title: Involvement of glycogen synthase kinase-3β in arsenic trioxide-induced p21 expression.
abstract: Arsenic trioxide (ATO) has been effectively used as a therapeutic agent to treat acute promyelocytic leukemia and solid tumors, via induction of cell cycle arrest or apoptosis. In our previous studies, we suggest that c-Jun might act as an adapter to regulate p21(WAF1/CIP1) (p21) expression in response to ATO. Therefore, how to regulate the c-Jun to bind to the p21 promoter was further elucidated. It has been reported that glycogen synthase kinase-3β (GSK-3β) can phosphorylate the C-terminus (Ser243) of c-Jun to decrease its protein stability and DNA-binding ability and can also increase the degradation of p21 in resting condition or under ultraviolet irradiation. Therefore, we hypothesized that ATO-induced p21 expression might be through the inhibition of GSK-3β. Using the DNA affinity precipitation assay, ATO could dephosphorylate the C-terminus (Ser243) of c-Jun to enhance its binding to the p21 promoter and resultant p21 expression. ATO, as well as LiCl (GSK-3β inhibitor), could induce GSK-3β(Ser9) phosphorylation and p21 expression in a time- and dose-dependent manner. Constitutively active GSK-3β, FlagGSKCA, and constitutively inactive GSK-3β, FlagGSKCI, were constructed to further confirm the involvement of GSK-3β in the ATO-induced p21 expression. However, the stability of p21 protein was increased by ATO, but not LiCl treatment using cycloheximide. Furthermore, ATO-induced GSK-3β(Ser9) phosphorylation was through the ERK pathway, but not the PI3K/Akt pathway. We suggest that, taken together, ATO-induced ERK phosphorylation could inhibit GSK-3β activity to dephosphorylate the C-terminus (Ser243) of c-Jun to increase p21 expression and resultant cell death.
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Tainan 701, Taiwan. huanghs@mail.ncku.edu.tw
authors.forename: Huei-Sheng
authors.initials: HS
authors.lastname: Huang
authors.forename: Zi-Miao
authors.initials: ZM
authors.lastname: Liu
authors.forename: Ya-Ling
authors.initials: YL
authors.lastname: Cheng
mesh_terms: D000077237:Arsenic Trioxide; D001152:Arsenicals; D001483:Base Sequence; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics*; D017931:DNA Primers; D005786:Gene Expression Regulation / Q000187:drug effects*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D047468:Immunoprecipitation; D010087:Oxides / Q000633:toxicity*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic
chemical_list: D001152:Arsenicals; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D017931:DNA Primers; D010087:Oxides; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D000077237:Arsenic Trioxide