A 17-kDa protein induced in rat myometrium by hormonal treatment

A 17-kDa protein mainly recovered in the myometrium fraction sedimenting at 10,000 g has been induced by estradiol treatment in spayed rats. Tamoxifen completely inhibited the effect of estradiol, and progesterone decreased it by 50%. The protein was scarce in unspayed animals and the level after estradiol treatment remained much lower than in spayed rats. Oral doses of the potent antiprogesterone RU 38486 increased the level of the 17-kDa protein in unspayed animals. It was not present in immature or gestating rats or in the endometrium or myometrial cell cytosol of any of the rats. Following electrophoretic purification, it bound calmodulin, but was not phosphorylated by cAMP protein kinases.