RESPONSIVENESS OF THE 5'-FLANKING REGION OF THE BRAIN TYPE ISOZYME OF CREATINE-KINASE TO ESTROGENS AND ANTIESTROGEN

The brain type isozyme of creatine kinase (CKB) has proven to be a useful early marker for the action of steroid and other hormones. An increase in the steady state level of mRNA for CKB was found within 30 min after estrogen stimulation of immature rat uteri. Cycloheximide treatment did not inhibit CKB induction. In order to study the molecular mechanism of this induction, 2.9 kb of the 5'-flanking region of CKB fused with the CAT reporter gene was cotransfected into ROS 17/2.8 and HeLa cells along with an expression plasmid for the human estrogen receptor. 17-beta-Estradiol at 10(-8) M or greater concentrations and the antiestrogen tamoxifen at 10(-6) M stimulated CAT activity. When given simultaneously with 17-beta-estradiol, tamoxifen showed a synergistic effect.