Modulation by phenylacetate of early estrogen-mediated events in MCF-7 breast cancer cells.
OBJECTIVE
Phenylacetate (PA) and its derivatives constitute a group of small aromatic fatty acids that have been of considerable interest due to their anticancer properties in a number of experimental systems. We previously showed that PA can inhibit the growth of estrogen receptor (ER)+ breast cancer cells and that this activity is, at least in part, mediated by the ability of the compound to inhibit transcriptional activation driven by estrogen response elements (EREs). We now shed additional light on the antiestrogenic action of PA by determining its effects on early events in the estrogen-signaling pathway.


METHODS
MCF-7 breast cancer cells were used in this study. ER-ERE binding activity, and subsequent effects on ER and progesterone receptors (PR), c-myc, and the cyclin-dependent kinase inhibitor p21ASF1/CP1/MDA-6 (p21) were evaluated using electrophoretic mobility shift assays, real-time RT-PCR, and western blotting methodologies. Effects of PA on p21 promoter activity were assessed in transient transfection experiments utilizing p21 promoter-reporter gene constructs.


RESULTS
We demonstrate that PA treatment can block ER-ERE binding activity and that this effect is accompanied by downregulation of PR and c-myc, two genes which are transcriptionally regulated by estrogen through novel-ER-binding sites. Suppression of c-myc by PA is followed by increased mRNA levels of p21, an effect that is mediated by PA activation of the p21 promoter. Forced overexpression of c-myc through co-transfection of MCF-7 cells with a c-myc expression plasmid prevented PA upregulation of p21 promoter activity.


CONCLUSIONS
These findings confirm the potent antiestrogenic properties of PA, indicate that its effects are mediated by inhibiting ER-ERE interactions, and suggest that downregulation of c-myc is an early event leading to increased p21 expression and cell growth inhibition.
Liu
Jingbo
J
Division of Research, Department of Gynecology and Obstetrics, Emory University School of Medicine, Atlanta, GA 30322, USA.
Li
Jing
J
Sidell
Neil
N
D000964:Antimetabolites, Antineoplastic / Q000737:chemistry / Q000494:pharmacology; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism* / Q000502:physiology; D000077267:Fulvestrant; D016259:Genes, myc / Q000187:drug effects / Q000235:genetics; D006801:Humans; D010648:Phenylacetates / Q000737:chemistry / Q000494:pharmacology*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D020218:Response Elements / Q000187:drug effects / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection
D000964:Antimetabolites, Antineoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004965:Estrogen Antagonists; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D004967:Estrogens; D010648:Phenylacetates; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D000077267:Fulvestrant; D004958:Estradiol; C025136:phenylacetic acid