Arsenite and cadmium promote the development of mammary tumors

Previous studies demonstrate that the heavy metal cadmium and the metalloid arsenite activate estrogen receptor-alpha in breast cancer cells by forming a high-affinity complex with the ligand-binding domain of the receptor and that environmentally relevant doses of cadmium have estrogen-like activity in vivo. The present study showed that in estrogen-receptor positive cells, arsenite and cadmium increased the global expression of estrogen-responsive genes and that an environmentally relevant dose of arsenite also had estrogen-like activity in vivo. Similar to estrogens, exposure of ovariectomized animals to arsenite induced the expression of the progesterone receptor, GREB1, and c-fos in the mammary gland and the expression of complement C3, c-fos, and cyclin D1 in the uterus and the increase was blocked by the antiestrogen ICI-182,780. When virgin female animals were fed a diet, that mimics exposure to either arsenite or cadmium, and challenged with the chemical carcinogen dimethylbenzanthracene, there was an increase in the incidence of mammary tumors and a decrease in the time to tumor onset, but no difference in the total number of tumors, tumor multiplicity, or total tumor volume. Together with published results, these data showed that environmentally relevant amounts of arsenite and cadmium had estrogen-like activity in vivo and promoted mammary tumorigenesis.

Estrogen-related receptor β activation and isoform shifting by cdc2-like kinase inhibition restricts migration and intracranial tumor growth in glioblastoma

Glioblastoma (GBM; grade 4 glioma) is a highly aggressive and incurable tumor. GBM has recently been characterized as highly dependent on alternative splicing, a critical driver of tumor heterogeneity and plasticity. Estrogen-related receptor β (ERR-β) is an orphan nuclear receptor expressed in the brain, where alternative splicing of the 3' end of the pre-mRNA leads to the production of 3 validated ERR-β protein products: ERR-β short form (ERR-βsf), ERR-β2, and ERR-β exon 10 deleted. Our prior studies have shown the ERR-β2 isoform to play a role in G2/M cell cycle arrest and induction of apoptosis, in contrast to the function of the shorter ERR-βsf isoform in senescence and G1 cell cycle arrest. In this study, we sought to better define the role of the proapoptotic ERR-β2 isoform in GBM. We show that the ERR-β2 isoform is located not only in the nucleus but also in the cytoplasm. ERR-β2 suppresses GBM cell migration and interacts with the actin nucleation-promoting factor cortactin, and an ERR-β agonist is able to remodel the actin cytoskeleton and similarly suppress GBM cell migration. We further show that inhibition of the splicing regulatory cdc2-like kinases in combination with an ERR-β agonist shifts isoform expression in favor of ERR-β2 and potentiates inhibition of growth and migration in GBM cells and intracranial tumors.-Tiek, D. M., Khatib, S. A., Trepicchio, C. J., Heckler, M. M., Divekar, S. D., Sarkaria, J. N., Glasgow, E., Riggins, R. B. Estrogen-related receptor β activation and isoform shifting by cdc2-like kinase inhibition restricts migration and intracranial tumor growth in glioblastoma.

Antimitotic activity of DY131 and the estrogen-related receptor beta 2 (ERRβ2) splice variant in breast cancer

Breast cancer remains a leading cause of cancer-related death in women, and triple negative breast cancer (TNBC) lacks clinically actionable therapeutic targets. Death in mitosis is a tumor suppressive mechanism that occurs in cancer cells experiencing a defective M phase. The orphan estrogen-related receptor beta (ERRβ) is a key reprogramming factor in murine embryonic and induced pluripotent stem cells. In primates, ERRβ is alternatively spliced to produce several receptor isoforms. In cellular models of glioblastoma, short form (ERRβsf) and beta2 (ERRβ2) splice variants differentially regulate cell cycle progression in response to the synthetic agonist DY131, with ERRβ2 driving arrest in G2/M.The goals of the present study are to determine the cellular function(s) of ligand-activated ERRβ splice variants in breast cancer and evaluate the potential of DY131 to serve as an antimitotic agent, particularly in TNBC. DY131 inhibits growth in a diverse panel of breast cancer cell lines, causing cell death that involves the p38 stress kinase pathway and a bimodal cell cycle arrest. ERRβ2 facilitates the block in G2/M, and DY131 delays progression from prophase to anaphase. Finally, ERRβ2 localizes to centrosomes and DY131 causes mitotic spindle defects. Targeting ERRβ2 may therefore be a promising therapeutic strategy in breast cancer.

Estrogen-related receptor β (ERRβ) - renaissance receptor or receptor renaissance?

Estrogen-related receptors (ERRs) are founding members of the orphan nuclear receptor (ONR) subgroup of the nuclear receptor superfamily. Twenty-seven years of study have yet to identify cognate ligands for the ERRs, though they have firmly placed ERRα and ERRγ at the intersection of cellular metabolism and oncogenesis. The pace of discovery for novel functions of ERRβ, however, has until recently been somewhat slower than that of its family members. ERRβ has also been largely ignored in summaries and perspectives of the ONR literature. Here, we provide an overview of established and emerging knowledge of ERRβ in mouse, man, and other species, highlighting unique aspects of ERRβ biology that set it apart from the other two estrogen-related receptors, with a focus on the impact of alternative splicing on the structure and function of this receptor.

