Inverse relation between estrogen receptors and cyclic adenosine 3':5'-monophosphate-binding proteins in hormone-dependent mammary tumor regression due to dibutyryl cyclic adenosine 3':5'-monophosphate treatment or ovariectomy.

During the growth arrest of 7,12-dimethylbenz(alpha) anthracene-induced rat mammary carcinomas following ovariectomy or N6, O2'-dibutyryl cyclic adenosine 3':5'-monophosphate (DBcAMP) treatment, a change in the specific estrogen and cAMP binding to tumor proteins is observed. Three days after ovariectomy or DBcAMP treatment of the hosts, cAMP binding increases 5- and 2-fold in the nuclei and cytosol of tumors, respectively, whereas nuclear and cytoplasmic estrogen binding decreases by 70 and 25%, respectively. These changes in cAMP- and estrogen-binding activities are detectable within 1 day after ovariectomy or DBcAMP treatment, and the changes are reversed when resumption of tumor growth is induced by the injection of estradiol valerate or cessation of DBcAMP treatment. When 7,12-dimethylbenz(alpha)anthracene-induced tumors fail to regress after ovariectomy or DBcAMP treatment, the change in estrogen and cAMP binding does not occur. Concomitant with the increase of cAMP-binding activity in regressing tumors are increases in histone kinase activity and the cAMP content of the tumors. These increases in cAMP-binding and protein kinase activities are blocked by cycloheximide. These data suggest an interaction between a steroid hormone and cAMP in the growth control of a hormone-dependent mammary tumor.