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-yearold 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.

Smad7 Regulates Dental Epithelial Proliferation during Tooth Development

“…Furthermore, abrogation of TGF-βRII and Smad2 function using antisense ODN increased the tooth size and advanced the stage of tooth formation during mandibular morphogenesis, owing to increased cell proliferation of enamel organ (Chai et al 1999;Ito et al 2001). In addition, Smad2 overexpression reduced the level of the oral epithelium proliferation (Alotaibi et al 2014). Known as an inhibitor of TGF-β superfamily, Smad7 can antagonize the canonical TGF-β signaling by interfering with the recruitment of Smad2/3 and induce degradation of ALK5 (Lebrun et al 1999).…”

Regulation of defensive function on gingival epithelial cells can prevent periodontal disease

“…An increase in the number of apoptosis-positive cells was recently reported in the gingival junctional epithelium of smad2 transgenic mice [31] . Furthermore, the overexpression of smad2 reduced the proliferation of the junctional epithelium [32] and induced alveolar bone loss by up-regulating TNF-α and receptor activator of nuclear factor kappa-B ligand (RANKL) in transgenic mice [33] . On the other hand, we demonstrated that A. actinomycetemcomitans induced apoptosis in gingival epithelial cells by activating the TGF-β receptor I-smad2-caspase-3 signaling pathway [34] .…”

Excessive retinoic acid inhibit mouse embryonic palate mesenchymal cell growth through involvement of Smad signaling

“…Smad2 and Smad3 were structurally very closely related and both were involved in signaling from TGF-β, Smad3 could form a complex together with Smad2 in order to regulate the target genes of TGF-βs. Over-expression of Smad2 inhibited the proliferation of junctional epithelium cells by down-regulating c-Myc and up-regulating p15 and p27 which leading to cellcycle arrest (Alotaibi et al 2014), and inhibited oral epithelial cell proliferation by increasing p15 and p21 (Shimoe et al 2014). However, Smad2 was not required for TGF-β-stimulated growth inhibition in hepatocytes (Ju et al 2006).…”