title: Cellular stress response in Eca-109 cells inhibits apoptosis during early exposure to isorhamnetin.
abstract: The flavonol aglycone isorhamnetin shows anti-proliferative activity in a variety of cancer cells. Previous work, from our laboratory showed that isorhamnetin inhibits the proliferation of human esophageal squamous carcinoma Eca-109 cells in vitro, but only after 72 h of exposure. This led us to propose that isorhamnetin exposure induces a cellular stress response that inhibits the antiproliferative and apoptotic effects of the compound during early exposure. To test this hypothesis, the present study examined the effects of isorhamnetin on Eca-109 cells during the first 72 h of exposure. Cell growth was assessed using the trypan blue exclusion assay, and expression of IκBα, NF-κB/p65, NF-κB/p50, phospho-Akt, Bcl-2, COX-2, Mcl-1, Bax, p53 and Id-1 were analyzed by Western blot. During the first 72 h of exposure, NF-κB/p65 and NF-κB/p50 accumulated in nuclei and expression of COX-2, Bcl-2 and Mcl-1 increased. In contrast, expression of IκBα and Bax fell initially but later increased. Expression of phospho-Akt and p53 showed no detectable change during the first 48 h. Pretreatment with the NF-κB inhibitor MG132 before exposure to isorhamnetin blocked the nuclear accumulation of p50 and p65, thereby inhibiting cell proliferation. These results show that during early exposure of Eca-109 cells to isorhamnetin, the NF-κB signaling pathway is activated and COX-2 expression increases, and this increase in expression partially inhibits isorhamnetin-induced apoptosis. Beyond 72 h of exposure, however, the apoptotic effect of isorhamnetin dominates, leading to inhibition of the NF-κB pathway and of cellular proliferation. These results will need to be taken into account when exploring the use of isorhamnetin against cancer in vivo.
authors.affiliation: Key Laboratory of Bio-resources and Eco-environment (Ministry of Education), College of Life Sciences, Sichuan University, Chengdu, Sichuan 610064, PR China.
authors.forename: C
authors.initials: C
authors.lastname: Shi
authors.forename: L Y
authors.initials: LY
authors.lastname: Fan
authors.forename: Z
authors.initials: Z
authors.lastname: Cai
authors.forename: Y Y
authors.initials: YY
authors.lastname: Liu
authors.forename: C L
authors.initials: CL
authors.lastname: Yang
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D051546:Cyclooxygenase 2 / Q000378:metabolism; D004938:Esophageal Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011794:Quercetin / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D016328:NF-kappa B; C047368:3-methylquercetin; D011794:Quercetin; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human