human breast cancer cytosols

When sodium molybdate is added at a final concentration of 20 mM, additional 85 and 4S progesterone (³ H-R5020) receptor can be detected in the cytosols from a number of human breast cancers. Additional estrogen receptor also could be measured in some cytosols, and a quantitative temperaturedependent conversion of 8S to 4S binding molecules achieved. Sodium molybdate also prevented the loss of binding activity that occurred when cytosols were incubated at 30° in the absence of added estradiol. In addition to increasing the amount of progesterone receptor, and to a lesser extent estrogen receptor that may be detected, elucidation of the mechanism by which this salt stabilized receptors should contribute to further understanding of how cytosol steroid receptor content and function is regulated.