Estrogens play a crucial role in the development of ovarian tumors; however, the signal transduction pathways involved in hormone action are still poorly defined. The orphan G protein–coupled receptor 30 (GPR30) mediates the nongenomic signaling of 17β-estradiol (E2) in a variety of estrogen-sensitive cancer cells through activation of the epidermal growth factor receptor (EGFR) pathway. Whether estrogen receptor α (ERα) also contributes to GPR30/EGFR signaling is less understood. Here, we show that, in ERα-positive BG-1 ovarian cancer cells, both E2 and the GPR30-selective ligand G-1 induced c-fos expression and estrogen-responsive element (ERE)-independent activity of a c-fos reporter gene, whereas only E2 stimulated an ERE-responsive reporter gene, indicating that GPR30 signaling does not activate ERα-mediated transcription. Similarly, both ligands up-regulated cyclin D1, cyclin E, and cyclin A, whereas only E2 enhanced progesterone receptor expression. Moreover, both GPR30 and ERα expression are required for c-fos stimulation and extracellular signal-regulated kinase (ERK) activation in response to either E2 or G-1. Inhibition of the EGFR transduction pathway inhibited c-fos stimulation and ERK activation by either ligand, suggesting that in ovarian cancer cells GPR30/EGFR signaling relays on ERα expression. Interestingly, we show that both GPR30 and ERα expression along with active EGFR signaling are required for E2-stimulated and G-1–stimulated proliferation of ovarian cancer cells. Because G-1 was able to induce both c-fos expression and proliferation in the ERα-negative/GPR30-positive SKBR3 breast cancer cells, the requirement for ERα expression in GPR30/EGFR signaling may depend on the specific cellular context of different tumor types. [Cancer Res 2007;67(4):1859–66]

The higher incidence of thyroid carcinoma (TC) in women during reproductive years compared with men and the increased risk associated with the therapeutic use of estrogens have suggested a pathogenetic role exerted by these steroids in the development of TC. In the present study, we evaluated the potential of 17β-estradiol (E2), genistein (G), and 4-hydroxyta-moxifen (OHT) to regulate the expression of diverse estrogen target genes and the proliferation of human WRO, FRO, and ARO thyroid carcinoma cells, which were used as a model system. We have ascertained that ARO cells are devoid of estrogen receptors (ERs), whereas both WRO and FRO cells express a single variant of ERα that was neither transactivated, modulated, nor translocated into the nucleus upon treatment with ligands. However, E2, G, and OHT were able either to induce the transcriptional activity of c-fos promoter constructs, including those lacking the estrogen-responsive elements, or to increase c-fos, cyclin A, and D1 expression. It is noteworthy that we have demonstrated that the G protein-coupled receptor 30 (GPR30) and the mitogen-activated protein kinase (MAPK) pathway mediate both the up-regulation of c-fos and the growth response to E2, G, and OHT in TC cells studied, because these stimulatory effects were prevented by silencing GPR30 and using the MEK inhibitor 2′-amino-3′-methoxyflavone (PD 98059). Our findings provide new insight into the molecular mechanisms through which estrogens may induce the progression of TC.

Leptin is a hormone with multiple biological actions, produced predominantly by adipose tissue. In humans, plasma levels correlate with total body fat, and high concentrations occur in obese women. Among its functions, leptin is able to stimulate normal and tumor cell growth. We demonstrated that leptin induces aromatase activity in MCF-7 cells evidencing its important role in enhancing in situ estradiol production and promoting estrogen-dependent breast cancer progression. Estrogen receptor α (ERα), which plays an essential role in breast cancer development, can be transcriptionally activated in a ligand-independent manner. Taking into account that unliganded ERα is an effector of mitogen-activated protein kinase (MAPK) signal and that leptin is able, via Janus kinase, to activate the Ras-dependent MAPK pathway, in the present study we investigate the ability of leptin to transactivate ERα. We provided evidence that leptin is able to reproduce the classic features of ERα transactivation in a breast cancer cell line: nuclear localization, down-regulation of its mRNA and protein levels, and up-regulation of a classic estrogen-dependent gene such as pS2. Transactivation experiments with a transfected reporter gene for nuclear ER showed an activation of ERα either in MCF-7 or in HeLa cells. Using a dominant negative ERK2 or the MAPK inhibitor PD 98059, we showed that leptin activates the ERα through the MAPK pathway. The N-terminal transcriptional activation function 1 appears essential for the leptin response. Finally, it is worth noting that leptin exposure potentates also the estradiol-induced activation of ERα. Thus, we are able to demonstrate that the amplification of estrogen signal induced by leptin occurs through an enhancing in situ E₂ production as well as a direct functional activation of ERα.

Cholesterol is essential for cell function and viability. It is a component of the plasma membrane and lipid rafts and is a precursor for bile acids, steroid hormones, and Vitamin D. As a ligand for estrogen-related receptor alpha (ESRRA), cholesterol becomes a signaling molecule. Furthermore, cholesterol-derived oxysterols activate liver X receptors (LXRs) or estrogen receptors (ERs). Several studies performed in cancer cells reveal that cholesterol synthesis is enhanced compared to normal cells. Additionally, high serum cholesterol levels are associated with increased risk for many cancers, but thus far, clinical trials with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have had mixed results. Statins inhibit cholesterol synthesis within cells through the inhibition of HMG-CoA reductase, the rate-limiting enzyme in the mevalonate and cholesterol synthetic pathway. Many downstream products of mevalonate have a role in cell proliferation, since they are required for maintenance of membrane integrity; signaling, as some proteins to be active must undergo prenylation; protein synthesis, as isopentenyladenine is an essential substrate for the modification of certain tRNAs; and cell-cycle progression. In this review starting from recent acquired findings on the role that cholesterol and its metabolites fulfill in the contest of cancer cells, we discuss the results of studies focused to investigate the use of statins in order to prevent cancer growth and metastasis.

Human and animal models have evidenced how estrogen insufficiency is associated with abnormal spermatogenesis and male infertility. We previously demonstrated that estradiol is able to influence both capacitation and acrosome reaction in human ejaculated spermatozoa. It remains to be elucidated whether the biochemical changes induced by estradiol, in a rapid nongenomic way, are mediated by a single estrogen receptor (ER) or by the two ER subtypes, ER alpha and ER beta. In the present study, we have first demonstrated the concomitant expression of ER beta and ER alpha in human ejaculated spermatozoa. By RT-PCR and Southern blot, transcripts of both ERs were detected. Western blot analysis showed ER alpha and ER beta proteins at the same size as the "classical" ERs. The localization of ER alpha and ER beta with the immunocytochemistry shows a differential distribution of the two ER subtypes, the former being prevalently located in the midpiece, but the latter being in the tail. Estradiol has been associated with sperm longevity; however, the mechanism through which estradiol acts in sperm survival was never investigated. Upon estradiol exposure, we observed an enhanced phosphorylation of the proteins involved in the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway like PDK1, Akt, GSK-3, Bcl-2, together with ERK1/2, which was also involved in cell survival signals. Moreover, such phosphorylations were reduced in the presence of ICI 182, 780, addressing the role of estradiol and ERs in sperm survival. For instance we have provided, for the first time, a different interaction of the two ERs with the PI3K/Akt pathway, because ER alpha interacts with the p55 regulatory subunit of PI3K, whereas ER beta interacts with Akt1. However, it still remains to be elucidated whether the functional role of each of the ER subtypes in sperm survival signaling is redundant or distinct.