[Show abstract][Hide abstract] ABSTRACT: Androgen receptor (AR) is an attractive target in breast cancer because of its frequent expression in all the molecular subtypes, especially in estrogen receptor (ER)-positive luminal breast cancers. We have previously shown a role for AR overexpression in tamoxifen resistance. We engineered ER-positive MCF-7 cells to overexpress aromatase and AR (MCF-7 AR Arom cells) to explore the role of AR in aromatase inhibitor (AI) resistance. Androstendione (AD) was used as a substrate for aromatization to estrogen. The nonsteroidal AI anastrazole (Ana) inhibited AD-stimulated growth and ER transcriptional activity in MCF-7 Arom cells, but not in MCF-7 AR Arom cells. Enhanced activation of pIGF-1R and pAKT was found in AR-overexpressing cells, and their inhibitors restored sensitivity to Ana, suggesting that these pathways represent escape survival mechanisms. Sensitivity to Ana was restored with AR antagonists, or the antiestrogen fulvestrant. These results suggest that both AR and ERα must be blocked to restore sensitivity to hormonal therapies in AR-overexpressing ERα-positive breast cancers. AR contributed to ERα transcriptional activity in MCF-7 AR Arom cells, and AR and ERα co-localized in AD + Ana-treated cells, suggesting cooperation between the two receptors. AR-mediated resistance was associated with a failure to block ER transcriptional activity and enhanced up-regulation of AR and ER-responsive gene expression. Clinically, it may be necessary to block both AR and ERα in patients whose tumors express elevated levels of AR. In addition, inhibitors to the AKT/IGF-1R signaling pathways may provide alternative approaches to block escape pathways and restore hormone sensitivity in resistant breast tumors.
Breast Cancer Research and Treatment 09/2014; · 4.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Several studies have demonstrated that thyroid hormone T3 promotes cancer cell growth, even though the molecular mechanism involved in such processes still needs to be elucidated. In this study we demonstrated that T3 induced proliferation in papillary thyroid carcinoma cell lines concomitantly with an up-regulation of cyclin D1 expression, that is a critical mitogen-regulated cell-cycle control element. Our data revealed that T3 enhanced the recruitment of the TRβ1/Oct-1 complex on Octamer-transcription factor-1 site within cyclin D1 promoter, leading to its transactivation. In addition, silencing of TRβ1 or Oct-1 expression by RNA interference reversed both increased cell proliferation and up-regulation of cyclin D1, underlying the important role of both transcriptional factors in mediating these effects. Finally, T3-induced increase in cell growth was abrogated after knocking down cyclin D1 expression. All these findings highlight a new molecular mechanism by which T3 promotes thyroid cancer cell growth.
Molecular and Cellular Endocrinology 10/2013; · 4.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The citrate carrier (CIC), a nuclear-encoded protein located in the mitochondrial inner membrane, plays an important metabolic role in the transport of acetyl-CoA from the mitochondrion to the cytosol in the form of citrate for fatty acid and cholesterol synthesis. Citrate has been reported to be essential for fibroblast differentiation into fat cells. Because peroxisome proliferator-activated receptor-gamma (PPARγ) is known to be one of the master regulators of adipogenesis, we aimed to study the regulation of CIC by the PPARγ ligand rosiglitazone (BRL) in 3T3-L1 fibroblasts and in adipocytes. We demonstrated that BRL up-regulated CIC mRNA and protein levels in fibroblasts, while it did not elicit any effects in mature adipocytes. The enhancement of CIC levels upon BRL treatment was reversed using the PPARγ antagonist GW9662, addressing how this effect was mediated by PPARγ. Functional experiments using a reporter gene containing rat CIC promoter showed that BRL enhanced CIC promoter activity. Mutagenesis studies, electrophoretic-mobility-shift assay and chromatin-immunoprecipitation analysis revealed that upon BRL treatment, PPARγ and Sp1 are recruited on the Sp1-containing region within the CIC promoter, leading to an increase in CIC expression. In addition, mithramycin, a specific inhibitor for Sp1-DNA binding activity, abolished the PPARγ-mediated up-regulation of CIC in fibroblasts. The stimulatory effects of BRL disappeared in mature adipocytes in which PPARγ/Sp1 complex recruited SMRT corepressor to the Sp1 site of the CIC promoter. Taken together, our results contribute to clarify the molecular mechanisms by which PPARγ regulates CIC expression during the differentiation stages of fibroblasts into mature adipocytes.
Biochimica et Biophysica Acta 01/2013; · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ziziphus extracts have been used in Traditional Chinese Medicine for the treatment of cancer.
In the present study we have investigated the effects of Ziziphus jujube extracts (ZEs) on breast cancer.
We evaluated the effects of increasing concentrations of ZEs on ERα positive MCF-7 and ERα negative SKBR3 breast cancer cell proliferation using MTT assays. Apoptosis was analyzed by evaluating the involvement of some pro-apoptotic proteins, including Bax, Bad, Bid and PARP cleavage by immunoblotting analysis. Moreover, the effects of ZEs treatment on apoptosis were tested by both DNA fragmentation and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) staining. By using chromatographic techniques, we identified the constituents of the effective extracts.
ZE1, ZE2, and ZE4 exerted significant antiproliferative effects on estrogen receptor alpha (ERα) positive MCF-7 (IC(50) values of 14.42, 7.64, 1.69μg/mL) and ERα negative SKBR3 (IC(50) values of 14.06, 6.21, 3.70μg/mL) human breast cancer cells. Remarkably, ZEs did not affect cell viability of both normal human fibroblasts BJ1-hTERT and nonmalignant breast epithelial MCF-10A cells. Treatment with ZEs induced cell death by apoptosis in both malignant breast cells. We found that the most effective extracts ZE2 and ZE4 shared a number of triterpenic acids, already known for their anticancer activities.
Our data provide a rational base for the use of Ziziphus extracts in the treatment of breast cancer in Traditional Chinese Medicine.
Journal of ethnopharmacology 03/2012; 140(2):325-32. · 2.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The combined treatment with nanomolar doses of the PPARγ ligand Rosiglitazone (BRL) and the RXR ligand 9-cis‑retinoic acid (9RA) induces a p53-dependent apoptosis in MCF7, SKBR3 and T47D human breast cancer cells. Since MCF7 cells express a wild-type p53 protein, while SKBR3 and T47D cells harbor endogenous mutant p53, we elucidated the mechanism through which PPARγ and RXR ligands triggered apoptotic processes independently of p53 transcriptional activity. We showed an upregulation of Bid expression enhancing the association between Bid/p53 in both cytosol and mitochondria after the ligand treatment. Particularly in the mitochondria, the complex involves the truncated Bid that plays a key role in the apoptotic process induced by BRL and 9RA, since the disruption of mitochondrial membrane potential, the induction of PARP cleavage and the percentage of TUNEL-positive cells were reversed after knocking down Bid. Moreover, PPARγ and RXR ligands were able to reduce mitochondrial GST activity, which was no longer noticeable silencing Bid expression, suggesting the potential of Bid in the regulation of mitochondrial intracellular reactive oxygen species scavenger activity. Our data, providing new insight into the role of p53/Bid complex at the mitochondria in promoting breast cancer cell apoptosis upon low doses of PPARγ and RXR ligands, address Bid as a potential target in the novel therapeutical strategies for breast cancer.