Selective concomitant inhibition of mTORC1 and mTORC2 activity in estrogen receptor negative breast cancer cells by BN107 and oleanolic acid.
Hormonal, targeted and chemotherapeutic strategies largely depend on the expression of their cognate receptors and are often accompanied by intolerable toxicities. Effective and less toxic therapies for estrogen receptor negative (ER-) breast cancers are urgently needed. Here, we present the potential molecular mechanisms mediating the selective pro-apoptotic effect induced by BN107 and its principle terpene, oleanolic acid (OA), on ER- breast cancer cells. A panel of breast cancer cell lines was examined and the most significant cytotoxic effect was observed in ER- breast lines. Apoptosis was the major cellular pathway mediating the cytotoxicity of BN107. We demonstrated that sensitivity to BN107 was correlated to the status of ERalpha. Specifically, the presence of functional ERalpha protected cells from BN107-induced apoptosis and absence of ERalpha increased the sensitivity. BN107, an extract rich in OA derivatives, caused rapid alterations in cholesterol homeostasis, presumably by depleting cholesterol in lipid rafts (LRs), which subsequently interfered with signaling mediated by LRs. We showed that BN107 or OA treatment in ER- breast cancer cells resulted in rapid and specific inhibition of LR-mediated survival signaling, namely mTORC1 and mTORC2 activities, by decreasing the levels of the mTOR/FRAP1, RAPTOR and RICTOR. Cotreatment with cholesterol abolished the proapoptotic effect and restored the disrupted mTOR activities. This is the first report demonstrating possible concomitant inhibition of both mTORC1 and mTORC2 activities by modulating the levels of protein constituents present in these signaling complexes, and thus provides a basis for future development of OA-based mTOR inhibitors.
Chu
Ruth
R
Bionovo Inc., Emeryville, CA 94608, USA.
Zhao
Xiaoyue
X
Griffin
Chandi
C
Staub
Richard E
RE
Shoemaker
Mark
M
Climent
Joan
J
Leitman
Dale
D
Cohen
Isaac
I
Shtivelman
Emma
E
Fong
Sylvia
S
D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002784:Cholesterol / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047629:Estrogen Receptor beta / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D031501:Gleditsia / Q000737:chemistry*; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D021962:Membrane Microdomains / Q000187:drug effects; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D046912:Multiprotein Complexes; D009828:Oleanolic Acid / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology; D011506:Proteins; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured
C493245:CRTC2 protein, human; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D046912:Multiprotein Complexes; D010936:Plant Extracts; D011506:Proteins; D014157:Transcription Factors; D009828:Oleanolic Acid; D045304:Cytochromes c; D002784:Cholesterol; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases