title: Ectopic AP4 expression induces cellular senescence via activation of p53 in long-term confluent retinal pigment epithelial cells.
abstract: When cells are grown to confluence, cell-cell contact inhibition occurs and drives the cells to enter reversible quiescence rather than senescence. Confluent retinal pigment epithelial (RPE) cells exhibiting contact inhibition was used as a model in this study to examine the role of overexpression of transcription factor AP4, a highly expressed transcription factor in many types of cancer, in these cells during long-term culture. We generated stable inducible RPE cell clones expressing AP4 or AP4 without the DNA binding domain (DN-AP4) and observed that, when cultured for 24 days, RPE cells with a high level of AP4 exhibit a large, flattened morphology and even cease proliferating; these changes were not observed in DN-AP4-expressing cells or non-induced cells. In addition, AP4-expressing cells exhibited senescence-associated β-galactosidase activity and the senescence-associated secretory phenotype. We demonstrated that the induced cellular senescence was mediated by enhanced p53 expression and that AP4 regulates the p53 gene by binding directly to two of the three E-boxes present on the promoter of the p53 gene. Moreover, we showed that serum is essential for AP4 in inducing p53-associated cellular senescence. Collectively, we showed that overexpression of AP4 mediates cellular senescence involving in activation of p53 in long-term post-confluent RPE cells.
authors.affiliation: Department of Biomedical Sciences, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biomedical Sciences, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong.
authors.forename: Matthew Man-Kin
authors.initials: MM
authors.lastname: Wong
authors.affiliation: Institute of Bioengineering, Zhejiang University of Technology, 18 Chaowang Road, Hangzhou 310014, China.
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Biomedical Sciences, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong. Electronic address: kaychiu@cityu.edu.hk.
authors.forename: Sung-Kay
authors.initials: SK
authors.lastname: Chiu
mesh_terms: D017209:Apoptosis; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence; D047369:Chromatin Immunoprecipitation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D012333:RNA, Messenger / Q000235:genetics; D016601:RNA-Binding Proteins; D060888:Real-Time Polymerase Chain Reaction; D055213:Retinal Pigment Epithelium / Q000166:cytology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C404766:REPIN1 protein, human; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D001616:beta-Galactosidase
keywords: AP4; Cellular senescence; Serum activation; p53