title: Suppression of Gadd45 alleviates the G2/M blockage and the enhanced phosphorylation of p53 and p38 in zinc supplemented normal human bronchial epithelial cells.
abstract: An adequate zinc status is essential for optimal cellular functions and growth. Yet, excessive zinc supplementation can be cytotoxic and can impair cell growth. Gadd45 plays a vital role as cellular stress sensor in the modulation of cell signal transduction in response to stress. The present study was designed to determine the influence of zinc status on Gadd45 expression and cell cycle progression in zinc deficient and supplemented normal human bronchial epithelial (NHBE) cells, and to decipher the molecular mechanism(s) exerted by the suppression of Gadd45 expression on cell growth and cell cycle progression in this cell type. Cells were cultured for one passage in different concentration of zinc: <0.4 muM (ZD) as severe zinc deficient; 4 muM as normal zinc level in culture medium; 16 microM (ZA) as normal human plasma zinc level; and 32 muM (ZS) as the high end of plasma zinc attainable by oral supplementation. Inhibition of cell growth, upregulation of Gadd45 mRNA and protein expression, and blockage of G2/M cell cycle progression were observed in ZS cells. In contrast, little or no changes in these parameters were seen in ZD cells. The siRNA-mediated knocking down of Gadd45 was found to relieve G2/M blockage in ZS cells, which indicated that the blockage was Gadd45 dependent. Moreover, the enhanced phosphorylation of p38 and p53 (ser15) in ZS cells was normalized after suppression of Gadd45 by siRNA, implicating that the enhanced phosphorylation of these proteins was Gadd45 dependent. Thus, we demonstrated for the first time that an elevated zinc status modulated signal transduction to produce a delay at G2/M during cell cycle progression in NHBE cells.
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, MD 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: Kai Y
authors.initials: KY
authors.lastname: Lei
mesh_terms: D001980:Bronchi / Q000166:cytology*; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects; D015032:Zinc / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D000097642:GADD45 Proteins
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D015032:Zinc; D048051:p38 Mitogen-Activated Protein Kinases; C439070:GADD45A protein, human; D000097642:GADD45 Proteins