title: Reactive oxygen species promotes cellular senescence in normal human epidermal keratinocytes through epigenetic regulation of p16(INK4a.).
abstract: Reactive oxygen species (ROS) can cause severe damage to DNA, proteins and lipids in normal cells, contributing to carcinogenesis and various pathological conditions. While cellular senescence arrests the early phase of cell cycle without any detectable telomere loss or dysfunction. ROS is reported to contribute to induction of cellular senescence, as evidence by its premature onset upon treatment with antioxidants or inhibitors of cellular oxidant scavengers. Although cellular senescence is known to be implicated in tumor suppression, it remains unknown whether ROS initially contributed to be cellular senescence in normal human epidermal keratinocytes (NHEK) and their malignant counterparts. To clarify whether ROS induce cellular senescence in NHEKs, we examined the effect of hydrogen peroxide (H2O2) on the expression of cellular senescence-associated molecules in NHEKs, compared to in squamous carcinoma cells (SCCs). Hydrogen peroxide increased the number of cells positive in senescence associated-β-galactosidase (SA-β-Gal) activity in NHEKs, but not SCCs. The expression of cyclin-dependent kinase (CDK) inhibitors, especially p16(INK4a) was upregulated in NHEKs treated with H2O2. Interestingly, H2O2 suppressed the methylation of p16(INK4a), promoter region in NHEKs, but not in SCCs. Hydrogen peroxide also suppressed the expression of phosphorylated Rb and CDK4, resulting in arrest in G0/G1 phase in NHEKs, but not SCCs. Our results indicate that the ROS-induced cellular senescence in NHEKs was caused by the upregulation p16(INK4a) through demethylation in its promoter region, which is not detected in SCCs, suggesting that ROS-induced cellular senescence contributes to tumor suppression of NHEKs.
authors.affiliation: Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Fukuoka 8140193, Japan; Department of Oral and Maxillofacial Surgery, Fukuoka Dental College, Fukuoka 8140193, Japan.
authors.forename: Mina
authors.initials: M
authors.lastname: Sasaki
authors.affiliation: Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Fukuoka 8140193, Japan. Electronic address: kajiya@college.fdcnet.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kajiya
authors.affiliation: Department of Oral and Maxillofacial Surgery, Fukuoka Dental College, Fukuoka 8140193, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Ozeki
authors.affiliation: Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Fukuoka 8140193, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Okabe
authors.affiliation: Department of Oral and Maxillofacial Surgery, Fukuoka Dental College, Fukuoka 8140193, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Ikebe
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D045744:Cell Line, Tumor; D016922:Cellular Senescence; D051358:Cyclin-Dependent Kinase 4 / Q000235:genetics / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics* / Q000378:metabolism; D019175:DNA Methylation; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism*; D044127:Epigenesis, Genetic; D059585:G1 Phase Cell Cycle Checkpoints / Q000235:genetics; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D017382:Reactive Oxygen Species / Q000819:agonists / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D015415:Biomarkers; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017382:Reactive Oxygen Species; D016160:Retinoblastoma Protein; D006861:Hydrogen Peroxide; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D001616:beta-Galactosidase
keywords: Cellar senescence; Cyclin-dependent kinase inhibitors; Normal human epidermal keratinocyte; Reactive oxygen species