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Many of the signaling responses induced by transforming growth factor-b (TGF-b) are mediated by Smad proteins, but there is evidence that it can also signal independently of Smads. Here, we provide evidence that multiple signal pathways induced by TGF-b1-including Src family tyrosine kinases (SFKs), generation of reactive oxygen species (ROS), de novo protein synthesis and E-cadherindependent cell-cell interactions-transactivate the epidermal growth factor receptor (EGFR), which in turn regulates expression of c-Fos and c-Jun. Immunoprecipitation and immunofluorescence staining showed that EGFR was phosphorylated on tyrosine in response to TGF-b1. EGFR transactivation required the activation of SFKs and the production of ROS via NADPH oxidase, but was not dependent on metalloproteases or the release of EGF-like ligands. In addition, the production of ROS was dependent on signaling by specific SFKs as well as de novo protein synthesis. Stable transfection of E-cadherin into MDA-MB-231 cells as well as E-cadherin-blocking assays revealed that E-cadherin-mediated cell-cell interactions were also essential for EGFR transactivation. Finally, EGFR transactivation was involved in the expression of c-Fos and c-Jun via the extracellular signal-regulated kinase signaling cascade. Taken together our data suggest that ligand release-independent transactivation of EGFR may diversify early TGF-b signaling and represent a novel pathway leading to TGF-b-mediated gene expression.

The importance of expression of matrix metalloproteinase (MMP) in keratinocyte migration is well established, but its role remains unclear. Here we investigated the function of MMP-14 in TGF-beta1-induced keratinocyte migration. TGF-beta1 stimulated cell migration and the expression of MMP-2, -9 in HaCaT human keratinocyte cells. When we lowered MMP-14 mRNA with siRNA, cell migration, and MMP-9 expression decreased. Furthermore, the MMP-14 siRNA also reduced activation of JNK in response to TGF-beta1, and a JNK-specific inhibitor decreased both cell migration and MMP-9 expression. Taken together, these results suggest that TGF-beta1-induced HaCaT cell migration is mediated by MMP-14, which regulates MMP-9 expression via JNK signaling.

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Purpose: This study was performed to elucidate the role of nuclear factor ĸB (NF-ĸB) in lens epithelial cell proliferation in the capsular bag model for this study. Methods: Capsular bags were prepared from porcine eyes and cultured in a 5% CO₂ atmosphere at 37°C. NF-ĸB translocation was confirmed by immunohistochemistry and Western blot analysis. The effects of sulfasalazine and SN50 peptide, inhibitors of NF-ĸB activation, were observed by light microscopy and scanning electron microscopy. Results: NF-ĸB was found in the cytoplasm of nonproliferated lens epithelial cells. However, NF-ĸB moved to the nucleus in proliferation cells, proliferating-cell-nuclear-antigen-positive cells. This translocation was inhibited by treatment with sulfasalazine or NF-ĸB SN50 peptide. These inhibitors also blocked lens epithelial cell migration from the equatorial to the posterior capsule. Conclusion: NF-ĸB controls proliferation and regulates the growth of lens epithelial cells. In this study, sulfasalazine and NF-ĸB SN50 peptide inhibited cell proliferation in the capsular bag model. These results suggest that the regulation of NF-ĸB in lens epithelial cells may modulate posterior capsule opacification.

Transforming growth factor-β (TGF-β) is known to be a causative factor in pathological fibrosis and the metastasis of cancer cells, through effects on molecules of the extracellular matrix (ECM). We evaluated the influence of TGF-β1 on the gene expression of matrix metalloproteinase-2 (MMP-2) in lens epithelial cells (LECs). The results showed that TGF-β1 induced the expression of mRNA for MMP-2 in LECs. Subsequently, in order to examine the role of MMP-2, we overexpressed MMP-2 in LECs by stable transfection. The MMP-2-overexpressing LECs showed typical indicators of a myofibroblast-like cell phenotype, such as multiple layers of cells, elongated morphology, and expression of α-smooth muscle actin. We also showed that an MMP inhibitor blocked the TGF-β1-induced morphological change in LECs. These results demonstrate that MMP-2 plays a role in the transformation of LECs, which has implications for the pathological fibrosis of these cells.