title: Enhanced Gadd45 expression and delayed G2/M progression are p53-dependent in zinc-supplemented human bronchial epithelial cells.
abstract: Zinc is an essential nutrient for humans; however, this study demonstrated for the first time that an elevated zinc status, created by culturing cells at optimal plasma zinc concentration attainable by oral zinc supplementation, is cytotoxic for normal human bronchial epithelial (NHBE) cells. p53 plays a central role in the modulation of cell signal transduction in response to the stress from DNA damage, hypoxia and oncogene activation. The present study was designed to determine whether the previously reported increased Gadd45 expression and delayed G2/M cell cycle progression in zinc-supplemented NHBE cells is p53-dependent, and to decipher the mechanisms responsible for the regulation of Gadd45 expressions by p53, and elucidate the Gadd45 functions in impaired cell growth and cell cycle progression in NHBE cells. Cells were cultured for one passage in different concentrations of zinc: <0.4 micromol/L (ZD) as severe zinc-deficient; 4 micromol/L (ZN) as normal zinc level in culture medium; 16 micromol/L (ZA) as normal human plasma zinc level; and 32 micromol/L (ZS) as the high end of plasma zinc attainable by oral supplementation. Inhibition of cell growth and upregulation of p53 mRNA and protein expression were observed in ZS cells. Most importantly, ZS treatment also enhanced Gadd45 nuclear protein level and promoter activity, decreased CDK1-Cyclin B1 level and delayed G2/M cell cycle progression. These changes were normalized to those observed in ZN by treating ZS cells with Pifitherin, an inhibitor of p53 transactivation activity. Thus, our findings support the p53 dependency of the Gadd45-CDK1/Cyclin B1-G2/M cell cycle progression pathway in ZS NHBE cells.
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, 20742, USA.
authors.forename: Rita S M
authors.initials: RS
authors.lastname: Shih
authors.forename: Stephen H K
authors.initials: SH
authors.lastname: Wong
authors.forename: Norberta W
authors.initials: NW
authors.lastname: Schoene
authors.forename: Jun Jun
authors.initials: JJ
authors.lastname: Zhang
authors.forename: Kai Y
authors.initials: KY
authors.lastname: Lei
mesh_terms: D052160:Benzothiazoles / Q000494:pharmacology; D001980:Bronchi / Q000166:cytology*; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002478:Cells, Cultured; D056744:Cyclin B1 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016195:G2 Phase / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014050:Toluene / Q000031:analogs & derivatives / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology*; D000097642:GADD45 Proteins
chemical_list: D052160:Benzothiazoles; D016203:CDC2 Protein Kinase; D056744:Cyclin B1; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D014050:Toluene; D016159:Tumor Suppressor Protein p53; D015032:Zinc; D000097642:GADD45 Proteins; C121565:pifithrin