Fyn tyrosine kinase increases Apolipoprotein E Receptor 2 levels and phosphorylation

Apolipoprotein E Receptor 2 (ApoER2) and the tyrosine kinase Fyn are both members of the Reelin pathway, a signaling pathway essential for the laminar formation of the cortex during development and proper dendritic spine density and long-term potential (LTP) in the adult brain. In the presence of extracellular Reelin, ApoER2 binds the intracellular protein Dab1, an adaptor protein that is phosphorylated by Fyn. However, direct interactions between ApoER2 and Fyn are not well defined. Here, we show that total levels of ApoER2 and surface levels of ApoER2 are increased by active Fyn. Via a separate mechanism, ApoER2 is also phosphorylated by Fyn, an event that peaks in the postnatal cortex at day 5 and can occur at multiple ApoER2 tyrosine residues. Dab1 is also involved in this phosphorylation, promoting the phosphorylation of ApoER2 by Fyn when it is itself phosphorylated. These results elucidate some of the intracellular mechanisms that give rise to a functional Reelin pathway.

Ligand-induced homotypic and heterotypic clustering of apolipoprotein E receptor 2

ApoE Receptor 2 (ApoER2) and the very low density lipoprotein receptor (VLDLR) are type I transmembrane proteins belonging to the LDLR family of receptors. They are neuronal proteins found in synaptic compartments that play an important role in neuronal migration during development. ApoER2 and VLDLR bind to extracellular glycoproteins, such as Reelin and F-spondin, which leads to phosphorylation of adaptor proteins and subsequent activation of downstream signaling pathways. It is thought that ApoER2 and VLDLR undergo clustering upon binding to their ligands, but no direct evidence of clustering has been shown. Here we show strong clustering of ApoER2 induced by the dimeric ligands Fc-RAP, F-spondin, and Reelin but relatively weak clustering with the ligand apoE in the absence of lipoproteins. This clustering involves numerous proteins besides ApoER2, including amyloid precursor protein and the synaptic adaptor protein PSD-95. Interestingly, we did not observe strong clustering of ApoER2 with VLDLR. Clustering was modulated by both extracellular and intracellular domains of ApoER2. Together, our data demonstrate that several multivalent ligands for ApoER2 induce clustering in transfected cells and primary neurons and that these complexes included other synaptic molecules, such as APP and PSD-95.

Metals and breast cancer

Metalloestrogens are metals that activate the estrogen receptor in the absence of estradiol. The metalloestrogens fall into two subclasses: metal/metalloid anions and bivalent cationic metals. The metal/metalloid anions include compounds such as arsenite, nitrite, selenite, and vanadate while the bivalent cations include metals such as cadmium, calcium, cobalt, copper, nickel, chromium, lead, mercury, and tin. The best studied metalloestrogen is cadmium. It is a heavy metal and a prevalent environmental contaminant with no known physiological function. This review addresses our current understanding of the mechanism by which cadmium and the bivalent cationic metals activate estrogen receptor-α. The review also summarizes the in vitro and in vivo evidence that cadmium functions as an estrogen and the potential role of cadmium in breast cancer.

The role of calcium in the activation of estrogen receptor-alpha

Environmental estrogen mimics, including metalloestrogens that can activate estrogen receptor-alpha (ERα), may contribute to breast cancer risk. However, the underlying mechanisms through which these molecular mimics activate the ERα are generally poorly understood. With concern to this important question, we investigated whether intracellular calcium may mediate the cross-talk between signaling pathways that activate ERα and the ligand-binding domain of ERα. MCF-7 cells treated with EGF, ATP, extracellular calcium, or caffeine to increase intracellular calcium triggered a rapid recruitment of ERα to estrogen-responsive promoters and stimulated expression of estrogen-responsive genes including pS2, complement C3, and progesterone receptor. Induction was blocked by an antiestrogen but also by the chelation of intracellular calcium. Treatment with extracellular calcium also increased the growth of MCF-7 cells through an ER-dependent mechanism. We found that EGF and extracellular calcium activated the C-terminus of ERα and the activation was blocked by the antiestrogen. Mechanistic investigations identified four potential sites on the solvent-accessible surface of the ERα ligand-binding domain as important for calcium activation of the receptor. Taken together, our results suggest that calcium mediates the cross-talk between ERα-activating signaling pathways and the ligand-binding domain of ERα providing a potential explanation for the ability of certain environmental metalloestrogens to activate the receptor.

Cadmium--a metallohormone?

Cadmium is a heavy metal that is often referred to as the metal of the 20th century. It is widely used in industry principally in galvanizing and electroplating, in batteries, in electrical conductors, in the manufacture of alloys, pigments, and plastics, and in the stabilization of phosphate fertilizers. As a byproduct of smelters, cadmium is a prevalent environmental contaminant. In the general population, exposure to cadmium occurs primarily through dietary sources, cigarette smoking, and, to a lesser degree, drinking water. Although the metal has no known physiological function, there is evidence to suggest that the cadmium is a potent metallohormone. This review summarizes the increasing evidence that cadmium mimics the function of steroid hormones, addresses our current understanding of the mechanism by which cadmium functions as a hormone, and discusses its potential role in development of the hormone dependent cancers.