Enzyme induction by estrogen.

The injection of estrogen into an immature or ovariectomized rat results in an increase in the specific activities of many uterine enzymes which can be detected, usually, within hours to days. The recent identification of the "estrogen-induced protein" as the brain type isozyme of creatine kinase (CKBB), provided an easily measurable enzyme marker, the mRNA of which doubles 1 h after estrogen injection. The increase in synthesis of CKBB from a high constitutive rate to a several-fold higher induced rate may be a more general response to hormonal stimulation in a mammalian system than the "all or none" induction exemplified by bacterial systems. This rapid estrogen-induced increase in the rate of CKBB synthesis is now reported in several rat reproductive organs; ovary, uterus, vagina and estrogen receptor-rich regions of the hypothalamus (anterior hypothalamus and median basal eminence) and preoptic areas, as well as in normal human breast tissue and in human breast tumors. The rapidity of CKBB induction makes it a favorable candidate marker for developing a cell-free induction system to study the interaction of the estrogen-receptor complex with specific loci in chromatin. For this purpose, molecular cloning of cDNA for CKBB is now under way.