Inhibition of tumor-associated fatty acid synthase activity antagonizes estradiol- and tamoxifen-induced agonist transactivation of estrogen receptor (ER) in human endometrial adenocarcinoma cells

Abstract

Overexpression of the lipogenic enzyme fatty acid synthase (FAS) is a common molecular feature in subsets of sex-steroid-related tumors including endometrium and breast carcinomas that are associated with poor prognosis. Pharmacological inhibition of tumor-associated FAS hyperactivity is under investigation as a chemotherapeutic target. We examined the effects of the mycotoxin cerulenin (a covalent FAS inactivator), and the novel small compound C75 (a slow-binding FAS inhibitor) on estradiol (E 2 )-and tamoxifen (TAM)-stimulated ERdriven molecular responses in Ishikawa cells, an in vitro model of well-differentiated human endometrial carcinoma. We evaluated the effects of FAS inhibition on E 2 -and TAM-induced estrogen receptor (ER) transcriptional activity by using transient cotransfection assays with an estrogen-response element reporter construct (ERE-Luciferase). Antiestrogenic effects of cerulenin and C75 were observed by dose-dependent inhibition of E 2 -stimulated ERE-dependent transcription, whereas FAS inhibitors did not significantly increase the levels of ERE transcriptional activity in the absence of E 2 . Moreover, pharmacological blockade of FAS activity completely abolished TAMstimulated ERE activity. To address the reliability of transient transfection assays, the effects of FAS inhibitors on E 2 -inducible gene products were evaluated. FAS blockade induced a dose-dependent decrease in E 2 -inducible alkaline phosphatase activity. E 2 -stimulated accumulation of progesterone receptor (PR) and HER-2/neu oncogene was abolished in the presence of FAS blockers. FAS inhibition also resulted in a marked downregulation of E 2 -stimulated ERa expression, and noticeably impaired E 2 -induced ERa nuclear accumulation. A dose-dependent decrease in cell proliferation and cell viability was observed after FAS blockade. A Cell Death ELISA, detecting DNA fragmentation, demonstrated that FAS inhibitors stimulated apoptosis of Ishikawa cells. The analysis of critical E 2 -and TAMrelated cell cycle proteins revealed an increase of both the expression and the nuclear accumulation of cyclindependent kinase inhibitors p21 WAF1/CIP1 and p27 Kip1 following FAS inhibition. To rule out non-FAS ceruleninand C75-related effects, we finally monitored ER signaling after silencing of FAS gene expression using the highly sequence-specific mechanism of RNA interference (RNAi).

Development of a stable dual cell‐line GFP expression system to study estrogenic endocrine disruptors

“…Tamoxifen and raloxifene were antiestrogens in MCF-7 cells but acted as ER agonists in Ishikawa cells, and exhibited partial estrogenic activities. This conclusion on tamoxifen is consistent with many other studies (Menendez et al, 2004;Shah et al, 2005), but the results with raloxifene differ from some studies and many of these former studies are inconsistent with each other. Raloxifene, a compound for osteoporosis treatment, is being tested for breast cancer therapy.…”

The extract of leaves ofAcer truncatum Bunge: A natural inhibitor of fatty acid synthase with antitumor activity

“…Overexpression of FAS is a common molecular feature in subsets of sex-steroid-related tumors [17,36] including endometrium and breast carcinomas, ovarian and prostate cancers. Pharmacological inhibition of tumour-associated FAS hyperactivity is under investigation as a chemotherapeutic target.…”

The mitochondrial H+-ATP synthase and the lipogenic switch

“…We and others have demonstrated that protection from cell death and the activation of growth factor signaling are just a few of the newly recognized roles of the lipogenic phenotype in cancer cells. [42][43][44][45][46] Moreover, shifting lipid acquisition from lipid uptake toward de novo lipogenesis enables cancer cells to dramatically alter their membrane properties and protects tumor cells from both endogenous and exogenous insults. 47 As lipogenicity increases, the degree of lipid saturation also decreases, and monounsaturated lipids are less susceptible to lipid peroxidation; together, these observations indicate that the lipogenic switch may protect cancer from free radicals.…”