Estrogen-Induced Apoptosis of Breast Epithelial Cells Is Blocked by NO/cGMP and Mediated by Extranuclear Estrogen Receptors

Abstract

Estrogen action, via both nuclear and extranuclear estrogen receptors (ERs), induces a variety of cellular signals that are prosurvival or proliferative, whereas nitric oxide (NO) can inhibit apoptosis via caspase S-nitrosylation and via activation of soluble guanylyl cyclase to produce cGMP. The action of 17β-estradiol (E(2)) at ER is known to elicit NO signaling via activation of NO synthase (NOS) in many tissues. The MCF-10A nontumorigenic, mammary epithelial cell line is genetically stable and insensitive to estrogenic proliferation. In this cell line, estrogens or NOS inhibitors alone had no significant effect, whereas in combination, apoptosis was induced rapidly in the absence of serum; the presence of inducible NOS was confirmed by proteomic analysis. The application of pharmacological agents determined that apoptosis was dependent upon NO/cGMP signaling via cyclic GMP (cGMP)-dependent protein kinase and could be replicated by inhibition of the phosphatidylinositol 3 kinase/serine-threonine kinase pathway prior to addition of E(2). Apoptosis was confirmed by nuclear staining and increased caspase-3 activity in E(2) + NOS inhibitor-treated cells. Apoptosis was partially inhibited by a pure ER antagonist and replicated by agonists selective for extranuclear ER. Cells were rescued from E(2)-induced apoptosis after NOS blockade, by NO-donors and cGMP pathway agonists; preincubation with NO donors was required. The NOS and ER status of breast cancer tissues is significant in etiology, prognosis, and therapy. In this study, apoptosis of preneoplastic mammary epithelial cells was triggered by estrogens via a rapid, extranuclear ER-mediated response, after removal of an antiapoptotic NO/cGMP/cGMP-dependent protein kinase signal.

Hops (Humulus lupulus) Inhibits Oxidative Estrogen Metabolism and Estrogen-Induced Malignant Transformation in Human Mammary Epithelial cells (MCF-10A)

“…3-[4, 5-Dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay was performed to measure cell viability as described previously (32). …”

SERMs Attenuate Estrogen-Induced Malignant Transformation of Human Mammary Epithelial Cells by Upregulating Detoxification of Oxidative Metabolites

“…MCF-10A cells are formally considered as ER(-), since estrogen does not induce proliferation; however, the presence of ER protein and mRNA has been determined in MCF-10A cells (37-41). Since the primary biological target of SERMs is ER, it was essential to determine if classical ER signaling via these proximal receptors was causal in modulation of oxidative metabolism to produce catechol estrogens.…”

cGMP signaling as a target for the prevention and treatment of breast cancer

“…Most notably, several studies have shown that activation of nitric oxide synthase (NOS) and the subsequent production of NO, an activator of sGC, promotes proliferation, invasion, and metastasis in various models of breast cancer [42][43][44][45]. Additionally, NOS expression in triple negative breast cancer correlates with poor prognosis [45].…”