title: Quercetin induces caspase-dependent extrinsic apoptosis through inhibition of signal transducer and activator of transcription 3 signaling in HER2-overexpressing BT-474 breast cancer cells.
abstract: Flavonoids are assumed to exert beneficial effects in different types of cancers at high concentrations. Yet, their molecular mechanisms of action remain unknown. The present study aimed to examine the effect of quercetin on proliferation and apoptosis in HER2-expressing breast cancer cells. The anti-proliferative effects of quercetin were examined by proliferation, MTT and clonogenic survival assays. The effect of quercetin on expression of apoptotic molecules was determined by western blotting. Luciferase reporter assay was performed to measure signal transducer and activator of transcription 3 (STAT3) transcriptional activity. ELISA assay was performed to measure intracellular MMP-9 levels. Immunocytochemistry was performed to evaluate the nuclear STAT3 level. The results revealed that quercetin inhibited the proliferation of BT-474 cells in a dose- and time-dependent manner. Quercetin also inhibited clonogenic survival (anchorage-dependent and -independent) of BT-474 cells in a dose-dependent manner. These growth inhibitions were accompanied with an increase in sub-G0/G1 apoptotic populations. Quercetin induced caspase-dependent extrinsic apoptosis upregulating the levels of cleaved caspase-8 and cleaved caspase-3, and inducing the cleavage of poly(ADP‑ribose) polymerase (PARP). In contrast, quercetin did not induce apoptosis via intrinsic mitochondrial apoptosis pathway since this compound did not decrease the mitochondrial membrane potential and did not affect the levels of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX). Quercetin reduced the expression of phospho-JAK1 and phospho-STAT3 and decreased STAT3-dependent luciferase reporter gene activity in the BT-474 cells. Quercetin inhibited MMP-9 secretion and decreased the nuclear translocation of STAT3. Our study indicates that quercetin induces apoptosis at concentrations >20 µM through inhibition of STAT3 signaling and could serve as a useful compound to prevent or treat HER2-overexpressing breast cancer.
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Hye-Sook
authors.initials: HS
authors.lastname: Seo
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Jin Mo
authors.initials: JM
authors.lastname: Ku
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Han-Seok
authors.initials: HS
authors.lastname: Choi
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Youn Kyung
authors.initials: YK
authors.lastname: Choi
authors.affiliation: College of Veterinary Medicine, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea.
authors.forename: Jong-Kyu
authors.initials: JK
authors.lastname: Woo
authors.affiliation: Department of Science in Korean Medicine, Graduate School, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kim
authors.affiliation: Department of Science in Korean Medicine, Graduate School, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Ilhwan
authors.initials: I
authors.lastname: Kim
authors.affiliation: Department of Applied Korean Medicine, Graduate School, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Chang Hyeok
authors.initials: CH
authors.lastname: Na
authors.affiliation: Department of Science in Korean Medicine, Graduate School, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Hansol
authors.initials: H
authors.lastname: Hur
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Bo-Hyoung
authors.initials: BH
authors.lastname: Jang
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Yong Cheol
authors.initials: YC
authors.lastname: Shin
authors.affiliation: Laboratory of Clinical Biology and Pharmacogenomics and Center for Clinical Research and Genomics, College of Korean Medicine, Kyung Hee University, Dongdaemun-gu, Seoul 02447, Republic of Korea.
authors.forename: Seong-Gyu
authors.initials: SG
authors.lastname: Ko
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D053613:Janus Kinase 1 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D008928:Mitochondria / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D053148:Caspase 3; D053181:Caspase 8; D053613:Janus Kinase 1; D020780:Matrix Metalloproteinase 9; D011065:Poly(ADP-ribose) Polymerases; D019253:Proto-Oncogene Proteins c-bcl-2; D011794:Quercetin; D018719:Erb-b2 Receptor Tyrosine Kinases; D050796:STAT3 Transcription Factor; D051028:bcl-2-Associated X Protein; C494086:STAT3 protein, human; C508053:ERBB2 protein, human; C507904:JAK1 protein, human; C579270:MMP9 protein, human