title: Baicalein induces G1 arrest in oral cancer cells by enhancing the degradation of cyclin D1 and activating AhR to decrease Rb phosphorylation.
abstract: Baicalein is a flavonoid, known to have anti-inflammatory and anti-cancer effects. As an aryl hydrocarbon receptor (AhR) ligand, baicalein at high concentrations blocks AhR-mediated dioxin toxicity. Because AhR had been reported to play a role in regulating the cell cycle, we suspected that the anti-cancer effect of baicalein is associated with AhR. This study investigated the molecular mechanism involved in the anti-cancer effect of baicalein in oral cancer cells HSC-3, including whether such effect would be AhR-mediated. Results revealed that baicalein inhibited cell proliferation and increased AhR activity in a dose-dependent manner. Cell cycle was arrested at the G1 phase and the expression of CDK4, cyclin D1, and phosphorylated retinoblastoma (pRb) was decreased. When the AhR was suppressed by siRNA, the reduction of pRb was partially reversed, accompanied by a decrease of cell population at G1 phase and an increase at S phase, while the reduction of cyclin D1 and CDK4 did not change. This finding suggests that the baicalein activation of AhR is indeed associated with the reduction of pRb, but is independent of the reduction of cyclin D1 and CDK4. When cells were pre-treated with LiCl, the inhibitor of GSK-3β, the decrease of cyclin D1 was blocked and the reduction of pRb was recovered. The data indicates that in HSC-3 the reduction of pRb is both mediated by baicalein through activation of AhR and facilitation of cyclin D1 degradation, which causes cell cycle arrest at the G1 phase, and results in the inhibition of cell proliferation.
authors: Department of Physiology, School of Medicine, China Medical University, Taichung 40402, Taiwan, ROC. yhcheng@mail.cmu.edu.tw
authors: Ya-Hsin
authors: YH
authors: Cheng
authors: Lih-Ann
authors: LA
authors: Li
authors: Pinpin
authors: P
authors: Lin
authors: Li-Chuan
authors: LC
authors: Cheng
authors: Chein-Hui
authors: CH
authors: Hung
authors: Nai Wen
authors: NW
authors: Chang
authors: Chingju
authors: C
authors: Lin
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D044950:Flavanones / Q000008:administration & dosage / Q000494:pharmacology*; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D009062:Mouth Neoplasms / Q000188:drug therapy* / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D044950:Flavanones; D018336:Receptors, Aryl Hydrocarbon; D016160:Retinoblastoma Protein; D019938:Cyclin D1; C006680:baicalein