Mammary glands from the estrogen receptor-a knockout (alphaERKO) mouse do not undergo ductal morphogenesis or alveolar development. Disrupted ERalpha signaling may result in reduced estrogen-responsive gene products in the mammary gland or reduced mammotropic hormones that contribute to the alphaERKO mammary phenotype. We report that circulating PRL is reduced in the female alphaERKO mouse. Implantation of an age-matched, heterozygous ERalpha pituitary isograft under the renal capsule of 25-day-old or 12-week-old alphaERKO mice increased circulating PRL and progesterone levels, and induced mammary gland development. Grafted alphaERKO mice also possessed hypertrophied corpora lutea demonstrating that PRL is luteotropic in the alphaERKO ovary. By contrast, ovariectomy at the time of pituitary grafting prevented mammary gland development in alphaERKO mice despite elevated PRL levels. Hormone replacement using pellet implants demonstrated that pharmacological doses of estradiol induced limited mammary ductal elongation, and estradiol in combination with progesterone stimulated lobuloalveolar development. PRL alone or in combination with progesterone or estradiol did not induce alphaERKO mammary growth. Estradiol and progesterone are required for the structural development of the alphaERKO mammary gland, and PRL contributes to this development by inducing ovarian progesterone levels. Therefore, the manifestation of the alphaERKO mammary phenotype appears due to the lack of direct estrogen action at the mammary gland and an indirect contributory role of estrogen signaling at the hypothalamic/pituitary axis.

No abstract

Protein arginine methyltransferase 5 (PRMT5) is a type II arginine methyltransferase that catalyzes the formation of symmetric dimethylarginine in a number of nuclear and cytoplasmic proteins. Although the cellular functions of PRMT5 have not been fully unraveled, it has been implicated in a number of cellular processes like RNA processing, signal transduction, and transcriptional regulation. PRMT5 is ubiquitously expressed in most tissues and its expression has been shown to be elevated in several cancers including breast cancer, gastric cancer, glioblastoma, and lymphoma. Here, we describe the identification and characterization of a novel and selective PRMT5 inhibitor with potent and activity. Compound (also called LLY-283) inhibited PRMT5 enzymatic activity and in cells with IC of 22 ± 3 and 25 ± 1 nM, respectively, while its diastereomer, compound (also called LLY-284), was much less active. Compound also showed antitumor activity in mouse xenografts when dosed orally and can serve as an excellent probe molecule for understanding the biological function of PRMT5 in normal and cancer cells.

Development of breast cancer involves genetic factors as well as lifetime exposure to estrogen. The precise molecular mechanisms whereby estrogens influence breast tumor formation are poorly understood. While estrogen receptor α (ERα) is certainly involved, nonreceptor mediated effects of estradiol (E2) may also play an important role in facilitating breast tumor development. A “reductionist” strategy allowed us to examine the role of ERα independent effects of E2 on mammary tumor development in ERα knockout (ERKO) mice bearing the Wnt-1 oncogene. Exogenous E2 “clamped” at early follicular and midluteal phase levels (i.e., 80 and 240 pg/ml) accelerated tumor formation in a dose-related fashion in ERKO/Wnt-1 animals (p = 0.0002). Reduction of endogenous E2 by oophorectomy (p < 0.001) or an aromatase inhibitor (AI) (p = 0.055) in intact ERKO/Wnt-1 animals delayed tumorigenesis as further evidence for an ER-independent effect. The effects of residual ERα or β were not involved since enhancement of tumor formation could not be blocked by the antiestrogen fulvestrant. 17α-OH-E2, a metabolizable but ER-impeded analogue of E2 stimulated tumor development without measurable uterine stimulatory effects. Taken together, our results suggest that ER-independent actions of E2 can influence breast tumor development in concert with ER dependent effects. These observations suggest 1 mechanism whereby AIs, which block E2 synthesis, would be more effective for breast cancer prevention than use of antiestrogens, which only block ER-mediated effects.