title: Smad2 overexpression reduces the proliferation of the junctional epithelium.
abstract: The overexpression of the intracellular signaling molecule of the transforming growth factor-beta family (TGF-β) Smad2 was found to induce apoptosis and inhibit the proliferation rate of oral epithelial cells. Therefore, the aim of this study was to investigate in vivo the effect of Smad2 overexpression on the proliferation rate of the junctional epithelium (JE). Smad2 overexpression was driven by the cytokeratin 14 promoter (K14-Smad2) in transgenic mice. The K14-Smad2 mice were compared with wild-type (WT) mice selected as the control group. Samples were stained with hematoxylin and eosin stains and analyzed by image analysis. Immunohistochemistry was conducted for proliferating cell nuclear antigen (PCNA) and c-Myc as markers of cell proliferation. The expression of cyclin-dependent kinase inhibitors (P15, P21, and P27) was determined by real-time polymerase chain-reaction (RT-PCR). The quantity of phosphorylated retinoblastoma (pRB) was determined with Western blots. The overexpression of Smad2 altered the area of the junctional epithelial cells in one-year-old K14-Smad2 mice. The area was 32,768 (± 3,473) μm(2) for the WT and 24,937.25 (± 1,965) μm(2) for the K14-Smad2 mice. There was a significant difference in the proliferation rates of the JE (PCNA-positive cells) between the WT and K14-Smad2 mice, 20.7% (± 1.1) and 2.1% (± 0.5), respectively. A significant difference in c-Myc expression occurred between experimental and control samples. The K14-Smad2 mice had a mean of 2.3% (± 0.6), and the WT mice had a mean of 20.1% (± 3.6). Smad2 overexpression up-regulated the mRNA expression of P15 by 2.3-fold and that of P27 by 5.5-fold in the K14-Smad2 mice. Finally, the pRB protein showed a 2.3 (± 0.5)-fold increase in K14-Smad2 mice when compared with WT mice. Smad2 overexpression inhibits the proliferation of JE cells by down-regulating c-Myc and up-regulating P15 and P27, which resulted in an increase in pRB, leading to cell-cycle arrest.
authors.affiliation: Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada Advanced Education in General Dentistry, Riyadh Military Hospital, Kingdom of Saudi Arabia.
authors.forename: M K
authors.initials: MK
authors.lastname: Alotaibi
authors.affiliation: Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Kitase
authors.affiliation: Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada cshuler@dentistry.ubc.ca.
authors.forename: C F
authors.initials: CF
authors.lastname: Shuler
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D049109:Cell Proliferation; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000032:analysis; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000032:analysis; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000032:analysis; D015536:Down-Regulation; D004846:Epithelial Attachment / Q000166:cytology*; D005786:Gene Expression Regulation / Q000235:genetics; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007150:Immunohistochemistry; D053547:Keratin-14 / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D047428:Protein Kinase Inhibitors / Q000032:analysis; D016271:Proto-Oncogene Proteins c-myc / Q000032:analysis; D016160:Retinoblastoma Protein / Q000032:analysis; D051899:Smad2 Protein / Q000235:genetics*; D015854:Up-Regulation
chemical_list: D050762:Cyclin-Dependent Kinase Inhibitor p15; D050759:Cyclin-Dependent Kinase Inhibitor p21; D053547:Keratin-14; C489428:Myc protein, mouse; D018809:Proliferating Cell Nuclear Antigen; D047428:Protein Kinase Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D016160:Retinoblastoma Protein; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D050760:Cyclin-Dependent Kinase Inhibitor p27
keywords: PCNA; c-Myc; cyclin-dependent kinase inhibitors; gingival biotype; retinoblastoma; transforming growth factor–beta