EFFECT OF CA-2+ AND SALT ON FORMS OF ESTRADIOL CYTOPLASMIC-RECEPTOR IN HUMAN NEOPLASTIC BREAST-TISSUE

Abstract

After incubation with [3H]estradiol, low salt sucrose gradient centrifugation of 250 human breast tumor cytosols demonstrated receptor-bound steroid in 4 S and 8 S forms. Cytosols prepared from 24 of these receptor-positive tumors were examined in the presence of KCl, Ca2+ and the serine protease inhibitor, phenylmethylsulfonyl fluoride. After incubation with KCl (0.4 M), interconversion of 8 S and 4 S forms was found in 1/2 of the 24 cytosols examined whose original low salt patterns contained well defined 4 S and 8 S peaks. When cytosols were made 4 mM in Ca2+ 15-30 min before the addition of KCl, an additional 4.5 S form was observed in low salt gradients in 18 tumors, and, in 6 tumors, inactivation of receptor occurred. The effects were not produced when Ca2+ and salt were added simultaneously. After 2-24 h of preincubation with Ca2+ of the same cytosols under the same conditions, an increased recovery of the .apprx.4 S receptor complex was observed in low salt gradient. These Ca2+ effects were inhibited if phenylmethylsulfonyl fluoride and Ca2+ were added simultaneously to cytosols prior to the addition of salt. Human mammary tumor cytosols may contain proteolytic activities that can be activated by Ca2+ and can effect irreversible changes in the salt-dissociated steroid receptor proteins which can be detected in sucrose density gradients.